Abstract:
Metal-coated thermo-plastic conveyor belt components and methods for their manufacture. Hinge rods, sprockets, and belt modules are coated with metal to increase their stiffness or wear resistance or to improve other performance characteristics.

Description:
BACKGROUND 
       [0001]    The invention relates to modular plastic conveyor belt components covered with a metal coating. 
         [0002]    Spiral belt conveyors are often used to convey products slowly through ovens, proofers, or freezers. Most spiral conveyors use metal belts with large open areas to transport products along a helical conveying path around a slowly rotating spiral drive tower. Because metal belts are inherently stiff, only a few rails below the belt are needed to support it. Lightweight, corrosion-resistant modular plastic conveyor belts are replacing metal belts in some spiral applications. In some retrofit situations, a plastic belt can be mounted directly on the existing spiral conveyor&#39;s support rails. But the beam stiffness of modular plastic conveyor belts across the belt&#39;s width is not so high as the beam stiffness of metal belts. Solid stainless steel hinge rods are often used to add beam stiffness to plastic belts. But solid metal rods add weight to the belt and, because of their stiffness, limit load-sharing to only the first couple of hinge elements at the outer side edge of the belt. 
         [0003]    Besides these problems specific to spiral belts, modular plastic conveyor belts are subject to wear at hinges and at drive surfaces where there is rubbing between the hinge eyes and hinge pins and between sprocket teeth and drive surfaces on the belts. 
       SUMMARY 
       [0004]    These shortcomings and others are overcome by conveyor belt components embodying features of the invention. Such components comprise a thermoplastic member adapted for use with a modular conveyor belt and having an outer surface covered, at least in part, by a metal coating. 
         [0005]    In another aspect of the invention, a method of making such a conveyor belt component comprises forming a thermoplastic member with an outer surface and adapted for use with a modular conveyor belt and covering at least a portion of the outer surface with a metal coating. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    These features and aspects of the invention, as well as its advantages, are better understood by referring to the following description, appended claims, and accompanying drawings, in which: 
           [0007]      FIG. 1  is a top plan view of a portion of a spiral conveyor belt having hinge rods embodying features of the invention; 
           [0008]      FIG. 2  is an enlarged cross-section of the hinge rod of  FIG. 1  taken along lines  2 - 2 ; 
           [0009]      FIG. 3  is a side view of a sprocket embodying features of the invention; and 
           [0010]      FIG. 4  is an oblique view of a portion of a conveyor belt module embodying features of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]      FIG. 1  shows a portion of a modular plastic conveyor belt interconnected by hinge rods embodying features of the invention. The belt  10 , which is suitable for traveling a helical path such as around a spiral conveyor&#39;s drive tower, comprises a series of rows  12  of one or more belt modules  14  connected together at hinge joints  16  by hinge rods  18 . Holes  20  through laterally spaced hinge elements, or eyes  22 , along a leading end of each row are aligned with holes through the interleaved hinge elements along a trailing edge of a leading row to form a lateral passageway across the width of the belt. Hinge rods received in the passageways between adjacent rows connect the belt together and allow it to articulate around sprockets. In this particular belt, some or all of the holes  20  are elongated in the direction of belt travel  24  to allow the inside edge  26  of the belt to collapse at the inside of a turn as the outside edge  27  expands. 
         [0012]    The belt is shown supported near the inside and outside edges by rails  28 . To limit the sag of the plastic belt between the rails, some or all of the hinge rods  18  are stiffened with a metal coating  30  or cladding along all or a major portion of their lengths. The rods increase the lateral beam stiffness of the belt to limit sag. For the spiral belt in  FIG. 1 , the end  32  of the hinge rod at the outside edge  27  of the belt is uncoated to give the outside edge of the belt enough flexibility to share belt pull across more of the outermost hinge elements. 
         [0013]    As shown in  FIG. 2 , the coated portion of the hinge rod  18  comprises an inner thermoplastic core  34  whose circular cylindrical outer surface  36  is covered by the thin metal coating  30  of uniform thickness. The core is a thermoplastic polymer, such as polypropylene, polyethylene, acetal, and nylon, formed by extrusion or molding. The metal coating is preferably a nanocrystalline metal alloy, e.g., nickel and nickel—iron alloys, fused to the polymeric core. The MetaFuse™ nanocrystalline metal/polymer hybrid technology developed by DuPont Engineering Polymers of Wilmington, Del., Morph Technologies, Inc., Integran Technologies, Inc., and PowerMetal Technologies is one technology useful in coating a thermoplastic material with a metal cladding to increase stiffness. That and other suitable metal-coating technologies are described in U.S. Pat. No. 7,354,354, “Article Comprising a Fine-Grained Metallic Material and a Polymeric Material,” Apr. 8, 2008, incorporated by reference. 
         [0014]    Each row of the belt of  FIG. 1  also has a narrow lateral beam  38  that varies in shape from generally sinusoidal to tapered to stepped from the outside edge  27  inward to the inside edge  26 . Coating all or a portion of the beam with a metal coating  39  increases the beam stiffness of the belt. The inside edge of the belt could be coated in metal  37  to resist wear against the drive tower. 
         [0015]    Conveyor belt components other than hinge rods may be made in a similar way to achieve these and other benefits. For example, a sprocket  40  for a modular conveyor belt is shown in  FIG. 3 . The sprocket comprises an injection-molded thermoplastic member  42 , portions of whose outer surface are covered with a metal coating. In particular, the sprocket&#39;s drive surfaces, or teeth  43 , have a metal coating  44  to decrease wear from the constant rubbing they undergo as they move into and out of contact with belt drive surfaces. A metal coating  46  is also shown bounding a central bore  48  through the sprocket. The metal coating fights wear on the bore&#39;s walls caused by the rubbing of a shaft against the walls. Thus, the metal coating is used in bearing regions that are subjected to frictional contact with other conveyor belt components. 
         [0016]    Another example of a metal-coated thermoplastic conveyor belt component is the belt module  50  of  FIG. 4 . Like the sprocket of  FIG. 3 , the belt module is largely made of a thermoplastic polymer in an injection molding process. A portion of its outer surface—in this case, the cylindrical walls of rod holes  52  though hinge elements  54 —is covered by a metal coating  56  to provide wear resistance to this bearing region of the belt module. 
         [0017]    Although the invention has been described with reference to a few preferred versions, other versions are possible. For example, the metal-coated hinge rod was shown coated along only a portion of its length, but could be coated along its entire length. And the rod was shown with a circular cross section, but its cross section could be oval, rectangular, or even asymmetrical. Some other conveyor belt components that could benefit from metal-coating include: the top edges of flights; drive-receiving surfaces in belt modules; the bearing surfaces supporting roller balls in ball belts; holddown guides in radius, spiral, or inclined belts; axles for fixed-axis rollers in roller belts. Metal coatings can also be used to provide thermoplastic conveyor belt components with electrical conductivity, magnetic properties, visible or otherwise detectable indicia, or aesthetically pleasing designs. As another example, other metal-coating processes, such as metal deposition, electroplating, and adhesive-bonding, could be used to stiffen thermoplastic conveyor belt members. So, as these few examples suggest, the scope of the claims is not meant to be limited to the preferred versions described in detail.