Dual Cylinder Automatic Screen Changers

Extrusion lines require the use of screen filters to remove unwanted materials like metals and waste products.  In order to automate the process, electrohydraulic systems have been introduced to control the screen changing.

As the unfiltered plastic is driven through the filter screen by a melt screw and melt pump, the build-up of unwanted materials causes the flow restriction to increase nonlinearly.  In order to keep material flowing at the required controlled rate and upstream pressure, the Automatic Screen Changer moves the used screen out of the flow path while another one is inserted. 

During the screen transfer, the screen positions must be dynamically controlled relative to the material flow and pressure variables, using closed loop position control. The position feedback is supplied by the MTS R-Series absolute position linear sensor mounted inside the hydraulic cylinders controlling the screen change.