Twin sheet pallet

A twin sheet pallet constructed by forming a lower polygonal plastic sheet to define an upwardly opening U-shaped groove around its periphery; forming an upper polygonal plastic sheet to define a plurality of circumferentially spaced upwardly opening U-shaped protrusions extending downwardly from the general plane of the sheet and sized to nest in the groove of the upper sheet; positioning the upper sheet over the lower sheet with the protrusions on the upper sheet nested at circumferentially spaced locations in the groove of the lower sheet; fusing the upper and lower sheets together to form double thickness U-shaped wall structures at the interfaces of the protrusions and the groove; and cutting aligned horizontally extending slots in the opposite sides of the U-shaped structures to allow entry of the forks of a forklift truck.

DESCRIPTION 
BACKGROUND OF THE INVENTION 
This invention relates to shipping and storage pallets and more 
particularly to plastic pallets embodying a twin sheet construction. 
Pallets have traditionally been formed of wood. Wood pallets, however, have 
many disadvantages. For example, they are subject to breakage and thus are 
not reusable over an extended period of time. Wood pallets also take up a 
considerable amount of valuable floor space in the warehouse when they are 
not in use. In an effort to solve some of the problems associated with 
wood pallets, plastic pallets have been employed with some degree of 
success. In one generally successfull form of plastic pallet design, a 
twin sheet construction has been used in which upper and lower plastic 
sheets are formed in separate molding operations and the two sheets are 
then selectively fused or knitted together in a suitable press to form 
reinforced double wall structure. Even these twin sheet plastic pallets 
have drawbacks however. Specifically, their under surfaces tend to be 
irregular so that movement of the pallet over irregular transfer surfaces 
and over various transfer devices such as conveyors is difficult and 
sometimes impossible. Further, the prior art twin sheet pallets have 
tended to creep or sag after a period of time. Further, the prior art twin 
sheet pallets fail to make provision to preclude tipping of the pallet off 
of the forks of a forklift truck in the presence of an unbalanced load on 
the pallet. 
SUMMARY OF THE INVENTION 
This invention provides a twin sheet plastic pallet which provides a 
continuous lower footprint to facilitate movement of the pallet over 
irregular transfer surfaces. The invention pallet is also extremely 
resistant to sagging or warping, even over extended periods of use. The 
invention pallet also provides lower straps which pass beneath the 
inserted forks of a forklift truck to preclude tipping of the pallet even 
in the presence of an unbalanced load on the pallet. 
The invention plastic pallet includes a lower polygonal plastic sheet 
defining an upwardly opening U-shaped groove around its periphery; and an 
upper polygonal plastic sheet defining a plurality of circumferentially 
spaced upwardly opening U-shaped protrusions extending downwardly from the 
general plane of the sheet and sized to nest within the groove of the 
lower sheet. In manufacture, the upper sheet is positioned over the lower 
sheet with the protrusions positioned at circumferentially spaced 
locations in the groove and the sheets are thereafter fused together in a 
compression molding process to form double thickness U-shaped wall 
structures at the interfaces of the protrusions and the groove, whereafter 
aligned horizontally extending slots are cut or routed in the opposite 
sides of the U-shaped structures to allow entry of the forks of a forklift 
truck. This structure provides a continuous lower footprint for the pallet 
to facilitate movement of the pallet over transfer surfaces, and provides 
straps to capture the lower faces of the forks of the forklift truck to 
preclude tipping of the pallet in response to unbalanced loads. The 
invention structure is also extremely strong and extremely resistant to 
sagging or warping, even over extended periods of use. 
According to a further aspect of the invention, the lower sheet includes a 
raised central portion within the groove which defines a hollow central 
area beneath the pallet into which the inner ends of the forks of the 
forklift truck may extend after passing through the aligned slots in the 
opposite sides of the U-shaped double thickness wall structures. 
According to another aspect of the invention, the central portion of the 
upper sheet within the protrusions is generally planar and generally at 
the level of the outer upper edges of the protrusions; the protusions have 
a depth at their outer walls generally corresponding to the outer wall 
depth of the groove; and the raised central portion of the lower sheet is 
below the plane of the outer upper edge of the groove so that, when the 
protrusions are nested in the groove, the central portions of the sheets 
form a spaced double wall construction. This spaced double wall 
construction adds significantly to the overall strength of the pallet and 
adds to its rackability. 
In the disclosed embodiment of the invention, the upper and lower sheets 
are rectangular and two peripherally spaced protrusions are provided along 
each side of the upper sheet so as to provide two sets of aligned slots 
along each side edge of the pallet for passage of the two forks of the 
forklift truck.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The basic inventive concepts of the invention pallet are schematically 
disclosed in FIGS. 1 and 2. Broadly, a lower sheet 10 is suitably molded 
to provide an upwardly opening generally U-shaped peripheral groove 12 
extending around its entire periphery; an upper sheet 14 is suitably 
molded to provide a plurality of circumferentially spaced upwardly opening 
U-shaped protrusions 16 extending downwardly from the general plane of the 
sheet and sized to nest within the groove 12 of the lower sheet; the upper 
sheet is positioned immediately over the lower sheet with the protrusion 
16 nested in groove 12 at circumferentially spaced locations around the 
groove with the sides of the protrusions contiguous with the sides of the 
groove, the bottoms of the protrusions contiguous with the bottom of the 
groove, and the peripheral edge 14a of the upper sheet immediately 
overlying and contiguous with the peripheral edge 10a of the lower sheet; 
and the sheets are fused or knitted together to form double thickness 
U-shaped wall structures 18 at the interfaces of the protrusions 16 and 
groove 12. Horizontally extending aligned slots 20 and 22 are then formed 
respectively in the opposite sidewalls 24 and 26 of U-shaped structures 18 
to allow entry of the forks of a forklift truck. The forks after passing 
through aligned openings 20 and 22 pass into a hollow central area 28 
defined beneath the raised central portion 30 of the lower sheet. Sheets 
10 and 14 may be molded in a vacuum forming process and may be formed of 
an organic polymeric material such as polyethylene, and the process 
whereby the sheets are knitted together to form the pallet may comprise a 
compression molding proces. 
A specific commercial embodiment of the invention twin sheet pallet is 
illustrated in FIGS. 3-6. With reference now to the finished pallet of 
FIGS. 3-6, sheets 10 and 14 are initially formed so that, when fused 
together, the double thickness outer wall 24 of U-shaped structures 18 is 
inset with respect to the single thickness outer wall 32 of the pallet 
between structures 18 so that outer slots 20, as best seen in FIG. 6, are 
inset and protected with respect to the outer wall of the pallet. Central 
portion 34 of upper sheet 14 is generally flush with peripheral edge 14a 
and the raised central portion 30 of lower skin 10 is spaced below the 
level of the peripheral edge 10a of lower sheet 10 so that, when the 
sheets are positioned together to form the finished pallet, central 
portion 30 of lower sheet 10 and central portion 34 of upper sheet 14 form 
a spaced double wall structure. Ribs 30a and 34a in central portions 30 
and 34 provide stiffness to the central area of the pallet and the central 
pallet area is further stiffened by a centrally downwardly projecting 
protrusion 30 b in lower sheet 10 coacting and knitted together with a 
centrally downwardly projecting protrusion 34b in upper sheet 14 to form a 
central leg or foot 38. Foot 38 is at the same level as the continuous 
circumferential footprint 40 provided by the under surface of groove 12 
and coacts with that footprint to provide firm, flat, sturdy footing for 
the pallet while not interfering with the inward intrusion of the forks of 
the forklift truck passing through any of the aligned slots 20, 22. The 
upper and lower sheets are also configured to provide inwardly projecting 
protrusions 42, in general alignment with foot 38, to further strengthen 
and stabilize the pallet. It will be understood that the upper and lower 
sheets are further convoluted, configured, internested, and knitted 
together, particularly in the corner areas of the pallet and the 
peripheral areas between adjacent U-shaped Figures 18, to provide further 
strength and rigidity for the pallet. 
The invention pallet will be seen to provide many important advantages. 
Specifically, the invention construction provides a continuous peripheral 
footprint on the bottom of the pallet so that the pallet can pass easily 
over various and irregular transfer surfaces and transfer devices such, 
for example, as conveyors. The invention construction also provides a 
rigid lower strap passing beneath the inserted forks of a forklift truck 
so that the pallet, even if unevenly loaded, will not tend to tip off of 
the forks as the pallet is lifted and transported by the forks. The 
invention construction also provides a very stiff and rigid pallet which 
resists bowing or warpage even over extended periods of use. The invention 
pallet is also extremely simple in construction and therefore relatively 
inexpensive to produce and yet is extremely sturdy so as to provide an 
extremely long useful life. 
Although a preferred embodiment of the invention has been illustrated and 
described it will be apparent that various changes may be made in the 
disclosed embodiment without departing from the scope or spirit of the 
invention.