1 SCREENING APPARATUS AND METHODS The present application is a divisional application from Australian Patent Application No. 2012201297, the entire disclosure of which is incorporated herein by reference. 5 FIELD OF THE INVENTION The present invention relates generally to apparatus for screening, separating or grading materials, principally for use in the mining industry. The present invention is particularly directed to a system for fixing screen panels to the support frame of a 10 vibratory screening machine. The apparatus is applicable for screening, separating and grading mining ores and other materials, and it will be convenient to hereinafter describe the invention in relation to that use. It is to be appreciated, however, that the invention is not limited to such apparatus and use. 15 BACKGROUND OF THE INVENTION A reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission that that document or matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims. 20 Screening apparatus of the type with which the invention is concerned is generally used for screening, grading, or separating materials such as mining ores and comprises an array of screen panels which are removably fixed to a frame to provide a continuous screen deck. The material to be screened is fed onto the deck at one 25 end and the apparatus is vibrated so that the material moves over and through its screening surface. One form of screen panel includes a steel frame moulded within a resilient plastic material, such as polyurethane. See for an example of such a screen panel, 30 Australian Patent No. 577767 (66006/86). The plastic moulding forms the major part of the panel and it is in the plastic moulding that the openings for screening are provided. <filename> 2 The screen panels in a screen deck are usually subject to wear, due to the abrasiveness of the mining ores or materials typically being screened, and thus the screens require periodical replacement. This presents a difficulty with the attachment of the panels to the deck frame, as the attachment must be secure and robust, but 5 preferably should also be releasable in a manner that is quick and easy. Systems have been developed in the past for fixing screen panels to a support frame of a screening deck, whereby individual panels can be removed and replaced when worn. One system used for fixing screen panels to a support frame is disclosed in 10 Australian patent 654091. The system of that patent provides an elongate U-shaped fixing member for securing to the support frame so as to extend longitudinally between side edge regions of adjacent screen panels. The fixing member has a pair of connection portions, with connection elements being provided along the outer side surfaces of the connection portions and the side edge faces of the screen panels. The 15 connection elements of each connection portion and an associated screen panel interconnect to hold the screen panels in position on the support frame. The connection portions are inwardly deflectable away from the side edge faces of the screen panels in order to disengage the connection elements and disconnect the screen panels from the fixing member. A retaining member is provided for insertion 20 between the connection portions to resist their inadvertent deflection, and thus maintain engagement between the connection elements when required. The above fixing system performs generally satisfactorily. However, one disadvantage is the relatively complex configuration of the outer side surfaces of the 25 connection portions and the side edge faces of the screen panels provided by the connection elements. That complexity can add to the cost of production of the screen panels. In addition, the connection elements can sometimes be susceptible to dirt accumulation during use and/or storage. That accumulation must be removed before complete and proper interconnection of the connection elements can be achieved 30 during screen panel installation, in turn leading to delays or difficulties with that installation. Where the removal of a panel from a deck is not straight forward and quick, the maintenance personnel can often look for alternative methods of removal that quickly <filename> 3 release the panel from the deck even though those methods might have other drawbacks. For example, it is known for maintenance personnel to cut out a portion of the moulded plastic material between the steel frame of a screen panel and to lift the panel forcibly from the deck by crane or other lifting equipment. This meets the 5 objective of quick removal but because it destroys the components fixing the panel to the frame of the deck, some of those components can be discharged into the screened material below the deck, thereby polluting that material with foreign matter. That foreign matter can be plastic pins for example. End users of the screened material dislike the material they purchase polluted in this manner. 10 In addition, the installation of a complete set of panels to a screening deck requires precise alignment of the panels adjacent to each other, so that the deck does not include gaps between adjacent panels. In fine screening applications, gaps between panels can provide a pathway for material to flow through the deck that would 15 otherwise be too large to pass through the screening openings in the panels. Thus, where the panels are not aligned precisely, the screened material will potentially include material that is of a different and larger grade to that intended. Also, gaps that exist between panels can allow ingress of fine material ("fines") into 20 the mechanisms that are used to fix the panels to the screening deck. This can have two disadvantageous consequences. Firstly, with the vibratory machine vibrating, the fines act as an abrasive against the fixing mechanism, often causing it to wear and thus loosen, and eventually to fail. Secondly, the fines can become highly compressed between components, such as in gaps created by wear, due to the 25 constant vibration and impact of ore in that condition, which can hinder the removal of panels and their fixing mechanisms. The compressed fines can also form layers that have to be removed before new parts are installed and removal can be time consuming and difficult. 30 Applicant has recognised the desirability to provide a screen panel fixing system which is simplified compared to some of the prior art arrangements and which provides for quick or quicker release of screen panels from a screen deck. SUMMARY OF THE INVENTION <filename> 4 According to the invention there is provided a screening apparatus, including: a plurality of spaced apart, substantially parallel elongate beams, a plurality of screen panels mounted to the beams to form a broad screening surface, each of the panels being generally square or rectangular to define four side 5 edges and the panels being mounted so that facing side edges of adjacent panels are in close facing relationship, the panels being mounted to the beams by elongate fixing members that extend in the longitudinal direction of the beams and that are fixed to the beams and engage opposite side edges of the panels, the fixing members having an elongate 10 base, an elongate web which is upstanding from the base and an elongate head at the top of the web and spaced from the head, each of the base and the web extending laterally on either side of the web, the fixing members defining an elongate recess between the base, the web and the head on each side of the fixing members and the side edges of the panels defining an elongate projection for receipt within the 15 recess, whereby the recesses on opposite sides of the fixing members receive the projections of the side edges of a pair of panels located on opposite sides of the fixing member. A screening apparatus according to the above form of the invention advantageously 20 simplifies the fixing member compared to some of the fixing arrangements of the prior art. A single centre web is provided and is configured to locate the side edges of a pair of panels on opposite sides of the fixing member. The base can present an upper facing surface on which a facing surface of a panel 25 can be supported. The head of the fixing member can have an inclined upper surface comprising a substantially central apex and a pair of surface portions that extend from the apex in a direction toward the beams, or in other words, downwardly towards the beams. Such 30 an arrangement can assist insertion of the side edge projection of a screen panel into the recess as the projection can slide along the inclined surface before entering the recess. In this respect, the projection has to be forced past the head to enter the recess and the inclined surface assists passage of the projection past the head.
5 The side edges of a pair of panels that connect to a fixing member can extend over the surface of the upper surface of the head so that the side edges engage in abutting relationship approximately at the apex. The abutting engagement is important to prevent passage of screening material between adjacent panels. The material of the 5 panels can be selected to slightly compress in abutting engagement and for this, the side edges of the panels can extend slightly beyond the apex so that when two panels are brought into connection with the fixing member, the compressing abutment takes place. 10 The materials that are used to form the components of the invention can be selected from any suitable materials. Polyurethane is a material that is suitable for panel construction and for construction of the fixing members. Other polymer materials can also be used as can metal, plastics and rubbers or any other suitable material. 15 A screening apparatus has also been developed that allows for some flexibility in the positioning of the panels in a deck, so that the panels can be aligned to eliminate gaps between adjacent panels. That development is claimed in Australian Patent Application No. 2012201297 and relates to a screening apparatus that includes: a plurality of spaced apart, substantially parallel elongate beams, 20 a plurality of screen panels mounted to the beams to form a broad screening surface, each of the panels being generally square or rectangular to define four side edges and the panels being mounted so that facing side edges of adjacent panels are in close facing relationship, each panel being mounted to a pair of beams along opposite side edges to bridge between a two adjacent beams, 25 the panels being mounted to the beams by elongate fixing members that extend in the longitudinal direction of the beams and that are fixed to the beams and engage opposite side edges of the panels, the fixing members including a pair of projections that extend through openings in the beams from an upper side of the beams, each projection being engaged on the underside of the beams by a 30 releasable connector to releasably connect the fixing members against release from the beams, the openings through which the projections extend being of a greater diameter than the outside diameter of the projections, so that the projections are a loose fit within the openings. <filename> 6 A screening apparatus of the above kind has various advantages, in particular that it allows shifting movement of the panels fixed to the fixing members on the beams, by the openings of the beams being of a greater diameter than the outside diameter of 5 the projections of the fixing members. This allows the panels to be shifted relative to one another and relative to the beams on which they are mounted, to ensure close fitting and aligned connection or engagement between side edges of adjacent panels. A screening apparatus of the above kind can minimise or even eliminate the prospect 10 of misalignment between panels of a screening deck. In some prior art decks, the panels are fixed in place once they are fixed to the beams. Accordingly, any inaccuracy in the fixing arrangements employed with those panels could leave gaps between the panels or misaligned panels. For reasons given earlier herein, misalignment of panels can result in inefficient performance of the screening deck. In 15 the screening apparatus as disclosed herein, once the panels are fitted to the beams through the fixing members, the panels can still be shifted relative to the beams, albeit only through a small amount of movement. That amount of movement however can be enough to ensure that the panels engage properly along side edges thereof and in proper alignment, as required for better performance. 20 The present invention further extends to a fixing member and a screen panel for the screening apparatus discussed above. For a better understanding of the invention and to show how it may be performed, 25 embodiments thereof will now be described, by way of non-limiting example only, with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates a portion of a screening deck according to one embodiment of the 30 invention. Figure 2 illustrates a fixing member according to the present invention. <filename> 7 Figure 3 is a cross-sectional view of a screen panel and fixing members connected together. Figure 4 is a view of a section of a longitudinal beam with a fixing member fitted 5 thereto. Figure 5 is a perspective view of a releasable connector in the form of a locking clip for use in the screening deck of Figure 1. 10 Figure 6 is an underneath view of the screening deck of Figure 1. DETAILED DESCRIPTION OF THE DRAWINGS With reference to Figure 1, a portion of a screening deck 10 is illustrated, comprising 15 a plurality of elongate, longitudinal beams each of which is formed from an angle of steel having a long portion 12 and a short portion 13 disposed substantially at right angles. While the beams extend in the longitudinal direction of the screening deck 10, the beams can equally extend perpendicular to the beams 11 and the invention applies to that form of screening deck as well. The beams 11 in a screening deck can 20 be of any length, such as increasing from 4' to 28' in 2' increments. The width dimensions likewise can be of any length, such as increasing from 2' to 14' in 2' increments. Metric sizes in screening decks are less common than imperial sizes. The deck 10 illustrated in Figure 1 is a portion of a deck only and does not show the 25 side edge beams that define the edge of the deck. The portion of the deck that is shown in Figure 1 is sufficient however to describe the invention. Six beams 11 are illustrated in Figure 1. In current machinery, the beams 11 are often spaced an imperial foot apart thus requiring nine beams for an 8' width. 30 The beams 11 extend parallel to one another and support screen panels 15 on the upper face of the short portion 13 of each beam 11. The panels illustrated in Figure 1 can be of any suitable size, but a common size is an imperial square foot (305mm x 305mm). However, alternative sizes of panels can be employed, such as 1' x 2' (305mm x 610mm). <filename> 8 As indicated above, the screening deck is one part of the overall screening apparatus. The deck is supported on a frame and is connected to a vibration generator. The vibration that is generated is significant and requires the panels 15 to be securely 5 fixed to the beams 11. The panels are also subject to wear over time and even though the fixing of the panels to the beams is required to be secure, the preference is also that the panels be easily releasable to facilitate replacement. The panels 15 include a plurality of openings through the top surface thereof for 10 screening product such as mining ore. The openings in the panel 15 can vary from large to very small depending on the size of the screened material which is to be produced. Typically, an ore is fed onto one end of the deck 10 and a vibrating arrangement 15 vibrates the deck 10 tending to shift the ore from one end to the other, with some of the ore passing through the openings of the panels 15 as it travels over the deck. Ore which does not pass through openings in the panels 15 is collected at the trailing end of the deck 10 opposite to the feeding end and can be retreated, such as re-crushed, or it can be used for other purposes or discarded. 20 Figure 1 shows several portions on the deck 10 that do not have panels installed. These vacant portions illustrate that the panels 15 can be removed when they have become worn or otherwise damaged. The portion of the deck 10 marked R, shows four missing panels, but otherwise illustrates fixing rails 20 to which panels 15 are 25 attached. The fixing rails 20 are fixed to the upper surface of the short portion 13 of the beams 11 and more detail on the construction of the fixing rails 20 and their connection to the beams 11 will be made later herein. The portion of the deck 10 marked R 2 shows three missing panels, and also shows 30 the upper surface 21 of the short portion 13 of the beams 11 with the fixing rails 20 absent. The screening deck 10 includes panels 15 shown in close proximity to each other. The preference is that the panels 15 actually make contact along their edges so that <filename> 9 there are no gaps between the panels when they are fitted. Any gaps between adjacent panels 15 can provide a pathway for the flow of material being screened. In some prior art arrangements, a cover strip has been applied between adjacent panels to overlie the junction at the upper surface of adjacent panels to cover any gaps 5 between them. However, the cover strip added another component to the fixing system of those kinds and therefore was not a satisfactory solution. In the present invention, in order to ensure a close fit between the side edges of the panels 15, a unique form of fixing member or rail (hereinafter "fixing rail") and fixing member or rail system has been invented. 10 Figure 2 is a perspective view of a fixing rail 20 according to one form of the invention and comprises a top surface 25 which is formed of two inclined surfaces 26 and 27 which meet at an apex 28. The top surface 25 forms part of a head 29 which extends from a web 30 while the web 30 extends from a base 31. The head 29 has a greater 15 lateral extent than the web 30 and so the head overlies the web 30 on each side of the web and as shown in Figure 2, forms a recess 32 with the base 31 on each side of the web 30. The underneath surface 33 of the base 31 is generally planar or flat. It is the surface 20 33 which rests on the upper surface 21 of the longitudinal beams 11. The base 31 extends laterally beyond the opposite sides of the web 30 and the head 29. The distal edge of the base 31 on each side of the web 30 is formed with an upwardly extending lip 39. The lip 39 is shown as extending fully along the length of the fixing rail 20, although this is not required in all forms of the invention. For example, the lip 25 39 could be provided only at each end of the base 31 and centrally between each end. Other discontinuous or intermittent arrangements of this kind could be employed. The fixing rail 20 includes a pair of projections in the form of locating posts 34 and 35 30 that extend from the base 31 away from the head 29. The post 34 comprises a first cylindrical section 36 and a second cylindrical section 37. The first cylindrical section 36 is of greater length but reduced diameter compared to the second cylindrical section 37. Accordingly, a step or shoulder 38 is formed at the junction between the <filename> 10 first and second cylindrical sections 36 and 37. The construction of the post 35 is identical to the post 34 as discussed above. The configuration of the fixing rail 20 is such as to capture a side edge of a panel 15 5 as shown in cross-section in Figure 3. In that figure, a panel 15 is shown connected between a pair of fixing rails 20 which are each of the same identical form. The side edges 40 of the panel 15 include an inclined face 41 which is inclined at approximately the same angle as the inclined surfaces 26 and 27 of the fixing rails 20. The side edges 40 further include recesses 42 to accept a portion of the head 29 and 10 they include a projection 43 to fit within the recesses R of the fixing rails 20. By this arrangement, an interconnection is created between the side edges 40 of the panels 15 and one side of a pair of facing fixing rails 20. It can be seen that the inclined face 41 extends to a side surface 44 and this surface 15 44 extends slightly beyond the apex 28 of the fixing rails 20. This slight extension beyond the apex 28 is to ensure abutting and preferably compressive contact between adjacent panels 15. Thus, it will be appreciated that in the arrangement of Figure 3, further panels 15 will be fitted to the sides of the fixing rails 20 not already connected to the illustrated panel 15. Those further panels 15 will have the same 20 construction as the illustrated panel 15 so that they will each include equivalent surfaces 44. Because those surfaces would, without any interference, extend just past the apex 28, the surfaces 44 of adjacent panels 15 will firmly abut each other. Moreover, because the side edges 40 of the panels 15 are of a flexible material, the edges 40 will compress in abutment. This ensures that in side to side contact 25 between adjacent panels 15, gaps are either minimised or eliminated. The construction of the fixing rails 20 and the panels 15 shown in Figure 3 also permit easy installation of a panel 15 into connection with the fixing rails 20. The fixing is made by inserting the projection 43 of one side edge 40 of the panel 15 into the 30 corresponding recess R of the fixing rail 20 with the panel at an angle, for example at 300. The panel 15 is then pivoted about the projection 43 in recess R to bring the other side edge 40 down toward the other fixing rail 20. Because the panels 15 and the fixing rails 20 are made of a flexible material, polyurethane for example, the other projection 43 can be forced into the recess R. The force load is one which any worker <filename> 11 would be expected to be able to apply manually. The fitting is thus simple and easy and requires no particular skill. The inclined surfaces 26 and 27 form a ramp for the side edge to slide down as the 5 panel 15 is rotated to bring the projection 43 into the recess R. When the projection 43 is captured in the recess R, the head 29 secures the panel 15 against lifting. The dimensions of the side edge 40 of the panel 15 and of the fixing rail 20 ensure the panels 15 are securely held in place. 10 The fixing rails 20 are fixed to the beams 11 by passing the projections (hereinafter "posts") 34 and 35 through openings 48 and 49 (see Figure 1) in the beam 11. The openings 48 and 49 can be of a greater diameter than each of the first and second cylindrical sections 36 and 37, or the openings can be of a greater diameter than just the first cylindrical section 36. Where the openings 48 and 49 have a greater 15 diameter than the second cylindrical section 37, each of the posts 34 and 35 can pass through the openings 48 and 49 easily. Alternatively, where the opening is of a greater diameter than the first cylindrical section 36 but not the second cylindrical section 37, the posts 34 and 35 are forced through the openings 48 and 49. 20 Figure 4 shows an underneath view of a section 50 of a longitudinal beam 11, with a fixing rail 20 applied to the upper surface 21 of the short portion 13. The post 35 is shown extending through the opening 49. It can be seen that the second cylindrical section 37 has cleared the opening 49 and is spaced below the lower surface 51 of the short portion 13. In the arrangement of Figure 4, the opening 49 is slightly of 25 reduced diameter compared to the second cylindrical section 37. Thus the section 37 must be forced through the opening 49 and in order to facilitate this, the section 37 includes a conical leading end 52. It will be appreciated that the clearance between the first cylindrical section 36 and 30 the opening 49 occurs for each of the locating posts 34 and 35. Thus, when the posts have been inserted through the openings 49, the fixing rails 20 have a degree of movement available to them relative to the beams 11, such as up to 8mm or more. That small amount of movement permits the rails to be moved so that the panels 15 can be shifted as necessary to bring adjacent side edges into abutting contact. That <filename> 12 differs from the prior art in which no flexibility of this kind is available. That is, the fixing systems of the prior art often requires precise manufacture of the components, because any inaccuracy could mean that the panels could be inaccurately positioned in the deck, leaving gaps between panels. Because of this, some prior art 5 arrangements employed the cover strips discussed above. In contrast, the present illustrated arrangement permits limited movement of the panels prior to final fixing, so that any inaccuracy in the component manufacture can be accommodated. Advantageously, this movement is in any direction lengthwise or widthwise of the screening deck. 10 In order to fix the fixing rail 20 to the beam section 50, a releasable connector in the form of a locking clip 55 is employed. The locking clip 55 is shown in perspective view on its own in Figure 5 and comprises arms 56 and 57 which extend on either side of a part cylindrical opening 58. The diameter of the opening 58 is sized to 15 snugly receive and engage against the first cylindrical section 36 of each of the posts 34 and 35. The locking clip 55 is formed of a flexible material which allows the arms 56 and 57 to splay outwardly so that the opening can accept the first cylindrical section 36 and to move back in to a position snugly about that section. The material can be polyurethane. 20 Installation of the locking clip 55 is simple. The clip 55 is simply pushed into place about the first cylindrical section 36 between the lower surface 51 of the beam 11 and the shoulder 38 of the locating posts 34 and 35. This can be by finger pressure, or more likely by a suitable tool, e.g. a hammer or mallet. To facilitate ease of 25 installation, the leading edge of the arms 56 and 57 is chamfered on each side. The thickness W of the locking clip 55 can be varied to suit different dimensions of beam and locating post length. What is preferred is that the wall thickness of the locking clip 55 forms a tight fit or a friction fit between the lower surface 51 of the 30 beam 11 and the shoulder 38 of the locating posts 34 and 35. The locking clip is intended to apply a load to the shoulder 38 to fix the fixing rail 20 in place against movement relative to the beam 11. Thus, once the locking clips 55 have been inserted, the fixing rails 20 should no longer have freedom for release of the locating posts 34 and 35 from the openings 48 and 49 of the beams 11. <filename> 13 The locking clip 55 includes a release projection 59 which is provided to facilitate release of the locking clip 55 from about the first cylindrical section 36 of the posts 34 and 35. Release of the locking clip 55 is required when the fixing rail 20 is to be 5 removed from the beams 11 upon wear or failure. The release is likewise simple as the projection 59 can be gripped by fingers or a suitable tool to physically withdraw the locking clip from the position shown in Figure 4. Once the locking clip 55 is removed, and this is the case in respect of the post 35 shown in Figure 4, the post 35 can be withdrawn from the opening 49. 10 Figure 6 illustrates an underneath view of the screening deck 10 of Figure 1 showing the locking clips 55 in position about the posts 34 and 35 of various fixing rails 20. A screening deck 10 is assembled by firstly arranging the beams 11 in position and 15 thereafter fixing the rails 20 to those beams 11. The fixing rails 20 can be positioned and the locking clips 55 applied and the panels 15 then fitted. The preference is to fit the clips 55 to the fixing rails from above the deck 10, rather than from below the deck 10. In fact, for safety reasons, access to the deck 10 from underneath may be restricted so that fitting of the fixing rails 20 must take place from above the deck. 20 With the fixing rails 20 in place, the panels 15 of a first row can be connected to the fixing rails 20. Advantageously, the use of oversize openings 48 and 49 allows movement of the panels and fixing rails relative to the beams 11 so that a snug abutting fit between side edges of adjacent panels can be created. The locking clips 25 55 can be arranged so as to allow movement of the fixing rails 20 and thus the panels 15 even though the locking clips are in place. The locking clips can resist movement of the fixing rails 20 and the panels 15 but not exclude it. Thus, by the use of the oversize openings 48 and 49, the screening deck 10 can be 30 formed without gaps between adjacent panels 15 and without the need for covers of the kind described above between adjacent panels. This differs from some prior art arrangements, in which the fixing rails 20 are fixed relative to the beams 11 without allowing for movement to ensure abutting engagement between adjacent panels. Because of this, gaps between panels can arise and this can allow screenings which <filename> 14 are produced to travel through the deck 10 and into the mechanism below it, or the screenings below it. Moreover, the construction of the fixing rails 20 comprising a central post and a head 5 which can be used to capture the side edge of a panel provides for quick and easy installation of panels to the fixing rails 20. The same arrangement also allows for quick and easy removal of panels, whereby simple insertion of a screw driver or other suitable removal tool at one end of a fixing rail can dislodge the panel from the fixing rail and the panel can thereafter be lifted or rotated out of engagement with the fixing 10 rail. Once disengagement of one side edge of the panel from a fixing rail has been made, the panel can easily be removed out of connection with the other fixing rail. Still further, once a worn or damaged panel has been removed, replacement with a another panel is a simple operation which involves inserting one side edge of the 15 panel into one of the fixing rails and thereafter rotating the panel to fit the other side edge into the opposite fixing rail. The apparatus described in relation to the figures is also very simple, comprising a limited number of parts. In fact, the fixing system simply comprises the fixing rails 20 20 and the pair of locking clips 55, each of which is identical. Thus, each fixing rail which can fix a pair of side edges of two panels, comprises three parts for installation, being the fixing rail itself and two locking clips. This differs from previous arrangements where a greater number of parts was required and this is disadvantageous from both a manufacturing and storage point of view, and an assembly point of view. In relation 25 to assembly, it needs to be kept in mind that once a screening apparatus is in place in a mining environment, down time of the screening machine for repair or replacement of panels can be costly and therefore a simple system to facilitate quick and easy panel replacement is desirable. Moreover, systems which do not foul the screened material are also desirable 30 The invention described herein is susceptible to variations, modifications and/or additions other than those specifically described and it is to be understood that the invention includes all such variations, modifications and/or additions which fall within the spirit and scope of the present disclosure. <filename>