Apparatus for continuously filtering plastic melt with noninterruptive purge

摘要

Apparatus is disclosed for continuously filtering a flow of melted plastic which includes a mechanism for purging the filter without interrupting continuous operation. A filter screen is disposed in a circular chamber within the filter housing. A collector plate including a plurality of radially oriented, triangularly shaped passages is disposed on the upstream side of the filter screen, defining triangular pockets for collecting contaminants that cannot pass through the filter screen. A collector head is rotatably disposed for selective registration with the collector pockets, and an indexing mechanism is included for sequentially stepping the collector head around the collector plate for momentary registration with each collector pocket. The collector head communicates with a contaminant discharge passage that is opened and closed in timed sequence with movement of the collector head. With the collector head in position over a triangular pocket and the contaminant discharge passage open, a part of the filtered plastic downstream of the filter screen reverses its flow through the screen and collector head, purging the screen by carrying collected contaminants with it. The discharge passage is opened for a short period of time so that the reverse flow for each pocket is a small discrete volume. Because of this, the combined discrete quantities of filtered plastic used in the screen purging process as the collector head cycles through communication with each pocket is held to a minimum, while at the same time insuring continuous filtering operation.