Patent ID: 6241932
Filing Date: 2001-06-05
Classification: B29C,B29K

Abstract:
A method of operating a two-stage injection molding machine communicating with a mold, the machine including a plasticizing screw to produce melt material, a shooting pot with an injection plunger, and a distributor valve interposed between said shooting pot, said plasticizing screw and said mold, said distributor valve operable to alternately place said shooting pot into fluid communication with said plasticizer and said mold, said method comprising the steps of:(a) injecting a previously plasticized amount of melt material from said shooting pot into said mold through said distributor valve;(b) waiting during a hold period for the previously injected shot to cool within said mold and injecting additional material to pack said mold to compensate for thermal shrinkage;(c) waiting during a cooling period for said shot to cool;(d) when said shot is cooled, opening said mold and ejecting the resulting finished part from said mold;(e) closing said mold and making said mold ready for another injection operation;(f) simultaneously with steps (a) through (e):(i) plasticizing an amount of melt material in said plasticizer;(ii) transferring said amount of melt material to said shooting pot through said distributor valve by co-ordinating the rotational and axial movement of the plasticizing screw with pulling back the injection plunger with the injection piston to proactively maintain the volume of said shooting pot substantially the same as the volume of melt received therein; and(g) repeating steps (a) through (f) for each injection cycle.