Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Shaping against forming surface
Patent
1980-05-22
1981-11-10
Pavelko, Thomas P.
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Shaping against forming surface
264 73, 264 75, 366 90, B29F 102, B29F 112
Patent
active
042997925
ABSTRACT:
A method for the injection molding of plastics material wherein the forward portion of the screw is designed such that mixing and shear of the material is minimized. This is advantageous when processing materials having diverse colorations so as to produce a mottled product, and also for processing glass reinforced materials wherein high shear processing would break the fibers thereby resulting in a lower quality product. Low shear processing of the material in the forward portion of the barrel is accomplished by providing a screw having a fully flighted rear portion, but a forward portion which is flightless so that a generally unobstructed, annular flow passage is formed between the cylindrical outer periphery of the flighted portion and the inner wall of the barrel. In a mottling application of the apparatus, materials of diverse coloration are softened by the flighted rear portion of the screw but not yet fully mixed so that distinct color patterns are present. When the material reaches the unflighted portion, it will be forced forwardly by the forward pressure developed as the screw continues to pump material forwardly, but the only shear imparted thereto is the gentle wiping action produced by the inner wall of the barrel and the outer periphery of the unflighted portion of the screw so that the streaked condition of the material remains intact. In the case of glass reinforced materials, the circumferential wiping action produced by the unflighted section of the screw aids in wet-out.
REFERENCES:
patent: 3230902 (1966-01-01), Grimm
patent: 3518721 (1970-07-01), Rukas
patent: 3689184 (1972-09-01), Morse
patent: 3841814 (1974-10-01), Eckhart
patent: 3876188 (1975-04-01), Koch
patent: 3945786 (1976-02-01), Bishop
patent: 4125582 (1978-11-01), Langlois
patent: 4183673 (1980-01-01), Easley
Hoffman John F.
HPM Corporation
Jeffers Albert L.
Pavelko Thomas P.
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