Apparatus for continuously filtering plastic melt with noninterruptive

Abstract

Apparatus for continuously filtering a flow of melted plastic which includes means for purging the filter without interrupting continuous operation. A filter assembly consists of a trap plate and breaker plate between which filters are disposed. The trap and breaker plates each defines triangularly shaped openings diposed in a circular array, each of which is subdivided into smaller passages for filtering larger contaminants. Individual filters also of triangular configuration are sandwiched between registering openings between the trap and breaker plates, each filter consisting of a fine and coarse screen. A collector head is rotatably disposed for selective registration with each of the openings of the trap plate, and an indexing mechanism is included for stepping the collector head for stationary registration with each opening. The collector head communicates with a contaminant discharge passage that is open and closed in timed sequence with movement of the collector head. When the contaminant discharge passage is opened, a part of the filtered plastic downstream of the filter assembly reverses its flow through the opening registering with the collector head, purging the filter screens by carrying collected contaminants. The contaminant-filled flow initially passes into a purge chamber of predetermined volume having a pressurized piston. After a predetermined volume has entered the chamber forcing the piston to retract, a valve breaks communication between the discharge passage and purge chamber, simultaneously establishing communication between the purge chamber and a contaminant discharge outlet, enabling the piston to evacuate the purge chamber and discharge the contaminants.