Blown film extrusion machines

Blown film extrusion processes utilize infrared heaters (IR), strategically located along the extrusion line, to maintain the required temperature for proper melting and processing of the plastic material. The NRG is an innovative solid state relay platform that encompasses switching, diagnostics and real-time monitoring and feedback via fieldbus in one solution. Specific to infrared heaters is the soft start function available on the RGC1P variants on the NRG platform. Through soft-start function, the inrush current of the heaters is eliminated thereby avoiding temperature shocks to the heaters but also avoiding possible temperature overshoots. Moreover, the real-time status of the heating elements can be monitored in real-time and data can be exchanged directly to the PLC via the NRG controller.

The RGC.P proportional controllers, also known as SCRs, can also be used to regulate the power to the heating element. The voltage at the output of the RGC.P can be varied via the level of the analog control input.
Both the RGS1P and RGC1P can be adjusted, via the front selector switch, to operate with soft start mode to reduce the initial high starting current typically associated with short-wave infrared (SWIR) lamps.
For 3-phase SWIR, the RGC3P includes specific models that are equipped with soft start function.

Heater breakdown and thermal runaway due to a shorted heater, are two critical issues in most plastic processes.
A failure of the heater will cause a drop in temperature in the heating zone, thereby increasing friction on the screw, resulting in overheating and barrel wear.
If a heater shorts out, the temperature in that specific area cannot be controlled and can cause the plastic to overheat resulting in significant material scrap.
The RGC1S solid state relay and contactor series integrates current monitoring to detect total and partial heater failures.
Based on a "teach" function, the RGC1S compares the measured current to the one stored during the "teach" function and checks for current deviations for up to 6 heaters connected to the relay.

Capacitive sensors are ideal for monitoring the level of plastic pellets in dosing equipment. Carlo Gavazzi capacitive sensors offer a very high immunity against external disturbance caused by high EMC and ESD events. With their TripleshieldTM technology, our capacitive sensors are industry leading products. The sensing face on the CA series can withstand temperatures up to 120ºC (248ºF).
Through IO-Link interface, the CA18 and CA30 sensors capabilities are further enhanced with logic, timer and logging functions as well as resulting in better process monitoring and the higher quality of the film.

When the plastic film is inflated, an ultrasonic sensor can be used to check the film loop tension and avoid film breakage. Three ultrasonic sensors can be placed around the cylinder of the blown plastic film, measuring the actual diameter of the plastic bubble, controlling the air pressure and maintaining a controlled diameter and thickness of the plastic film.
The UA18 and UA30 ultrasonic sensors can be used to accomplish this functionality.