US 20060201402 A1
A plastic pallet, for use with fork lift devices and which meets requirements associated with food handling, has a thermoplastic deck made of two sheets which are spaced part by rigid plastic foam. There are steel beams running in an x-pattern within the foam of the deck. The deck sheets each have a multiplicity of relatively large truncated conical depressions. Holes in the centers of the depressions provide water and air passageways through the deck. The deck sheets are welded together at the locations of the depressions and at their outer edges. The base rails are reinforced by steel beams which are sealed within.
1. In a pallet for transporting goods, of the type having a base, a multiplicity of spaced apart columns extending upwardly from the base, and a top mounted on the columns which top comprises a rectangular deck, the improvement which comprises:
a deck comprising
a top sheet having a substantially planar upper surface, for receiving goods placed on the deck;
a bottom sheet, spaced apart from and substantially parallel to the first sheet; and,
rigid plastic foam with the space between the sheets;
wherein, at least one of said sheets has a multiplicity of spaced apart truncated conical depressions;
wherein the sheets are attached to each other at their edges and at the locations of said truncated conical depressions.
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15. A pallet for transporting goods, comprising:
a base, comprised of outer rails running in a rectangular pattern and cross rails connecting the centers of opposing side outer rails;
metal beams within the rails of the base;
eight peripheral columns and one center column extending upwardly from the base;
a rectangular top mounted on the peripheral columns, for receiving goods, the top comprising a frame and a rectangular deck, wherein the periphery of the deck is attached to the frame, and the center of the deck is attached to said center column;
wherein the deck comprises:
a top sheet having a substantially planar upper surface, for receiving goods placed on the pallet, and a multiplicity of spaced apart truncated conical depressions;
a bottom sheet, spaced apart from and substantially parallel to the first sheet; and,
rigid plastic foam with the space between the sheets;
wherein the sheets are joined together along their outer edges and at the locations of each of said truncated conical depressions; and,
wherein the deck has a multiplicity of holes located within the bottoms of said top sheet depressions, for passage of water or air through the deck.
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20. The method of making a pallet for transporting goods, wherein the pallet comprises a base, a multiplicity of spaced apart columns extending upwardly from the base, and a top mounted on the columns which top comprises a frame and a rectangular deck attached to the frame; wherein the deck comprises a top sheet having a substantially planar upper surface, for receiving goods placed on the deck; a bottom sheet, spaced apart from and substantially parallel to the first sheet; and, rigid plastic structural foam with the space between the sheets, connecting sheets; wherein, both sheets have a multiplicity of spaced apart truncated conical depressions; and, wherein the sheets are attached to each other at their edges and at the locations of said truncated conical depressions; which method comprises:
a) injection molding plastic to form a body which comprises said frame, said bottom sheet of said deck with said multiplicity of depressions according to a first pattern;
b) thermoforming plastic sheet to form a top sheet of the deck, the deck having a multiplicity of spaced part truncated conical depressions in a pattern which mirrors said first pattern;
c) welding the top sheet to the body, so the periphery of the frame is attached to the frame and so the bottoms of the depressions are attached to the bottoms of the depressions of the bottom sheet; wherein the sheets are spaced apart from each other except where they are welded; and,
d) injecting plastic material into the space between the sheets to form a rigid foam their, where the form is bonded to the sheet surfaces.
21. The method of
This application claims benefit of provisional patent application Ser. No. 10/657,379, filed on Mar. 1, 2005.
The present invention relates to molded plastic pallets, of the type used with forklift devices for transporting goods.
Commercial plastic pallets for use with fork lift devices have often been made of familiar thermoplastics, which would appear to provide them with a number of potential advantages over wood pallets, including better durability and moisture resistance. A common plastic pallet, which can be made in the present invention, is often referred to in the U.S. as a GMA pallet. It has a 40 inch×48 inch rectangular base, eight columns running up from the periphery of the base, and a rectangular deck. A comparable European pallet is a 1000 mm by 1200 mm pallet. The Grocery Manufacturers of America (GMA), Washington, D.C., U.S., in conjunction with other organizations, has published a document entitled “Recommendations on the Grocery Industry Pallet System” (1992). From that and other references, for a GMA pallet to gain acceptance by large commercial users in the U.S. it must have certain dimensions and meet strength and durability requirements. “Recommended Test Protocol for Plastic Pallet, Version 3” (1998) published by Virginia Tech, Blacksburg, Virginia, U.S., sets forth mechanical performance and test requirements for pallets including a warehouse racking test. ISO 8611:1991 and proposed Underwriters Laboratories (UL) Standard 2417 specify similar mechanical performance and testing standards. UL Standard 2335 specifies fire tests and performance for warehouse pallets made of plastic. The disclosures of the foregoing documents are hereby incorporated by reference. Commercial purchasers may have their own standards which can be somewhat more demanding.
When pallets are uses in connection with food goods, they often must meet the requirements of the U.S. Food and Drug Administration, such as those at Section 7 of American National Standard/NSF International Standard No. 2 (ANSI/NSF 2-1996), hereafter called NSF requirements or NSF standards. Among the requirements are that a pallet ought not to have small cavities or crevices which could harbor microorganisms and insects, or which are hard to clean. There are also limitations on the kinds of exposed metals which can be used. Pallets for transporting food goods also often have to sustain frequent sharp temperature changes.
In pallets not specifically intended for use with food goods, it is quite common to have ribbed and perforated decks, since that helps minimize the weight and cost of plastic in the pallet. However, although the decks embody good plastic structural design, they are not helpful in meeting NSF requirements. On the other hand, if the deck is a smooth continuous surface, then the resultant lack of means for draining and air circulation is disadvantageous. So, there are conflicting aims which the present invention seeks to resolve.
Another barrier to the success of many plastic pallets has been an inability to also meet the demanding mechanical strength requirements of GMA pallets. One way of achieving strength has been to incorporated steel beams within the tops and bases of plastic pallets, See U.S. Pat. No. 6,705,237 of Moore et al., No. 6,955,128 of Apps et al., and No. 5,868,080 of Wyler et al. However, if such beams are exposed, or if there are narrow crevices in their vicinity, then the NSF requirements may not be met. Other problems associated with the use of steel beams can be thermal fatigue which arises from differential thermal expansion, and unacceptable increases in pallet cost or weight.
Thus, there is a need for continuing improvements in pallets used for carrying food goods, to meet the various technical requirements. Any improved pallet must also be economic to manufacture and low in weight.
An object of the invention is to provide a pallet with features which meet both the GMA and NSF requirements, and which are economic to make. A further object is to provide a plastic pallet for use in food service, which pallet is strong and light and which is free of a multiplicity of recesses and crevices, especially with respect to the deck.
In accord with the invention, a pallet has a rectangular top which comprises a deck made of two spaced part sheets, at least one of which has a multiplicity of spaced apart truncated conical depressions. The sheets are attached to each other at the locations of the depressions and at their edges. The space between the sheets is filled with rigid plastic structural foam. The foam enables the top sheet to resist impact loads, and provides bending strength to the deck and pallet as a whole. Preferably, metal beams run diagonally from corner to corner in an x-pattern between the sheets and within the foam material of the deck. The pallet preferably has a frame which forms the periphery of the top and the deck attached to the frame, so it is inset from the outer edge of the top.
In an embodiment of the invention, mating flat bottom circular conical depressions are present in both the top sheet and the bottom sheet. The flat bottoms of the mating depressions are welded to each other at the approximate center plane of the deck; and there is a hole for passage of water or air through the deck at the bottom of each depression. In alternative embodiments, the depressions may be present in one sheet only and the other sheet may be flat; and, some of the depressions have an oblong shape so they are suited for manual grasping of the pallet. The depressions are large, compared to features of decks in the past. The depressions are arranged in four spaced apart arrays having the approximate shape of equilateral triangles; thus, there are regions between the arrays where the x-pattern beams run.
In an embodiment of the invention, the pallet is shaped like a GMA 40×48 pallet. The pallet has a base, columns extending upwardly from the base, and a top mounted on the columns, for receiving goods. The base is comprised of rails arranged in a rectangular pattern; and the deck has aforesaid x-pattern of beams. The diameter of each depression is at least 3 percent of the length or width of the deck, and there is at least one depression for every 25 square inches of deck area. The pallet is preferably made of thermoplastic, such as high density polyethylene or polypropylene, the rigid foam is made of polyurethane and the beams are made of steel.
In one mode of constructing the pallet, the deck is fabricated separately from the rest of the pallet by making and joining together two thermoformed sheets. When joined together, with placement of the metal beams, if desired, foam plastic is formed between the sheets. Then the deck is welded to an injection molded top or frame of the pallet. In another mode of constructing the pallet, a pallet body is made by injection molded of plastic; the bottom sheet has depressions and is formed as an integral part of the frame of the body, which provides various advantages including more uniform thickness sheet and fewer potential crevices. The top sheet is thermoformed and attached to the bottom sheet edges and depressions, after placement of the beams. In both embodiments, the rigid foam is formed by injection of material into the space.
The metal parts are sealed within the plastic of the pallet and thus are protected from contact with food goods and corrosion. The combination of a two-sheet deck having rigid plastic foam, metal beams within the deck interior, and metal beams in base, provides good strength to a pallet. The large depressions in the surfaces of the deck are easily cleanable; and the simplicity of design means there is an absence of hard to clean crevices, cavities and passageways. The holes through the deck at the locations of the depressions provide good drainage and air circulation.
The foregoing and other objects, features and advantages of the present invention will become more apparent from the following description of preferred embodiments and accompanying drawings.
The invention is mostly described in terms of a pallet having the dimensions of a 40 inch by 48 inch by 5 to 6 inch high GMA pallet. The essential design of the pallet, except for the top, is in accord with the pallet described in U.S. Pat. No. 6,705,237 of Moore, the disclosure of which is hereby incorporated by reference. The invention will be useful with other pallets which have different kinds of bases and different shapes. Parts of the pallet are injection molded, and may be made with gas assistance. See U.S. Pat. No. 5,401,459. The several parts or subassemblies of the pallet may be joined as an assembly by known thermoplastic fabrication methods, for example, by mechanical means, by hot plate welding, vibratory welding, or ultrasonic welding. See, for instance, U.S. Pat. Nos. 6,250,234 and 6,283,044. The thermoplastic parts of the pallet may be made of commercial grade polypropylene, high density polyethylene (HDPE) or other polyolefin. The examples herein are described in terms of HDPE. Other plastics, including thermoset plastics and engineered plastics, may. Since the pallets and parts comprise metal reinforcing beams they may be characterized as predominately plastic.
Pallet 20 is shown in
Frame 24 forms the periphery of the top of the pallet. By definition the frame is an open rectangle. Deck 22 spans the interior opening of the frame, and it and whatever portion of the frame is exposed comprise the pallet surface which receives goods for transporting. Deck 22 is comprised of two thermoformed plastic sheets 44, 46, which are joined to each other by welding of the sheets and by adhesion of rigid thermoset foam. Deck 22 has a multiplicity of truncated circular conical depressions 42 in its essentially planar horizontal surface; and preferably, it also has a multiplicity of elongated slot openings 74 proximate the corners and center of the pallet, to enable a worker to manually grasp the pallet.
First, the non-deck elements are described in detail. The base is comprised of outer rails 31 which form a rectangle. The opposing side centers of the outer rails are connected by cross rails 33. Eight columns 28 extend upwardly from the base; and top 90 is mounted on the columns. There are two openings 34 on each side of the pallet for fork entry; they are nominally 3.2 inches high and 12 inches or more wide. Center column 29 extends upwardly from the intersection of the two cross rails 33. Deck 22 is attached to both the frame 24 of the top and to the center column.
Rectangular cross section steel beams 50 run within the HDPE outer rails 31 of the base. Similar steel beams 45 run within the thermoplastic cross rails 33. The beams provide reinforcement to the base and pallet as a whole, in cooperation with the structural parts of the top. The combination of features makes the pallet suited for use in storing goods on open beam warehouse racks and in meeting certain other GMA pallet strength requirements. Beams are preferably shaped and incorporated within the base in accord with the teachings of U.S. Pat. No. 6,705,237 of Moore et al. See also the teachings of U.S. Pat. No. 6,955,128 of Apps et al. and U.S. Pat. No. 5,868,080 of Wyler et al. The disclosures of the foregoing patents are hereby incorporated by reference. The beams preferably are light steel box beams having a multiplicity of lightening perforations along their vertical edges. They are formed and shaped generally as described in U.S. Pat. No. 6,705,237. At final assembly, spaces within the rails which are in proximity of the beams, and the interiors of the beams themselves, are preferably filled with rigid foam so the beams are well captured within the molded plastic parts. See the Moore patent.
Beams 50, 45 are not attached, as by welding, to each other at their intersections, although they may be in other embodiments. Preferably, the beams are constructed and positioned so that when the plastic of the rails softens as a result of the heat from a fire, the beams will be released their attachments, thus enabling the pallet to collapse due to the weight of itself and goods, which can help mitigate the rate of heat release. See the commonly assigned U.S. patent application entitled “Fire collapsible beamed pallet,” bearing Atty. No. EPC-2443 filed on Feb. 21, 2006 herewith by R. Moore et al., the disclosure of which is hereby incorporated by reference.
Pallet 20 is preferably constructed by injection molding the body 70 so it comprises the frame, the hollow columns and major portions of the base rails. When the pallet is assembled, metal beams are inserted into lengthwise open cavities that are provided on the underside of the molded base rails of body. Then, cover plate 54 is the welded to the bottom of the body, to seal the cavities and the beams within the pallet, protecting them from contact with the external environment. See
With further reference to
In the invention, at least one of the deck sheets has a multiplicity of spaced apart conical depressions. As shown in
After the deck assembly has been made, the flange 49 of the deck assembly is welded to ledge 80 of frame 24. The portion of the frame which defines ledge 80 preferably comprises a multiplicity of open cavities, bounded by transverse ribs. See
Beams 53 of the deck 22 run in an x-pattern as shown in
While the deck is preferably set within the frame that forms the periphery of the top of the pallet, in an alternate embodiment, the deck may extend to the outer edge of the top or frame. Conversely, it may be desirable to inset the deck from the edge by a greater amount than shown in the Figures, Lengthwise impact absorbers may be placed in proximity to the outer edges of the frame, particularly within the bridge parts of the frame which span the fork lift openings 34 of the pallet. The object of such alternative is to reduce the adverse effect on the deck of horizontal impact blows on the top of the pallet. See the commonly owned patent application entitled “Plastic pallet having impact resisting plastic top” bearing Atty. No. EPC-2437 and filed on Feb. 21, 2006 by D. Swistak et al., the disclosure of which is hereby incorporated by reference.
The top surface of deck 22 has a multiplicity of spaced-apart truncated conical depressions 42. They are large compared to the deck perforations which characterize the prior art. For example, the diameter of the preferred embodiment 1.8 inch diameter circular depression is greater than 3 percent of the length or width of the top. The two sheets of the deck are welded together at each depression location. As shown in
In an exemplary 40 inch×48 inch GMA pallet like that shown in
In the exemplary GMA pallet configuration, adjacent depressions 42 are spaced apart center-to-center by nominally 3.5 inches and have the following nominal dimensions and features: The major or base diameter (at the deck surface) is about 1.8 inches; the minor or apex diameter (at the bottom of the depression and center plane of the deck) is about 1.3 inches. The depth of each depression is nominally 0.5 inches. The sidewalls slope at about 25 degrees to the vertical axis of the conical shape. The diameter of each hole 55 is about 0.75 inches. In an exemplary GMA pallet there are a total of 72 depressions, counting the hand-holes. Thus, there is one depression for each 20-25 square inches of deck area.
In an exemplary pallet deck which includes x-pattern beams, the depressions are arranged in four essentially equilateral triangular shape arrays. Each array has a triangle base running along and centered on an edge, as the pallet is viewed looking downwardly. See
Other than when the depressions form hand holes, the depressions shown in
While the depressions have been described in terms of equilateral circular cones, in the generality of the invention the horizontal cross section of the depressions may be other than round, for instance, it may be rectangular or non-round. And the depressions may be asymmetric with respect to a vertical axis running through a hole or the center of the depression. When a reference is made herein to a diameter associated with a depression, for any non-circular depression that shall mean the diameter of a circular depression having the same area. The sheets of the deck may have other texturing in addition to any depressions, for instance, corrugations; and, the upper surface of the top sheet may have an anti-slip or other surface finish treatment.
Obviously, when the depressions in one sheet are intended for mating with depressions in the other sheet, then the pattern or arrangement of depressions on one sheet has to mirror the pattern or arrangement on the other sheet. The depression pattern, which encompasses the number, sizing, locations, spacing of the depressions, may be varied within the invention. There are several considerations in the choice of depression parameters. They include: The depressions and associated holes ought to be sufficiently large, so that they do not become easily plugged, and so that they can be readily cleaned should debris accumulate within. A multiplicity of depressions is desirable because they strengthen the sheets of the deck as does any texturing. But if the depressions are either too large or too many in number, the result may be insufficient planar surface for supporting certain kinds of goods; and, there may be an unacceptable diminution in section modulus and resultant rigidity and strength of the deck. If there are too few depressions, then the desired draining or venting can suffer. Engineering analysis and design choice can be used to trade off the different parameters relating to depressions, according to the particular needs of the pallet user.
Preferably, within the limitations of the foregoing factors, when depressions have through holes, some will be preferentially located so that any fire sprinkler water which falls onto the deck can fall onto the rails 33, 31 of the base, to help suppress burning there. See related U.S. patent application entitled “Sprinkler friendly pallet” of R. Brochu, bearing Atty. No. EPC-2440, filed on Feb. 21, 2006, the disclosure of which is hereby incorporated by reference.
Particular structural foams are desirable for filling the spaces between the sheets of the deck. A preferred material is a polyurethane foam having a density of 2 to 4 pounds per cubic foot; for example, such as Elastopor polyurethane Product No. P12570R available from BASF Corporation, Wyandotte, Mich., U.S. The foam is a two-component system consisting of an isoncyanate component and a polyol blend component and is formed in place by chemical reaction. As known in the art, the interior surfaces of the top and bottom sheets, which are in contact with the foam, are preferably pre-treated by flame or electric charge devices, so there is a good bond between the sheet and the foam.
At final assembly, the same rigid foam is also placed within the hollows 72 of the columns and in any spaces in the base rails, including the interiors of the beams. When the thermoset polyurethane structural foam is so placed, it can provide the pallet with additional strength and can have a favorable effect on fire test performance, such as that measured by UL 2335. The foam material constituents may be deposited into the diverse cavities of the pallet by means of access ports not shown in the Figures. After filling, the ports are preferably sealed with plugs or sealant, or by means or spin-welded plastic nubs, as described in a related U.S. patent application entitled “Pallets having multi-purpose nubs” of D. Swistak et al., bearing Atty. No. EPC-2444, filed on Feb. 21, 2006. The disclosures of both the foregoing patents are hereby incorporated by reference.
The preferred rigid foam by design has relatively low shear strength compared to the other plastic parts of the pallet. Thus, during cool down after fabrication, and during thermal cycling in use, a beam may differentially thermally expand lengthwise relative to the foam and rest of the pallet, by shearing the foam which unavoidably passes through the beam perforations. See the related U.S. patent application entitled “Thermoplastic pallet having thermoset foam-filled or foam-coated structural parts” of R. Moore, bearing Atty. No. EPC-2140, filed on even date herewith.
The HDPE or thermoplastic material of the pallet may comprise known commercial flame retardant, depending on requirements related need to be met, such as the fire test requirements of Underwriters Laboratories (UL) Standard 2335. Likewise, the foam may incorporate a flame retardant.
While the invention has been described in terms of a pallet with a base, the invention may be used with pallets which have downwardly extending columns only, and on base connection the bottoms of the columns, which in such instance may be called feet. While it is preferred to have the above-described reinforcing beam patterns, e.g., the x-pattern in the deck and rectangular pattern in the base, alternative beam patterns may be used. A pallet may have fewer or no beams, although strength will be probably be inadequate for GMA pallet purposes. Fusion welding is the only presently known economic way of continuously joining mating parts. However, the term welding as used herein shall encompass the use of adhesives and chemical bonding, should strong and economic products become commercially available.
The advantages of the invention have been described in the Summary and above. Although this invention has been shown and described with respect to a preferred embodiment, it will be understood by those skilled in this art that various changes in form and detail thereof may be made without departing from the spirit and scope of the claimed invention.