Method of and means for adjusting the flow of plastic material in an extruder cylinder

Claim 3

In an extruder comprising a cylinder and a rotatable feed screw coaxially disposed in said cylinder, said feed screw having threads for advancing a plastic mass under pressure in a predetermined axial flow direction, the improvement wherein said feed screw is provided downstream of said threads with an unthreaded extension forming with said cylinder an annular flow space with a first collar having a cylindrical outer surface, said cylinder being provided in the region of said flow space with a second collar having a cylindrical inner surface whose axial dimension substantially equals that of said outer surface, the radius of curvature of said inner surface exceeding that of said outer surface by substantially less than the width of said flow space whereby a constricted passage for said plastic mass is formed between said surfaces upon axial alignment of said collars, one of said collars being axially shiftable with reference to the other collar between a position of mutual aligngent and a position of complete relative offset of said surfaces whereby the effective axial length of said constricted passage is variable between zero and a maximum value with development of a pressure differential in said flow path varying as a linear function of said axial length.

Claim 4

In an extruder comprising a cylinder and a rotatable feed screw coaxially disposed in said cylinder, said feed screw having threads for advancing a plastic mass under pressure in a predetermined axial flow direction, the improvement wherein said feed screw is provided downstream of said threads with an unthreaded extension forming with said cylinder an annular flow space with a first collar having a cylindrical outer surface, said cylinder being provided in the region of said flow space with a second collar having a cylindrical inner surface whose axial dimension substantially equals that of said outer surface, the radius of curvature of said inner surface exceeding that of said outer surface by substantially less than the width of said flow space whereby a constricted passage for said plastic mass is formed between said surfaces upon axial alignment of said collars, one of said collars being axially shiftable with reference to the other collar between a position of mutual aligngent and a position of complete relative offset of said surfaces whereby the effective axial length of said constricted passage is variable between zero and a maximum value with development of a pressure differential in said flow path varying as a linear function of said axial length.

Claim 5

The improvement defined in claim 2 wherein the axially shiftable collar is said second collar.

Claim 6

The improvement defined in claim 3 wherein said cylinder is axially divided into an upstream section enveloping said threads, a downstream section axially spaced from said upstream section, said upstream and downstream sections lying on opposite sides of said first collar, and a middle section carrying said second collar, said middle section being axially shiftable and bridging said upstream and downstream sections in all positions of adjustment thereof.

Claim 7

The improvement defined in claim 4 wherein said cylinder further includes a tubular member rigid with one of the axially spaced sections thereof and defining therewith a recess confronting said middle section, the latter having a pair of abutments within said recess engageable with respective end faces of said recess for limiting the shifting of said middle section to a distance substantially equaling the axial dimension of said collars.

Claim 8

The improvement defined in claim 5 wherein said middle section has a threaded outer surface confrontIng said recess, further comprising a nut rotatably lodged in said recess in engagement with said threaded surface and guide means for holding said middle section against rotation.

Claim 9

The improvement defined in claim 6 wherein said guide means comprises a sleeve fixedly mounted in said recess alongside said middle section, said nut and said sleeve being provided with axially extending formations matingly engaging each other.

Claim 10

The improvegent defined in claims 7 wherein said cylinder has an arcuate slot communicating with said recess, said nut being provided with peripherally spaced holes accessible through said slot for enabling manual rotation thereof.

Claim 11

The improvement defined in claim 5 wherein said tubular member is rigid with said downstream section and extends around said middle section with said recess terminating in the region of said threads, said upstream section having a tubular skirt which projects into said recess toward said first collar and slidably supports a segment of said middle section adjoining said second collar.

Claim 12

The improvement defined in claim 2 wherein said downstream section is provided with a radially extending rods bearing upon said extension beyond the range of axial shift of said middle section, said extension being provided with a multiplicity of peripherally spaced ribs adjoining said pins on the upstream side for fractionating the flow of plastic mass issuing from said constricted passage.