Abstract:
A plastic pallet includes a hollow lower part provided with ribs and runners, and an upper part provided with ribs and welded to the lower part. The lower part has a recessed border and the upper part has an edge that is bent downwards, covering the edge of the lower part.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is the U.S. National Stage of International Application No. PCT/IB2011/050372, filed Jan. 28, 2011, which designated the United States and has been published as International Publication No. WO 2011/092649 A1 and which claims the priority of Swiss Patent Application, Serial No. 00117/10, filed Feb. 1, 2010, pursuant to 35 U.S.C. 119(a)-(d). 
     BACKGROUND OF THE INVENTION 
     The invention relates to a plastic pallet. 
     A plastic pallet is known, for example, from CH-A-685 549, and is made of an upper part or deck and a lower part with longitudinal runners which are interconnected by mirror welding. The top side and the bottom side are provided with ribs, giving the pallet a lower weight while still retaining the necessary stability. For additional reinforcement, metal pipes may be provided in crescent-shaped cut-outs disposed in the ribs of the lower part. The ribbing of the upper part matches the geometry of the ribbing of the bottom part, so that the end faces of the ribs of both parts are welded together. For connecting the upper part congruently with the lower part, these parts must be produced with precision in a high-quality production process. In particular, the ribs of the upper part and the ribs of the lower part must be exactly aligned with each other so that the pallet has at the edges a smooth surface without burrs. 
     In addition, a closed pallet with a so-called milling line is described in EP-A-1970318, wherein the upper part and the lower part are connected with one another at the edges. When the upper part is welded to the lower part, a bead is formed which must be removed in a milling process so that the pallet has a smooth surface. The problem with the milling process and the weakening of the material in the edge region of such a plastic pallet are described therein in detail. The bead is milled manually by an operator, so it depends on the operator&#39;s abilities whether more or less material is milled away. 
     It is an object of the present invention to provide a plastic pallet specify which allows easy manipulation when the upper part is connected to the lower part with a smooth border. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, this object is achieved by a holder for a plastic pallet having a hollow lower part with ribs, runners and a border, and an upper part with a ribs and welded to the lower part. The border of the lower part has a protruding shoulder and is recessed in relation to the upper part. The upper part has a downwardly bent edge which encompasses the border of the lower part. A front end of the bent edge is supported on the protruding shoulder and welded to the protruding shoulder. An upper edge of the border is welded to a bottom side of the upper part, forming a crumple zone between the edge and the border. 
     The novel plastic pallet has the great advantage that a smooth full-surface connection between the upper and the lower part can be achieved with high precision and with a smooth border. This eliminates reworking of the border. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       Further advantages of the invention can be inferred from the dependent claims and from the following description in which the invention is explained in detail with reference to an exemplary embodiment illustrated in the schematic drawings. It is shown in: 
         FIG. 1  a plastic pallet in a welded-together state 
         FIG. 2  the lower part of the plastic pallet from above, 
         FIG. 3  the lower part of the plastic pallet from below, 
         FIG. 4  the lower part of the plastic pallet with metal tubes from above, 
         FIG. 5  the upper part or deck of the plastic pallet from above, 
         FIG. 6  the upper part from below, 
         FIG. 7  a partial cross-section through the plastic pallet in the direction A of  FIG. 2 , 
         FIG. 8  a partial cross-section through the plastic pallet in the direction B of  FIG. 2 , 
         FIG. 9  a modified embodiment of the plastic pallet from above, and 
         FIG. 10  the modified embodiment of the plastic pallet from below. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the Figures, the same reference numerals are used for the same elements, and the explanations for a particular reference number apply to all Figures, unless a different explanation is explicitly given. 
       FIG. 1  shows a plastic pallet  1  with an upper part or deck  2  and a lower part  3  having runners  4  arranged in rows with lateral recesses  5  and  6 . The upper part has a perfectly smooth surface, so the pallet can be easily cleaned and has no discontinuities where dirt or bacteria could accumulate, and is therefore ideally suited for applications in hygiene and clean room applications. 
       FIG. 2  shows the bottom part  3  from above, which has a rib structure  11  in the cavities  12  for significant weight savings and for providing mechanical stability. Furthermore, semicircular recesses  13  configured to receive reinforcing tubes  21  made of metal or a suitable hard plastic material are provided in the rib structure  11  (see  FIG. 4 ). In addition, first projections  14  shaped as circular cylinders are distributed uniformly over the surface. Circular cylindrical pipe sections or cylinders  15  configured for engagement with centering pins  22  of the upper part  2  are disposed at the corner regions of the bottom part  3  (see  FIG. 6 ). The pipe sections or cylinders  15  include four small vertical webs  18  regularly distributed on the inner edge, which operate to center the pin  22 . In addition, a slightly recessed border  16  with protruding projections  17 , which is configured to be encompassed by the downwardly bent edge  23  of the upper part, is disposed on the short sides of the lower part  3  (see  FIGS. 6 and 7 ). 
       FIG. 3  shows the upper part  3  from below, with the longitudinal runners  4  with a ribbed profile  24  now clearly visible. Furthermore, the circular-cylindrical projections  14 , which are formed to have less depth in the shallower areas, are also visible from below. The center longitudinal runner  40  has corresponding rectangular recesses  41  in the region of the recesses  5  and  6 , which are produced by molding with an injection mold and mold cores. 
       FIG. 4  shows a perspective view on the upper part  3  from above, wherein the reinforcing tubes  21  are herein made of metal or a suitable rigid plastic such as polycarbonate (PC) or polyoxymethylene (POM). Rectangular recesses  43  and  44  are here also disposed on both sides of the central reinforcing tube  21  in the region of the recesses  5  and  6 , which are required for demolding of the central longitudinal runner  40 . 
       FIG. 5  shows the upper part or deck  2  from above, whereas  FIG. 6  shows the upper part or deck  2  from below. A ribbed structure  25  with semicircular recesses  26  for the reinforcement tubes  21  is here also evident. Moreover, cross-shaped second protrusions  27  are provided, which each have a surrounding projecting ring  28  and which face the circular-cylindrical projections  14  when the upper part  2  is placed on the lower part  3 . In addition, projecting pins  22 , which fit into the circular-cylindrical pipe sections  15  of the lower part  3 , are arranged in the corner regions. These pins  22  are formed as annular cylinders and have outwardly facing webs  29  which are connected to an outer ring  30 . When the upper part  2  is placed onto the lower part  3 , the outer ring  30  rests on the respective pipe section  15 , while leaving a small clearance between the pins  22  and the pipe sections  15 . The upper part  2  and bottom part  3  are then joined together by friction welding or vibration welding. The upper part  2  is hereby welded together with the lower part  3  in an orbiting or rapid reciprocating movement. Thus, the first protrusions  14  of the upper part  2  are welded together with the second protrusions  27  of the lower part  3 , and the outer rings  30  are likewise welded together with the pipe sections  15 . However, other welding processes such as mirror welding may be used. Also visible is the peripheral curved edge  23  of the upper part  2 , which is provided with perpendicular, inwardly pointing webs  31 , which operate to align the edge  23  of the upper part  2  with respect to the border  16  having the protrusions  17  of the lower part  3 . The projections  17  add stability to the shorter sides of the border  16 , so that these are not carried along at their top edge by the upper part  2  in the longitudinal direction during vibration welding. In this way, a particularly stable connection between the upper part  2  and the lower part  3  is also attained at the shorter sides of the pallet. The aforedescribed joint produced by vibration welding is particularly economical, because removal of protruding ridges is entirely eliminated. 
       FIG. 7  shows a partial cross section through the plastic pallet  1  in the direction A of  FIG. 2 , clearly showing the circumferentially curved edge  23  of the upper part  2  and the rim  16  of the lower part  3 . A circumferential shoulder  32  is also visible, on which the front end of the bent edge  23  is supported, i.e. where the edge  23  is welded to the shoulder  32  during vibration welding. The upper edge of the border  16  is also welded to the underside of the upper part  2 . This produces a so-called a crumple zone, i.e., provides double protection against lateral damage to the pallet: when the welded connection between edge  23  and the shoulder  32  detaches due to damage, the welded connection between the border  16  and the upper part  2  still remains intact. At the same time, a smooth border of the pallet  1  is attained, which does not require finishing. The outer wall  33  below the shoulder  32  is arranged with an inward offset. 
       FIG. 8  shows a partial cross-section through the plastic pallet  1  in the direction B of  FIG. 2 ; the outer wall  33  is formed substantially flush with the edge  23  in this region. 
     As is apparent from the above, the plastic pallet  1  has the same dimensions both at the top of the deck  2  as well as at the runners  4 —at least in the corner areas important for transport and further handling. Thus, the plastic pallet  1  can be used in more demanding applications as a complete replacement for the well-known wooden pallets (Euro-Pallets). 
     The reinforced plastic pallet  1  prepared in this way and equipped with reinforcement tubes  21  has a static load capacity of approximately 7,500 kg. The dynamic load capacity is between 1,000 and 1,300 kg. 
       FIGS. 9 and 10  show a modified embodiment of the plastic pallet according to the  FIGS. 1 to 8 , wherein four reinforcing tubes  35 ,  36 ,  37  and  38  are now provided in the longitudinal direction. Since the center reinforcing tubes  36  and  37  are arranged on both sides of the longitudinal runner  42 , the upper part or deck  2  has a closed weld with the lower part  3 , thus preventing water from entering between these two parts. To prevent this in the first embodiment of the plastic pallet  1 , an absolute seal must be provided between the deck  2  and the lower part  3  in the area of the openings  43  and  44  on both sides of the center reinforcing tube  21  (see  FIG. 4 ). This cannot always be guaranteed when using vibration welding. The embodiment of the plastic pallet  1  of  FIGS. 9 and 10  has the additional advantage that the center longitudinal runner  42  is closed and thus prevented from inadvertently getting stuck at the rectangular openings  41  (see  FIG. 3 ). In all other aspects, the embodiment of the variant according to  FIGS. 9 and 10  is constructed identical to the embodiment of  FIGS. 1 to 8 . 
     For attaining better centering on a lattice frame, the corner regions  45  of the outer longitudinal runners  4  are provided with a protruding outer edge  46 , which matches the contour of the deck  2 .