EP0229775B1

EP0229775B1 - Liquid extraction stage for an extruder

Info

Publication number: EP0229775B1
Application number: EP19860903501
Authority: EP
Inventors: Ivor Fenwick Boyne
Original assignee: GAY'S (HAMPTON) Ltd
Current assignee: GAY'S (HAMPTON) Ltd
Priority date: 1985-06-03
Filing date: 1986-06-03
Publication date: 1991-04-24
Anticipated expiration: 2006-06-03
Also published as: EP0229775A1; JPS62503083A; WO1986007306A1; AU601685B2; GB8513948D0; AU5967186A

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

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.
United States patent specification No 2567219 shows a liquid extractor of the kind having a tapered screw and barrel arrangement. Liquid is squeezed progressively from the material as it is fed forward by the screw arrangement. A difficulty with such systems is in drainage of the liquid. Simple drainage holes for the liquid readily become blocked. An object of the present invention is to provide improved liquid extraction.
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 characterised in that at least one channel is provided along the barrel to allow liquid to be drawn out against the direction of flow of the material and removal means are provided which comprises a second screw arrangement is provided at the input end of the barrel 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′ 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

1. A liquid extraction stage for an extruder comprising a tapered barrel (9) in which is mounted a tapered screw arrangement (1, 2), the barrel having an input (10) 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 (1, 2) in the barrel (9), the barrel (9) and screw arrangement (1, 2) being such that as the material is fed from input (10) to output the space available is reduced and the material in progressively compressed characterised in that at least one channel (12) is provided along the barrel (9) to allow liquid to be drawn out against the direction of flow of the material and removal means are provided which comprises a second screw arrangement (14, 15) is provided at the input end of the barrel (9) coupled to rotate with the first screw arrangement (1, 2) the second screw arrangement (14, 15) being of opposite sense to the first so as to draw liquid from the barrel as the screw arrangement rotate.

2. A liquid extraction stage as claimed in claim 1 wherein the removal means comprises a substantially vertical chamber (16) into which the liquid is fed and which has a stationary helical member (17) mounted axially within the chamber and means (18) 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 (17).

3. A liquid extraction stage as claimed in either of the preceding claims wherein a constriction to the flow of material is provided at the output end of the barrel (9).

4. A liquid extraction stage as claimed in claim 3 wherein the constriction comprises a set of mixing discs (11) with restricted passages therethrough.