The plant has four large plastic extrusion machines. Each relies on 15 wrap-around resistance heating elements. It seems a day doesn’t go by when at least one of these elements fails and an extruder stops producing parts. Unfortunately, it may take over an hour for an operator to notice the interruption.
How can you get a handle on this problem?
First, install temperature alarms to reduce the wait time for knowing about the problem. That should improve product flow. The cause could be constant or occasional undervoltage or “single phasing” in the supply. In the event of undervoltage, the heaters will draw more current and thus fail prematurely. If you lose a phase, that means five of those heaters are offline and the other ten may be drawing more current to maintain temperature; install a phase loss monitor at the supply.
If you have PLC control, use the output of the phase loss monitor as a signal to reduce the setpoint temperature (to prevent burnout) and sound an alarm. Use a power analyzer to see what’s going on with the supply, so you can fix the underlying problem.
