Transfer molding insulation unit

An apertured insulation unit having opposite side-faces and adapted for interposition between (A) a mold having at least one cavity in which elastomeric stock can be cured in the form of said cavity and (B) an open ended chamber of an injection unit from which elastomeric stock can be expelled and transferred through said insulation unit to the cavity of said mold, with said mold and said injection unit being arranged for relative axial movement therebetween into and out of confining relation to said insulation unit at the respective opposite side-faces of the latter so as to enable the elastomeric stock in said chamber to be pressed against said insulation unit, and said insulation unit when so confined serving, without separation of said mold or said injection unit from said insulation unit, to prevent the curing of the elastomeric stock remaining in said injection unit with the curing of the portion of said stock transferred to said cavity;

• said insulation unit comprising a first plate having first and second faces and constituted of a thermal-insulatory material, and a second plate having first and second faces and constituted of a different material having a greater tensile strength and a lower capacity to resist heat-transfer than said first plate, said second plate being arranged to be interposed between said injection unit and said first plate with said first faces of said first and second plates directed toward each other, said second face of said first plate defining the one of said side-faces of said insulation unit to be directed toward said mold, said second face of said second plate defining the one of said side-faces of said insulation unit to be directed toward said injection unit, and said first and second plates each having at least one aperture, with each said aperture in each plate being aligned with a corresponding aperture in the other plate, through which elastomeric stock is transferable, said second plate constituting means for preventing the elastomeric stock in said injection unit from coming into adhering engagement with said first face of said first plate.

In combination, a mold having at least one cavity in which elastomeric stock can be cured in the form of said cavity, and an apertured insulation unit interposable between said mold and an injection unit from which elastomeric stock can be expelled and transferred through said insulation unit to the cavity of said mold, said mold and injection unit being movable axially relative to one another into and out of pressing association with respective opposite side-faces of said insulation unit, said insulation unit serving to prevent curing of elastomeric stock remaining in said injection unit with the curing of a portion of said stock transferred to said cavity without separation of said mold or injection unit from said insulation unit, said mold including a top plate having a sprue-constituting aperture communicating with said mold cavity, and said insulation unit including a plate constituted of thermal-insulatory material having an aperture communicating with said sprue-constituting aperture;

• wherein the improvement comprises vent means formed at least in part in said top plate and communicating with said mold cavity for directing the outflow of gas collected in said cavity during filling of the latter with and the curing therein of elastomeric stock, and said vent means comprises a second aperture formed in said top plate, and a blind recess formed in said insulation plate and communicating via an open end thereof with said second aperture.