Die assembly for extruding multilayer parisons

Claim 1

A die assembly for extruding multilayer parisons which comprises a parison programming shaft, having a lowermost end; a core pin which is attached to said lowermost end of said parison programming shaft; a mandrel which encircles said parison programming shaft; a plurality of control rings which are mounted on said mandrel at predetermined intervals; a plurality of sleeves which are installed around said mandrel, and each said sleeve has an outside wall that is provided with an inclined groove and has a lower part which is of an inverted frustoconical shape; each said sleeve having an inner wall, with a lower end, an annular rib formed on said lower end of said inner wall of each said sleeve, a housing which holds therein the above members; the housing having a bottom part; a controlling member to control the resin quantity of the outer layer of parisons, said controlling member is movably attached to said bottom part of said housing and around the lowermost of said sleeves; said housing bottom part having a bottom face; a die supporting member which is attached to said bottom face of said housing; and a die which is supported by said die supporting member and which encircles said core pin a resin passage in said die assembly is defined and regulated by each of said control rings together with said annular rib that is formed on said lower end of the respective said inner wall of said sleeve at said ring, by said controlling member acting together with said lowermost sleeve, and by said die acting together with said core pin.