AU731011B2 - Improved ore screening panel - Google Patents

Description

AUSTRALIA

Patents Act TRUE COPY COMPLETE SPECIFICATION STANDARD PATENT I certify that the following o pages are a true and correct copy of the description and claims of the original complete specification in respect of an invention entitled: Improved Ore Screening Panel Name of Applicant: Richardson Pacific Limited [A c N 004 067 243] Signature: Improved Ore Screening Panel This invention relates to improvements in ore screening panels used in the separation and grading of materials in the mining and quarrying industries.

Background to the invention Australian patent 482212 proposed a modular screening panel system for ore screening decks which is now widely used by the mining industry and replaced the 0io earlier screening cloths, and large wire screening frames. The screening panels were all of the same size [eg. 300mm] and made of reinforced polyurethane. The panels are adapted to be secured to an underlying support frame using dependent •spigots which are a force fit into corresponding apertures in the support frame.

Patent 517319 provided an alternative method of securing the panels to the frame •15 using a pin expanded fastening concept.

A difficulty encountered in using these panels is that the screening apertures can *become clogged with material failing to pass through the apertures. When a portion o of a screen deck is affected in this way it is said to be blinded and a blinded screen is less efficient because of the reduction in open area. Blinding of screening panels is most prevalent in dry screening where there is no water to wash out the apertures and where the aperture size is below 10mm. Problems are encountered also in dry screening where the water content of the ore is high enough to encourage agglomeration of ore fines.

Patent 538559 attempted to address this problem by making the ribs which define individual screen apertures of different flexural strengths by varying the cross sectional dimensions or internal reinforcements..

Patent 608392 also sought to overcome this problem by providing greater flexibility to the periphery of each aperture. Thiswas achieved by providing zigzag ribs 3o extending across the panel to define screening apertures between the ribs. The self cleaning action is thus dependent on the shape and arrangement of the apertures in the screening surface.

It is an object of this invention to improve the self cleaning action of screening panels in a manner which is independent of the aperture configuration or construction.

Brief description of the invention To this end the present invention provides a flexible ore screening panel adapted for mounting on a screening deck, which includes a screening surface integrally formed on a reinforcing frame part of which lies below said screening surface, wherein the screening surface is only attached to the frame at its periphery.

The panel is cast, injection moulded or vulcanised elastomeric material, preferably polyurethane, having embedded within it reinforcing bars which define the outer edges of the panel and extend across the inner area of the 1: 5 panel to provide support to the screening surface. The reinforcing can be of plastic or metal. Steel has conventionally been used, but fibre reinforced plastics are preferred because of their lighter weight and resistance to *corrosion. The minimum reinforcing used is a set of edge bars and a cross bar extending from one edge to the opposite edge parallel to the remaining 20 two edges. In this arrangement there is no connection or attachment between oo *the screening surface and the cross bar.

Unexpectedly this modification has a dramatic effect on the ability of the screening surface to be self cleaning. The surface is able to flex and vibrate in a manner akin to a screening cloth. In the prior art the screening surface was always rigidly supported by the reinforced sub-frame of the panel.

In another embodiment of this invention the reinforcing bars are located only about the periphery of the panel. This achieves the same flexibility across the screening surface. Under light load conditions the panels without central reinforcing function effectively and are self cleaning. However under heavier loads the absence of any support can lead to undue stretching of the surface or even damage it.

This invention is applicable to any modular screening panel including those of the type described in patent specifications 482212, 517319, 538559, 608392 and 644293. The disclosures of these patents are incorporated herein by reference.

The method of manufacturing the panels according to this invention is the same as for conventional panels as outlined in the above mentioned patents with the modification of omitting the reinforcing bars which lie beneath the screening surface or severing the connection between the screening surface and the reinforcing ribs. This can be achieved by cutting with a hot wire or blade to separate the reinforcing rib from the screening surface or inserting a releasable plate into the mould to prevent the surface portion of the panel 0io from becoming attached to the support rib.

Detailed description of the invention S.i A preferred form of the invention will now be. described with reference to the drawings in which: Fig. 1 is a plan view of one screening panel in accordance with the invention; 15 Fig. 2 is side view of the panel shown in fig. 1; Fig. 3 is a fragmentary plan view of a screen deck with a panel as shown in *:fig.l in place; Fig. 4 is a view along the line 4-4 of figure 1.

2o The screening panel 10 is apart from the modification proposed by this invention a conventional modular screening panel. It will be made from polyurethane or some other hard wearing plastic or rubber material and have a shore hardness of 70-90 selected to correspond to the type of particulate ore to be screened.

The screening surface 12 is shown with the zigzag ribs 14 forming apertures 32 as disclosed in patent 608392. However any aperture configuration may be utilised with this invention. The panel 10 is stiffened by the reinforced peripheral frame 16 and the central cross rib18 which extends between two opposed sides of the frame 16. The whole panel is an integral unit moulded about reinforcing bars which are embedded in the frame 16 and the cross rib 18. The reinforcing bars embedded in the frame may be of steel or rigid plastic such as fibre reinforced plastic.

In order to secure the panel in place on the screen deck 25, the panel 10 has a series of protrusions 22 dependent from the frame 16 and composed of the same material as the panel. The protrusions shown are of the kind proposed in patent 482212 and are headed spigots with shoulders 24 which abut the underside of the support frame 26. The support frame 26 is of L or U section steel and has a series of holes 28 to accept opposing pairs of protrusions 22 from abutting panels 10. In the case of headed spigots 22 as shown the protrusions are forced through the holes 28 so that the shoulders 24 lie on the underside of frame 26. Alternatively the shouldered protrusions can be replaced by grooved protrusions used in combination with protrusion expanding pins as taught in patent 517319.

The improvement provided by this invention can best be seen in figure 4 where the slit 17 shows the separation of the screening surface 12 from the reinforced cross rib 18. Rib 18 provides support for the surface 12 but the 15 separation created by slit 17 ensures that the surface can vibrate across the full area of the surface 12 thus providing an increased amplitude of vibration which is believed to be the reason for the observed improved self cleaning action of the panel's screening surface. This improvement varies with the size and configuration of the screening apertures but is still observable in the case 20 of the self cleaning zigzag rib apertures as taught in patent 608392. The most effective aperture sizes are those below 10mm where blinding is most prevalent with conventional screens.

The slit 17 can be created by using a mould insert to separate the cross rib 18 from the panel surface 12 during the casting or injection moulding of the panel. An alternative method is to form the slit by cutting with a hot wire after the panel is formed.

In an alternative form of the invention the reinforcing bar is omitted from rib 18. This reduces the rigidity of cross bar 18 and increases the flexibility of the surface 12 and improves the self cleaning of the screening apertures in the surface 12. Care needs to be taken with this embodiment of the invention to ensure that the screening surface is not subjected to loads that could rupture the panel.

The screening surface 12 can be stiffened to counteract its increased k flexibility by providing dependent ribs beneath the surface or by increasing the thickness of the surface 12 of the panel 10. By varying these parameters an optimum panel can be designed for a particular ore and screen deck loading.

Panels according to the embodiment of figures 1 to 4 were tested in the dry screening of iron ore having a relatively high moisture content. Conventional panels with aperture sizes below 10mm, used in screening this ore, regularly suffer from blinding and reduced screening throughput. When the modified panels of Figures 1 to 4, having a range of aperture sizes below 10 mm' were 0io used, blinding was reduced and screening throughput increased.

From the above it can be seen that the present invention provides an improved self cleaning panel that is independent of aperture configuration which was the method previously proposed in patents 538559 and 608392.

The self cleaning action achieved by the present invention is more effective Is than the prior proposals and requires no modification to the moulds apart from the need for an additional insert.

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