The Case of the Destroyed Plywood

By Robert Morrison

I worked as an assistant supervisor with a major furniture manufacturer until 2003 when the company moved operations overseas. I was in the plywood portion of the manufacturing operation. We used an automated plywood press in from another factory. A German engineer came in to install the machine and get it ready for operation. He showed me how the machine operated and how to do troubleshooting and maintenance.

The machine consisted of a 20 ft. feed belt in front, the actual press, and the belt on the rear that accepted the material after it was pressed. Plywood was loaded on the front belt, when the belt became full, an eye caused the press to activate both the front belt and a Mylar belt that ran through the press.

It was synchronized so that the plywood was transferred to the Mylar belt and taken into the press. Trip switches on the drive chains triggered the belts to stop and the plates of the press to close when all the wood was under the plate. The Mylar belt was actually two belts end to end. As one belt went into the heated press the other rotated under the machine to cool down.

After a period of time, the Mylar belts would become brittle and would need to be replaced. This is where the trouble started. The belts were held tight by two metal rods that spanned the width of the press. One was simply to attach the belt to, the other had a ratcheting action to apply tension to keep the belt flat in the press. I removed the old belts and put the new ones on.

When the machine was started up it was out of sequence. When the wood was drawn into the machine via the belt, instead of rapidly going in and the press closing, it would slow down to a crawl and the wet plywood would curl up in the machine. By the time the press closed the wood was curled up and it was destroyed.

When the Mylar belts were attached on the rollers on the end, a lock pin was used to secure it to keep it from unrolling. I worked on this machine for three days. I was lying in bed when it hit me. The only thing that told the machine where it was in the sequence was the trip switches. The next morning I went in, started the machine and watched as one of the lock pins that were installed backwards hit one of the trip switches on its way through the press. Because of the design of the pins they could only be installed in one direction for proper operation.