Abstract:
A weldless aluminum pallet has slats that interlock with outside and inside stringers to form the pallet without need for permanent attachment points. Grooves in the stringers receive a projection on each slat, holding the slat in place. Preferably, a single projection extends along the length of the slat body. The projection is shaped to cooperate with the groove such that the slat attaches perpendicularly to the stringers. The groove is shaped to retain the slat&#39;s projection by friction fit, creating an interlocking joint. The front and rear slats on each face may be fastened to the stringers by screws or other removable fasteners. Pure aluminum or an aluminum alloy may be used, and the material may be tempered using known tempering techniques. The preferred material is 100% recycled 6005-T6 aluminum alloy. The parts are preferably extruded but alternatively may be molded or otherwise die cast.

Description:
FIELD OF INVENTION 
       [0001]    This invention relates to pallets. This invention relates particularly to an aluminum pallet that exceeds standard load-bearing requirements and is assembled without permanent attachment of the parts. 
       BACKGROUND 
       [0002]    The pallet is known to be the most commonly utilized structural base for transportation and storage of unit loads of goods. Pallet designs provide varying degrees of versatility with respect to the two main requirements of a pallet—bearing the weight of the load and being lifted by a jacking device, such as a forklift. Additional key aspects of a pallet design are ease of cleaning and sanitization, cost, expected useful life, reliability for reuse, and reparability. 
         [0003]    Generally, size and load-bearing requirements for pallets are nationally and internationally standardized. A common variant in pallet designs is therefore the material from which the pallet is made, because the material type significantly affects ease of cleaning, cost, reusability, and reparability of the pallet. Known pallets are made of wood, paper, plastic, or certain metals including steel and aluminum. Due to their low cost, wood pallets are the most common. However, wood pallets suffer significant drawbacks. Relative to plastic and metal, wood is not strong and becomes weaker with age. The structural integrity of a wood pallet may be weakened when stored in excessively humid or dry conditions. A broken part on a wood pallet cannot be repaired, and may create dangerous splinters. Wood pallets can catch fire. Contact with liquids can damage or weaken a wood pallet, making it hard to clean. Wood pallets are subject to International Standards for Phytosanitary Measures No. 15 (“ISPM 15”), which requires specific treatments of wood to ensure that invasive insects, bacteria, or viruses are not present. These treatments increase the cost of the pallet and replacement parts and subject shippers to inspection violations if the wood does not meet the standard. 
         [0004]    Certain plastic compounds are a marked improvement over wood as a pallet material. For example, high-density polyethylene is stronger and often lighter than wood, can be cleaned with liquids and acidic chemicals, and is not subject to ISPM 15. The plastic pallet may have a longer useful life. However, plastic also has drawbacks. A plastic pallet costs about 10 times the cost of a wood pallet. Plastic parts are generally not reparable. Plastic remains a fire hazard and is subject to deformation when stored in excessive heat or with heavy loads thereon. 
         [0005]    Metal pallets are relatively new designs, currently comprising about 1% of in-use pallets. Known metal pallet designs use steel or aluminum to resolve many of the drawbacks of both wood and plastic, depending on the intended use. Both steel and aluminum are resistant to rust and degradation, can be cleaned and sanitized with liquids and acidic chemicals, are not subject to ISPM 15, and are stronger than wood and plastic. Metal pallets are fire resistant and may be reparable, depending on the damage. Metal pallets will not deform in heat or under heavy loads. Metal pallets are comparable or cheaper in cost than plastic, and may be cheaper than wood over the long run due to the longevity and durability of each pallet. One drawback of metal is its weight, and so aluminum is the preferred metal because it is significantly lighter than steel of comparable size. 
         [0006]    While aluminum is proving to be the preferred pallet material, the few known designs suffer the common drawback of being assembled using one of two fastening mechanisms: screws or welding. Screw-attachment designs are deficient due to the number of screws required for secure attachment of slats to stringers. Each slat needs at least two screws at each attachment point to each stringer. For a typical 40 inch pallet with 7 5-inch slats and 3 stringers, this equates to six holes in each slat, 14 holes in each stringer, and 52 screws. Such a design incurs significant manufacturing and assembly costs. Similar cost issues plague welded designs, which require the expensive services of a professional welder to assemble or repair the pallets. While the problem of missing screws is resolved, a new issue arises in that welds are permanent attachments. Thus, a welded pallet cannot be disassembled and is not easily repaired. An aluminum pallet design that is equally reliable, but less expensive to manufacture, assemble, and disassemble compared to existing aluminum pallets is needed. 
         [0007]    Therefore, it is an object of this invention to provide an aluminum pallet that may be assembled without permanent fasteners. It is a further object that the pallet be assembled with a minimum of removable fasteners. It is a further object that the pallet be formed of interlocking parts. Another object of the invention is to provide a pallet that meets the size and load-bearing standards of the pallet industry, is fireproof and rustproof, can be easily cleaned and sanitized, and can be assembled and disassembled with ease. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention is an aluminum pallet having interlocking parts that allow assembly of the pallet into its production form without the need for permanent attachment points, such as welds. Further, the aluminum pallet is assembled using a minimum of removable fasteners, preferably screws. Pure aluminum or an aluminum alloy may be used, and the material may be tempered using known tempering techniques. The preferred material is 100% recycled 6005-T6 aluminum alloy. The parts are preferably extruded but alternatively may be molded or otherwise die cast. 
         [0009]    The parts include a plurality of slats attached to a plurality of stringers, selected to form the desired stringer design pallet. Preferably, the parts form a double-face or reversible pallet. A slat has a body with a top surface, on which goods are placed, and a bottom surface; and at least one projection extending from the bottom surface of the body. Preferably, a single projection extends along the length of the slat body. The projection is shaped to cooperate with a groove formed into each stringer, such that the slat attaches perpendicularly to the stringers. The groove is shaped to retain the slat&#39;s projection by friction fit, creating an interlocking joint. The groove and projection may have any interlocking cross-sectional shape. Each stringer has as many grooves as the pallet has slats. Two of the stringers are outside stringers, each outside stringer having one or two lips projecting vertically from the outside edge of the stringer. The lips are abutted by the slats when the slats are in place, preventing the slats from extending past the outside edge of the outside stringers. The remaining stringers are inside stringers, which may be attached by fasteners to the slats at a desired distance from the outside stringers. 
         [0010]    Methods of making a weldless aluminum pallet are also disclosed. First, slats and stringers having the above-described features are extruded from extrusion dies. Preferably, the grooves are formed into the stringers after extrusion. Three extrusion dies are needed—one each for the slat, the outside stringer, and the inside stringer. The outside stringer has one lip if the pallet is single-faced, and two lips if the pallet is double-faced or reversible. After extrusion, the parts are cut to the desired length. The grooves are then formed into each stringer, preferably uniformly spaced along the length of the stringer, by drilling. The first slat is taken up and its projection is inserted at the slat&#39;s proximal end through corresponding grooves in the inside stringers, and then into the corresponding groove in the first outside stringer until the slat body abuts the lip on the first outside stringer. The insertion is repeated with each slat, and then the second outside stringer is placed onto the slats&#39; projections at the slats&#39; distal ends. The stringers are then fastened to the front and back slats to finish the pallet. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a top perspective view of the preferred embodiment of the pallet. 
           [0012]      FIG. 2  is a top view of the pallet of  FIG. 1 . 
           [0013]      FIG. 3  is a top perspective view of an alternative embodiment of the pallet. 
           [0014]      FIG. 4  is a bottom left perspective view of the preferred slat. 
           [0015]      FIG. 5A  is a front cross-sectional view of the preferred slat taken along line  5 - 5  of  FIG. 4 . 
           [0016]      FIG. 5B  is a front cross-sectional view of an alternative slat. 
           [0017]      FIG. 6  is a top left perspective view of the preferred outside stringer. 
           [0018]      FIG. 7A  is a front cross-sectional view of the preferred outside stringer configured for a light-duty pallet, taken along line  7 - 7  of  FIG. 6 . 
           [0019]      FIG. 7B  is a front cross-sectional view of the preferred outside stringer configured for a heavy-duty pallet, taken along line  7 - 7  of  FIG. 6 . 
           [0020]      FIG. 8  is a left side view of the preferred outside stringer. 
           [0021]      FIG. 9  is a top left perspective view of the preferred inside stringer. 
           [0022]      FIG. 10A  is a front cross-sectional view of the preferred inside stringer configured for a light-duty pallet, taken along line  9 - 9  of  FIG. 9 . 
           [0023]      FIG. 10B  is a front cross-sectional view of the preferred inside stringer configured for a heavy-duty pallet, taken along line  9 - 9  of  FIG. 9 . 
           [0024]      FIG. 11  is a flowchart illustrating the preferred method of making the pallet. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    Referring to  FIGS. 1 and 2 , there is illustrated the preferred embodiment of the present invention, designated generally as  10 , which is a weldless aluminum pallet comprising interlocking parts. The pallet  10  generally may have any design known in the industry as a “stringer design,” in that the pallet  10  has at least two outside stringers  11  and at least one inside stringer  12 , to which a plurality of slats  13  are attached. By way of example, the possible pallet  10  designs may include: single-faced, in which slats  13  are arranged to form a top load-bearing face, and the opposite or “bottom” slats  13 , if any, do not form a load-bearing face; double-faced, in which slats  13  are arranged to form top and bottom load-bearing faces; and reversible, in which the pallet  10  is double-faced and the top and bottom faces are identical. The faces are substantially planar in a plane parallel to the plane defined by lines X and Y in  FIG. 2 . Any pallet  10  design may further be flush, having slats  13  that do not hang over the outer edges of the outside stringers  11 ; or winged, having top slats  13  or top and bottom slats  13  extending beyond the outer edges of the outside stringers  11 . The preferred pallet  10  is a double-faced pallet  10  having 1 inside stringer  12 , 5 top slats  13  and 3 bottom slats  13 . A reversible pallet  10  having 7 top slats  13  and 7 bottom slats  13  is shown in  FIG. 3 . The designs shown in  FIGS. 1-3  are flush pallets  10 . The dimensions of the pallet  10  are chosen to conform to a standardized pallet size. The preferred embodiment conforms to the international standard of 48 inches by 40 inches, wherein 48 inches is the stringer  11 ,  12  length. The pallet  10  may have any desired height, typically chosen according to the desired use, but preferably the height is between 4 and 5 inches. 
         [0026]    The present inventive pallet  10  is made of aluminum, which may be pure aluminum or an aluminum alloy. Preferably, the material is 6005-T6 aluminum alloy, representing the most favorable combination of strength and cost-effectiveness. The selection of aluminum alloyed with magnesium and silicon is easier to extrude than other alloys, and can be hardened to near-steel strength. Other alloys and degrees of tempering may be used. The preferred alloy allows the parts of the pallet  10  to be extruded with a wall thickness of as thin as 0.094 inches. Because the weight of the pallet  10  is a significant concern, the present invention contemplates a preferred heavy-duty and a preferred light-duty design. The preferred heavy-duty pallet  10  has stringers  11 ,  12  with 0.125 inch thick walls. The preferred light-duty pallet  10  has stringers  11 ,  12  with vertical walls that are 0.094 inches thick. The horizontal exterior walls of the light-duty stringers  11 ,  12  remain at 0.125 inches thick in order to receive the neck of the slats&#39;  13  projections as described below. Further, the light-duty stringers  11 ,  12  may be up to an inch shorter than the heavy-duty stringers  11 ,  12  to further reduce the weight of the pallet  10 . The light-duty pallet  10  may be about 50%-80% of the weight of the heavy-duty pallet, most preferably about 75%, depending on the chosen pallet design. 
         [0027]    Referring to  FIGS. 4 ,  5 A, and  5 B, the slat  13  comprises a slat body  30  having an outer surface  31  and an inner surface  32 . The outer surface  31  represents a portion of the top or bottom face of the pallet  10 ; that is, the outer surfaces  31  of all of the top slats  13  form the top face of the pallet  10 , and the outer surfaces  31  of all of the bottom slats  13  form the bottom face of the pallet  10 . The outer surface  31  is substantially flat and may be planar, as shown in  FIG. 5A . The outer surface  31  may alternatively be textured to increase the amount of friction between the face of the pallet and the goods placed thereon. The outer surface  31  may be serrated, as shown in  FIG. 5B , or ribbed, or have nodes or treads formed thereon. Preferably, the texture is one that can be formed during the extrusion process, as in the serration shown in  FIG. 5B . Alternatively, the texture may be added to the outer surface  31  after the extrusion process, such as by applying a textured coating. The inner surface  32  is planar and contacts the stringers  11 ,  12  when the pallet  10  is formed. The slat body  30  may have any dimensions conducive to forming the pallet. The preferred height is 0.125 inches, giving the preferred slat  13  sufficient load-bearing capacity. The preferred width is about 5 inches. The length of the slat body  30  depends on whether the pallet  10  is flush or winged, with the preferred slat body  30  measuring 39.75 inches in length. 
         [0028]    At least one projection  33  extends out from the inner surface  32  substantially perpendicularly to the inner surface  32 . Preferably, there is 1 projection  33  centrally located on the top surface  32 . The projection  33  is preferably integral with the slat body  30  and is extruded together with the slat body  30 . The projection  33  comprises a neck  34  connected to the top surface  32 , and a tongue  35  connected to the neck  34 . The projection  33  is configured to cooperate with a groove formed into the stringers  11 ,  12  as described below, such that the slat  13  interlocks with the stringers  11 ,  12  to form the pallet  10 . Preferably, the neck  34  is about 0.125 inches square in cross-section. The tongue  35  is substantially wider than the neck  34 , having a cross-sectional shape that provides substantial contact with the surfaces of the groove in each stringer  11 ,  12  to hold the slat  13  securely to the stringers  11 ,  12 . The preferred cross-sectional shape of the tongue  35  is illustrated in  FIGS. 5A-B , being a circle having a radius of about 0.219 inches, with segments removed from the top and bottom of the circle so that the height of the tongue  35  is about 0.313 inches. The preferred height of the projection  33  is therefore about 0.438 inches. 
         [0029]      FIGS. 6-8  illustrate the preferred outside stringer  11 . The outside stringer  11  has two vertical walls—an outside wall  51  and an inside wall  52 . A horizontal top wall  53  and horizontal bottom wall  54  connect the outside wall  51  to the inside wall  52 , leaving the outside stringer  11  substantially hollow. It will be understood that for double-faced, reversible, and double-winged pallets  10 , the top wall  53  and bottom wall  54  are interchangeable; that is, the outside stringer  11  is symmetrical about the midpoint of the vertical walls, so “top” and “bottom” merely identify the wall and do not require one wall to be disposed above or below the other. The outside stringer  11  is preferably 2 inches wide and between 4 and 5 inches high, including the height of the lips  58  described below. 
         [0030]    One or more ribs  55  may further connect the outside wall  51  to the inside wall  52 , adding structural stability to the outside stringer  11 . A notch  56  may be formed into the outside wall  51 . The notch  56  provides a place to insert a pallet  10  tag (not shown), such as a radio frequency identification (“RFID”) tag, or a wireless (“WIFI”) tag. The pallet tag is placed in the notch  56  so that it does not protrude from the outside wall  51 . The notch  56  may be sized to accommodate the desired pallet tag. The preferred heavy-duty pallet  10  has a notch that is 2.375 inches wide and 0.406 inches deep, accommodating a CONFIDEX model 3000072 or similar RFID tag. The preferred light-duty pallet  10  has a notch that is 1.375 inches wide and 0.25 inches deep, accommodating a CONFIDEX model HAO122B75 or similar RFID tag. The outside stringer  11  may have a plurality of screw bosses  57  formed onto the inner surfaces of the outside wall  51 , inside wall  52  or both. The screw bosses  57  each receive a fastener used to secure a cap  61  onto either end of the outside stringer  11 . 
         [0031]    The outside wall  51  may comprise one or two lips  58  that extend vertically past the top wall  53 , bottom wall  54 , or both walls  53 ,  54 . The lips  58  serve to abut the ends of the slats  13 , retaining the slats  13  in position and preventing the slats  13  from hanging over the edge of the outside stringer  11 . A lip  58  is preferably the same height as a slat  13  so it does not project above the face of the pallet  10 . The number and orientation of the lips  58  will depend on the pallet  10  design: a single-faced flush pallet  10  may have a lip  58  on the top, and may also have a lip  58  on the bottom if slats  13  are to be attached thereto; a double-faced or reversible flush pallet  10  may have lips  58  on the top and bottom; a single-winged pallet  10  may have a lip  58  on the bottom; and a double-winged pallet  10  will not have any lips  58 . 
         [0032]    A plurality of grooves  62  are formed into the outside stringer  11 . The grooves  62  project vertically inward from at least the top wall  53 , and also from the bottom wall  54  if slats  13  are used to form a bottom face. As shown in  FIGS. 6 and 8 , one groove  62  is needed for each slat  13 , so that the preferred outside stringer  11  has five grooves  62  in the top wall  53  and three grooves  62  in the bottom wall  54 . A groove  62  is shaped to receive the projection  33  on a slat  13 , so that the projection  33  fits tightly in the groove  62 . Specifically, the groove  62  substantially encloses the tongue  35 , coming into close proximity or contact with the neck  34  so that the tongue  35  can only move along its axis, which is parallel to line X in  FIG. 2 , and cannot rotate within the groove  62 . In the preferred embodiment, the groove  62  comprises a circular punch  63  passing through the inside wall  52 , and a channel  64  passing through the top wall  53  or bottom wall  54 . The channel  64  starts at the inside wall  52  and extends to the lip  58  if there is one, or to the outside wall  51  if there is no lip  58 . A second punch  63  may pass through the outside wall  51  if there is no lip  58 . The grooves  62  are preferably uniformly spaced along the length of the outside stringer  11 , with the grooves  62  for front and back slats  13  being located 2.5 inches inward from the ends of the outside stringer  11  so that the front and back slats  13  are flush with the ends of the stringers  11 ,  12 . 
         [0033]      FIGS. 9-10B  illustrate the preferred inside stringer  12 . The inside stringer  12  has vertical walls  81  and horizontal walls  82  that form a rectangle. Preferably, the inside stringer  12  is 2 inches wide and between 3.75 and 4.75 inches high. Like the outside stringer  11 , the inside stringer  12  may have screw bosses  57  for attaching caps  61  to the ends, and a rib  55  for reinforcing the structure. Preferably, the inside stringer  12  has a second rib  55  to add further stability, due to the added force exerted on the inside stringer  12  by heavy loads. Grooves  62  are formed into the inside stringer  12  as described above, so that the grooves  62  are aligned with the grooves  62  in the outside stringers  11 . 
         [0034]    The stringers  11 ,  12  and slats  13  may be molded, extruded, or otherwise die cast. Extrusion is preferable due to the workability of the preferred alloy and the much lower cost of producing extrusion dies over producing molds. The pallet  10  parts may be produced using as few as 2 extrusion dies, depending on the chosen pallet  10  design. For example, a double-wing pallet  10  has identical outside stringers  11  and inside stringer  12 , so only 2 dies are needed—1 for the stringers  11 ,  12  and 1 for the slats  13 . Preferably, however, there are 3 extrusion dies because the pallet  10  is flush, the design benefiting from two lips  58  on each outside stringer  11 . 
         [0035]    Referring to  FIG. 11 , three extrusion dies are used in a method of making the preferred pallet  10 . The preferred aluminum alloy is extruded  100  through the dies, creating 8 feet of outside stringer  11  material, 4 feet of inside stringer  12  material, and 26.5 feet of slat  13  material. The parts are then cut  105  to length: 2 outside stringers  11  are cut to 48 inches in length, 1 inside stringer  12  is cut to 48 inches in length, and 8 slats  13  are cut to 39.75 inches in length. The grooves  62  are then formed  110  into the stringers  11 ,  12 , with 5 grooves  62  on the top and 3 grooves  62  on the bottom. Most preferably, the grooves  62  are formed  110  using a 2-part process. First, the punches  63 , preferably about 0.875 in diameter, are formed into the inside walls  52  of the outside stringers  11 , and into both vertical walls  81  of the inside stringer  12 . Then, the channels  64  are formed, each having a width of about 0.125 inches. The channels  64  on the outside stringers  11  extend from the punches  63  to the lips  58 , and the channels  64  on the inside stringer  12  extend fully along the horizontal walls  82  from punch  63  to punch  63 . The grooves  62  may be formed one at a time, but preferably grooves  62  that are horizontally aligned on a stringer  11 ,  12  are formed simultaneously using a computer numerical controlled (“CNC”) machine tool. This is done to minimize the chance of misalignment of the grooves  62 , so that the slats  13  may interlock precisely with the stringers  11 ,  12 . 
         [0036]    Once the grooves  62  are formed  110 , a first slat  13  is taken up and its projection  33  is slid  115  through one of the grooves  62  in the inside stringer  12 . Then, the proximal end of the first slat&#39;s  13  projection  33  is inserted  120  into the groove  62  in the first outside stringer  11  that aligns with the groove  62  used on the inside stringer  11 . The projection  33  is inserted  120  until the slat body  30  abuts one of the lips  58 . The sliding  115  and insertion  120  are then repeated  125  with the other slats  13 , until each groove  62  in the inside stringer  12  and first outside stringer  11  contains a projection  33  from a slat  13 . Then, the second outside stringer  11  is placed  130  over the slat  13  projections  33  at the slats&#39; distal ends, by feeding the projections  33  into the grooves  62  on the second outside stringer  11 . 
         [0037]    The parts may then be secured in place by tapping  135  screw holes in the front slats  13   a  and rear slats  13   b . See  FIGS. 1 and 2 . In the preferred embodiment, only 12 screws are needed: 1 screw for each stringer  11 ,  12  in each of the 2 front slats  13   a  and 2 rear slats  13   b . Preferably, two of the screw holes are tapped  135  within 0.25 inches of each end of the slats  13   a ,  13   b  so that the screw may catch a portion of a screw boss  57  to improve its hold in the outside stringers  11 . The third screw hole is preferably tapped  135  at the midpoint of the slat  13   a ,  13   b  so that the inside stringer  12  is secured substantially centrally between the slats  13 . Once the screw holes are tapped  135 , screws  83  are screwed into the slats  13   a ,  13   b  and stringers  11 ,  12  to finish the pallet  10 . Optionally, caps  61  may be attached to the ends of the stringers  11 ,  12 . The caps  61  are preferably attached using screws that extend into the screw bosses  57 . 
         [0038]    While there has been illustrated and described what is at present considered to be the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made and equivalents may be substituted for elements thereof without departing from the true scope of the invention. Therefore, it is intended that this invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.