Apparatus for filtering melted plastic

Abstract

The disclosure is directed to apparatus for filtering a flow of melted plastic prior to use in an injection molding machine. The apparatus includes a cylindrical filter screen disposed in a cylindrical chamber to define an inner inlet chamber and outer outlet chamber. The incoming plastic enters the interior of the filter screen through an axial passage formed in the screen side wall. The material is thereafter forced radially outward through small filtration openings formed through the screen side wall, leaving filtered material and contaminants at the inner wall. Purging or cleaning of the filter screen is effected by a reciprocating shaft that passes through the cylindrical filter screen and partly defines the inner chamber. The shaft carries an imperforate cylindrical sleeve which slides axially through the inner chamber, wiping the inner cylindrical surface of the filter screen as it goes. At the time that it passes by the filter screen, the cylindrical screen blocks communication between the inlet and inner chamber. However, the trailing edge of the sleeve is still exposed to the incoming plastic, which serves to force the sleeve axially beyond the screen, carrying with it the filtered material and contaminants, which are thereafter discharged from the exhaust ports.