By Guy Laverty, HLI Midwest Territory Manager
Company: Bemis Corporation, Terre Haute, IN
An extruder operator at Bemis installed an extruder screw in a barrel but failed to install the drive key in the screw. The gearbox drives the screw via the drive key. Through operation and friction, the screw had welded itself to the inside bore of the gearbox.
When the operator shut the extruder down for a screw change (different material/different screw), he encountered difficulty in removing the screw. Repairmen hooked up a 50-ton hydraulic jack to pull out the screw. After trying this with no success, they hooked up a 100-ton jack. After maximum pressure, the screw broke loose.
When the operator tried to install the new screw, it would not seat into the gearbox. Repairmen rechecked and recleaned all mating parts. The operator tried to install the screw again with no success. The repairmen suspected some type of misalignment. Bemis called Hamar Laser to check the extruder.
I set up the laser system on the 8″ extruder. The end of the barrel readings were -.040 vertical and -.179 horizontal. The horizontal readings were very unusual. I started making horizontal moves. By using horizontal jackscrews only about .040 of movement was possible. I took more readings and checks. I concluded that when the repairmen removed the screw with the 100-ton jack, they had sprung the barrel support between the barrel and gearbox.
With the barrel support being sprung out of specification, there are only two means of bringing the barrel back to horizontal center. One is removing the support and having it remachined in the machine shop, which would take a few days in this case. The second choice is to place shims between the barrel and support to bring the barrel back to center.
I chose to install shims between the barrel and support due to the fact that the company urgently wanted to resume production. After my final adjustments, the live readings were -.012 vertical and .004 horizontal. Perfect readings would be -.010 to -.012 vertical and .000 horizontal.
This was an unconventional barrel alignment. The time expended was approximately 6 hours. Numbers were acquired in 20 minutes. The screw slipped in by hand (!) and the extruder was running great.