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Full text of "Modern Mechanical Engineering Vol-I"

262                              HEAVY  MACHINERY

In order to determine whether the pedestal cover is binding down the
bearing, immediately before the cover is put on, a strand or two of soft
lead wire is laid across the top pad or outside machined surface of the bearing
and the pedestal cover then bolted down; if, on lifting the cover again, the
lead wire is not flattened down " to nothing ", additional liners must be put
under the top pad, and the test repeated till the desired result is obtained.
Unless this precaution is taken, there is liable to be a considerable amount of
vibration when the plant is running, and this will result in " hammering "
of the bearings and the running of the plant will get rapidly worse. In in-
vestigating vibration troubles in high-speed plant, it is always wise to
examine the bearings first of all, for clearance and for tightness in the
pedestal.

Before finally closing up the bearings, oil should be pumped through
the lubricating system in order to see that each bearing is receiving an ample
supply of oil. When tunning up a set such as described above, the utmost
care should be taken. As soon as the spindle just starts to move round,

the engineer in charge should have a quick run
round in order to locate any unusual noises,
sign of smoke, or evidence of heat, and be pre-
pared to shut down instantly if necessary. The
running-up for the first time frequently takes
several hours, during the greater part of which
the set is being run at slow speed, which is
very gradually increased; this gives any trouble
time to show up at lower speed, and gives the
man in charge a better chance to avert trouble

Fig. 15.—Bearing showing Sides          .         •/• ^i        i   r    ^ •      i                      ,rn            i

scraped away for Oil Clearance         than if the defect IS Shown Up at full Speed.

Joints.—In considering the best type of

material for making any given joint, while the principal point is the
tightness of the joint under working conditions, due regard must be paid
to the time and labour involved in breaking the joint, removing the old
material, and remaking the joint when such a course becomes necessary,
e.g. opening up or dismantling machinery for inspection. There are some
materials which make excellent joints, but which are removed only with
the very greatest difficulty.

There are a large number of jointing materials on the market to-day,
for all of which special advantages are claimed. Some of these materials
are in sheets, others in powder or paint, and some in metal, wire, sheet,
and net, and nearly every engineer has his own particular method of making
any given joint, which he claims is superior to any other method; only a
general statement, therefore, can be made as follows:

For Steam-joints (flanged).—The joint faces are very carefully scraped,
bedded on a small, portable, plane table, and, before being bolted together,
are wiped over very lightly with graphite or some graphitic paint, or even
left without any jointing material at all. Alternatively, a Taylor corrugated
joint ring is used, which has previously been filled with one or other of the