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Full text of "A method making possible the utilization of an Illinois joint clay, by A.V. Bleininger and F.E. Layman. An Attempt to determine the amount of heat utilized from a down-draft kiln by the waste heat drying system"

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UNIVERSITY OF ILLINOIS LIBRARY AT URBANA-CHAMPAIGN 







UNIVERSITY OF ILLINOIS BULLETIN 

Vol. VI APRIL. 5, 1909 No. 25 



LEntered February 14, 1902, at Urbana, Illinois, as second-class matter 
under Act of Congress of July 16th, 1894.] 



BULLETIN No. 10, DEPARTMENT OF CERAMICS 

C. W. ROLFE. Director 



A METHOD MAKING POSSIBLE THE UTILIZATION 
OF AN ILLINOIS JOINT CLAY 

BY 
A. V. BLEININGER AND F. E. LAYMAN 



AN ATTEMPT TO DETERMINE THE AMOUNT OF HEAT 

UTILIZED FROM A DOWN-DRAFT KILN BY 

THE WASTE HEAT DRYING SYSTEM 



By A. V. BLEININGER 



1908-1909 



PUBLISHED FORTNIGHTLY BY THE UNIVERSITY 



AN ATTEMPT TO CALCULATE THE AMOUNT OF 

HEAT UTILIZED FROM A DOWN-DRAFT 

KILN BY THE WASTE HEAT 

DRYING SYSTEM.* 

BY 

A. A'. Bleininger. 



In a test made some time ago the heat distribution of 
a down-draft kiln employed for burning hard building 
brick was calculated, based upon careful measurements of 
the kiln and exit temperatures, the composition of the 
waste uases, the fuel and the asbes, together with the 
weight of the coal and of the ware. The result was 
summarized as follows ; 

Heat lost by the fuel gases 27.:^', 

Theoretical Heat required to burn 

the bricks ....19.55^ 

Heat lost by unburnl carbon in ash.. :>.r>l', 

I leaf taken up by kiln and lost by 

radiation '.....49.G1% 

At the close of the burn a 30-inch goose-neck was 
inserted into the door of the kiln which connected with an 
underground flue leading to the dryer. The air was thus 
drawn from the kiln by means of the large fan located at 
the dryer. A draft gauge was then connected with the 
^■oose-neck for determining the "head" caused by the pull 
of the fan. This was found to be quite uniform and equal 
to 14 divisions of the Richardson-Lovejoy petroleum gauge 
which corresponds to about 1 4 inch of water by actual 
measurement. A thermo couple was likewise inserted into 
the goose-neck which was replaced later by thermometers. 

*Read at the Annual Meeting of the American Ceramic Society Rochester, N. Y., 
Feb. lst-3rd, 1909 



Iii this manner the temperature of the air leaving the kiln 
was carefully measured for 108 hours. 

In attempting - to calculate the amount of heat ex- 
hausted from the kiln by means of the fan we must know 
first the velocity of the air through the pipe. This it was 
only possible to approximate, since the draft gauge was not 
calibrated against an anemometer. The final value of the 
velocity accepted is lower than the actual velocity, 
since no attempt was made to use the Pitot tube cor- 
rection factor, which is greater than unity. The theo- 
retical velocity calculated from the head shown by the 
gauge, giving a lower value was hence used, neglecting the 
decrease in the viscosity of the hot air and other factors 
due to cooling between the kiln and the fan. This, it is 
believed, did not introduce any significant error, since evi- 
dently the velocity was fairly uniform throughout the test. 
The velocity is thus calculated from the formula. 

V= V2 jr. h 

d 2 
v = velocity in meters per second. 
g = gravity constant = 9.8 m. 
h = head of water, expressed in 

meters = 0.00 - m. 
d,= density of air at 0° C. 
d._.= density of water at 0° C. 

substituting we have 

v = VKU5 '. 0.006 '. 772 = 9.4(3 m. 

The velocity of the air was taken to be !>.."> in. per 

second. 

The time was divided into nine periods of 12 hours 
each and the mean exit temperature calculated for every 
period. These were found to be as follows : 

0— 12 hours 885° C. 

12— 24 hours 715° 

24 — 36 hours 640° 

30 — 48 " 540° 

48— 60 " : 435° 

60— 72 " 355° 

72— S4 " 265° 

84— 96 " 185° 

96—108 " 135° 

With a pipe diameter of 30 inches and using the velo- 
city above calculated we have a discharge of 4.18 en. in. 
per second or of 180,576 en. in. during 12 hours. Owing 
to the fact that the test was carried on during the dryest 



and hottest part of the summer, with an average tempera- 
ture of about 20°, the humidity approximated at 50%. 
This figure is purely a guess, since the hygrometer was 
found to have been broken during transit. However, the 
introduction of the atmospheric moisture factor is not an 
important one, numerically. Assuming a vapor tension 
of 8.7 mm, the volume of steam introduced for the volume 
of air given above would be 21194 eu. m. The barometric 
pressure was taken to be 750 mm. 

There remains now to calculate the weights of air and 
steam taken through the pipe for each period as well as the 
heat removed. This is illustrated for the first period as 
follows :• 

273 

Air....l80576 . 1.27.") . 865 . 0.237=11,127,000 kg. Cals. 

27.3 - 885 
27:5 

Steam.. 2094 . 0.797 . 865 . 0.48= 103,300 kg. Cals. 

273 + 885 — 

Total heat removed by air and steam 11,290,300 kg. Cals. 

In this calculation 0.237 and 0.48 are the specific heats 
of air and steam respectively. Tabulating the results we 
obtain : 

Period Total number of kg. Calories 

1 11,290,300 

2 10,032,820 

:; 10.264.ol0 

4 9.067,880 

5 8,858,130 

(i 8.003,050 

7 6,883,290 

8 5,444,750 

!> 4,260,190 

Total 75,364.980 kg. Cals. 

The coal used during the burn had a calorific value 
of 6200. Hence the weight of coal equivalent to the 
amount of heat drawn from the kiln would be 

74 462 308 

=12155 kg. "or 

6200 

20,741 pounds. During the entire burn 95,045 pounds of 
coal were used. The heat exhausted from the kiln during 
cooling then equals 28.1% of the total heat introduced, so 
that the heat distribution could be rearranged as follows : 



Heat lost by flue gases 27.33% 

Theoretical heat required to burn 

the ware :... 19.55% 

Heat lost by imburut carbon in ash 3.51% 
Heat stored by kiln and ware and 

recovered for drying purposes.... 28.10% 
Heat lost by radiation and left in 

kiln and ware unused 21.51% 



100.00% 
The recovered heat thus amounts to the equivalent of 
practically 400 pounds of coal per thousand bricks, or 
speaking more correctly, about 130 pounds of coal per ton 
of burnt clay, which is more than the heat theoretically re- 
quired to burn the bricks. It is evident that not all of this 
heat is used in drying bricks, some of it is lost on the way 
to the dryer and in the latter itself. That a considerable 
amount of the heat is derived from the hot kiln walls is 
apparent from the comparison of the figures in the final 
distribution. Owing to the fact that this test was carried 
on in summer, the results show the most favorable condi- 
tions under which this particular kiln operates. In winter 
the heat actually available for drying would be consider- 
ably less, owing to the increased loss by radiation during 
cooling. 



A METHOD MAKING POSSIBLE THE UTILIZATION 
OF AX ILLINOIS JOINT CLAY.* 

BY 

A. V. Bleiningek and F. E. Layman. 

A large part of Northern and Central Illinois is cov- 
ered by the so-called joint clays which arc of glacial ori- 
gin and vary in depth from one to five feet. These (days are 
weathered to different depths and in this condition they 
form the basis of a considerable brick industry. They are 
red-burning surface clays, extremely fine in "rain, 
but as is characteristic of glacial deposits, admixed with 
mineral detritus of all kinds. In a number of localities, 
however, they are quite uniform in composition for consid- 
erable areas ami free from excessive amounts of rock de- 
iiris, gravel, etc. 

In the weathered condition they usually work up quit" 
well into bricks and tiles though they are sometimes liable 
to check in burning. Some distance below the surface, 
however, they are apt to show a peculiar behavior in dry- 
ing, giving rise to characteristic splitting and cracking'. 

When made into bricks they split through vertically 
into more or less regular cubes, the same thing being ob- 
served when a bank is stripped and the surface is drying 
out. The loss arising from this peculiarity in attempting 
to make clay products out of this material is quite con- 
siderable, since the checking occurs in the drying as well 
as in the burning, the latter being due probably to incipi- 
ent cracks. 

A typical deposit of this character is found on the 
land of Mr. J. W. Stipes, close to the city of Urbana, 111. 
This clay is extremely line grained, red burning, very 
sticky and plastic but not high in bonding power. Within 

*Read at the Annual Meeting of the American Ceramic Society, Rochester, N. Y., 
Feb. lst-3rd, 1909 



a foot of the surface it has been (■hanged by weathering so 
that it does not show the peculiarity mentioned above to a 
striking degree but at a somewhat greater depth its true 
joint structure appears. There arc no differences in color 
noticeable between the weathered and the unweathered por- 
tion, both are of about the same yellow. The clay is com- 
paratively free from mineral debris and stands up remark- 
ably well in the kiln. Though at present used for the man- 
ufacture of soft-mud bricks and burnt in up-draft kilns, 
this process does not do the clay justice and does not bring 
eut its best colors, as a down-draft kiln would do. It vit- 
rifies between cones 3 and 1. When burnt at a lower tem- 
perature it produces a fine red color. 

It has been realized from experience that both weath- 
ering and thorough air drying help considerably in over- 
coming the difficulties encountered in the use of this clay. 
Hence, by allowing it to freeze through the winter it would 
become quite workable in the spring. The difficulty is, 
however, in being sure that all of the clay has been suffi- 
ciently weathered, and though the drying loss may be re- 
duced, some loss in burning may still be found to occur. 
the same thing applying to the air drying. 

Considering the benefit derived from air drying, it was 
proposed to carry this process further and to dry the clay 
at higher temperatures. For this purpose a sample was 
taken from that part of the bank, used by the Sheldon 
Brick Company, that had given the most trouble. 

In the preliminary work, small samples of this clay 
were dried in a laboratory air bath at 100, 200 and 300°C. 
These were then pulverized, passed through an eight mesh 
screen, tempered, wedged and pressed into bars, 10" x |" 
x i/o" in a brass mould. A portion of the undried 
clay was also wedged and pressed in the same mould. 
After drying in the air at ordinary temperature the linear 
shrinkages were determined. It was found that the bar 
made from the undried clay warped very badly as well as 
the bar made from the clay dried at 100°, but that the bars 
moulded from the clay dried at 200° and 300° showed very 
little warping. 



The linear shrinkages were as follows: 

Undried Clay _10.3 Per cent, 

Clay dried at 100 ..... 9.7 " " 

Clay dried at 200 7.3 " 

("lav dried at 300°.. 7.1 " 

In tempering the dried clay it was observed that the 
sample dried at 100 still possessed the sticky nature of 
the undried clay, while the charge dried at 200° had lost to 
a very large extent this characteristic property. At the 
same time a certain granular appearance was noticed as 
well as a slight change in color from yellow to reddish. 
The sample dried at 300 worked practically the same as 
I he one heated to 200°. Hence, it was obvious that what- 
ever changes had taken place in the structure of the clay 
occurred at aboul 200 <\ and this was the temperature 
chosen in tin 1 work that followed. 

In order to bring out the changes caused by this dry- 
ing treatment, still further experiments were made. A 
sample of the undried clay was taken and divided into two 
parts. One-half was dried at 200° in a laboratory oven, the 
other half was left as it was. Both of these batches were 
placed in porcelain jar mills of one gallon size, together 



Trfins. 


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_curv£5 5h0win6 the 
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D^lfrD AT £00 °C \ 


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Df?\SrD PiT 200° C. 








































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1 1 1 1 1 1 



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iLt 

i- no 



I.5C 

1.25 

IZC 

I 15 
I.IO 

1° 



ti 

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■5 \0 \5 SO S5 2>0 35 

PeR Cetnit of- Dry Clry, 5y Weight, iiss Sup 



with sufficient distilled water to make a fairly thick slip, 
and ground for one hour. The grinding action of these 
small mills is very slight so that the fineness of grain was 
affected hut little. Each of the two slips was passed 
through an 80 mesh sieve. 

The viscosity of each of the slips was then determined 
by means of n Coulomb viscosimeter which had been con- 
structed in the Department of Ceramics, University of Illi- 
nois, for the purpose of studying clay slips, as described in 
Vol. X, Trans. Am. Ceramic Society. 

The amount of (day held in suspension in the slips was 
determined by evaporating the slips to dryness and weigh- 
ing in small metal pans. In order to obtain the viscosities 
<>f lower concentrations, the slips were diluted with water, 
thoroughly stirred up and tested as before. 

In the accompanying curves we observe clearly what 
great changes have been brought about by the drying treat- 
ment. It is evident that this change involves the structure 
of the colloidal portion of the clay, since naturally neither 
the size of grain was altered nor anything added to or sub- 
tracted from the (day in drying. Just how long a time 
would be required to bring back the clay to its original 
state of viscosity, if this is possible at all, would be an 
interesting question. 

We observe from the curves that for instance in the 
case of the fresh (day a viscosity of 1.18 is reached with 
20% of clay, while for the same viscosity 35% of the dried 
(day is required. The latter therefore shows a marked de- 
crease in the viscosity characteristic of plastic clays. 

In order to bring out the differences between the un- 
dried and the dried clay still further, another series of 
tests was made by taking these (days alone and in several 
proportions and making them up into round discs, 3*4 i n - 
in diameter and 7/8 in. thick. For this purpose the fresh 
clay was thoroughly wedged, while the dry clay was pul- 
verized and passed through a 10 mesh screen, made up with 
water and tempered. The discs were made by batting the 
clay into a slab between two guides and passing a roller 
over the latter so as to obtain uniform thickness. The 
slabs were then cut into discs by means of a tin biscuit 
cutter and when sufficiently stiff they were repressed on a 



hand screw press provided with a corresponding round die. 
Ten trials of each serif's were placed in a Seger volnmino- 
meter and the volume determined by displacement in kero- 
sene after having been immersed in petroleum for 24 hours. 
The same process was repeated after the discs were dry. 
The average of ten determinations was taken as the drying 
shrinkage. The dry test pieces were all placed in a Caul- 
kins mnftie kiln, tired with oil and burnt to cone 4, this 
temperature having previously been determined as the best 
maturing point of the clay. Each of the ten trial pieces of 
the several series which had been measured for drying 
shrinkage, was, after burning, again placed in the volu- 
lninometer and the volume determined. The balance of 
the trials were placed in water with one face exposed and 
allowed to stand for 48 hours, this period of time having 
been established as the point beyond which practically no 
farther absorption took place. They were then divided 
into classes according to the absorption found. 

At the same time discs were made in similar manner 
from (Jalesbnrg shah- which, however, were tired at cone 2, 
the best temperature for this material. The results of this 
work are collected in the following tables, the shrinkage 
being expressed by per cent in volume. The percentages of 
loss are based upon 200 discs made from the undried Ur- 
bana clay, 200 of the dried Urbana clay, and 125 discs of 
A, 15, and C. 



Kind of Material 


>> 

S -a 

u .a 

c 

11 
P 


bo 

~ a 
(J oo 

(S cs 

- I* 

p ~ 


Urbana Clay 
25% dried, 
75% undried 


Urbana Clay 

50% dried, 

50% undried 


0.2"E 


it 
u 

|| 

6 sz 

o 


MARK 


u 


ID 


A 


B 


c 


G 


Amount of tempering water, in 














% of dry \vt 


33.5 


29.9 


32.0 


31.9 


31.0 




Drying Shrinkage in %, by vol.... 


41.2 


29.3 


39.1 


35.8 


34.1 


7.5 


Burning Shrinkage in %, by vol... 


21,1 


20.6 


21.0 


21.0 


20.9 


16.2 




32.0 


0.5 


26.0 


15.3 


9.7 




Burning loss in ,r } - 


1.3.0 


4.0 


9.1 


11.0 


12.9 


2.5 


Total loss in % 


47.(1 


4.5 


35.1 


26.3 


22.6 


2.5 



From these results it is apparent that the pre-heating 
of the day has greatly decreased the drying shrinkage, the 
difference being 11.9 per cent in volume or nearly 4 per cent 
in linear shrinkage, assuming for practical purposes that 
the linear shrinkage is one-third of that in volume. A cur- 
ious fact is also the decreased burning shrinkage, so that 
the total shrinkage is decreased from 62.3% by volume to 
49.9$ , resulting in a difference of 12.4%. Or, expressed 
in linear dimensions, the decrease in total shrinkage is 
from 20.7% to 16.6%. The loss in drying which took place 
in the open laboratory at ordinary room temperature has 
been decreased from 32.0 to 0.5%, a gain of 31.5%. The 
gain in burning loss was 11%' and in the total loss 42.5%. 

As to the mixtures of preheated and undried clay, we 
observe that the shrinkage and losses decrease roughly 
with the increase of preheated clay and thus these results 
verify the observations on the preheated clay itself. 

Since there is a possibility from the practical stand- 
point of the drying and burning losses that the same re- 
sults would be obtained by the addition of sand to the clay, 
a short series was carried through in which 5, 10 and 15% 
of sand passing the 8-mesh sieve were added to the undried 
Urbana clay. Of each sand mixture 125 discs were made. 
The results of this work are collected in the following table 
in which the data for the undried and the preheated clay 
are repeated for the sake of comparison : 



Kind of Material 



U 






.2 — « 

a j- o & 



'*>1« 



§2 



'^.5 5 



MARK | U 

Amount of tempering water, in % 

of dry \vt | 33.5 

Drying Shrinkage in %, by vol | 41.2 

I 
Burning Shrinknge in %, by vol | 21.1 

Drying loss in % | 32.0 

I 
Burning loss in % | 15.0 

I 
Total loss in % | 47.0 



UD 



1) 



F 



29.9 
29.3 



32.0 
39.1 



20.0 | 20.2 

I 

0.5 ! 6.1 

4.0 | 11.3 

I 

4.5 I 17.4 



31.5 

37.6 

19.3 

5.2 

33.0 
38.2 



31.1 

35.2 
18.0 
5.0 
42.0 
47.0 



From these results we observe that the drying shrink- 
age has been decreased somewhat ami the drying loss a 
good deal, roughly by about 25%. The burning shrinkage 
also has been reduced, but unfortunately the burning loss, 
though showing an improvement in the .V, sand mixture, 
increased very rapidly with more sand. As compared with 
the total loss of the preheated clay, the gain has been but 
small and at least as far as the sand used was concerned 
this remedy offers but little hope for practical improve- 
ment since the losses arc still too great. Tin 1 advantage of 
preheating this joint clay is seen from the small loss in dry- 
ing and burning. An explanation of the ineffectiveness of 
the sand mixture perhaps is due to the fact that the clay 
itself is not changed in its physical properties and we have 
here simply a case of dilution. With larger amounts of 
sand we also have in burning certain volume changes 
which appear to be opposed to each other, so that strains 
are produced which result disastrously. 

In order to show whether the Urbana joint clay after 
having been burnt apparently to a sound body really was 
free from incipient checking, it was determined to make 
rattler tests. For this purpose the burnt discs, tree from 
flaws, were first graded according to their water absorp- 
tion and compared with discs made from Galesburg shale 
which had burnt to the best degree of maturity. 

The rattler test was made in a Scheibell mill, consist- 
ing of a chilled iron receptacle, elliptical in cross section, 
with a long axis 23 in. in length and a short axis of 7y 2 
in., revolving 31 revolutions per minute. The rattler was 
first standardized with a mixture of iron jackstones in the 
shape of I 1 4 in. cubes weighing on an average 0.9 pound 
and Iceland pebbles with an average length of 3% in- and 
a width of 2% in. The average weight was 0.7 pound. In 
the standardization the Galesburg discs were used, 
five of them in a charge which weighed about 2.2 pounds. 
The combination giving the most constant results was used 
for the comparative tests of the joint clay discs with the 
Galesburg test pieces. In each case the results were 
checked. Finally, two charges were used, 2-C, containing 
75 pounds of pebbles and 50 pounds of jackstones and 2-D, 



consisting of 100 pounds of pebbles and 50 pounds of jack- 
stones. In using charge 2-C the mill was about % full 
and with 2-1) it was y~ full. The time of running was one 
hour. It was found that 2-< 1 was a more severe charge than 
2-D on account of the element of impact introduced by the 
mill being less full. 

The rattler losses are tabulated as follows : 



All disc* apparently perfect and shown 
an absorption of 195 and less 


g 

2- 

% 1 


-C 


2- 


-D 








% Loss 




( ialesburg shale, G 





9.S 


9.7 


5.5 


5 


5 


Urbana clav, preheated, U. D 





12.3 


12.8 


4.0 


4 


5 






14.7 


14.5 


5.0 






25$ preheated & 75 9? undried Urbana clay, 


\ 


11.5 










509? preheated & 509? undried Urbana clay, 


B 


11.8 









7595 preheated & 25 95 undried Urbana clay 
9595 undried Urbana clay, 595 sand. 1) .. 


CI 


11.8 










12.5 
12..1 





5.9 
(1.2 




9095 undried Urbana clay, 109$ sand. K 







8595 undried Urbana clay, 1595 sand. F 




14.1 




7.4 












These results show plainly that preheating has im- 
proved the resistance of the joint clay to abrasion decid- 
edly, not, of course, due to any change affecting the min- 
eral and chemical structure of the (day itself, but to the 
elimination of drying defects, incipient cracks and strains 
caused in drying. If it were possible to dry tin 1 fresh (day 
without injury it would possess the same resistance to ab- 
rasion exhibited by the preheated material. The Urbana 
clay is evidently more brittle than tin 1 Galesburg shale, but 
it is harder, due to the fineness of grain of the joint clay. 
One might venture to say, judging from the above compari- 
son, that the latter could probably be used as a paving 
material for streets which are not subject to heavy travel, 
provided, however, that the clay would correspond uni- 
formly to the sample tested in this work, which is some- 
what questionable in the case of glacial deposits. 



The addition of sand, according to the above results, 
contributes nothing to the resistance to abrasion, though 
it shows an improvement over the undried (day by lessen- 
ing the checking in drying. 

CONCLUSIONS. 

From the results of this work it is evident that the 
faults of the joint (day have been overcome by this pre- 
liminary drying treatment at 200°C. The sticky 
nature of the clay has been destroyed, tin 1 drying 
shrinkage reduced greatly and the burning shrinkage 
partly, while the losses in drying have been practically 
eliminated and The burning loss lowered most decidedly. 
If, therefore, this preheating can be carried on econom- 
ically in properly constructed dryers, either tired directly 
or making use of the waste heal of kilns, the treatment 
thus suggested ought to find more extensive practical ap- 
plication. 

At the same time there must be remembered that the 
dry clay can be disintegrated and screened more cheaply 
than the clay coming wet from the bank, thus enabling the 
manufacturer to remove the impurities, such as gravel, 
lime, pebbles and other mineral detritus, which are espe- 
cially liable to be present in the glacial clays, more cheaply 
and thoroughly, besides making the operator independent 
of weather conditions. Also it is thus possible to produce 
wares of a higher grade from low grade material and in 
districts where other clays are lacking. Tt is self-evident 
that the increased cost of production caused by this treat- 
ment may be prohibitory in localities where it is possible 
to find (days which do not require this kind of preparation. 
The matter of the preliminary drying of clay is not new, 
but the changes brought about by it have not been clearly 
recognized and its importance in certain cases not consid- 
ered. It ought to lie especially applicable for higher 
grades of ware such as roofing tiles, hollow ware, terra 
cotta, etc. 

In regard to the cost of drying clays by the rotary 
dryer, which is the most efficient apparatus for this pur- 
pose, some data have been obtained from two firms, A and 
P.. 



Firm A recommends a rotary dryer, heated by direct 
Siring, <><> in. in diameter and If! ft. long. This aparatus 
is encased in brick. The clay is fed automatically and at 
a constant rate, this being very important. About 35,000 
common and from 5,000 to 6,000 fire brick are required in 
the construction. The total weight of the dryer is about 
40 tons. The cost of the dryer, complete, is $3000, to 
which the freight is to be added. This machine will dry 
15 tons of clay per hour. It will require 8 — 12 horse- 
power to operate and for a material containing 15 r r <>f 
moisture the fuel consumption would be about 500 pounds 
of coal per hour, at the rate of 15 tons of clay for the same 
length of time. Including labor and depreciation the cost 
of drying is estimated at 10 cents per ton. 

The firm B estimates the cost of the dryer to be $3,500 
and cost of erection at $600. The power required is 20 
horse-power and the fuel consumption 60 pounds of good 
( oal per ton of bank clay. The cost of drying is estimated 
to be 12 cents per ton of bank (day. 

In this connection we must remember also that the 
size of the brick moulds, etc., must be reduced in order to 
correspond to the decreased shrinkage of the preheated 
clay, though this do;>s not mean that a saving is effected. 

Further work is necessary to determine to what ex- 
tent this method may be applied to materials other than 
the joint clay discussed in these tests. 

Practically all the laboratory work of this investiga- 
tion was done by the junior writer, Mr. F. E. Layman, the 
senior writer having planned the experiments and assisted 
in writing up the results. The means for carrying on the 
tests were furnished by the Ceramic Department of tin 1 
University of Illinois, through Prof. C. W. Rolfe, the 
director. 



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