Abstract:
There is proposed a rail member [see:  102 ] comprising a resiliently flexible elongate substrate comprising first and second major surfaces, the member comprising at least one channel formation [see:  202 ] formed transversally relative to the longitudinal axis of the elongate substrate across at least one of the first or second major surfaces, according to a first embodiment, an insert [see:  304 ] is positioned between the first and second major surfaces; according to a second embodiment, an insert [see:  304 ] ex tends longitudinally along the member.

Description:
FIELD 
       [0001]    The present invention relates to a rail member and rail system. Particularly, but not exclusively, the present invention relates to a rail member and rail system to be used on a gantry crane. 
       BACKGROUND 
       [0002]    Rail pads are used in rail systems to support rails and reduce shock and vibration in a rail system which may be due, for example, to the use of the rail system for supporting a rail for a large structure such as a gantry crane. 
         [0003]    Rail systems for supporting such structures are usually supported along their length by a resilient pad interposed between the base of the rail and a support surface for the rail such as a steel girder. The support typically lies on a concrete foundation and provides for load distribution over the foundation. The resilient pads absorb and distribute the loads that act on the rail when a wheel of the crane passes by. 
         [0004]    Existing pads typically comprise a steel insert disposed between two rubber layers and have longitudinal grooves in their upper surface. The purpose of these grooves is to give the pad an initial softness when a vertical load, which may be due to a crane wheel running over the rail immediately above the rail pad, is applied. When the load increases the grooves flatten as the pad deforms, which causes the pad to become stiffer thereby reducing bending stresses in the rail. 
         [0005]    The sustained loading on the rail pad can cause multiple problems in the rail pad. Lateral tearing can manifest along the edge of the steel insert, particularly where the steel insert terminates in line with the bottom of a groove so there is a very small cross section of rubber. Sustained loading on the pad also results in axial splitting along the centre of the pad and the steel insert. 
         [0006]    The pad may also displace due to lubrication from fluids that are within the recess of a crane rail. This fluid can sit in the grooves of the pad and when a wheel from a crane passes over the rail this fluid is pushed back and forth along the longitudinal groove and cannot escape. This generates a hydraulic effect within the grooves. The presence of the fluid within the grooves means the grooves cannot flatten when a vertical load is applied which causes increased stresses on the rail pad and ultimate failure along the grooves. Such fluids may also contain water that will cause aquaplaning and subsequent lateral displacement of the rail pad. 
         [0007]    Aspects and embodiments were devised with the foregoing in mind. 
       SUMMARY 
       [0008]    Viewed from a first aspect, there is provided a rail member comprising a resiliently flexible elongate substrate comprising first and second major surfaces, the member comprising at least one channel formation formed transversally relative to the longitudinal axis of the elongate substrate across at least one of the first or second major surfaces. 
         [0009]    Such transversally formed channels enable fluid, which may include water, and other detritus (hereinafter “debris”) that becomes deposited in the channels to be pumped out. As the wheel passes over the rail the channel is closed and the cross section of the channel is reduced which causes the fluid trapped in the channels to be pumped away from the rail and out of the rail member rather than allowing the fluid to be moved axially backwards and forwards along the longitudinal axis of the rail pad. Pumping the fluid away from the channels reduces the hydraulic effect of the debris that is trapped in the channels. This reduces the stresses on the rail pad due to sustained loading from, say, a crane wheel, and potential aquaplaning of the pad due to water becoming trapped in the channels. 
         [0010]    The rail member may comprise a plurality of channels formed transversally relative to the longitudinal axis of the elongate surface. Increasing the number of channels provides the effect of a network of channels which increases the amount of debris that can be pumped out from the rail member as one passage of a wheel will apply a load sufficient to clear more than one channel. 
         [0011]    The plurality of channels may be arranged in a number of directions transverse to the longitudinal axis of the substrate. The plurality of channels may be transversally arranged in opposing directions relative to the longitudinal axis of the elongate substrate. The plurality of channels may also form diamond-shape formations. 
         [0012]    Providing a plurality of channels that are diagonally aligned in a number of directions means that the effect of the diagonally aligned channel, i.e. the pumping of debris away from the rail pad, can be amplified as it can take place irrespective of the direction of the movement of the object that is applying the load to the rail pad, for example a crane wheel. 
         [0013]    Optionally, the channels may be formed at an angle of  45  degrees to the longitudinal axis of the substrate. 
         [0014]    The rail member may also be tapered along at least a part of one or both of its longitudinal side edges. The taper may form a chamfer along the longitudinal axis. Using a tapered rail member reduces the stress concentration around the steel insert during loading. 
     
    
     
       DESCRIPTION 
         [0015]    An embodiment will now described by way of example only and with reference to the following figures, in which: 
           [0016]      FIG. 1  schematically illustrates a transverse sectional view through a rail system comprising a rail pad in accordance with the embodiment; 
           [0017]      FIG. 2  schematically illustrates a rail member in top side view with a sectional line A-A across a diagonal of the rail member; 
           [0018]      FIG. 3  schematically illustrates a cross-sectional view of the rail member across the A-A sectional line; 
           [0019]      FIG. 4 a    schematically illustrates the cross section of the channel in the absence of loading from the crane wheel; 
           [0020]      FIG. 4 b    schematically illustrates the cross section of the channel in the presence of loading from the crane wheel; and 
           [0021]      FIG. 5  schematically illustrates a tapered portion of a rail pad in accordance with an embodiment of the present invention. 
       
    
    
       [0022]      FIG. 1  illustrates a general overview of a rail system  100  comprising a plurality of elongate rail pads  102  in accordance with the embodiment. The rail system  100  further comprises an I-section rail  104 , a plurality of pairs of clips  106  and a steel girder  108 . The rail pads  102  are interposed end-to-end between the rail  104  and the steel girder  108  along the length thereof. The pairs of clips  106  are spaced apart at intervals along the end of the rail and serve to hold the rail  104  and rail pads  102  in-situ along the length of the girder  108 . The steel girder lies on a foundation  110  which is fixed to the ground  112 . The rail  104  may be fixed directly to the foundation or to another elongate support surface. 
         [0023]    A rail system of the type illustrated in  FIG. 1  can be used for a gantry crane but can be used for other systems that require a rail system. The wheels of a gantry crane will move on the rail  104  during operation and apply considerable loads to the rail  104 . 
         [0024]      FIG. 2  schematically illustrates a top view of the rail pad  102  with a diagonal section line A-A. The longitudinal axis of the rail pad  102  extends co-axially with line Y. The rail pad  102  comprises a series of v-shaped spaced apart channels  202  (the channels are not enumerated separately to aid clarity) that are aligned diagonally relative to longitudinal axis Y at an angle of approximately  45  degrees on the top surface of the rail pad  102 . 
         [0025]    In the described embodiment the channels  202  are formed in the top surface of the rail pad but one or more channels could similarly be formed in the bottom surface of the rail pad  102 . Approximately 45 degrees means 45 degrees to within standard engineering tolerances in this area. An angle of 45 degrees is a simpler angle to implement from a tooling perspective. 
         [0026]    As can be seen in  FIG. 2 , the channels  200  are moulded or otherwise formed to extend across the top surface of the pad in a plurality of directions. One or more of the channels  200  may be parallel to one or more of the other channels  200 . One or more other channels  200  may be oriented transversely relative to one or more of the other channels  200  and the longitudinal axis Y. One or more channels  200  may form diamond-shaped formations on the respective top surface of the rail pad  102 . 
         [0027]    The structure of the rail pad  102  and the action of the channels  200  to provide a conduit for debris can be better understood from a cross-sectional view of the channel as illustrated in  FIG. 3 .  FIG. 3  illustrates a cross section of the rail pad  102  along the sectional line A-A. The lower part of  FIG. 3  also illustrates an end portion of the rail pad  102  in magnified view. 
         [0028]    We now describe the structure of the rail pad  102  of the embodiment with reference to  FIG. 3 . The rail pad  102  is produced by disposing a thin steel reinforcement  304  between two resiliently deformable layers  302 A,  302 B, which may be formed of an elastomeric material such as rubber. This is achieved by extrusion or compression moulding. Typically, the pads  102  are around  12  metres long but vary in width according to the rail they will be used for. The clips  106  constrain the rail pads  102  against lateral movement. The longitudinally-extending steel reinforcement  304  acts to prevent snaking of the rail pads  102 , which can occur due to sustained loading causing the rail pad  102  to displace laterally at points between the adjacent pairs of clips  106 . The longitudinally-extending reinforcement  304  can be of any material which is more resilient than the resiliently deformable material of the layers  302 A,  302 B. Although it is preferred that the resiliently deformable material completely surrounds the longitudinally-extending reinforcement  304 , the reinforcement  304  may be exposed, for example on the underside of the pad  102 . 
         [0029]    We will now describe, using the cross-sectional diagrams of  FIGS. 4 a  and 4 b   , the changing cross section of the channels  200  due to loading on the rail  104  from a crane wheel. 
         [0030]      FIG. 4 a    illustrates an unloaded position wherein the rail  104  is sat in its unloaded position on the rail pad  102 . The magnified portion of  FIG. 4 a    illustrates the cross section of the channels  202  in this position. In this position, it can be seen from  FIG. 4 a    that the channels  200  are non-zero in cross-sectional area where the base is much narrower than the mouth. 
         [0031]      FIG. 4 b    illustrates a loaded position wherein the rail  104  is sat in a position where load is applied by a crane wheel  402  in the direction of arrow X. The loading in the direction of arrow X forces the rail  104  towards the rail pad  102 . 
         [0032]    The resilient flexibility of the rail pad  102  means the rail pad  102  will compress under the loading from the rail  104  which substantially reduces the cross section of the channel  202 . It can be seen from  FIG. 4 b    that the cross sectional area of the channel  202  has become effectively zero due to the loading in the direction of arrow X. This means that any debris occupying the channel  202  will be pushed out of the rail pad  102  due to the hydraulic effect caused by the loading of the rail  104  on the rail pad  102  and the diagonal alignment of the channels relative to the longitudinal axis of the rail pad  102 . 
         [0033]    In use, a crane wheel will move backwards and forwards in the direction of Y along rail  104  and deposit debris in the channels  202 . 
         [0034]    The diagonally aligned channels  202  provide a conduit for the debris deposited by the movement backwards and forwards along rail  104 . Each of the channels  202  comprise a start point at an interior point on the rail paid  102 , i.e. a position that could be considered to be inside the surface on which the channel is formed and an end point parallel with the Y-axis, i.e. the channel leads out of the rail pad  102 . 
         [0035]    The conduit provided by the channels  202  enables the rail pad  102  to be flushed of debris. This is achieved as the vertical loading applied by the crane wheel will push the rail  104  down onto the rail pad  102  to seal the channel  202  and cause the pad  102  to compress by around  1 mm but this can vary dependent upon the vertical load applied by the crane wheel. The compression of the pad  102  results in compression of the channel  202 . The compression of the channel  202  reduces the cross section of the channel  202  which forces the debris out of the channel  202 . Pushing the debris out of the channel  202  causes the debris to be expelled from the rail pad  102 . 
         [0036]    The resilient flexibility of the rail pad  102  means that after the loading has been applied and then relieved by the passing of the crane wheel, the rail pad  102  will recover its original shape to enable the expulsion of the debris to be iterated multiple times, thereby keeping the channels  202  clear of debris and reducing the effect of the debris on the positioning of the rail pad  102 . That is to say, by keeping the channels clear of debris the lateral displacement of the rail pad  102  due to lubrication of the rail pad  102  by fluids is reduced. 
         [0037]    Orienting the channels  202  diagonally also provides the additional advantage that they are not parallel with the rail  104 . This reduces the manifestation of weak points due to the channel  202  which propagate through the rail pad  102  and cause splits to propagate along the rail pad  102  due to sustained loading from the forward and backward movement of the crane wheel. 
         [0038]    Optionally or additionally, the edge of the rail pad  102  in the longitudinal direction Y may, at least in part, be tapered to form a chamfer along at least a part of the longitudinal edge of the rail pad  102 . This is illustrated in  FIG. 5 . 
         [0039]      FIG. 5  illustrates an end view of the rail pad  102  comprising channels  202  and thin steel reinforcement  304 .  FIG. 5  also comprises a magnified portion of the end  502  of the rail pad  102  in the direction Y. The end  502  is tapered. The thin steel reinforcement  304  terminates within the tapered end  502 . 
         [0040]    Steel reinforcement  304  is bonded to the rubber layers in such a way that the pad acts as a bridge bearing. During loading, as the tapered portion  502  is not generally compressed by the loading, the stress concentration around the steel reinforcement  304  is removed as the steel reinforcement  304  terminates within the tapered end  502 . Removing the stress concentration around the steel reinforcement reduces the lateral displacement of the rail pad  102 .