Abstract: An extruder wherein the housing which defines a passage for the flow of foamed plastic material at elevated pressure and temperature to the shaping station contains a reciprocable carrier of one or more filters. The carrier has a filter compartment and is movable relative to the housing between a first position wherein the plastic material must flow from the inlet of the passage, through the compartment and the filter therein, and on to the outlet of the passage, and a second position in which the compartment is sealed from the passage. An expansion chamber in the housing and/or in the carrier communicates or can be caused to communicate with the compartment in the second position of the carrier so as to allow for a controlled reduction of pressure of plastic material before the compartment is made accessible for removal of inspection of the filter in the compartment. The compartment is thereupon rendered accessible, either in the second position of the carrier or by moving the carrier to a further position.

Abstract: Apparatus for filtering a stream of plasticized synthetic plastic material in an extruder has a housing with four or more channels connecting a material-admitting inlet with a material-discharging outlet. The housing is formed with parallel bores each of which receives a single reciprocable cylindrical carrier of two or more filters or two independently reciprocable cylindrical carriers of discrete filters. Each carrier can be moved between a first position in which its filter or filters register with discrete channels of the housing and at least one additional position in which its filter or one of its filters is accessible. At least 75 percent of filtering capacity remains available when a filter is being inspected, cleaned or replaced. The carriers seal those channels which are not in line with filters while the carriers are out of their first positions.