GB1570290A

GB1570290A - Extruder

Info

Publication number: GB1570290A
Application number: GB53307/75A
Authority: GB
Original assignee: University of Waterloo
Current assignee: University of Waterloo
Priority date: 1975-12-31
Filing date: 1975-12-31
Publication date: 1980-06-25
Also published as: DE7640811U1; JPS5290568A; IT1067327B; DE2659182A1

Description

(54) EXTRUDER (71) We, THE UNIVERSITY OF WATER- LOO, an Institution of higher learning and a corporation incorporated by Private Statute of the Province of Ontario, Canada, of University Avenue, Waterloo, Ontario, Canada, respectively, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method of and apparatus for treating viscous materials, and is applicable for example to the extrusion of polymeric materials Rotating disc-type extruders have been suggested in place of conventional screw extruders. Such disc-type extruders have almost universally involved introduction of polymer or other material to be treated to the periphery of the disc, subjection of the material to shear forces between a rotating plate and a stationary surface, movement of the material centripetally and removal of the material axially of the rotating disc, so that the highest shear rate is applied initially to the unmolten material and the lowest shear rate is applied at the discharge point.

The present invention is based on a different principle, according to which the viscous material to be treated is conveyed under the influence of shear forces and viscous drag along a predetermined flow path.

Thus according to one aspect of the present invention, a method of treating viscous material to be extruded, which com prises : - confining the viscous material between first and second members providing respective substantially coaxial surfaces of revolution defining a space to which the material is fed at a first location adjacent the common axis of said surfaces, at least one of the surfaces having contouring means defining with the other a curvilinear flow path extending from said location to a radially remote location, relatively rotating said members with respect to their common axis to subject the viscous material to shear forces to cause the material to flow along the curvilinear flow path to said radially remote location, the cross-sectional area of the flow path diminishing progressively from the first location to said radially remote location such that the viscous material is subjected to progressively increasing pressure in the direction of flow, and removing the viscous material from said space at said radially remote location.

In a preferred method according to the invention, the contoured surface is provided by a rotating disc having a pair of spaced lateral side walls on one face thereof and which extend in a spiral from the first location to the second location. The other adjacent surface engages the viscous material, the viscous material being subjected to shear forces by location of the disc relative to the other surface. The treated material may be caused to flow from the disc periphery towards its axis over the face of the disc opposite to the contoured face, the material being collected at the axis for removal.

According to another aspect of the present invention, apparatus for treating viscous material comprising a stationary housing providing an interior cavity, a disc rotatably mounted in the cavity for driven rotation about its axis, the disc and the housing providing a pair of adjacent cooperating surfaces defining a space for receiving viscous material to be treated, one of the cooperating surfaces having contouring means to define with the other a curvilinear flow path extending from a first location adjacent the disc axis to a second location radially remote therefrom, the cross-sectional area of the flow path diminishing progressively from said first location to said second location such that viscous material is, in use, sub jected to progressively increasing pressure in the direction of flow, an inlet communicating with said space at the first location for the supply of viscous material thereto, an outlet communicating with said space at the second location for the removal of treated viscous material therefrom, and drive means for rotating the disc in the sense to subject the viscous material to shear forces whereby the material is caused to flow along said flow path from the first location to the second location.

In order that the invention may be readily understood, several embodiments thereof will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a side-elevational part-sectional view of an extrusion apparatus constructed in accordance with one embodiment of the invention; Figure 2 is a front elevational view of a disc used in the embodiment of Figure 1 as the pumping element; Figure 3 is a sectional view taken on line 3-3 of Figure 2; Figures 4 to 9 are sectional views of alternative feed, extrusion and removal arrangements.

Referring to Figures 1 and 2, plastics pellets 1, or other liquid or solid extrudable material, are fed to a hopper 2 and pass through the hopper 2 into a throat 3 and then.ce onto the flights of a conveying screw and drive axle 4. The extrusion unit 5 is maintained at the required temperatures in the various zones thereof through the use of heaters 6, 7 and 8.

A drive motor 9 is started and its rotational speed is adjusted through a suitable control element. The motor 9 effects rotation of the conveying screw 4 and a disc 10 which is attached thereto in a cavity of the extrusion unit 5. This causes the pellets or other extrudable material 1 to be conveyed onto the central portion of the facing spiralled face of the disc 10.

The centrally conveyed material is sheared between a pair of spiral flights 11 formed on the disc 10 and the immediately adjacent heated backplate 12. The flights 11 have a decreasing depth radially outwardly of the axis of the disc 10, thereby defining a flow path whose cross-section area progressively diminishes in the direction of the material flow as seen in Figure 3, to compensate for bulk density changes in the melting polymer.

The combined effect of heat conduction from a backplate 12 and mechanical work of the flights of the spiral 11 causes the extrudable material 1 to liquify, if it is not already molten. The progressively diminishing crosssectional area of the flow path is such that the material is subjected to a positive pumping action as the disc is rotated, that is to say, the material is subjected to progressively increasing pressure in direction. The viscous drag of the material 1 on the flights 11 forces the material towards the periphery 13 of the disc 10 and into an annular gap between the periphery 13 and an adjacent stationary wall, from whence it flows over a conical downstream face 14 of the disc and into an axial discharge port 15.

The conical rear face 14 of the disc 10 also may be contoured to mix and interchange volume elements of the material.

Such contouring also may assist in the conveyance of the material to the discharge port 15.

The introduction of the material to be extruded at an inlet adjacent the centre of the disc 10 and the removal of extruded material at an outlet adjacent the periphery of the disc 10 allows a low shear rate to be used on the material when it is first fed and a gradually increasing shear rate to be applied until the material is melt discharged at high shear at the periphery 13. This arrangement provides satisfactory laminar mixing of the molten material along with positive centrifugal or radially outward pumping.

The disc 10 may be perforated in the regions where the extrudable material has been sufficiently liquefied, to provide additional or alternative discharge outlets from the spiralled face of the disc 10.

In Figure 1 heaters 6, 7 and 8 are shown associated with the backplate. However in general heaters and coolers may be associated with the disc 10 and/or the backplate 12 depending on the desired function of the unit.

Clearance between the disc 10 and the backplate 12 may be adjusted by use of a thrust element 22 to vary the mixing of the material being extruded. Bearing 16 is provided to resist the thrust generated in the extrusion process and bearings 17 and 18 provide axial support for the rotational elements 4 and 10. The clearance adjustment mechanism may be omitted, if desired.

The whole assembly is mounted on a suitable frame 19 by means of supports 20 and 21. In normal operation, the discharge port 15 may be connected to a conventional shaping orifice and takeoff system. Venting of the unit 5 may be provided, if desired, to allow discharge of air or volatile materials.

Using the equipment illustrated in Figures 1 and 2, extrusions have been made with various materials at various rotational speeds, gap sizes between walls 10 and 12, temperatures and back pressures. Such materials as low density polyethylene, high density polyethylene, polystyrene, poly(ethylene terephthalate), nylons, unplasticized poly(vinyl chloride), epoxy resins, styrenebutadiene rubber and polypropylene have been successfully extruded in this apparatus, and and without fillers and reinforcements, such as, chopped glass fibres.

While the extruder may be used particularly for the extruding of plastics materials and rubbers, there are many other materials which may be beneficially treated and ex extruded in the apparatus of the invention.

For example, bread dough may be mixed, compounded and discharge from the equipment and plasticizers may be compounded with polymers, such as, polyvinyl chloride.

The apparatus may be used for the shear and thermal degradation of polymers or for cross-linking of polymers concurrently with their extrusion. Further, the apparatus may be used for graft polymerization and extrusion by combining and shearing a feed consisting of polymer, monomer and other ingredients.

Figures 4 to 9 illustrate differing configurations of extrusion unit 5 which may be used in place of the specific configuration illustrated in Figures 1 and 2.

In Figure 4, the feed of material through the hopper 2 occurs offset from the axis of the disc 10. In Figure 5, the feed of material through the hopper 2 occurs axially of the disc 10, the drive shaft 4 is connected to the opposite side of the disc 10 and the exit 15 is perpendicular to the axis of the disc 10.

In Figure 6, the disc 10 is mounted for rotation about a vertical axis while otherwise the unit 5 has the construction shown in Figure 4. Similarly, Figure 7 represents a vertical axis mounting of the construction shown in Figure 5.

Figure 8 shows a modified form of disc 10, in which the face bearing the spirals 11 is conically shaped. In Figure 9, a peripheral drive gear is provided for driven rotation of the disc 10 and the exit 15 is provided axially of the disc 10.

Additionally, it is possible to provide the spirals 11 integrally formed with the stationary backplate 12 rather than with the rotative disc 10, with the disc 10 being smooth surfaced. Alternatively, both the backplate 12 and the disc 10 are provided with spirals.

While the disc 10 is shown as having a double spiral, a single spiral, a multiplicity of spirals with varying and various geometries, interrupted spirals, and spirals with nonspiral mixing sections as well as other suitable contouring may be employed. The spiral flights do not have to be a continuous band.

The contoured surface of the rotatable disc may be varied within limits, provided that such contours cause the extrudable material to flow substantially in a radially outward direction away from the axis of the disc, by the combined presence of such contours and rotation of the disc. Vanes of various appropriate configurations would be included in the scope of this invention.

Spiraled, elevated flights are a preferred embodiment of the invention since the resulting relatively long path of flow of an element of extrudable material from the central portion of the spiral to the edge of the rotatable disc subjects the material element to considerable shear strain and this is beneficial in many cases in the extrusion and mixing of rubbers and thermoplastics.

Other contours and variations of those illustrated in the embodiments described herein will be evident to those skilled in the art and are included in the scope and principles of this invention if their presence in conjunction with the rotation of the disc causes extrudable material which encounters the disc near its central region to be transported in a net radial direction away from the central region.

The invention, therefore, provides an inexpensive and simple apparatus for the effecting of the efficient extrusion of thermoplastics, rubbers and fluids. The apparatus permits operation with little power for effecting extrusion and provides consistent discharge rates and operations which are easily controlled. The centrifugally directed pumping action and simple construction, material feed and discharge arrangements distinguish the machine of this invention from prior art extruders.

WHAT WE CLAIM IS:- 1. A method of treating viscous material to be extruded which comprises: confining the viscous material between first and second members providing respective substantially coaxial surfaces of revolution defining a space to which the material is fed at a first location adjacent the common axis of said surfaces, at least one of the surfaces having contouring means defining with the other a curvilinear flow path extending from said location to a radially remote location, relatively rotating said members with respect to their common axis to subject the viscous material to shear forces to cause the material to flow along the curvilinear flow path to said radially remote location, the cross-sectional area of the flow path diminishing progressively from the first location to said radially remote location such that the viscous material is subjected to progressively increasing pressure in the direction of flow, and removing the viscous material from said space at said radially remote location.

2. A method as claimed in claim 1, wherein said contoured surface defines a spiral flow path.

3. A method as claimed in claim 1, wherein said contoured surface is provided

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. been successfully extruded in this apparatus, and and without fillers and reinforcements, such as, chopped glass fibres. While the extruder may be used particularly for the extruding of plastics materials and rubbers, there are many other materials which may be beneficially treated and ex extruded in the apparatus of the invention. For example, bread dough may be mixed, compounded and discharge from the equipment and plasticizers may be compounded with polymers, such as, polyvinyl chloride. The apparatus may be used for the shear and thermal degradation of polymers or for cross-linking of polymers concurrently with their extrusion. Further, the apparatus may be used for graft polymerization and extrusion by combining and shearing a feed consisting of polymer, monomer and other ingredients. Figures 4 to 9 illustrate differing configurations of extrusion unit 5 which may be used in place of the specific configuration illustrated in Figures 1 and 2. In Figure 4, the feed of material through the hopper 2 occurs offset from the axis of the disc 10. In Figure 5, the feed of material through the hopper 2 occurs axially of the disc 10, the drive shaft 4 is connected to the opposite side of the disc 10 and the exit 15 is perpendicular to the axis of the disc 10. In Figure 6, the disc 10 is mounted for rotation about a vertical axis while otherwise the unit 5 has the construction shown in Figure 4. Similarly, Figure 7 represents a vertical axis mounting of the construction shown in Figure 5. Figure 8 shows a modified form of disc 10, in which the face bearing the spirals 11 is conically shaped. In Figure 9, a peripheral drive gear is provided for driven rotation of the disc 10 and the exit 15 is provided axially of the disc 10. Additionally, it is possible to provide the spirals 11 integrally formed with the stationary backplate 12 rather than with the rotative disc 10, with the disc 10 being smooth surfaced. Alternatively, both the backplate 12 and the disc 10 are provided with spirals. While the disc 10 is shown as having a double spiral, a single spiral, a multiplicity of spirals with varying and various geometries, interrupted spirals, and spirals with nonspiral mixing sections as well as other suitable contouring may be employed. The spiral flights do not have to be a continuous band. The contoured surface of the rotatable disc may be varied within limits, provided that such contours cause the extrudable material to flow substantially in a radially outward direction away from the axis of the disc, by the combined presence of such contours and rotation of the disc. Vanes of various appropriate configurations would be included in the scope of this invention. Spiraled, elevated flights are a preferred embodiment of the invention since the resulting relatively long path of flow of an element of extrudable material from the central portion of the spiral to the edge of the rotatable disc subjects the material element to considerable shear strain and this is beneficial in many cases in the extrusion and mixing of rubbers and thermoplastics. Other contours and variations of those illustrated in the embodiments described herein will be evident to those skilled in the art and are included in the scope and principles of this invention if their presence in conjunction with the rotation of the disc causes extrudable material which encounters the disc near its central region to be transported in a net radial direction away from the central region. The invention, therefore, provides an inexpensive and simple apparatus for the effecting of the efficient extrusion of thermoplastics, rubbers and fluids. The apparatus permits operation with little power for effecting extrusion and provides consistent discharge rates and operations which are easily controlled. The centrifugally directed pumping action and simple construction, material feed and discharge arrangements distinguish the machine of this invention from prior art extruders. WHAT WE CLAIM IS:-

1. A method of treating viscous material to be extruded which comprises: confining the viscous material between first and second members providing respective substantially coaxial surfaces of revolution defining a space to which the material is fed at a first location adjacent the common axis of said surfaces, at least one of the surfaces having contouring means defining with the other a curvilinear flow path extending from said location to a radially remote location, relatively rotating said members with respect to their common axis to subject the viscous material to shear forces to cause the material to flow along the curvilinear flow path to said radially remote location, the cross-sectional area of the flow path diminishing progressively from the first location to said radially remote location such that the viscous material is subjected to progressively increasing pressure in the direction of flow, and removing the viscous material from said space at said radially remote location.

3. A method as claimed in claim 1, wherein said contoured surface is provided

by a rotating disc having a pair of spaced lateral side walls on one face thereor and which extend in a spiral from said first location to said second location, the other surface engaging the viscous material, the viscous material being subjected to shear forces by rotation of the disc relative to said other surface.

4. A method as claimed in any one of the preceding claims, wherein said viscous material is formed by melting a material to be treated under the influence of heat and shear forces adjacent the upstream end of the flow path and gradually increasing the shear rates along said flow path as a function of the distance of the viscous material along said flow path from said first location.

5. A method as claimed in claim 4, wherein the material to be treated is particulate polymeric material.

6. A method as claimed in claim 3, wherein said second location is at the periphery of the disc.

7. A method as claimed in claim 6, including flowing the treated viscous material from the disc periphery towards the axis thereof over the face of the disc opposite to said one face and collecting the viscous material at the axis for removal.

8. A method for treating viscous material as claimed in claim 1,,,,and substantially as hereinbefore described with reference to and as illustrated by Figures 1 to 3 or any one of the Figures 4 to 9 of the accompanying drawings.

9. Apparatus for treating viscous material comprising a stationary housing providing an interior cavity, a disc rotatably mounted in the cavity for driven rotation about its axis, the disc and the housing providing a pair of adjacent cooperating surfaces defining a space for receiving viscous material to be treated, one of the cooperating surfaces having contouring means to define with the other a curvilinear flow path extending from a first location adjacent the disc axis to a second location radially remote therefrom, the cross-sectional area of the flow path diminishing progressively from said first location to said second location such that the viscous material is, in use, subjected to progressively increasing pressure in the direction of flow, an inlet communicating with said space at the first location for the supply of viscous material thereto, an outlet communicating with said space at the second location for the removal of treated viscous material therefrom, and drive means for rotating the disc in the sense to subject the viscous material to shear forces whereby the material is caused to flow along said flow path from the first location to the second location.

10. Apparatus as claimed in claim 9, wherein said curvilinear flow path is spiral.

11. Apparatus as claimed in claim 10, wherein said contoured surface is defined by one face of the disc, said one face of the disc being concavely dished and having a pair of spaced lateral side walls thereon which extend spirally from said first location to said second location to define the spiral flow path.

12. Apparatus as claimed in any one of claims 9, 10, and 11 wherein the disc has a conically shaped face on the opposite side thereof to the aforesaid cooperating surface thereof, which conically shaped face cooperates with an interior wall of said cavity to define a space communicating with said outlet for receiving the treated viscous material, the apparatus further comprising axially located removal means communicating with the last-mentioned space.

13. Apparatus as claimed in any one of claims 9 to 12, including an adjustment mechanism for adjusting the spacing between said adjacent cooperating surfaces.

14. Apparatus as claimed in claim 10 substantially as hereinbefore described with reference to and as illustrated by Figures 1 to 3 or any one of Figures 4 to 9 of the accompanying drawings.