Horizontally supported planar surfaces – Industrial platform – Having plastic load-contacting surface
Reexamination Certificate
1998-07-01
2001-06-26
Chen, Jose V. (Department: 3624)
Horizontally supported planar surfaces
Industrial platform
Having plastic load-contacting surface
Reexamination Certificate
active
06250234
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of reinforcing a plastic pallet, and more particularly to a method of reinforcing a plastic pallet by applying a plurality of sheet strips along relatively weak structural portions of the pallet to form a plurality of substantially rectangular hollow vertical cross-sections along the length of the relatively weak structural portions for improved stiffness.
BACKGROUND ART
Replacing wood pallets with plastic pallets has been a goal for many years. The advantages of the plastic pallets are many as compared to wood, including greater durability, lighter weight, more consistent dimensions, improved cleanliness, water resistance, higher residual value for recycling, and no nails which may damage products being supported thereon.
One major hurdle to overcome with plastic is the cost. Plastic pallets are more expensive than wood by three to five times. This cost can be offset by the number of trips or shipments that can be achieved with plastic versus wood pallets. Another major hurdle is the stiffness of plastic pallets. Racking loaded pallets in warehouses for up to 30 days is common, and the combination of low tensile strength and creep limit the use of plastic.
There are three conventional methods of overcoming these weaknesses. The first is to add reinforcement such as steel or a composite to the pallet. This generally adds significant cost and weight and complicates recycling of the pallet. The second is to make the pallet taller. This limits the height of product to be stacked on the pallet. The third is to use reinforced or engineered resins. Again, this adds significant cost and weight. All three obviously limit the acceptance of plastic pallets.
U.S. Pat. No. 3,580,190 provides a partial solution to the stiffness problem by attaching top and bottom sheets
22
,
24
to the structural network
23
, as shown in
FIG. 1
thereof. However, this solution does not resolve the bending stiffness problem because large lateral and longitudinal unsupported areas still exist, such as in areas
26
,
37
,
38
,
49
and
50
. In other words, this design merely further stiffens the support column areas
67
,
68
,
69
,
97
,
98
,
99
,
28
,
30
,
32
, which already provide substantial stiffness merely as a result of their height. The weakness of this design is apparent in column 6, lines 60-71, where Fowler recommends the use of a material having a flexural modulus (or Young's modulus) greater than about 200,000 psi. Such a high modulus material is apparently required because the structure described does not provide significant resistance to deflection along the length and width of the pallet. High modulus materials add substantial cost to the pallet.
Further complicating the problem, modern pallets typically require large openings for receipt of pallet jacks. For example, the pallet shown in
FIGS. 1-3
includes a top deck portion
16
supported on a plurality of support columns
18
, which are attached to support rails
20
, which form the bottom deck
19
. Such structure cooperates to form two large openings
11
,
13
on each side of the pallet
10
, as well as four bottom openings
15
formed in the lower deck
19
. In this configuration, the rails
20
of the lower deck
19
are typically structurally weak, resulting in poor deflection stiffness. Such problems have proven very difficult to overcome because of the very thin nature of the lower deck
19
. Similarly, the thin design of the top deck
16
results in the same deflection problem between columns
18
.
Because pallets are exposed to significant abuse, any solution to the stiffness problem must not adversely effect the impact strength of the pallet.
Accordingly, a need exists for improving the stiffness of modern plastic pallets configured to receive a pallet jack, without reducing impact strength of the pallet.
SUMMARY OF THE INVENTION
The present invention provides a method of reinforcing a modern plastic pallet by affixing sheet strips along relatively weak structural portions of the pallet to form a plurality of substantially rectangular hollow vertical cross-sections along the length of the relatively weak structural portions for improved stiffness without loss of impact strength.
More specifically, the present invention provides a method of reinforcing a plastic pallet having a thin top deck portion, a plurality of support columns extending from the top deck portion and a plurality of support rails connected to the support columns to form a thin bottom deck portion, wherein the support rails each include a sheet portion with a plurality of vertical ribs extending therefrom. The method includes the step of welding a plurality of plastic sheets to the vertical ribs between the support columns to form a plurality of substantially rectangular hollow vertical cross-sections along the length of the support rails for improved stiffness. It is contemplated that the substantially rectangular hollow vertical cross-sectional areas may be filled with a secondary material, such as structural foam for improved structural integrity.
Accordingly, an object of the present invention is to provide a method of structurally reinforcing a modern plastic pallet configured to receive a pallet jack, in a manner which improves stiffness without loss of impact strength.
The above object and other objects, features and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.
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Brooks & Kushman P.C.
Chen José V.
Rehrig Pacific Company
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