LIQUID EXTRACTION STAGE FOR AN EXTRUDER

Abstract: A liquid extraction stage for an extruder for materials such as food-stuffs and hygroscopic plastics has a compressor comprising a tapered screw arrangement (1, 2) in a tapered barrel (9). Progressive compression occurs as the material is fed by the screw arrangement and liquid is squeezed out. The liquid is drawn out along channels (12) by a removal device (14, 15) to an outlet chamber.

Description: LIQUID EXTRACTION STAGE FOR AN EXTRUDER The invention relates to a liquid extraction stage for an extruder. In extruding and mixing materials such as food-stuffs, hygroscopic plastics or the like it is desirable as a preliminary measure to remove excess liquid. Such materials may be compressed to squeeze liquids out but it is difficult to achieve effective liquid extraction and removal on a continuous basis suitable for continuous extrusion processes. The prevent invention seeks to provide a satisfactory solution. According to the invention there is provided a liquid extraction stage for an extruder comprising a tapered barrel in which is mounted a tapered screw arrangement, the barrel having an input for accepting material from which liquid is to be extracted and an output to which the material is fed by rotation of the screw arrangement in the barrel, the barrel and screw arrangement being such that as the material is fed from input to output, the space available is reduced and the material is progressively compressed; and removal means for removing from the barrel liquid which has been squeezed from the material. It is envisaged that the screw arrangement may comprise a single screw, the barrel being correspondingly a single barrel. However, preferably the screw arrangement comprises twin screws which mesh and the barrel is of correspondingly double barrel shape. The threads of the screws of a twin-screw arrangement may be of opposite hand, namely one left- hand and one right-hand. The screws must then be rotated in opposite directions. Preferably, however, the twin screws have threads of the same hand and, in use, rotate in the same direction. Preferably the barrel is arranged substantially horizontally and the base of the barrel i is provided with space to allow the liquid to be drawn back against the direction of flow of the material. Such space may be provided by modification of the shape of the base of the barrel, or preferably by one or more channels running along the base of the barrel. The removal means may comprise a second screw arrangement at the input end of the barrel and coupled to rotate with the first screw arrangement, the second screw arrangement being of opposite sense to the first so as to draw liquid from the barrel as the screw arrangements rotate. In a preferred arrangement the removal means comprises a substantially vertical chamber into which the liquid is fed and which has a stationary helical member mounted axially within the chamber and means- are provided for rotating the wall of the chamber in such a direction as to encourage downward withdrawal of liquid and entrapped material by co-operation with the helical member. The liquid extraction stage of the present invention is particularly suitable for direct connection to a screw extruder having a screw or screws coupled to the extraction screw or screws at the output end of the barrel. However, in an alternative arrangement, the extruder may be mechanically independent from the extractor, material being fed through a conduit from the extractor to the extruder. The invention will further be described with reference to the accompanying drawings, of which:- Figure 1 is a side elevation, sectioned in part, of a liquid extraction stage of an extruder in accordance with the invention; Figure 2 is a plan view, sectioned in part, of the extractor stage of Figure 1 ; and Figure 3 is a cross-sectional elevation taken at 'A-A 1 of Figure 1. Referring to the drawings, the extraction stage comprises a twin screw arrangement having screws 1 and 2, which both have right-handed threads. The screws are mounted on parallel axes 3 and 4 and are driven in the same direction by a motor and gear-box arrangement (not shown) coupled at 5. Screws 1 and 2 are tapered inwardly in a forward direction indicated by arrow 6. The threads of the screws mesh closely and have a constant pitch. The screw axes 3 and 4 are parallel and because of the tapered threads, the root shafts 7 and 8 of the screws taper equally and oppositely to the taper of the threads. The screws fit closely in a tapered double barrel 9 which has a hopper inlet 10 for the supply of material from which material is to be extracted. The hopper is at the inlet end of the barrel. At the outlet end there is a constriction consisting of a set of mixer discs 11 which have small channels therethrough. Rotation of the screws feeds material from the hopper towards the mixer discs and in so doing compresses the material. Compression is effected also by the tapering shape of the screws. It will be seen that the volume available for the material within the threads of the screws decreases progressively towards the output end. Thus, as material is fed forwards it is compressed. Compression of the material squeezes liquid from it. Channels, of which one is illustrated at 12 in Figure 1 , run along the base of the barrel to allow the liquid to be drawn out in the rearward direction to a liquid removal arrangement 13. Extraction of liquid is facilitated by a pair of meshing screw threads 14, 15 on the shafts of screws 1 and 2. Threads 14 and 15 are of the opposite sense to the threads of screws 1 and 2. Thus, as the shafts rotate, the threads 14 and 15 co-operate to draw liquid back in the opposite direction to the flow of material. The liquid is fed to a vertical cylindrical chamber 16 which has a stationary helical coil 17 of wire situated axially. The wall of the cylinder is rotatable in bearings 18 and is driven in such a direction as to ensure that any material in the cylinder is drawn down by co-operation with the coil. Thus, any material carried back with the liquid which otherwise might block the drainage system is worked down the cylinder and out. In order to assist flushing of the drainage path there is a system for spraying water or other suitable liquid from jets 19 into the cylinder. Figure 3 shows the cylinder and coil arrangement and arrows 20 and 21 illustrate the direction of rotation of the screw shafts. The screw shafts are extensions of the screw shafts 22, 23 (Figure 1 ) of a twin screw extruder to which the material is fed from the mixer discs. It will be noted that the barrels 24, 25 of the extruder and the liquid removal screws respectively are parallel-sided and not tapered, in distinction to the walls of the extractor barrel 9 which are tapered.

Claims: CLAIMS 1. A liquid extraction stage for an extruder comprising a tapered barrel in which is mounted a tapered screw arrangement, the barrel having an input for accepting material from which liquid is to be extracted and an output to which the material is fed by rotation of the screw arrangement in the barrel, the barrel and screw arrangement being such that as the material is fed from input to output, the space available is reduced and the material is progressively compressed; and removal means for removing from the barrel liquid which has been squeezed from the material. 2. A liquid extraction stage as claimed in claim 1 wherein the screw arrangement comprises twin screws which mesh and the barrel is of correspondingly double barrel shape. 3. A liquid extraction stage as claimed in claim 2 wherein the twin screws have threads of the same hand^and, in use, rotate in the same direction. 4. A liquid extraction stage as claimed in any of the preceding claims wherein a constriction to the flow of material is provided at the output end of the barrel. 5. A liquid extraction stage as claimed in claim 4 wherein the constriction comprises a set of mixing discs with restricted passages therethrough. 6. A liquid extraction stage as claimed in any of the preceding claims wherein the barrel is arranged substantially horizontally and at least one channel is provided along the base to allow liquid to be drawn out against the direction of flow of the material. 7. A liquid extraction stage as claimed in any of the preceding claims wherein the removal means comprise a second screw arrangement at the input end of the barrel and coupled to rotate with the first screw arrangement, the second screw arrangement being of opposite sense to the first so as to draw liquid from the barrel as the screw arrangements rotate. 8. A liquid extraction stage as claimed in any of the preceding claims wherein the removal means comprises a substantially vertical chamber into which the liquid is fed and which has a stationary helical member mounted axially within the chamber and means are provided for rotating the wall of the chamber in such a diπection as to encourage downward withdrawal of liquid and entrapped material by co-operation with the helical member. 9. A liquid extraction stage as claimed in any of the preceding claims wherein the outlet end of the barrel is coupled to a screw extruder, the extruder screw or screws being a continuation of the extraction screw or screws. 10.* A liquid extraction stage as claimed in claim 9 wherein the extractor and extruder are double screw arrangements of the co-rotating kind.

Inventors: BOYNE IVOR FENWICK, BOYNE, IVOR, FENWICK (DECEASED)
Applicants: BOYNE IRIS HEIR OF BOYNE IVOR, HAMPTON GAY S LTD, BOYNE, IRIS (HEIR OF BOYNE, IVOR, FENWICK (DECEASE, GAY'S (HAMPTON) LIMITED
Application year: 1986
Main classification: B30B9
IPC codes: B30B9