초록 ▼

This invention relates to a method and molding screw for injection molding. The molding screw has a fixed inner screw mounted within a rotatable and reciprocally movable outer screw. The outer screw is continuously rotated throughout the injection cycle to (1) counter the back flow of melt material

This invention relates to a method and molding screw for injection molding. The molding screw has a fixed inner screw mounted within a rotatable and reciprocally movable outer screw. The outer screw is continuously rotated throughout the injection cycle to (1) counter the back flow of melt material around the screw, (2) subject the melt material surrounding the inner screw to a vigorous mixing action, (3) add additional thrust to inject the melt material into the mold, and (4) return the outer screw to its initial starting position. A rod-type electrical heater is internally positioned in the fixed screw to maintain the temperature throughout the melt material surrounding the inner screw at a substantially constant value which is substantially equal to the barrel temperature.

대표청구항 ▼

An injection molding screw comprising: an elongate barrel having first and second end portions and having a bore extending along the length of the barrel, the barrel having at the first end portion thereof means for receiving sold plastic particulate material into the bore of the barrel, a first scr

An injection molding screw comprising: an elongate barrel having first and second end portions and having a bore extending along the length of the barrel, the barrel having at the first end portion thereof means for receiving sold plastic particulate material into the bore of the barrel, a first screw positioned within the bore of the barrel and having a helical feed thread on the outer surface thereof defining a feed channel for the plastic material, the screw being rotatable relative to the barrel in a direction to advance particulate material along the barrel bore from the first end portion thereof toward the second end portion thereof, the screw being reciprocal within the barrel while it is being rotated between a forward position and a retracted position with the screw moving toward the first end portion of the barrel as it moves from its forward position to its retracted position and toward the second end portion of the barrel as it moves from its retracted position to its forward position, the screw having a cylindrical cavity therein, the cavity having an opening at the end thereof facing the second end portion of the barrel, and a plurality of drain openings through the screw providing fluid communication between the outer surface of the screw and the cavity, a second screw positioned within the bore of the barrel and having a helical thread on the outer surface thereof, one end portion of the second screw being in engagement with the second end portion of the barrel and the other end portion of the second screw projecting into the cavity, the one end portion of the second screw having an outlet opening through which all of the melt of the particulate material can pass from the cavity through the opening and out of the barrel. a first heater located with respect to the first screw to heat the particulate material between the first screw and the barrel to produce a melt that can pass through the drain openings in the first screw into the cavity, and a second heater located with respect to the second screw to heat the melt in the cavity to a temperature substantially equal to the temperature of the melt between the first screw and the barrel, whereby particulate material received at the first end portion of the barrel can be advanced toward the second end portion thereof by rotation of the first screw while the screw is in its retracted position with the first heater heating the material and producing a melt that can flow through the drain openings in the first screw into the cavity, and with the temperature of the melt in the cavity being maintained by the second heater until the first screw is reciprocated to its forward position while it continues to rotate and thereby drive melt from the cavity through the outlet opening in the second screw.