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Full text of "Modern Mechanical Engineering Vol-I"

254

HEAVY MACHINERY

little red lead mixed with thin machine oil on the journal, and then rubbing
it uniformly over the journal till almost dry. The bottom half-bearing is
then put on the journal and rocked backwards and forwards a few times;
the high or " hard " spots of the bearing will be marked with red lead, and
must be carefully scraped down with a curved scraper; the red lead should
be smeared uniformly over the journal before the bearing is again marked.
This process is continued till the bearing is marked pretty uniformly. The
top half-bearings are also tried for marking, and the hard spots removed,
but the marking process is not carried so far, or is so complete, as in the
case of the bottom halves. (An exception is made in the case of bearings
for reciprocating plant, where the pressure comes on the top and bottom

half-bearings alternately, and the
necessity, therefore,1 exists for
the marking and scraping of both
halves to be done very care-
fully.) After all the bearings
have been scraped, the bottom
halves are put in position in the
pedestals or housings, and the
centre line, previously used, is
again stretched through in order
to align the actual bearings.

The bearings of high-speed
turbine plant are invariably pro-
vided with means for adjusting
the bearing relative to the pe-
destal or housing, both vertically
and horizontally. The vertical
adjustment is usually made by
means of liners, both at the top

and the bottom of the bearing: the adjustment sideways is made either by
liners or by two tapered steel wedges on either side. The bearings, also,
are frequently made self-aligning by the provision of spherical seatings
in the housings, but this degree of self-alignment is slight, and is provided
simply to allow the bearings to take up a comfortable position on the
journals, and to remove stresses due to slight inaccuracies of alignment,
or due to alteration of alignment, caused by stresses in the castings or
settling of foundations, &c. One of the most convenient and widely used
bearings is the padded bearing, on which there are packets of thin liners
at the top, and bottom, and sides, consisting of sheets of steel, varying
in thickness from -005 up to -025 in., each set of liners being covered by
a steel pad, through which screws pass and secure the pad and liners to
the bearing. By removing a liner, say -005 in., from one side pad to the
other, the whole bearing is moved over -005 in.; in the same way the bearing
can be raised or lowered by very fine stages.

Before the turbine spindle is put in position, it is advisable to raise the

Fig. 9.—Padded Bearings, showing Adjusting Liners
behind Steel Pads