Troy, MI (USA), October 5, 2009
Automotive CVJ Boots of DuPont™ Hytrel® Thermoplastic Elastomer Stretch the Limits of Durability
As DuPont™ Hytrel® thermoplastic elastomer in constant-velocity joint (CVJ) boot applications turns 25 years old, it notes as accomplishments more than 1 billion boots in service without material failure – each surviving 150,000 miles of continuous flexing, pelting and thermal cycling.
That means a vehicle equipped with Hytrel® CVJ boots can travel a distance equal to circumventing the Earth’s equator 6 times, while boots made of rubber will make the 25,000 mile trek only twice.
Constant-velocity joints allow a rotating shaft to transmit power from the transmission to the wheels, and the boots protect that critical component from contaminants outside and keep lubricants inside. Any cracks or tears in the boot can lead to CV joint failure.
“In the late 70s, when automakers turned to front-wheel drive vehicles to meet fuel economy standards, boots were typically rubber, which don’t offer the flex fatigue and contaminant resistance of Hytrel®,” said Eric Randa, DuPont Automotive chassis segment manager. “Thermoplastic elastomers were a huge step change – all of the sudden the durability was more than doubled so consumers no longer had to deal with boot failure, engineers could now design smaller, more compact, less costly boots, and automakers could worry less about service-life limitations.”
Today, vehicles sport four or more inboard and outboard CVJ boots, prop shaft boots and rear wheel drive boots and the vast majority are made with thermoplastic elastomers, such as Hytrel®. DuPont™ Vamac® Ultra ethylene acrylic elastomer is often selected for hot side inboard CVJ boots for its combination of the cost effectiveness, broad temperature range, grease resistance and puncture-resistant toughness.
The original CVJ boot for General Motors-Saginaw Steering Division molded by ABC Group Inc. of Canada is nominated for a Society of Plastics Engineers Hall of Fame award, granted annually to applications that have been in continuous use for 10 years or more, and that have made a significant and lasting contribution to the application of plastics in automobiles. The inaugural application reduced weight by 40%, significantly reduced piece price and manufacturing tooling costs compared with rubber it replaced, while establishing a “service for life” benchmark that eliminates the need for replacement under normal driving conditions.
DuPont currently offers a portfolio of products to balance performance and cost and plans to launch several new lower-cost grades with improved processing in the next year. “Today Hytrel® serves as the benchmark for excellent balance of grease resistance, high temperature durability, low temperature flexibility and historically proven performance,” said Randa. “We continue to optimize the portfolio so that we can help the industry manage costs without impacting durability.”
Compared with rubber, Hytrel® invites thinner design for better packaging in tight spaces, vastly improves performance and durability for greater service life. Compared with co-polyesters, Hytrel® delivers the optimal combination of flexibility and stiffness, protecting against expensive repairs.
DuPont Automotive offers more than 100 materials and products to the global automotive industry and through its global application development network is committed to delivering cost-effective solutions to help reduce vehicle weight for better fuel economy and CO2 emission reductions, to integrate part functionality to simplify assembly and eliminate cost; and help bring invention to market fast, better and more cost-effectively.
DuPont is a science-based products and services company. Founded in 1802, DuPont puts science to work by creating sustainable solutions essential to a better, safer, healthier life for people everywhere. Operating in more than 70 countries, DuPont offers a wide range of innovative products and services for markets including agriculture and food; building and construction; communications; and transportation.