GB1602585A - Screening device - Google Patents

Description

(54) SCREENING DEVICE (71) We, PETER ALAN MORRIS and JOHN ROTHWELL, both British Subjects, respectively of 174 Locks Road, Locksheath, Southampton, Hampshire S03 6LE, and 4 Odeon Buildings, Bridgwater, Somerset, 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: The present invention relates to a screening device for removing foreign matter frown a flowable material.

The problem of replacing a clogged screen in a screw extruder is not a new one. As long ago as 1950, Lodge in U.S. Patent No. 2,507,311 was working on the straining of particulate material from the output of a Banbury mixer and commented as follows: "Various types of strainers are employed to strain the compound immediately after it has been discharged from the mixing machine. In general they consist of a cylinder having a rotating stock screw therein which forces the mixed compound through a screen suitably positioned across the end of the cylinder. When the screen becomes clogged up with foreign matter it is necessary to either clean the screen or replace it with another screen. In either case the screen changing operation of the preesnt type of straining apparatus results in a substantial loss of operating time for the straining machine. Since the extruding apparatus re quires a continuous supply of compound, the shutdown period of the straining apparatus must be as short as possible." One way of solving this problem using replaceable slide blocks is described in U.S.

Patents Nos. 2,763,308, 2,786,504 and 2,838,084 (Samler). There is, however, a likelihood of air being entrained in the material from the screw extruder at the time when the screen is changed which is not acceptable when the output from the screw extruder is used directly, e.g., for injection moulding, and one method of remedying this deficiency described in U.S. Patent No 3,033,256 (Schrenk) is to provide first and second flow paths each having a screen within them, flow being directed to one or the other path by means of a plug valve and bleed channels being provided to direct material to the "stand-by" path to remove the air therein before the "stand-by" path is placed on stream.

The slide block method has recently been adapted to permit flushing of a slide block in a "stand-by" position to remove air therefrom, as described in U.S. Patent No. 3,804,758 (Cooper and Morris) and this technique has been employed with considerable technical and commercial success.

It is an object of the invention to provide a simple technique for enabling a screening device used in association with a screw extruder to be operated continuously and for foreign matter to be removed therefrom without shutting down the extruder and without risk of air being entrained in the material from the extruder during the screen changing operation.

Broadly stated the invention provides a screening device for removing foreign matter from a flowable material, comprising a body having an inlet and a generally cylindrical internal cavity, a filter drum rotatably supported in the body cavity so that its outer surface defines with the inner surface of the body defining the said body cavity an annular chamber in fluid communication with the inlet, an outlet in fluid communication with an internal cavity in the drum, the outer surface of the drum having at regular angular spacings flow sectors in which generally radial flow passages communicate the body cavity with the drum cavity via a filter element and intervening solid sectors, a flushing tube extending into the body cavity with its inner end face in seating engagement with the outer surface of the drum and dimensioned in conformity with the drum sectors so that the interior of the tube normally communicates with a single flow sector or solid sector and means for rotating the filter drum between a normal position in which a solid sector is in sealing engagement with the flushing tube and a flushing position in which a flow sector engages the flushing tube and material from the drum cavity can back flush the filter element.

Other preferred features will be apparent from the appended claims to which attention is hereby directed.

An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 is an exploded view showing the major parts of a screening device; Figure 2 is a view in vertical axial section of the screening device; Figure 3 is a transverse section of the screening device of Figure 2 taken on the line A-A and looking in the direction of the arrows; and Figure 4 is a transverse section of the screening device of Figure 2 taken on the line B-B and looking in the direction of the arrows.

In the drawings, a screening device includes a block generally indicated as 10 having an inlet 12 and an outlet 14 in opposed faces interconnected by a bore 16 which has a relatively narrow inlet portion, a divergent intermediate portion and a generally cylindrical portion 17 bounded at the front end by a con vergent region 19 having a bearing surface 21 recessed to accommodate a seal 23. The inlet face of the block is arranged to be secured to, the outlet of a screw extruder. An elongate aperture 18 or 50 communicates the front portion 17 of the bore 16 with the lower face of the block. An end plate 20 is secured over the front face of the block and has an outlet 22 positioned to be in alignment with the inlet 12.

The inner face of the plate 20 is recessed to accommodate a worm wheel 24 in meshing engagement with a worm 26 supported at either end in bearings in the front plate and having a drive spindle 28 extending front the lower face of the plate 20 and connected via a flex ible coupling 30 and a transmission 32 to an electric motor 34. The central region of the worm wheel has an axial bore conforming to the outlet 22, and an annular recess in the inner face of the front plate 20 about the outlet 22 receives a seal 25 which isolates the circumference of the worm wheel from the material passing through the axial bore therein to the outlet 22.

A barrel 36 extends from the worm wheel 24 and is received in the bore 16 in the block.

It has an axial bore which communicates via the bore in the worm wheel with the outlet 22 and which defines an internal cavity. Radial through holes in the barrel communicate the internal cavity with the outer cylindrical surface of the barrel which is recessed to support a cylindrical filter element 38 which may be a wire gauze or may be a sintered glass material.

A sleeve has a rounded conical rearwardly facing nose 40 and a hollow cylindrical base region 42 whose inner cylindrical surface is dimensioned to fit over the barrel 36 and filter element 38. The forward end of the base region 42 abuts the rear face of the worm wheel 24 to which it is secured by screws or other suit able means, and its outer cylindrical surface is rotatably supported by the bearing surface 21 and is fluid-tightly engaged by the annular seal 23. As is apparent from Figure 1 and Figure 3 the cylindrical surface of the sleeve has equi-angularly spaced sectors 48 containing radial through holes 46 and intervening solid sectors 51 in which there are no such through holes. The through-holes 44 formed in the region of the barrel underlying the filter element 38 are also disposed in sectors conforming to the sectors 48 and separated by solid sectors 51 in which no through holes are present, and the sleeve is assembled to the barrel at such an angular orientation that the holes or apertures 46 overlie and communicate with the holes or apertures 44. The outer circumferential and nose end surfaces of the sleeve conform to and are closely spaced radially inwards from the surface defining the bore 16 to define an- annular flow passage from which plastics material can flow radially through the holes 44 and 46 into the cavity within the barrel 36 and thence out through the bore in worm wheel 24 and to the outlet 22.

The lower face of the block is formed with an elongate aperture 18 or 50 communicating with the cylindrical region 17, the dimensions of the aperture conforming to one of the apertured sectors 48 of the sleeve. A hollow slide 52 has its inner end face 54 curved so as to seat against the outer cylindrical surface of the sleeve and has a flange 56 at its outer end which can be secured to the block 10 by bolts or other suitable means. The flow passage 58 within the slide may be brought into register with a selected one of the apertured sectors 48 to allow a reverse flow of polymer material from the cavity within the barrel 36 through the filter element 38 and the flow passage 58 to the exterior of the screening device, or such flow may be blocked off by bringing one of the solid sectors 51 into register with the slide 52.

Proper seating between the inner end of the slide 52 and the outer surface of the sleeve may be obtained by appropriately slackening or tightening bolts securing the flange 56 to the lower face of the block 10.

A pressure sensor 60 has its inner end in communication with the flow passage or bore 16 for sensing the pressure of plastics material therein. When a region of the filter element 38 underlying one or more of the apertured regions 48 becomes blocked, the pressure in the passage 16 rises, and when the pressure rises above a predetermined value, an ON signal is transmitted to a pre-set time switch 62 which is electrically connected to the motor 34 for controlling the operation thereof.

Heater plates 64 are disposed in contact with three faces of the block 10 and are effective to maintain the plastics material flowing through the screening device in a fluid state.

In operation, one of the solid sectors 51 of the sleeve is normally in contact with the inner end of the slide 52 so that the slide passage 58 is closed off from the interior of the screening device.

Plastics material flows through the inlet 12 and is directed by the nose region 40 of the sleeve into an annular flow path about the sleeve as indicated by the arrows until it reaches the cylindrical region of the sleeve, where the direction of flow becomes generally radial through the holes or passages 46, the filter element 38 and the holes or passages 44 into the cavity within the barrel 36. Filtered material flows oat through the outlet 22. When one or more operative regions of the filter element becomes blocked, a rise of pressure within the flow path is detected by the pressure sensor 60 which signals the time switch 62 to bring an adjacent apertured sector 48 into register with the flow passage 58 of the slide.

Plastics material flows in reverse direction through the relevant region of the filter element to back flush impurities from the filter element and so clear that region of the filter element.

After an appropriate time period, the time switch 62 again energises the motor 34 to rotate the next solid sector into engagement with the flow passage 58. The switch 62 may be programmed to back-flush a single sector 48 or it may be programmed to produce a 360 degrees rotation of the worm wheel 24 to clear all the sectors. It is possible that clearing only one or two sectors 48 at a time will prove satisfactory in operation because the one or two sectors adjacent the passage 58 in the direction of rotation of the wheel 34 will be the most heavily blocked by impurities. Means (not shown) may also be provided to initiate the cleaning cycle manually.

It will be appreciated that only one of the flow zones is in contact with the flushing tube at any one rime, and there is always maintained a flow path between the inlet and the outlet via the other flow zones. The change in internal pressure consequent on the back-flushing operation is not great, so that operation of the screw extruder does not need to be interrupted while the back-flushing operation is being carried out.

WHAT WE CLAIM IS 1. A screening device for removing foreign matter from a flowable material, comprising a body having an inlet and a generally cylindrical internal cavity, a filter drum rotatably supported in the body cavity so that its outer surface defines with the inner surface of the body defining the said body cavity an annular chamber in fluid communication with the inlet, an outlet in fluid communication with an internal cavity in the drum, the outer surface of the drum having at regular angular spacings flow sectors in which generally radial flow passages communicate the body cavity with the drum cavity via a filter element and intervening solid sectors, a flushing tube extending into the body cavity with its inner end face in seating engagement with the outer surface of the drum and dimensioned in conformity with the drum sectors so that the interior of the tube normally communicates with a single flow sector or solid sector and means for rotating the filter drum between a normal position in which a solid sector is in sealing engagement with the flushing tube and a flushing position in which a flow sector engages the flushing tube and material from the drum cavity can back flush the filter element.

2. A device according to Claim 1, wherein the filter drum comprises a hollow cylindrical barrel having a recess on its outer cylindrical surface within which is supported a tubular filter element and a cylindrical region of a sleeve which overlies the barrel and filter element, the cylindrical portion of the sleeve having angularly spaced radially apertured zones defining the flow sectors and the barrel having angularly spaced radially operated zones conforming to the flow sectors in the sleeve and in alignment therewith.

3. A device according to Claim 1 or 2, wherein the filter drum is secured to a worm wheel having a central through hole via which the drum cavity communicates with the outlet and supported on the body for rotation via a worm.

4. A device according to Claim 3, wherein the worm is driven by an electric motor, and a timing device is connected to the motor for controlling rotation of the drum relative to the flushing tube.

5. A device according to Claim 4, wherein the timing device is operable to cause the motor to rotate the drum from a position in which a first solid sector is in engagement with the flushing tube in a position in which an adjacent flow sector is in engagement with the flushing tube, to retain the flow sector in communication with the flushing tube for a time sufficient to remove foreign matter from the drum, and then to rotate the drum to a position in which a second solid sector on the opposite side of the flow sector from the first solid sector is in engagement with the flushing tube.

6. A device according to Claim 5, wherein a sensor is provided for feeding a signal indicating the pressure of the plastics material in the body cavity and operable to initiate rotation of the drum via the motor and timing device when the pressure in the body cavity rises above a predetermined level.

7. A screening device for removing foreign matter from flowable material substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

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

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. passage 58 is closed off from the interior of the screening device. Plastics material flows through the inlet 12 and is directed by the nose region 40 of the sleeve into an annular flow path about the sleeve as indicated by the arrows until it reaches the cylindrical region of the sleeve, where the direction of flow becomes generally radial through the holes or passages 46, the filter element 38 and the holes or passages 44 into the cavity within the barrel 36. Filtered material flows oat through the outlet 22. When one or more operative regions of the filter element becomes blocked, a rise of pressure within the flow path is detected by the pressure sensor 60 which signals the time switch 62 to bring an adjacent apertured sector 48 into register with the flow passage 58 of the slide. Plastics material flows in reverse direction through the relevant region of the filter element to back flush impurities from the filter element and so clear that region of the filter element. After an appropriate time period, the time switch 62 again energises the motor 34 to rotate the next solid sector into engagement with the flow passage 58. The switch 62 may be programmed to back-flush a single sector 48 or it may be programmed to produce a 360 degrees rotation of the worm wheel 24 to clear all the sectors. It is possible that clearing only one or two sectors 48 at a time will prove satisfactory in operation because the one or two sectors adjacent the passage 58 in the direction of rotation of the wheel 34 will be the most heavily blocked by impurities. Means (not shown) may also be provided to initiate the cleaning cycle manually. It will be appreciated that only one of the flow zones is in contact with the flushing tube at any one rime, and there is always maintained a flow path between the inlet and the outlet via the other flow zones. The change in internal pressure consequent on the back-flushing operation is not great, so that operation of the screw extruder does not need to be interrupted while the back-flushing operation is being carried out. WHAT WE CLAIM IS

1. A screening device for removing foreign matter from a flowable material, comprising a body having an inlet and a generally cylindrical internal cavity, a filter drum rotatably supported in the body cavity so that its outer surface defines with the inner surface of the body defining the said body cavity an annular chamber in fluid communication with the inlet, an outlet in fluid communication with an internal cavity in the drum, the outer surface of the drum having at regular angular spacings flow sectors in which generally radial flow passages communicate the body cavity with the drum cavity via a filter element and intervening solid sectors, a flushing tube extending into the body cavity with its inner end face in seating engagement with the outer surface of the drum and dimensioned in conformity with the drum sectors so that the interior of the tube normally communicates with a single flow sector or solid sector and means for rotating the filter drum between a normal position in which a solid sector is in sealing engagement with the flushing tube and a flushing position in which a flow sector engages the flushing tube and material from the drum cavity can back flush the filter element.

2. A device according to Claim 1, wherein the filter drum comprises a hollow cylindrical barrel having a recess on its outer cylindrical surface within which is supported a tubular filter element and a cylindrical region of a sleeve which overlies the barrel and filter element, the cylindrical portion of the sleeve having angularly spaced radially apertured zones defining the flow sectors and the barrel having angularly spaced radially operated zones conforming to the flow sectors in the sleeve and in alignment therewith.

3. A device according to Claim 1 or 2, wherein the filter drum is secured to a worm wheel having a central through hole via which the drum cavity communicates with the outlet and supported on the body for rotation via a worm.

4. A device according to Claim 3, wherein the worm is driven by an electric motor, and a timing device is connected to the motor for controlling rotation of the drum relative to the flushing tube.

5. A device according to Claim 4, wherein the timing device is operable to cause the motor to rotate the drum from a position in which a first solid sector is in engagement with the flushing tube in a position in which an adjacent flow sector is in engagement with the flushing tube, to retain the flow sector in communication with the flushing tube for a time sufficient to remove foreign matter from the drum, and then to rotate the drum to a position in which a second solid sector on the opposite side of the flow sector from the first solid sector is in engagement with the flushing tube.

6. A device according to Claim 5, wherein a sensor is provided for feeding a signal indicating the pressure of the plastics material in the body cavity and operable to initiate rotation of the drum via the motor and timing device when the pressure in the body cavity rises above a predetermined level.

7. A screening device for removing foreign matter from flowable material substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.