GB2264881A

GB2264881A - Mounting and tensioning arrangements for screens

Info

Publication number: GB2264881A
Application number: GB9205517A
Authority: GB
Inventors: Ola Bjorklund; Alexander Ritchie; George Souter
Original assignee: Alfa Laval Separation AB
Current assignee: Alfa Laval Separation AB
Priority date: 1992-03-13
Filing date: 1992-03-13
Publication date: 1993-09-15
Anticipated expiration: 2012-03-13
Also published as: EP0630294A1; CA2131030A1; NO943384L; WO1993017798A1; NO943384D0; GB9205517D0; GB2264881B

Abstract

In vibratory screening apparatus, a screen unit (10) consists of a sheet of flexible mesh material (10A) having rib elements (14) of a hard rubber or like material moulded onto mutually parallel fore-and-aft side edge portions. The screen unit (10) is mounted by inserting the rib elements (14) into slit tubular holders (13) one of which is anchored to one side support member (12) in the screening apparatus and the other of which is shiftable bodily to tension the mesh material (10A) by pneumatic actuators (18) connected to a single pressure source. The actuators (18) draw the shiftable holder (13) to a fixed location against the opposite side support member (11) and set with reference to a predetermined width dimension of the screen unit (10) so that the mesh material (10A) is made evenly taut by the actuators (18). Thus, changing of the screen unit (10) can be effected rapidly with reduced risk of mesh distortion due to uneven tensioning. Final tensioning is effected by shiftable support bars (20) extending fore-and-aft between the side support members (11, 12) in known manner.

Description

MOUNTING AND TENSIONING ARRANGEMENTS FOR SCREENS This invention relates to screens and to screen mounting and tensioning arrangements in screening apparatus for use, for example, in the separation of solids from a slurry.

In known vibratory screening apparatus, a sheet of woven mesh material is disposed between laterally spaced support members extending fore-and-aft with respect to the direction of travel of the material to be screened. The mesh material is effectively mounted or carried on the support members. The mesh must be placed under tension to obtain an effective screening action.

One presently popular mounting and tensioning arrangement is shown in United Kingdom Patent Specification No. 1326133 (FMC Corporation) in which the fore-and-aft edge portions of a mesh screen unit are reinforced with sheet metal strip material folded to define a hook configuration as viewed in cross-section and cooperable with similarly configured tensioners shiftable by means of a plurality of screw adjusters spaced along the fore-and-aft directions. When the screen unit is installed and the mesh material tensioned, the mesh is pulled against a set of mutually parallel laterally-spaced support bars which extend fore-and-aft between the support members and serve to sub-divide the full lateral span of the mesh. Usually, these support bars are disposed to lie not in the plane common to that containing the tensioners. Thus, the mesh surfaces define a cambered configuration.A similar arrangement is shown in United States Patent Specification No. 4846352 (Bailey), but in which the mesh is first tensioned by laterally shiftable tensioners along the edges of the screen unit and then further tensioned and clamped by inflatable support bars adapted to shift against the mesh in a direction normal to its surface.

A principal disadvantage of these prior proposals is that several mutually independent screw adjusters constitute a time-consuming method of applying tension to a screen unit, difficult to use in certain environments such as oil rigs, and prone to problems attributable to corrosion and seizing of screw-threaded elements. The secondary tensioning using the inflatable support bars shown in United States Patent Specification No. 4846352 has a desirable feature of rapid action, but depends upon the accuracy of the primary tensioning to avoid distortion of the mesh which distortion can seriously impair the screening performance.A disadvantage of inflatable or shiftable support bars for tensioning is that without any provision for primary tensioning, the screen unit must be mounted with a minimum of slack in the mesh material because otherwise either the support bars cannot easily be shifted sufficiently to produce a required tension or excessive shifting of the support bars induces distortion or uneven tension in the mesh material. The fitting of a screen unit into screening apparatus can be difficult if freedom of movement is limited due to a minimum of slack in the mesh material.

An object of the present invention is to provide screen mounting and tensioning arrangements in screening apparatus, whereby the disadvantages and/or shortcomings outlined above are obviated or mitigated.

According to the present invention, there is provided screening apparatus comprising substantially mutually parallel and laterally spaced side support members extending in a fore-and-aft direction, a screen unit having a flexible mesh material extending between the support members, relatively rigid holding means engaging side edge portions of the mesh material along the fore-and-aft dimension thereof, several adjustable means spaced along at least one support member and connected to the holding means of at least one side edge portion of the mesh material and operable to draw this holding means towards the adjacent support member, and support bars extending fore-and-aft between the support members and shiftable normally to the general plane of the mesh material for supporting the latter; characterised in that actuating means is arranged to operate the adjustable means substantially in unison to shift the holding means for the said one side edge portion of the mesh material to a fixed location relative to said adjacent support member, and that said fixed location is set with reference to a predetermined width dimension of the screen unit so that the mesh material is made evenly taut by the actuating means.

In the screening apparatus of the present invention, the provision of the fixed location set with reference to the predetermined width dimension of the screen unit makes practically feasible the in-unison shifting of the adjustable means, which is time saving, coupled with obtaining consistent uniform mesh tension in successive screen units which are prefabricated to have the stated width dimension.

Because the said fixed location is set with reference to the width dimension of the separately made screen unit, it follows that the mentioned holding means should engage the edge portions of the mesh material without undue lost-motion or dimensional variation.

Thus, preferably the said holding means comprises outer elements each in the form of a longitudinally slit tube connected to the said adjustable means or to a said support member, and rib means attached to each side end portion of the mesh material and received within the respective tube; characterised in that each rib means is of moulded construction formed in a mould or die cavity by a settable material flowed around the respective side edge portion of the mesh material to enclose said side edge portion.

Further, according to the present invention, there is provided a screen unit for use in screening apparatus as aforesaid, the screen unit comprising a sheet of mesh material having mutually substantially parallel side edges, and rib means attached to each said side edge for holding the mesh material; characterised in that each rib means is of moulded construction formed in a mould or die cavity by a settable material flowed around the respective side edge portion of the mesh material to enclose said side edge portion.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which: Fig.1 is a diagrammatic cross-sectional elevation of part of screening apparatus having screen mounting and tensioning arrangements in accordance with the present invention; Fig. 2 is a cross-sectional elevation similar to parts of Fig. 1, showing a modification; Fig. 3 is a perspective view showing diagrammatically parts of a split mould and a portion of screen mesh therebetween prior to a moulding operation for making a screen unit in accordance with the present invention; and Fig. 4 is a perspective view of part of a screen unit in accordance with the present invention.

In Fig. 1 of the drawings, part of a vibratory screening installation for use in the separation of solid particles from a slurry consists of a screen unit 10 having a sheet of flexible mesh material 10A which extends between substantially rigid parallel side support members 11, 12 which extend fore-and-aft in the screening apparatus with respect to the direction of travel of material lOB to be screened. The fore-and-aft edge portions of the mesh material 10A are engaged by holding means 13, 14 along the entire fore-and-aft dimension of the screen unit 10 and, in conjunction with support bars 20, transmit tension to the mesh material 10A as further explained hereunder.In operation of the screening apparatus, the support members 11, 12 and the support bars 20, all of which are part of the vibratory assembly of the apparatus, are subjected to a cyclic shaking motion which is imparted to the screen unit 10 for screening action generally in known manner.

The holding means 13, 14, as seen in Fig. 1, are positioned at respective fixed locations relative to a support member 11, 12. Thus, in the case of the support member 12, the right hand part 13 of the screen edge holding means is secured to the support member 12 by means of a conventional screw-threaded fastener 12A; and in the case of support member 11, the corresponding left hand part 13 is releasably held in abutment with the inside face of the support member 11.

The holding means 13, 14 consists of ribs 14 of a pliable material, for example a hard rubber, which is moulded onto the edge portions of the mesh material 10A as described hereunder. The pliable ribs 14 extend effectively for the full fore-and-aft length of the mesh material 10A and by virtue of their pliability the screen unit 10 can be manipulated by bending during fitting where there are restrictions on free space in the vicinity of the screening apparatus. Alternatively, each rib 14 is defined by several (two or more) mutually separate rib sections moulded from either a hard rubber like (pliable) material or a relatively rigid plastics material. The ribs 14 are of circular cross-sectional configuration and are received within the parts 13 which take the form of relatively rigid longitudinally slit tubes which extend fore-and-aft for the full length of the screen unit 10.

This arrangement provides a dimensionally consistent coupling of the screen unit to the tubes 13 with reference to the screen width dimension W.

Welded to each tube 13 is a flat bar 13A which also extends the full fore-and-aft length of the screen unit 10. The bars 13A improve the rigidity of the holding means and also assist in stopping flow of material 10B around the sides of the screen unit 10. If required, sealing strips 13B are disposed between the support members 11, 12 and the respective flat bars 13A.

As mentioned above, the tube 13 associated with the support member 12 is fixed thereto. The tube 13 associated with the support member 11 has attached thereto several adjustable means in the form of rods 15 which are mutually spaced along the length of the support member 11 and extend laterally through openings 16 in this support member. The inner end of each rod 13 is welded to or otherwise secured to the adjacent tube 13; and the outer end of each rod 15 is coupled to a common thrust plate 17. Between the thrust plate 17 and the outer side of the support member 11 there is provided an actuator 18 operable to act on the thrust plate 17 and the support member 11 to shift the rods 15 outwards in unison thereby to draw the adjacent tube 13 bodily against the support member 11 and to keep the tube 13 at this fixed location.

Also, the actuator 18 is operable (by deactivating) to permit inward movement of the adjacent tube 13 thereby to slacken the screen unit 10. In Fig. 1, the actuator 18 is in the form of an elongate pneumatic bladder (known per se), and it will be understood that a single source of pneumatic pressure will effect unison operation of all the rods 15 through the thrust plate 17. To this end, as shown in Fig. 1, the actuator 18 is connected by conduit 18A to a single pneumatic pressure source by way of a control valve 18B operable to charge and exhaust the actuator means 18 as required. Compressed air at a pressure of about 120 lbs/in2 (8.44 Kgm/cm2) is suitable.

Intermediate the support members 11, 12, the screening apparatus is provided with fore-and-aft extending releasable tensioning means 19 for acting on the lower face or underside of the mesh material 10A. Each tensioning means 19 consists of a vertically shiftable support bar 20 which is guided on a carrier beam 21, and shifted by means of a pneumatic bladder actuator 22. The arrangement is such that admission of pneumatic pressure within the bladder 22 effects upward shifting of the support bar 20 to act upon and further tension and support the mesh material 10A. To this end, such bladder 22 is connected by a conduit 22A to the said pneumatic pressure source by way of a control/exhaust valve 22B. It is to be understood that when the support bars 20 are in their lowermost position, they lie just clear of the mesh material 10A as shown in Fig. 1.The fully tensioned configuration of the mesh material 10A is shown in Fig. 2.

Optionally, the support bars 20 are provided with stops in the form of flanges 20A for limiting upward movement of the support bars 20. Thus, by means of pre-determined dimensions for the sides of the support bars 20, the flanges 20A abut the upper flange of the beam 21 when the required final tension in the mesh material 10A is reached. In a modification of this arrangement, adjustable stops are provided for limiting upward movement of the support bars 20.

Figs. 3 and 4 are concerned with the production of the screen unit 10. In Fig. 3, a piece of mesh material 10A is placed between the members 23, 24 of a split mould which defines cavities 25 of circular cross-section (when the mould parts 23, 24 are together) for forming parallel ribs. The mesh material 10A extends into the cavities 25. A settable material (not shown) such as a thermosetting resin or hard rubber compound is introduced into the cavities and the completed screen unit 10 is stripped from the mould when the settable material has solidified and/or cured. If necessary, surplus mesh material is trimmed from the outsides of the ribs 14. The thus predetermined width of the screen unit 10 (taken between the centres of the ribs 14) corresponds with the dimension W in Fig. 1.

In a modification of the moulding above described, the members 23, 24 define a series of cavities spaced apart longitudinally so that the ribs 14 are constituted by the previously mentioned separate rib sections such as are shown in the right hand side of the screen unit 10 in Fig.

4.

The mounting and tensioning arrangements described above operate as follows. For the insertion of a new screen unit 10 into the screening apparatus, the actuator means 18 and 22 will be depressurised or deactivated allowing the left hand tube 13 to move inwards away from the support member 11, and also allowing the support bars 20 to adopt their lowermost position. Thus, a fresh screen unit 10 may be inserted into the apparatus, feeding the ribs 14 (or separate rib sections) into the respective slit tubes 13. This can be done with relative ease since the left hand tube 13 (as seen in Fig. 1) can be inwardly positioned corresponding with an adequately slack condition of the mesh material 10A.When the screen unit 10 is fully inserted, the actuator means 18 is pressurised thereby rapidly drawing the adjacent tube 13 to its predetermined fixed location in abutment with the inside of the support member 11. Thus, both screen edge portions and holding means are accurately positioned. The mentioned fixed location and the screen unit width dimension W are mutually related in that one is set with reference to the other so that the mesh material 10A is made evenly taut by the actuating means 18. It is envisaged that the setting will be made initially so that approximately 50% of the desired working tension force is applied to the mesh material 10A by the primary action of the actuating means 18.Thereafter, pressuring of the bladders 22 urges the support bars 20 upwards to produce whatever final tension is required in the mesh material 10A with minimised or no risk of causing distortions or unevenness of the mesh material such as might impair its screening performance.

In Fig. 2, parts corresponding with those in Fig. 1 are given the same reference numerals. In this modification, the rods 15 are provided with screw threaded portions and adjustable stops in the form of nuts 15A.

During initial assembly of the screening apparatus, if the support members 11, 12 are not mutually parallel with sufficient accuracy, then the nuts 15A are used to set the adjacent tube 13 at its fixed location relative to the support member 11 so that the tube lies sufficiently parallel with its counterpart secured to the support member 12. In this modification, the material 10B on the screen unit 10 during use is prevented from flowing around the left hand side of the screen unit 10 by means of a retaining plate 13C which is attached to the rods 15 and the adjacent flat bar 13A and which extends the full fore-and-aft length of the screen unit 10.

Further modifications within the scope of the appended claims include providing the screen unit 10 with laterally shiftable adjustable means 15 and actuators 18 at both sides thereof; and using hydraulic instead of pneumatic actuators. Also, the actuating means 17, 18 may comprise a series of annular bladders, one around each rod 15 and acting either on a single pressure plate 17 or on corresponding separate pressure plates.

Claims

1. Screening apparatus comprising substantially mutually parallel and laterally spaced side support members (11, 12) extending in a fore-and-aft direction, a screen unit (10) having a flexible mesh material (10A) extending between the support members (11, 12), relatively rigid holding means (13, 14) engaging side edge portions of the mesh material (10A) along the fore-and-aft dimension thereof, several adjustable means (15) spaced along at least one support member (11) and connected to the holding means (13, 14) of at least one side edge portion of the mesh material (10A) and operable to draw this holding means (13, 14) towards the adjacent support member (11), and support bars (20) extending fore-and-aft between the support members (11, 12) and shiftable normally to the general plane of the mesh material (10A) for supporting the latter; characterised in that actuating means (17, 18) is arranged to operate the adjustable means (15) substantially in unison to shift the holding means (13, 14) for the said one side edge portion of the mesh material (10A) to a fixed location relative to said adjacent support member (11), and that said fixed location is set with reference to a predetermined width dimension (W) of the screen unit (10) so that the mesh material (10A) is made evenly taut by the actuating means (17, 18).

2. Screening apparatus according to claim 1; characterised in that the actuating means (17, 18) comprises one or more actuators (18) operable by means of fluid under pressure, said one or more actuators (18) being connected to a single source of fluid under pressure by way of a control valve means (18B).

3. Screening apparatus according to claim 2; characterised in that the one or more actuators (18) is/are pneumatic actuators.

4. Screening apparatus according to any one of the preceding claims; characterised in that the holding means (13, 14) comprises for each side of the mesh material (10A) a longitudinally slit tube (13), and rib means (14) secured to the side edge portion of the mesh material (10A) and received within the tube (13) with the mesh material (10A) extending through the slit of the tube (13).

5. Screening apparatus according to claim 4; characterised in that said rib means (14) comprises several mutually separate rib elements arranged in a series along the mesh edge portion.

6. Screening apparatus according to claim 4 or 5; characterised in that the rib means (14) is of moulded construction formed in a mould or die cavity (25) by a settable material flowed around the mesh material edge portion.

7. Screening apparatus according to any one of claims 4 to 6; characterised in that the rib means (14) is made of a flexible or pliable material.

8. Screening apparatus according to any one of claims 4 to 7; characterised in that the rib means (14) is of circular cross-sectional configuration.

9. Screening apparatus according to any one of the preceding claims; characterised in that the adjustable means (15) comprises several rods (15) which extend through respective openings (16) in the support member (11), the inner end of each rod (15) being attached to the adjacent holding means (13, 14), and the outer end of each rod (15) being coupled to the actuating means (17, 18).

10. Screening apparatus according to any one of the preceding claims; characterised in that said fixed location is the location of the holding means (13, 14) when the latter abuts the support member (11) over the full fore-and-aft length of the holding means (13, 14).

11. A screen unit for use in screening apparatus according to any one of the preceding claims, the screen unit comprising a sheet of mesh material (10A) having mutually substantially parallel side edges, and ribs means (14) attached to each said side edge for holding the mesh material (10A); characterised in that each rib means (14) is of moulded construction formed in a mould or die cavity (25) by a settable material flowed around the respective side edge portion of the mesh material (10A) to enclose said side edge portion.

12. A screen unit according to claim 11; characterised in that the rib means (14) comprises several mutually separate rib elements arranged in a series along the mesh edge portions.

13. A screen unit according to claim 11 or 12; characterised in that the rib means (14) is made of a pliable or flexible material.

14. A screen unit according to any one of claims 11 to 13; characterised in that the rib means (14) is of circular cross-sectional configuration.