Title of Invention

AN APPARATUS FORFILTERING THERMOPLASTIC SYNTHETIC PLASTIC MATERIAL

Abstract

An apparatus for filtering thermoplastic synthetic plastic material has a screw (5) bearingly supported within a housing (1) for rotation around its longitudinal axis for the transport and preferably also plasticizing of the synthethic plastic material. This material is supplied to the screw (5) through an intake opening (7) into the housing (1) and leaves the housing (1) through an exit opening (8). The screw (5) is subdivided into two sections (9, 10) disposed one behind the other in axial direction. A filter (40) provided with penetration openings (25) is disposed in the flow of the synthetic plastic material that is disposed between these two sections (9, 10), which filter (40) is disposed within the housing (1) between the two sections (9, 10) of the screw (5) so that it subdivides the interior of the housing. The filter (40) is connected for common rotation with at least one of the screw sections (9, 10). At least one scraper (26) mounted in the housing (1) engages the upstream side of the filter (40) and strips off coarse impurities from the filter when the filter (40) is rotated and conveys the impurities into a collecting space (27) that is in connection with the interior of the housing.

Full Text

Apparatus for Filtering Thermoplastic Synthetic Plastic Material The invention refers to an apparatus for filtering thermoplastic synthetic plastic material, having a screw bearingly supported within a housing for rotation around its longitudinal axis for the transport and preferably also plasticising of the synthethic plastic material that is supplied to the screw into the housing through an intake opening and leaves the housing through an exit opening, for example a nozzle, wherein the screw is sutxlivided into two sections disposed one behind the other in axial direction and wherein a filter provided with penetration openings for the synthetic plastic material is disposed in that flow of the synthetic plastic material that is disposed between the two sections. An apparatus of this kind has become known (EP 600,924 B). Within this known construction the two screw sections are separated from each other by a sealing section that is by-passed by the processed synthetic plastic material via a by-pass leading out of the housing. A filter is arranged in this by-pass by which impurities contained in the thermoplastic synthetic plastic material to be processed are retained. This known apparatus is well suitable for fine-grained impurities as far as they do not constitute a too high impurity portion within the synthetic plastic material. If, however, the synthetic plastic material to be processed contains iDoarser impurity fractions, for example small stones or metal parts, as crown caps, paper clips, wire stitches or the like, the filter and the filter channels of the known apparatus become quickly blocked, so that the filter cannot more accomplish its function. The invention has at its object to improve a construction of the initially described kind so that filtering of coarse impurities can be done reliably and at a low price without that the filter must be frequently exchanged. The invention solves this task by the features that the filter is disposed within the housing between the two screw sections so that it subdivides the interior of the housing and is connected for common rotation with at least one of the screw sections, and that a scraper carried by the housing engages the upstream side of this filter, which scraper scrapes off coarse impurities from the filter when it is rotated and conveys these impurities into a collecting space being in connection with the interior of the housmg. This filter retains the coarse impurities so that this filter is passed only by the synthetic plastic material and fine impurities contained therein, if any. If the latter impurities are disturbing, a fine filter, for example of the initially described construction or disposed at the end of the screw, can follow. By the continuous scraping off the coarse impurities by means of the scraper, the upstream side of the inventive coarse filter is kept free from adsorption and depositions so that also coarse impurities do not block the penetration openings of the filter, but are compulsorily continuously conveyed off into the collecting space. When the volume of this collecting space is sufficiently dimensioned, the apparatus can operate for a long time without that there is a danger of a break down because of blocking the filter. It is known within an extruder for synthetic plastic material (EP 689.918 A) to dispose a stationary fine filter within the housing between a supply screw and the extruder nozzle for the separation of impurities contained in synthetic plastic material, and to scrap off the impurities collecting on the upstream side of the fine filter by means of a scraper rotating together with the screw. For the filtering of coarse impurities, this apparatus is not useful. According to a further embodiment of the invention, the filter is disposed at a member separate from the screw sections or constitutes such a member. This is advantageous when manufacturing and, if desired, enables one to change over already existing plants in the sense of the invention. A particular favorable construction consists within the spirit of the invention in that the filter is constituted by a shaft section constituting the separate member and being disposed between the two screw sections and being provided with an annular flange having the penetration openings, this shaft section being connected for common rotation on at least one of its front ends with the neighboring screw section. This results in a simple easily exchangeable and reliable construction. Connecting for common rotation can be made by a screw section, what has the advantage that this connection, if desired, can easily be detached at any time, but, if the direction of rotation of the screw sections and of the thread direction of this screw connection are efficiently chosen, in operation the screw connection is automatically tightened so that an undesired detachment is not possible. A particular favorable construction consists within the spirit of the invention in that the shaft section at the upstream side of the filter has a less diameter than at the downstream side. Thereby, at the upstream side of the filter there is a space for the impurities scraped off by the scraper. Further, advantages are obtained if the penetration openings of the filter have a cross section that increases in flow direction of the synthetic plastic material. This avoids that solid bodies entered into a penetration opening can be crammed in the penetration opening, thereby blocking the filter. A particular suitable construction consists within the spirit of the invention in that the scraper is provided with a scraping edge engaging a cylindrical section of the filter, particulariy a cylindrical section of the shaft section, which cylindrical section immediately neighbors the upstream side ends of the penetration openings. Thereby, the coarse impurities are compulsorily conveyed off in a continuous and reliable manner. A preferred embodiment of the invention consists in that the housing has a central section surrounding the separate member and being detachably connected to its neighboring housing sections so that after dismounting this central housing section, the separate member carrying or constituting the filter can be put off the housing. Thereby, the filter or the member constituting or carrying it, respectively, constitutes an easily excfiangeable member, wliat results in advantages when replacing or cleaning. Within the invention, the scraper can be disposed within a tube connected laterally to the housing, in particular to its detachable central section, which tube with its interior constitutes at least a portion of the collecting space. This results in a low-cost construction because the members necessary for mounting the scraper at the same time serve for confining the collecting space. Within this, it is suitable, to mount the scraper adjustably within the tube in a direction perpendicularly to the axis of the screw, in order to enable one to adapt the position of the scraper to manufacturing tolerances and to wear occurring during operation. In order to enable one to easily exchange the scraper, when necessary, within the spirit of the invention the tube is detachably connected to the housing, in particular to its detachable central section. Further, it is suitable if the tube has a detachable closure cap, in particular a screw cap, at its end opposite the housing, because after detaching this closure cap the collecting space confined by the tube is accessible for emptying or cleaning. The collecting space can be provided with a closure valve so that a, preferably automatic, emptying of the collecting space is possible during operation. In the drawing an exemplary embodiment of the invention is schematically shown. Fig. 1 shows an axial section through the inventive apparatus. Fig. 2 is a section taken along the line II - II of Fig. 1 in a somewhat enlarged scale. The apparatus for filtering thermoplastic synthetic plastic material has a housing 1 that comprises an intake section 2, a central section 3, coaxially disposed thereto, and an exit section 4, also coaxially disposed thereto. Within the housing 1, a screw 5 is bearingly supported for rotation around its longitudinal axis and is driven for rotation in direction of the arrow 6 by a drive means, not shown. The thermoplastic synthetic plastic material to be processed is supplied to the screw 5 through an intake opening 7 of the intake section 2 of the housing 1. The screw 5 conveys the synthetic plastic material within the housing 1 toward an exit opening 6 disposed in the exit section 4, which opening can be formed by an extruder nozzle. Preferably, the synthetic plastic material is also plasticised during this conveyance. The screw 5 has two sections 9, 10 disposed one behind the other in axial direction, the section 9 being disposed substantially within the intake section 2, and the section 10 substantially being disposed within the exit section 4. The two screw sections 9, 10 are connected to each other for common rotation via a separate member 11, and this by means of threaded trunnions 12 or 13 provided at this member 11 or at the screw section 10, respectively, which trunnions are screwed into corresponding threaded bores 14 or 15 of the screw section 9 or of this member 11, respectively. The direction of the threads of these screw sections is so chosen that, when the screw 5 is rotated in direction of the arrow 6, no loosening of these screw connections occurs, but a tightening of them. The member 11 constitutes a shaft section 41 connected for common rotation to the screw sections 9, 10 and has two cylindrical sections 16, 17 adjoining the sections 9 or 10 of the screw 5, the diameters of the sections 16, 17 preferably being equal to each other and also equal to the core diameter of the screw sections 9 or 10. The volutions 18 or 19 of the screw sections 9 or 10 are continued on the sections 16, 17 of the member 11. The outer diameter of these volution continuations is equal to that of the volutions 18 or 19 of the screw 5, so that the inner diameter of the housing sections 2, 3 and 4 is always the same. At the transition locations of the volutions 18, 19 of the member sections 16, 17 to the screw sections 9 or 10, steps of the screw volutions may occur, they are not disturbing. Conical sections 10 or 21 adjoin the cylindrical sections 16 or 17 and merge into cylindrical sections 22 or 23, from which the section 22 has a greater length - measured in axial direction of the screw 5 - than the section 23. The two sections 22, 23 are interconnected to each other by a flange 24 of the memiber 11, the outer diameter thereof being equal to the outer diameter of the screw sections 9, 10. The synthetic plastic material, if desired plasticised, can pass this flange 24 through penetration openings 25 disposed within it. The penetration openings 25 are disposed along at least one circle, preferably along a plurality of circles, around the axis of the screw 5. In the embodiment shown, only one of these circles of openings is shown, the inlet openings of the penetration openings 25 of this circle being disposed substantially centrally between the periphery of the section 22 and the inner wall of the housing section 3, when seen in radial direction of the member 11. The exit openings of the penetration openings 25 preferably have their periphery flush to the cylindrical section 23 of the member 11. Suitably, the penetration openings 25 have a circular cross section that enlarges in flow direction of the synthetic plastic material. The size of the cross section of the penetration openings 25 is so chosen that there results a filter 40 for coarse impurity particles of the processed synthetic plastic material, in particular for bigger solid particles, as stones, metal clips or the like. By the increasing cross section of the penetration openings 25 it is ensured that a solid particle that has entered a penetration opening 25 cannot be clogged within the penetration opening 25. The solid parl:icles retained by the flange 24 collect at the upstream side of the flange 24 and are taken along in direction of the arrow 6 when the screw 5 rotates, since the sections 16, 20, 22, 24, 23, 21, 17 of the member 11 constitute a shaft section 41 rotating together with the screw 5. This enables one to compulsorily convey off these impurities continuously by means a scraper 26 from the interior of the housing 1 into a collecting space 27 being in connection with this interior of the housing. This collecting space 27 is confined by a tube 28 screwed laterally (with respect to the axis of the screw 5) to the central section 3 of the housing 1 and being in connection via an opening 29 of the wall of the housing section 3 with its interior. This opening 29 is intersected by the scraper 26 which at its end disposed within the housing section 3 is provided with two scraping edges 30 engaging the periphery of the cylindrical section 22 of the member 11 and the flange 24, so that the solid particles are continuously conveyed off also from this surface. As it can be seen, when the screw 5 is rotated, the pointed end of the scraper 26 brushes over the penetration openings 25. Since this pointed scraper end is bent against the direction of rotation of the screw 5 (arrow 6, Fig. 2), a force component acts onto the solid particles scraped off which tends to compulsorily convey these particles out of the annular space 31 neighboring the penetration openings 25 towards the collection space 27. This is supported by the centrifugal force and by the pressure of following solid particles. The scraper 26 is adjustably mounted in the tube 28 so that its position relative to the screw 5 and relative to the flange 24 can be adjusted, for example when assembling or for compensation of manufacture tolerances or after re-sharpening of the pointed scraper end. For this, the scraper 26 has two elongated openings 32 (Fig. 2) which are penetrated by two screws 33 with sufficient play, which screws together with a clamping plate 34 clamp the scraper 26 to the wall of the tube 28. The tube 28 has on its end opposite the screw 5 a detachable closure cap 35 formed as a screw cap which is screwed onto screw threads 36 of the tube. This results in a tight closure which efficiently avoids pressure losses in the synthetic plastic material conveyed by the screw 5. After detaching the closure cap 35, the collecting space 27 is accessible from the outside, for example for inspection or cleaning. The tube 28 is inserted into a recess 37 (Fig. 1) of the central section 3 of the housing 1 and is screwed to the housing central section 3 by means of screws 38 (Fig. 2). If desired, a plurality of tubes 28 with scrapers 26 mounted therein may be provided, distributed around the axis of the housing 1. Instead of the screw cap 35, each tube 28 may be provided with a valve by which the collecting space 27 Ccin be emptied. This valve can be actuated automatically, for example hydraulically or pneumatically or by means of electromotive forces, for example in dependence from the time so that the collecting space 27 is emptied in pre-determined time intervals. Another possibility consists in to automatically empty the collecting space 27 in dependence from the pressure of impurity particles collected in the collecting space. In order to facilitate mounting and in order to enable one to easily exchange the member 11 constituting the coarse filter, the sections 2, 3, 4 of the housing 1 are detachably connected with each other and this by means of screws 39 (Fig. 1) abutted on flanges of these housing elements. If the coarse filter 40 is already sufficient, no further filter is necessary for cleaning the synthetic plastic material. However, there are no problems to dispose a further finer filter in the flow of the synthetic plastic material following the coarse filter 40, when seen in flow direction of the synthetic plastic material. The exit opening 8 must not be an extruder nozzle. For example, if the screw 5 is no extruder screw but merely agglomerates the synthetic plastic material or merely conveys it, for example towards the inlet opening of a housing of a further screw, if desired, formed by an extruder screw, then the exit opening 8 can be constructed and disposed in any desired manner, for example also on the side wall of the exit section 4, therefore not axially directed as this is shown in Fig. 1. In particular, the latter construction will be given if the screw 5 is driven from the exit-side end, therefore, in contrast to the disposition according to Fig. 1, at which the (not shown) drive means of the saew 6 are disposed at the inlet-side end thereof. We Claim: 1. Apparatus for filtering thermoplastic synthetic plastic material, having a screw bearingly supported within a housing for rotation around its longitttdinal axis for the transport of the synthetic plastic material that is supplied to the screw into the housing through an intake opening and leaves the housing through an exit opening, wherein the screw is subdivided into two screw sections disposed one behind the other, when seen in axial direction, and wherein a filter provided with penetration openings for the synthetic plastic material is disposed in that flow of the synthetic plastic material that is disposed between the two sections, characterized in that the filter (40) is disposed within the housing (1) between the two sections (9, 10) of the screw (5) so that it subdivides the interior of the housing and is connected for common rotation with at least one of the screw sections (9, 10), and that a scraper (26) carried in the housing (1) engages the upstream side of this filter (40), which scraper scrapes off coarse impurities from the filter (40) when the filter (40) is rotated and conveys these impurities into a collecting space (27) being in connection with the interior of the housing. 2. Apparatus as claimed in claim 1, wherein the filter (40) is disposed at a member (11) separate from the screw sections (9, 10) or constitutes such a member (11). 3. Apparatus as claimed in claim 2, wherein the filter (40) is constituted by a sheft section (14) constituting the separate member (11) and being disposed between the two screw sections (9, 10) and being provided with an annualar flange (24) having the penetration openings 25), this shaft section being connected for common rotation on atleast one of its front ends to the neighboring screw section (9 or 10). 4. Apparatus as claimed in claim 3, wherein the connection for common rotation is a screw cormection (12,14 or 13,15). 5. Appai-atus as claimed in claim 3, wherein the shaft section (41) has a diameter on the upstream side of the filter (40) that is less than at the dowrustream side. 6. Apparatus as claimed in claim 1, wherein the penetration openings (25) have a cross section that increases in flow direction of the synthetic plastic material. 7. Apparatus as claimed in claim 1, wherein the scraper (26) is provided with a scraping edge (30) engaging a cylindrical section (22) of the filter (40), which cylindrical section (22) immediately neighbors the upstream side ends of the penetration openings (25). 8. Apparatus as claimed in claim 7, wherein the pointed end of the scraper (6) forming the scraping edge (30) is bent against the direction of rotation (arrow 6) of the screw (5). 9. Apparatus as elainted in claim 2, wherein the housing (1) has a central section (3) surrounding the separate member (11) and being detachably connected to its neighboring housing section (2, 4) so that after dismounting this central housing section (3), the separate member (12) carrying or constituting the filter (40) can be put off the housing 10. Apparatus as claimed in claim 1, wherein the scraper (26) is disposed within a tube (28) connected laterally to the housing (1), which tube with its interior constitutes at least a portion of the collecting space (27). 11) Apparatus as claimed in claim 10, wherein the scraper (26) is mounted adjustably within the tube (28) in a direction perpendicularly to the axis of the screw (5) and in direction of the axis of the screw. 12) Apparatus as claimed in claim 10 or 11, wherein the tube (28) is detachably connected to the housing (1). 13) Apparatus as claimed in claims 10 to 12, wherein the tube (28) on its end opposite the housing (1) is provided with a detachable closure cap (35). 14) Apparatus as claimed in claims 10 to 12, wherein the tube (28) is provided with a valve by which the collecting space can be emptied. 15) Apparatus as claimed in claim 14, wherein the valve can be actuated hydraulically or pneumatically or by means of electromotive forces. 16) Apparatus as claimed in claims 1 to 15, the penetration openings (25) are disposed along at least one circle around the axis of the screw (5). An apparatus for filtering thermoplastic synthetic plastic material has a screw (5) bearingly supported within a housing (1) for rotation around its longitudinal axis for the transport and preferably also plasticizing of the synthethic plastic material. This material is supplied to the screw (5) through an intake opening (7) into the housing (1) and leaves the housing (1) through an exit opening (8). The screw (5) is subdivided into two sections (9, 10) disposed one behind the other in axial direction. A filter (40) provided with penetration openings (25) is disposed in the flow of the synthetic plastic material that is disposed between these two sections (9, 10), which filter (40) is disposed within the housing (1) between the two sections (9, 10) of the screw (5) so that it subdivides the interior of the housing. The filter (40) is connected for common rotation with at least one of the screw sections (9, 10). At least one scraper (26) mounted in the housing (1) engages the upstream side of the filter (40) and strips off coarse impurities from the filter when the filter (40) is rotated and conveys the impurities into a collecting space (27) that is in connection with the interior of the housing.

Documents:

in-pct-2001-781-kol-abstract.pdf

in-pct-2001-781-kol-claims.pdf

IN-PCT-2001-781-KOL-CORRESPONDENCE 1.1.pdf

in-pct-2001-781-kol-correspondence.pdf

in-pct-2001-781-kol-description (complete).pdf

in-pct-2001-781-kol-drawings.pdf

in-pct-2001-781-kol-examination report.pdf

in-pct-2001-781-kol-form 1.pdf

in-pct-2001-781-kol-form 18.pdf

in-pct-2001-781-kol-form 2.pdf

in-pct-2001-781-kol-form 26.pdf

IN-PCT-2001-781-KOL-FORM 27.pdf

in-pct-2001-781-kol-form 3.pdf

in-pct-2001-781-kol-form 5.pdf

IN-PCT-2001-781-KOL-FORM-27.pdf

in-pct-2001-781-kol-granted-abstract.pdf

in-pct-2001-781-kol-granted-claims.pdf

in-pct-2001-781-kol-granted-correspondence.pdf

in-pct-2001-781-kol-granted-description (complete).pdf

in-pct-2001-781-kol-granted-drawings.pdf

in-pct-2001-781-kol-granted-examination report.pdf

in-pct-2001-781-kol-granted-form 1.pdf

in-pct-2001-781-kol-granted-form 18.pdf

in-pct-2001-781-kol-granted-form 2.pdf

in-pct-2001-781-kol-granted-form 26.pdf

in-pct-2001-781-kol-granted-form 3.pdf

in-pct-2001-781-kol-granted-form 5.pdf

in-pct-2001-781-kol-granted-priority document.pdf

in-pct-2001-781-kol-granted-reply to examination report.pdf

in-pct-2001-781-kol-granted-specification.pdf

in-pct-2001-781-kol-granted-translated copy of priority document.pdf

IN-PCT-2001-781-KOL-PA.pdf

in-pct-2001-781-kol-priority document.pdf

in-pct-2001-781-kol-reply to examination report.pdf

in-pct-2001-781-kol-specification.pdf

in-pct-2001-781-kol-translated copy of priority document.pdf