Cooling Friction

New friction formulas and wide drums give fleets braking alternatives


The Federal government of the U.S., in concert with Canada, in the late 1990s charged the National Highway Traffic Safety Administration (NHTSA) and various heavy-duty industry associations, manufacturing corporations, truck fleets, and other related government agencies to reduce the number of traffic deaths involving class 6, 7, 8 trucks and trailers. After much debate, it was determined that the technology available to the industry could support a 30 percent reduction in stopping distances. It now appears the new stopping distance rules will be implemented in 2008 or 2009 but not necessarily for all vehicle types.

Fact: The newer, extended service S-cam brake shoe and systems and the new air disc brake systems both can achieve the new stopping distance standards.

Fact: Wider S-cam drum brake systems on front steer axles, drive axles and trailer axles are proven to easily meet the proposed new standards.

Fact: Newly developed drum brake friction formulas, now in the marketplace for three to four years, utilizing transfer film/cohesive technology along with specially designed metallic fibers, create higher brake torque, less fade, lower operating temperatures, and much-improved wear for both the brake lining and for the brake drum. These new drum brake friction materials, while somewhat higher in cost, prove to be a much better "value proposition"for truck fleets, because they last much longer than conventional friction formulas and provide improved stopping power.

For example, Brake Pro, Ltd.'s CCM™ friction product line (conformable, cohesive, metallic) was launched in 2002 as CM243™, designed to meet FMVSS121 performance standards at 25,000 to 29,000 pound axle ratings. The CCM™ formulations combine three unique formulation concepts into one material matrix. The CCM™ formulas use a specially-designed rubber system to enhance conformability (friction beds in with the drum much quicker), which reduces "hot spots"and improves wear. Cohesive technology is incorporated in the CCM™ formulas through the use of specific materials, which deposit a 2-3 micron thick layer of film on the surface of the drum and lining creating a "like on like"material braking surface, which reduces wear, reduces operating temperature, and allows the effective use of higher friction levels (more stopping power). These two concepts are combined with specially designed metallic fibers, which increase heat transfer characteristics in the lining, which reduces brake-operating temperatures. The net result of these new formulations is lining with higher brake torque output, lower operating temperatures (30-50°F), and improved wear/life.

Fact: Highway accidents can currently be reduced through the use of good quality, legitimate components, particularly brake lining and brake drums.

Today North America is being inundated with brake products manufactured in South America and in Asia, which do not meet industry-acceptable standards of performance. Over the past two years, Brake Pro, Ltd. has run FMVSS121 dynamometer and dynamometer wear/temperature tests on numerous imported brake linings. Unfortunately, more than 50 percent fail the 121 tests and do not complete the wear/temperature test cycle. Some of these linings actually fail the power stop portion of the 121 test after only five successive stops. These linings lost their torque output, won't meet the stopping distance criteria, require in excess of 100 psi to complete a stop, and also fail the fade and recovery portions of 121. This seriously dangerous friction is being marketed throughout North America and contradicts government and industry efforts to improve safety.

If your lining supplier cannot show you legitimate 121 test data on all of the various linings you use, then change suppliers.

NHTSA and industry groups like TMC and HDBMC could help reduce traffic accidents and improve stopping distances today by designing and implementing higher performance standards and by making those performance standards a legal requirement.

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