Abstract:
A crawlertrack for a ski trail grooming machine comprises a number of parallel belts joined to one another by cross members. Each belt is made of an elastomer reinforced by a textile carcass. The belt has a row of holes for attaching the cross member. The supporting warp threads of the carcass are made of aramid and flatly extend parallel to the outer sides of the belt.

Description:
[0001]     The present invention is a continuation of PCT/CH2004/000194 filed 31 Mar. 2004. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     Caterpillars for ski-run vehicles consist of several parallel belts which are connected together with lateral carriers. Conventional belts of this kind consist of an elastomer which is reinforced by a textile carcass. These known carcasses consist of several bands layed one over another of polyamide webs. The useful life of such belts is approximately one fifth of the useful life of the ski-run track vehicle.  
         [0003]     The present invention aims at increasing the life-span of such belts. This task is solved by the combination of features of the claims.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0004]     In accordance with the foregoing, the present invention comprises a crawlertrack belt of an elastomer reinforced by a textile carcass. The belt has at least one row of cylindrical holes extending in a longitudinal direction. Laterally-extending carriers are fastened to the belt through the holes. The carcass comprises at least one web with bearing warps arranged parallel to each other and are shaped and parallel with respect to the outside surfaces of the belt. The warps are of an aramid construction.  
         [0005]     Because aramid has a much higher tension strength than polyamide, the carcass can be much thinner. This improves the alternating bending stability significantly. Thus, the useful life of the belts is considerably improved. By the considerably higher stiffness of aramid compared with polyamide, the danger of injury when a belt tears is considerably reduced and the load distribution on the various belts of the caterpillar is improved.  
         [0006]     Preferably the bearing warp yarns consist of several twines and are twisted in a sense contrary to twist the twines. The twines are twisted in the same sense as the threads or yarns from which they are found. At an equal number of windings per meter the result is that the yarn filaments in the center of the twines are approximately parallel to the length direction of the twines. This results in the highest possible strength and stiffness of the twines.  
         [0007]     A particularly high life duration is achieved when all of the bearing aramid-yarns are arranged in a single plane, i.e. in a single layer of the web. This results in an even distribution of the load on all bearing yarns, as well over guide rollers or drive rollers. The elastomer layer on the outside of the belt is preferably thicker than on the inside for wear considerations.  
         [0008]     For manufacturing of the belt, the carcass is soaked with liquid epoxy resin and thereafter used such that a thin epoxy layer of about 1% of the weight of the carcass surrounds the carcass. A latex solution adapted to the elastomer to be applied is then applied to the carcass. After curing, the latex layer surrounds the carcass with a level of at least 10% of the weight of the carcass. Onto this latex layer the elastomer is vulcanised on both sides at about 160° C. by calendering.  
         [0009]     The manufacturing method described above results in a particularly durable connection between the carcass and the elastomer. The through holes of the at least one row of holes are preferably cut by a high pressure water jet. Conventionally these holes are punched, which results in frayed hole edges and irregular hole walls. These disadvantages can be avoided by water jet cutting. The load transfer between the belt and the lateral carriers is thereby improved. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     An exemplary embodiment of the invention is hereinafter described with reference to the drawings, in which  
         [0011]      FIG. 1  shows a perspective view of caterpillar belt of a ski-run track vehicle;  
         [0012]      FIG. 2  shows a longitudinal section through a caterpillar belt;  
         [0013]      FIG. 3  shows a partial view of a carcass; F.  
         [0014]      FIG. 4  shows the structure of the twines;  
         [0015]      FIG. 5  shows the structure of a cord yarn;  
         [0016]      FIG. 6  shows a further embodiment of the belt in a lateral section; and  
         [0017]      FIGS. 7 and 8  show two variants of the connection of two belt ends to form an endless belt in longitudinal section. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]      FIG. 1  shows schematically the structure of a caterpillar  10  of a ski-track vehicle. The caterpillar  10  is guided over two rollers  11  spaced from one another, of which one is connected to a drive unit. The caterpillar  10  comprises several parallel belts  12  each having at least one row of throughgoing holes or orifices  13 . Lateral carriers  14  of aluminium are screwed to each of the belts  12  through the holes. The longitudinal extension of the carriers  14  extends parallel to the axis of the rollers  11 .  
         [0019]     Each belt  12  consists of an elastomer  15  in which a textile carcass  16  is embedded. In the embodiment shown in  FIGS. 2 and 3 , the carcass  16  consists of a single web layer in which bearing warps  17  are unwaved and lie parallel to the outside surfaces  18  of the belt  12  and consist of an aramid. In the embodiment of  FIG. 3 , the warps  17  are connected together by wefts  19  of a polyamide. In the example of  FIG. 2 , the carcass has linearly throughgoing wefts  20  on both sides of the warps  17 . On one side of the warps  17  these linearly extending wefts could also consist of an aramid. This results in a particularly high resistance to piercing of the carcass  16 . The wefts  20  are connected together by further warps  21  of a polyamide. These waved warps  21  contribute practically nothing to the longitudinal strength but serve to hold the carcass  16  together. As shown in  FIG. 2 , the orifices  13  may be reinforced by tubular rivets  22 .  
         [0020]      FIGS. 4 and 5  show the structure of the bearing warps  17 . The warp  17  of  FIG. 5  is a cord which is wound in the opposite sense than the twines  28  of  FIG. 4  from which it is formed. In the represented embodiment the cord is wound clockwise or Z, whereas the twines  28  are wound counter clockwise or S. The three yarns  29  of a twine  28  are wound in the same sense as the twine  28 , in the example shown counter clockwise or S. Each yarn  29  consists of several hundred, e.g. about one thousand aramid filaments  30 . The winding number of the filaments  30  per meter in the yarn  29  is approximately equal to the number of windings per meter of the yarn  29  in the twine  28 , and (at least for the middle belts  12   a  of the caterpillar  10 ) approximately equal to the windings per meter of the twines  28 . This results in the highest possible strength and stiffness of the bearing warps  17 . The number of windings is exaggerated in the drawing. 60 windings per meter have shown to be optimal. For the outermost belt  12   b  of the caterpillar  10  of the ski-track vehicle the winding number of the twines  28  in the warps  17  is preferably somewhat higher. Thereby the stiffness of these belts is lower than those of the middle belts  12   a . This can be of advantage in turns.  
         [0021]     A further embodiment is shown in  FIG. 6  in lateral section. The carcass  16  consists in this case of a web according to  FIG. 3  in which the wefts  19  are considerably thinner than the warps  17 , and additionally with a covering web  34  on each side of first web of a polyamide, aramid, or polyester. The covering web  34  is coated with an elastomer on both sides. Instead of the covering web, an elastomer foil can be used, e.g. one with short fibers of an aramid.  
         [0022]     As depicted in  FIGS. 7 and 8 , for manufacturing of the endless belts, the ends  35 ,  36  of the belt of e.g. 10 m length with the structure described are ground down on opposite sides over a length L of e.g. 30 cm parallel to the outside surfaces  18  to the bearing warps  17 . The two ends  35 ,  36  are then vulcanised together over the length L such that the warps  17  of the two ends  35 ,  36  touch. Thereby, a tensile strength of over 70% of the one of the belts is achieved.  
         [0023]     With conventional belts with several layers of reinforcing webs the above described method of connection is not possible. In conventional belts the belt ends are either connected by hinges or by finger splicing. All these connections do not reach the strength of the described overlapping splicing.  
         [0024]     With the described overlapping splicing there results a step  37  on both outer surfaces  18  of the height of the diameter d of the bearing warps  17 . In the application of caterpillars for ski-track vehicles, these steps hardly disturb operation. In other applications it may be advantageous to grind off these steps  17 , which is shown schematically in  FIG. 7  in phantom.  
         [0025]     An even stronger connection results when the grinding surfaces  38  are tilted by a small angle d/L against the outer surfaces  18 , as shown in  FIG. 8 . Thereby the steps  37  are avoided. The bending strength of the belts is constant even over the connecting region. The angle d/L is preferably approximately 0.05°, and in any case smaller than 0.5°. The grinding surfaces  38  are still approximately parallel to the outside surfaces, in contrast to conventional tilted splicings.