Monitoring during calandering of thermoplastic materials
Calendering is an industrial technique where thermoplastic materials are passed through multiple heated rollers until a film arises. Examples of materials that are processed in this way are e.g. PVC, linoleum, rubber.
With the pressure and temperature of the rollers, but also by using scrapers/knives the thickness of the material could be influenced. Then the arised film is cooled down and can be further processed into a final product. Here it can rolled up and be further processed as an end product or semi-finished product or the film is provided with a layer of coating. To determine whether the calendering is well adjusted, during this process measurements are are carried out:
Measuring thickness with displacement sensors
By placing a sensor on the top and on the bottom of the material/ the plate, the thickness can be defined. This is determined by measuring the distance of the sensor to the material from both sides. It is also possible to use the first measurement as a reference value. Then accurately checking if the applied coating is thick enough.
Because you set up 2 sensors on the top and bottom you are free of vibration and other factors that influence the measurement. To remain an equal distance between the sensors, a U-profile is used. These are available in different sizes and lengths.
The L-LAS-LT-37-MA-SL is a master/slave displacement sensor from Sensor Instruments that is capable to carry out an accurate thickness measurement during calendering. The sensor has a measuring rang of 35 up to 39 mm, an accuracy of 1μm and measuring frequency of 200 Hz. With the potentiometer the tolerances can be set up. The master is furthermore provided with a LED-display to adjust the measuring range and the sensitivity. Finally, this laser has a RS232 interface and is equipped with 2 digital inputs, 3 digiital outputs and 1 analog output.
Measuring the width with ultrasonic sensors
The output of calendering can vary. Certainly in the case that a virgin product is processed into film. After a while the material cools down which can result in variations in the width. By carrying out a measurement from both sides, the width of the end product can be mapped. Here an ultrasonic sensor from microsonic can be used that is specially developed for the web edge control, so the regulation of the width of passing material.
The bks+6/FIU is an ultrasonic sensor which is suited for doing a width measurement during calendering of materials. The sensor includes a emitter and receiver in one fork housing. Here the emitter sends sound pulses to the receiver. If a material is detected between the fork, the sound pulse is (partially) subdued. Then a analog signal is sent via IO-Link or via the PNP- or NPN switch. This takes place on both sides of the passing material and this way can be determined if it has the desired width. Or that adaptions are needed. Finally, the sensor has a measuring range up to 40 mm, a reaction time of 6 ms and is equipped with a 5-pin M12-connector.
