The olive cannery warehouse where I worked as maintenance supervisor and Plant Engineer used an automatic, pallet stretch wrapper for the stacked pallets of cased olive cans. 

The pallet handling consisted of a photoelectric-eye sensor controlled infeed conveyor, the pallet was wrapped, and then a short outfeed conveyor removed the plastic wrapped pallets. The pallets were handled with 4-ton electric forklift trucks.

We had several smaller, stand-alone stretch wrap machine, but they could not handle the full time load for long. The large stretch wrapper broke down on swing shift. The next morning I had to rent another smaller stretch wrapper and have one of the other stretch wrapper repaired.

With Three, single-feed stretch wrap machines, the forklift operators could barely keep up with the labeling lines output. We ran six labeling lines.

A work crew of one electrician and one mechanic was assigned to the large stretch wrap machine to identify the problem and effect repairs. The wrapper would get to a certain point in the PLC program and stop with the pallet partially wrapped.

The stretch wrapper had an early PLC controller in it with a relatively short PLC program running the machine. We had a print out of what was supposed to be the complete program. There was a button sequence where a technician could reprogram the CPU with a stored copy of the program.

The shift electrician had used the sequence to reprogram the wrapper the night before. All the problems started just prior to the reprogramming.

We had no "reader" or "burner" for the memory in the wrapper. I contacted the manufacturer's representative and he said the equipment that we were using had been discontinued and he had no idea where to locate the programming equipment I would need. He said he would locate it and let me know as soon as possible.

In the meantime, the work crew had pulled the rotating top platform off to check the load bearings. The platform had large, steel balls in a greased track that supported the rotating platform. 

The grease in the track had dried. The mechanic cleaned the track and bearings and greased the track. The electrician was checking out the three Horsepower, Direct Current, special motor on the main drive.

He thought there might be a problem with the motor, so I told him to remove the motor and bench-test the motor in the shop. I checked with a vendor to determine the cost and availability of a replacement.

The cost of a new motor was $3000. There was only one available, so I got permission to order it right away. If we didn't need the motor, I could return it for credit with payment of shipping and a restocking fee.


The motor tested ok in the shop and was reinstalled. The mechanic replaced the rotating platform. When the motor started, the platform would move very slowly and then the motor would trip. The rotating platform had to be removed to access the motor and drive box. 

The rotating platform was removed. The motor was started with only the gearbox for a load and ran great with no tripping or overload on the amps. 

The motor and gearbox were removed and the rotating platform was reinstalled temporarily. We tried to rotate the platform by hand and could barely move it. It was very tight.

The platform was removed and the steel balls in the heavily greased track were checked for movement. The steel balls would move, but the grease was definitely exerting friction on each steel ball. 

There were a lot of balls. Apparently, the total amount of friction from the grease was enough to cause the motor to overload. The amount of grease in the track had to be reduced, substantially.

Each ball had to be removed by hand a wiped clean of about 98% of the grease. The tracks were wiped clean of the majority of grease and then the balls were replaced. The platform was reinstalled and moved easily.

We thought we had repaired the machine. The platform was removed and the motor/gearbox drive was reinstalled. The platform was reinstalled and the machine was tested. The wrapper started and ran to the same point and again stopped early without finishing the wrap.

That was a very disappointing moment. We had been working on the machine for nearly three days already. Pressure was being exerted from the front office to get the wrapper finished. I returned the D.C. motor to the vendor for credit.

The manufacturer's rep had called with a location for a programming machine. There was only one in the US and it was in South Carolina. I had already paced an order to rent it and to have it sent to the plant.

I contacted an Electrical Contractor in Fresno that specialized in troubleshooting and repairs of PLC controlled equipment. They said they could handle the repairs if I could get the programming equipment. 

I told them that it was scheduled to be here on the next morning, a Saturday. The contractor sent two men. They worked 12 hours on Saturday and I told them to come in on Sunday as well. I stopped by to offer assistance and help when I could. 

On Sunday, they told me that it was as if something was missing from the program. I told them to write a piece of code to finish it up to get it to run. After five more hours on Sunday, the contractors called me in my office to tell me they had finally located and solved the problem.

There was one line of code missing from the copy of the program that we had. Someone in the past had added a limit switch on the central tower of the wrapper, wrote and entered one line of code to the program and neglected to write the additional line on the paper or to save the code in the permanent memory of the machine.

Therefore, the machine ran fine until there was a problem and the electrician reloaded the old program into the machine's memory. That eliminated the additional line of code and stopped the machine from completing the pallet wrap. It worked just like a time bomb waiting to go off and shut the piece of equipment down.

Problem finally solved for under $5000. Less than half of what a new, single-feed wrapper would have cost. The large wrapper was paced back into service on Monday and the rental was returned to the equipment rental company.

Feel free to copy this article in it's entirety as long as you include the credits below. Thank you for spreading the knowledge.

Author: Larry Bush 
Profile: Electrician in industrial, construction, marine, and food industries for 47 years, with 22 of those years in management.
URL: http://www.reliability-consultant.com