Extruder

Abstract

An extruder (1) comprising a feed port (10), the feed port is configured to direct material towards a barrel region of an extruder, the feed port comprising a passageway, the passageway arranged to be in communication with the barrel region (11) of the extruder, and the passageway comprises a transverse cross-sectional shape which comprises three substantially rectilinear side surfaces (4a, 4b, 4c) which are arranged substantially orthogonally, and a fourth side (4d) which is non-orthogonally angled relative to two of the side surfaces which are adjacent to the fourth side.

Claims

1. An extruder, comprising: a barrel region; a feed port configured to direct material toward said barrel region, the feed port comprising a passageway in communication said barrel region and the passageway having a transverse cross-sectional shape defined by three adjacent side surfaces one being substantially orthogonal to the other two, and a fourth side surface of the transverse cross-sectional shape that is non-orthogonally angled relative to said three adjacent side surfaces.

2. The extruder of claim 1, in which each of the side surfaces is substantially linear in transverse cross-section.

3. The extruder of claim 1, in which one of the side surfaces is longer than an opposing side surface.

4. The extruder of claim 1 in which the side surfaces are connected at rounded junctions.

5. The extruder of claim 1, wherein said fourth side has an angle of inclination relative to an adjacent side within a range of from 40 degrees to 70 degrees.

6. The extruder of claim 1, wherein the passageway of the feed port has a substantially constant cross-section extending over at least a portion of the passageway.

7. The extruder of claim 1, wherein the passageway of the feed port has cross-sectional shape defined as a trapezium.

8. The extruder of claim 1, wherein the passageway of the feed port has three substantially rectilinear side surfaces arranged substantially orthogonally, and a fourth side that is non-orthogonally angled relative to two adjacent side surfaces.

9. The extruder of claim 8, wherein only two of said side surfaces are parallel.

10. The extruder of claim 1, further comprising a conical transition region.

11. The extruder as claimed in claim 10 in which the conical transition region is at least partially defined by a conical surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Various embodiments of the invention will now be described, by way of example only, with reference to the following drawings in which:

(2) FIG. 1 is longitudinal cross-sectional view of an extruder,

(3) FIG. 2 is a perspective view of an upper half of a barrel block,

(4) FIG. 3 is a perspective view of a lower half of a barrel block,

(5) FIG. 4 is a transverse section of a feed port,

(6) FIG. 5 is a transverse section through an upper barrel block half, and

(7) FIG. 6 is a perspective view of the volumetric envelope of material flow.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(8) With reference to the figures there is now described a twin screw extruder 1, suitable for processing of polymer in powdered and/or granular form. As will be described in more detail below, the configuration of the feed port and the barrel region give rise to improved material intake and flow characteristics, which leads to improved operational performance of the extruder. The extruder 1 comprises an upper barrel block 2 and a lower barrel block 3. The upper barrel block and the lower barrel block may collectively be referred to as a barrel (block) assembly. The upper barrel block 2 is shaped so as to be located on top of the lower barrel block 3. Each of the blocks 2,3 comprises a respective shaped surface, and the shaped surface of each block 2, 3 is complementary to the other such that the two surfaces define an internal barrel region 11 when the two blocks 2, 3 are brought together. The surfaces defined by each block 2, 3 include two side-by-side constant diameter (overlapping) bore portions, each defining substantially one half of each bore. Both bores are of substantially the same diameter. The bores comprise substantially part-cylindrical (inwardly facing) surfaces.

(9) Each bore, accommodates a respective flighted screw 50 (as shown in FIG. 5). Each screw is driven by a respective drive 30 (FIG. 1). Material is fed into a feed intake 10 by way of a feed chute 20. The lower part of the feed chute 20 matches (is complementary to) the profile in the upper backing block 2. The upper part of the feed chute 20 is formed to match that of the particular dosing feeder depending on the particular application for which the extruder is used.

(10) As seen in FIG. 1, each of the barrel blocks 2, 3 further defines surfaces for a transitional region 12, which is located upstream of the barrel portions, and towards a respective distal end region of each of the blocks 2, 3.

(11) With combined reference to FIGS. 2 and 3, the surfaces 2b of the block 2 and surfaces 3b of the block 3, collectively define the transitional region. (The transition region may also be termed a feed region). The surfaces 2b comprise substantially conical portions which taper in a downstream direction. The surfaces 3b are, to a lesser extent than the surfaces 2b, also substantially conical surface portions. The transitional region communicates with the bores. The profiled (internal) surfaces which define the transitional region 12 may be termed a feed liner or barrel liner.

(12) Reference is now made to FIG. 4 which shows a plan view of the feed port 10 of FIG. 1, formed by a passageway in an upper barrel casing block 4 taken on section A-A. The feed port 10 has substantially constant shape and dimensions throughout the depth of the casing block 4. The transverse cross-sectional profile of the feed intake comprises a quasi- or modified-trapezium shape, which comprises side surfaces 4a, 4b, 4c and 4d. Each of the side surfaces is substantially rectilinear. The side surfaces 4a and 4c are substantially parallel, and the transverse extent or length of the side surface 4c is longer than that of the side surface 4a. Said side surfaces 4c, 4d are connected by way of curved junctions 4e, The side 4a is arranged substantially orthogonal to the side 4, and the side 4b orthogonal to the side 4c. It may be noted that the extruder 1 also comprises a lower casing block 5, which is located underneath the lower barrel block 3.

(13) The side surface 4d is configured at an incline or non-orthogonal angle to each of the adjacent side surfaces 4a and 4c. The side surface 4d is arranged at an angle of substantially 65 degrees relative to the side surface 4c. The feed intake 10 extends through substantially the full depth of the casing block 4.

(14) Reference is now made to FIG. 5 which shows the cross-section on B-B (see FIG. 1), through the upper barrel block 2, parallel with the direction of its length. This view shows the pathway provided for the material enlarges as it extends through the upper block 2, and develops into a modified shape (in comparison to that of the feed inlet portion which is formed in the upper casing 4. The enlarged region creates increased volume allowing more material to be present within the feed area, thereby increasing the potential throughput. The modified trapezium shape is angled towards the material flow effectively guiding the material into the twin bores. As can also be seen in FIG. 5, the conical profile surfaces 2b are shown, tapering down towards the diameter of the bores. Also shown in FIG. 5 are screws 50, which are shown as having a variable geometry along the axes of rotation.

(15) Particular mention is now made of the screw geometry of the flighted screws 50, with reference to FIG. 5. The screws are arranged in the barrel region as twin, self-wiping co-rotating screws. As will be described in more detail below, each screw has a variable screw geometry, along the respective axis of rotation of each screw. Two portions of each screw will be discussed, namely what will be termed a feed portion and a work portion, denoted (at least for schematic/explanatory purposes) by reference numerals I and II, respectively. The feed portion is arranged to convey material received through the feed port to the work portion. The work portion is downstream of the feed portion, and is arranged to impart an energy, through compression forces, to the material. The feed portion of each screw 50 comprises a single helical flat fronted screw portion 50a. As can be seen in FIG. 5, the screw portion 50a has relatively large pitch, (shown by the reference P), thus advantageously maximising available volume for the material as it is received in the barrel. Progressing in a downstream, axial direction, the screw portion 50a continues, at substantially the same pitch. However, a second screw portion, referenced 50b, is introduced. The second screw portion 50b is offset from the screw portion 50a. The second screw portion 50b has a pitch which is substantially that of the first screw portion 50a. Both of the first screw portion 50a and the second screw portion 50b, in the work portion of the screw, have curved side walls as is evident from FIG. 5. This therefore alters the channel profile 55, as compared to the channel profile 56 at the feed section of the screws. The channel volume in the work portion of the screws provides a reduced volume as compared to the channel volume in the feed portion of the screws. It is also to be noted that what may be termed the free volume, i.e. the (inner) volume of the barrel as defined by its internally facing walls, less the volume occupied by the screws, is greater in the feed region as compared to the work region, of the extruder.

(16) It is to be noted that the extent, in situ, of feed portion of each screw 50 largely/substantially corresponds to, or is substantially located within, the extent of the enlarged transition volume of the barrel assembly. It is also to be noted that the work portion of each screw 50 (which comprise the two helical screw formations 50a and 50b) is substantially located with its respective bore.

(17) The combination of the shape of the inlet port 10, the form of the barrel/feed liner in the transitional region 12, in particular advantageously dramatically reduce torque spikes, enabling the extruder to operate at higher rates of throughput. Our studies have shown how the profiled barrel liner and screws allow lighter materials, to fall towards the bottom of the feed area and into the screw flights rather than accumulate in the feed port. The special geometry of the screws within the feed area prevent materials bouncing off the surface of the screws and also allow more materials to fall into the screw flights at an increased rate.

(18) Additional advantages of the extruder high intake feed system include: increased profitability, resulting from increased throughput; increased component reliability, resulting from reduced torque spikes which the components would otherwise be subjected to.

(19) It will be appreciated that although particular mention has been made to the processing of polymer materials, and to low density/low bulk materials, the feed intake arrangement and/or the screw geometry may (either singularly or in combination) be beneficially used with both non-food materials and foodstuffs.