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SB 2h 31fl

THE CAR WHEEL

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IFT OF

THE

CAR WHEEL

GIVING THE RESULTS OF A
SERIES OF INVESTIGATIONS

GEO. L. FOWLER, M. E.

«a&

IUCHAfiDB.GAB&
Mante£«r of Sale*,
Crocker Building,

San Francisco - Cat

PUBLISHED BY THE SCHOEN
STEEL WHEEL COMPANY
PITTSBURGH, PA., 1907

/,x

H^ '

The Fleming Press, New York
10726

• • *•••• e %

£JG*!1V:/*W:

435963

4 • •««.«.

FOREWORD

The solid forged and rolled steel wheel, referred
to in the following pages of this book, was devel-
oped and first manufactured by Mr. Charles T.
Schoen, the pioneer builder of high capacity steel
freight cars, and former president of the Pressed
Steel Car Co.

In the exploitation of large capacity cars Mr.
Schoen was confronted with the problem of getting
wheels to meet the requirements. The cast iron
wheels put under these ioo,ooo-lbs. capacity cars
failed repeatedly and the situation became serious.
For instance, one railroad, which had in service
several thousand of these cars, at one time con-
sidered the expedient of marking all of them down
to 8o,ooo-lbs. capacity in order to reduce the load
on the wheels.

The majority of wheel failures occur on moun-
tain roads with steep grades and sharp curves where
long and heavy brake applications are necessary, and
the wheel flanges are subjected to severe shocks.

Steel-tired wheels had given satisfactory service
under passenger cars running over these mountain
roads; but they were out of the question for freight
equipment because of their prohibitive cost. The
economical value of the high capacity car to the
railroads having been demonstrated, the problem
was to produce a wheel equal to or better than the
steel-tired wheel in strength and at a cost for mileage
less than that of the cast iron wheel.

Mr. Schoen began his experiments in 1898, and
early in 1901 the first machinery for making these

wheels was designed. The Schoen Steel Wheel Co.
was organized on May n, 1903, and the business
of making solid forged and rolled steel wheels
established for the first time on a commercial basis.

The enterprise has been a success from the
start, fully justifying the large expenditure of money
required in development work, and for the installa-
tion of the necessary machinery. At the present
time the company has a plant in operation, located
at Pittsburgh, Pa., capable of producing 250,000
wheels a year, and in connection with it open hearth
furnaces with an annual capacity of 100,000 tons of
steel for making the blooms from which the wheels
are forged and rolled. The entire process from raw
material to finished wheels is under the direct con-
trol and supervision of the company.

The Schoen solid forged and rolled steel wheel
has proven such a pronounced success in America
that it has attracted the favorable consideration of
foreign railways. To supply this European and
Colonial demand, The Schoen Steel Wheel Co.,
Limited, of Great Britain, was organized. The
works are situated in Leeds, Yorkshire, and have
an annual capacity of 100,000 wheels.

Schoen Steel Wheel Co.

Pittsburgh, Pa.
November, 1907

PREFACE

When this investigation of wheels and tires was
first undertaken its ultimate scope had not been
decided upon, and it was the expectation that it
would end when the first few comparative results had
been obtained. It was made solely for the purpose
of securing information regarding the standards of
quality of metal and workmanship that must be met
in the development of a new industry, the success
of which depended on the production of a wheel
that would at least meet the present requirements of
railroad traffic. There was no intention of publish-
ing the results, and this accounts for the apparently
unfinished condition of much of the work. As
soon as sufficient data had been obtained in one
line of investigation to serve as a working basis,
attention was turned to another branch of the sub-
ject. Results obtained in the various tests referred
to, therefore, must not be accepted as complete, but
the records of the work so far done are made public
with the thought that if they serve no other pur-
pose the attention of railroad officers will be attracted
to the field of railroad dynamics, as yet unexplored.

In the presentation of the results obtained no
attempt has been made to harmonize them with pre-
vious theoretical deductions, nor has any attempt
been made to build a theory upon them as a basis.
Only elementary mathematical calculations have been
introduced in order to show about what can probably
be expected from a continuance of investigations
along the same lines.

Such a piece of work as this could not, of

necessity, be carried on without material assistance
from the railroads, wherever track and rolling stock
was required, or defective and worn-out material was
to be obtained. Such assistance has been generously
and cheerfully given whenever it has been asked for.
Acknowledgments are due to Messrs. A. W. Gibbs,
D. F. Crawford, Wm. Mclntosh, G. W. Wildin,
J. F. Deems, and Prof. Wm. Campbell, for materials
furnished for examination and for assistance, and to
Messrs. E. G. Ericson of the Pennsylvania Lines
West, J. E. Childs, E. Canfield and G. W. West
of the New York, Ontario & Western, and J. F.
Deems of the New York Central, for the use of
track and rolling stock.

GEO. L. FOWLER,

New York
November, 1907

ESIGN OF THE SOLID FORGED
AND ROLLED STEEL CAR
WHEEL.

WITH a wheel made of one solid piece
of steel having the requisite physical properties, it
follows that a design can be used differing radically
from a wheel having the center and the tire separate.
The tire of a steel-tired wheel must be of such a thick-
ness that it will admit of a reasonable amount of wear
and at the same time leave enough metal in that
part of the tire which is scrapped to insure strength
against breakage during the last days of the life of
the wheel. With the solid forged and rolled steel
wheel, having the rim integral with and stiffened
by the web, more wear can be safely allowed than
where the stretching or breakage of the tire under
the rolling and pounding action of service must be
provided against. The solid forged and rolled steel
wheel resembles somewhat the cast iron wheel in
section, the difference being in the web, where there
is a single plate instead of double plates and no
brackets as in the standard cast iron wheel.

The details of the dimensions of car wheels vary
with the requirements of the railroads using them.
There is a wide difference of opinion as to the best
proportions for the thickness of the rim, while the
dish and length of hub are determined to a great
extent by the details of truck construction. This is
especially so in electric railway work, where the wheel
must be made to fit in between the motor on the
inside and the journal boxes on the outside. Ordi-
narily the dish of the wheel is determined by the

SOLID FORGED AND ROLLED STEEL WHEEL FOR ENGINE TRUCK.

-36' Of*.

SOLID FORGED AND ROLLED STEEL WHEEL FOR PENNSYLVANIA R.R.

SOLID FORGED AND ROLLED STEEL WHEEL FOR. AMERICAN CAR AND
FOUNDRY CO.

SOLID FORGED AND ROLLED STEEL WHEEL FOR TRAILER TRUCK
INTERBOROUGH RAPID TRANSIT CO.

SOLID FORGED AND ROLLED STEEL WHEEL FOR ELECTRIC STREET CARS.

/O'

SOLID FORGED AND ROLLED STEEL WHEEL FOR CLEVELAND AND SOUTH-
WESTERN TRACTION CO.

SOLID FORGED AND ROLLED STEEL WHEEL FOR PHILADELPHIA RAPID

TRANSIT R.R.

size of the journal box and its location relatively to
the tread; but the form given to the web dishing,
the thickness of the rim and the size of and shape of
the flange and tread are matters for individual con-
sideration in each case.

In wheels intended for steam railroad service the
treads and flanges are uniform, corresponding to
the M. C. B. standard. The variations in design
are found in the webs and hubs, the thickness of
rims, and occasionally a variation in the height of the
flanges is allowed if the wheels are intended for
engine trucks.

Examples of these variations are shown in the
accompanying diagrams. Thus, of two engine
truck wheels illustrated one has a dished web, by
which some yield is secured to compensate for the
variations in the diameter of the rim due to tempera-
ture changes, while on the other hand the wheel
with a straight web is preferred by some motive
power departments for exactly the same service.

The wheel for the Pennsylvania Railroad has a
rim 2 inches thick at the outer face of the tread, and
the web is straight in section from the bend at the
hub to the bend under the rim. The wheel for the
American Car& Foundry Co. is thicker in the rim,
and the web has a curved contour designed to com-
pensate for expansion and contraction of the rim.
Again, in the wheel designed for the Interborough
Rapid Transit Co. the thickness of the rim has been
increased to 3 inches although the diameter is but 31
inches. This wheel also has the curved contour web.

In electric service will be found the widest variations
of practice. Street railways keep the floor of the

car as close to the rails as possible, so as to facilitate
the entrance and exit of passengers. At the same
time it is necessary to maintain a minimum diame-
ter of wheel in order to provide sufficient clearance
between the street pavement and the lowest point
of the motors. The thickness of the rim is therefore
determined by adding to the minimum allowable
radius of the wheel a sufficient thickness of metal to
raise the car to the maximum height deemed advis-
able, and this dimension represents the amount of
metal to be worn away.

The wheel designed for the interurban cars of the
Cleveland & Southwestern Traction Co. is an
interesting example of a compromise between the
M. C. B. standard wheel for steam roads and the
lighter wheel ordinarily used in street railway work.
The cars are heavy and the speed is moderately
high, necessitating a web and hub of considerable
strength and a flange high enough to hold the car
to the rails at the speeds attained in the open coun-
try and yet low enough to permit the wheels to pass
over the rails and special work in the city.

COMPARATIVE PHYSICAL AND
CHEMICAL TESTS OF SOLID
FORGED AND ROLLED STEEL
WHEELS, STEEL TIRES AND
CAST IRON WHEELS.

ALL the tires and wheels referred to in this work
were bought in the open market, chosen at random,
and tested under identical conditions in comparison
with each other. They represent the principal brands
in use giving satisfactory service, and the results
stand on the basis of each sample representing the
average of its class and brand. They will be desig-
nated as Tires A, B, C and D, Wheels E and F and
Schoen Wheel.

Tests were made of the tensile strength, including
the limit of elasticity, per cent, of elongation, and the
reduction of area at the point of fracture. The steels
were tested for hardness by a drop of the Martel scale.
Abrasion tests were made in order to find the resist-
ance of the several materials to grinding at various
points below the tread. Specimens were also cut
for the determination of the specific gravity of the
metals at different points below the tread. Chemi-
cal analyses were made from samples of each tire
and wheel taken from a point below the center of
the tread. Finally, a series of microphotographs
were taken of etched specimens of the metals in
order to show their structure and the relation of that
structure to the physical and chemical properties
previously determined independently.

The chemical analyses for carbon were all made
by the combustion process and the tensile tests were

LOCATION OF TENSILE TEST SPECIMENS.

made in the usual manner, using test pieces 2 inches
long between marks. The reason for choosing this
length was that the curvature of the treads of the
wheels and tires made it impossible to cut longer
ones. These specimens were cut from the points C,
D, and E, as indicated on the diagram showing
the location of tensile test specimens. These test
pieces were cut on a chord of the tire and gave an
available length of 2 inches on the reduced area J
inch in diameter, the center of which was carefully
located at the point indicated on the drawing. The
tensile tests were made in an Olsen testing machine
of 100,000 Ibs. capacity, and the results obtained are
given in detail in the following table marked "Com-
parative Tests of Steel Wheels and Tires."

The averages of these are collected and pre-
sented in a condensed form in the table marked

woo

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Ffl
H

AVERAGE OF COMPARATIVE TESTS OF STEEL WHEELS
AND TIRES.

Tire or Wheel.

"O'N

Ill

Si .

CTire

A "

D "

B "

E Wheel

F «

Schoen Wheel

"•35

20.90
15.40

7.40
14.90

8.66

15.89

"-45
29.50

19-33
6.87

12.32

116,761
I24,0l8

114,519
113,610

"4,477
124,386

"3.352
121,951
104,095
107,989
111,184
110,857
121,523

77.J33
91,646
95,008

82^388

95.58o

104,124

66.06

73-89
81.92
83.18
72.63
83-50
86.45

818
817
783
799
872

875
1125

"Average of Comparative Tests of Steel Wheels
and Tires."

From this table it will be seen that in the wheels and
tires examined the average maximum tensile strength
varied from 113,610 Ibs. to 124,386 Ibs. per sq. in.
of section; that the elongation in 2 inches varied
from 7.40 per cent, to 20.90 per cent.; the limit of
elasticity from 66.06 per cent, to 86.45 Per cent- of
the maximum tensile strength; and the hardness
from 783 to 1125 points on the Martel Scale.

In reviewing these results it is necessary to con-
sider the relative influence of the chemical composi-
tion on them. This is given in the table marked
" Chemical Composition of Steel Wheels and Tires."

As would be expected the low carbon content of
the D tire is accompanied by comparatively low
tensile strength, high ductility and low hardness.

At the same time it is evident that the work put

CHEMICAL COMPOSITION OF STEEL WHEELS
AND TIRES.

Wheel.

Carbon.

Phos-
phorus.

Sulphur.

Manga-
nese.

Silicon.

C Tire

o 616

o 048

O OI I

o 698

O 7O£

A "

o 716

O OCK

o 023

O 7 c?

U.JU^)

o 26"?

D "

O <?71

O O7 S

o 0^8

"•oJ

O 76"?

O COO

B "

0.676

U-WS

o 06 1

o oi<

087^

<j.^wy
O 2 C4

E Wheel

0.646

O.O7I

O O2Q

0.078

w>«34

O 24Q

F «
Schoen Wheel . . .

0.631
0.690

0.081
O.OI2

0.042
0.000

0.775

0.870

O.24I
0.094

on the wheel is an influential factor in all of these
results and there is a variation of tensile strength
and ductility that is not fully accounted for by the
variation of carbon content. Take as an extreme
example the E wheel and the Schoen wheel. There
is a variation of but .044 per cent, in carbon, and
yet the maximum tensile strength of this E wheel
was but 113,610 Ibs. per sq. in. while that of the
Schoen wheel was 124,386 Ibs. with a correspond-
ing elongation in 2 inches of 7.40 per cent, and
8.66 per cent, respectively, while the limit of elas-
ticity was 72.63 per cent, and 86.45 per cent, of the
tensile strength respectively. The actual variation
in limit of elasticity was much greater, because of the
higher base of comparison with the Schoen wheel;
the limit of elasticity of the E wheel being but 79.12
per cent, of that of the Schoen wheel. In making
these tensile tests great care was exercised not only
in the preparation of the specimens, but in making the
tests themselves. The machine was run slowly after
a stress of 50,000 Ibs. had been reached, so that the
limit of elasticity could be very accurately determined.

COMPARATIVE RESULTS OF PHYSICAL TESTS OF

SCHOEN STEEL WHEELS WITH OTHER

WHEELS AND TIRES.

*Q Q) CO

**H

1-
o $

J*g

Tire or Wheel.

>£££

1^1

°|1

6 a1

fi c

c °

I-S

*S*§2

§'1

*H ^

Schoen Wheel . . .

IOO.OO

I OO.OO

IOO.OO

100.00

IOO.OO

A Tire

QQ.7O

131.06

02.94

100.71;

88.02

85.47

72.62

C "

Q7.8?

128.98

93.28

74.08

76.41

72.71

D «
B « • . . . .

93-23

92.07

241.34
177.84

239-45
156.90

85.66

88.86

91.25
91.47

94.76

96.22

69.60
71.02

F Wheel

Q2.O7

172.01;

91.22

91.79

96.59

77.78

E "

QI 74

8S.4";

cc.76

QI.4Q

79.12

84.01

77. ci

A comparison of the results obtained with all
wheels and tires with those obtained with the Schoen
steel wheel are given in the table marked "Com-
parative Results of Physical Tests of Schoen Steel
Wheels with Other Wheels and Tires" in which the
results obtained with the Schoen wheel are taken
as a base, and the results obtained with the other
wheels and tires are given in percentages of that base.
From this table it appears that the Schoen wheel
leads all of the others in the items of tensile strength,
limit of elasticity, per cent, of limit of elasticity to
ultimate strength and in hardness.

The tests for hardness were made with a drop
arranged with a pyramidal punch. The principle
on which this work was done was to measure the
force of a blow delivered by the punch on the smooth
face of the metal to be tested, as well as the amount

of metal displaced by the blow. This method of
testing was devised by Col. J. T. Rodman of the
United States Army. It was afterwards developed
and formulated by Lieut. Col. Martel of the French
army and was then adopted as a standard test by
the French government. The results obtained are
known as the degrees of hardness by the Martel
scale. By his investigations Col. Martel showed
that the amount of metal displaced by the punch
varied inversely as the hardness and directly as the
weight of the drop and the height of the fall.

In this investigation the Rodman pyramidal punch
was used. It was fastened to a drop weighing, to-
gether with the punch, 2.2616 kilograms, and the
height of fall was 600 millimeters. The punch was
of hardened tool steel, carefully ground to form, and
it withstood the work without deformation.

The specimens for the test were cut from the tires
and wheels at the same points as the tensile test
pieces as indicated at C, D, and E, and the results
obtained are given with the other physical properties
in the several tables.

These tests show the Schoen wheel to have been
the hardest of the seven specimens tested, and that
the D tire was the softest. This was to be expected
judging from the carbon content; but we note that
while the A tire has a higher percentage of carbon
than the Schoen wheel, for some reason the latter is
the harder of the two.

For the abrasion tests a cylinder J inch in diameter
was cut from a point near the center of the tread of
each wheel, extending vertically down into the body
of the metal. This was placed in a frame, with the

end that was at the tread resting on an emery
wheel. A load of 2 Ibs. nj oz. was put on the
upper end of the cylinder to hold it down on the
wheel. This weight was selected after some pre-
liminary trials made to ascertain the pressure that
could be used without heating the material or grind-
ing it away too rapidly so as to make the count
smaller than would be convenient for making com-
parisons. To this weight must be added the weight
of the cylinders themselves, which varied about
0.54 oz., a variation which was duly considered and
the proper allowance made therefor, although it is
practically a negligible quantity.

The wheel used was made by the Carborundum
Co., and was io^9¥ inches in diameter and f inch
thick when new. At the conclusion of the tests the
wheel was worn to a diameter of io/¥ inches. It was
known on the maker's schedule as Grit 120; Grade
H., Bond G 9. It was run at a speed of about
2,500 revolutions per minute.

While grinding, a constant and uniform stream of
water was kept running on the wheel and specimen,
and at the conclusion of the test the specimens were in-
variably cool and showed no signs of heating whatever.

The counting of the revolutions was done by means
of a special counter coupled to the shaft and having a
worm meshing with a gear of 25 teeth mounted on a
shaft to which a revolution counter was attached. The
reading of the counter was, therefore, multiplied by
25 to obtain the number of revolutions of the wheel.

In addition to the regular tests, a cylinder was
cut from the same position in a chilled cast iron
wheel, and the results of its abrasion test, as well as

60,000

DIAGRAM OF ABRASION TESTS OF STEEL TIRES AND WHEELS, SHOWING

RELATION OF RATIO OF WEAR AT VARIOUS DEPTHS BELOW TREAD

TO REVOLUTIONS OF EMERY WHEEL.

those of the wheels and tires, have been plotted and
shown in the illustration, "Diagram of Abrasion Tests
of Steel Tires and Wheels." The abscissas indicate the
location of the metal below the tread, and the ordinates
the number of revolutions of the wheel required to
grind off J- inch from a cylinder J inch in diameter.
It will be noted that in every test there is a rise
in the number of revolutions at a point about J
inch below the surface of the tread, or for the space
between J inch and f inch. Had the work been
done in rotation this peculiarity might have been
attributed to a change in the texture of the wheel,
glazing, heating the material, or a similar cause.
The tests were started, however, before all of the
cylinders had been finished, and those from the A,
B, C and D tires were well along when a start was
made with the cylinder cut from the Schoen wheel.
This was worked down in rotation with those from
the tires, when that from the E wheel was intro-
duced, and this was followed in the same way by that
of the F wheel, so that the wheel structure itself is
responsible for the diagram. By reducing these
diagrams to an average the results are as follows:

AVERAGE ABRASION PER *A IN. OF TIRES AND WHEELS.

Tire or Wheel.

Revolutions.

Linear Feet.

Schoen Wheel ,
E Wheel . .

32.635

•7Q 66O

86,483

C Tire . .

28 20 C

01, ^4^

B " ....

26 72O

/4>/4j
60 7^8

F Wheel . .

2 C 54.O

67 68 1

A Tire

•3»j^w

2"? 27O

6 1 666

D "

21 4.4 C

Cast Iron Wheel . .

5,485

!4>535

Reducing these to percentages on the basis of the
Schoen Wheel we have:

Tire or Wheel

Per Cent.

Schoen Wheel

IOO.OO

E Wheel

QI.QC

C Tire

86.42

B «

8065

E Wheel

78 26

A Tire

71.10

D " .

1 J

OC.7I

Cast Iron Wheel

1 6.8 1

From this it appears that the resistance of the
Schoen wheel to abrasion was greater than that of
any of the other wheels and tires with which it was
compared. The cast iron wheel gave the lowest
resistance of any cylinder tested. The wheel was of
good material, with a depth of chill of about f inch.

An explanation of the peculiar rise in the number
of revolutions required to grind these tires between
J inch and f inch will be brought out in the dis-
cussion of the microphotographs. The examination
made of the specific gravities of the metal of the
tires and wheels at different points below the surface
of the tread also tends to show a reason for the
peculiar rise in the rate of abrasion by the emery
wheel. From this examination it appears that with
slight local aberrations the density of the material
increases from the tread down to a depth of about
I inch and then decreases down to 2 inches. A few
observations made below these depths show that
there is again a tendency to increase in density as
the inner edge of the tire is approached. There was,

however, a variation of this condition found in the
rim of the Schoen wheel. Although there was
a tendency to follow the general behavior of the
other specimens it was along a wavy line corre-
sponding, but not in exact location, with the variation
in the texture of the grain which will be brought out
in the microphotographs to be discussed later.

Another peculiarity that was developed is the
relation of hardness, resistance to abrasion and ten-
sile strength to the specific gravity of the material.

It will be noted that the rate of wear of the cast
iron wheel, as shown on the diagram, was much
greater than that of any of the steel tires or wheels.
The rapid fall in the number of revolutions per J
inch of metal removed as the chill was worn away is
easily accounted for, but it was not expected that the
variations from the results obtained with the steel tires
would be so great as they were. In the laboratory
the metal and wheel were kept cool, so that at no
time did the temperature rise, even on the face of
the specimen, above that of the hand. As these
abrasive tests have been checked in other ways, as
will be shown later, it appears that the avoidance
of heat is the explanation of the great difference.

It must be borne in mind that the primary object
of these investigations was to ascertain to what extent
the metal entering into the construction of the Schoen
wheel fulfilled the requirements of actual service
as determined by comparison with other wheels
already upon the market and doing satisfactory work.

The conclusions to be drawn from a general re-
view of the results obtained in this investigation are
as follows :

From the physical tests of the metal of the Schoen
solid forged and rolled steel wheel, it appears that
it is the strongest of any of the tires and wheels
examined. This strength appears in the maximum
stress to which the metal was subjected, the point at
which rupture took place and the limit of elasticity,
all of which were higher than in any other wheel or
tire, with the single exception of that of the A tire.
This tire had a breaking load exceeding that of the
Schoen wheel by but 428 Ibs. per sq. inch of section,
an amount that is unimportant.

The limit of elasticity, as expressed both in actual
figures and in the percentage of the total load, was
far higher in the Schoen wheel than in any of the
others.

The ductility of the metal of the Schoen wheel,
as indicated by the elongation of the tensile test
pieces, is less than that of any of the other speci-
mens with the exception of the E wheel. Here
there is a difference of nearly 15 per cent, in favor
of the Schoen wheel, despite the fact that the E
wheel contains nearly .05 per cent, less carbon.
This is probably due to the difference in the amount
of work put on the two wheels.

In hardness the Schoen wheel stands the highest
on the scale. This is shown in another way by the
abrasion tests, which show the Schoen wheel to be
the slowest of any to grind away.

In specific gravity the Schoen wheel is the highest.

The chemical composition is of course a matter
that is regulated by specifications and a review of
these since the introduction of steel-tired wheels
has shown a steady advance in the carbon content.

The makers of the Schoen wheel have placed
their wheel next to the highest in carbon con-
tent. This explains, in part, the high ultimate
tensile strength, although it cannot account for
it altogether because the Schoen wheel leads the A
tire, which has a higher carbon content, in elasticity
and maximum load, and in ductility is above the E
wheel having a lower carbon content. In this analysis
special attention is directed to the sulphur, not a
trace of which could be found in the Schoen wheel
specimens under examination.

ICROGRAPHIC RECORDS SHOW-
ING THE PENETRATION OF
WORK AND CHARACTER OF
HEAT TREATMENT.

THE physical properties of the steel in these wheels
and tires having been determined, an examination
with the microscope was made of samples from
each. In the preparation of the specimens for this
work strips were cut from each wheel and tire in
accordance with the lines shown on the diagram.
The numbers 1,2,3 an(^ 4 are f°r tne identification
of the strips and are used in connection with
the photographs, all of which were made with a
magnification of 88 diameters.

SECTION OF TIRE SHOWING LINES OF LOCATION OF MICROPHOTOGRAPHS

Referring first to the microphotographs of the D
tire, Nos. I to 6, Nos. I to 5 were taken in strip
No. 4, at the tread and at J inch, \ inch, and I inch
below the tread respectively, and No. 6 at I inch
below the tread in strip No. 3. These photographs
show an exceedingly fine granular structure, indi-
cating careful heat treatment, a low average per-
centage of carbon and an abundance of ferrite. The
structure becomes somewhat coarser as the metal is
penetrated and the normal structure is reached at
a depth of about i in. It will also be seen that
there is a slight difference between the structures of
the metal as illustrated by the two photographs Nos.
5 and 6 which were taken at a depth of i in. below
the tread in strips 4 and 3 respectively. No. 5 is
the finer, showing that the metal received more
work at that point than it did deeper in on
strip No. 3. This D tire had the finest grain
and the most uniform structure of the samples
examined. On the other hand, the photographs
corroborate the chemical analysis of low carbon
content, possibly down to 0.50 per cent., as indi-
cated by the proportion of ferrite (white) and
pearlite (black).

Next in order of fineness of grain comes the C, B
and A tires respectively. Here again the relative
amounts of ferrite and pearlite give an approximate
indication of the amount of contained carbon, from
which it would appear that the B and C tires would
not run over 0.60 to 0.65 per cent, while the A may
rise to 0.70 per cent,

The material of the B tire shows a practically
uniform texture of grain throughout its whole depth,

AT EDGE OF TREAD.

No. 2. % IN. BELOW TREAD.

No. 5 i IN. BELOW TREAD. No. 6. i IN. BELOW TKEAI

MICROPHOTOGRAPHS OF TIRE D. 88 DIAMETERS.

No. 9. % IN. BELOW TREAD. No. 10. i IN. BELOW TREAD.

MICROPHOTOC.'RAFHS OF TIRE C. 88 DIAMETERS.

with no decarbonization at the tread due to heat
treatment, although this is undoubtedly due to the
tire having been turned before being examined.

In the C tire, which was new, it will be seen that
the outer layer of the material next to the tread, as
indicated by the photograph No. 7, was decarbonized
by the action of the heat treatment to which it was
subjected. The presence of ferrite is very marked
all the way across the tread, but below the surface,
as indicated by the photographs Nos. 8, 9 and 10,
which were taken at depths of J in., J in., and I in.
below the tread respectively, the grain assumes the
normal condition for the steel at its finishing tem-
perature, although it is somewhat finer at the edge
strips Nos. I and 4 than in the center strips Nos.
2 and 3, indicating failure of the work to penetrate
the center.

The A tire has such a high carbon content that
the absence of excess ferrite causes the grain to become
obscure; it was possible to bring the formation out in
part only by oblique illumination. When viewed
under the microscope with the light adjusted to
the best advantage a decided coarsening of the grain
is noted at successive points below the tread. For
example, at the surface the grains are apparently about
the same size as those immediately below the decar-
bonized shell of the tread in the C tire, but the grain
coarsens rapidly, and at a depth of i in. it is some-
what coarser than that of the C tire. The structure is
interpreted from the microphotographs in the accom-
panying diagram made at the same magnification.

The E wheel has an exceedingly coarse structure with
traces throughout of inequality of carbon content

and disappearance of the grain. This is especially
noticeable in photographs Nos. 19 and 20 and ap-
pears in the others to a greater or less extent, showing
an unevenness of structure that is suggestive of cast
steel. This is discussed elsewhere in connection
with a shelled-out wheel of the same make. The
penetration of work was apparently very slight as is
shown by the large size of the grains in No. 17, taken
at the surface of the tread, and the increasing size of
structure as shown in Nos. 18, 19 and 20 taken at
depths of J in., ^ in., and i in. respectively.

The F wheel has a coarser grain than the A, B or
C tire and is slightly coarser than that of the D tire.
The carbon content appears to be about the same
as that of the C tire, or somewhat above 0.60, and
this is checked by the chemical analysis. The sur-
face decarbonization which is so marked in the case
of the C tire appears in this one also, as indicated
by the increase of the amount of ferrite accom-
panied by softening of the surface. The large size
of the grain in this wheel, as illustrated by photo-
graphs Nos. 21 to 26, is caused by the heat treat-
ment to which this wheel was subjected. There has
evidently been no work put upon it after the final
heating. This also explains why there is compara-
tively little enlargement of the grain going down
from the surface of the tread. The photograph No.
21 was taken at the surface of the tread and the others
followed at depths of J in., J in., I in., 2| in., and
2§ in. respectively.

The B tire is typical of the others and needs only
a word of explanation of the microphotographs Nos.
27 to 30, which were taken at the surface of the

No. 15. y2 IN. BELOW TREAD. No. 16. i IN. BELOW TREAD.

MICROPHOTOGRAPHS OF TIRE A. 88 DIAMETERS.

//v.

INTERPRETATION OF GRAIN STRUCTURE IN TIRE A AT VARYING DISTANCES
BELOW SURFACE OF TREAD.

tread and at depths of J in., J in., and \ in. re
spectively. From these the gradually increasing size
of the grain is apparent, though from its large di-
mensions, even at the tread, it would appear that this
particular tire was finished at a high temperature.

The microphotographs of the Schoen wheel show
that for the first J in. of depth it has the finest
structure of any of the wheels and tires examined,
but below this depth its grain increases in size in a
comparatively uniform manner, though with a varia-
tion to be noted later. The steel contains but a trace
of ferrite, indicating that the carbon content is about
the same as that in the A tire. Here again, owing
to the absence of sufficient ferrite to outline the grain
clearly, it was necessary to photograph by oblique
illumination, and it was under this light that the ac-
companying sketches to show the grain's size were
made. The microphotographs closely check the
abrasion tests and the determinations of specific
gravity.

There are two well-defined zones in the rim of
the Schoen wheel that are evidently due to the
rolling. One is at a depth of J in. and the other
f in. below the surface of the tread. This is best
illustrated by the accompanying diagram of the
microstructure in the Schoen wheel, in which the
four strips and the location of the microphotographs
are roughly indicated.

Strip No. I shows a very fine grain at the surface
with carbon well below 0.50 per cent. This structure
runs down for about ^ in., where there begins a
gradual increase of the grain size until the normal
dimensions are reached at about TV in. below the top

No. 19. % IN. BELOW TREAD. No. 20. i IN. BELOW TREAD.

MICROPHOTOGRAPHS OF WHEEL E. 88 DIAMETERS.

of the flange. The first -fa in. is formed of a very
fine mixture of about equal proportions of ferrite
and pearlite, and below this the ferrite gradually dis-
appears and the grains increase in size. At a depth
of -YZ in. the ferrite appears as a discontinuous band
or envelope around the grains of pearlite, indicating
that the carbon content is about 0.70 per cent. This
increase in the size of the grains continues down-
ward until they reach their maximum at a depth of
about i in.

In strip No. 2 there is the same fine-grained sur-
face structure (a) corresponding to that of No. I.
The depth of this decreases from one side of the
strip to the other and is about ^ in. thick at the
corner. This structure is shown in the photograph
No. 31. On the right hand side two zones will be
seen, one of which, starting at /i, is of very fine
pearlite. The point of maximum coarseness is at ci.
This is not really a coarse grain in itself, for it is
fine even when compared with that of the D tire.
Below ci there is an abrupt change to extreme fine-
ness again at /2. This is followed by a gradual
increase in the size of the grain down to C2,
where the normal structure is found at a depth of
about i in.

In strip No. 3 there is the same fine grain at the
surface, as shown in the photograph No. 32, which
extends down to a depth of about -^ in. The ex-
treme outside shows almost entire absence of car-
bon, or nearly pure ferrite. This is followed by a
gradual increase in the amount of carbon until, at
a depth of about -^ in., a fine grain structure almost
wholly of pearlite is indicated at fi. Next comes a

uniform increase in the size of the grains until they
reach their maximum at the point marked ci, where

there is an abrupt change to a structure of great
£ i • i • • • &

fineness which in turn increases in size to a maxi-
mum at c2, when there is a second abrupt change
to extreme fineness at /3. Below this there is a
gradual increase in the grain size until the normal
structure is reached at about i in.

In strip No. 4 there is the same decarbonized outer
layer (a) which is about ^ in. thick at the center,
thickening towards the right in the direction of the
edge of the wheel rim. This structure differs in
appearance from the corresponding area in No. 3,
due to the distortion of the grain by mechanical
treatment of the metal after ferrite or pure iron
became excessive as the result of burning out the
carbon on the surface of the steel. The size of the
grain increases from fine at /i, to a maximum coarse-
ness at ci, J in. below the surface where there is
the same abrupt change as before to a fine structure
at /2. This will be seen by a reference to photograph
No. 38. The grain again increases to a maximum
coarseness at cz, with another change to extreme
fineness at /3, at a depth of about | in. Beyond
this point the grain increases uniformly until the
normal size is reached at a depth of I in., as indi-
cated by photograph No. 36, and the diagram of
grain sizes.

These changes in grain size are accounted for by
the successive heat and mechanical treatments to
which the Schoen wheel was subjected.

The conclusions drawn from this work with the
microscope are practically the same as those reached

No. zz. Y% IN. BELOW TREAD.

\ '•. \

. *-<

No. 23. % IN. BELOW TREAD

No 24. i IN. BELOW TREAD.

No. 25. ^l^ IN. BELOW TREAD. No. 26. 2% IN. BELOW TREAD.

MICROPHOTOGRAPHS OF WHEEL F. 88 DIAMETERS.

by a study of the physical and chemical tests. It is
apparent that the Schoen wheel is quite equal to
the best tires, as regards depth of finish and the
fineness of the grain in the steel.

N9I.

N?2.

N?3.

DIAGRAM ILLUSTRATING GRAIN STRUCTURE OF SCHOEN STEEL WHEEL.

//Af.

INTERPRETATION OF GRAIN STRUCTURE IN SCHOEN WHEEL AT VARYING
DISTANCES BELOW SURFACE OF TREAD.

No. 29. % IN. BELOW TREAD. No. jo. % IN. BELOW TREAD.

MICROPHOTOGRAPHS OF TIRE B. 88 DIAMETERS.

No. 33. i/jj IN. BELOW TREAD. No. 34. % IN, BELOW TREAD.

M1CROPHOTOGRAPHS OF SCHOEN STEEL WHEEL. 88 DIAMETERS.

No. 37. AT OUTER EDGE OF TREAD. No. 38. % IN. BET.OW OUTER EDOE OF TREAD.

MICROPHOTOGRAPHS OF SCHOEN STEEL WHEEL. 88 DIAMETERS

HE SHELLED-OUT WHEEL.
A POSSIBLE EXPLANATION OF
THE CAUSES OF WHEEL AND
TIRE FAILURES.

THE service that can be expected from any wheel
depends on the soundness and homogeneity of the
metal of which it is composed. Irregularity of tex-
ture must necessarily result in irregular wear, while
local defects are apt to result in an immediate failure.
Of such failures one that is the cause of much an-
noyance and trouble is that known as shelling out.
It was for the purpose of ascertaining, if possible,
the causes of this shelling out of wheels and tires
that an examination with the microscope of a num-
ber of defective tires that had failed in service was
undertaken.

The Rules of Interchange of the Master Car Build-
ers' Association define a shelled-out wheel as one
"with a defective tread on account of pieces shelling
out." This is a poor definition; it may be supple-
mented by saying that the common understanding
of a shelled-out wheel is one in which pieces from
the tread have flaked off, due to inherent defects in
the metal, such as the laminations so frequently
found in wrought iron boiler-plates. It will be
seen later that the analogy in the case of steel wheels
is very close. The cause of shelling out of cast
iron wheels is outside of this investigation and will
not be considered.

The samples of defective material investigated
include one of each brand of wheel and tire pre-
viously referred to in these pages, and were obtained

from several railroad companies. Each of these
wheels and tires had one or more shelled-out spots
on the tread, and there were also places on each
where no signs of shelling out could be detected.
The general appearance of two samples is shown in
the accompanying photographs, and these may be
considered as characteristic of all.

A section was taken at the spot where the worst
shelling was found and another through a place on
the tread where the metal showed no external signs
of deterioration. These sections were then cut into
strips whose centers lay along the lines I, 2, 3, and
4 respectively. (See page 29.) The strips were then
polished, etched and photographed. The photo-
graphs were taken at the tread, and at intervals
approximately J in., J in., f in., and J in. below.
This was not strictly followed in all cases, since the
examination was governed, to a certain extent, by the
structure of the material examined, as it appeared
under the microscope.

Nos. 39 to 42 show the structure of the C tire at
the point where the worst shelling out occurred. In
strip No. i, which ran down into the wheel from the
flange, the metal shows a fairly good fine-grained
structure at the edge and well down into the rim.
In No. 39, which was taken at J in. below the edge,
spots of manganese sulphide are visible. The metal
shows a good structure in all of the strips down to
J in. in depth, wherever the photographs avoid the
serious defects. In No. 40, however, which was
taken from strip No. 3, there is a distinct flaw due
to the presence of slag. The same kind of flaw
appears, very pronounced, in the photographs Nos.

41 and 42, which were taken from strips Nos. 2 and 3
respectively, and through which a continuous line
of slag extends. At other points adjacent to these
defective places normal conditions and structure of
metal were found.

Photographs Nos. 43 and 44 were taken from
points on strip No. 3, at depths of J in. and J in.,
cut from an apparently solid piece of metal, and yet
they show the presence of pronounced slag flaws.
These flaws had not developed into shelled-out spots,
but it is reasonable to suppose that it was only a
matter of time when they would have done so.

Comparing this defective C tire with the sound
new tire, the absence of a decarbonized surface on
the defective tire is to be noticed, while it was very
apparent in the new tire and can be clearly seen in
photograph No. 7 (page 33). This is accounted for
by the fact that the defective tire was in service and
this soft outer shell had been worn away.

The balance of the material of the defective C
tire is normal in structure, except that the manganese
sulphide globules are large. Its failure is readily
accounted for by the slag flaws found scattered
through the whole body of the material as shown in
Nos. 40 to 44.

The B tire failed from the same cause as the C
tire. The structure of the metal is normal through
a large part of the sections, but contains occasional
slag cracks, and the characteristic markings of manga-
nese sulphide, as shown in No. 45. In the other
parts of the tire precisely the same conditions exist as
in the C tire, namely, slag cracks, as shown in Nos.
46, 47, and 48, which were taken at various depths,

and where no indication of shelling out had appeared
at the time that the tire was removed from service.
The presence of such large slag veins as those shown
in Nos. 46 and 47 leaves no room for doubt as to
the cause of failure. The presence of manganese
sulphide was also indicated in the new B tire, but
no slag veins are revealed.

Nos. 49 and 50 were taken from the defective A
tire. If the metal of this tire is compared with that
of the sound new tire, it will be seen that there is no
variation in the normal structure of the material to
indicate a difference in the wearing quality, so that
the failure of the shelled-out tire is undoubtedly due
to the slag flaws clearly shown in the photographs.

In the shelled-out D tire normal structure was
found but interspersed with slag cracks as in the
other defective tires. These are shown in Nos. 51
to 54, some of which were taken close to the edge
of the tread. In some places there were spots of
manganese sulphide near the edges, but the cause
for failure is the presence of the slag flaws that form
planes of extreme weakness. In photograph No. 51
such a flaw is shown, which eventually must have
caused shelling out. Another example of the same
sort is shown in No. 51.

In the E wheel the slag flaws can be seen in Nos.
55 and 56, which were taken from the shelled-out
portion. In No. 55 there is a distortion of the
slag defects due to the forging, and in No. 57 there
can be seen a slag crack which existed in the metal
with no visible defect on the surface.

The material in this particular wheel is bad in every
particular. The carbon content is low, apparently

ranging from 0.35 to 0.40 per cent. The effect of
both the work and heat treatment is practically nil and
the structure looks like that of untreated cast steel or
a metal that has been overheated. The surface shows
the effect of cold rolling in the mixture of ferrite and
slag, the whole having a schistose appearance. The
presence of so much slag, as shown in Nos. 55, 56
and 57, renders the wheel totally unfit for service.
The grain is coarse, as is seen in photos Nos. 58 and
59, and resembles that in the new wheel of the same
brand that was examined. The carbon content of
the new wheel, however, was apparently much
higher.

In the shelled-out portion of the F wheel the slag
flaws also appear well down in the metal. (SeeNos.6i
and 62.) What was said of the defective E wheel
applies to the F wheel. The carbon content seems
to be low, while the presence of large quantities
of slag, photograph No. 62, caused the many lines
of weakness along which rupture occurred.

At the time this examination was being made three
specimens of the Schoen solid forged and rolled steel
wheel were obtained, two from shelled-out wheels and
one from a section of a wheel that had been purposely
burned in heating during manufacture. An examina-
tion of the photographs of the two defective wheels,
Nos. 67 to 70, shows that there are defects in the interior
of the metal that were undoubtedly the cause of the
shelling out, but there is no evidence of slag. The
same characteristics are to be noted in Nos. 65 and
66 of the specimen that had been purposely burned.
The three specimens are examples of burned steel
in which there is no evidence of slag.

From these photographs it is evident that the
cause of the failure of all of the wheels and tires,
except the Schoen wheels, was due to the pres-
ence of slag flaws occurring near the surface of
the tread.

It appears, therefore, that there are at least two
causes for the shelling out of steel tires and wheels,
namely, slag flaws and overheating.

SHELLED-OUT STEEL TIRE AND WHEEL;

No. 39. AT }£ IN. BELOW SHELLED SPOT. No. 40. AT EDGE OF SHELLED SPOT

No. 41. SHOWING SLAG CRACKS.

No. 42. SHOWING SLAG CRACKS.

No. 4j. ys IN. BELOW TREAD OF SOLID No. 44. % IN. BELOW TREAD OF SOLID

METAL. METAL.

MICROPHOTOGRAPHS OF SHELLED-OUT TIRE C. 50 DIAMETERS.

No. 45. AT

IN. BELOW SHELLED-OUT
SPOT.

No. 46. SLAG CRACK IN SOLID SECTION
OF TIRE.

No. 48. MANGANESE BISULPHIDE SPOTS.

No. 47. SLAG CRACK IN SOLID PART OF
TIRE.
MICROPHOTOGRAPHS OF SHELLED-OUT TIRE B.

No. 49. AT EDGE OF SHEI.LED-OUT SPOT.

No. 50. SLAG FLAW NEAR EDGE OF SOLID

METAL.
MICROPHOTOGRAPHS OF SHELLED-OUT TIRE A.

No. 51. SLAG CRACK NEAR EDGE OF

SHELLED-OUT SPOT.

No. 52. AT EDGE OF SHELLED-OUT SPOT.

No. 53. SLAG CRACK NEAR EDGE IN No. 54. SLAG % IN. BELOW TREAD IN

SOLID METAL. SOLID METAL.

MICROPHOTOGRAPHS OF SHELLED-OUT TIRE D. 50 DIAMETERS.

No. 55. AT EDGE OF SHELLED-OUT SECTION. No. 56. Vi« IN. BELOW TREAD OF SHELLED-

orx SECTION.

No. 58. STRUCTURE % IN. BELOW TREAD

No. 57. SLAG AT EDGE OF SOLID METAL.

No. 59. STRUCTURE AT EDGE OF TREAD. No. 60. SLAG AT CENTER OF TREAD.

MICROPHOTOGRAPHS OF SHELLED-OUT WHEEL E. 50 DIAMETERS.

No. 63. STRUCTURE % IN. BELOW TKEAD. No. 64. STRUCTURE yz IN. BELOW TREAD.

M1CROPHOTOCRAPHS OF SHELLED-OUT WHEEL F. 50 DIAMETERS.

No. 69. No. 70.

MICROPHOTOGRAPHS OF .BURNED METAL OF SCHOEN STEEL WHEEL.
50 DIAMETERS.

BURNED METAL OF SCHOEN STEEL WHEEL

OME AREAS OF CONTACT BE-
TWEEN WHEELS OF VARIOUS
DIAMETERS UNDER LOADS AND
THE RAIL.

THE mutual compression between the wheel and
the rail when under a load has an important bearing
on the durability of both and also on the adhesion of
the wheels when used as drivers. The investigation
was made with various types of cars and locomotives
to determine: the area of contact between the wheel
and the rail; the average pressure exerted per square
inch over this area; the accumulated pressure at
the center of this area; the yield of the metal in both
the rail and the wheel under the imposed load; the
relative action of the wheel and the rail under load;
the comparative action of wheels of different diam-
eters, and the comparative action of steel and cast
iron wheels.

Through the courtesy of Mr. J. F. Deems, General
S. M. P. of the New York Central Lines, the pre-
liminary work involving the use of cars and loco-
motives was done at the West Albany yards of the
New York Central & Hudson River R.R. A concrete
pier was built under one of the rails of a level piece
of track to secure a firm foundation. A section
about 10 in. long was cut out of the rail and a
short piece with perfect contour was inserted on
top of the pier. The car or locomotive under
which a wheel was to be examined was run
over this short section of rail and one wheel
allowed to rest upon it. The wheel was then
raised with its mate so that the section could be

removed and the top smeared with a thin coating
of red lead. The piece of rail was then replaced
and the wheel lowered upon it with its whole load.
This made a spot on the red lead the size of
the area of contact of the wheel and the rail.
The wheel was again raised, the section of the
rail removed, and the area of contact, as indicated
by the spot on the red lead, transferred to
tracing cloth. The rail was again smeared and
replaced, and the wheel was turned through
one quarter of a revolution and the work
repeated.

In the supplementary work in the laboratory a
section of a yS-in. tire, a section of a steel wheel and
a section of a cast iron wheel were used. One of
these sections was fastened to the plunger of the
testing machine and was raised and lowered on the
heads of short sections of rails resting on the platen
of the same. The size and shape of the contact
area was obtained by the interposition between the
tire and rail section of a piece of white tissue paper
resting on a sheet of carbon paper which made
the imprint on the white paper.

The tests at West Albany were made with three
cars and two locomotives. In all 32 contacts were
obtained, and plaster of Paris casts were taken of
the treads of the wheels at all points at which the
contact areas were obtained. Some of the wheels
were new, while others were partly worn, a condition
that evidently had much to do with the shape and
size of the spot.

These areas were carefully measured with a
planimeter and gave the following average results:

Wheels Used Under.

Total Weight
on Wheels
in Lbs.

Average of
Area Contact.

Average Weight
per Sq. In. of
Area in Lbs.

Cafe Car (35 in.) ....

6,075

•2325

28,700

Gondola (33 in.) . . . .

M.575

•3775

40,100

Consolidation Driver (63 in.)

17,325

•335°

52,080

Atlantic Driver (78 in.) . .

19.995

.6325

31,820

Atlantic Trailer (485/ie in.) .

19,210

•4725

44,400

Dining Car (34^5 in.). . .

9.4I5

.2600

37^70

In these tests the influence of weight and diameter
is partially illustrated. The two wheels of the At-
lantic engine, for example, carry about the same
weight. The areas of contact are nearly in an in-
verse ratio to the diameters. Comparing the wheels
of the cafe and dining cars, the wheel with the
heavier load has much the greater weight per sq. in.
of area, showing that the metal does not yield in
direct proportion to the weight, at least within the
limits of the loads here imposed.

In the laboratory the first series of tests made was
to apply pressures, increasing by small increments,
to the tread of a 36-in. steel wheel resting on an 8o-lb.
rail. The lowest load applied was 500 Ibs. This
was increased by increments of 500 Ibs. up to

123 4

CONTACTS OF 35-IN. STEEL-TIRED WHEEL UNDER CAFE CAR.
WEIGHT ON WHEEL, 6,075 LBS.

CONTACTS OF 3&-INCH WORN CAST IRON WHEEL UNDER GONDOLA CAR.
WEIGHT ON WHEEL, 14,575 LBS.

1 2

CONTACTS OF 78-IN. STEEL-TIRED DRIVING WHEEL, ATLANTIC
LOCOMOTIVE. WEIGHT ON WHEEL, 19,995 LBS.

20,000 Ibs.; then by increments of 1,000 Ibs. up to
30,000 Ibs.

The second series was made with the same wheel
resting on a loo-lb. rail, starting at a load of 500 Ibs.
and increasing by increments of 500 Ibs. up to 2,000
Ibs; then by increments of 1,000 Ibs. up to 10,000
Ibs.; then by increments of 2,000 Ibs. up to 30,000 Ibs.

The third series was made with a j8-in. tire on an
8o-lb. rail, starting at 500 Ibs. and then increasing
by increments of 500 Ibs. to 2,000 Ibs.; then by

CONTACTS OF 48%6-IN. STEEL-TIRED TRAILER TRUCK WHEEL, ATLANTIC
LOCOMOTIVE. WEIGHT ON WHEEL, 19,210 LBS.

increments of 1,000 Ibs. to 8,000 Ibs.; then by 2,000
Ibs. to 30,000 Ibs. and from that point by increments
of 2,500 Ibs. to 40,000 Ibs.

The fourth series was made with the 78-in. tire on
a loo-lb. rail, starting at 500 Ibs. and increasing by
increments of 500 Ibs. to 2,000 Ibs. ; then by 1 ,000 Ibs.
to 8,000 Ibs.; then by 2,000 Ibs. to 30,000 Ibs., and
finally by 2,500 Ibs. to 35,000 Ibs.

The fifth series was made with the section of a
cast iron wheel 33 ins. in diameter. This was tested
on a loo-lb. rail only, starting at 500 Ibs.; increasing
by 500 Ibs. increments to 20,000 Ibs.; then by 1,000
Ibs. to 30,000 Ibs.; then by 2,500 Ibs. to 40,000 Ibs.;
then by 5,000 Ibs. to 150,000 Ibs.

The sixth series was made with a 36-in. steel
wheel on a loo-lb. rail, and started at a load of
50,000 Ibs. which was increased by increments of
10,000 Ibs. to 150,000 Ibs.

The results obtained from these tests have been
plotted on the accompanying diagram and average
lines drawn which show the accumulated pressure
per sq. in. of area under the actual loads imposed,
the lines being an average of the results obtained.
It will be seen, on comparing the lines of the 36-in.
steel wheel and of the 33-in. cast iron wheel, that
there is comparatively little difference up to a load

500 Lbs.

Av. Pressure per
Sq. In. 7 143 Lbs.
Area .07 Sq. In.

«*

5,000 Lbs.

Av. Pressure per

Sql In. 62, 500 Lbs.

Area .08 Sq. In.

10,000 Lbs.

Av. Pressure per

Sq. In. 100,000 Lbs.

Area .10 Sq. In.

15,000 Lbs.

AV. Pressure per

Sq. In. 100,000 Lbs.

Area .15 Sq. In.

20,000 Lbs.

Av. Pressure per

Sq. In. 86.956 Lbs.

Area .23 Sq. In.

25,000 Lbs.

Av. Pressure per

Sq. In. 92, 555 Lbs.

Area .27 Sq. In.

30,000 Lbs.

Av. Pressure per

Sq. In. 96,774 Lbs.

Area .31 Sq. In.

CONTACTS BETWEEN 36-IN. STEEL-TIRED WHEEL AND 80-LB. RAIL.

500 Lbs.

Av. Pressure per

Sq. In. 16,666 Lbs.

Area .03 Sq. In.

5,000 Lbs.

Av. Pressure per

Sq. In. 62.500 Lbs.

Area .08 Sq. In.

10,000 Lbs.

Av. Pressure per

Sq. In. 71, 428 Lbs.

Area .14 Sq. In.

16,000 Lbs

Av. Pressure per

Sq. In 94,1 17 Lbs.

Area 17 Sq In.

20,000 Lbs.

Av. Pressure per

Sq. In. 105,263 Lbs.

Area .19 Sq. In.

26,000 Lbs.

Av Pressure per

Sq. In. 108,333 Lbs.

Area .24 Sq. In.

30,000 Lbs.

Av. Pressure per

Sq. In. 11 5,384 Lbs.

Area .26 Sq. In.

CONTACTS BETWEEN 36-IN. STEEL-TIRED WHEEL AND lOO^LB. RAIL.

500 Lbs.

Av Pressure per

Sq. in. 25 000 Lb*.

Area 02 Sq In

5,000 Lbs

Av. Pressure per

Sq. In. 62,500 Lba/

Area .08 Sq. In.

10,000 Lbs.

Av Pressure per

Sq In 71,428 Lbs.

Area 14 Sq. m

16000 Lbs.

Av Pressure per

Sq In 80,000 Lbs

Area 20 Sq In

20,000 Lbs.

Av Pressure p«r

Sq. In. 90, 909 L fas'.

Area .22 Sq In.

26,000 {.£*.

Av. Pressure per

Sq. In 100,000 Lbs.

Area .26 Sq. in.

30,000 Lbs.

Av Pressure per

Sq. In 100,000 Lbs.

Area SO Sq In

85,000 Lbs.

Av.. Pressure per

fl, In, 102,941 J.b».

Area .34 Sq In

40,000 Lbs

Av. Pressure per

6q. In. 111,111 Lb«

Area 36 Sq. In

CONTACTS BETWEEN 78-IN. STEEL-TIRED WHEEL AND 80-LB. RAIL.

500 Lbs.

Av. Pressure per

Sq In 16,666 Lbs.

Area .03 84. In.

10,000 Lbs.

Av, Pressure per

Sq. In 83 333 Lbs

Area 12 8q In.

16,000 Lbs.

Av Pressure per

Sq. In. 106,666 Lb»

Area '5Sq In.

20,000 Lbs

Av Pressure per

Sq In 105,263 Lbs

Area 19 Sq In

26,000 Lbs.

Av. Pressure per

5a In. 100,000 Lb».

Area .26 84. In.

30,000 Lbs.

Av. Pressure per

Sq. In. 103,448 Lbs.

Area .29 Sq. In.

85,000 Lbs

Av Pressure per

Sq. In, 109,376 Lbe

Area .32 Sq In

CONTACTS BETWEEN 78-IN. STEEL-TIRED WHEEL AND JOO-LB. RAIL.

50,000 Lbs.

Av. Pressure per

•Sq. In. 131,578 Lba.

"Area .38 Sq. Jn.

60,000 Lbs.

Av. Pressure per

Sq. In. 127,659 Lbs

Area .47 Sa. In.

70,000 Lbs.

Av. Pressure per

Sq. In 129,629 Lbs.

Area .54 Sq. In.

80,000 Lbs.

Av. Pressure per

Sq. In, 137,288 Lbs.

Area .59 Sq. In.

90,000 Lbs.

Av Pressure per

Sq. In. 135,757 Lbs.

Area .66 Sq. In

100,000 Lbs

Av Pressure per

Sq. ln.J38,888 Lb*

Area' 72 Sq. In

11 0,000 Lbs.

AV. Pressure per

Sq. In. 137,500 Lbs

Area .80 Sq. In.

120,000 Lbs.

Av Pressure per

Sq In, 141,176 Lbs

Area .85 Sq. In

CONTACTS BETWEEN 36-IN. STEEL WHEEL AND 100-LB. RAIL.£

of 22,500 Ibs., after which the load per sq. in. increases
more rapidly with the cast iron wheel than with the
steel wheel. At a load of 37,500 Ibs. there is a
marked breaking down of the metal in the cast iron

130,000 Lbs.

Av. Pressure per

Sq. In. 141 ,304 Lbs

Area .92 Sq. In.

140,000 Lbs.

Av. Pressure per

Sq. In 137,254 Lbs.

Area 1.02Sq. In.

150,000 Lbs.

Av. Pressure per

Sq In. 144 230 Lbs.

Area 1.04 S«j, In.

CONTACTS BETWEEN 36-IN. STEEL WHEEL AND 100-LB. RAIL.

wheel showing that the crushing strength has been
exceeded.

A tentative explanation of this phenomenon is
that the hard chilled cast iron wheel is practically
unyielding and that, when the load is imposed, the
whole of the compression takes place in the rail. The
area of contact is small and the average pressure per
sq. in. of area is high. The yield in the rail holds,
for a time, against the increasing load, thus cutting
down the size of the area between 22,500 Ibs. and
40,000 Ibs. The wheel itself then takes a permanent
set, increasing the area of contact very rapidly and
lowering the average. In the case of the steel wheel,
yielding takes place in both the wheel and the rail,

500 Lbs.

Av. Pressure per
Sq. In. 9,090 Lbs.
Area .055 Sq. In.

1 •*

1,000 Lbs.

Av. Pressure per

Sq. In. 14,285 Lbs.

Area .07 Sq. In.

2,500 Lbs.
Av. Pressure per
Sq. In. 33,333 Lbs.
Area .075 Sq. In.

3,500 Lbs.

Av. Pressure per

Sq. In. 43,750 Lbs.

Area .08 Sq. In.

4,500 Lbs.

Av. Pressure per

Sq. In. 50,000 Lbs.

Area .09 Sq. In.

6,000 Lbs.

Av. Pressure per

Sq. In. 54,545 Lbs.

Area .11 Sq. In.

10,000 Lbs.

Av. Pressure per

Sq. In. 83,333 Lbs.

Area .12 Sq. In.

11, 500 Lbs.

Av. Pressure per

Sq. In. 88,461 Lbs.

Area .13 Sq. In.

13,500 Lbs.

Av. Pressure per

Sq. In. 96,428 Lbs.

Area .14 Sq. In.

14,500 Lbs.

Av. Pressure per

Sq. In. 96.666 Lbs

Area .15 Sq. In.

15,000 Lbs.

Av. Pr'esaure per

Sq. In 93,750 Lbs

Area .16 Sq. In.

16,500 Lbs.

Av. Pressure per

Sq. In. 97,058 Lbs.

Area .17 Sq. In.

17,500 Lbs.

Av. Pressure per

Sq. In. 94.444 Lbs.

Area .18 Sq. In.

19,000 Lbs.

Av. Pressure per

Sq. In. 100,000 Lbs,

Area. 19 Sq. In.

25,000 Lbs.

Av. Pressure per

Sq In 125,000 Lbs»

Area .20 Sq. in.

27,000 Lbs.

Av. Pressure per

Sq. In. 128,571 Lbs.

Area .21 Sq. In.

28,000 Lbs.

Av. Pressure per

Sq. In. 127,272 Lbs.

Area .22 Sq In.

30,000 Lbs.

Av. Pressure per

Sq. In. 130,434 Lbs.

Area .23 Sq. In.

32,500 Lbs.

Av. Pressure per

Sq. In. 130,000 Lbs.

Area ,25 Sq. In.

35,000 Lbs.

Av. Pressure per

Sq. In. 134,615 Lbs.

Area .26 Sq. In.

CONTACTS BETWEEN 33-IN. CAST IRON WHEEL AND 100-LB. RAIL.

with the result that an equilibrium is established on
a smaller area and the actual breaking down of the
metal occurs under a higher pressure.

In the case of the cast iron wheel it will be
noted that the curve of average pressure shows a
break and yield of the material at a load of 27,000
Ibs., though it rises again and makes a second com-
plete break at 37,500 Ibs., from which there is no
recovery. In the case of the steel wheel the break-
down does not occur until a load of 50,000 Ibs. is
reached, and even then there is a gradual and prac-
tically uniform advance to 150,000 Ibs.

In the tests of both the cast iron wheel and the
steel wheel, the permanent set was all in the rail.
Both wheels were carefully examined with a micro-
scope after the load of 150,000 Ibs. had been imposed
and the tests were completed, and no appearance
of yielding or cracking of either could be detected.
The rail, on the other hand, showed signs of a perma-
nent set under a load of 20,000 Ibs., and this set
increased with the increasing loads. The rail was
examined immediately after applying loads of 12,000,
15,000, 25,000, 30,000, 35,000, and 40,000 Ibs. The
spot or depression left by the wheel could be seen
after the 20,000 Ibs. load had been imposed, but not
before.

The difference between the areas of contact of the
wheels under cars and locomotives and the wheels
tested in the laboratory, in which the area was
larger, is probably due to the fact that the wheels
under the cars and locomotives were worn somewhat
hollow and so fitted the rail head to a greater extent.
In service, however, the swinging of the wheels from

.87

37,500 Lbs.

Av. Pressure per

Sq. In. 138,888 Lbs.

Area .27 Sq. In.

40,000 Lbs.

Av. Pressure per

Sq. In. 137,777 Lbs.

Area .29 Sq. In.

45,000 Lbs.

Av. Pressure per

Sq. In. 136,363 Lbs.

Area .33 Sq. In.

50,000 Lbs.

Av. Pressure per

Sq. In. 121,951 Lbs.

Area .41 Sq. In.

55,000 Lbs.

Av.. Pressure per

Sq. Jn. 119.565 Lbs.

Area .46 Sq: In.

59,000 Lbs.

Av. Pressure per

Sq. In. 118,000 Lbs.

Area .50 Sq. In.

65,000 Lbs.

Av. Pressure per

Sq. In. 118 181Lbs.

Area .55 Sq. In.

70,000 Lbs.

Av. Pressure per

Sq. In. 118,644 Lbs.

Area .59 Sq. In.

75,000 L'bs.

Av. Pressure per

Sq In. 122,950 Lbs.

Area .61 Sq. In.

CONTACTS BETWEEN 33-IN. CAST IRON WHEEL AND 100-LB. RAIL.

88:

80,000 Lbs.

Av. Pressure per

Sq. In. 126,983 Lbs.

Area .63 Sq. In.

85,000 Lbs.

Av. Pressure per

Sq. In. 116,666 Lbs

Area .72 Sq. In.

90,000 Lbs.

Av Pressure per

Sq. In. 121, 621 Lba.

Area .74 Sq. In.

95,000 Lbs

Av. Pressure per

Sq. In. 121,794 Lbs.

Area 78 Sq. In.

100,000 Lbs.

Av. Pressure per

Sq. In. 120,481 Lbs.

Area .83 Sq. In.

105,000 Lbs.

Av. Pressure pot

Sq. In. 117,977 Lbs.

Area .89 Sq In.

110,000 Lbs.

Av. Pressure per.

Sq. In. 118,279 Lbs.

Area .93 Sq. In.

11 5,000 Lbs.

Av. Pressure per-

Sq. In. 116,161 Lbs.

Area .99 Sq. In.

120,000 Lbs.

Av. Pressure per

Sq In. 115,384 Lbs.

Area 1.04 Sq. In.

CONTACTS BETWEEN 33-IN. CAST IRON WHEEL AND 100-LB. RAIL.

125,000 Lbs.

AV. Pressure per

Sq. In. 119.047 Lbs.

Area 1.05 Sq. In.

130,000 Lbs.

Av. Pressure per

Sq. In. 117,117 Lbs.

Area 1.11 Sq. In.

135,000 Lbs.

Av. Pressure per

Sq. In. 119,469 Lbs.

Area 1.13Sq. In.

140,000 Lbs.

Av. Pressure per

Sq. In. 130,434 Lbs.

Area 1.15 Sq. In.

CONTACTS BETWEEN 33-IN. CAST IRON WHEEL AND 100-LB. RAIL.

one side of the track to the other brings the projec-
tions on the outer edge of the rim against the rail,
undoubtedly causing a much higher load to be put
on a smaller area of contact than was applied in the
laboratory.

The permanent set taken by the rail at so low a
load as 20,000 Ibs. raised the question of the

maximum pressure imposed at the center of the area
of contact. It was assumed that when the wheel
first touched the rail the area of contact would be a
mathematical point if both surfaces were perfectly
smooth and true. As the load is increased the
metal in both the wheel and rail yields and the area
of contact increases. This increase is from the center
out to the edge, and the pressure per unit of area is
evidently at a maximum at the center and decreases
to nothing at the edge. In order to estimate approx-
imately the maximum pressure it was assumed that
the metal in the area on which a load had once been
imposed always sustained it, and by building up
from the center by increments the final load was at-
tained. Take the case of the 36-in. steel-tired wheel
on the loo-lb. rail. An area of .03 sq. in. sustained the
initial load of 500 Ibs., with an average pressure of
1 6,666 Ibs. per sq. in. By increasing this load to 5,000
Ibs. the area is increased to .08 sq. in. If this extra
4,500 Ibs. which was applied be considered as loaded
uniformly over the whole area, there would be an
average increase of pressure of 56,250 Ibs. per sq. in.
or 56,250+16,666 = 72,916 Ibs. per sq. in. on the
original .03 sq. in. which carried the initial load of
500 Ibs. This assumption runs the load up to an
exceedingly high limit, possibly too high, as it gives
a pressure of more than 170,000 Ibs. per sq. in. at the
center of the area of contact, with a load of 20,000 Ibs.
In considering the results obtained in this investi-
gation, it must be borne in mind that the areas of
contact were all obtained under static loads. Run-
ning conditions must necessarily be more severe
and impose higher stresses. In an investigation

145,000 Lbs.

Av Pressure per

Sq. In. 123,931 Lbs.

Area 1.17 Sq. In.

150, 000 Lbs.

Av. Pressure per

Sq. In. 124,049 Lbs.

Area 1.21 Sq. In.

CONTACTS BETWEEN 33-IN. CAST IRON WHEEL AND 100-LB. RAIL.

conducted several years ago it was found that the
stresses in truck and body bolsters, while a car is in
motion, are from 20 to 50 per cent, more than the
stresses due to static loads alone. If this is true for parts
located above the springs, there must certainly be an
equal or greater increase at the point of contact be-
tween the wheel and the rail. Then, too, the blows
received from passing over low joints or worn frogs,
will raise the pressure between the wheel and the
rail to a point which the tests under static loads have
shown to be excessive. For example, the wheels,
under a car of 100,000 Ibs. capacity with a 10 per
cent, overload, carry an approximate static load of
18,750 Ibs. each. A drop of yV in. is equivalent to a
blow of about 97 foot Ibs. If the drop is checked by
a yield in the rail of three-eighths of the amount of
the drop (yf * in.) the pressure on the rail will amount
to 50,000 Ibs. This is certainly excessive.

Comparing the steel and cast iron wheels, it ap-
pears that no damage was done to either wheel under

LOAD //V POUA/DS

DIAGRAM SHOWING THE RELATION BETWEEN WEIGHTS ON WHEELS, AND
THAT ON THE AREA OF CONTACT BETWEEN THE WHEEL AND THE RAIL.

a static load of 150,000 Ibs. If the two wheels are
subjected to the pounding action of service, however,
the result cannot fail to be the earlier disintegration
of the harder, more unyielding and more brittle
material. Exact comparative data along this line
are not yet available.

The conclusions to be drawn from this part of
the work may be summed up as follows :

The average pressure imposed on the metal of the
wheel and rail is within safe limits at low loads, but
when a load of 20,000 Ibs. is reached the elastic limit
of the metal is passed and a permanent set appears
in the rail.

The accumulated pressure at the center of the area
of contact is excessive at comparatively small loads,
and is only prevented from doing injury by the support
of the surrounding metal. How far this compression
extends into the body of the two pieces of metal in
contact is not known, but presumably it extends down
to the base of the rail and into the hub of the wheel.

Under a static load the rail yields first, owing,
probably, to the fact that the metal of the surface of
the head of the rail is not as well supported by the
metal below as in the case of the wheel.

The effect of difference of diameter in wheels carry-
ing the same load is insignificant and is only appreci-
able when the difference is great. Hence it is imma-
terial so far as stresses on the wheel or rail are
concerned, whether small or large wheels, within the
limits of practice, are used.

A hard, unyielding cast iron wheel inflicts more
damage on the rail than a steel wheel, and the wear
of the rail will be greater with the cast iron wheels
than with the steel wheels.

It is probable that the reason why the damage
that would be expected from heavy wheel loads in
service does not immediately appear, is that the rail,
by bending under the passing wheel, increases the
area of contact and thus relieves the surface stresses.

COEFFICIENTS OF FRICTION BE-
TWEEN WHEELS AND RAILS.
TRACTIVE VALUES. SKIDDING
AND SLIPPING.

THE resistance of a wheel to slipping on the rail
depends upon two causes frequently confused, but
which are to be considered separately. These are
friction and abrasion.

Frictional resistance is due to the roughnesses of
the two surfaces in contact, and may be compared to
the lifting of the weight to be moved over the suc-
cessive inequalities of the surface on which it rests.
Abrasion, on the other hand, involves the removal
or cutting away of the particles of the masses in
contact. The slipping of a wheel, such as would
produce a flat spot, involves both frictional resist-
ance and abrasion. If there was no slipping of
the wheel on the rail there would be no wear, pro-
vided the rolling action did not produce sufficient
pressure on any one point to crush the metal or
cause it to flow. But there is always more or less
slip even on a straight line.

There are two kinds of slipping to which car
wheels may be subjected. One is the skidding
action due to the locking of the wheels by the brake-
shoes. The other form occurs when the driving
wheels of electric motor cars, for instance, are turned
faster than the corresponding rate of motion of the
car and the whole periphery of the wheel slides
over the rail. In order to determine whether the
resistances to these two kinds of slipping were the
same certain experiments were made.

ARRANGEMENT OF APPARATUS TO TEST THE FRICTIONAL RESISTANCE OF
CAR WHEELS TO SKIDDING.

The apparatus was designed to produce, as nearly
as possible, the actual conditions of track work.

Two pieces of steel rails of 75 Ibs. section, one of
which had been worn smooth in service, the other a
piece of new rail, together with a section of a steel
wheel and a section of a cast iron wheel, with the
treads of both smooth and free from imperfections,
were used for the tests. The testing machines were
made by Tinius Olsen & Co., one with a capacity of
100,000 Ibs. and the other a capacity of 50,000 Ibs.

The apparatus is shown in the accompanying
illustrations for the skidding movement. The wheel
section was set on the rail and loaded by the 100,000
Ibs. capacity machine. It was then slipped over the
rail by a pull on the connection rod reaching to
the other machine which measured the amount of
the pull required to slip the wheel on the rail.

Y/w//////////^^^^

TfSTMC AMCHM£

ARRANGEMENT OF APPARATUS FOR TESTING THE FRICTIONAL RESISTANCE
OF CAR WHEELS TO SPINNING.

In loading the wheel, the pressure was applied
through a plate resting on two rollers. In this way
the friction, except that between the wheel and the
rail, was reduced to practically nothing.

For the spinning motion, the bearing plate above
the rollers was made convex and the bottom plate
resting on the top of the wheel was made concave,
both surfaces being concentric with the tread of the
wheel. A pull on the wheel, therefore, caused it to
roll under the bearing plate as though it were re-
volving on its own center. The arrangement of this
is clearly shown in the diagram.

The force required to move the wheel on the rail
was weighed by a bell crank with a knife-edge bear-
ing, resting on a heavy casting attached to the bed

plate of the small testing machine. The vertical arm
was attached to the pull rod and the end of the
horizontal arm had a bearing on a wedge or knife
edge that was forced down by the platen of the
machine.

The wheel section was placed in position on the rail
and weighted with a predetermined load. Pressure
was then applied to the wedge on the small machine.
This pressure was transferred through the bell crank
as a pull on the connecting rod. When slipping
occurred, the event was marked instantly by the drop
of the beam of the small machine. The movement of
the wheel over the rail usually amounted to about
-fa in. As the object of the investigation was to
determine the friction at rest no attempt was made
to measure the pull after the first slip occurred.
This was markedly less than that required to start
the movement from a state of rest.

Separate tests were made with steel and cast
iron wheels on the old and new rails, for both the
skidding and spinning motions. In loading the
wheels, the weights were increased by regular incre-
ments of 2,000 Ibs. up to 30,000 Ibs. Three tests
were made with each loading and for each condition
of wheel movement. The average of the three tests
in each case is given in the accompanying table.

There was so little difference in the pull required
to slip the wheels on the old and new rails that an
average of the results obtained is given as the resist-
ance to spinning and skidding of the two wheels on
a steel rail.

The table shows that the resistance to spinning of
the steel wheel is somewhat greater than that of the

COEFFICIENTS OF FRICTION BETWEEN WHEELS
AND RAILS.

Kind of Motion

Load on Wheel

Spinning

Skidding

Steel

Cast Iron

Steel

Cast Iron

Wheel.

2,000

•259

•243

.285

.287

4,000

.240

.215

.254

.259

6,000

•234

.208

.245

.254

8,000

.228

.206

.246

.242

10,000

.215

.204

.238

•233

1 2,000

.212

.205

•237

.223

14,000

.207

.199

•233

.226

16,000

.204

.I96

.232

.219

18,000

.204

.I98

.231

.2I9

20,000

.201

.194

.236

.220

22,000

.205

.191

.238

.223

24,000

.204

.192

•235

.224

26,OOO

.205

189

.232

.223

28,OOO

.203

.186

.236

.217

3O,OOO

.203

.183

•234

.214

cast iron wheel, a fact which is brought out more
forcibly in the table of coefficients of friction, in
which the coefficient of the steel wheel is invariably
higher than that of the cast iron.

It also appears from this table that the coefficient
of friction of the steel wheel decreases as the load is
increased, up to a pressure of about 15,000 Ibs., after
which it is practically constant. The coefficient of
friction of the cast iron wheel decreases rather rapidly,
like that of the steel wheel, up to a load of 15,000
Ibs., after which it falls away slowly, though a
tendency to decrease with the increase of load is
manifest.

As regards skidding, the values of the coefficients
of the two wheels bear the same relation to each other

as they do for spinning. The coefficient of resistance
is greater for the steel wheel than for the cast iron
wheel, and there is the same falling off in the value
of the coefficient as the load is increased up to about
15,000 Ibs., after which that of the steel wheel is
nearly constant, while that of the cast iron wheel
continues to fall away slowly. It would be difficult
to explain these phenomena without the data ob-
tained in the investigations previously described,
made to determine the area of contact between the
wheel and the rail, and the relative rate of abrasion
of the steel and cast iron wheels on the emery wheel.
The results of those investigations also serve to ex-
plain why the coefficient for a skidding wheel is
higher than the coefficient for a wheel that is spinning.
In the case of the cast iron wheel, it was shown in
the preceding chapter that the imposition of a heavy
load caused a breaking down of the metal in the
rail at a certain point, while no such failure occurred
with the steel wheel under the same load. The cast
iron wheel being rigid, inelastic and incompressible
on the tread, was forced down into the metal of the
rail, causing the rail to do all of the yielding needed
to produce the area of contact obtained, with the
result that it was soon compressed beyond its elastic
limit and given a permanent set. The steel wheel
yielded as well as the rail, thus relieving the rail of
a part of its compression and increasing the area of
contact. This behavior of the two wheels explains
in part the results obtained in these tests. In ad-
dition, it must be remembered that the normal co-
efficient of friction is greater between steel and steel
than it is between cast iron and steel.

When the cast iron wheel is loaded on the rail it
indents the rail, in proportion to the pressure ap-
plied, without being distorted itself. If, then, it is
turned, as by a motor, it simply revolves in the concave
depression in the rail, without undergoing any de-
formation itself and with no resistance other than
that of overcoming the friction between the surfaces
of the wheel and rail. The steel wheel, on the
other hand, is itself compressed as well as the rail,
so that when it is turned a continuous progressive
compression of the tread is set up, equal to the
amount of the original compression. Hence, the
resistance to turning will be equal to the frictional
resistance plus that set up by this compression.

It was shown that the cast iron wheel was cut
away much more rapidly under the emery wheel
than were the steel tires and wheels. In the tests
for skidding, the loads were successively applied
without readjusting the wheel on the rail, with
the result that the steel wheel was skidded about
ij in. and the cast iron wheel about I in. This
was done under loads increasing from 2,000 Ibs.
up to 30,000 Ibs. Under this treatment the steel
wheel developed a slid-flat spot about -f$ in. long,
and the cast iron wheel a spot about | in. long. In
both cases the rail was spotted and the metal was
rolled up in folds, indicating the direction of the
motion of the wheel. The piece of rail used with
the steel wheel was spotted for a distance of about
if in., while the piece used with the cast iron wheel
was spotted for a length of about i\ in. This
abrasion of the cast iron wheel probably accounts
for the lower resistance to skidding as compared with

101

the steel wheel. For the same weight and for the
same distance of skidding, the amount of metal
abraded from the cast iron wheel was in almost
exactly the same ratio to that removed from the steel
wheel, as is shown in the diagram of abrasion tests.

It will be remembered that, for the lower wheel
loads, the investigation of contact areas showed that
there was comparatively little difference between the
areas obtained with cast iron wheels and with steel
wheels, and that it was inferred that the total com-
pression of the metal was approximately the same
in both cases. Under these circumstances it would
be expected that, if the power required to distort the
metal of a steel rail and tire were the same, the
resistance to skidding of the steel wheel and the cast
iron wheel would also be the same. But, owing to
the more rapid abrasion of the cast iron wheel, as
soon as it begins to skid it wears, and by thus in-
creasing the area of contact it lessens the depression
of the rail, decreases the amount of metal to be
distorted, lowers the resistance to the motion, and
makes the coefficient of friction of skidding less on
the cast iron wheel than on the steel wheel.

This depression of the rail due to the imposition of
the wheel load accounts for the higher coefficient of
friction obtained with a skidding wheel than with a
spinning wheel. With a wheel spinning there is no
continuous deformation of the metal of the rail to be
effected. In skidding there is a depression of the
rail to be carried forward like a wave, which natural-
ly raises the resistance and makes the coefficient
greater than where slipping over one spot alone
takes place.

102

While it is not safe to draw rigid conclusions from
the limited amount of data obtained, it does appear
that inasmuch as the steel wheel offers greater re-
sistance to spinning it is better adapted for use as the
driving wheel of an electric car than the cast iron
wheel; and further, its higher coefficient of friction
renders it less liable to skidding.

This matter of wheels skidding, with the conse-
quent development of flat spots on the tread, was
considered of enough importance to warrant further
investigation.

It has been noted by many other investigators
that steel wheels do not flatten as readily as cast iron
wheels. By some this is attributed to the fact that
small flat spots once formed on the tread of a steel
wheel may be rolled out, whereas they have a tend-
ency to grow larger on cast iron wheels. The
abrasion and skidding tests which have been made
seem to show, however, that it is the lower resistance
to grinding of the cast iron wheel that accounts for
the more rapid development of these flat spots.

To briefly recapitulate, these tests showed that the
rate of grinding of the first J in. below the tread was
about 4.64 times as fast in the cast iron wheel
as in the Schoen steel wheel. For the second
J in. the ratio became 6.37 and for the third | in.
15.93, showing the rapid decrease of wearing resist-
ance of the cast iron wheel below the surface. In
the skidding tests in the laboratory the effects were
confined to the metal close to the surface, and it
was found that, with the same amount of skidding,
the amount of metal removed was about 5.12 times
as great on the cast iron wheel as on the steel wheel.

103

A further check on these figures was afterwards ob-
tained by taking the time required to remove approxi-
mately the same amount of material from the treads
of cast iron and steel wheels in a wheel grinding
machine. It was found that it took from four to
five times as long to grind down the steel wheels as
it did to grind the cast iron wheels. In all of the
foregoing investigations the metal of the wheel under
test was kept cool, either by a stream of water
or by doing the work so slowly that natural radia-
tion counteracted the tendency to heat, and the
temperature of the metal was not raised above 100
deg. Fahr.

For the purpose of ascertaining whether the re-
sults of these investigations were comparable with
the results obtained in actual railroad service, when
the wheels were locked and skidded under a car,
series of tests were made by skidding the wheels
under a loaded car.

Through the courtesy of the New York, Ontario
& Western Railroad a piece of track and a suitable box
car were supplied for the tests. One pair of wheels
and axle were removed from under the car, and
replaced by an axle on which a Schoen steel wheel
and a new cast iron wheel had been pressed. These
wheels were 33^ in. and 33 in. in diameter, respect-
ively. This pair of wheels was placed at the end of
the car, and was fitted with two brake-beams, so that
twice the usual brake-shoe pressure could be applied
on the wheels. By this means the wheels could
be held in a fixed position throughout a run. But
it was more difficult to hold the wheels at low speed
than at high speed.

104

The car was loaded until the weight on the pair of
wheels to be tested was exactly 24,000 Ibs. The car
was then hauled back and forth over a piece of track
1,850 ft. long. The brake was set and the wheels skid-
ded for the whole distance. The car was hauled at
two speeds, namely, three and twelve miles an hour.

When the car was hauled at a speed of three miles
an hour, flat spots were made on the steel wheel about
.30 sq. in. in area, while the spots formed on the cast
iron wheel were .80 sq. in. in area. These areas
correspond to diameters of about f in. and i in.
respectively, though the spots on the cast iron wheel
were elongated to about if in., which indicated some-
what more metal removed. The volume of metal
abraded from the cast iron wheel was about 5! times
greater than that from the steel wheel.

While the movement was slow the wheels remained
cool. But when the speed was increased to twelve
miles an hour heating took place and the cutting
was more rapid on the steel wheel.

For the first 1,850 ft. run the areas of the flat spots
produced at a speed of 12 miles an hour averaged
8.125 scl- ms> on tne steel wheel and 4.445 s(l- ms- on
the cast iron wheel. The estimated amount of
metal worn away was 4.63 times as much with the
steel wheel as with the cast iron wheel.

When the skidding was continued the rate of wear
increased very rapidly with the cast iron wheel, while
there was little increase with the steel wheel. At
the end of the run of 3,700 ft. the area of the flat
spot on the steel wheel was 8.43 sq. ins., an increase
of .305 sq. in., while the area of the spot on the cast
iron wheel was 5.72 sq. ins., an increase of 1.275 sq. m-

105

From this it appears that the cast iron wheel wore
away more rapidly than the steel wheel after the
hard surface metal had been broken through.

The indications are that in skidding a short dis-
tance at low speed a cast iron wheel is more apt to
develop a flat spot than is a steel wheel. On the
other hand, if the skidding continues for some dis-
tance at a high speed, the wheel becomes heated and
then the steel wheel is the first to yield, unless the
surface chill of the cast iron wheel has already been
worn through.

106

ATERAL THRUST OP WHEELS
AGAINST THE RAILS. BREAK
ING STRESSES OF WHEEL
FLANGES.

IT is generally admitted that cast iron wheels under
high capacity cars are giving unsatisfactory service
and, because of their inherent lack of strength, are
a source of danger. Prior to 1905 little was known
of the strength of these wheels except that they had
a shorter life and gave far more trouble from flange
breakage under the high capacity cars than they
had under cars with a capacity of only 60,000 Ibs.
In that year Professor Goss made some tests in
the laboratory of Purdue University to ascertain
the strength of the flanges of cast iron wheels.

Six new wheels and one wheel which had broken
in service were tested. The wheel to be tested was

APPARATUS FOR TESTING STRENGTH OF WHEEL FLANGES.

107

TABLE OF BREAKING STRESSES OF WHEEL FLANGES.

No.
of
Test

Breaking
Load.
Lbs.

No. of Wheel.

Point of Application
of Load.

Remarks.

52,850

M. C. B. 19413

Between brackets

47.75°

Opposite "

49,35°

Between "

53»4°o

Opposite "

62,850

M. C. B. 19410

Between "

48,700

Opposite "

58,250

Between "

58,000

Opposite "

74,850

M. C. B. 19254

Between "

72,200

Opposite "

87,000

Between "

68,550

Opposite "

99,300

(e) 650 Ibs.

Between "

100,000

Opposite "

105,900

Between "

68,200

««

Opposite "

f Wheel

79»35°
52.3oo

J9558

« «
Between «

1 broke
I through
l_rim.

111,600

(f ) 700 Ibs. Tape I

Opposite «

87,000

Between '

109,900

Opposite '

98,900

M( 1904 M. C. B. )
(s) 1 700 Ibs. Tape 2 J

K <«

98,900

il l«

mounted on a strong mandrel secured to the base
of the testing machine in such a manner that it could
not slip, and a punch was forced down against the
flange in the same way that the rail presses against
it in service. Pressure was applied until the flange
broke. The general arrangement of the apparatus
is shown in the illustration on page 107. The punch
A was bolted to the head of the machine. It was
prevented from springing away from the work by
a roller bearing against a bracket which was bolted
to the platen of the machine.

108

AVERAGES OF BREAKING STRESSES OF WHEEL
FLANGES.

Average Breaking
Load. Libs.

No. of Wheel.

Remarks.

5°,837

19,413

Taken from service

56,95°

19,410

« «< «

75,65°
52,3°°

19,254
19,558

Broken wheel taken
from service.

Three of the wheels tested, Nos. 19,413, 19,410
and 19,254, were new wheels of M. C. B. dimen-
sions. The fourth, No. 19,558, was a piece of a
wheel which had broken in service. In addition to
these specimens three new wheels were tested which
were especially designed to give increased flange
strength. These were marked

(e) 650 IBs.

(f) 700 Ibs. Tape i

(g) 700 Ibs. " 2

Wheels (e) and (f ) were of a reinforced flange design
and wheel (g) was the then proposed Standard of
the M. C. B. Association with reinforced flange.

Four tests were made with each of the M. C. B.
standard wheels, and from two to four tests with
each of the others. The results are given in detail
in the Table of Breaking Stresses of Wheel Flanges.

Three of the tests made on the (e) wheel showed a
flange strength of approximately 100,000 Ibs., while
the fourth test (16) gave only 68,200 Ibs. In view
of this wide difference an attempt was made to get
a fifth test from this wheel by applying pressure
to the flange midway between two of the breaks

109

previously made, with the result that the wheel broke
through the rim at 79,350 Ibs.

Test No. 1 8 was made on a piece of a wheel
which had broken in service and the holding device
which had been employed for new wheels had to
be supplemented by additional clamping for the
test. For this reason it is not known whether the
results obtained from the fragments are entirely com-
parable with those obtained from the whole wheels.

It will be seen from these tests that not only were
there wide variations in the strength of flanges of
wheels of similar design but in different parts of
the flange of the same wheel. Reinforcing the flange
added to the strength, but even in individual wheels
thus reinforced there is a variation from 68,200 Ibs.
to 105,900 Ibs. in the breaking strength.

These tests cover practically all that is known of
the strength of the cast iron wheel to resist the
thrust on the rail. In order to ascertain approxi-
mately the relative strength of the steel wheel under
similar conditions a Schoen wheel was tested in
the same way. The work was done under a power-
ful hydraulic press and the flange broke off under a
load of 526,612 Ibs. This was more than 4.7 times
the load required to break the strongest part of the
reinforced flange and more than 1 1 times the load re-
quired to break the weakest of the standard flanges.

The ratio of 4.7 to I corresponds fairly closely
with the ratio of the tensile strength of the two
metals. It has been seen that the tensile strength
of the steel of the Schoen wheel is about 124,000
Ibs. In some tests of cast iron that have been made
it was found that samples of gray iron made from

TRACK APPARATUS FOR ASCERTAINING WHEEL AND RAIL PRESSURES.

Ill

first-class wheel mixtures broke at from 16,000 Ibs.
to 17,000 Ibs, while test specimens, carefully ground
from the white chilled iron of a car wheel, broke
under loads as high as 36,000 Ibs.

The lack of any data on the stresses to which
wheels are subjected in service, other than that
based on theoretical calculations, necessitated the
carrying out of a series of investigations which
would throw some light on the subject from a practi-
cal standpoint. The object was to determine the
lateral thrust to which the wheels under high capac-
ity freight cars may be subjected when moving over
curves at different speeds, and, if possible, to develop
the law in accordance with which the thrust in-
creases as the speed of the car is increased.

As an investigation of this kind had never before
been undertaken, it was necessary to design and
build a special piece of apparatus.

The device as a whole may be divided into two parts :
the track apparatus and the recording instrument.

The track apparatus consisted of a section of rail
3 ft. long held in position in the track and free to
move outward by an amount sufficient to exert a
pressure on a hydraulic cylinder in proportion to
the lateral thrust against it.

The recording instrument was set on a small table
placed about 7 ft. from the track and was connected
with the cylinder of the track apparatus by a J-in.
brass pipe. It consisted of an ordinary pressure gauge,
having a maximum registration of 200 Ibs. per sq. in.,
a recording pressure gauge and a pressure pump by
which an initial pressure could be put on the whole
system of piping. The ordinary pressure gauge was

113

S f£* HOUR

~& PCRHOUR

*. £.-•

JD47 IBLE& FEJ* HOUR
SAMPLES OP SPEED K.ECBTKAT1OKS.

one made by the Utka Steam Gauge Co. and was
fitted with a diaphragm spring. It was carefully test-
ed and the dial calibrated before being put in service.

The recording pressure gauge was a modification
of the Metropolitan recording gauge made by
Schaeffer & Budenberg. The clockwork in it was
removed and the paper drum driven by hand, so
that a record of indefinite length could be obtained.
The fact that this paper was driven by hand ex-
plains the irregularity of the intervals elapsing be-
tween the passage of the several wheels of the cars.
This gauge also had a maximum registration of 200
Ibs. per sq. in. with a pen travel of 4 ins., the width
of the paper. A Bourdon tube was used as the
spring for this gauge. It was calibrated for each
set of tests by the Utka gauge and its indications
marked on the paper on which the record was taken.

The piping and all spaces filled with liquid were
so arranged that air pockets were entirely eliminated

and before work was commenced it was definitely
ascertained that the whole space was completely
rilled with liquid free from bubbles of air.

The speed of the experimental car as it passed
the instrument was registered by means of two
trips placed alongside the track and arranged to be
struck by one of the journal boxes of the car as it
passed. The trips closed an electric circuit passing
through one of the coils of a double registering
Morse telegraph instrument. When the trip was
struck by the journal box, the circuit was tem-
porarily broken and the pen lifted, leaving an open-
ing in the line drawn on the strip of paper traveling
through the instrument. The time was indicated
by a clock making and breaking an electric circuit
at half-second intervals. This circuit passed through
the other coil of the register. The two records were
made side by side and the intervals between the
breaks, on the otherwise continuous line, showed the
time elapsing between the striking of the two trips.
These trips were spaced 66 ft. apart, so that the speed
of the passing car could be readily calculated. Speci-
mens of these records are shown in the accompanying
diagram where the car was moving at 9.14, 13.26,
14.21, 2 1.8 1, and 30.61 miles per hour, respectively.

Through the courtesy of the Pittsburgh, Cincin-
nati, Chicago & St. Louis Ry., facilities were sup-
plied for making this investigation of wheel stresses.
The instrument was placed in the outer rail near the
end of a curve of 1,307 ft. radius or about 4° 25'.
The elevation of the outer rail was 3! ins., which is
correct for a speed of 36.66 miles per hour. At the
point where the records were taken the car was well in

EXAMPLES OP LATERAL THRCST
TOTAL WEIGHT,

5107

/730M1L£S />£* HOUR

DIAGRAMS OP LOADED COAL CAR.
OR 4° «' CURVE.

OF LATERAL THRUST
WITH CARS OF

T10XS OF LOADED COAL TRAINS,
LBS. CAPACITT.

on the curve, with the trucks set in die normal posi-
tion, and all the elements of entering the curve were
removed. It may be added that the curve was a
simple one, with no easement at either end.

On the approach of a train, or the experimental
car, an initial pressure was put on the piping
system, in order that the movement of the register-
ing pen might be reduced to a minimum and with
it the effect of the inertia of the parts. This initial

it*

pressure was varied according to the speed . In opera -
don the actual movement of the floating rail was
imperceptible. The levers divided the actual move-
ment by five at the diaphragm, which yielded only
enough to take die expansion of the Bourdon tube
and the diaphragm of the pressure gauge, when
delivering from a cylinder 6 in, in diameter.

Records were taken of a number of passing trains,
and also a special series of measurements was made
with a loaded coal car run at different speeds over
the apparatus. Some of the records are shown in
the accompanying diagrams,

In the records of the loaded coal trains, taken as
they pafffi, no memorandum of the weights of the
cars was obtained. The weights were, however,
approximately the same, and yet there were wide
variations in the lateral thrusts of the wheel against
the rait For example: In the train moving at
9,35 miles per hour these thrusts varied from 2,260
Ibs, to 7,2 1 o Jbs., with an average of 4,835 Ibs. On
another train, moving at 12x35 miles per hour, the
thrust varied from 7,070 Ibs. to 10,605 Ibs., with an
average of 8,205 Ibs.; while on another, moving at
4-04 miles per hour, the average was 5,543 Ibs., with
a range from 4450 to 6,635 ">*• ^n one case a car reg-
istered a thrust of 16,175 Iks. wnen moving at 14-35
miles per hour. This wide variation in the lateral
thrust of different cars in the same train at the instant
of passing the apparatus was still more strikingly
shown jn the senes of tesn made with a single car.

The tests with a single car consisted of 33 runs over
the apparatus, at speeds varying from 4.57 to 31-25
miles per hour. The car used was a hopper-bottom

coal car of 100,000 Ibs. capacity and weighing,
when empty, 39,500 Ibs. It was designated as of
the Gl class of the Pennsylvania Lines West. The
total weight of the loaded car was 142,300 Ibs.

This car, after being started some distance from
the apparatus, was cut loose from the engine and
allowed to drift over the track instrument.

The following table gives the records that were
made:

Test
No.

Speed.
M.p. H.

Wheel

No.

Lateral Thrust.
Lbs.

4-57

2,470

1,415

1,695

1,415

7.63

1,695

1,415

10.43

»»S4S

1,770

1,695

7.39

2,400

1,415

8.57

2,120

1,270

1,415

8.20

1,840

1,415

118

Test

No.

Speed.
M. p. H.

Wheel
No.

Lateral Thrust.
Lbs.

9.60

1,695

1,415

1,270

««

IO.2I

3,250

3,"o

4,240

3,250

9.60

3.535

3,535

««

<«

4,240

(«

3»i95

9.60

3.535

(«

3,250

4,380

<«

3,250

15.62

3,"o

««

2,970

2,400

11.00

4,950

4,240

3,96o

«<

(«

3,8i5

I6.SS

4,525

3»535

4,525

««

3,395

I4.I8

3,8i5

3,535

«<

««

5,935
4,665

12.63

3,393

«<

3,25o

4,857

<«

3,25°

119

Test
No.

Speed.
M. p. H.

Wheel
No.

Lateral Thrust.
Lbs.

13-33

I
2

4,810
4,8 10

«<

7,350
5,800

TEST OF AUGUST 6TH, 1907.

17
«(

9.14
«

6,645
5,655

«(

4,95°

4,240

13.26

8,055

7,775

7,635

6,645

13.66

10,460

«<

7,490

(«

2O
«<

13.27
u

7,210

6,645

6,500

<«

1 6.2 1

4,665

«<

(«

«(

6,220

««

18.00

7,210

6,645

«i

17.58
«

6,785
6,360

7,775

(«

6,645

14.21

9,895

((

«<

9,470

10,320

««

8,480

Test
No.

Speed.
M.p. H.

Wheel
No.

Lateral Thrust.
Lbs.

10.91

2,825

3,110

18.46

10,320

9,100

10,605

10,320

21.81

4,950

7,490

5,230

19.03

16,785

7,350

5,090

25.10

5.655

5'655

5.655

3.675

25.10

io,745

9.330

10,180

9,615

27.91

10,605

9,895

9,615

3i;25

10,035

8,200

11,025

7,775

30.61

12,445

11,310
12,865

9,190

I II

/QOOO

^6,000

DIAGRAM OF LATERAL THRUST OF LEADING WHEEL OF FORWARD TRUCK
OF LOADED COAL CAR. TOTAL WEIGHT, 142,300 LBS., ON 4° 25' CURVE.

The column headed "Wheel No." indicates the
order in which the wheels passed over the apparatus.
Thus: I indicates the front wheel of the forward
truck; 2, the second wheel; 3, the front wheel of the
rear truck, and 4 the rear wheel. The blank spaces
in the column of lateral thrust indicate no record
obtained, because of the fact that the initial pressure
put on the apparatus was greater than the wheel

122

thrust, so that the thrust produced no movement of
the pen. Throughout the whole series of tests the
weather was fine and the rail dry.

For convenience of reference and comparison the
lateral thrusts of the front wheel of the forward
truck have been plotted on the accompanying dia-
gram. This diagram shows graphically the wide
variations in the lateral thrust of the wheel. From
it it is impossible to deduce any positive ratio be-
tween the speed and the thrust, but it shows that
there is a relationship and that the higher the speed
the greater the thrust. There are a number of
records for the first wheel, extending from about
7.63 miles an hour to 16.55 miles an hour that lie in
a straight line drawn from just below the record of
31.25 miles an hour of 10,035 Ibs. The line drawn
through these points is represented by the equation:

T = 333V- 800

in which

V = Lateral thrust of wheel in Ibs.
T = Speed in miles per hour.

This must be regarded as a tentative formula only
and one which evidently will not hold for very low
speed. But from the records that have been obtained
it gives the lowest values and therefore it cannot be
criticized as being too high.

Attention is also called to the fact that the pres-
sure seems to increase directly as the speed and not
as the square of the speed which is the rate of in-
crease of the centrifugal force. The probable rea-
son for this is that none of the speeds recorded were
equal to or exceeded the speed corresponding to
the superelevation of the outside rail. Therefore,

centrifugal action has no effect. In running around
a curve the car must be deflected from the tangent
at a certain rate, and this requires a certain definite
amount of power. If, then, this power is exerted in
a short period of time, a higher pressure will be put
against the rail than if the time was longer, and,
therefore, the pressure will vary inversely as the
time. So that if the car passes around the curve in
half a minute the pressure will be twice what it
would be if a minute was required. Hence the
pressure at thirty miles an hour would be twice
that at fifteen miles an hour.

When the speed exceeds that for which the super-
elevation is calculated centrifugal action will then
begin to manifest itself, and there will then be a
more rapid rise of pressure than would be found
from the equation given on page 123. This additional
increase would be in the ratio of the square of the
speed. For example: At a speed of 36.66 miles
per hour the centrifugal effect is balanced by the
superelevation of the outer rail on the curve on
which these investigations were made. At 40 miles
per hour the centrifugal force is 1.19 times as great,
and this 19 per cent, additional manifests itself as
additional lateral thrust above that called for by the
formula.

Taking the car under consideration, weighing
142,300 Ibs., the centrifugal action would be 9,648
Ibs. at 36.66 miles per hour, 11,481 Ibs. at 40
miles per hour, and 14,568 Ibs. at 45 miles per
hour. The excess centrifugal force to be dis-
tributed among the four wheels of the car at
40 and 45 miles an hour would be, therefore,

124

1,833 Ibs. and 4,920 Ibs. respectively. If 25 per
cent, of this is taken by the front wheel, which
is a low estimate of what would actually be im-
posed, there would be an extra load of 458 Ibs. and
1,230 Ibs. added to the stress given by the formula
for that imposed on the front wheel. This then
becomes

11,408 Ibs. at 36.66 miles per hour
12,978 Ibs. at 40 miles per hour
15,415 Ibs. at 45 miles per hour

It must be remembered that these are minimum
values, and that blows due to soft spots in the track,
kinks in the curve, bent rails, low joints and cramped
side bearings will greatly increase this thrust. Suffi-
cient data, however, has not yet been obtained to
warrant any estimate of how much this increase
would be. The diagram shows that stresses far
above those found from this tentative formula are
imposed on the wheels.

The extreme case occurred in test No. 19, where
the thrust was 6,711 Ibs. in excess of that found
from the formula. If the blow or cramping which
caused this excessive thrust at 13.66 miles per hour
was to occur at a speed of 45 miles per hour, the
thrust that might be expected would be 22,126 Ibs.,
and if it were to be increased in proportion to the
speed it would become more than 36,000 Ibs. This
may be an extreme and exceptional case, but the
results obtained seem to indicate that at least as
great a stress as this should be provided for.

Referring again to the tests of flange strength made
in 1905 by Professor Goss, in the 23 tests that were

made, the pressures required to break the flange
ranged from 47,750 Ibs. to 109,900 Ibs., with an
average of 75,874 Ibs. This gives a possible factor
of safety of a little more than 2.5 when the maximum
stress is taken at 30,000 Ibs., but it drops to a little
more than 1.5 when the strength of the weakest
wheel is taken as the basis of comparison. This is
for new wheels. When they have become somewhat
worn the strength of the flange is less and the factor
of safety is decreased still more. If this loss of
strength in the old wheel is taken at 10 per cent.,
because of metal worn away, the strength of the
weakest wheel used in the tests referred to would be
42,975 Ibs., and this would allow a factor of safety
above a maximum load of 30,000 Ibs. of about 1.4.

In this comparison it has been assumed that a car
of 100,000 Ibs. capacity will deliver the maximum
thrust to the wheel on a 4^ degree curve at 45 miles
per hour. This assumption was made because the
data was obtained from such a curve. It is evident
that greater stresses would be imposed on curves of
sharper radius. The outer thrust, where centrifugal
action is eliminated, would probably vary inversely
as the radius of curvature. There is no data, as yet,
to support this position, but it appears probable.
If on further investigation this relation is found to
hold, then, instead of a thrust of 12,520 Ibs. being
put on the wheel, as in the case of a car moving over
the 4° 25' curve at 40 miles an hour, there will be a
thrust of nearly 22,800 Ibs. when the same speed is
maintained over a curve of 8°. To this must be
added the extra stresses that may be set up by blows,
cramping of the wheels between the rails, the binding

126

of side bearings and other causes which may result
in an increase of the normal stress.

But one weight of car and one arrangement of
wheel base has been here considered. There is, as
yet, no data to give any idea as to the effect of weight,
its distribution on the wheels or the height of the
center of gravity, all of which are undoubtedly
important.

On the other hand, in this discussion, the whole
lateral thrust is considered as resisted by the flange.
Under ordinary running conditions this is not the
case, for the frictional resistance of the tread of the
wheel on the rail must be subtracted from the total
thrust. In the car under consideration the weight
on the front wheel was 17,900 Ibs. If the coefficient
of friction is taken at 0.25 then 4,475 Ibs. should be
subtracted from the pressure given. This would
reduce the maximum pressure, as it has been cal-
culated for a speed of 45 miles per hour, to 31,525
Ibs. and the probable minimum to 10,930 Ibs. It
must be remembered, however, that the frictional
resistance is apt to fail suddenly and that at all speeds,
even where the frictional resistance of the tread on
the rail is greater than the lateral thrust, there must
be a pressure on the flange in order to effect the
deflection of the car on the curve.

In this comparison the front wheel of the leading
truck only has been considered, because it is on this
wheel that the heaviest lateral thrust is imposed.
The table shows that, in general, the maximum
lateral thrust is on the first wheel; the thrust on the
second is less; on the third it falls between the first
and the second, and on the fourth it is the lowest.

In considering the advisability of using cast iron
wheels under high capacity cars, it should be borne
in mind that the cast iron wheel averages approxi-
mately one-half the life under the cars of IOO,OQO
Ibs. capacity that it does under cars of 60,000 Ibs.
capacity. The use of the heavy braking pressure on
long grades has been the cause of many failures,
because of the additional strains set up due to the
heating by the brake shoe. There is a consequent
expansion of the rim, and the actual resisting
strength of the flange is lowered below that shown
in the laboratory tests, which were made with the
wheel cold and the metal at its maximum strength.
Roads having long, steep grades usually have
numerous sharp curves also, and the wheels are
likely to be subjected to the most severe stresses
when they are least able to resist them. If the lateral
thrust on the flanges of wheels, under a loaded car of
100,000 Ibs. capacity, runs up as high as 30,000 Ibs.,
and the actual breaking strength of the flanges of
cast iron wheels varies from 45,000 Ibs. to 105,000
Ibs. under the most favorable conditions, the
question seems pertinent, is it safe to use such
wheels under high capacity cars, in view of the fact
that cast iron wheels deteriorate rapidly with wear
and successive brake-shoe heating?

The answer depends upon what the user deems a
proper factor of safety for such service or the
risks he can afford to run.

128

PRESENTATION OF THE ADVAN-
TAGES CLAIMED FOR THE
SCHOEN SOLID FORGED AND
ROLLED STEEL WHEEL AS
BASED UPON THE RESULT OF THE
INVESTIGATIONS SET FORTH IN THE
FOREGOING CHAPTERS, TOGETHER
WITH THE DEMONSTRATION OF
SERVICE TESTS.

BY THE SCHOEN STEEL WHEEL CO.

THE investigations of the physical and chemical
properties of car wheels outlined in the preceding
chapters show what is being done in the manufac-
ture of car wheels and steel tires and the require-
ments which must be met in service. Acting
upon the accepted theory that steel must have a
maximum amount of work put upon it to insure its
integrity and efficiency, consideration of cast steel
wheels has been ignored. It has been shown that
the metal in the Schoen solid forged and rolled
steel wheel is in all respects equal to if not better
than the metal in standard brands of steel tires and
wheels as regards physical properties. It would
naturally be expected then that these wheels should
compare favorably in wearing qualities and strength
in actual service. This expectation has been com-
pletely fulfilled by the wheels which have been running
under tenders, freight and passenger cars, and street
and interurban electric cars. The Schoen solid forged
and rolled steel wheel has been found to give mater-
ially greater mileage for the same limit of wear than
steel-tired wheels under exactly the same conditions.

1*9

TOTAL

N9503
M/LEXQE P£ft fc

- 322/7

N2522

TOTAL WEAR .346 M/LEAGE PEfi^' WEAfi- 33/43
WEAR OF SCHOEN STEEL WHEELS UNDER POSTAL CARS.

MITFAPF OF/513 AN° ^=154,732.
MILEAGE OF j ^ ANJ) 522 = 184i539.

130

As a fair example of what has been done with
these wheels in heavy passenger car service the fol-
lowing record is given of a test made on wheels
placed under postal car No. 6545, running on the
Pennsylvania Railroad between New York and St.
Louis: The car weighed 154,000 Ibs., carried on
two six-wheel trucks, giving a weight per wheel of
12,833 Ibs. The wheels under this car ran 184,539
miles with a wear ranging from .348 in. to .378
in., or an average of .365 in. The mileage per
iV in. of wear was 25,618. The tread was main-
tained at all times in smooth condition and the
wear on all of the wheels was remarkably uniform
and even.

Twelve pairs of wheels from the same lot were
placed under one truck each of four postal cars on
various runs. The average mileage of these wheels
up to the time of first turning was 109,018, with a
minimum of 87,375 mn<es and a maximum of 141,170
miles. The pair of wheels giving this maximum
mileage were worn .3185 in. and .2785 in. respectively.
An average wear of .2597 in. in 109,018 miles was
obtained from all 12 pairs, which is at the rate of
419,703 miles per inch or 26,231 miles per -^ in.
of wear. If the amount of metal removed by turning
is added to the actual wear these figures are reduced
to 234,202 miles per inch and 14,638 miles per yg-
in. of wear. The causes of removal of these wheels
were 3 pairs for worn treads, 3 pairs for cut journals,
I pair for a loose wheel, I pair for a thin flange and
3 pairs for hollow and built-out flanges. At the
time this record was taken the remaining pair of
wheels had not been removed.

In electric traction work, where the service is
much more severe than on steam roads, be-
cause of the greater number of stops and the bad
condition of the rails, and because of the fact that
the majority of the wheels are motor driven, the
mileage is less, but is still sufficiently high to show a
decided advantage for the solid forged and rolled
steel wheel over the cast iron wheel. The records of
the Brooklyn Rapid Transit Co. show that from
these wheels there was obtained a mileage per TV in.
of wear of 6,500 miles under electric freight cars
running on the surface lines, and from 8,520 miles to
9,750 miles under motor passenger cars. This is at
the rate of about .0961 in. and .0641 in. respectively
per 10,000 miles run, with the wheels still remaining
in such good condition that turning was unnecessary.
Still better results were obtained with these wheels
under elevated motor cars of the same company.
The records show wear at the rate of TV in. per
10,850 miles run, or a reduction of .0575 in. per
10,000 miles. The flange and tread were still in
good condition after having been worn down f in.
and more. The accompanying tables and diagrams
illustrate in a striking manner the remarkable service
obtained by these wheels on this road and substan-
tiate all of the claims made for them for electric
railway work.

From the data here presented it will be a simple
matter to compare the value of the solid forged and
rolled steel wheel with the value of the cast iron
wheel in similar service. Dividing the life of the
steel wheel by the life of the cast iron wheel gives
the number of cast iron wheels required for an

134

NS 21773

WEAR OF SCHOEN STEEL WHEELS ON BROOKLYN RAPID TRANSIT R.R.

133

N2 920+

WEAR OF SCHOEN STEEL WHEELS ON BROOKLYN RAPID TRANSIT R.R.

134

WEAR OF TREAD — SCHOEN ROLLED STEEL WHEELS.

1
<u •

•g

S s

'5 «j

S .

S tt

Type of Truck.

•2§

"2 E

Jo'

•§,

1 s

Lbs.

In.

Freight Truck .
Motor Truck . .

9358
9359
9199

Flanged

4,394
4,394
10,825

30^8
30^8

19,500

58,500

None

.1923
.1923
.1282

58,500
58,500
204,100

" " . .

9204

10,825

32}^

58,500

.1282

204,100

" "

9188

7,482

32%

42,600

.1466

85,400

ElevatedRailway

9190

7,482

32%

42,600

.1466

85,400

Coach . . .
ElevatedRailway

"773

Flangeless

4,262

29%6

70,650

.115

18Ae

10,8 1 1

Coach . . .

21774

4,262

*9^

70,650

.1061

10,811

equivalent mileage. The cost of renewals of the
cast iron wheels must be added to the first cost
and credit allowed for the scrap value of the old
wheels removed.

There are other items of cost, however, which,
although difficult to accurately estimate are, never-
theless, important. It must be remembered that
each car has an earning capacity which is lost when-
ever the car is in the shop for renewals or repairs,
and this should be credited to the steel wheel which
involves no such loss. Again, if the number of shop-
pings for wheel defects can be materially reduced
the same volume of traffic can be handled with fewer
cars, thus saving investment in rolling stock and,
what is almost as important in large cities, saving in
expensive storage space. These advantages, tangible
and intangible, have been so thoroughly demonstrated
to street railway officers by the experience of a few

'35

33-IN. STREET-CAR WHEEL.

34-IN. STREET-CAR WHEEL.

roads which early began to use solid steel wheels,
that there is a large and growing demand for
them in every class of electric service. For inter-
urban roads especially, where the speeds are
frequently as high as those obtained on steam
railroads, solid steel wheels have been generally
adopted for reasons of safety. The solid steel

136

33-IN. WHEEL FOR THE UNITED ELECTRIC RAILWAYS AND ELECTRIC
CO. OF BALTIMORE, MD.

34-IN. WHEEL FOR CITY AND INTERURBAN SERVICE, DESIGNED FOR SANDERSON
PORTER, CONTRACTORS AND ENGINEERS.

wheel offers all of the advantages of wear claimed
for the steel-tired wheel at a much smaller cost,
and in addition greater safety, because of the im-
possibility of parts coming loose. When compared
with steel-tired or built-up wheels, in which the
parts are shrunken on or bolted in place, and
therefore liable to become slipped under the com-
bined effect of expansion due to brake-shoe heat-
ing and the torque of the motor, the advantages
of a solid steel wheel for traction purposes become
immediately apparent.

i37

a3-IN. STREET-CAR WHEEL FOR NEW YORK CITY RAILWAY CO.

-ai\-

34-IN. STREET-CAR WHEEL FOR PENNSYLVANIA AND MAHONING VALLEY
TRACTION CO.

The solid forged and rolled steel wheel was origi-
nally developed to meet the severe requirements of
service under high capacity freight cars and it is in
this field that it has the widest possibilities of appli-
cation. That there is a demand for these wheels is
shown by the fact that more than 150,000 are now
in use, 55,000 of them in service under 100,000 Ibs.
capacity cars, and the number is steadily increasing.

It is difficult to make an estimate of the mileage
cost of freight car wheels because of the incomplete
records usually kept. From the best statistics avail-
able, however, it appears that the mileage obtained
from cast iron wheels under 100,000 Ibs. capacity
cars is between 25,000 miles and 30,000 miles.

138

33-IN. STEEL WHEEL.

34-IN. SUBWAY MOTOR-TRUCK WHEEL FOR THE INTERBOROUGH RAPID
TRANSIT CO., NEW YORK.

From the tests made of Schoen solid forged and rolled
steel wheels under postal cars on the Pennsylvania
Railroad it was found that there was obtained an
average mileage of 14,638 per TV in., including wear
and turning. Under heavy tenders, the mileage
averaged 7,000 per ^ in. of wear and turning. The
average of these two figures, 10,800 miles per -& in.
of wear and turning, may be taken as the probable
average service which can be obtained from these
wheels under high capacity freight cars. The
wheels furnished to the Pennsylvania Railroad for
freight cars have a rim 2 in. thick with limit groove
for wear cut f in. in from the inner edge. This gives

139

U 34' Dl

_|_ ,

34-IN. STREET-CAR WHEEL FOR CHICAGO CITY RAILWAY CO.

34-IN. STREET-CAR WHEEL FOR CONSOLIDATED RAILWAY CO.,
NEW HAVEN, CONN.

a wearing thickness of ij ins. available for service.

At 10,800 miles per ^ in. of wear, the total mileage

which can be obtained from these wheels is 20 x

10,800=216,000 miles as against 30,000 miles for cast

iron wheels, or a little more than seven times the life.

If the first cost of a cast iron wheel is taken at $10

and its scrap value at $5, then the cost of cast iron

wheels to give a life equivalent to the life of one

Schoen solid forged and rolled steel wheel would be:

7 cast iron wheels at $10 each $70

7 scrap wheels (credit) at $5 each $35

Actual cost of cast iron wheels

140

AXLE AND WHEEL DESIGN SUBMITTED BY THE SCHOEN STEEL WHEEL CO.

AS REQUESTED BY THE CENTRAL ELECTRIC RAILWAY COMMITTEE ON

STANDARDIZATION FROM THEIR REPORT DATED MAY 23, 1907.

AXLE AND WHEEL DESIGN SUBMITTED BY THE SCHOEN STEEL WHEEL CO.,

AS REQUESTED BY THE CENTRAL ELECTRIC RAILWAY COMMITTEE ON

STANDARDIZATION FROM THEIR REPORT DATED MAY 23, 1907.

|4-«A— idSB*F— 63' W£

I JL _ 77' -jj— H

K
P

-f

AXLE AND WHEEL DESIGN SUBMITTED BY THE SCHOEN STEEL WHEEL CO.

AS REQUESTED BY THE CENTRAL ELECTRIC RAILWAY COMMITTEE ON

STANDARDIZATION FROM THEIR REPORT DATED MAY 23, 1807.

AXLE AND WHEEL DESIGN SUBMITTED BY THE SCHOEN STEEL WHEEL CO.

AS REQUESTED BY THE CENTRAL ELECTRIC RAILWAY COMMITTEE ON

STANDARDIZATION, FROM THEIR REPORT DATED MAY 23, 1907.

142

The original cost of the solid forged and rolled
steel wheel may be taken at $20 and its scrap value
at the end of its life at $5. Its total cost, therefore,
would be $15 as against $35 for the equivalent num-
ber of cast iron wheels required to give the same
mileage. It is assumed that the cost of turning the
solid steel wheel the required number of times during
its life would equal the cost of removing and re-
placing the cast iron wheels on the axle.

The accompanying diagram shows graphically
the comparative mileage, cost and strength of
the ordinary cast iron wheel and the Schoen

MILEAGE Of CAST IRON WHCCL
MlieAG^OFSCHOENFORGE^ANDROLLEDSTEEL WMEEl

COST PER 1000 MttES OF CAST IRON WHEELS DURING LIFE OF ONE SCHOEN STEEL WHEEL
COST PER '000 MILES OF ONE SCHOEN STEEL WHEEL

CAST IRON WHEEL BASED UPON ITS ELASTIC LIMIT

CHART OF COMPARATIVE VALUES OF THE SCHOEN FORGED AND ROLLED

STEEL WHEEL, AND THE CAST IRON WHEEL FOR LARGE CAPACITY

FREIGHT CARS AND COACHES.

solid forged and rolled steel wheel. The first
two lines show the comparative mileage, the next
two show the comparative cost per 1,000 miles
run, and the last two lines show the comparative
safety of the two wheels based on the elastic
limits of the metal of which they are made. The
mileage is as 7 to I in favor of the steel wheel and the
cost per 1,000 miles is as 2 to i in its favor. The
elastic limit of cast iron as shown on the chart is

143

that given by Unwin: 10,500 Ibs. in tension and
21,500 Ibs. in compression with a mean of 16,000 Ibs.
The elastic limit of the steel wheel is taken at 107,457
Ibs., a ratio of 6.7 to i in favor of the steel wheel.
If the actual breaking strength of the flanges had been
used in proportioning the relative lengths of these
lines their ratio would have been as 8.6 to i in favor
of the steel wheel as against the old M. C. B. stand-
ard cast iron wheel and 5.3 to I in favor of the steel
wheel as against the new reinforced flange cast iron
wheel. It is evident, therefore, that the ratio of 6.7
to i, as given on the chart, is conservative.

Cast iron wheels under high capacity cars are a
known source of danger, and on most mountain roads
a careful inspection of every wheel is made when a
freight train stops at the foot of a long grade. This
costs time and money, and even then the inspec-
tion is not always successful in detecting incipient
failures which develop later with disastrous results.
The loss of earning capacity of cars standing idle
awaiting shopping for wheel defects is important
in times of congestion of traffic. It is a fact that
many roads are prevented from realizing the full
benefit of large overload carrying capacity simply be-
cause the cast iron wheels are not considered safe
to carry such loads.

In the foregoing pages many and important ad-
vantages of the Schoen solid forged and rolled steel
wheel have been demonstrated. Careful examina-
tions of the metal of which the wheel is made have
shown it to possess better physical properties than
the best steel tires and wheels on the market. Ex-
perience in service, with wheels under freight and

144

passenger cars, locomotive tenders and electric
cars, proves that the wearing quality is superior
to the best of its competitors. The investigation
of the lateral thrust of the wheel against the
rail gives conclusive evidence that the cast iron
wheel, even when made of the best material and
with the flange reinforced as in the latest designs, is
not safe under high capacity cars at any but the
lowest speeds. Finally, it has been shown that the
solid forged and rolled steel wheel can be applied
under freight cars in place of cast iron wheels with
an actual saving of $7 per 100,000 miles run, or $56
per 100,000 car miles. In considering the question
of car wheels for any service, therefore, from the
standpoint of safety, mileage or cost, the solid forged
and rolled steel wheel stands in front of all others.

The Schoen Steel Wheel
Company's works at
McKees Rocks, Pa.

149

Hydraulic presses, each with
a capacity of eighteen million
pounds, are used to forge
the Schoen Solid Steel
Car Wheel.

The most ingenious
mechanism is required tc
roll and finish a Schoen
Solid Steel Car Wheel.

153

One of the electric
manipulators used for
handling the steel blooms i
the manufacture of Schoe
Solid Steel Car Wheels.

Various types of hydraulic
presses are used in forging
Schoen Solid Steel
Car Wheels.

'55

It : . .,,' .--..• • • «

., fj- f ?•' *• ». *

Twelve hundred horse-
power engines are coupled
each rolling mill used in I
manufacture of Schoen
Solid Steel Car Wheels.

«57

These hydraulic presses wer<
all especially designed to
forge Schoen Solid Steel
Car Wheels.

'59

View in one of the power
houses of The Schoen Steel
Wheel Company's plant
at McKees Rocks, Pa.

161

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THIS BOOK IS DUE~^N THE LAST DATE
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