"Screen Panel"

Cross-Reference to Related Applications

The present application claims priority from Australian Provisional Patent Application No 2005904922 filed on 7 September 2005, the content of which is incorporated herein by reference. Introduction

The present invention relates generally to the field of water purification and treatment and is concerned particularly with a screening panel for removing solid material from a liquid in an early stage of a water purification system. Such screening panels are to be found, for example, in band screens and rotary screens in water and waste treatment plants, and may have an overall effective screening area varying in size depending on the application from less than 100 cm ² to substantially more than 500 cm ² .

Background to the Invention

In a typical case, a panel may measure in the order of 10 cm x 15 cm or more and be provided with perhaps many hundreds of perforations depending on their size. A complete screen would be made up of a number of (for example, from 10 to 80) panels. Such screening panels have conventionally been made from perforated steel plate or from woven or welded wire mesh or plastics material. Where steel plate is used, the perforations can be formed by punching or drilling out the steel plate. Where woven or welded wire mesh is used, square holes are often formed and a high percentage of open area can be provided, even with relatively small aperture sizes of for example a few mm. Screens of plastics material may be moulded in their final shape or fabricated and the holes in the panel may be formed in the moulding process or punched or drilled in the cases of a fabricated panel.

It is common for band screens to have guides arranged in a closed path which engage the edges of the screen panels to locate them and guide them in their required path into and out of the fluid being screened. The panel edges which are guided by these channels must be provided with wear resistant bearing surfaces or other mechanism to prevent rapid wear of the panels and the guide channels when in use. Plastic panels, particularly when made of polyurethane or a similar wear resistant material are better suited to this application than metal panels. Unfortunately it is difficult to achieve high open areas in plastic screens.

When a panel in a band screen wears and requires replacing the removal is moderately complex and requires removal of the band from the supporting channels and disengagement of the worn panel from the band before the process is reversed with the new panel inserted. This is the case whether it is the screening surface or the mounting portion of a conventional band screen panel.

Summary of the invention

The present invention provides a screening panel for use in band screens for removing solid material from a flowing liquid by means of a plurality of screening panels, the screening panels each comprising a frame formed of a plastics material and being provided with connection means at opposite ends of the frame, each of the connection means being arranged to co-operate with complementary connection means of an abutting end of an adjacent panel to provide a pivotable connection there between, whereby the plurality of panels form an endless band, each panel frame having an opening extending from one surface to an opposing surface of the panel frame and a screen element removably fastened over the at least one opening, the screen element having a plurality of holes formed therein to provide fluid communication through the panel.

The use of a removably fastened screen element allows the screen member to be removed and replaced without removing the band from the guide channels or disassembling the band.

The screen element of preferred embodiments may be made of a different material to the frame and thus may be selected to provide optimum performance for the particular circumstances, hi particular the screen element may be made of woven or welded wires such as Profile wire (or wedge wire) giving a high open area. Alternatively the screen element might be formed from a metal or plastics plate in which holes are drilled or punched for ease of fabrication. Further the screen element may be provided with an undulating surface to increase the effective surface area and consequently the open area of the screen element. The screen element is preferably attached to the panel frame by clips formed integrally with the screen element and enable easy replacement of the screen element on the frame. Replaceable screen element also make the changing of aperture specification easier as the frame does not change allowing lower inventory costs and enabling rapid change of specifications for an installed band screen. The preferred construction of the screen panels with a strong plastics frame and a replaceable screen element provides a robust and durable solution. In particular

because the screen element can be made of a material suited to the application, the system is readily adapted to difficult environments. For example, if the liquid being screened is corrosive the screen element may be made out of a corrosion resistant material such as stainless steel. Embodiments of the screen panel may have aperture sizes ranging from 10 mm to as little as 1/2 mm.

Preferably, the holes are of circular cross-section so as to ensure uniformity of screening but other shapes such as square, rectangular hexagonal and triangular holes may also be employed. The screening panel frame may be moulded from any plastics material that has suitable moulding characteristics, including a composite plastics material, such as, for example, a fibre-reinforced plastics material. One especially preferred material is polyurethane.

Brief Description of the Drawings

A number of embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a screening panel for use on a band screen;

FIG. 2 is an elevation view of a band screen employing panels similar to that of Fig. 1;

FIG. 3 is a top view of the band of Fig. 2;

FIG. 4 is a perspective view of a frame of the screening panel of Fig. 1;

FIG. 5 is a perspective view of a screen element of the screening panel of Fig. 1 ;

FIG. 6 is a perspective view from the bottom of the screening panel of Fig. 1 ; FIG. 7 is a top view of a screening panel similar to the screening panel of Fig. 1 but with a different hole specification;

FIG. 8 is a side view of an alternative screen element to the screen element of Fig. 5;

FIG. 9 is atop view of the screen element of Fig. 8; and. Fig. 10 is a top view of a screening panel similar to the screening panel of Fig. 1 but with a parallel array of profile wires instead of a perforated plate as the screening element.

Detailed Description of Preferred Embodiments

Referring to FIG. 1, the screening panel shown is suitable for use on a band screen of the type illustrated in FIGS. 2 and 3.

The panel 10 comprises a moulded polyurethane frame 17 and a screen element 11 with a plurality of apertures 16. The frame 17 of each panel 10 excluding the connection knuckles 12 and 15 is about 20 mm thick, has a length of about 130 mm and a width of about 150 mm. The connection knuckles 12 and 15 extend from opposite ends of the frame and co-operate with gaps 14 and 13 between the knuckles 15 and 12 respectively of adjacent panels, such that a pin may be passed through holes 18 in connection knuckles 15 of one panel and connection knuckles 12 of an adjacent panel to join the panels with a hinged joint. In the illustrated embodiment, the outer diameter of the knuckles 12, 15 is in the order of 40 mm and the diameter of the holes 18 is in the order of 26 mm.

In the embodiment illustrated in Fig 1, the screen element 11 has apertures 16 which are drilled or punched through the thin metal plate or sheet material (in the order of 2 mm thick) of the screen element. The apertures 16 occupy in the order of 30% of the total area of each panel 10 and are of circular shape, however the open area will vary depending on the size and configuration of the openings. The apertures 16 of the illustrated embodiment have a diameter of about 4 mm and are arranged in offset rows with a pitch of 7 mm between rows however other hole diameters in the range of 1 to 20 mm and pitches of in the order of 1.75 times the hole diameter may be provided depending on the application.

Referring to Fig 2 and 3 the screening panels 10 are mounted as a single row about a path defined by guides 20, 28 of a band screen 21, and are driven by a driving sprocket 22 to rotate the screen panels 10 into and out of the liquid 23, 24 being screened. A set of walls 25, 26 divide the liquid yet to be screened from the liquid that has passed through the screen, the front walls extending from the front of the guides 20 to the sides of the container in which the liquid is flowing and the wall 26 closing the area defined by the rear guides 28. While the illustrated embodiment shows a single row of panels, in certain instances, two or more such rows of panels may be provided in side by side abutting relationship to increase the screening area. As indicated by arrows in FIG. 3, liquid 23 enters the band screen system 21 through the opening 29 between the walls 25 and flows outwardly through the screening panels 10 passing around the lowermost part of the guides 20 which are submerged. Thus, the screening side 31 of each panel 10 faces radially inwards, and the liquid 23 on the inlet side is

presented to the surface 31 to be screened and passing to the outlet side as screened liquid 24.

As mentioned above the construction of the screen panel 10 comprises a frame

17 to which is fitted a screen element 11. The frame 17 of a screen panel 10 is illustrated in Fig. 4 without the screen element fitted. The frame comprises longitudinal outer members 41 and transverse outer members 42 and longitudinal inner members 43 and transverse inner members 44 which together define a plurality of openings 45. The longitudinal outer members 41 and transverse outer members 42 have recesses 46 along their inner upper surfaces and the upper surfaces of the longitudinal inner members 43 and transverse inner members 44 are flush with the recesses 46 to provide a support surface for the screen element 11.

The knuckles 12, 15 which join adjacent screen panels extend from the outer surfaces of the transverse outer members 42.

Slots 34 are provided in the longitudinal outer members 41 and the transverse outer members 42 at the outer extremities of the recesses 46 to receive clips extending from the screen element 11 to retain the screen element in engagement with the frame

17 when the screen element sits in the recesses 46 and rests on the longitudinal inner members 43 and transverse inner members 44.

Turning to Fig. 5, the screen element 11 has a plurality of downwardly projecting clips 36 with inwardly pointing flanges 37, extending from its outer edges and located to co-operate with the slots 34, such that by springing the clips outwardly and inserting them into the slots 34 and then releasing the clips, the clips 46 engage the slots 34 with the flanges 37 extending under the longitudinal outer members 41 and the transverse outer members 42 to retain the screen element 11 in position on the frame 17. An underside view of the screen panel 10 with the screen element 11 clipped to the frame 17 is illustrated in Figure 6, while Fig. 7 shows a top view of a panel 10 with a screen element 11 fitted having a different hole size. Removal of a screen element 11 to replace it with a new screen panel in the case of wear or if the screening size requires change is simply a matter of springing the clips outwardly to allow the clips to be withdrawn from the slots 34 in the longitudinal outer members 41 and the transverse outer members 42.

Figs. 8 and 9 illustrate an alternative screen element 11 having a wavy surface defined by peaks 51 and troughs 52 running in a direction preferably corresponding to the transverse direction of the screen panel 10. By providing a wavy surface the open area on the screen can be increased for the same projected area, however it makes fabrication of the clips along two sides of the screening element more difficult as they

cannot be simply folded out of the same sheet of material and will either require welding or a more complex stamping operation. The peaks 51 and troughs 52 will preferably define a wave amplitude and a wavelength each of which is in the range of 1.5 to 3 times the diameter of the holes 16. The angles defined by the converging faces of the waves (measured at their mid points) are preferably in the range of 70 ° to 110° . In one preferred embodiment the holes 16 are 4 mm in diameter with a pitch of 10 mm and are arranged in offset rows spaced by 7 m, while the waves have a wavelength and amplitude of 10 mm and the angle of the faces is 90° .

Fig. 10 shows a top view of an alternative embodiment in which a panel 10 is fitted with a screen element 39 having a plurality of parallel wedge wires welded to a supporting structure (not shown).

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.