A large automatic forming machine sometimes shuts down on its own. This hasn’t been reported to maintenance before, because the operator has always been able to restart it after taking a ten-minute break. This area of the plant recently got a new production supervisor, and she noticed the operator wasn’t at his workstation and that the forming machine wasn’t running. She found him in the break room polishing off a small microwave pizza. She asked him what was going on and why he didn’t stay with the machine to assist the maintenance tech. That’s when he reluctantly told her he hadn’t “yet” contacted maintenance. So, she did.

In fact, she stayed at the workstation with the operator to witness the maintenance interview. The operator was vague about when these shutdowns were occurring or how many had occurred in the past week. The responding tech did a quick examination and did not see anything obvious, such as debris stuck in the material path. He contacted his supervisor, who escalated the case to the “A Team” of which you are a member. Now it’s your job to figure out what the problem is and make sure it gets fixed. Where do you start?

Answer to Quiz

The operator’s supervisor will surely agree that the first thing to fix is the reporting process. Just because a given operator wants to enjoy an extra pizza break doesn’t mean unscheduled production interruption is acceptable. The production supervisor was right to report this, but did she spot a one-off with this operator or is this break-taking behavior systemic? Is this operator actually causing the shutdown, and conveniently not reporting it to maintenance so he has a ready-made excuse for slacking off on the job? Have that discussion with her and offer to provide whatever assistance she needs. Suggest that she assign a different operator to this particular machine, if she has not done so already. Whether the current operator is causing the shutdown or not, his taking a break before notifying maintenance or his own boss makes him a problem.

Next, look at the equipment itself. If it is shutting down (on its own) yet is able to be restarted in the time it takes someone to heat up and eat a small pizza, it is likely that thermal protection is kicking in. You have many options available for verifying or even calibrating this system. A simple approach, if it’s an analog system, is to temporarily affix a temperature probe (these are available for DMMs and also as stand-alone devices) to the same spot where the system has its own temperature sensor and compare the two temperature readings. But if it’s a temperature switch, you will need a sand bath or similar to calibrate it. Calibration of a temperature system is a slow process; install a spare in the meantime.

You can also look for contributors to high temperature:

• Maybe there’s an error in how the machine is being programmed and run. Consult the operating guide that should have come with the machine or contact the manufacturer.
• Is the ambient temperature on all sides of the machine within the specified operating limits? Or is some heat source located too close to the machine on one side? Not just process heat, but vents of dry type transformers or sunlight magnified by a window. Is there adequate airflow around the machine?
• Check to see if it is properly bonded. Improper bonding can allow undesired current to flow through the machine, and current flow generates heat.

Be sure you check the power:

• Perform a power quality analysis on the branch circuit. A decent portable power quality analyzer should be sufficient. Look for voltage imbalance, low voltage, excess third and fifth harmonics, and power factor. On this last one, correct at the branch circuit supply to machine not at the service.
• It is possible that transient overvoltages are knocking this machine offline. If you simply install a Type-3 SPD for the branch circuit, you are wasting your money because a large transient can jump across its terminals. Instead, use staged protection going from the supply (service or separately derived source) with a Type 1 SPD at the source and a Type 2 SPD at the feeder.
• Check the machine documentation to determine if any Type 4 SPDs are used in the machine. It is possible there is something wrong with these, consult with the manufacturer.

This is a solid start, and it should be enough. But if the problem still persists, there is probably either some malfunction in the forming machine itself or Purchasing was forced to switch to a cheaper, but inferior, supplier. Before asking the manufacturer to send out a tech, check with Purchasing to see if there has been a materials change relevant to that forming machine within a few months of when the problem began. How can you tell when it began? The supervisor can determine that by sitting in the Personnel office with each neighboring operator one at a time. One, if not all, of them will be able to say when the pizza breaks began.