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Polyurethane RIM Process Produces Aviation Wheel Chocks that Pass Materials Challenges with Flying Colors

Bayer MaterialScience AG : 04 March, 2002  (Company News)
Aviation wheel chocks designed and manufactured by RIMSTAR Inc., of Louisville, Colo., look simple enough. But don' be fooled.
What you don't see is years of development to meet stringent performance specifications mandated by the U.S. Air Force, such as chemical resistance, the ability to handle heavy loads and sustain aircraft rollover, good traction and the ability to retain these properties in a wide range of climatic conditions. In the end, polyurethane reaction injection molding (RIM) technology from Bayer Corporation helped RIMSTAR pass these material challenges with flying colors.

RIMSTAR molds the wheel chocks, which are designed to prevent an aircraft from rolling when not in use, using the BayflexŮ elastomeric polyurethane RIM system from Bayer's Polyurethanes Division. This system is ideal for applications requiring excellent strength and durability.

Chock Full of Engineering

For many years, wheel chocks were little more than wooden blocks. However, the wood chocks could splinter with use, causing a potential safety hazard or 'F.O.D.' (foreign object damage) that can severely damage jet engines. Furthermore, their life span was short, lasting roughly six months to one year.

With 30 years of experience working with polyurethanes, John Duvall, President of RIMSTAR, said the advantages of the RIM process include faster processing, fewer secondary operations, molded-in color, and the ability to design and mold-in reinforcing ribs that cut part weight without sacrificing strength. This last benefit was very important to this application, according to Duvall, and they all contributed to lower production costs.

'The military wanted to decrease the weight of the chocks, yet they had to handle heavy loads and sustain rollover,' he said, adding that a B-52 aircraft rollover is the equivalent of 495,000 pounds. 'The chocks formed from the Bayflex system look solid from the outside. But the molded-in ribs let us reduce the weight, yet still meet the other performance criteria,' he explained.

Another key material requirement was the ability to retain physical properties at extreme climatic conditions - from -40 degrees to 160 degrees Fahrenheit. 'This is very important, because most military aircraft are kept outside, and the chocks must perform whether they are used in the Arctic or a desert,' explained Duvall. He said the service life of thepolyurethane RIM chocks is seven to 10 years.

RIMSTAR molds aviation wheel chocks in various sizes, ranging from 12 to 56 inches long and five to eight inches wide, and three to six inches high. The chocks are manufactured exclusively for Checkers Industrial Products Inc., of Louisville, Colo., and are marketed worldwide under the trade name Tigerchocks1.

The market for Tigerchocks has expanded from the U.S. Air Force to all branches of the military and now to commercial airlines, as well. In its most high-profile application, RIMSTAR molded Tigerchocks in Robin Egg Blue and adorns them with a silk-screened Presidential seal for use with Air Force One.

Designing and manufacturing the polyurethane RIM chocks to meet U.S. Air Force specifications took several years, said Duvall, and Bayer was involved in the project early on. Bayer's technical support included finite element analys is (FEA) of the chock design and other material testing.

'I have a high level of confidence in the consistency of Bayer's polyurethane products,' said Duvall. 'Furthermore, they have the best technical service in the business. We use 100 percent Bayer polyurethane products in our manufacturing operations.'
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