Abstract:
The present invention relates to an improved rail that may be utilized in hydrostatic bearing levitation system, and manufacturing method thereof. Hydrostatic bearing levitation systems uses fluid pressure to support and guide heavy loads as they move along a track system. Improvement comprises use of suitable aluminum alloy and hard anodizing coating with polyterafluoroethylene sealing.

Description:
[0001]     This application claims priority benefits from Canadian Patent Application No. 2,550,347 filed Jun. 16, 2006, the disclosure of which is incorporated herein by reference.  
       FIELD OF THE INVENTION  
       [0002]     The present invention is related to an improved rail that may be utilized in hydrostatic bearing levitation systems, in which fluid pressure is used to support and guide heavy loads as they move along a track system.  
       BACKGROUND OF THE INVENTION  
       [0003]     While the principle of utilizing air pressure to support and guide a load as it moves along a track is not new, improvements in load-carrying efficiency have been achieved through the implementation of a system using rail sections having concavely curved upper surface and by providing load supporting members which have a convexly curved compliant outer surface for mating with the rail surface. Nozzles leading from an air plenum within the rail through the upper wall exit at the curved upper surface thereof and are angled with respect to three orthogonal planes, one of which is tangent to the rail surface where the nozzle axis intersects that surface. The nozzles are angled so that their net effect is a fluid film wedge reaction on the load supporting member which directs it in the desired direction and which also tends to displace the load and the supporting film wedge towards one side of the rail. The principles outlined in very basic terms above are applicable to material handling systems, as in single-rail systems operating as an air-conveyor for transporting cylindrical objects such as paper rolls, or in twin-rail track systems for transporting pallets from a loading or unloading dock into or out of a transporting trailer, or holding and feeding pallets in and through a gravity flow racking system, and they are also applicable to so-called “people-movers” such as inter- or intra-urban transportation systems. The principles underlying the systems briefly outlined above are covered in one or more Canadian patents including Canadian Patent Nos. 950,853 issued on Jul. 9, 1974 for “Air Conveyor”; 1,002,565 issued on Dec. 28, 1976 for “Vehicular Transportation System”; 1,066,645 issued on Nov. 20, 1979 for “Air Film Supported and Guided Load Support Member”; 1,167,797 issued on May 22, 1984 for “Air Conveyor Components”; and 2,099,265 issued on Oct. 29, 2002 for “Runner For Air Conveyor System”; and U.S. Pat. No. 4,838,169 issued on Jun. 13, 1989 for “Minimum Filler Runner For Air Conveyor System”.  
         [0004]     In general, the aforementioned systems may be broadly characterized as compliant hydrostatic bearing levitation systems for moving heavy loads along supporting rails. The systems utilize “shoes” or “runner” of cellulose or like material wound tightly about a collapsible core and enclosed by a deformable but stiff cover of flexible plastic or metal, in which the shoes exhibit low friction properties when in juxtaposition with a trough-like section of support rail, curved at a radius only slightly greater than that of the shoe. The shoes move freely in and along the rail(s) when small nozzles in the curved rail surface exhaust fluid therethrough under pressure in particular patterns to create fluid cavity cells and fluid lubricated seal areas under the shoes, the shoes being guided by the fluid film wedge formed with the curved contour of the rail section.  
         [0005]     While the structures, which utilize the air film technology, have proven to be very effective, further research into the real-life requirements resulted in significant improvements, especially with respect to the rail construction for improving durability of the rail.  
         [0006]     In systems as described in Canadian Patent No. 1,167,797, a rail has been extruded from commercial aluminum stock for obtaining maximum durability. However, over time, friction between the rail and the runner causes wear on the surface of the rail. The wear began to cause a build up of aluminum oxide on the runner surface that comes in contact with the rail. Aluminum oxide is a relatively sticky, abrasive substance, which increases the frictional forces on the rail surface, collects dirt and degrades the system performance. Thus, in order to avoid build up, a type of lubrication is required.  
         [0007]     One solution would be to form a silicon film over the surface of the rail. It is usually formed using a special silicone based spray; however, there are a few drawbacks with silicon solution. Firstly, this application is not permanent, thus it requires reapplying silicon spray periodically once every three to six months. Another drawback is that many plants, especially automobile plants, do not allow using spray silicon in their plant for various reasons. Therefore, this solution has limited usage.  
         [0008]     Yet, another solution was to use molybdenum sulfide, which is applied in powder form and brushed onto the concave upper surface of the rail. However, like silicon solution, periodical applications of the powder are required, and it is difficult to apply.  
         [0009]     The present invention solves the abovementioned drawbacks by providing hard coating with permanent lubricant finish on the upper surface of the rail.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention relates to an improved rail that may be utilized in hydrostatic bearing levitation system, in which fluid pressure is used to support and guide heavy loads as they move along a track system. Improvement comprises use of suitable aluminum alloy and hard anodizing coating with polyterafluoroethylene sealing.  
         [0011]     According to one aspect of the invention, it provides a rail structure of a hydrostatic bearing levitation system comprises a shallowly transversely concave upper wall member, a pair of generally vertical, longitudinally extending side walls, each wall being inset from a corresponding edge of the upper wall member, a generally planar lower wall member extending transversely outwardly beyond each side wall, partition wall means extending between the upper and lower wall members so as to define at least two longitudinally extending ports within the rail, a plurality of nozzles communicating through the upper wall member with the ports, the nozzles being longitudinally aligned in groups such that there is a space between longitudinally adjacent groups for each of the ports and such that each group associated with one port is positioned generally laterally opposite a space between adjacent groups associated with the other of the ports, each nozzle being angled with respect to a longitudinally extending plane which is tangent to the outer curved surface of the upper wall member where the axis of the nozzle intersects the outer surface, the nozzles of each group being directed generally towards the edge of the rail closest theretouse, wherein a upper surface of the upper wall member is applied with a corrosion resistant coating.  
         [0012]     According to another aspect of the invention, it provides a method of improving durability and corrosion resistance of a rail structure for a hydrostatic bearing levitation system comprises the steps of: (i) extruding from a corrosion resistant aluminum alloy the rail structure comprising a shallowly transversely concave upper wall member, a pair of generally vertical, longitudinally extending side walls, each wall being inset from a corresponding edge of the upper wall member, a generally planar lower wall member extending transversely outwardly beyond each side wall, partition wall means extending between the upper and lower wall members so as to define at least two longitudinally extending ports within the rail, a plurality of nozzles communicating through the upper wall member with the ports, the nozzles being longitudinally aligned in groups such that there is a space between longitudinally adjacent groups for each of the ports and such that each group associated with one port is positioned generally laterally opposite a space between adjacent groups associated with the other of the ports, each nozzle being angled with respect to a longitudinally extending plane which is tangent to the outer curved surface of the upper wall member where the axis of the nozzle intersects the outer surface, the nozzles of each group being directed generally towards the edge of the rail closest theretouse; and (ii) applying a corrosion resistant coating on the outer surface of the rail structure. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The invention will now be described in more detail with reference to the accompanying drawings, in which:  
         [0014]      FIG. 1  illustrates a typical prior art SAILRAIL® arrangement comprising a rail, a runner and a pallet;  
         [0015]      FIG. 2  illustrates a cross-section of the rail, the runner and the pallet along the line  2 - 2  of  FIG. 1 ;  
         [0016]      FIG. 3  illustrates coating layers of the concave upper surface of the rail according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]      FIG. 1  illustrates a typical SAILRAIL® arrangement  10  as described in U.S. Pat. No. 4,838,169 comprising a rail  12 , a runner  14  and pallet  16 . The rail  12  has a transversely shallowly concave upper surface  18  through which nozzles  20  extend. The nozzles are arranged in staggered aligned groups with one set  22  of groups communicating with an internal port, or plenum  24 , and the other set  26  communicating with another internal port, or plenum  28 . Each individual nozzle  20  is angled relative to the longitudinal axis of the rail and with respect to a tangent at the rail surface. Preferably the nozzles of set  22  are angled toward the edge  30  while the nozzles of set  26  are angled toward the edge  32 .  
         [0018]     The pallet  16  can be of any desired form as, for example, a sheet of plywood, plastic, steel, or fabricated from other suitable material. The design of the pallet per se does not form a part of the present invention. It must, of course, be sufficiently strong to support the intended load without any significant deformation or vibration when loaded and moving.  
         [0019]     The structure of nozzles  20  and configuration are determined to permit the formation of separate levitation “footprint” cells of fluid film propagation or dispersion along the length of a runner  14  and also aids in the creation of “dither” or vibration in the runner  14 , a phenomenon which is known to reduce friction between the runner  14  and the concave upper surface  18  of the rail  12 .  
         [0020]      FIG. 2  illustrates a cross-section of the pallet  16 , runner  14 , and rail  12  along the line  2 - 2  of  FIG. 1 . Runner  14  is attached to the pallet  16  by a fastening means  52 . Runner  14  is resting on the concave upper surface  18  of the rail  12 . The rail  12  comprises a shallowly transversely concave upper wall member  45 , a generally planer lower wall member  47 , and a pair of generally vertical, longitudinally extending side walls  46 . The rail  12  further comprises a plurality of partition wall means extending between the upper  45  and lower wall members  47  so as to define at least two longitudinally extending ports  24  and  28  within the rail  12 . A plurality of nozzles  20  are communicating through the upper wall member  45  with the ports  24  and  28 . The nozzles  20  are longitudinally aligned in groups such that there is a space between longitudinally adjacent groups for each of the ports  24  and  28  and such that each group associated with one of the ports  24  and  28  is positioned generally laterally opposite a space between adjacent groups associated with the other of the ports  24  and  28 . Each nozzle  20  is angled with respect to a longitudinally extending plane which is tangent to the outer curved surface  18  of the upper wall member  45  where the axis of the nozzle  20  intersects the outer surface  18 , the nozzles  20  of each group are directed generally towards the edge  30  or  32  of the rail  12 , whichever is the closest.  
         [0021]     While rail  12  could be fabricated and extruded from a copolymer such as polyvinylchloride (PVC) or reinforced polyethylene, in order to obtain most durability and operational efficiency, rail  12  is extruded from commercial aluminum stock. Originally, the concave upper surface  18  of the rail  12  is covered with a corrosion resistant coating, i.e. clear anodized surface finish. Even though the friction between the runner  14  and the concave upper surface  18  of the rail  12  is reduced by air film, this does not stop causing wear on the concave upper surface  18  of the rail  12 . This wear causes un-coated aluminum to be exposed to air. Since aluminum is very reactive to atmospheric oxygen; a thin layer of aluminum oxide quickly forms on the exposed surface. In fact, the hardness of aluminum oxide in its crystalline form makes aluminum oxide suitable for use as abrasive. It also sticks and cumulates on the surface of the runner  14  and causes even more friction (and wear) between the runner  14  and the concave upper surface  18  of the rail  12 , thus affecting the system performance and durability. Accordingly, lubrication between the runner  14  and the concave upper surface  18  and much more durable finish for the concave upper surface  18  of the rail  12  were required for avoiding such wears and buildups.  
         [0022]     One solution would be to form a silicon film over the surface  18  of the rail  12 . It is usually formed using a special silicone based spray applied over the surface  18 ; however, there are a few drawbacks with silicon-based solution. Firstly, this application is not permanent, thus it requires reapplying silicon spray periodically once every three to six months. Another drawback is that many plants, especially automobile plants, do not allow using silicon spray in their plant for various reasons for maintaining their quality. Therefore, this solution has limited scope of usage.  
         [0023]     Yet, another solution was to use molybdenum sulfide (or moly powder), which is applied in powder form and burnish into the concave upper surface  18  of the rail  12 . However, like silicon solution, periodical applications of the powder are required, and it is, also, difficult to apply, as it requires burnishing it into the surface  18  by rubbing with a certain cloth or brushing. In order to solve these problems, the construction of the rail  12  was needed to be re-engineered from its material to its surface finishing.  
         [0024]     The rail improvement of the present invention utilizes corrosion resistant aluminum alloy, preferably uses Aluminum 6061-T6561, which provides appropriate joining characteristics for connecting with other rails  12 , good acceptance of applied coatings; an optimal combination of strength, workability and high resistance to corrosion required to extrude the rail  12 . The concave upper surface  18  of the rail  12  should be carefully constructed so that there is no abrasion on the surface  18 . However, even with the corrosion resistant aluminum alloy and clear anodization finish on no-abrasion surface, wears and build-ups were still causing the problem, thus further strengthening durability and resistibility to corrosion on the surface  18  of the rail  12  is required.  
         [0025]     For enhancing durability and resistance to corrosion on the surface  18  of the rail  12 , a hard-anodized treatment with a coating material, preferably polyterafluoroethylene (or TEFLON®) sealing, is applied to the upper surface  18  of the rail  12 .  FIG. 3  illustrates coating layers of the concave upper surface  18  of the rail  12 . The aforementioned anodizing process produces a coating layer  101  on the surface  102  of the rail  12 , which is uniform, much harder and denser than natural oxidation. In the preferred embodiment of the present invention, the thickness of this anodizing coating should be about 0.002 inch. Then, a layer of polyterafluoroethylene  100  is applied to seal the hard-anodized surface  101  for protecting the hard anodized surface  101 . Because of porous structure of the hard anodized surface  101 , polyterafluoroethylene partially permeates into the micro-pores and partially bonds the hard anodized surface  101 . The layer of polyterafluoroethylene  100  further provides a permanently lubricated surface of the rail  12 , thus it is no long required to apply lubricant, such as silicon or moly powder, periodically.  
         [0026]     The rail structure improvement of the present invention comprises use of suitable aluminum alloy and hard anodizing coating with polyterafluoroethylene sealing for enhancing durability and providing a permanent lubricant on the surface of the rail. It is to be understood that the embodiments and variations shown and described herein are merely illustrations of the principles of this invention and that various modifications may be implemented by those skilled in the art without departing from the spirit and scope of the invention.