This invention relates to pallets for supporting freight, goods or other materials, and more particularly to a pallet made of synthetic resin for use with a fork lift.
Pallets made of molded plastic material have distinct advantages over those made of wood or metal. Wood pallets are heavy; are subject to warpage, splintering and splitting; are nonuniform in strength; and gain significant weight when wet. Metallic pallets typically are expensive and, in the case of steel, heavy and subject to corrosion. Plastic pallets, while stronger, lighter and more durable than wooden pallets, nevertheless have shortcomings of their own.
In an effort to minimize mold costs, some plastic pallets have been designed as modular units which consist of a plurality of identical molded elements that are snapped, fused or otherwise secured together to make a complete pallet. Examples of this type of pallet are disclosed in U.S. Pat. Nos. 4,051,787; 4,597,338; and 5,197,395. However, this is a compromise scheme which usually yields a pallet that is made of more material (and is therefore heavier and has a higher material cost) than would be required if the upper and lower portions of the pallet were optimally designed to serve their diverse purposes.
Specifically, the top deck of a pallet should have relatively small openings so as to adequately support the load across substantially the entire upper surface of the pallet; it must be stiff enough (usually afforded by substantial ribbing) to prevent excessive bending, either when resting on the forks of a fork lift, or resting on the supports that separate the upper and lower decks; and its upper surface should not have recesses or crevices which could collect water or dirt. The top decks of the pallets disclosed in the aforementioned patents have these features. In contrast, the bottom of the pallet, which normally is intended to rest on a substantially solid surface, such as a floor, deck, shelf or rack, need not have as much material on its underside in contact with the supporting surface. Thus, the bottom deck of a plastic pallet may have relatively large openings, and may have exposed ribs, recesses and crevices on its underside, as long as the design provides adequate support for the loaded pallet. An upper pallet deck which is inverted to serve as a lower deck thus would have more material than actually required to perform the functions of a lower deck.
FIGS. 8-19 of U.S. Pat. No. 4,051,787 depict examples of a pallet which has relatively large openings in its bottom deck. However, the structure surrounding these openings appears to be quite thick and massive, with a large, closed bottom surface area that would contact a supporting surface. The bottom deck thus would appear to contain more material than is actually required.
Some pallets which comprise identical molded halves require a plurality of separate fastening elements to secure the halves together. U.S. Pat. Nos. 2,699,912 and 5,197,395 disclose examples of these types of pallets. The use of separate fastening elements introduces added cost and assembly time to pallet construction.
Efforts to minimize the amount of plastic material used in a pallet have led some to devise hybrid constructions wherein discrete reinforcing rods are integrated onto the molded pallet. An example is disclosed in U.S. Pat. No. 4,316,419, which uses metal reinforcing rods that are inserted into channels molded into the pallet. The problem with these types of pallets is that they require separately manufactured additional components, and additional assembly steps.
Another problem with plastic pallets in general is that their surfaces tend to be slippery. Measures must be taken to prevent the load from sliding off the pallet; to keep stacked pallets, whether loaded or not, from sliding off one another; and to keep the pallet from sliding off the forks of the fork lift. Common anti-slip measures involve the use of anti-slip coatings or rubber inserts, such as pads or grommets, placed in strategic locations. Examples are shown in FIGS. 20-25 of U.S. Pat. No. 4,051,787. One problem with these anti-slip measures is that they require the installation of additional parts or materials. Further, anti-slip coatings can wear away, while inserts can work loose and fall off during use, rendering them ineffective.
In the bottled beverage industry, filled and capped bottles are placed in bottle crates, which are loaded onto pallets and moved about using a fork lift. The crates typically are of the low depth variety, such that the bottles project above the upper edges of the crates. As long as the bottles are of uniform height, it is desirable to stack several loaded pallets on top of one another so that they can be moved about collectively by fork lift, and efficiently stored in a stacked configuration either on a floor or on a shelf or rack. The bottom deck of the pallet must be designed so that the load of one pallet is evenly distributed over the closures of the bottles on the subjacent pallet. Existing pallet constructions do not adequately address this need.