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United States Patent 4723847
Douris , ê et al. February 9, 1988

Apparatus for varying pressure within a screw channel

Dray February 9, 1988

Abstract

This invention relates to apparatus for continuously varying the pressure within a screw channel of a plasticating machine by way of a variable restriction in the screw channel. The apparatus includes a cylindrical barrel, a shaft rotatable within said barrel having a substantially circular cross-section and a longitudinal axis for rotation concentric with the barrel. The shaft is provided with a helical screw channel which is defined between successive turns of at least one helical flight integrally formed with the shaft. At least one radially movable first member is disposed at a right angle to said axis within the channel at a location along the axis and is located within the channel at a location along the axis at which the material being processed is substantially melted. A reciprocatively movable second member is disposed within a cylindrical bore through said shaft along the axis of rotation, the second member having a conical end portion which cooperates with an inner end of said first member such that said first member is movable in a radially inward or outward direction in response to the reciprocating movement of the second member. The inward or outward location of the first member provides a continuously variable restriction in the screw channel which increases or decreases pressure in an upstream direction within the channel.