Patent Application
20150360809
This invention relates generally to pallets and more particularly to four-way entry pallets with improved resistance to damage.
Wood pallets are in widespread use for shipping products between manufacturers, distributors, and retailers. The vast majority of pallets in current use are constructed with a top deck formed of solid wood boards coupled with a bottom deck formed of solid wood boards. The top and bottom deck boards can be coupled together in a variety of ways to form the assembled pallet. Two-way entry pallets typically employ long stringers as spacer members for coupling the top deck boards and bottom deck boards, while four-way entry pallets (which are becoming more popular because of the greater ease of use that four-way entry allows) typically employ horizontal stringers to aid in holding and strengthening the top deck boards together and wood blocks as spacer members to couple the bottom deck boards to the top deck boards through the stringers. Wood pallets are typically of simple design and can be repaired when damaged in use. The Uniform Standard for Wood Pallets”, Copyright 2012, National Wooden Pallet and Container Association (referred to herein as the “NWPCA bulletin”), Alexandria, Va. 22314-2805, describes several types of conventional pallets.
The pool pallet system was developed as a means of controlling overall pallet usage cost and to limit destruction of timberlands used to provide wood for pallet construction. In the pool pallet system, a provider operates service centers to supply pallets and to receive returned pallets. When a pallet is returned to the service center, the pallet owner performs any needed repairs before returning the pallet to service. This process can continue as long as the pallet can, at a reasonable cost, be satisfactorily repaired and returned to service. Commonly used pool pallets have the advantage of being fabricated and repaired using common woodworking and fastening techniques that help make the pallet pool system cost-effective. This means the parts needing to be repaired can be readily deconstructed from the pallet. One particularly useful type of pallet used in the “pool” system is a 4-way entry block pallet with a full perimeter bottom deck.
Four-way entry pallets include a top deck, a bottom deck and spacer members. The top deck includes a pair of end members and a plurality of intermediate load supporting members. The bottom deck is provided with openings to accommodate the wheels of a hand transport. The top and bottom decks are separated by means of spacer members including longitudinally extending stringers on which are mounted spacer blocks, often of plywood or a composite material. The deck members, stringers and spacer blocks are typically mechanically fastened with, for example, nails or screws. Typically, nine blocks are installed at the corners of the pallet and intermediately of the end and side members to provide access to the pallet by the forks of a forklift or hand transport (pallet jack). In certain instances, the forks of a forklift truck can make contact with the lead boards of the decks and/or block members during alignment. If the force is significant, the lead boards and/or block members can be damaged. Many common types of pallet damage, and the requirement for their repair can be found in “Uniform Standard for Wood Pallets”, Copyright 2012 by the National Wooden Pallet and Container Association, Alexandria, Va. 22314-2805.
A number of suggestions have been made to reduce damage to lead boards for upper decks, including end-caps or protective parts for the access end of the pallet, multi-ply laminated boards (e.g. U.S. Publication No. 2011/0005435 to Renck et al.), pultruded boards (e.g. U.S. Publication No. 2006/0081158 to Ingham), and energy absorbing structures for the lead boards. However, because the added cost of these materials cannot typically be recovered, and because of the relative ease of repairing wood pool pallets, these improvements are not used widely in pool pallet systems of major North American pool pallet providers.
Another mode of damage is possible when a pallet jack is used to transport a pallet. A pallet jack, unlike a forklift, has forks that also serve as a base and includes wheels. In order to lift a pallet with a pallet jack, the fork is wheeled into the inner space of the pallet and then lifted, typically hydraulically. Hitting or running into the lower lead board can damage that board in the same manner as the lead board on the top deck of the pallet. Damage can also occur on the bottom deck of the pallet when a pallet jack is inserted into the pallet incorrectly so that the wheels of the pallet jack reside on a board of the bottom deck, rather than in the space designed for them. In this situation, the action of the forks of the pallet jack can force the top and bottom sections apart and can cause splitting or cracking of the boards of the bottom deck and can also lead to loss of an entire board if the mechanical fasteners fastening the board to the block spacer are pulled out.
When a pallet is entirely constructed of relatively cheap materials, these defects can be cost effectively managed by simply replacing the damaged board with another board of the same relatively cheap material. However, when pallets are constructed of combinations of material, for example, wood planks or boards and a relatively expensive energy attenuating lead board, such as a multi-ply laminated or a pultruded lead board, replacement of the lead board after damage and/or loss can become excessively costly. Thus these energy attenuating lead board materials are often undesirable even though they can reduce damage at the lead board position on a pallet deck and allow such a hybrid pallet a longer useful life.
According to an embodiment of the invention, a pallet having a top deck comprising a first top deck lead board at a first end of the top deck and a second top deck lead board at a second end of the top deck, opposite the first, at least one intermediate board positioned between the first and second top deck lead boards, and a plurality of spacer members coupled with the top deck, the pallet comprises a bottom deck sub-assembly comprising: a first bottom deck lead board at a first end of the bottom deck sub-assembly and a second bottom deck lead board at a second end of the bottom deck sub-assembly, opposite the first, and at least one intermediate board extending between the first and second bottom deck lead boards and fastened to an adjacent first and second bottom deck lead board to form a joint between the at least one intermediate board and the adjacent first and second bottom deck lead boards. The joint between the at least one intermediate board and the adjacent first and second bottom deck lead board has a joint strength in tension of 450 Newtons or greater and the bottom deck sub-assembly is coupled with the top deck through the plurality of spacer members to form the pallet. The first bottom deck lead board or the second bottom deck lead board can comprise an oriented plastic composite or fiber filled thermoplastic material.
These and other features and advantages of the present invention will become better understood to those of ordinary skill in the art when considered in connection with the following description and drawings:
“Solid state” refers to a polymer (or polymer composition) that is below the softening temperature of the polymer (or polymer composition). Hence, “solid state drawing” refers to drawing a polymer or polymer composition that is below the softening temperature of the polymer (or polymer composition). “Solid state die drawing” refers to drawing a polymer or polymer composition that is below its softening temperature through a shaping die.
“Polymer composition” comprises at least one polymer component and can contain non-polymeric components. A “filled” polymer composition includes discontinuous additives, such as inorganic or organic fillers.
An “orientable polymer” is a polymer that can undergo induced molecular orientation by solid state deformation (for example, solid state drawing). An orientable polymer can be amorphous or semi-crystalline (semi-crystalline polymers have a melt temperature (Tm) and include those polymers known as “crystalline”). Desirable orientable polymers include semi-crystalline polymers, and in particular, linear polymers (polymers in which chain branching occurs in less than 1 of 1,000 polymer units). Semi-crystalline polymers can be particularly desirable because they can result in greater increase in strength and flexural modulus than amorphous polymer compositions. Semi-crystalline polymer compositions can result in 4-10 times greater increase in strength and flexural modulus upon orientation over amorphous polymer compositions.
An “orientable polymer phase” is a polymer phase that can undergo induced molecular orientation by solid state deformation (for example, solid state drawing). Typically, 75 wt % or more, even 90 wt % or more or 95 wt % or more of the polymers in the orientable polymer phase are orientable polymers based on total orientable polymer phase weight. All of the polymers in an orientable polymer phase can be orientable polymers. An orientable polymer phase may comprise one or more than one type of polymer and one or more than one type of orientable polymer.
“Oriented polymer composition article”, “OPC” and “oriented polymer composition” are interchangeable and refer to an article made by orienting the polymers of a polymer composition. An oriented polymer composition comprises polymer molecules that have a higher degree of molecular orientation than that of a polymer composition extruded from a mixer.
“Weight-percent” and “wt %” are interchangeable and are relative to total polymer weight unless otherwise stated.
“Softening temperature” (Ts) for a polymer or polymer composition having as polymer components only one or more than one semi-crystalline polymer is the melting temperature for the continuous phase polymer in the polymer composition.
“Melting temperature” (Tm) for a semi-crystalline polymer is the temperature half-way through a crystalline-to-melt phase change as determined by differential scanning calorimetry (DSC) upon heating a crystallized polymer at a specific heating rate. Tm for a semi-crystalline polymer can be determined according to the DSC procedure in ASTM method E794-06. Tm for a combination of polymers, and for a filled polymer composition, can also be determined by DSC using the same test conditions in ASTM method E794-06. If the combination of polymers or filled polymer composition only contains miscible polymers and only one crystalline-to-melt phase change is evident in the a DSC curve, then Tm for the polymer combination or filled polymer composition is the temperature half-way through the phase change. If multiple crystalline-to-melt phase changes are evident in a DSC curve due to the presence of immiscible polymers, then Tm for the polymer combination or filled polymer composition is the Tm of the continuous phase polymer. If more than one polymer is continuous and they are not miscible, then the Tm for the polymer combination or filled polymer composition is the highest Tm of the continuous phase polymers.
“Softening temperature” (Ts) for a polymer or polymer composition having as polymer components only one or more than one amorphous polymer is the glass transition temperature for the continuous phase of the polymer composition.
If the semi-crystalline and amorphous polymer phases are co-continuous, then the softening temperature of the combination is the lower softening temperature of the two phases. If the polymer composition contains a combination of semi-crystalline and amorphous polymers, the softening temperature of the polymer composition is the softening temperature of the continuous phase polymer of the polymer composition.
“Glass transition temperature” (Tg) for a polymer or polymer composition is the temperature half-way through a glass transition phase change as determined by DSC according to the procedure in ASTM method D3418-03. Tg for a combination of polymers and for a filled polymer composition can also be determined by DSC under the same test conditions in D3418-03. If the combination of polymer or filled polymer composition only contains miscible polymers and only one glass transition phase change is evident in the DSC curve, then Tg of the polymer combination or filled polymer composition is the temperature half-way through the phase change. If multiple glass transition phase changes are evident in a DSC curve due to the presence of immiscible amorphous polymers, then Tg for the polymer combination or filled polymer composition is the Tg of the continuous phase polymer. If more than one amorphous polymer is continuous and they are not miscible, then the Tg for the polymer composition or filled polymer composition is the highest Tg of the continuous phase polymers.
If the polymer composition contains a combination of semi-crystalline and amorphous polymers, the softening temperature of the polymer composition is the softening temperature of the continuous phase polymer or polymer composition.
“Drawing temperature” refers to the temperature of the polymer composition as it begins to undergo drawing in a solid state drawing die.
“Linear Draw Ratio” is a measure of how much a polymer composition elongates in a drawing direction (direction the composition is drawn) during a drawing process. Linear draw ratio can be determined while processing by marking two points on a polymer composition spaced apart by a pre-orientated composition spacing and measuring how far apart those two points are after drawing to get an oriented composition spacing. The ratio of final spacing to initial spacing identifies the linear draw ratio.
“Nominal draw ratio” is the cross sectional surface area of a polymer composition as it enters a drawing die divided by the polymer cross sectional area as it exits the drawing die.
An OPC is “similar” to another OPC if its composition is substantially the same as the other OPC in all respects except those noted in the context where the similar OPC is referenced. Compositions are substantially the same if they are the same within reasonable ranges of process reproducibility.
“ASTM” refers to ASTM International, formerly American Society for Testing and Materials; the year of the method is either designated by a hyphenated suffix in the method number or, in the absence of such a designation, is the most current year prior to the filing date of this application.
“Multiple” means at least two.
“And/or” means “and, or as an alternative.”
Ranges include endpoints unless otherwise stated.
Temperatures are given in degrees Celsius, abbreviated as “C” unless otherwise stated.
Flexural modulus (modulus of elasticity (MOE)) and flexural strength (modulus of rupture (MOR)) are measured according to ASTM method ASTM D-6109-05, “Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastic Lumber and Related Products.” Per ASTM D-6109-05, a force versus displacement under a four point bending load is measured. The force versus displacement curve is converted to a stress versus strain curve and the MOE and MOR are subsequently determined from the curve according to the methods set forth in ASTM D-6109-05.
Density is measured according to ASTM method ASTM D-792-00.
“Block”, “spacer”, and “spacer block” are used herein interchangeably. A block is a rectangular, square, multisided, or cylindrical deck spacer, often identified by its location within the pallet as corner block, end block, edge block, inner block, or center or middle block.
A “deck board” is a pallet element or component of a pallet top or bottom, perpendicular to stringers or stringer boards.
“Stringer and “stringer board” are used interchangeably herein. A stringer is a continuous, longitudinal, solid, built up, or notched beam component of a pallet, supporting and spacing deck components, often identified by its location as edge (side) or interior (center) stringer.
“Spacer member” refers to the pallet member which directly or indirectly couples the top deck boards to the bottom deck boards. In some cases, the spacer member may be in the form of a stringer board which couples the top deck boards together and through which the bottom deck boards are coupled with the top deck to form the assembled pallet. The stringer boards may also reinforce the pallet structure. A stringer pallet is an example of such a configuration. Alternatively, the spacer member may be in the form of blocks which are used to couple the top deck and the bottom deck together. An example of this type of configuration is a block pallet. It is also within the scope of the invention for a combination of stringer boards and blocks to be used to form the pallet. An example of this type of configuration is also sometimes referred to as a block pallet in which one or more stringer boards are used to couple the top deck boards together and a plurality of blocks are coupled with the stringer boards and the bottom deck boards to form the assembled pallet. The spacer members can also provide space between a top deck and a bottom deck of a pallet to allow entry of the forks of a forklift to lift and move the pallet.
“Gang nail”, “gang nail plate”, “gang nail connector plate”, “mending plate” and “truss plate” are used interchangeably and refer to a sheet of galvanized steel, with pointed prongs that are cut and bent perpendicular to a plate face of the gang nail, allowing it to be hammered or pressed into a number of surfaces simultaneously. The prongs are often of triangular shape and the gang nail typically has several prongs or teeth per square inch of plate.
A “corrugated fastener” is a thin strip of sheet metal that has a pattern of alternating grooves and is typically made from 18 to 22 gauge sheets of stainless or cold-rolled steel. Typically, increased joint strength is observed as the number of corrugated fasteners used to fasten a joint is increased. Also, typically, if two or more corrugated fasteners are used in a given joint, improved joint strength is observed when they are placed so that they are not parallel to one another.
“Readily deconstructed” in the context of a pallet assembly means that a worker using his hands and/or unpowered hand tools, e.g., a claw hammer, can remove a pallet board that has been damaged in less than 5 minutes, and still continue to use the pallet assembly without the damaged, removed portion. Damage can include damage to the board itself or damage to the connection between the board and one or more parts of the pallet assembly, such as damage to one or more fasteners, pull through of a fastener, and/or pull out of a fastener. Removal of the damaged portion of the pallet assembly may include removal of adjacent portions that were not damaged.
A wood pallet can be any of those described as wood pallets in Uniform Standard for Wood Pallets”, Copyright 2012, National Wooden Pallet and Container Association (referred to herein as the “NWPCA bulletin”), Alexandria, Va. 22314-2805, but is not limited to these pallet designs, especially when pallets are designed for geographies other than North America. A top deck of a pallet can consist of one or more than one deck board transverse to the length direction of the pallet. A bottom deck can be a single board with wheel openings or, preferably, can have 3 or more often up to 5 boards, while still leaving space for a pallet jack to enter and lift a pallet. Between the top deck and the bottom deck are spacers that may be stringers, as is common in two-way entry pallets, or spacer blocks as is typical in four way entry pallets, or a combination of stringers and spacer blocks. A non-limiting list of suitable natural wood species can be found in Annex B, Wood Species Classes, “Uniform Standard for Wood Pallets”, Copyright 2012, NWPCA.
Four-way entry pallets include a top deck, a bottom deck and spacer members. The top deck of a pallet, in some instances may be constructed of a single deck board, but more typically consists of two or three or more deck boards and in some cases can consist of as many as nine or more deck boards. The top deck typically includes a pair of end boards (also referred to as lead boards) and a plurality of intermediate load supporting deck boards. The bottom deck is provided with a relatively large surface area, but with openings to accommodate the wheels of a transport apparatus (e.g. pallet jack).
In a conventional block pallet, the top and bottom decks are separated by means of spacer members which can include longitudinally extending stringers and/or mounted spacer blocks, often of wood, laminated wood layers (plywood) or a wood composite material. The spacer blocks can be square in horizontal cross-section, but are more typically rectangular so that the bottom perimeter deck board can be attached to the blocks. Typically, nine blocks are installed at the corners of the pallet and intermediately of the end and side members to provide access to all four sides of the pallet by the forks of a forklift or hand transport (pallet jack). The spacer bocks need not be all of the same size, although the blocks are usually the full width of the members that overlay them.
The deck boards 20a-g are provided at right angles to the stringer boards 18 and extend for the full length 21 of the pallet 10. The two deck boards 20a and 20g located at the outside opposite edges of the pallet 10 are commonly referred to as lead boards or end boards. The top deck 12 can include any number of deck boards 20a-g that are all the same width or of different widths. As illustrated in
The pallet 10 can be constructed manually or can be constructed using machines built for that purpose. In one illustrative method of constructing a pallet, the top deck 12 of
In one illustrative method of fastening the bottom deck 14 to the top deck 12 and spacer pallet assembly 33, the top deck 12 and spacer pallet assembly 33 are positioned so that the top deck 12 is facing toward a floor or work table surface with the spacer pallet assembly 33 facing upward. The bottom deck boards 34, 29, 31 are laid out on the top deck 12 and spacer pallet assembly 33 with the bottom deck lead boards 29 positioned above the top deck lead boards 20a, 20g and the edge boards 34 and bottom center deck board 31 positioned above the stringer boards 18. The bottom deck boards 34, 29, 31 can be fastened using fasteners 42 to the top deck 12 and spacer assembly 33. In this construction, a thickness of the bottom deck 14 is typically as thick as a single bottom deck board 34, 29, 31.
A source of damage to pallets can arise when, in certain instances, the forks of a forklift truck or pallet jack make contact with the lead boards 20a, 20g or 29 of the top deck 12 or bottom deck 14, respectively, and/or block members 16 or 17 during insertion of the forklift into the pallet 10 for lifting. If the force is significant, the lead boards 20a, 20g, 29 and/or block members 16, 17 can be damaged. A number of suggestions have been made to reduce damage to lead boards for upper decks, including end-caps or protective parts for the access end of the pallet, multi-ply laminated boards (e.g. U.S. Publication No. 2011/0005435 to Renck et al.), pultruded boards (e.g. U.S. Publication No. 2006/0081158 to Ingham), and energy absorbing structures for the lead boards (U.S. Pat. No. 8,261,673 to Ingham).
Because a pallet jack operates differently than does a forklift, a pallet jack, unlike a forklift, has forks that serve as a base and also includes wheels. Thus, an additional opportunity for pallet damage is possible when a pallet jack is used to transport a pallet. In order to lift a pallet with a pallet jack the fork is wheeled into the inner space of the pallet and then lifted, typically, hydraulically.
Referring now to
When the pallet 10 is entirely constructed of relatively cheap materials, for example, boards from wood species such as pine or oak, damage can be cost effectively managed by deconstructing the damaged portion of the pallet 10 and replacing the damaged or lost board with another board of the same relatively cheap material. However, when pallets 10 are constructed of more expensive materials, deconstructing the damaged portion of the pallet 10 and replacing the damaged or lost board with another board of the same, more expensive material, may not be cost effective. For example, in order to mitigate lead board damage, more expensive materials, such as a laminated board or a pultruded composite board, can be used to form the lead board. However, when this more expensive lead board does get damaged and needs replacement or becomes lost, the replacement costs compared to more economic wood boards of oak or pine can become economically unfeasible and thus can make these more expensive materials undesirable for use, even though the more expensive materials can make the lead board more resistant to damage.
The embodiments of the invention described herein provide a bottom deck sub-assembly in which each bottom deck board is coupled to an adjacent bottom deck board and wherein at least the bottom deck lead boards are made from a fiber filled thermoplastic or oriented plastic composite material. The fiber filled thermoplastic or oriented plastic composite provides an increase in impact strength of the deck boards as determined by the constrained impact test described herein compared to conventional deck board materials made of wood or wood plastic composite materials. The deck boards of the sub-assembly can also be coupled with one another to provide a predetermined joint strength to inhibit separation of a bottom deck board from the sub-assembly. The joint strength can be selected such that a joint strength of the bottom deck board joints is greater than a joint strength between the bottom deck sub-assembly and the spacer members. Alternatively, or additionally, the bottom deck board joint strength can be selected to prevent or minimize the likelihood that a damaged bottom deck board is readily deconstructed and separated from the adjacent bottom deck boards by hand and/or using unpowered hand tools, or even using some predetermined powered tools. The bottom deck sub-assembly described herein can minimize problems associated with bottom deck lead board damage, subsequent loss of that board, and the need to replace the expensive lead board when damaged, as described above for the conventional pallet 10. The bottom deck sub-assembly can also, with some types of pallet manufacturing equipment, simplify the overall pallet assembly process.
As used herein, the bottom deck sub-assembly refers to a pair of bottom deck lead boards coupled to one another through at least one additional board. In an exemplary embodiment, the bottom deck sub-assembly includes a pair of bottom deck lead boards coupled with a pair of bottom deck edge boards and/or a center board. It is also within the scope of the invention for the sub-assembly to optionally include additional boards coupled with the lead boards and/or the edge or center boards. It is also within the scope of the invention for the bottom deck sub-assembly to be provided as a unitary sub-assembly in which each bottom deck board is coupled with the adjacent bottom deck board independent of the coupling of the bottom deck with the top deck. When provided as a unitary sub-assembly, the bottom deck sub-assembly can be pre-assembled and then coupled to a top deck of a pallet as a single unit. While the bottom deck sub-assembly is described in the context of the conventional pallet 10 having a top deck 12 and spacer blocks 16, 17, the bottom deck sub-assembly described herein can be used with any type of pallet having a top deck and spacer members in the form of blocks and/or stringers, or any other type of spacer member, and may be configured for use with any type of pallet, non-limiting examples of which include two-way, four-way, or euro pallets. While the four-way entry pallet 10 is illustrated as a block pallet in which the spacer members include a combination of stringers and spacer blocks, it is also within the scope of the invention for the four-way entry pallet 10 to be in the form of a stringer pallet in which the spacer members are in the form of stringers and which may also include openings for side entry of a pallet transportation device. It is also within the scope of the invention for the pallet 10 to be a two-way block or two-way stringer pallet.
Referring now to
The fastener 108 may be any type of mechanical fastener, non-limiting examples of which include corrugated fasteners, truss plates, connector plates, particularly truss plates of the gang nail type, or any other type of fastening or fasteners know in the art to give strength to a joint between two adjacent boards. The fasteners 108 may be applied in any orientation with respect to the direction of orientation, grain or fiber direction of the deck boards 102, 104, and 106. A desired joint strength may be engineered by using gang nails and by choosing the number of prongs per unit area, the total area of the gang nail, the type of metal used, and the size of the prong. These fasteners 108 provide great joint strength and are not readily removed so that the bottom deck sub-assembly 100 cannot be readily deconstructed when gang nail-type fasteners are used. As illustrated in
The dimensions of the bottom deck sub-assembly 100 can be selected based on the dimensions of the top deck to which the bottom deck sub-assembly 100 is to be coupled. For example, as illustrated in
The bottom deck sub-assembly 100 can be used with any type of pallet, such as a two-way or four-way block pallet (see for example block pallet 10 of
The top deck boards of the hybrid pallet 110 which may be used with the bottom deck sub-assembly 100 may be any known in the art, such as the top deck boards 20a-g of the block pallet 10 of
Referring now to
The bottom deck lead board 202 can be coupled with the bottom deck edge boards 204 and the bottom deck center board 206 at the shiplap joint 220 by causing the joint portions 222 and 224 to adhere to one another using any suitable non-mechanical fastener. Non-limiting examples of non-mechanical fastener joining include solvent welding, solvent based adhesives and thermal welding. A particularly preferred adhesive joint is an overlapping joint of the shiplap type where the overlapping faces are thermally welded. For example, the joint portion 222 and/or the joint portion 224 can be heated to melt the surface of the joint portion 222 and/or the joint portion 224 and the joint portions 222 and 224 can be overlapped and pressure applied to form the joint 220. In another example, the joint portion 222 and/or the joint portion 224 can be provided with an adhesive, such as a solvent-based adhesive, to adhere the joint portion 222 to the joint portion 224. In yet another example, the joint portions 222 and 224 can be adhered using an ultrasonic weld.
It is also within the scope of the invention for the bottom deck lead board 202 to be coupled with the bottom deck edge boards 204 and the bottom deck center board 206 by a butt weld, which can include solvent welding, solvent based adhesives, or thermal welding, for example.
Similar to the bottom deck sub-assembly 100, the dimensions of the bottom deck sub-assembly 200 can be selected based on the dimensions of the top deck to which the bottom deck sub-assembly 200 is to be coupled with. For example, as illustrated in
It is also within the scope of the invention for the bottom deck sub-assembly to be assembled using a combination of the fastener 108 of the bottom deck sub-assembly 100 of
The bottom deck sub-assembly 100, 200 consists of fiber filled thermoplastic or oriented plastic composite boards in at least the lead board position 102, 202 and is assembled with mechanical fasteners (bottom deck sub-assembly 100) or adhesive fastening (bottom deck sub-assembly 200) to provide the bottom deck subassembly 100, 200. The bottom deck edge boards 104, 204 and bottom deck center board 106, 206 can be made of the same or different material than the bottom deck lead boards 102, 202. In one example, the bottom deck edge boards 104, 204 and/or the center board 106, 206 can also be made from a fiber filled thermoplastic or oriented plastic composite material to provide these boards with protection against damage from a forklift or pallet jack. Alternatively, the bottom deck edge boards 104, 204 and/or the center board 106, 206 can be of wood of any suitable species, such as pine or oak, or a wood composite material.
The bottom deck sub-assembly 100, 200 can be entirely or partially made from fiber filled thermoplastic boards or OPC boards. The fibrous filler in the fiber filled thermoplastic is believed to improve the impact resistance and break strength of such boards making them suitable in the lead board position. Any fiber filler known in the art is useful, including but not limited to naturally occurring fibers, such as flax or bamboo, glass fiber, carbon fiber, polyester fiber, aramid fiber and the like. In general, longer fibers provide a greater impact resistance than shorter fibers.
OPC refers to an article made by orienting the polymers of a polymer composition and comprises polymer molecules that have a higher degree of orientation than that of a polymer composition extruded from a mixer. OPC boards are OPC articles in the shape of boards with a length, a thickness, and a width wherein the cross-sectional shape is substantially rectangular. OPC boards can be produced using a solid state die drawing process which elements are described in U.S. Pat. No. 8,142,697 to Nichols et al. and in U.S. Pat. No. 8,871,130 to Nichols et al., the contents of which are incorporated herein by reference in their entirety. For use in pallets, the length, width and thickness can be any dimensions suitable for the desired pallet design. Standard pallets dimensions depend on the geography, and industry of use. For example, the length can vary from 600 mm to 1200 mm and the width can vary from 400 mm to 1200 mm. European pallets typically require deck boards of 1000 mm length, but may be as short as 600 mm.
Suitable oriented plastic composite (OPC) boards may be made by the following process. Selected plastics materials and additives are introduced to an extruder and, after processing in the extruder, are extruded through a die and calibrator to produce a hot billet (extrudate) of the extruded material which is moved by a puller to a temperature conditioning stage, where the material is cooled below its softening temperature Ts. The cooled extrudate is then drawn, using a puller, in a solid state die draw stage through a solid state drawing die at a drawing temperature that aligns the long chains of the polymer in the lengthwise direction of drawing and then cooled with a cooling tank to a cutting temperature to form a continuous OPC drawn piece. The OPC drawn piece is subsequently fed using pullers or other means to a saw, to cut the OPC drawn piece to a desired length to produce an OPC board. The OPC board may be later cut to a shorter length if desired.
As described above, an orientable polymer is a polymer that can undergo polymer alignment. Orientable polymers can be amorphous or semi-crystalline. Herein, “semi-crystalline” and “crystalline” polymers interchangeably refer to polymers having a melt temperature (Tm). While not meaning to be limited by any theory, polyolefins are believed to undergo cavitation in combination with filler particles, because polyolefins are relatively non-polar and as such adhere poorly to filler particles. Linear polymers (that is, polymers in which chain branching occurs in less than 1 of 1,000 monomer units such as linear low density polyethylene) are even more desirable.
Non limiting examples of suitable orientable polymers include polymers and copolymers based on polystyrene, polycarbonate, polypropylene, polyethylene (for example, high density, very high density and ultra-high density polyethylene), polyvinyl chloride, polymethylpentane, polyamides, polyesters (for example, polyethylene terephthalate) and polyester-based polymers, polycarbonates, polyethylene oxide, polyoxymethylene, and combinations thereof. A first polymer is “based on” a second polymer if the first polymer comprises the second polymer. For example, a block copolymer is based on the polymers comprising the blocks. Preferred orientable polymers include polymers based on polyethylene and polypropylene, examples of which include linear polyethylene having a weight average (Mw) or number average (Mn) from 50,000 to 3,000,000 g/mol; preferably from 100,000 to 1,500,000 g/mol; more preferably from 750,000 to 1,500,000 g/mol.
Polypropylene (PP)-based polymers (that is, polymers based on PP) are one example of a particularly preferred orientable polymer for use in the present invention. PP-based polymers generally have a lower density than other orientable polyolefin polymers and, therefore, facilitate lighter articles than other orientable polyolefin polymers. PP-based polymers also offer greater thermal stability than other orientable polyolefin polymers. Therefore, PP-based polymers, made by any of the means known in the art may also form oriented articles having higher thermal stability than oriented articles of other polyolefin polymers. Suitable PP-based polymers include PP homopolymer; PP random copolymer (with ethylene or other alpha-olefin present from 0.1 to 15 percent by weight of monomers); or PP impact copolymers. It is preferred to use a PP-based polymer that has a melt flow rate of greater than 0.3 g/10 min., preferably greater than 1 g/10 min., more preferably greater than 1.5 g/10 min., and even more preferably greater than 2 g/10 min., while at the same time having a melt flow rate of less than 8 g/10 min., preferably less then 6 g/10 min., more preferably less than 4 g/10 min., and even more preferably less than 3 g/10 min. It is also preferred to use a PP-based polymer that has 55% to 70%, preferably 55% to 65% crystallinity.
PP obtained from either industrial or commercial recycle streams, including filled or reinforced recycled PP, may be used. The recycled PP may range from 0 to 100% of the orientable polymer used in the orientable polymer composition.
PP can be ultra-violet (UV) stabilized, and desirably can also be impact modified. Particularly desirable PP can be stabilized with organic stabilizers. The PP can comprise titanium dioxide or be free of titanium dioxide pigment.
The oriented polymer composition can further comprise fillers, including organic fillers and inorganic fillers. OPC articles can have filler levels from 10 wt % up to 60 wt %. Organic fillers, because they are less dense than inorganic fillers can often be as low as 10 wt % and as high as 35 wt %, 40 wt % or even higher. Organic fillers can be cellulosic or synthetic polymers. Cellulosic fillers include cellulosic materials such as wood fiber, wood powder and wood flour and are susceptible, even within a polymer composition, to decomposition, mold and mildew when exposed to humidity. Furthermore, cellulosic fillers can harbor pests that can be problematic for use of a pallet in international use.
Fillers are preferably, inert inorganic fillers. Inorganic materials do not suffer from some of the challenges of organic fillers. Inorganic fillers are either reactive or inert. Inert fillers can be more preferred than reactive fillers in order to achieve a stable polymer composition density. However, inorganic fillers are generally denser than organic fillers. For example, inert inorganic fillers for use in the present invention typically have a density of at least two grams per cubic centimeter. Therefore, polymer compositions comprising inorganic fillers typically can contain more void volume than a polymer composition comprising the same volume of organic fillers in order to reach the same polymer composition density.
Non-limiting examples of inert inorganic fillers include talc, clay (for example, kaolin), magnesium hydroxides, aluminum hydroxides, dolomite, titanium dioxide, glass beads, silica, mica, metal fillers, feldspar, Wollastonite, glass fibers, metal fibers, boron fibers, carbon black, nano-fillers, calcium carbonate, and fly ash. Particularly desirable inert inorganic fillers include talc, calcium carbonate, magnesium hydroxide, or clay. The inorganic filler can comprise one, or a combination of more than one inorganic filler. More particularly, the inert inorganic filler can be any one inert inorganic filler or any combination of more than one inert inorganic filler. Embodiments of the invention can have 20 wt % or more, 25 wt %, 35 wt %, 45 wt %, 50 wt %, 55 wt % or more, or even 60 wt % filler. Embodiments in which the inorganic filler level is between about 40 wt % and 55 wt % are preferred because cavitation can increase and density decrease (void volume increases) as filler level increases in this range.
Solid state die drawing is different from extrusion, in which the material is pushed through a die in a hot, flowable state above the glass transition temperature Tg of the material, and pultrusion, where the material is both pushed and pulled. Solid state die drawing involves pulling the material having a softening temperature Ts at a temperature below its melt temperature Tm through a drawing die using drive rollers or drive tracks or belts (caterpillars) so that the material is under a state of tension and the die drawing occurs at a drawing temperature Td below the polymer composition softening temperature Ts. The drawing temperature Td is ten or more degrees below the polymer softening temperature, including, 15, 20, or even 30 degrees below Ts. Generally, the drawing temperature Td range is 40° C. or less below the polymer composition's Ts in order to achieve a linear draw ratio using economically reasonable draw rates. (Higher rates are preferred on economic grounds.) It is preferred to maintain the temperature of the polymer composition at a temperature within a range between the polymer composition's Ts and 50° C. below Ts inclusive of endpoints, while the polymer composition is drawn. Preferably, the polymer composition is cooled after exiting the drawing die prior to cutting to length. Subsequently, the board can be treated to provide a length dimension stable board.
Drawing causes the long polymer chains of the material to elongate (or straighten) and generally align in the direction of drawing. The individual polymer chains or groups of polymer chains can be somewhat entangled and also mechanically bonded to one another, giving the material great strength and toughness that can be greater than that of typical un-oriented plastic material or even some types of woods used to fabricate wood articles.
Fillers and additives can be incorporated with the orientable polymer to make an orientable polymer composition. Such fillers function as impediments to polymer chain alignment during solid state drawing and have the effect of introducing cavitation into the material as the polymer chains are forced to slide past and detach from the particles during their elongation. Such cavitation reduces the density of the composite polymer material. The filler particles can vary in size, shape and selection (blends). Other additives may include pigments, fire retardants, and other additives known in the art. Some of these fillers, such as fire retardants, may comprise hard particles and may have a beneficial dual purpose as both a fire retardant and as a portion of, or all, the filler constituent of the polymer composition if cavitation of the material is desired.
Generally, the extent of cavitation (that is, amount of void volume introduced due to cavity formation during orientation) is directly proportional to filler concentration. Increasing the concentration of inorganic filler, since it is typically of higher density than the matrix thermoplastic, increases the density of a polymer composition, but also tends to increase the amount of void volume resulting from cavitation in the oriented polymer composition. Particularly desirable embodiments of the present filled oriented polymer composition article have 25 volume-percent (vol %) or more, preferably 35 vol % or more, more preferably 45 vol % or more void volume and even 55 vol % or more based on total polymer composition volume.
Additional void volume may be created by the use of foaming agents, either exothermic or endothermic. Herein, “foaming agent” includes chemical blowing agents and decomposition products therefrom. Foaming agents include, but are not limited to moisture introduced as part of a filler, for example wood flour or clay, or by chemicals that decompose under the heating conditions of the billet extrusion process, Chemical blowing agents include the so-called “azo” expanding agents, certain hydrazide, semi-carbazide, and nitroso compounds, sodium hydrogen carbonate, sodium carbonate, ammonium hydrogen carbonate and ammonium carbonate, as well as mixtures of one or more of these with citric acid or a similar acid or acid derivative. Another suitable type of expanding agent is encapsulated within a polymeric shell. Blowing agent may be used up to at least 1.5 wt % blowing agent to achieve density reductions compared to an un-foamed billet of up to 20% or even more. Measure weight percent blowing agent relative to total oriented polymer composition weight.
The following examples illustrate embodiments of the present invention and not necessarily the full scope of the present invention. While the exemplary embodiments are described in the context of OPC materials, it will be understood that the scope of the invention is not limited to such materials, but may also include fiber filled thermoplastics. Fiber filled thermoplastics, particularly those that include longer fibers, such as long glass fibers, generally have high impact performance.
Pallets were constructed similar to the conventional pallet 10 of
Test Top Deck Construction
The top deck 12 used in the comparisons was similar to that shown in
The top deck is assembled by laying the nine blocks 16, 17 on a fabrication surface so that the length dimension 25 of the larger blocks 16 lies in the direction of the width dimension 22 of the pallet. Then the stringer boards 18 are placed on the blocks 16, 17 at the correct positions followed by the lead boards 20a, 20g and the intermediate deck boards.
The top deck lead boards 20a, 20g are attached (fasteners 32) to each of the end blocks 16 with six 3 inch (75 mm) long, 0.120 inch (3.05 mm) diameter Grip Rite brand ring shank nails from Prime Source Building Products Inc. installed with a Hitachi NR90AE 3.5 inch strip nailer. The top deck center board 20d is attached to each of the three interior smaller blocks 17 with three of these same type of nails. Two of these nails are also used wherever intermediate deck boards 20b, 20f overlapped the spacer blocks 16. The remaining nails 32 in the intermediate deck boards are 1.25 inch (31.8 mm) long, 0.090 inch (2.29 mm) diameter hot dipped galvanized ring nails purchased from CLS Metal Fasteners, Grand Rapids Mich., and were installed with a Bostich Model N66 Industrial siding nailer.
The conventional comparative bottom deck and the exemplary bottom deck sub-assemblies were created from several different materials and using several different assembly methods and coupled with the above described test top deck 12 through the stringer boards 18 and spacer members 16, 17 for comparison as described below.
Table 1 illustrates the joint strength in tension for exemplary fastening methods for the bottom deck sub-assemblies 100, 200. To determine the joint strength in tension, two OPC boards were joined using the mechanical fasteners as noted in Table 1. The boards were then placed in a mechanical testing device of the constant-rate-of-crosshead-movement type with one fixed member carrying a grip and one movable member carrying a second grip in a position such that the joint could be tested in tension. The grip area is 4.9 inches (12.45 cm) in length and the full width of the board being tested and has four beads of approximate height 0.0625 inches (1.58) running across the board in the board width direction. Each end of the boards making up the joint to be tested are secured in the grips by tightening eight bolts on each of the top and bottom grips, four on each of the grip plate edges. The boards were then pulled in tension at a rate of 1 inch/minute (2.54 cm/min.). The joint break force is determined at failure of the fastener, including pull-out or breakage of the fastener and is reported in Newtons. The results of that testing are shown in Table 1. When more than one joint of the same type is tested, the results are an average of the strength of the joints tested.
The bottom deck lead boards for the conventional, comparative pallets, and the exemplary bottom deck sub-assembly were the same dimensions as the top deck lead boards and for each of the examples and the comparative examples was as indicated in Table 3. The bottom deck edge and center boards were of the material indicated in Table 3 of thickness 0.688 inch (17.48 mm) and width 5.5 inch (140 mm) and length 37 inch (940 mm). For the exemplary bottom deck sub-assemblies, the boards of the bottom deck were joined into a sub-assembly as described in Table 1, depending on the type of joint specified in Table 1.
The exemplary bottom deck sub-assembly was attached with fasteners to the top deck 12 through the spacer blocks 16, 17 with the Grip Rite 3 inch (76.2 mm) long, 0.120 inch (3.05 mm) diameter ring shank nails using the nail pattern shown in
The conventional, comparative pallets and the exemplary hybrid pallets were tested using the pallet jack test procedure described below. Because each pallet consists of two bottom deck lead boards, two tests were performed on each pallet, one on each of the two bottom lead deck boards. The pallet jack was positioned and the hydraulic system was used to lift the top deck upward and away from the bottom deck. The pressure gauge on the pallet jack was monitored and the gauge reading was noted when failures occurred. During and after the test, the pallets were examined to determine which of the failure modes of Table 2 had occurred during the test. Results were recorded and are compiled in Table 3.
The pallet jack lift test was performed on the comparative and exemplary hybrid pallets of Table 3 as follows. Place a pallet on the warehouse floor so that a pallet jack can be inserted in the entry position beneath one set of top and bottom deck lead boards. Place a second pallet, upon which a 1200 pound (545 kilogram) weight is loaded, on the top deck of the test pallet so that a front edge of the weighted pallet is aligned vertically with a front edge of the test pallet (i.e. the front edges of the lead boards of the weighted pallet are aligned with the front edge of the lead board to be tested). A pallet lift jack, equipped with a pressure gauge capable of measuring the pressure of the hydraulic system of the pallet jack is inserted into the test pallet so that the lead wheels of the pallet jack are centered on the bottom deck lead board to be tested, similar to the scenario illustrated in
Breakage Pressure (psi)=1072*Gauge reading (psi)−229.4 (Equation 1)
Equation 1 was determined by applying known weights to a pallet deck and recording the gauge reading required to lift the loaded pallet, fitting the resulting graph of actual load weight versus gauge reading to a straight line equation using a linear regression software program. The breakage pressure, i.e. the break force, can be converted from pounds per square inch (psi) to megapascals (Mpa).
Subsequent to the test, the bottom deck lead board which was tested was examined and the observations were recorded in Tables 3A and 3B according to the failure modes described in Table 2.
Tables 3A and 3B illustrate the lift jack test breakage pressure and pallet failure mode results for pallets having a conventional or non-bottom deck sub-assembly structure and pallets having a bottom deck sub-assembly structure, respectively.
1Yellow pine is No 2 pine board, nominal 1 inch by 6 inch, purchased from Sequin Lumber, Bay City MI, and machined to the required dimensions for use in pallets.
2Oak is pallet grade oak purchased from Hugo Brothers Pallet Manufacturing, Kawkawlin, MI
3WPC1 is Veranda brand decking, a wood plastic composite manufactured by Fiberon from Home Depot. It was planed to a thickness of 0.688 inch (17.48 mm) specified for pallet boards and used at the purchased width of 5.375 inches (13.65 cm).
4WPC2 is Azek brand decking, a cellular PVC/wood composite produced by Azek Building Products, a Division of CPG International, Scranton PA, USA. It was planed to a thickness of 0.688 inch (17.48 mm) specified for pallet boards and used at the purchased width of 5.375 inches (13.65 cm).
5OPC1 and OPC2 are oriented plastic composite boards and are produced at the required thickness and width. The orientable composition base polymer is polypropylene Inspire 404 from Braskem, Philadelphia, PA and is filled with 48 wt % calcium carbonate No. 10 white.
Table 3A compares the effect of different bottom deck board materials on the lift jack test breakage pressure and the pallet failure modes for conventional/non-bottom deck structures. Pallets having a conventional bottom deck structure made from wood or a wood plastic composite (WPC) material exhibited lower lift jack test breakage pressures than similar pallets made using an oriented polymer composition (OPC) material. As can be seen in Table 3A, all of the pallets having a conventional bottom deck structure in which the bottom decks boards are nailed to the spacer blocks and are not coupled with adjacent deck boards exhibited failure mode 6. In some cases, bottom decks boards can be damaged to such an extent, such as by breakage of the board itself, that the board needs to be removed and/or replaced in order for the pallet to remain operable.
In some failure modes, a board can be separated or loosened from the pallet, but the board itself is still usable. In these cases, and particularly when the boards are made of more expensive materials, it is more cost effective to reuse the separated or loosened board. In a pool pallet system, when a board becomes separated from the pallet or is damaged such that separation can be achieved without special tools (e.g. a hammer or crowbar) and/or by hand with little effort, the damaged board is removed and typically discarded or lost, even when it is feasible to reuse the same board. When the damaged board is made of a relatively inexpensive material, such as wood, removal of the board can be cost effectively addressed by replacing the missing board. However, when more expensive materials, such as the WPC and OPC materials of WPC Examples 1-3 and OPC Examples 1-3, replacement of the damaged board can become cost prohibitive, especially in a large pool pallet system where boards may be damaged over and over again. Table 3A demonstrates that while exhibiting some increase in robustness compared to wood, the WPC Examples 1-3 and OPC Examples 1-3 all still exhibited failure mode 6, requiring replacement of the damaged or discarded board(s) and are thus not a cost effective solution for maintaining pallets.
Table 3B compares the effect of different bottom deck board materials on the lift jack test breakage pressure and the pallet failure modes for pallets assembled using the bottom deck sub-assembly. Table 3B demonstrates that the exemplary bottom deck sub-assembly structure described herein in combination with the use of OPC material for forming the deck boards addresses the problem of failure mode 6 in which the damaged lead board is discarded or lost. Decreasing the likelihood that the expensive lead board is discarded or lost can provide substantial cost savings in maintaining pallets. The bottom deck sub-assembly structure couples the lead board with the other boards of the sub-assembly and thus, even when the lead board is damaged and becomes separated or partially separated from the spacer blocks, the damaged lead board is still connected with the remaining sub-assembly boards and thus cannot be readily deconstructed. This can facilitate maintaining the damaged lead board with the sub-assembly, such as for example by re-fastening or fixing damaged fastening, rather than removing the damaged lead board
WPC Examples 4-6 of Table 3B, exhibited failure modes, such as failure mode 4 in which the lead board breaks in the direction of board width, which would result in a need for the damaged board to be removed and replaced. While WPC Examples 4-6 were not readily deconstructed as a result of the joint strength between the bottom deck boards of the sub-assembly, because the damaged board is connected with the other boards in the sub-assembly, removal of the damaged board can become time consuming and may require special tools. In some cases, the entire sub-assembly may need to be removed to replace the damaged board and/or the replace the entire sub-assembly. Thus, even the combination of the more expensive WPC material and the bottom deck sub-assembly may not provide the desired cost effective solution for maintaining pallets.
In contrast, when OPC materials are used to form the bottom deck sub-assembly and assembled with a top deck to form a hybrid pallet (Hybrid Examples 1-8), none of the hybrid pallets demonstrate failure modes 3 or 4, which would require removal and replacement of the broken board, and further, none of the hybrid pallets demonstrated pallet failure mode 6.
Tables 3A and 3B further illustrate examples that used OPC boards (OPC Examples 1-5 and Hybrid Examples 1-8) and demonstrate that OPC boards did not split or crack when acted upon by a pallet jack in this test procedure. As demonstrated in Table 3B, the only failure modes for the Hybrid Examples 1-8 related to the fastener coupling the test board to the spacers. This type of damage can be easily repaired by simply re-fastening the lead board to the spacer blocks, either with the existing fasteners or with new fasteners. Thus, it is preferred that the materials and the structure of the bottom deck sub-assembly be selected such that the boards of the sub-assembly do not break, split, or crack before the connection between the spacer members and the bottom deck boards is broken or weakened.
When the OPC deck boards are joined together using gang nails or by thermal welding (Hybrid Examples 1-8), while the joint between the bottom deck boards and the spacer members may be broken or weakened, the bottom deck boards are still joined with the adjacent bottom deck boards, decreasing the likelihood that a damaged bottom deck board is removed and discarded or lost. Tables 3A and 3B demonstrate that it is the combination of the OPC materials and the bottom deck sub-assembly structure that provides a bottom deck structure that is sufficiently robust to resist board breakage during the pallet jack lift test and which further inhibits removal of a damaged or loosened bottom deck board and in this manner the hybrid pallet can provide a solution for pallet management having an increase in cost effectiveness.
The lead board constrained impact strength test was performed on boards made of traditional wood or wood plastic composite materials and exemplary OPC materials. Place a pallet upside down on the warehouse floor so that a section of the bottom deck lead board nailed to a spacer block is centered so that a dart can be dropped on the bottom deck lead board. The dart has a weight of 6.29 kg (13.85 pounds) and the dart face which impacts the bottom deck lead board is a short section of standard nominal 2 inch×4 inch lumber (3.8 cm by 8.9 cm) affixed to weights to provide the dart weight. The dart is raised sequentially from the lowest test height for the test apparatus to the lowest test height at which bottom deck lead board failure is observed. Failure is defined as splitting according to any one of the definitions of pallet damage set forth in sections 7.1.3 through 7.1.5 or missing board as set forth in sections 7.1.6 through 7.1.12 of the NWPCA bulletin. The impact strength is reported in units of energy (Joules) and is the dart mass multiplied by the drop height and the acceleration of gravity.
One common source of damage to lead boards is from the forklift or pallet jack running into the lead boards during alignment of the forks. A preferred material will be tough enough to withstand contact with the forklift or pallet jack without suffering damage that requires the board to be replaced. As described above, replacement of a damaged board forming part of the bottom deck sub-assembly can decrease the cost effectiveness of the hybrid pallet and thus should be minimized. The constrained impact strength in Joules is determined as described for the Determination of Lead Board Constrained Impact Strength and is representative of the toughness of the board, i.e. the ability of the board to withstand damage from contact with the forklift or pallet jack. As demonstrated in Table 4, oak is tougher than pine, which are both tougher than WPC1 and WPC2, as illustrated by the constrained impact test. OPC1 is significantly tougher than both the wood species, oak and pine, and the WPC materials, as demonstrated by the constrained impact test. In order for the hybrid pallet to be cost effective, the lead board needs to be at least as tough as the wood species to withstand impact from the forklift or pallet jack and minimize the number of times the bottom deck boards of the sub-assembly need to be replaced. The OPC 1 material has significantly higher constrained impact strength and did not fail under the test conditions, which indicates that the OPC lead board is more resistant to impact damage than the wood species or the WPC material, and thus less likely to require replacement due to impact forces. In a preferred embodiment, the constrained impact strength of the material used in the lead boards of the bottom deck sub-assembly is at least comparable to that of the wood species typically used in pallets and thus the preferred constrained impact strength of the bottom deck lead boards is not less than 95 Joules, preferably not less than 113 Joules, more preferably not less than 131 Joules, and still more preferably not less than 190 Joules.
As discussed above, one of the challenges of using more robust, and thus typically more expensive materials to form the pallets, is that when pallet boards are damaged in a way such that they could be re-used, they are typically discarded or lost, rather than re-used, which can significantly increase the overall cost of maintaining the pallet. This can negatively impact the benefits of using a material that is more resistant to damage, such as an OPC material. In order to address this challenge, Applicants have found that when the bottom deck is made from OPC boards, it is desirable to provide the bottom deck as a sub-assembly in which the bottom deck boards are connected to adjacent bottom deck boards to inhibit removal of a damaged or loosened bottom deck board from the pallet. In one embodiment, the joint strength between adjacent bottom deck boards is greater than a joint strength between the bottom deck boards and the spacer members. In this manner, when a bottom deck board is damaged such that it is loosened or disconnected from the spacer members, the damaged bottom deck board is still connected with at least one adjacent bottom deck board, thus minimizing the likelihood that the damaged board will be separated from the pallet and lost or discarded. Alternatively, or additionally, the joint strength between adjacent bottom deck boards can be selected such that if the bottom deck board is damaged it is not readily deconstructed from the remainder of the sub-assembly.
The joint strength may be provided by a number of methods of adhering the side boards to the lead boards, including but not limited to nailing or gang-nailing, corrugated fasteners, thermal welding or solvent based welding or adhesives, or a combination of one or more of these methods. In one example, the number and type of fasteners joining the boards of the bottom deck sub-assembly can be selected to provide the desired joint strength based on the desired decrease in the incidence of discarded or lost boards. In an exemplary embodiment, any joints between the edge and lead boards have a joint strength greater than that of the pull out strength of the fasteners joining the bottom deck sub-assembly to the spacer blocks so that the joints between the bottom deck boards remains relatively undamaged in the pallet jack lift test. Therefore, according to one embodiment of the invention, it is desirable that the joint strength be two times, three times or even more than the strength of the joint between the spacer blocks and the bottom deck sub-assembly to minimize the damage during the pallet jack lift test.
One challenge in pallet management, particularly in pallet pool systems, is the incidence of discarded or lost boards as a result of users removing damaged boards rather than repairing them. Typically, users will remove damaged boards using their hands or unpowered tools, such as a hammer or crowbar, which may be available on site. As has been discussed, replacement of the discarded or lost boards can become cost prohibitive as the cost of the board increases and thus decreasing the incidence of discarded or lost boards that could otherwise be re-used can provide significant cost savings. The number and type of fasteners joining the boards of the bottom deck sub-assembly can be selected to provide the desired joint strength based on the desired decrease in the incidence of discarded or lost boards. Thus, the joint strength can be selected to resist separation of a board from the sub-assembly by hand, such as a joint strength when pulled in tension of at least 450 Newtons. In another example, the joint strength can be selected to be higher to resist both separation by hand and separation by unpowered hand tools, such as a claw tooth hammer, such as a joint strength when pulled in tension of at least 1200 Newtons and preferably at least 5000 Newtons. The joint strength can further be selected to resist separation by certain powered tools to further decrease the rate of incidence of discarded or lost boards, depending on the particular pallet management system. It will be understood that a joint strength that resists separation can vary depending on the strength of an individual and the type of tools available to the individual, the joint strength can be selected to provide the desired decrease in the incidence of discarded or lost boards. As demonstrated by methods 2, 3, and 4 in Table 1, several exemplary bottom deck sub-assemblies have a joint strength of greater than 10,000 Newtons, making it extremely difficult for a user to separate a board from the sub-assembly and thus decreasing the likelihood that a damaged board is discarded or lost. The joint strength can be selected based on the desired resistance to removal as well as taking into consideration additional factors related to the sub-assembly and hybrid pallet, such as manufacturing costs, type of materials, assembly method, intended use, etc. and can be at least 450 Newtons, preferably at least 1200 Newtons, more preferably at least 5000 Newtons, and even 10,000 Newtons or greater.
In warehouse storage racks, loaded pallets are typically only supported by the edges of the pallet. Thus, pallets, particularly the bottom deck of a pallet, must resist excessive deflection when loaded pallets are stored in a rack. The materials used to form the pallet bottom deck boards are selected to provide the resistance to deflection based on the intended use of the pallet. In the exemplary embodiment shown in Table 4 the OPC material has a flexural modulus of at least 3.55±10% GPa. The boards may be selected to provide a lower or higher flexural modulus and may be selected to have a flexural modulus greater than 2.75 GPa (400M psi), more preferably greater than 3.25 GPa, even more preferably greater than 3.75 GPa, still more preferably greater than 4.25 GPa and even still more preferably greater than 4.75 GPa, for example, depending on the intended use of the pallet. OPC boards are particularly desirable because they do not fail in a flexural modulus test and can be bent a full 180 degrees, while having a significant elastic modulus.
The embodiments of the invention provide for a pallet having a bottom deck sub-assembly in which at least the bottom deck lead boards are made from a material that is resistant to impact damage and damage as a result of an improperly aligned pallet jack or forklift and further provides a bottom deck sub-assembly which inhibits separation of a damaged, but re-usable board from the pallet, thus decreasing the likelihood that a damaged or loose lead board is discarded rather than repaired.
Additional non-limiting embodiments contemplated by the present invention include:
A method of forming a pallet comprising the following steps: coupling a plurality of top deck boards comprising at least a first and second top deck lead board and at least one intermediate board positioned between the first and second top deck lead boards, with a plurality of spacer members; forming a bottom deck sub-assembly by coupling a first bottom deck lead board at a first end of the bottom deck sub-assembly and a second bottom deck lead board at a second end of the bottom deck sub-assembly, opposite the first, with at least one intermediate board extending between the first and second bottom deck lead boards to form a joint between the at least one intermediate board and the adjacent first and second bottom deck lead boards, wherein the joint between the at least one intermediate board and the adjacent first and second bottom deck lead board has a joint strength in tension of 450 Newtons or greater; and coupling the bottom deck sub-assembly with the top deck through the plurality of spacer members to form the pallet, wherein the first bottom deck lead board or the second bottom deck lead board comprises an oriented plastic composite or fiber filled thermoplastic material.
According to one embodiment, a pallet has a top deck coupled with a bottom deck through a plurality of spacer members. A plurality of fasteners join the top and bottom decks with the spacer members to couple the top deck, bottom deck, and spacer members into an assembled pallet. The bottom deck is provided as a sub-assembly comprising at least two lead bottom deck boards and at least one additional bottom deck board, each bottom deck board coupled with at least one other bottom deck board by a bottom deck joint, and wherein each board of the bottom deck sub-assembly is further coupled with at least one of the plurality of spacer members to couple the bottom deck sub-assembly with the top deck. The bottom deck joints can be configured to have a predetermined joint strength. In one embodiment, the predetermined joint strength corresponds to a strength such that the bottom deck boards of the bottom deck assembly are not readily deconstructed by hand and/or with unpowered hand tools. Alternatively, or additionally, the deck boards of the bottom deck assembly are configured such that the predetermined joint strength of the bottom deck joint is greater than a joint strength between the bottom deck sub-assembly and the spacer members.
To the extent not already described, the different features and structures of the various embodiments of the invention may be used in combination with each other as desired. For example, one or more of the features illustrated and/or described with respect to one of the bottom deck sub-assemblies 100 or 200 can be used with or combined with one or more features illustrated and/or described with respect to the other of the bottom deck sub-assemblies 100 or 200. That one feature may not be illustrated in all of the embodiments is not meant to be construed that it cannot be, but is done for brevity of description. Thus, the various features of the different embodiments may be mixed and matched as desired to form new embodiments, whether or not the new embodiments are expressly described.
While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation. Reasonable variation and modification are possible within the scope of the forgoing disclosure and drawings without departing from the spirit of the invention defined in the appended claims.
This application claims the benefit of U.S. Provisional Patent Application No. 62/010,607, filed Jun. 11, 2014, which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62010607 | Jun 2014 | US |
