Method and means for making high molecular weight polyethylene sheets

Claim 3

A method of processing high molecular weight polyethylene according to claim 1 which includes the step of relieving the inward pressure at the finishing die while moving the resin in said one direction.

Claim 4

Apparatus for extruding high molecular weight polyethylene having a molecular weight in excess of 1,000,000 comprising a major die having an inlet end and an outlet end, a ram reciprocably mounted for movement within the inlet end of the major die, means for introducing successive charges of granular resin into the inlet end of the major die in advance of the retracted ram, a plurality of thermal zones in said major die and spaced axially along its length, means for heating said thermal zones above the crystalline melting point of the resin, means for imparting intermittent inward movement to said ram to move the resin through said thermal zones and out from the outlet end of the major die, and a finishing die for inducing a back pressure of sufficient magnitude on the extruded resin after it leaves the major die to create a reservoir of extruded resin adjoining the outlet end of the major die and of greater cross-sectional dimension than the internal cross-sectional dimension of the major die, said finishing die being spaced beyond the outlet end of said major die a sufficient distance to provide clearance for said reservoir and spaced sufficiently close to the outlet end of said major die to be engageable with the extruded sheet while in its amorphous state, and said finishing die including a platen on opposite sides of the axis of the major die.

Claim 5

Apparatus for extruding high molecular weight polyethylene having a molecular weight in excess of 1,000,000 comprising a major die having an inlet end and an outlet end, a ram reciprocably mounted for movement within the inlet end of the major die, means for introducing successive charges of granular resin into the inlet end of the major die in advance of the retracted ram, a plurality of thermal zones in said major die and spaced axially along its length, means for heating said thermal zones above the crystalline melting point of the resin, means for imparting intermittent inward movement to said ram to move the resin through said thermal zones and out from the outlet end of the major die, and a finishing die for inducing a back pressure of sufficient magnitude on the extruded resin after it leaves the major die to create a reservoir of extruded resin adjoining the outlet end of the major die and of greater cross-sectional dimension than the internal cross-sectional dimension of the major die, said finishing die being spaced beyond the outlet end of said major die a sufficient distance to provide clearance for said reservoir and spaced sufficiently close to the outlet end of said major die to be engageable with the extruded sheet while in its amorphous state, and said finishing die including a platen on opposite sides of the axis of the major die.

Claim 6

An apparatus for processing high molecular weight polyethylene according to claim 3 wherein means are provided for imparting reciprocable movement to at least one platen of said finishing die transversely of the axis of the major die in synchronization with axial reciprocation of said ram.

Claim 7

Apparatus for processing high molecular weight polyethylene according to claim 3 wherein said finishing die includes means for limiting lateral movement of said extruded sheet under pressure of said platens.

Claim 8

Apparatus according to claim 3 wherein the platens of said finishing die are heated above room temperature but below the crystalline melting point of the high molecular weight polymer.

Claim 9

Apparatus according to claim 2 wherein second pressure means are positioned adjacent said finishing die, said additional pressure means exerting a constant predetermined pressure on the extruded sheet.

Claim 10

Apparatus according to claim 7 which includes sensing means adjacent said reservoir and responsive to an increased size of said reservoir beyond a predetermined point to relieve the pressure on said second pressure actuating means.

Claim 13

A method of processing high molecular weight polyethylene according to claim 9 which includes the additional step of altering the cross-sectional dimension of the resin sheet within the extruder while cooling the resIn to a temperature within said range of 270* to 330*F.

Claim 14

A method of processing high molecular weight polymers according to claim 9 which includes the additional step of changing the cross-sectional dimension of the resin sheet after it leaves the extruder and beyond the reservoir while continuing to cool the resin sheet.

Claim 15

A method of processing high molecular weight polyethylene according to claim 10 which includes the additional step of changing the cross-sectional dimension of the resin sheet after it leaves the extruder and beyond the reservoir while continuing to cool the resin sheet.

Claim 16

Apparatus for altering the shape of extruded high molecular weight polymers while in an amorphous state following extrusion, said apparatus comprising a finishing die spaced outwardly from the outlet end of an extruder, said finishing die including a platen on opposite sides of the longitudinal axis of the extruded sheet, a spacer element arranged laterally on each side of the axis of the path of travel of the extruded sheet, each spacer element being of a height equal to the desired height of the extruded sheet, and said spacer elements being spaced apart a distance equal to the desired width of the finished sheet.

Claim 17

Apparatus for altering the shape of extruded high molecular weight polymers while in an amorphous state following extrusion, said apparatus comprising a finishing die spaced outwardly from the outlet end of an extruder, said finishing die including a platen on opposite sides of the longitudinal axis of the extruded sheet, a spacer element arranged laterally on each side of the axis of the path of travel of the extruded sheet, each spacer element being of a height equal to the desired height of the extruded sheet, and said spacer elements being spaced apart a distance equal to the desired width of the finished sheet.

Claim 18

A structure according to claim 13 wherein the height of the spacer elements is less than the corresponding internal dimension of the major die and wherein the distance between the spacer elements is greater than the width of the major die.

Claim 19

A structure according to claim 13 wherein the height of the spacer elements is greater than the corresponding dimension of the major die and wherein the distance between the spacer elements is less than the internal width of the major die.

Claim 20

A structure according to claim 13 wherein an altering die is interposed between the major die and said finishing die, said altering die having vertical and transverse dimensions falling between the corresponding dimensions of the finishing die and the inside dimensions of the major die.