1 Adjustable rollers for a discharge door system The present invention relates to an apparatus which ensures correct opening and closing of a door along rollers in a slideable door system. In particular, the present invention relates to improvements in discharge door systems of rail wagon grain and mineral sand hoppers. 5 BACKGROUND OF THE INVENTION A grain and mineral sand hopper including a bottom discharge door slideable on rollers is taught in the present Applicant's co-pending Australian patent application no. 2009238310, the contents of which are incorporated by reference herein. It is to be understood that this is but one application of the present invention, and that the roller apparatus taught herein could equally well 0 be applied to other applications involving a slideable door. Some problems have been encountered using the discharge door system of the abovementioned patent application, as well as other similar slideable discharge door systems, both post-manufacture and during the life of the door systems. It is inevitable that when new wagons are built, the fixed rollers which support the door slide will not always align perfectly 5 and contact the door, this being due to engineering tolerances and other factors. During use, wear and tear causes further misalignment of the rollers. Over time, the rollers which are intended to always contact a surface of the moving door slide become misaligned and hence whilst some rollers do maintain contact, others do not. The result of misalignment is that the load on the door is not evenly distributed across the 20 rollers and, in some cases, the door has been known to lift or ride up the supporting frame during opening. This is especially prevalent when there is a load bearing down on the door as is the case in a bottom discharge system. Thus, the use of existing roller apparatus lends itself to increased component repair and replacement costs. The present Applicant has thus recognised the need to be able to adjust the position of 25 each roller just after manufacture, and also throughout the life of the door system, to ensure equal contact is made with the associated door at all times. It is therefore an object of the present invention to overcome at least some of the aforementioned problems or to provide the public with a useful alternative.
2 SUMMARY OF THE INVENTION The invention provides a roller assembly for use with a discharge door of a rail wagon, comprising a frame including first and second parallel members, the first member including first mounting holes and the second member including second mounting holes coaxially aligned on 5 common axes with the first mounting holes,axle mounts including an axle aperture located in the mounting holes, and at least one roller with an axle mounted in the axle apertures of opposing axle mounts, wherein the axle apertures of the axle mounts are offset from the common axes of the coaxial mounting holes in which the axle mounts are mounted and wherein the axle mounts are rotatable in the mounting holes thereby allowing the position of the rollers to be adjusted. 0 Preferably the axles are bolts. In preference wherein the axle mounts include opposing flat sides thereby allowing the axle mounts to be readily grasped and rotated and are threadedly engage the mounting holes. 5 Preferably roller assembly as in any of the preceding claims, wherein the roller is a roller bearing. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of this 0 specification, illustrate several implementations of the invention and, together with the description, serve to explain the advantages and principles of the invention. In the drawings: Figure 1 illustrates an underside perspective view of a rail hopper chute and associated discharge door system including a prior art roller assembly; Figure 2a illustrates a cross sectional view of a roller bearing supported inside a frame and 25 forming part of an improved roller assembly according to the present invention, the fixed bolt, sleeve and roller bearing being a lowermost position such that the bearing does not make contact with the door plate; Figure 2b illustrates in cross section the right adjustable nut forming part of the improved roller assembly of Figure 2a which when rotated causes the fixed bolt, and hence 30 the associated sleeve and roller bearing to move towards the door plate; 3 Figure 2c illustrates a right hand end view of the improved roller apparatus including the adjustable nut and the fixed bolt in the position shown in Figure 2a; Figure 3a illustrates a cross sectional view of a roller bearing supported inside a frame and forming part of an improved roller assembly according to the present invention, 5 the fixed bolt, sleeve and roller bearing being an uppermost position such that the bearing makes contacts with the door plate; Figure 3b illustrates in cross section the right adjustable nut forming part of the improved roller assembly of Figure 3a which when rotated causes the fixed bolt, and hence the associated sleeve and roller bearing to move away from the door plate; 0 Figure 3c illustrates a right hand end view of the improved roller apparatus including the adjustable nut and the fixed bolt in the position shown in Figure 3a; Figure 4 illustrates a side view of the hopper bin of Figure 1 and a discharge door system slideable above the improved roller apparatus of the present invention; and Figure 5 illustrates an enlarged perspective view of three rollers forming part of the 5 improved roller apparatus of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detailed description of the invention refers to the accompanying drawings. Although the description includes exemplary embodiments, other embodiments are possible, and changes may be made to the embodiments described without departing from the spirit and scope 20 of the invention. Wherever possible, the same reference numbers will be used throughout the drawings and the following description to refer to the same and like parts. The present invention relates to an improved roller assembly 10 for particular use in association with a sliding discharge door system 12 associated with a rail hopper chute for carrying grain, minerals and the like. Figure 1 illustrates such a hopper chute 14 including a main 25 chute body 16, a slide door assembly 18, a locking mechanism 20 (which will not be described in detail herein for the purpose of brevity), and a prior art roller assembly 22. In brief, hopper chute 16 has an angled rectangular opening 24 which allows for gravitational discharge of materials, the front edge of the opening 24 being higher than the rear edge. Hopper chute body 16 also include top flanges 26 and 28 for attaching the body 16 to the 4 underside of a rail wagon hopper or the like (not shown), longitudinal side beams 30 and 32, and a transverse end beam 34 extending there between, for supporting various other components as described below. The sliding door assembly 18 includes a frame comprising frame members 38 and 40 5 suspended from an upper lip 42 which lines the sides and the rear of the chute opening 24. The side frame members 38 and 40 form part of the roller assembly 22 which includes a plurality of rotatable rollers 44, above which is supported a door slide 46 which is free to move between open and closed positions. The rollers are rotatable about pins 47 which extend through the frame members 38 and 40 and are not adjustable, but may indeed misalign over time for various 0 reasons, resulting in individual rollers and sometimes entire roller assemblies having to be replaced. Figure 1 illustrates the discharge door system 12 when the door slide 46 is in the open position. The locking mechanism 20 is used to prevent manual opening of the door slide 46, and for safety reasons in connection with automated opening. There is both a hydraulic and manual 5 means for opening and closing the door shown which, again, will not be described herein. The door slide 46 is therefore supported, both in the open and closed positions, between the rollers 44 and the lip 42 which lines part of the opening 24. When door slide 46 is in the closed position the upper surface of the door slide 46 partially seals the opening 24 by maintaining a very fine clearance with lip 42. 20 This door system is essentially self cleaning and self draining by way of gravity in that material is able to run off the angled door slide 46. It is far less likely for material to accumulate, minimising contamination and health issues, and the possibility of product being jammed when the door is dragged open. It is to be understood that this is but one embodiment of the present invention and that the improved roller system 10 could equally well be applied to other discharge 25 door systems. A problem which may be encountered over time is that some rollers 44 may become misaligned and hence will cease making contact with the door slide 46. Some of the problems which arise from roller misalignment are mentioned in the preamble of the invention. Turning to the roller assembly 10 of the present invention, the readers is directed to 30 Figures 2a-2c and 3a-3c in particular. There is shown a cross section through the assembly 5 transversely across one roller bearing 50. Figure 4 illustrates that there are five roller bearings 50 per assembly, however, this will depend on the size of the door slide 46 and other factors, and so the present invention is not intended to be limited to a particular number of rollers. For example, some applications may require only the one roller. As per the prior art roller assembly, it is 5 preferred that there are two roller assemblies 10 per door slide, each assembly extending longitudinally and spaced apart from one another on opposed sides of the door in a parallel arrangement. The present invention allows for each roller 50 in the assembly to be adjusted to compensate for misalignment that may occur throughout the life of the roller assembly 10. In 0 particular, the invention allows for rollers that are no longer contacting the door slide surface to be adjusted to contact the surface again. This will now be described in more detail. Each assembly 10 includes two elongate frame members 52 and 54 between which is housed each of the roller bearings 50. Extending partially through each frame member 52 and 54 from the outside-in are two rotatable hexagonal nuts 56 and 58 which are configured identically. 5 The nut heads are thus located on the outside of each frame member 52 and 54 and can be rotated using an appropriate tool such as a spanner. In preference, each nut 56 and 58 is threadably associated with each frame member 52 and 54, although, other fastening means which allow for rotation of the nuts could equally well be used. Aside from being rotatable, the position of each nut 56 and 58 relative to the frame members 52 and 54 and door slide 46 will not change. 0 Each opposed rotatable nut 56 and 58 includes an off-centre or eccentric aperture 60 extending therethrough for housing the shaft section 62 of a bolt 64. The head section 66 of the bolt 64 is shown in the drawings on the right hand side of frame 54 and the engaging nut 68 and associated washer 70 are shown on the left hand side of frame 52. Because the bolt is fixed eccentrically inside the nuts, the skilled addressee would realise that rotation of any one of the 25 nuts 56 or 58 inside the frame members causes the bolt 64 to move in a circular motion about the central transverse axis of the nuts (for example, when viewing the bolt from the side as per Figures 2c and 3c), but more importantly, in an up-down vertical motion (for example, when viewing the bolt as per the cross sectional views of Figures 2a and 3a). Because of a difference in diameter between the bearing bore and the bolt shaft portion 30 62, a cylindrical sleeve 72 is used to fill the void and two annular washers 74 and 76 are used to maintain the roller bearing 50 in a central position between the frame members 52 and 54. The skilled addressee will thus appreciate that any vertical displacement of the bolt 64 will result in 6 corresponding vertical displacement of the sleeve 72 and hence the roller bearing 50. Thus, the position of each roller 50 relative to the door slide 46 can be adjusted by a simple rotation of any one of the hexagonal nuts 56 or 58. Figures 2a-2c illustrate components of the assembly 10 when the nuts 56 and 58 have 5 been rotated to a position in which their eccentric holes 60 and hence the bolt 64, bolt shaft 62, sleeve 72 and roller 50 are at their lowermost, hence the roller 50 not making contact with the door slide 46. Figures 3a-3c illustrate components of the assembly 10 when the nuts 56 and 58 have been rotated to a position in which their eccentric holes 60 and hence the bolt 64, bolt shaft 62, sleeve 72 and roller 50 are at their uppermost, hence the roller now making contact with the 0 door slide 46. Therefore, the position of any one of the rollers relative to the door slide can be adjusted between a first position that is closest to the door slide to a second position that is most far away by rotating any one of the nuts on either side of that roller by 180 degrees. The nuts are obviously adjustable to any point between these two positions, and although not shown, the 5 assembly 10 could include some form of locking means to ensure that when a desired distance from the door slide has been reached, the nuts will not rotate any further, although it is not envisaged that there will be undesired movement of the nuts. In a preferred embodiment, the distance between inner surfaces of the two frame members 52 and 54 is 25mm, the diameter of apertures through the frame members which 0 receive the hexagonal nuts is approximately 20.5mm, the length of the cylindrical sleeve 72 which fits between the frame members is approximately 24mm, the bolt shaft diameter and hence the diameter of apertures extending through the hexagonal nuts and the sleeve is approximately 12mm, and the distance by which the aperture through the hexagonal nuts is offset from centre is approximately 2mm allowing for a maximum vertical displacement of 25 4mm. The disclosure of these dimensions and tolerances are not intended to limit the scope of the present invention in any way, and it is to be understood that they will inevitably change to suit different applications. Figure 5 illustrates in a more clear, enlarged view three of the rollers 50 forming part of the roller assembly 10 with arrows 80 indicating the ability for their vertical position to be 30 altered. Over time, should any one of the rollers 50 start to misalign and shift away from the door slide 46 thereabove, one can simply rotate the corresponding hex nut 58 until the roller reaches a desirable height again. Thus, provided the rollers are checked for contact with the door slide 46 7 regularly, load will always be distributed equally along each assembly 10, there will be no impediment to opening and closing of the doors resulting from misalignment, and the possibility of damage to the door system will be greatly minimised. Further advantages and improvements may very well be made to the present invention 5 without deviating from its scope. Although the invention has been shown and described in what is conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope and spirit of the invention, which is not to be limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent devices and apparatus. 0 In any claims that follow and in the summary of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprising" is used in the sense of "including", i.e. the features specified may be associated with further features in various embodiments of the invention.