Screen changers provide an effective method of filtering polymer melts. The removable ‘screen packs’ can be rapidly changed by the operator (typically in under 5 minutes) without having to unfasten any nuts and bolts. A screen pack with the desired filtration level is fitted into the housing within a ‘screen bearing piston’ . The screens can be changed even whilst production continues. With the 2 channel K-SWE model 2 screens are normally in the operating position.
When to change screens?
The inlet pressure to the screen changer can be monitored.
A rise in pressure indicates that the screens are becoming blinded by contamination. Once the pressure has reached a predetermined limit an alarm can signal the need to change screens. The screen bearing piston is moved hydraulically out of the housing to the screen change position.
The operator simply removes the dirty screen pack and installs a new one (the old pack can be discarded as they are inexpensive)
4-Channel Backflush screen changer for PET extrusion application
The 4- channel backflush screen changer is rapidly establishing a global standard for extrusion processes utilising varying amounts of PET bottle flake mixed with virgin PET pellets. The backflush control system automatically detects a rise in pressure as the screens become blocked by dirt particles. Once the backflush setpoint is reached the plc control automatically moves one screen from production to the ‘backflush position’ whilst extrusion of the product continues. During screen change 75% of filtration area remains in production. The system can automatically clean screens between 30 and 100 times, which means dramatically less operator intervention at the extrusion line is required.