AU716271B2 - An improved trommel screen - Google Patents

Description

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT C. e* b.c.

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Invention Title: Applicant: AN IMPROVED TROMMEL SCREEN LETTELA PTY LTD the best method of performing it known to me: 1 CAkWINWORD\SIMONE\SYDNEVI455609A.DOC 2 AN IMPROVED TROMMEL

SCREEN

The present invention relates generally to screening, separating or grading of material, and in particular to a screening apparatus commonly referred to as a trommel screen. The apparatus is applicable for screening, separating and grading ores and it will be convenient to hereinafter describe the invention to this exemplary application. It is to be understood, however, that the invention is not limited to this particular application.

A trommel screen is generally cylindrical or frusto-conical and incorporates a central axis about which the screen rotates. The screen has an external frame which typically incorporates a plurality of supporting rings interconnected by struts. A plurality of screen panels form an inner surface of the screen and are mounted to the external frame. The screen has opposite ends spaced along this axis, one being the feed end through which ore or other material is introduced into the interior of the screen, the other being the discharge end. Apertures are formed in the screen panels to provide ore screening and separation. The aperture size may vary between the panels and typically will increase from the feed to the discharge ends so that the trommel screen is operable to separate the ore into different sizes. Alternatively, the aperture size of the panels may be the same throughout the trommel screen such that it is operable to only screen one size of the material.

~Due to the abrasive nature of the ore, the screen panels require regular *removal and replacement. In the past, the panels of the trommel screen have been bolted to the external frame. A rigid fixing arrangement is required to fix "the panel screens as these screens in operation are subjected to complex S 25 loading due in part to the curvature of the screen panels.

*.jWhile these previous fixing systems have been effective, the screen panels cannot be removed and replaced rapidly. As a consequence the screening effectiveness and efficiency of the trommel screen is diminished because of the significant down time requirements for screen panel maintenance.

An aim of the present invention is to ameliorate this problem and provide an improved fixing system for the screen panels which facilitates the rapid removal and replacement of the panels.

C.\My DvcUmeots\KATE\SPECI\16500-97.doc In one broad aspect, the present invention provides apparatus for screening ores, including an external frame of generally frusto-conical or cylindrical shape, an inner circumferential wall formed from a plurality of screen panels releasably connected to the external frame through an arrangement of interfitting projections and recesses.

In a preferred form, the screen apparatus includes a plurality of fixing rails secured to the apparatus frame. The fixing rails including one of either the projections or recesses and wherein the screen panels incorporate the other of the projections and recesses. In this way, the screen panels are secured to the fixing rails by interfitting of the projections into the recesses.

In one form, the fixing rails are mounted to extend circumferentially about the frame. In another form the fixing rails extend generally in the direction of the axis of the screen apparatus.

In one form, the screen panels abut in side by side relationship such that the inner circumferential wall of the screening apparatus is substantially continuous. In one form, each screen panel has a typically square or rectangular plan shape having a pair of opposite side edge regions and a pair of opposite upstream and downstream end edge regions. Further, each screen S.panel preferably has an inner screening surface for receiving ore or other oooo 20 material to be screened and an outer surface which is in facing relationship with i.I the external frame. Apertures extend through the screen panel between the inner and outer surfaces to provide for ore screening and separation.

Preferably at least one of either the side edge regions or the end edge regions engages with the fixing rail. In one form, this engagement is continuous 25 along the entire length of the edge region. In another form the screening panel engages the fixing rail only along a portion of the respective edge regions.

In one form, the opposite edge regions which are engaged with the fixing rail are laterally stepped so as to provide a relief recess in which a portion of the fixing rail is located. In this arrangement, the portion of the fixing rail which is located within this relief recess incorporates one of either the projections or recesses with the other being located within this relief recess.

In one form, adjacent screen panels are releasably connected to a single fixing rail. In a preferred form, the fixing rail is located wholly within a space S formed by the relief recesses of two adjacent abutting screen panels.

C:\My Documents\KATE\SPECI\l6500-97.doc In one form, the panels are releasably tonnected to the fixing rails through a snap fit arrangement. In one form, the projections are formed on the screen panels and interfit with recesses located on the fixing rails. Preferably the projections are continuous along the respective edge regions and have a constant cross section which includes an enlarged head portion which is interconnected to the panel by a stem portion. In this way, the projections have the general appearance of a rail. Preferably the recesses in the fixing rail are in the form of channels and incorporate opposing re-entrant portions which define a pair of abutment shoulders.

Preferably the fixing rail further includes a connection portion which forms at least one side of the recess and which is resiliently flexible. In this way, the projections interfit with the recess through a snap fit engagement caused by deflection of this connection portion. Once in proper engagement, the connection portion returns to its rest position to retain the projection within the recess with the head portion abutting against the two abutment shoulders of the recess.

Preferably, the fixing rails are cast or moulded from a plastics material, such as polyurethane, and may be internally reinforced by one or more metal elements, such as steel strips. It should be appreciated that other alternative °oo° 20 materials and methods of production may be equally applicable. Furthermore the fixing rails may be mountable on the external frame structure through any a suitable arrangements or alternatively the fixing rail may be integrally formed as part of the external frame. In one form, the rails include spaced slots which receive fastening means such as bolts to secure the fixing rail to the frame.

25 The screen panels may be similarly cast or moulded from plastics material, such as polyurethane and may be internally reinforced with one or more metal elements such as steel bars. In one form the screen panels are moulded or cast in a curved plane. In another form the screen panels are cast or moulded in a flat arrangement. Those screen panels may be flexible in at least one direction so CAMy Documents\KATE\SPECI\16500-97.doc that they can assume the curved shape once installed. With this arrangement any reinforcing elements are adapted to extend in the direction of an axis about which the panels can be flexed. Alternatively, the flat screen panels may be cast or moulded rigid and then curve formed in a subsequent operation, such as roll bending. In that arrangement, there is no limitation on the directions in which any reinforcing elements extend and, in particular, those elements may extend both along and about the axis of panel curvature.

In a further aspect, the present invention provides a screen panel and fixing rail of the type described above for use in a screening apparatus of generally frusto-conical or cylindrical shape.

An advantage of the apparatus according to the present invention is that the fixing systems provides for simple and rapid removal and replacement of individual screen panels from the screening apparatus frame. In a preferred form, the panels can be simply snapped into engagement with the fixing rail. On 15 removal of the panel, a screwdriver or similar implement can be used to lever S•open the recess by deflecting the connecting portion outwardly. A portion of the projection can then be removed from the recess. The remainder of the projection can be removed from the recess merely by "peeling" the projection out of engagement with the recess.

20 Furthermore, the fixing system of the apparatus is able to resist the loading induced on the screen panel during operation of the trommel screen thereby :..-.maintaining the screen panels in the correct position.

It will be convenient to hereinafter describe an embodiment of the invention in greater detail with reference to the accompanying drawings. The particularity of these drawings in the related description is not to be understood as superseding the generality of the preceding broad description of the invention.

In the drawings: Figure 1 is a perspective view of a trommel screening apparatus; Figure 2 is a sectional view to an enlarged scale along section lines 11-11 of Figure 1; Figure 3 is a sectional view to an enlarged scale along section lines 111-111 of Figure 1; Figure 4 is a plan view of a screen panel of the apparatus of Figure 1; DJH: IR445609 25.3.97 Figure 5 is a partial perspective view of the screen panel of Figure 4; Figure 6 is a perspective view of a fixing rail of the apparatus of Figure 1; Figure 7 is a sectional view along section lines VII-VII of Figure 6; and Figure 8 is a sectional view along section lines VIII-VIII of Figure 6.

As illustrated in the drawings, a trommel screen apparatus 10 is disclosed of generally cylindrical shape. The screen has an external frame 11, which in the illustrated arrangement incorporates a series of support rings 12 interconnected by struts 13. A plurality of screen panels 14 form an inner surface of the apparatus 10 and are mounted to the external frame.

The apparatus 10 is rotatable about its central axis and incorporates a feed end 15, through which ore is introduced into the interior of the screen and an opposite discharge end 16. Trunnions are formed at each of the opposite ends •and 16 and are adapted to be connected to a drive arrangement (not shown) for rotating of the apparatus 15 The panels 14 are adapted to be mounted to the external frame 11 through S" a snap fit arrangement. More specifically the panels 16 are adapted to engage fixing rails 18 which in the illustrated arrangement extend circumferentially around the apparatus 10 and are connected to respective support rings 12.

As illustrated in Figures 4 and 5, each screen panel 14 has a typically 20 square or rectangular plan shape having a pair of opposite side edge regions 19 and a pair of opposite upstream and downstream end edge regions 20. Each ":screen panel 14 has an inner screening surface 21 for receiving ore or other *material to be screened, and an outer surface 22 which is in facing relationship with the external frame 11. Apertures 23 extend through the screen panel between the inner and outer surfaces to provide for ore screening and separation.

In the illustrated arrangement, the opposite upstream and downstream edge regions 20 include projections 24 which are adapted to interfit with recesses formed in the fixing rail 18. In the illustrated arrangement each of the upstream and downstream edge regions 20 is laterally stepped so as to provide a relief recess 26. The projections 24 extend downwardly into this relief recess 26 and are in the form of rails which extend along the entire respective edge region Each projection 24 includes an enlarged head region 27 which is connected to the edge region by a narrow stem 28.

DJH: IR445609- 25.3.97 The screen panels are cast or moulded from plastics material, such as polyurethane and may be internally reinforced with one or more metal elements such as steel bars. In the illustrated form the screen panels are moulded or cast in a substantially flat arrangement and are adapted to be flexible so that they can assume the curved shape required once installed within the screen apparatus In this arrangement, the reinforcing elements (not shown) are adapted to extend along the screen panel between the upstream and downstream end edge regions so that the panel can assume its required curved shape. In an alternative form, the screen panels are preformed into their curved shape.

As best illustrated in Figures 6-8, the fixing rails 18 are of elongate form and incorporate two parallel recesses 25 which are in the form of channels which extend in the longitudinal direction of the fixing rail 18. Each channel has a cross section which is complementary to the cross section of the projections 24. The 0:0: channels include re-entrant portions 29 on their opposing inner side which form a 15 pair of downwardly facing abutment shoulders o *The channels 24 are formed adjacent respective opposite sides 31 of the fixing rail 18. In this way connection portions 32 are formed between the channels 24 and the respective sides 31 of the fixing rail with one side of the connection portion 32 forming an inner side of the recess 25. The connection portions are sized such that they are flexible thereby enabling the projections 24 to be interfitted into the recesses 25 in a snap fit arrangement through outward deflection of the respective connection portions 32.

The fixing rails 18 are cast or moulded from a plastics material, such as polyurethane, and in the illustrated arrangement are internally reinforced by metal elements. In the illustrated arrangement, a base metal strip 33 extends substantially along the entire length of the fixing rail 18. Furthermore while the fixing rails may be mounted to the external frame structure through any suitable arrangement, in a preferred form they are adapted to be bolted to the external frame 11. In this arrangement, the fixing rail 18 incorporates a plurality of spaced slots 34 which extend along the length of the fixing rail 18. To improve the strength of the fixing rail 18 additional steel strips 35 are located around the spaced slots 38.

DJH: IR445609 25.3.97 8 In the illustrated arrangement, the fixing rails 18 are adapted to be flexed such that they can be mounted circumferentially onto the support rings 12 of the external frame 11. It should be appreciated that in an alternative form, the fixing rails may also extend longitudinally along the screen apparatus 10 generally in the direction between the feed and discharge ends 15,16. In this arrangement the projections are formed on the side edge regions 19 of the respective panels in addition to, or in replace of, the projections 24 on the upstream and downstream end edge regions 20. Furthermore, depending on the diameter of the external frame 11, a single fixing rail 18 may be used to extend around the entire inner surface. In an alternative form a plurality of fixing rails are mounted to each of the supporting rings 12.

Figures 2 and 3 illustrate details of the interengagement of the screen panels 14 with the fixing rail 18. As illustrated in Figure 2, the fixing rail is adapted to locate within the relief recess 25 of the screen panel to which it is connected. In 15 the illustrated arrangement, the panels are adapted to be secured in side by side S"abutment. To achieve this along the circumferential join lines between adjacent panels, the fixing rail 18 is adapted to be wholly contained within the space defined by the relief recesses 25 of abutting screen panels 14.

Figure 2 illustrates the connection of the screen panel located closest to the discharge end 16 of the apparatus 10. In this arrangement as the screen panel 14 is located at the end, an end locking strip 36 is fixed to the free recess 25 on the endmost fixing rail 18. A similar locking strip (not shown) is provided at the feed end. The only difference with the feed end locking strip is that it incorporates a downwardly extending flange which is adapted to abut against the side 31 of the fixing rail 18.

Figure 3 illustrates a sectional view of the abutment of adjacent panels 14 in the longitudinal direction of the screen apparatus 10. As can be seen, these side edge regions 19 of the panels are not secured to the external frame 11 but are merely arranged in an abutting arrangement with one another. It should be appreciated that if required the side edge regions could be secured to the external frame through a similar arrangement as to the interconnection of the upstream and downstream end edge regions DJH: IR445609 25.3.97 9 An advantage of this fixing system is that it provides for simple and rapid removal and replacement of individual screen panels from the screen apparatus frame. The panels can simply be snapped into engagement with the fixing rail to install the panels. On removal of the panels a screwdriver or similar implement can be used to lever open the recess by deflecting the connection portion outwardly. Once part of the projection is removed from the recess, the remainder of the projection can be removed merely by peeling the screen panel out of engagement with the recess on the fixing rail.

Finally, it is to be understood that various alterations, modifications and/or additions may be introduced into the construction and arrangement of the parts previously described with departing from the spirit or ambit of the invention.

o .o *f DJH: IR445609 25.3.97

Claims (24)

1. Apparatus for screening ores, including an external frame of generally frusto-conical or cylindrical shape, an inner circumferential wall formed from a plurality of screen panels releasably connected to the external frame through an arrangement of interfitting projections and recesses.

2. Apparatus according to claim 1, further including a plurality of fixing rails secured to the external frame, the fixing rails including one of either the projections or recesses and wherein the screen panels incorporate the other of the projections and recesses.

3. Apparatus according to claim 2, wherein the fixing rails are mounted to extend circumferentially about the frame.

4. Apparatus according to claim 2, wherein the inner circumferential wall extends about an axis of the screen apparatus and wherein the fixing rails extend generally in the direction of said axis.

5. Apparatus according to any preceding claim, wherein the screen panels abut in side by side relationship such that the inner circumferential wall of the screening apparatus is substantially continuous.

6. Apparatus according to any one of claims 3 to 5, wherein each screen oooe panel has a generally square or rectangular plan shape having a pair of opposite side edge regions and a pair of opposite upstream and downstream i end edge regions, whereas at least one of either the side edge regions or the end edge regions engages with the fixing rail.

7. Apparatus according to claim 6, wherein the screen panels are formed in a curved plane. a oo0 25

8. Apparatus according to claim 6, wherein the screen panels are formed in a flat arrangement and are deformed so as to assume a curved shape when t connected to the external frame.

9. Apparatus according to any one of claims 6 to 8, wherein the edge regions engaging with the fixing rail are laterally stepped so as to provide a relief recess, a portion of the fixing rail being located within the relief recess and incorporating one of either the projections or recesses with the other being located within said relief recess.

C\My Documents\KATE\SPECI\1650-97.doc Apparatus according to claim 9, wherein the fixing rail is located wholly within a space formed by the relief recesses of two adjacent abutting screen panels.

11. Apparatus according to any one of claims 6 to 10, wherein the panels are releasably connected to the fixing rails through a snap fit arrangement.

12. Apparatus according to any one of claims 6 to 11, wherein the projections have a constant cross section including an enlarged head portion and a stem portion.

13. Apparatus according to claim 12, wherein the recesses are in the form of channels and incorporate opposing re-entrant portions which define a pair of opposed abutment surfaces engaged with the head portion of respective said projections.

14. Apparatus according to claim 13, wherein at least one side of each recess includes a connection portion, said connection portion being resiliently deformable so as to enable the head portion of an interfitting said projection to locate within said recess in abutting relationship with said opposed abutment surfaces.

15. Apparatus according to any one of claims 6 to 14, wherein the o r projections are located on opposite edge regions of each screen panel. o° 20

16. Apparatus according to any one of claims 2 to 15, wherein each fixing rail is elongate and extends in a longitudinal direction between opposite first and second ends, each said fixing rail including a respective said recess extending generally in said longitudinal direction.

17. Apparatus according to any one of claims 2 to 16, wherein the fixing rails S- 25 include spaced slots which receive fastening means to secure the fixing rail to p= the external frame.

18. Apparatus according to any one of claims 2 to 17, wherein the fixing rails are cast or moulded from a plastics material.

19. Apparatus according to any preceding claim, wherein the screen panels are cast or moulded from a plastics material.

Apparatus according to claim 18 or 19, wherein the plastics material is polyurethane.

21. A screen panel for use in an apparatus according to any one of the A preceding claims. C \My Documents\KATE\SPECI\16500-97.doc 12

22. A fixing rail for use in an apparatus according to any one of claims 2 to wherein the fixing rail is adapted to secure said screen apparatus screen panels to said external frame.

23. Apparatus for screening ores, substantially as herein described with reference to the accompanying drawings.

24. A screen panel substantially as herein described with reference to the accompanying drawings. A fixing rail substantially as herein described with reference to the accompanying drawings. DATED: 2 December, 1999 PHILLIPS ORMONDE FITZPATRICK Attorneys for: LETTELA PTY. LTD. S. 0* C:\My Documents\KATE\SPECI\16500-97.doc