Extruders that have been exposed to fire
Vol. 21 #2, October 1994
The recent articles on repairing used equipment and flushing gear boxes to keep rust from acting as a grinding mechanism on bearings suggests some of the problems often found on extruders that have been exposed to fires.
First of all, gearboxes are seldom warped severely in ordinary fires. Clues to the heat of the fire may be found in what items are destroyed. Insulation will burn off at about 600° F. Aluminum will melt at about 1000° F.
Most steels will not significantly lose their temper under these conditions.
Water is often a worse enemy than fire. Equipment is often left for long periods of time before insurance claims are settled. If they can be drained and flushed with new oil, considerable damage can be avoided.
Most of the residue left is carbon and it sticks tenaciously. It must be cleaned off moving parts, particularly bearing surfaces. While it is almost always economical to replace small bearings, the cost of large bearings makes extending their life attractive. Often, extruders are not subjected to high load conditions in their reconditioned life. This greatly reduces thrust loads in particular. We have successfully disassembled large thrust bearings for thorough cleaning and inspection.
It is not advisable to sandblast any unit containing bearings, even though new bearings are installed. Residual sand can shorten bearing life. Other blasting materials, such as nut shells, are considerably safer to use.
In rebuilding extruders, supplying abundant lubrication to all parts is most important. Alignment is also critical. If these two elements can be assured, good life can be expected.
- R. Miller
See also:
- Buying used extrusion equipment
- Used extruders
- Extruder alignment
- Machinery installation
- Thrust bearings
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