Filter-changing system for molten plastic

DETAILED DESCRIPTION I claim: 1.
In combination with an extruder producing a stream of pressurized molten plastic, a filter assembly comprising: an inlet plate formed with a Y-shaped inlet passage having a substantially circular-section upstream end adapted to receive the stream of pressurized molten plastic from the extruder, the inlet passage branching downstream of its upstream end and having a pair of downstream ends opening at substantially circular downstream ports; an outlet plate fixed spacedly downstream of the inlet plate and formed with a Y-shaped outlet passage having a substantially circular-section downstream end, the outlet passage being branched upstream of its downstream end and having a pair of upstream ends opening at substantially circular upstream ports aligned with the downstream ports; a rotatable filter disk engaged between the plates and formed with a circularly annular array of substantially circular-section throughgoing holes each defining a respective substantially circular seat, the ports and holes being laterally spaced from each other such that in predetermined positions of the disk the ports open into two adjacent holes; drive means for displacing the disk between respective angularly offset positions in each of which two of the holes are aligned between the ports for flow through them from the upstream ports to the downstream ports; and a respective substantially circular filter unit in each of the holes.
2.
The filter assembly defined in claim 1 wherein each filter unit comprises a perforated disk having an upstream face provided with a layer of filter medium.
3.
The filter assembly defined in claim 1 wherein the upstream and downstream passages respectively have substantially cylindrical upstream and downstream end portions opening at the respective upstream and downstream ends.
4.
The filter assembly defined in claim 1 wherein the filter-disk holes are spaced apart by a predetermined angular distance, the upstream ports being spaced from each other by the same distance, the downstream ports being aligned with the respective upstream ports