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Twin-sheet thermoformed postal pallets: they deliver!

Twin-sheet thermoforming is gaining new-found respect as an economical process for making structural parts that can compete with injection molding and structural foam (see cover story, p. 30). Of the wide variety of applications in which twin-sheet forming is finding a niche, the one with major-volume potential is shipping pallets.

Today presswood has 98% of the U.S. pallet market, totaling an estimated 530 million units last year alone. That figure is up 7.7% from roughly 492 million pallets in 1992, according to the National Wooden Pallet and Container Association, Arlington, Va. However, the twin-sheet thermoformed plastic pallet has garnered favor in one small segment of the market, the U.S. Postal Service. And the USPS's move to plastic pallets is drawing attention from other industries that could follow suit.

Last year, the USPS awarded contracts to the three companies that manufactured twin-sheet formed HDPE pallets as part of a USPS test. According to Paul Seehaver, USPS manager of mail transport equipment, the initial contract included 2.6 million pallets from TriEnda Corp., Portage, Wis.; 200,000 from Shuert Industries Inc., Sterling Heights, Mich.; and 319,000 from Cadillac Products Inc., also of Stealing Heights. All three companies made the twin-sheet formed pallets on rotary machines manufactured by Brown Machine Div. of John Brown Plastics Machinery, Beaverton, Mich. Sources at all three pallet producers cite the quality of both machine performance and technical help from Brown as reasons for their equipment selection. Adds Brown product manager Richard Roe, "The cost of making the plastic pallet falls because we can build our machines to run even faster than before for quicker cycle times."


Last year, the Postal Service tested its standard presswood fiber pallet against three types of structural-foam pallets made by different companies and against four types of twin-sheet thermoformed pallets, one each from TriEnda and Shuert and two from Cadillac. The pallets were subjected to simulated real-life environmental conditions.

The USPS then measured the performance of each pallet under load. Pallets were rejected if they had broken legs, pallet-deck deformation of 0.5 in. under load, cracks of 6 in. or longer through the center of the pallet, or holes in the pallet deck as large as the surface area of the leg opening. Results of the 61-day test were made public early last year in USPS's "Pallet Life Cycle Test Report."

The plastic pallets were selected based on their ability to meet the USPS criteria (including ability to support a minimum load of 2500 lb and strength retention at different temperatures), as well as their outright advantages over wood or structural foam. For one thing, the plastic pallets weigh roughly 19 to 27.5 lb, versus more than 50 lb for presswood. Also, presswood pallets aren't nestable, unlike plastic. Consequently, about two to three times as many plastic pallets could be stacked in a given height as wood pallets.

In addition, the HDPE pallets were more readily recyclable than presswood - another USPS goal - and could be designed to permit four-way entry for a pallet jack or forklift to facilitate handling.

The USPS test report says the HDPE pallets averaged 55.93 test cycles per pallet, vs. 20-40 for structural foam and 7.1 for presswood. (A test cycle simulated one trip with loading, transporting, and unloading stresses.) Greater durability makes up for higher cost: Twin-sheet pallets cost $15-$16; presswood cost $7 each. Structural-foam pallets are 54% more expensive than thermoformed versions.


Seehaver says the USPS is happy to replace presswood pallets with a product that doesn't look shoddy or constantly break under load or during transport from one postal depot to another. The plastic pallets are used for major Third-Class and First-Class customers, such as TV Guide and the telephone companies, which ship millions of units annually.

Seehaver says the USPS is looking to replace all of its pallets with twin-sheet formed plastic. The Postal Service is not ordering any more presswood pallets and is considering solicitation of bids for a similar number of plastic pallets this year as it purchased in 1994. Seehaver says the next pallet solicitation may carry even tougher deformation and load-carrying requirements.

In addition, the USPS is looking to award contracts for development of a twin-sheet thermoformed hamper for mail conveyance, which is normally constructed of canvas with a wood floor and steel structure. The Postal Service is currently testing 55,000 rotomolded hampers.

Thermoformers have other ideas for expanding the market for twin-sheet pallets. Lyle Shuert, president of Shuert Industries; R.J. Williams Jr., chief financial officer of Cadillac; and Thomas Pintar, v.p. of sales and marketing at TriEnda, all point to food handling in the grocery industry as the newest emerging market for plastic pallets. Cadillac sales and marketing director David DeMocker pegs grocery-pallet usage conservatively at six million units annually.

Plastic pallets have the advantage that customers can color-code their plastic pallets to keep track of them for retrieval from supermarkets. "But plastic pallets are not rackable," DeMocker says, meaning they cannot be used for long-term storage unless they have steel-reinforced inserts. Wood pallets still offer the best long-term rackability, but they can't be nested. "The holy grail will be a plastic pallet that's rackable and nestable and affordable," DeMocker concludes.

Cadillac's Bob Williams adds that other potential markets for thermoformed pallets include the automotive, pharmaceutical, textile, rubber, and chemical industries.
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Title Annotation:Postal Service's use of plastic pallets
Author:Knights, Mikell
Publication:Plastics Technology
Date:Aug 1, 1995
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