Apparatus for replicating centrally apertured video disc records

Claim 2

In apparatus, for injection molding an article having a central aperture, having an injection nozzle for injecting a molten mixture into an annular cavity of uniform thickness formed by a first mold half and a second mold half, said injection gate being positioned intermediate the injection nozzle and the cavity, an injection gate comprising: a sprue passage of substantially circular cross-section and having a first end and a second end, and said first end being adapted to contact the injection nozzle and to receive a molten mixture exciting the injection nozzle; an annular shaped gate passage having a first end and a second end, and being formed by a plurality of concentric annular shaped sections positioned intermediate said second end of said sprue passage and said cavity; each of said sections having a different average thickness for regulating the pressure of the molten mixture as the mixture passes therethrough prior to entering the cavity; and said first end of said gate passage having a greater thickness than the second end of said gate passage for providing restriction to the passage of the molten material through said gate passage and for achieving a minimum disturbance to material flow of the molten material as it flows through said gate passage.

Claim 3

An injection gate as recited in claim 1 wherein the annular shaped gate passage further comprises: a first annular section having a first end and a second end and having a uniform radial length and having a gradually diminishing thickness across its radial length beginning at said first end and continuing to said second end, and said first end being positioned to receive the injected molten mixture from said sprue passage for providing a partial reservoir for said molten mixture as it abruptly leaves said sprue passage and for removing a portion of the stress carried within the molten mixture due to said abrupt change; a second annular section having a first end and a second end and having a uniform radial length and having a uniform thickness across its radial length, and said first end being positioned to receive the injected molten mixture from said second end of said first annular passage for providing a further reservoir for said molten mixture and for establishing a charge of said molten mixture of dimensional stability with the dimension of the cavity; a third annular section having a first end and a second end, and having a uniform radial length and having a gradually diminishing thickness across its radial length beginning at said first end and continuing to said second end, and said first end being positioned to receive the injected molten mixture from said second end of said second annular section for partially restricting the free flow of molten mixture from said reservoir section into the cavity for reducing stress forces in the molten mixture injected into said cavity; and a fourth annular section having a first end and a second end, and having a uniform radial length and having a uniform thickness across its radial length, and said first end being positioned to receive the injected molten mixture from said second end of said third annular section and said second end being positioned to inject said molten mixture into the cavity with minimum disturbance.