US 6959650 B2
A Conveyorable Plastic Thermoformed Pallet, having a support member and support legs with outer walls, internal walls and inner walls, is utilized to transport product on a conveyor system. The Pallet is made using a twin-sheet thermoforming process that requires two molds for an upper sheet of thermoplastic material and a lower sheet of thermoplastic material. The upper sheet forms a top deck of the support member and the internal walls of the support legs. The lower sheet forms the underside of the support member, the inner walls of the support legs, and leg bottoms. Both sheets are fused to form the twin-sheet outer walls. The upper sheet also forms web strips which stabilize the walls of the support legs and prevent deflection of the walls.
1. A twin-sheet thermoformed pallet comprising:
a substantially planar support member formed from an upper sheet of thermoplastic material and a lower sheet of thermoplastic material, the upper sheet forming a top surface of the support member and the lower sheet forming a bottom surface of the support member;
at least two support legs depending from the support member, the external structure of each leg formed from the lower sheet and the internal structures of each leg formed from the upper sheet, the lower sheet forming the legs extending across the width of the pallet with a substantially flat leg bottom;
an opening in the top surface of the support member formed where the upper sheet folds to form the internal structures of the support legs; and
a plastic webbing in the opening wherein the webbing connects the sides of the opening and partially fills the opening.
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12. A twin-sheet thermoformed plastic pallet comprising:
a substantially planar support member formed by an upper and lower thermoplastic sheet;
the lower sheet forming the underside of the support member and the external walls of at least two support legs extending downward from the support member;
the support legs including reinforced impact zones on the sides of the legs and a cantilever on the ends of the legs;
the upper sheet forming the top surface of the planar support member, internal walls extending into the support legs, and openings in the top surface formed where the upper sheet folds to create the internal leg walls; and
a web strip positioned inside the opening formed by the upper sheet, the web strip partially filling the opening and fusing the sides of the opening together.
13. A method for forming a twin-sheet plastic pallet comprising:
forming a lower plastic sheet by heating the sheet to a heated, flowable state and drawing the heated lower sheet against a bottom mold by vacuum, where the molded lower sheet forms an underside for the substantially planar surface of the upper sheet, and external walls of support legs extending from the bottom of the planar surface;
forming an upper plastic sheet by heating the sheet to a heated, flowable state and drawing the heated upper sheet against a top mold by vacuum, where the molded upper sheet forms a substantially planar upper surface and internal walls for pallet legs, formation of the internal walls also Conning openings in the upper surface;
while the upper and lower sheets are still heated, bringing the upper and lower sheets together to fuse the upper and bottom portions of the substantially planar surfaces together, and to fuse the internal walls formed by the upper sheet with the external walls of the support legs formed by the lower sheet;
forming a web strip between the internal walls and the external walls of the support legs to stabilize the walls and minimize the openings in the upper surface.
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The present invention generally relates to pallets and, more particularly, to plastic pallets for use on conveyor systems.
Pallets are commonly used to store and transport loads in many industries. Because plastic pallets are lighter and more durable than traditional wooden pallets, plastic pallets are replacing wooden pallets in many industries. Lighter plastic pallets are easier to move than wooden pallets and add less weight to a shipment of product, resulting in decreased transportation costs.
Besides the weight benefits of plastic pallets, wooden pallets have to be replaced more frequently than plastic pallets. Wooden pallets can become warped if exposed to moisture, making them difficult to use with a forklift or in a stack of load bearing pallets. Further, the nails necessary for constructing the wooden pallets can become loose, damaging product or causing personal injury.
Despite these benefits, some industries have not replaced wooden pallets with plastic pallets. Industries using conveyor systems, in particular, have not converted to plastic pallets. Wooden pallets used on conveyor systems have additional problems that could be solved by plastic pallets. Loose nails from a wooden pallet can get caught on the conveyor system, impeding product flow along the conveyor system and damaging the rollers of the conveyor system. The wooden pallets absorb liquid, making them heavier and creating cleanliness problems.
Despite these disadvantages, wooden pallets are still used with conveyorable systems because they offer more necessary advantages over current plastic pallets. Current plastic pallets are not as stiff as wooden pallets, resulting in dented plastic pallet legs, and dented pallet legs do not work well on the rollers of a conveyor system. Conventional twin-sheet plastic pallets have large openings in the deck surface, allowing product to fall into the openings, and attempts to decrease the size of the openings have required smaller support leg surfaces, which also do not work as well on conveyor rollers. Therefore, plastic pallets have not been used for applications requiring conveyor transportation of palleted goods.
A thermoformed pallet of this invention has a substantially planar support member with broad support legs having generally flat bottom surfaces. The support member has a top deck surface formed by an upper sheet of thermoplastic material and a lower surface formed by a lower sheet of thermoplastic material. The upper and lower thermoplastic sheets also form the support legs. The lower thermoplastic sheet forms the external walls of the support legs and the upper thermoplastic sheet forms the internal reinforcing walls of the support legs. The support legs extend across the width of the pallet and have one opening in the bottom surface of each leg that runs parallel to the direction of the pallet along a conveyor.
In a preferred embodiment, the top deck has openings where the upper sheet folds to form the internal walls of the support legs. The openings are partially filled with a web strip, which minimizes the volume of the opening and stabilizes the walls formed by the upper sheet.
It is an object of the present invention to provide an improved twin-sheet thermoformed plastic pallet with support legs for use with a conveyor system.
It is a further object of the present invention to provide an improved pallet with increased stiffness and durability.
These and other inventive features, advantages, and objects will appear from the following Detailed Description when considered in connection with the accompanying drawings in which similar reference characters denote similar elements throughout the several views and wherein:
Referring to the drawings in greater detail,
The pallet is formed by a dual mold thermoforming process, where a top mold (not shown) forms the upper sheet 26 and a bottom mold (not shown) forms the lower sheet 28. The upper and lower sheets are made from thermoplastic sheets of substantially uniform thickness.
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In a preferred embodiment, the opening 34 is a generally continuous, substantially linear opening extending across the width of the top deck 42. The opening 34 extends into the support member 22 approximately to the bottom of the support leg. The opening 34 is partially filled at intervals with a web strip 38 to stabilize the sides of the opening. In a preferred embodiment, the opening has four web strips evenly spaced apart along the opening, although the number and spacing could be varied. The web strip 38 is formed where the portions of the upper sheet 26 creating the opening 34 are positioned closer together. The sides of the opening 34 fuse together at these positions to form the web strip 38.
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The opening also has stiffness ribs 60 positioned along the sides of the opening 34 and extending from the top deck 42 to the bottom 43 of the opening. As shown in
The support member 22 also has handles 49 formed into the support member. In a preferred embodiment, the support member has a total of four handles, with two handles placed on each side of the pallet and each handle positioned between two of the support legs. The handles 49 extend through the support member 22 and are generally oval shaped.
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The internal walls 32 of the support legs 24 are also the sides of the openings 34 formed by the upper sheet 26. The internal walls 32 serve to reinforce the support legs, helping them maintain their structure even when supporting a product load. The internal walls 32 serve to decrease leg wall deflection common with conventional twin-sheet pallets.
The inner walls 39 formed by the lower sheet 28 also form the inverted V-shaped opening 41 in the center of the support leg 24. Each inner wall 39 is parallel to the internal wall 32 located on that same side of the opening 41, as shown in FIG. 3. The inner walls are not parallel to each other, just as the internal walls are not parallel to each other. These inner walls 39 provide greater stiffness in the support leg and also reduce deflection of the walls, which is common with conventional plastic pallets. With conventional pallets, the walls of the support legs bow under the weight of product loads, causing the bottom 30 of the leg to bow as well, losing contact with the surface under the pallet. The pallet deforms over time, creating a leg bottom that only contacts the surface it is placed on at the edges of the leg bottom. A pallet deformed in this way does not move smoothly across rollers
The lower sheet 28 also forms the leg bottoms 30, which are generally flat. The leg bottoms 30 have a gap created by the inverted V-shape opening 41 that extends substantially the length of the leg. The opening 41 does not extend to the ends of the leg bottom 30, where the leg is flat with no gaps or openings. The leg bottoms of this invention perform better on the rollers of a conveyor system than traditional pallets because they only have openings running parallel to the direction of the pallet along the rollers. The openings 41 do not provide an edge to get caught on the rollers, which can impede product flow along the conveyor system.
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The pallet is manufactured using a twin-sheet thermoforming process where two sheets of thermoplastic material, the upper and lower sheets, are thermoformed together into the shape of the pallet by using two vacuum molds, a top and a bottom mold. The upper sheet is heated until it is malleable and then mounted on the top mold, where the vacuum ports of the top mold draw the heated thermoplastic sheet against the mold, conforming to the shape of the mold. The same process is repeated with the lower sheet and the bottom mold. Once the two sheets have conformed to the molds, the sheets are brought together to form the pallet and the molds are separated from the upper and lower sheets.
The top mold has two ribs for each support leg that extend substantially across the width of the pallet. In a preferred embodiment, the mold ribs have four equally spaced recesses that form the half-circle bulges of the web strips. The number and spacing of recesses can vary depending on the size and structural needs of the pallet. The mold ribs are narrowed at this point, bringing the two sides of the upper sheet into close position when forming the pallet. The recesses in the mold ribs also create a small opening between the half-circle bulges, where the two sides of the upper sheet folded around the mold rib are not separated by the rib. As the upper sheet is drawn across the top mold, the proximity and temperature of the half-circle bulges across from each other creates the web strip 38. The two sides of the upper sheet fuse together at that point when the mold no longer separates them.
The bottom mold has mold ribs running along the center of each support leg to form the inverted V-shaped opening in the legs. These ribs are uniform and extend the length of the legs.
When both sheets have been formed to the molds, and while they are both still heated, the molds are positioned together to form the pallet. The sheets melt together where the molds match up in desired positions to create the support member and the support legs.
Thus, a conveyorable plastic thermoformed pallet and method for making pallet is disclosed which utilizes internal walls, inner walls, and web strips to prevent deflection of the support walls in the support legs of the pallet thereby enhancing the stiffness and durability of the pallet and the suitability of the pallet for use on a conveyor system. While preferred embodiments and particular applications of this invention have been shown and described, it is apparent to those skilled in the art that many other modifications and applications of this invention are possible without departing from the inventive concepts herein. It is, therefore, to be understood that, within the scope of the appended claims, this invention may be practiced otherwise than as specifically described, and the invention is not to be restricted except in the spirit of the appended claims. Though some of the features of the invention may be claimed in dependency, each feature has merit if used independently.