Extruder Heaters and Controls For Polyethylene Film Lines
- Are temperature controllers for each extruder zone checked for excessive temperature override or insufficient heating?
- Are the melt temperature and pressure indicators and the screw tachometer and drive ammeter which all indicate extruder operation stability — frequently monitored and maintained?
- Are all heater bands and thermocouples around the extruder head,
adapter and die checked for loose wires? Be sure the power is off when a check is made.
- Is the wiring for the heater bands correctly connected, e.g., not “in series” if “in parallel” is required or vice versa.
- Are thermocouple leads correctly connected to their corresponding extruder zones?
- Are all the heater bands for a specific extruder zone of the same size and watt density?
- Are the die heater band terminals not aligned in a row? If they are aligned in a row, the resulting cool spot can create a gauge band in the film.
- Is the extruder regularly checked for loose thermocouples, burned-out heater sections and loose or broken wires?
- Is there a specific instrument that checks for overheating in the extruder drives?
- If the extruder is water-cooled, are the feed throats cool to the touch?
Inefficient plumbing that does not force all of the air out of the water cooled chambers of the feed throat can cause poor circulation and hot spots on the surface of the feed throat.
Resin can melt and stick to these hot surfaces, bridge and interrupt the resin feed to the extruder. The result is a reduction in output, surging, or in time, the complete loss of feed and shutdown of the extruder.
- Has the automatic barrel water cooling system been checked recently? This can be done by lowering the set point of the barrel zone temperature controller for a moment, listening for the pumps to start and observing a temperature drop on the instrument.
- If air is used in automatic barrel cooling, has the blower exhaust beenchecked for hot air output?
- If water cooling is used on the screw, are both the incoming and outgoing
water flows at the correct temperatures?
Cooling water is normally fed through a siphon tube to the end of the screw. The outgoing water modifies
the temperature of incoming water before it reaches the end of the screw. Otherwise, if the incoming water were too cold, it could freeze the melt..
- Are all the extruder water systems filtered and are all the filters checkedregularly?