Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Shaping against forming surface
Patent
1991-06-03
1994-06-28
Kuhns, Allan R.
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Shaping against forming surface
26432816, B29C 4573
Patent
active
053244737
ABSTRACT:
Methods and apparatus for molding a thermoplastic article bring the surface of the mold cavity above the flow stress relaxation temperature of the molten plastic during molding of a part sufficiently long enough to relax the resin at the surface of the molded part and produce negligible residual stress. The surface of the mold cavity is maintained above the flow stress relaxation temperature of the molten plastic as the center of molten plastic in the mold cavity cools from a temperature above the solidification temperature toward the solidification temperature, thereby reducing flow-induced and temperature gradient induced stresses in the solidified mold material of the molded part. The heat of the molten plastic introduced into the mold is used as the source of the heat for heating the surface of the mold cavity. A layer of thermal flow control material about the mold cavity has a mathematical product of thermal conductivity, specific heat and density and appropriate thickness, so that heat from the molten plastic introduced into the mold cavity raises the temperature of the surface of the mold cavity above the flow stress relaxation temperature of the plastic being molded. The methods and apparatus are particularly useful for the molding of amorphous and crystalline resin parts and for rewritable optical data storage discs and optical lenses with minimized birefringence.
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