Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting
Patent
1988-06-02
1990-03-13
Heitbrink, Jill L.
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
264 406, 26432814, 264349, 366 90, 366145, 366146, 425143, 425208, 425587, B29C 4550
Patent
active
049081691
ABSTRACT:
Method for improved melt quality of thermoplastics processed in reciprocating-screw molding, especially optical injection molding processes. In a reciprocating-screw injection-drive unit (4) is a barrel (53) and screw (15). Screw (15) is double flighted throughout its melting or transition zone (2), to form melt channel (48) and solids channel (50) separated by melt-filtering flight element (47), and kept in fluid communication by melt-transfer apertures (47 or 55 or 56) or substantially nonvertical ramped barrier flight geometry (not shown). The largest energy input for melting is directly provided by thermal conductivity, via electrical resistance heating elements. The primary source of such heat is by such elements (35) mounted internal to screw (15), and operating in an open loop control with respect to melt temperature sensor (22); secondary heat sources are elements (12, 13, 14, 29) mounted external to barrel (53) and nozzle (33) and operating in a closed loop manner with respect to barrel temperature sensing device (17, 19, 21, 30) and/or melt temperature sensor (22). By screw geometry designed to keep the solids bed (24) continuously under compression and by suitable numbers and sizes of apertures (47 or 55 or 56), melt films are continuously transferred away from the screw's and barrel's heated surfaces as fast as they are formed, thereby minimizing residence times at peak temperature and maintaining maximal heat transfer rates.
REFERENCES:
patent: 4000884 (1977-01-01), Chung
patent: 4501498 (1985-02-01), McKelvey
"Screw and Barrel Technology", Spirex Corporation, Youngstown, Ohio, 1985, booklet.
"Internally Heated Screw for all TG Injection Molding Machines", Reed-Prentice Division, Package Machinery Company, Mass., brochure.
Galic George J.
Maus Steven M.
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