Patent ID: 8056334

Claim:
A method of recovering energy in a plastic pipe manufacturing process utilizing a sealing gasket compression molding process in which a gasket molding material is placed in a cavity having a predetermined shape, the cavity being formed between a fixed mold member and a movable mold member, pressure being applied between the respective fixed and movable mold members to cause the gasket molding material to conform to the shape of the mold cavity, the method comprising the steps of: positioning a Stirling engine in proximity to the fixed and movable mold members, the Stirling engine having a heating cycle and a cooling cycle which alternately heat and cool a fixed volume of compressible gas; using heating changes which occur as a result of operation of the molding process to power the Stirling engine; providing a forming mandrel having an inner end and an outer end and having an outer working surface; locating a pipe sealing gasket formed in the compression molding process at a first circumferential position on the outer working surface of the mandrel; forming a belled pipe end about the sealing gasket by first heating a female end of the plastic pipe using the heat recovered by the Stirling engine and then forcing the heated female pipe end over the outer working surface of the mandrel and over the sealing ring, whereby the heated female end of the plastic pipe flows over the sealing ring to form a retention groove for the sealing gasket within the female pipe end; thereafter cooling the female pipe end to form a female, belled pipe end followed by retracting the belled pipe end with its retained sealing gasket from the working surface of the mandrel.