WO1997046456A1

WO1997046456A1 - Twin sheet pallet

Info

Publication number: WO1997046456A1
Application number: PCT/US1997/009524
Authority: WO
Inventors: Darrell Haywood, Jr.; Jeffrey James Haun
Original assignee: Bigelow Packaging
Priority date: 1996-06-04
Filing date: 1997-06-03
Publication date: 1997-12-11
Also published as: AU3154197A

Abstract

A pallet (10) for supporting and transporting loads thereon comprising a first thermoplastic sheet (12) having a generally planar upper load bearing surface (16) and a lower surface (18). A second thermoplastic sheet (14) having a plurality of supporting legs (22) for elevating a portion of the pallet a selected distance above the surface on which the pallet is resting. A series of truncated frusto-conical strengtheners (24) extending between the first and second sheets. Each of the strengtheners is connected to the first sheet and the second sheet so as to position the first and second sheets in fixed parallel spaced relation to each other to thereby define a rigid pallet for supporting a load on the upper surface thereof.

Description

TWIN SHEET PALLET FIELD OF THE INVENTION

The present invention relates generally to pallets and, more particularly, to twin-sheet plastic pallets.

BACKGROUND OF THE INVENTION

Pallets have long been used to transport and store a wide variety of goods. Traditionally pallets were constructed of wood. However, wood pallets are subject to breakage and over an extended period of time do not stand up to repeated use. More recently, pallets have been made from plastic. Plastic pallets have the advantage of consistent physical characteristics and have a longer reusable life. Pallet designs using an upper and lower molded plastic sheet which are fused together to form a twin sheet structure have become very popular. Although much more durable, twin sheet plastic pallets have a much higher initial cost than either wood pallets or single sheet plastic pallets. Pallet manufacturers have consequently focused on obtaining a twin sheet plastic pallet which maximizes the strength of the pallet relative to the amount of plastic used. The importance of this fact is made more apparent because industry standards which limit the minimum leg height and overall height of the pallet.

In an attempt to maximize the strength of twin sheet pallets, manufacturers have adopted several different approaches. One such approach has been to use cylindrical embossed portions and stiffening fins extending between the first and second sheets of the pallet to provide additional strength as disclosed in U.S. Patent No. 3,604,368 to Baxter. Similarly, U.S. Patent No. 5,197,396 to Breezer et al . discloses the use of a plurality of teardrop shaped posts which receive bolts for bolting the first and second sheets together. The Breezer et al. '396 patent and related U.S. Patent No. 5,413,052 also disclose octagonally shaped plastic support columns which help to carry the loads applied to the top sheet .

A different technique is disclosed in U.S. Patent No. 5,042,396 to Shuert which relies on the use of a convexly bowed insert assembly having a pair of matingly notched steel beams. The insert assembly is inserted between the first and second sheets of the pallet to provide additional strength thereto.

U.S. Patent No. 5,401,347 patent to Shuert discloses the use of opposed frusto-conical hollow bosses integrally formed in the first and second sheets of the pallet. Each of the frusto-conical hollow bosses is fused to the corresponding opposed hollow boss along their adjacent angled sides in an intermeshing relationship.

Another approach taken by pallet manufacturers to obtain a stronger pallet has been to have bosses formed in rows on each of the first and second sheets, such that these rows of bosses are in staggered relation to each other. The tops of the opposed bosses are fused together to form vertical columns. Examples of this type of pallet may be seen in U.S. Patent Nos. 4,879,956 and 4,428,306 to Shuert, and European Patent Application No. 597,572 to Constantino.

U.S. Patent Nos. 5,143,778 and 5,108,529 to Shuert disclose a twin pallet and related method having portions of the first and second sheets which are fused together along angled sides thereof while leaving an air space in an upper portion between the portions. Although several different approaches have been taken to maximize the strength of twin sheet pallets, existing pallets have not yet achieved the optimum amount of strength for the amount of plastic used in forming the pallet.

SUMMARY OF THE INVENTION In view of the foregoing background, it is therefore an object of the present invention to provide a twin sheet plastic pallet that has high structural strength while minimizing the amount of plastic required. These and other objects, features, and advantages of the present invention are obtained by providing a pallet for supporting and transporting a load thereon comprising a first thermoplastic sheet which has a generally planar upper load bearing surface and a lower surface. A second thermoplastic sheet is provided having a plurality of supporting legs for elevating a portion of the pallet a select distance above the surface on which the pallet is resting. A series of truncated pyramidal shaped strengtheners are provided which extend between the first sheet and the second sheet . Each of the strengtheners has a truncated upper portion connected to the first sheet and a base portion connected to the second sheet so as to position the first and second sheets in fixed parallel space relation to each other and to thereby define a rigid pallet for supporting a load on the upper surface thereof.

In order to maximize the load distribution and enhance the strength of the pallet, the strengtheners are integrally formed on the second sheet and extend upwardly therefrom so as to be fused to the lower surface of the first sheet. As a result, the twin sheet pallet takes advantage of the broadening of the truncated pyramidal shape to assist in distributing any load applied to the upper surface of the first sheet . To further enhance this load distribution capability of the pallet, the strengtheners preferably cover substantially entirely the upper surface of the second sheet .

The first and second sheets each preferably have correspondingly greek key style shaped peripheral edge portions. These greek key style shaped peripheral edge portions are fused together in interlocking engagement. The greek key style shape peripheral edge portions provide improved overall strength to the pallet because of the non-linear fusion and increased surface area. Because of this greek key style shape peripheral edge to the pallet, the pallet can withstand much higher shear force than a conventional linearly fused pallet having parallel peripheral edge portions. The truncated pyramidal shaped strengtheners also preferably have a plurality of reinforcement ribs to further enhance the load bearing capability of the pallet. Ideally, at least one reinforcement rib is located on at least one side of each strengthener. Advantageously, a pair of reinforcement ribs are located on opposed sides of the strengthener and a single rib is located on opposite sides of a majority of the strengtheners to thereby provide improved strength characteristics for these strengtheners and thereby improve overall load distribution and strength of the pallet .

Beneficially, the first sheet includes a plurality of first supporting legs which are received in corresponding second supporting legs provided in the second sheet for providing additional strength and stability to the pallet .

To improve the usefulness of the pallet, it is beneficial to provide the upper surface of the first sheet with a non-slip surface to thereby minimize any undesirable movement of the load placed on the pallet. Preferably, the non-slip surface is achieved by elevated ribs comprising a series of Xs when viewed from the corner of the pallet and a series of interrupted intersecting diagonally spaced ribs which cooperate to form opposed spaced parallel sides of the square surrounding and separating each of the series of Xs . The configuration of the non-slip surface limits undesirable movement of the load in any direction. The use of the elevated ribs provides the additional benefit of raising the load above the plane of the upper surface so as to minimize any damage to the load by moisture. This is accomplished by having any undesirable moisture collect between the elevated ribs to minimize moisture settling on the load carried by the pallet. The elevated ribs not only serve the functional purposes set forth above, but also provide an aesthetically appealing design to the upper surface of the pallet.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings which form a portion of the original disclosure of the invention: FIG. 1 is a perspective view partially cutaway illustrating a plastic pallet in accordance with the present invention;

FIG. 2 is a top plan view partially cutaway and partially in phantom of a portion of the plastic pallet shown in Fig. 1;

FIG. 3 is a cross sectional view taken along line 3-3 of Fig. 2; and

FIG. 4 is an exploded view of the first sheet and second sheet of the pallet shown in Fig. 3.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter, in which the preferred embodiments of the invention are set forth. This invention may however, be embodied in many different forms and should not be construed as limited to the embodiments described herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art to which this invention relates.

Referring more particularly to the drawings, Figs. 1 through 4 illustrate an embodiment of a pallet, generally indicated as 10, according to the present invention. The pallet 10 is a twin sheet configuration having a first sheet, generally indicated as 12 and a second sheet, generally indicated as 14.

As best seen by comparing in Figs . 1 and 4 , the first sheet 12 has a generally planar upper load bearing surface 16 and a lower surface 18. In this embodiment of the invention, the first sheet 12 has a plurality of support legs 20 which extend downward from the lower surface 18. The second sheet 14 also has a plurality of corresponding support legs 22 which are adapted to receive the corresponding support legs 20 from the first sheet 12 therein as shown in Figs. 1, 3, and 4. This cooperative seating of the support legs 20 in the support legs 22 provides the pallet 10 with additional strength and rigidity, especially since the support legs of a pallet are subject to such abuse from fork lifts (not shown) and the like during use.

The second sheet 14 also has a plurality of strengtheners 24 integrally formed or connected to an upper surface 26 thereof. Each strengthener 24 has a truncated pyramidal shape, with a truncated top 28, as shown in Figs. 1, 3, and 4, and a broad base 30 located in engagement with the upper surface 26 of the second sheet 14. As shown in the drawings, each strengthener 24 has at least one reinforcing rib 32 on at least one side of the strengthener. As best shown in Fig. 2, the number of reinforcing ribs 32 which are formed on each strengthener 24 depends where the strengthener is located on the upper surface 26 of the second sheet 14. Those strengtheners 24 which are located away from a peripheral edge 34b of the second sheet 14 and away from the plurality of support legs 22 have a single rib 32 located on opposed sides of the strengthener and a pair of ribs located on the other opposed sides thereof, for a total of six reinforcing ribs per strengthener. This number of reinforcing ribs 32 is reduced due to space considerations for strengtheners 24 which are located adjacent the peripheral edge 34b and/or one of the plurality of support legs 22, see for example, the strengtheners identified as 24' and 24'' in Fig. 2. In each instance, reinforcing ribs 32 have been eliminated from one or more sides of strengtheners 24' and 24" . To assist in providing the maximum desired strength to the twin sheet pallet 10, the strengtheners 24 are integrally formed in or are connected to the upper surface 26 of the second sheet 14 and cover substantially entirely the upper surface thereof. The orientation of each strengthener 24 is such that the truncated top 28 is located remote from the upper surface 26 of the second sheet 14 and the base 30 is connected to or integrally formed in the second sheet . This orientation of each strengthener 24 provides the pallet 10 with improved load distribution characteristics and enhances the strength thereof.

As illustrated in Fig. 1, the peripheral side edges 34a and 34b of the first sheet 12 and the second sheet 14, respectively, have a greek key style configuration. This greek key style configuration of the peripheral edges 34a and 34b of the first and second sheets 12 and 14 provides the pallet with greatly increased shear strength because of the non¬ linear engagement of the first and second sheets and because of the increased surface area of the interlocking or intermeshing connection. The first sheet 12 and the second sheet 14 are fused together, by heating or other conventional means for joining thermoplastic sheets, so as to position the first and second sheets in fixed parallel spaced relation to each other to thereby define the rigid pallet 10 capable of supporting a load on the upper surface 16 thereof.

This combination of the greek key style peripheral edges 34a and 34b of the first and second sheets 12 and 14, and the configuration of the strengtheners 24, the pallet has a greatly increased strength. The resultant pallet 10 according to the present invention has a dynamic load bearing capability of between at least 4,000lbs and 12,000lbs and a static load bearing capability of between at least 20,000lbs and 60,000lbε. As is readily understood by those skilled in the art to which the invention relates, these load bearing numbers can be greatly enhanced by the inclusion of steel reinforcements. The upper surface 16 of the pallet 10, shown best in Figs. 1 and 2, has a non-skid or non-slip surface. This non-slip upper surface is achieved by a plurality of elevated ribs 36 shown in Figs. 1 and 2. The elevated ribs 36 are connected to or integrally formed in the upper surface 16 of the first sheet 12 and have a height of approximately .070 to .080 inches. It is to be understood that this height may vary as desired, depending on the individual use of the pallet while remaining within the spirit of the present invention.

In the embodiment shown, the elevated ribs 36 form a series of spaced apart "+s" or "Xs", depending upon the direction from which they are viewed, and a series of interrupted diagonally spaced ribs which cooperate to form opposed spaced parallel sides of a square surrounding and separating each of the series of "Xs" . This pattern of the elevated ribs 36 is not only aesthetic, but also limits unwanted movement, in any direction, of a load (not shown) placed thereon. The elevated ribs 36 also raise the load above the upper surface 16 of the first sheet 12, which helps to keep the load from being damaged by any unwanted moisture. Any moisture caused by leakage of the contents or which otherwise may fall onto the pallet, will fall between the elevated ribs 36 and thereby prevent the bottom of the load from getting and/or remaining wet. Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed. Although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, and that modifications and embodiments are intended to be included within the scope of the appended claims.

Claims

WHAT IS CLAIMED:

1. A pallet for supporting and transporting loads thereon comprising: a first thermoplastic sheet having a generally planar upper load bearing surface and a lower surface; a second thermoplastic sheet having a plurality of supporting legs for elevating a portion of the pallet a selected distance above the surface on which the pallet is resting; and a series of truncated pyramidal shaped strengtheners arranged in staggered offset relationship in parallel rows extending between said first sheet and said second sheet, each of said strengtheners having a truncated upper portion connected to said first sheet and a base portion connected said second sheet, to position said first and second sheets in fixed parallel spaced relation to each other and to thereby define a rigid pallet for supporting a load on said upper surface thereof .

2. A pallet according to Claim 1 wherein said strengtheners are integrally formed on said second sheet and extend upwardly therefrom so as to be fused to said lower surface of said first sheet.

3. A pallet according to Claim 1 wherein said strengtheners cover substantially entirely said second sheet .

4. A pallet according to Claim 1 wherein said first sheet and said second sheet have correspondingly greek key style shaped peripheral edge portions for interlocking engagement.

5. A pallet according to Claim 1 wherein each of said strengtheners includes a plurality of reinforcing ribs.

6. A pallet according to Claim 5 wherein at least one reinforcing rib is located on at least one side of said strengthener.

7. A pallet according to Claim 5 wherein a pair of reinforcing ribs is located on each of a first pair of opposed sides of at least one of said strengtheners and a single rib is located on each of a second pair of opposed sides of said at least one of said strengtheners.

8. A pallet according to Claim 1 wherein said first sheet includes a plurality of first supporting legs and said second sheet includes a corresponding plurality of second supporting legs.

9. A pallet according to Claim 8 wherein said first supporting legs are received in said second supporting legs for providing additional strength and stability to the pallet.

10. A pallet according to Claim 1 further comprising elevated ribs on said upper surface of said first sheet to provide a non-slip surface and to raise loads placed thereon above said upper surface of said first sheet.

11. A pallet according to Claim 10 wherein said elevated ribs comprise a series of Xs, when viewed from a corner of said pallet and a series of interrupted intersecting diagonally spaced ribs which cooperate to form opposed spaced parallel sides of a square surrounding and separating each of said series of Xs.

12. A pallet for supporting and transporting loads thereon comprising: a first thermoplastic sheet having a generally planar upper load bearing surface and a lower surface, and said first sheet having greek key style shaped peripheral edge portions; a second thermoplastic sheet having a plurality of supporting legs for elevating a portion of the pallet a selected distance above the surface on which the pallet is resting, and said second sheet having greek key style shaped peripheral edge portions corresponding in shape with said first sheet for mating engagement therewith; and a series of truncated pyramidal shaped strengtheners extending upward from said second sheet, which cooperate with said greek key style shaped peripheral edge portions to position said first and second sheets in fixed parallel spaced relation to each other to thereby define a rigid pallet for supporting a load on said upper surface thereof.

13. A pallet according to Claim 12 wherein said strengtheners are integrally formed on said second sheet and extend upwardly therefrom and are fused to said lower surface of said first sheet.

14. A pallet according to Claim 12 wherein said strengtheners cover substantially entirely said second sheet .

15. A pallet according to Claim 12 wherein each of said strengtheners includes a plurality of reinforcing ribs.

16. A pallet according to Claim 14 wherein at least one reinforcing rib is located on at least one side of said strengtheners.

17. A pallet according to Claim 15 wherein a pair of reinforcing ribs is located on each of a first pair of opposed sides of at least one of said strengtheners and a single rib is located on each of a second pair of opposed sides of said at least one of said strengtheners.

18. A pallet according to Claim 12 wherein said first sheet includes a plurality of first supporting legs and said second sheet includes a corresponding plurality of second supporting legs.

19. A pallet according to Claim 18 wherein said first supporting legs are received in said second supporting legs for providing additional strength and stability to the pallet.

20. A pallet according to Claim 12 further comprising elevated ribs on said upper surface of said first sheet to provide a non-slip surface and to raise loads placed thereon above said upper surface of said first sheet.

21. A pallet according to Claim 20 wherein said elevated ribs comprise a series of Xs, when viewed from a corner of said pallet.

22. A pallet according to Claim 21 wherein said elevated ribs comprise a series of interrupted intersecting diagonally spaced ribs which cooperate to form opposed spaced parallel sides of a square surrounding and separating each of said series of Xs.

23. A pallet for supporting and transporting loads thereon comprising: a first thermoplastic sheet having a generally planar upper load bearing surface having a plurality of elevated ribs thereon and a lower surface having a plurality of first supporting legs formed therein; a second thermoplastic sheet having a plurality of supporting legs for elevating a portion of the pallet a selected distance above the surface on which the pallet is resting and said first supporting legs received in said supporting legs of said second sheet for providing additional strength and stability to the pallet; and a series of truncated pyramidal shaped strengtheners arranged in staggered offset relationship in parallel rows extending between said first sheet and said second sheet, each of said strengtheners connected to said first sheet and said second sheet so as to position said first and second sheets in fixed parallel spaced relation to each other to thereby define a rigid pallet for supporting a load on said upper surface thereof.

24. A pallet according to Claim 23 wherein each of said strengtheners includes a truncated upper portion connected to said first sheet and a base portion connected said second sheet .

25. A pallet according to Claim 23 wherein said strengtheners are integrally formed on said second sheet and extend upwardly therefrom and are fused to said lower surface of said first sheet.

26. A pallet according to Claim 23 wherein said first sheet and said second sheet have correspondingly greek key style shaped peripheral edge portions for interlocking engagement.

27. A pallet according to Claim 23 wherein each of said strengtheners includes a plurality of reinforcing ribs.

28. A pallet according to Claim 23 wherein said elevated ribs comprise a series of Xs, when viewed from a corner of said pallet.

29. A pallet according to Claim 28 wherein said elevated ribs comprise a series of interrupted intersecting diagonally spaced ribs which cooperate to form opposed spaced parallel sides of a square surrounding and separating each of said series of Xs .

30. A pallet for supporting and transporting loads thereon comprising: a first thermoplastic sheet having a generally planar upper load bearing surface having a plurality of elevated ribs arranged in a series of Xs and a series of spaced ribs separating each of said series of Xs to provide a non-slip surface and to raise loads placed thereon above said upper surface of said first sheet; and a second thermoplastic sheet connected to said first sheet, said second sheet having a plurality of supporting legs for elevating a portion of the pallet a selected distance above the surface on which the pallet is resting; said first sheet including greek key style shaped peripheral edge portions and said second sheet including greek key style shaped peripheral edge portions corresponding in shape with said greek key shaped peripheral edge portions of said first sheet for mating engagement therewith to thereby define a rigid pallet for supporting a load on said upper surface thereof.

31. A pallet according to Claim 30 wherein said series of spaced ribs cooperate to form opposed spaced substantially parallel sides of a square surrounding each of said series of Xs .