As the recycling of plastic continues in the United States, there is a great need for the increased utilization of recycled products. Some of the plastic being recycled is extruded into a product known as plastic lumber, which is similar in shape and texture to its wood counterpart. Recycled plastic lumber offers many of the same features as wood with several benefits.

The pallet industry utilizes large amounts of both hardwood and softwood. As the price of wood lumber continues to rise, many segments of this industry are looking for an alternative to wood. Plastic lumber, made from post-consumer plastic, is a good alternative. The pallet industry has introduced injection molded and thermoformed plastic pallets, but these pallets are made mainly from virgin plastic. Most plastic pallets are made using plastic injection molding processes, which is very expensive. Alternatively, the pieces of the pallet are fastened using metallic screws or bolts, which present stress points for fracture and failure, and separation problems upon recycle. This invention addresses the need for an inexpensive and reliable method of joining plastic lumber to form durable plastic lumber pallets.

The invention consists of a machine for forming plastic lumber pallets from plastic runners and plastic cross members. It comprises 1) a cross-member support for supporting one of the pallet cross members, 2) a runner support member for maintaining at least one of the runners in essentially transverse relation with the cross member, and 3) a hot plate positioned between the cross member and one of the runners, and heating and melting simultaneously a portion of the top of the cross member and a portion of the bottom of the runner.

In addition, the runner support member is formed so as to maintain at least two of the runners spaced apart with respect to each other. A pneumatic vertical movement unit moves the runner support members in an up-and-down direction. A transverse movement unit moves the hot plate in essentially a transverse direction with respect to the cross-member support. A parallel movement unit moves the hot plate in a direction essentially parallel to that along the cross-member support. Finally, a vertical movement unit moves the hot plate in an up-and-down (vertical) direction. Such movement allows the hot plate to be inserted between the runner and cross member and withdrawn when a portion of the runner and cross-member surfaces have been heated to a molten state.

A pressure application member applies pressure to a layered assembly of the hot plate positioned between the cross member and one of the runners during the hot plate heating process in which the hot plate melts simultaneously a portion of the top of the cross member and a portion of the bottom of the runner. The pressure application member also applies pressure to an assembly of a molten portion of the top of the cross member in contact with a molten portion of the bottom of the runner to form the weld or bond between the cross member and the runner. A vertical movement unit is used to move the pressure application member in an up-and-down direction so as to apply pressure to the heating and welding assemblies.

A base such as an assembler table is used to mount the cross-member support, the runner support members, the hot plate, and the pressure application member. The pallet assembler table is comprised of four legs, two ends, and two sides. The table is jointed with fasteners such as nuts or bolts for a modular construction, or by welding for a more permanent structure. Welding the table is especially suited for large production runs of pallets of the same size. The machine is especially effective for making plastic lumber pallets from solid plastic lumber, especially lumber made from recycled plastics.

In comparison to wood pallets, the plastic pallets manufactured in this process are tougher, more weather resistant, and have better integrity. Further, they have longer field lives and are well acclimated to reuse.

This work was done by Edison Welding Institute, and is available through the technology licensing marketplace. For more information, visit

NASA Tech Briefs Magazine

This article first appeared in the October, 2011 issue of NASA Tech Briefs Magazine.

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