FILTER SCREEN ASSEMBLY

Abstract: A filter screen assembly comprises a rectangular principal frame (12) of moulded plastics material and subdivided by crosspieces (14,16) to form sub-areas (18). Each sub-area receives as a releasable snap-fit a plastics moulded insert (20) in the form of a sub-frame carrying one or more tensioned screen meshes (Figure 1). A peripheral sealing gasket may seal the joint between each sub-area (18) and the insert (20)

Description: Field of the invention This invention relates to a filter screen assembly, more especially a filter screen assembly of the kind which in use is located in the vibrating basket of a filtering machine for the treatment of slurries or the like. Background to the invention A filter screen assembly conventionally comprises a steel frame with one or more filtering meshes secured and tensioned over its area. In use, the mesh can become damaged, creating holes through which can pass material which the mesh is intended to hold back. Replacement of the mesh in such an event is expensive and time consuming, requiring removal of the frame from the machine, removal of the damaged mesh, replacement by a new mesh and tensioning of the latter, and replacement of the frame in the machine. It is known to effect patching of a damaged mesh with metal sheet patches or, in the case of a multiple mesh assembly, to bond the two meshes together at the site of damage. The former procedure results in diminished throughput, whilst the latter results in reduced efficiency of the so-called blinding action which is intended to take place in use, whereby the differential vibrations of the two meshes serve to dislodge material tending to clog the upper mesh. Both procedures, whilst being more economical than replacement of a complete mesh, suffer from the problem that they are just as time consuming as a complete mesh replacement. In US-A-2792906 there is disclosed a filter screen assembly of a type comprising a principal frame the area of which is subdivided by integrally formed crosspieces into a plurality of equally sized and shaped sub-areas, and a corresponding plurality of removable inserts each in the form of a sub-frame carrying a filter mesh. DE-U-8235215 discloses a filter arrangement in which individual inserts are secured to a supporting frame by a plurality of fasteners passing through apertures in the inserts. It is an object of the present invention to provide an improved filter screen assembly which assists in providing a solution to the above-described problem. The invention According to one aspect of the present invention a filter screen assembly of the type described above and as defined in the preamble of claim 1 is characterised in that the principal frame and the inserts are made of a moulded plastic material, in that each insert carries a tensioned filter mesh, and in that the outer periphery of each insert co-operates with a mutually shaped inner periphery of the crosspieces defining the corresponding sub-area, such that each insert is individually removable as a releasable press fit or snap fit in its corresponding sub-area. According to another aspect of the invention, there is provided a method of enabling repair of a damaged filter screen assembly as hereinbefore defined, and comprising the step that when in use the screen assembly is damaged, only the insert containing the site of damage is removed and is replaced by a fresh insert carrying an undamaged mesh. Other features of the invention are defined in the dependent claims herein contained. Description of Embodiment A filter screen assembly in accordance with the invention is exemplified in the following description and with reference to the accompanying drawings, in which:- Figure 1 is an exploded perspective view of the filter screen assembly; and Figures 2 and 3 are enlarged cross-sectional views on the lines 2-2 and 3-3 of Figure 1, respectively. Referring to the drawings, a rectangular principal frame 10 is moulded of glass-fibre reinforced polyester resin compound. The frame 10 consists of a border 12 subdivided by integrally formed cross-pieces 14 and 16 into equally shaped and sized sub-areas 18. An insert for each sub-area comprises a sub-frame 20 moulded of like material and carrying a screen mesh (not shown) tensioned over its area in a conventional manner. The peripheries of the sub-areas 18 of the principal frame 10 and of the sub-frames 20 are mutually shaped, at least along two opposite sides, to enable the insert to be secured as a press fit or snap fit into the sub-area, as by means of cooperating grooves and projections. One possible configuration will be clear from Figures 2 and 3. A thermally re-activatable isocyanate glue may be employed to achieve a more secure releasable fixing, if desired. Rubber sealing gaskets (not shown) may also be employed to seal the peripheral joints between the sub-areas and the inserts, again if desired or expedient. In use, when a screen mesh becomes damaged, it is only necessary to replace the insert containing the site of damage by a fresh insert. In some instances this may be possible without even necessitating the requirement to remove the filter screen assembly from the vibratory basket of the filtering machine.

Claims: A filter screen assembly comprising a principal frame (10) the area of which is subdivided by integrally formed crosspieces (14, 16) into a plurality of equally sized and shaped sub-areas (18), and a corresponding plurality of removable inserts (20) each in the form of a sub-frame carrying a filter mesh, characterised in that the principal frame and the inserts are made of a moulded plastic material, in that each insert (20) carries a tensioned filter mesh, and in that the outer periphery of each insert co-operates with a mutually shaped inner periphery of the crosspieces defining the corresponding sub-area, such that each insert is individually removable as a releasable press fit or snap fit in its corresponding sub-area. An assembly according to claim 1, characterised in that the moulded plastic material is glass-fibre reinforced plastic material. An assembly according to claim 2, characterised in that the plastic material is a mouldable polyester compound. An assembly according to any one of claims 1 to 3, characterised in that the principal frame (10) is square or rectangular and divided by crosspieces extending in mutually perpendicular directions parallel to its sides (12). An assembly according to any of claims 1 to 4, characterised in that two or more inserts (20) are secured or securable in overlying relationship in each sub-area of the principal frame (10). An assembly according to any of claims 1 to 4, characterised in that each insert has two or more overlying meshes. An assembly according to any of claims 1 to 6, characterised by a peripheral seal carried by the principal frame or by the insert to seal the joint therebetween. A method of enabling repair of a damaged filter screen assembly according to any of claims 1 to 7, and comprising the step that when in use the screen assembly is damaged, only the insert containing the site of damage is removed and is replaced by a fresh insert carrying an undamaged mesh.

Inventors: SOUTER, GEORGE LAWRENCE
Applicants: UNITED WIRE LIMITED
Application year: 1988
Main classification: B01D35
IPC codes: B01D29, B01D25, B01D35, B07B1