Page 263 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

Power Transmission Gears 245

hub, the key should be split on the protruding end to fill only the keyway
to maintain proper shaft balance.
If an interference fit is used, heat the coupling hub uniformly until
there is sufficient clearance to place it on the shaft. It is important that the
coupling be heated uniformly and that care is taken so that localized spots
are not overheated (maximum 500°F). An ideal way to do this is by using
a heated oil bath. In placing the coupling hub on the shaft, do not pound
directly on the coupling with a steel hammer, but use lead or rawhide
mallets so as not to damage the coupling hub or shaft. A temporary
spacer block placed between the coupling hub and the gear housing is
helpful in preventing the coupling hub from sliding too far onto the shaft.
Many gear drives are being furnished with keyless, hydraulic dilation
coupling-hub-to-shaft fit. These coupling hubs must be properly mounted
and fitted to develop enough torque-carrying capacity between the shaft
and hub. The amount of advance on the shaft is dependent on the amount
of taper and transmitted load. Improper mounting can cause these hubs to
turn on the shaft and destroy the fit. In some cases, repair is not possible
and the gear or pinion is destroyed. Obtain instructions from the vendor
for the particular keyless coupling fit before mounting; also, refer to the
section on coupling installation in Chapter 9, Volume 3 of this series.

Basic lnstallatlon Procedures

Generally, after a suitable foundation has been laid and coupling hubs
mounted, an installation procedure should start with securing the driving
or driven machine (whichever is more permanently settled) and rough-
aligning the gear unit to it. Jacking screw holes are provided on the base
flange for bringing the gear unit to the same horizontal plane as the con-
necting shaft. Once there, the gear unit should be supported on broad,
flat shims located adjacent to and on each side of the foundation bolt
holes. Next, move the unit on its shims until the gear shaft is in the same
vertical plane as the connecting shaft with the correct spacing between
coupling hubs.
At this point, the operating positions of driven and driving shafts,
which will be different from the cold static positions, should be antici-
pated, and desired cold positions for each established based on that infor-
mation. Final alignment is established by moving the shaft of the ma-
chine that is not tied down from its present cold position to its desired
cold position by adjusting the machine very slightly at the base.
After final cold alignment is achieved and before tightening the foun-
dation bolts, be sure that the base sets evenly on all shims so that there
will be no distortion when the foundation bolts are fastened. After tight-