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Full text of "Modern Mechanical Engineering Vol-I"

FITTING AND  ERECTING

263

jointing materials in paint or putty form. For joints in pipes carrying super-
heated steam,the joint rings should be made of corrugated nickel. Alternatively,
a joint ring can be cut from a sheet of jointing material and, before being
put in position, painted on both sides with thin graphite paint—or a ring
can be cut out of thin copper gauze, and the latter then thoroughly filled
with red-lead putty, or other jointing material, before being put in position.
For low-pressure steam joints the latter is a favourite method, the addition
of a strand or two of lead wire threaded round the gauze adding to its effi-
ciency. In the steam systems of collieries, where low-pressure steam is
used without superheat, ordinary rubber joint rings are frequently used
with success on systems up to 100 Ib. per square inch.

The main joint between the top and bottom halves of a turbine cylinder
is usually made by smearing jointing material of the consistency of thick
cream on the bottom half, and
then adding a strand or two of
lead wire at the low-pressure
end, and soft copper wire, about
No. 27 gauge, at the H.P. end,
and then bolting the top half
down solidly.

It is advisable in the case of
all steam-joints, or joints where
the temperature is likely to be
high, to go round all the bolts in
the joint as the temperature is
being raised. This is known as
" following up " the joint, and it
is invariably possible to get an
extra turn or half-turn on the
bolts and nuts when the joint is
heated up. If this is not done,

there is a danger of the jointing material being blown out and the joint
having to be remade, and in some cases necessitating a shut-down.

For Joints in Water-pipes, rubber insertion is used mostly; the rubber
joint ring should be put on dry; some men smear the rubber with tallow
or grease, hoping to make a more effective joint, but grease and oil only result
in rotting rubber and should therefore not be used.

An excellent joint for flanged water-pipes can be made by a ring of thin
copper gauze filled in with red-lead putty, and a strand of lead wire threaded
through.

Oil Joints.—Special oil-jointing material in sheet form makes the best
joint; this consists of a strong paper boiled in soft soap and caustic soda.
Alternatively, ordinary steam jointing material of the asbestos-sheet type is
frequently used, but care is taken to paint the joint ring with shellac dissolved
in methylated spirit, immediately prior to being bolted up. For large, flat
surfaces, soft soap smeared thinly over the surfaces, and a piece of lead wire

Fig. 16.—Copper Gauze Joint Ring with Lead Wire
woven in and filled with Red-lead Putty