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 REBUILDING AND HARD-FACING CRUSHER
ROLL SHELLS (Continued)
5. Roll shells must be kept round and both shells
1. Worn crusher shells should be cleaned to prevent
rebuilt to the same diameter. Out-of-round shells
arc interference, weld metal contamination, and
produce a variation in the crushing zone, resulting
possible porosity.
in unsatisfactory control of material size. In
addition, unnecessary wear and strain are imposed
2. The ground should be made directly to the roll
on the bearings and shafts.
shell being welded to avoid arcing through the
bearings. A rotating ground attached to the roll
6. Weld beads are subjected to tension as they cool; to
shaft end will provide a positive contact.
minimize surface checking or cracking, deposits
are sometimes peened while hot to produce plastic
3. Cracks in the roll shell should be repaired before
flow and to change tension to compression.
rebuilding. A chamfering rod can be used to gouge
out any cracks down to sound metal. The crack
7. Weld beads must not be deposited over the roll
should be filled with recommended alloys prior to
edge. Base metal cracking generally begins here.
rebuilding.
The beads should be started and stopped about 1 in.
short of the roll edge (Figure 2-64), or at least far
4. Where extensive welding is planned on one-piece
enough from the edge to allow sufficient clearance
shells, wedge bolts should be loosened before
for cheek plates.
welding begins and retightened after the roll shell
has cooled. This allows for expansion and
contraction of the shell and reduces the possibility
of cracking, breaking, or warping (Figure 2-63).
2-68
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