FILTER APPARATUS

Abstract: A filter apparatus (2) for filtering solids from liquid media. The filter apparatus comprises a filter medium (8) secured to an elongate retaining body (9). The retaining body is inserted into slotted tubes (6), which are placed on the supporting structure of the filter apparatus thus securing the filter media to the supporting structure of the filter apparatus. This allows easy insertion and exchange of filter media to the filter apparatus.

Description: Filter Apparatus The present invention relates to filter apparatus such as drum filters and pan filters and to a method of installing a filter medium on the supporting structure of a filter apparatus. At present, filter media such as filter cloths are retained to their supporting apparatus, usually a drum or pan, by wedging the filter media into a groove around the edge of the filtration area with synthetic ropes or similarly configured extrusions. Metal mesh or soft wound wire cable has also been used. The installation of the filter media down into the groove is normally achieved by means of caulking tools, such as a bolster-shaped device with a perspex blade that is struck by a large rubber mallet. US 5,124,037 describes a filter cloth retaining device for a pan filter comprising a tubular gasket which is expandable and which locks the filter media inside the groove on inflation. US 4,308,143 describes a filter cloth retaining device for a drum filter comprising a flexible metal device inserted over the filter cloth which is retained in axial slots spaced circumferentially around the drum. UK Patent No. GB 2088809A describes the use of metal mesh or soft wound wire cable to enhance the hold of the cable in the caulking groove. Numerous problems are associated with these known devices and methods for filtration. Firstly, the rope wedging the filter media into the groove needs to be a very tight fit in order to be maintained within the groove, particularly when air is blown back through the filter media in order to discharge the filter cake. Furthermore considerable strength and effort is required to fit the rope within the caulking groove. This can lead to injuries being inflicted on the filter media installation personnel, in particular finger and hand injuries, elbow and ligament strains, and so forth. This problem is further exacerbated when installing filter media on pan filters as the installers have to kneel, which is another common reason for injury. A further problem relating to known caulking methods is that the caulking rope needs to absorb a significant amount of the product being filtered in order to swell, so that full pressure can be applied to blow back air for filter cake discharge. Production time is lost after initial start-up of the process due to the waiting time taken for the rope to swell. Further to this, the rope may become hard depending on the process conditions and subsequently require several hours of washing in order for it to soften and allow it to be removed during replacement of the filter media. Alternatively pneumatic chisel guns are required to remove the hard ropes, resulting in damage to the caulking grooves. An object of the present invention is to provide a retaining method which eliminates the need for repetitive, intensive, physically demanding and somewhat dangerous manual labour while reducing the risk of cloth damage during installation. A further object of the present invention is to provide devices for filtering which eliminate the need for lengthy washes to soften caulking devices such as ropes and allow the filter to be run at full capacity right from start-up. According to a first aspect of the present invention there is provided a filter apparatus comprising a filter medium and a supporting structure for the filter medium, wherein the filter medium is secured to an elongate retaining body for securing the filter medium to a slotted tube of the supporting structure, wherein the slotted tube is configured solely to receive the retaining body therein on sliding the retaining body into the tube, the filter medium extending through the slot of the slotted tube. The elongate retaining body preferably extends along a significant portion of the filter medium and may be elastomeric. The elastomeric retaining body may be bonded to the filter medium by conventional means such as stitching, hot air welding or ultra-sonic bonding, or may be extruded directly onto the fabric. The retaining body may comprise natural or synthetic rubber. The elongate retaining body may extend along two opposing edges of the filter media and is ideally between 6mm and 10mm in diameter and is ideally substantially 8mm in diameter. Preferably, the elongate retaining body extends along two of the filter media edges and the remaining filter media edges may be secured to the supporting structure of the filter apparatus by conventional caulking methods. Alternatively, a simple bolt- down metal strip may be used to secure the remaining edges of the filter media to the supporting structure of the filter apparatus. The slotted tube may be inserted into grooves along two of the edges of the filter apparatus. The size of the assembly formed by two adjacent slotted tubes is preferably from 30mm to 35mm in diameter and is ideally substantially 32mm in diameter. According to a second aspect of the present invention there is provided a method of securing a filter medium to the supporting structure of a filter apparatus, wherein the filter medium is secured to an elongate retaining body for securing the filter medium to a slotted tube of the supporting structure, and wherein the slotted tube is configured solely to receive the retaining body therein on sliding the retaining body into the tube, the filter medium extending through the slot of the slotted tube, the method comprising the step of sliding the retaining body into the tube to obtain a tensioned filter medium retained to the filter apparatus. Preferably the elongate retaining body of the filter medium is inserted at one opening of the slotted tube of the supporting structure and the filter medium is pulled to the other end of the slotted tube thereby obtaining a tensioned filter medium retained to the filter apparatus. Further to this, clamps are preferably used which allow the installers to pull the filter medium along the slotted tube. The present invention may be used in connection with devices for filtering on a substantially horizontal plane as well as rotary devices for filtering i.e., pan filters as well as drum filters. In the case of a pan filter, the elongate retaining body of the filter medium is fed into the slotted tube at the narrow end (neck) of the filter panel and then the filter medium is pulled outwardly from the pan filter centre to the wide end of the panel. The filter media is inserted via the two edges along which the elongate retaining body is secured, into the two slotted tubes which extend along the longitudinal edges of the pan filter. Preferably, the remaining edges of the filter medium are secured at the inner and outer perimeters of the pan filter via a bolt-down metal strip. Altematively, conventional caulking methods may be used to secure the filter medium at the inner and outer perimeters of the pan filter, wherein the edges of the filter medium which are secured to the inner and outer perimeters of the pan filter preferably do not have an elongate retaining body secured thereto. The method used to install filter fabrics to a vacuum drum filter is similar to that mentioned above in relation to a pan filter. A slotted tube is installed longitudinally along the drum, and the elongate retaining body of the filter medium is fed into the slotted tube and pulled along the length of the drum. A slotted tube is preferably installed between every second panel of a drum filter. The groove remaining between each slotted tube is used to provide tension to the filter media via a bolt-down metal strip which is secured to each central groove. A simple bolt-down metal strip may also be used to secure the filter medium to the drum filter at the periphery of the drum filter. Alternatively, conventional caulking methods may be used in place of a bolt-down metal strip at the central groove and at the peripheral edges of the drum filter. The retaining system according to the invention is preferably sized to allow it to fit into the same area as the existing caulking grooves used in conventional pan and drum filters. Consequently, there is no loss of filtration area and installation costs are minimised. In order that the present invention may be more readily understood specific embodiments thereof will now be described by way of example only and with reference to the accompanying drawings in which:- Fig. 1 is a perspective view of a part of a pan filter table in accordance with the present invention; Fig. 2 is an enlarged view along line A-A of Fig. 1 ; Fig. 3 is an enlarged view along line B-B of Fig. 1 ; Fig.4 is a perspective view of a rotary drum filter in accordance with the present invention; and Fig. 5 is an enlarged view along line C-C of Fig. 4. Figures 2 and 3 also illustrate the enlarged views along lines A-A and B-B respectively of Fig. 4. Referring to the drawings and in particular Fig. 1 , a part 1 of a circular pan filter table comprises two filtering apparatus in accordance with the present invention, each filter apparatus 2 having a groove 3 provided around the edge thereof. The filtering apparatus is shaped to form a narrow end 4 at the centre of the pan filter table and a wide end 5 at the periphery of the pan filter table. Referring also to Fig. 2, a slotted tube 6, having a slot 7, is inserted into the groove 3 along the longitudinal edges 10 of the filter apparatus 2. The slotted tube 6 is placed in the groove 3 so that the slot opening 7 faces upwardly. A filter medium such as a filter cloth 8, has secured thereto an elongate retaining body 9, such as an elastomeric extrusion, along two opposing edges of the filter cloth. Said elastomeric extrusion 9 is slidably inserted into the slotted tube 6 at the narrow end 4 of the filter apparatus 2. Once inserted, the elastomeric extrusion 9 being circular in cross section and larger than the size of the slot 7 of the slotted tube 6, is thus retained within the slotted tube. The filter cloth 8 extends through the slot 7 and is retained over the whole surface of the filter apparatus 2. Once the filter cloth is inserted and the elastomeric extrusions 9 retained along the longitudinal edges 10 of the filter apparatus, the remaining edges of the filter cloth 8 are secured along groove 3 at the narrow end 4 and the wide end 5 of the filter apparatus 2. Referring to Fig. 3, the securing mechanism at the wide end 5 of the filter apparatus 2 is shown. The filter cloth 8 is placed in the groove 3 and a metal strip 14 secures the filter cloth into the groove via a bolt 15. The tension on the filter cloth can be altered at this securing point. Fig. 4 shows a rotary drum filter 16, wherein the drum filter is made up of a series of filter panels 17. A slotted tube 19 is inserted between every second filter panel along grooves 18. The enlarged view along line A-A showing how a filter cloth is retained to the drum filter panel is shown in Fig. 2 and is identical to that of a pan filter table. A filter cloth is inserted to the drum filter panel at either end 19 or 20. Referring to Fig. 5, the filter cloth 8 is retained in the central groove 21 via a metal strip 22 which is placed on top of the filter cloth and a bolt 23 which holds the metal strip 23 and filter cloth 8 in place. The above embodiments have been described by way of example only. Many modifications and variations are possible.

Claims: CLAIM? 1. A filter apparatus comprising a filter medium and a supporting structure for the filter medium, wherein the filter medium is secured to an elongate retaining body for securing the filter medium to a slotted tube of the supporting structure, wherein the slotted tube is configured solely to receive the retaining body therein on sliding the retaining body into the tube, the filter medium extending through the slot of the slotted tube. 2. A filter apparatus as claimed in claim 1 , wherein the elongate retaining body extends along a substantial portion of the filter medium. 3. A filter apparatus as claimed in claim 1 or claim 2, wherein the elongate retaining body is elastomeric. 4. A filter apparatus as claimed in claim 3, wherein the elongate retaining body comprises natural or synthetic rubber. 5. A filter apparatus as claimed in any preceding claim, wherein the retaining body is bonded to the filter medium by stitching, hot air welding, ultrasonic bonding or extrusion directly onto the filter medium. 6. A filter apparatus as claimed in any preceding claim, wherein the elongate retaining body extends along two opposing edges of the filter media. 7. A filter apparatus as claimed in any preceding claim, wherein the elongate retaining body is approximately 6mm to 10mm in diameter. 8. A filter apparatus as claimed in claim 7, wherein the elongate retaining body is approximately 8mm in diameter. 9. A filter apparatus as claimed in any of claims 6 to 8, wherein the elongate retaining body extends along two opposing edges of the filter media and the remaining filter media edges are secured to the supporting structure of the filter apparatus by conventional caulking methods. 10. A filter apparatus as claimed in claim 9, wherein a bolt-down metal strip is used to secure said remaining edges of the filter media to the supporting structure of the filter apparatus. 11 . A filter apparatus as claimed in any preceding claim, wherein the slotted tube is inserted into grooves along two edges of the supporting structure. 12. A filter apparatus as claimed in claim 11 , wherein the size of an assembly formed by two adjacent slotted tubes is approximately 30mm to 35mm in diameter. 13. A filter apparatus as claimed in claim 12, wherein the size of the assembly is approximately 32mm in diameter. 14. A method of securing a filter medium to the supporting structure of a filter apparatus, wherein the filter medium is secured to an elongate retaining body for securing the filter medium to a slotted tube of the supporting structure, and wherein the slotted tube is configured solely to receive the retaining body therein on sliding the retaining body into the tube, the filter medium extending through the slot of the slotted tube, the method comprising the step of sliding the retaining body into the tube to obtain a tensioned filter medium retained to the filter apparatus. 15. A method of securing a filter medium to the supporting structure of a filter apparatus as claimed in claim 14, wherein the elongate retaining body of the filter medium is inserted at one opening of the slotted tube of the supporting structure and the filter medium is pulled to the other end of the slotted tube thereby obtaining a tensioned filter medium retained to the filter apparatus. 16. A method of securing a filter medium to the supporting structure of a filter apparatus as claimed in any one of claims 14 or 15, wherein clamps are used to pull the filter medium along the slotted tube. 17. A filter apparatus as claimed in any one of claims 1 to 13, comprising a pan filter apparatus for filtering on a substantially horizontal plane, wherein the pan filter apparatus comprises at least one filter panel having a narrow end at the centre of a pan filter table and a wide end at the perimeter of the pan filter table. 18. A method of securing a filter medium to the pan filter apparatus of claim 17, wherein the elongate retaining body of the filter medium is fed into slotted tubes, which extend along two longitudinal edges of the filter panel, at the narrow end of the filter panel and pulled from the pan filter centre to the wide end of the filter panel. 19. A method as claimed in claim 18, wherein the remaining edges of the filter medium are secured at inner and outer perimeters of the pan filter via a bolt-down metal strip. 20. A method as claimed in claim 19, wherein the remaining edges of the filter medium are secured at the inner and outer perimeters via conventional caulking methods. 21 . A filter apparatus as claimed in any of claims 1 to 13, comprising a rotary filter, wherein at least one slotted tube is installed longitudinally along a drum, said drum comprising a plurality of filter panels. 22. A method of securing a filter medium to the rotary filter apparatus of claim 21 , wherein the elongate retaining body of the filter medium is fed into the slotted tube, said slotted tube being positioned between the drum filter panels, the filter medium is then pulled along the length of the drum. 23. A filter apparatus substantially as hereinbefore described with reference to the accompanying drawings. 24. A method of securing a filter medium to a filter apparatus substantially as hereinbefore described with reference to the accompanying drawings.

Inventors: TEBBUTT DAVID JOHN, TEBBUTT, DAVID, JOHN
Applicants: SCAPA GROUP PLC, TEBBUTT DAVID JOHN, TEBBUTT, DAVID, JOHN
Application year: 1996
Main classification: B01D33
IPC codes: B01D33, B01D46