Extrusion of plastic and the like

Claim 2

A vented extruder for extruding plastic and the like containing gaseous components to be removed comprising a heated extruder barrel having a main internal surface of revolution closely surrounding an extruder screw to enable mixing, working and conveying of plastic along said barrel, and a drive means for said screw, said extruder having a feed portion, a first conveying portion, a second conveying portion, and a vent communicating with the interior of said barrel at a position between said first and second conveying portions, there being a relieved area in said main barrel surface, said vent communicating directly with the space defined by said relieved area providing a vented space to which the plastIc is exposed, the screw having a flight portion in the region of said relieved area whereby plastic reaching said relieved area can be carried with rotation of said flight portion across said area to recontact the main barrel surface to enable resumption of normal conveying of said plastic along the barrel length, circumferentially beyond said vent in the direction of travel of said screw flight said relieved area including a guiding surface to cause plastic to gradually converge to the confines of said main barrel surface.

Claim 3

The extruder of claim 1 wherein said guiding surface comprises a second surface of revolution formed in the material of said barrel, said second surface of revolution having a radius of curvature less than the radius of the corresponding portion of the main barrel surface.

Claim 4

The extruder of claim 2 wherein said vented space is elongated in the axial direction of said barrel and said guiding surface is cylindrical having an axis parallel to but spaced from the axis of the main barrel surface.

Claim 5

The extruder as claimed in claim 1 including at a position in advance of said vent, relative to the direction of travel of said flight, a surface gradually diverging from said main barrel surface to said vented space.

Claim 6

The extruder of claim 4 wherein said gradually diverging surface comprises a surface of revolution formed in the material of said barrel.

Claim 7

The extruder of claim 5 wherein both said guiding and diverging surfaces have the same curvature formed from the same center.

Claim 8

The extruder of claim 6 wherein said vented space includes an axially elongated slot formed through the thickness of said barrel.

Claim 9

The extruder as claimed in claim 1 wherein a first opening extends from said main barrel surface to the exterior of said barrel and a second opening extends from an intermediate portion of said first opening to said exterior of said barrel, the external end of said second opening adapted to communicate with a source of vacuum.

Claim 10

The extruder as claimed in claim 8 wherein said first opening provides a view port there being a transparent cover device whereby the end of said first portion of said vent at the exterior of said barrel may be sealed.

Claim 11

The extruder as claimed in claim 8 including a cover device for covering the exterior of said first opening, said cover device adapted to be retained in position by the pressure differential created when a source of vacuum communicates with said second opening.

Claim 12

The extruder as claimed in claim 10 wherein said cover device is mounted upon said barrel by two serially connected hinges.

Claim 13

The extruder as claimed in claim 8 wherein said first opening has a dimension parallel to the axis of said barrel which is greater than its dimension along a circumference of said barrel.

Claim 14

The extruder as claimed in claim 12 wherein said second opening is defined by a plurality of passages extending from axially spaced locations of said first opening.

Claim 15

The extruder as claimed in claim 12 wherein said first opening has the dimension of at least one inch in the direction of the circumference of said barrel.

Claim 16

The extruder of claim 12 wherein said dimension of said first opening in the direction parallel to the axis of the barrel is at least as long as the pitch of the said screw flight.

Claim 17

The extruder as claimed in claim 8 wherein the longitudinal axis of said second opening projects through the exterior end of said first opening, whereby said second opening is readily accessible from said end of said first opening for inspection and cleaning.

Claim 18

The extruder of claim 1 wherein the cross-sectional area of the interior of the barrel unoccupied by the substance of said screw is greater in the region of said vent than in regions of said first and second conveyor portions, said second conveyor portion having a conveying rate characteristic at least as great as said first conveyor portion, the increased volume available for plastic in the region of said vent adapted To accommodate transient variations in actual rate of movement of the plastic without blocking said vent.

Claim 19

The extruder of claim 17 wherein said vented space includes a region spaced more than one fourth inch from the main barrel surface and a vent line communicates with said vented space in said region.

Claim 20

The extruder as claimed in claim 17 wherein said screw comprises a longitudinally disposed root and a flight wherein the diameter of said root adjacent said vent is less than its diameter in the first and second conveyor portions of said extruder.

Claim 21

The extruder of claim 1 wherein said barrel is segmented, the portion of said barrel at said vent being separate from preceding and following sections of said barrel.

Claim 22

An extruder for extruding scrap plastic and the like comprising a hopper, a heated extruder barrel containing an extruder screw having a screw flight, a drive means for said screw, wherein said extruder has a feeder comprising initial portions of said barrel and screw, said initial screw portion having means for liquid cooling, the internal surface of said initial barrel portion having rotation retarding formations extending along the length thereof, said initial barrel portion having a forced feed fluid cooling system for cooling the surface of said retarding formations.

Claim 23

An extruder for extruding scrap plastic and the like comprising a hopper, a heated extruder barrel containing an extruder screw having a screw flight, a drive means for said screw, wherein said extruder has a feeder comprising initial portions of said barrel and screw, said initial screw portion having means for liquid cooling, the internal surface of said initial barrel portion having rotation retarding formations extending along the length thereof, said initial barrel portion having a forced feed fluid cooling system for cooling the surface of said retarding formations.

Claim 24

The extruder of claim 21 wherein said forced feed fliud cooling system is a liquid cooling system comprising a sleeve surrounding said initial portion of said barrel, said sleeve provided with apertures through which cooling liquid is supplied and removed.

Claim 25

The extruder as claimed in claim 21 wherein said rotation retarding formations comprise grooves, the major component of the length of said grooves being in the axial direction of said barrel.

Claim 26

The extruder of claim 23 wherein each of said grooves has the shape of a longitudinal section of a cylinder of a radius substantially less than that of said barrel.

Claim 27

The extruder as claimed in claim 24 wherein each of said grooves is circumferentially spaced from each of the remainder of said grooves by a cylindrical land surface centered on the axis of said barrel.

Claim 28

The extruder of claim 24 wherein the surface of said rotation retarding formations is smooth having a roughness measurement of no more than 20 RMS.

Claim 29

The extruder as claimed in claim 21 wherein a thermal barrier is provided between said initial barrel portion and the remainder of said barrel.

Claim 30

The extruder as claimed in claim 27 wherein said thermal barrier comprises a region of reduced thickness of the barrel wall.

Claim 31

An extruder for extruding scrap plastic and the like comprising a hopper, a vertically arranged extruding barrel extending downward from said hopper to an extruding die, an extruder screw extending throughout the length of said barrel, a drive means for said screw, said extruder having a feeder comprising initial portions of said barrel and screw both of which are provided with liquid cooling means, the internal surface of the cooled barrel defined by a plurality of axially extending retarding grooves.

Claim 32

An extruder for extruding scrap plastic and the like comprising a hopper, a vertically arranged extruding barrel extending downward from said hopper to an extruding die, an extruder screw extending throughout the length of said barrel, a drive means for said screw, said extruder having a feeder comprising initial portions of said barrel and screw both of which are provided with liquid cooling means, the internal surface of the cooled barrel defined by a plurality of axially extending retarding grooves.

Claim 33

The extruder of claim 29 wherein the upper end of said screw defines a bearing surface, an agitator shaft is coaxial with said screw and is rotatably positioned by said bearing surface, said agitator shaft extending upwardly through said hopper, said shaft carrying a hopper agitator, said means for driving said screw connected to the lower end thereof and drive means above said hopper connected to said agitator shaft.

Claim 34

A heated extruder including a screw having a shank extending beyond the extruder outlet, means for driving said screw, a seal defined with said shank for the molten plastic within said extruder, said seal comprising a plurality of portions each of which extends no more than 180* around the circumference of said shank, said portions being attached to each other to define an inner seal surface approximately congruent to the surface of said shank but radially floAting with respect thereto, and means for anchoring said seal from rotation with said shank.

Claim 35

A heated extruder including a screw having a shank extending beyond the extruder outlet, means for driving said screw, a seal defined with said shank for the molten plastic within said extruder, said seal comprising a plurality of portions each of which extends no more than 180* around the circumference of said shank, said portions being attached to each other to define an inner seal surface approximately congruent to the surface of said shank but radially floAting with respect thereto, and means for anchoring said seal from rotation with said shank.

Claim 36

The extruder of claim 31 capable of extruding such plastics as polystyrene including, within the shank, a hollow thermal isolation volume disposed outwardly from the outlet point of said extruder, liquid cooling means for cooling shank portions located outwardly of said thermal isolation volume, said seal surrounding the shank at a portion containing said cooling means, said seal omitting liquid cooling.

Claim 37

The extruder of claim 31 wherein said means for anchoring comprises moment arm means constructed and arranged to restrain said seal for rotation without imposition of detrimental side loading.

Claim 38

The extruder of claim 33 wherein said moment arm means comprises moment arm of a length greater than four diameters of said shank.

Claim 39

A scrap recovery system for converting scrap plastic film and sheeting into reusable pellets, the system including a grinder adapted to produce fluff comprised of pieces of the original film or sheet and an extruder for receiving and melting said scrap pieces and extruding it as a fluid stream, said extruder comprising a hopper arranged to channel said scrap pieces downwardly, a vertically arranged extruder barrel containing an extruder screw having a screw flight extending throughout the length of said barrel and a drive means for said screw, said extruder having a scrap feeder comprising initial portions of said barrel and screw adapted to receive said scrap pieces from the hopper and feed a mass of the pieces downward within the confines of said barrel for subsequent compression, heating and discharge as a fluid stream, said initial screw portion being integral with portions of the screw downstream thereof and having internal passage means for liquid cooling, the internal surface of said initial barrel portion having rotation retarding means in the form of open grooves extending along the length thereof, said internal cooling liquid passage and said grooves having a mutual extent along the full length of said scrap feeder.

Claim 40

A scrap recovery system for converting scrap plastic film and sheeting into reusable pellets, the system including a grinder adapted to produce fluff comprised of pieces of the original film or sheet and an extruder for receiving and melting said scrap pieces and extruding it as a fluid stream, said extruder comprising a hopper arranged to channel said scrap pieces downwardly, a vertically arranged extruder barrel containing an extruder screw having a screw flight extending throughout the length of said barrel and a drive means for said screw, said extruder having a scrap feeder comprising initial portions of said barrel and screw adapted to receive said scrap pieces from the hopper and feed a mass of the pieces downward within the confines of said barrel for subsequent compression, heating and discharge as a fluid stream, said initial screw portion being integral with portions of the screw downstream thereof and having internal passage means for liquid cooling, the internal surface of said initial barrel portion having rotation retarding means in the form of open grooves extending along the length thereof, said internal cooling liquid passage and said grooves having a mutual extent along the full length of said scrap feeder.