NEW HEAT SHIELD OF DUPONT ZYTEL HTN PROTECTS MERCEDES DIESEL'S BEAUTY COVER
19 May 2006 - DuPont Engineering Polymers

Powerful modern diesel engines generate a lot of heat in the tightly packed engine compartment. Conventional, relatively inexpensive nylons used under the hood for large covers soon meet their thermal tolerance limits. That is why DaimlerChrysler chose an efficient and cost-effective solution for its new 3-liter six-cylinder diesel engines: a heat shield made of PPA-based (polyphthalamide) DuPont Zytel HTN high-performance paolyamide to protect the multi-functional beauty cover made of glass- and mineral-reinforced nylon from local overheating. Tier-1 supplier Woco Industrietechnik GmbH, of Bad Soden-Salmünster, Germany, developed these parts and supplies them to DaimlerChrysler.

Jürgen Weigel, product group leader in Woco's development department for acoustic components, commented: "When the engine is running, temperatures directly above the turbocharger can be significantly higher than permissible for covers made of conventional nylon types. That is why we protect large areas of this part with a heat shield made of Zytel HTN, which we fix onto the underside of the beauty cover, using ultrasonic welding. In the area where the highest temperatures occur, there is an opening in the beauty cover, through which the heat shield with its aeration slits can be seen; these slits are needed for heat dissipation. Thanks to the very good surface characteristics of parts molded from Zytel HTN, we have no difficulty in meeting aesthetic requirements without any additional painting."

Together with DuPont, Woco selected a Zytel HTN 51G35 for the heat shield: this is a 35 percent glass-fiber reinforced grade from the 51 series, which are PPA-based resins. They provide the lowest water absorption and highest glass transition temperature of the Zytel HTN range. "The high glass-fiber content and the optimized arrangement of the attachment points provide the protective shield with the required stiffness, despite low wall thickness. This helps to avoid the possibility of undue vibration of the part, which measures 500 mm in length and width. And thanks to the excellent aging properties of the material, there is no discoloration or other degradation effects, despite the high temperatures, on the visible areas of the class-A surface," said Weigel.

Zytel HTN bridges the gap between traditional engineering plastics and expensive high-performance speciality polymers. It combines high thermal resistance (heat distortion temperature up to 288°C) with low moisture absorption and easy processibility. High resistance to brake fluids, lubricants and fuels, as well as to aggressive cleaning liquids, makes Zytel HTN an ideal material for under-the-hood applications. Thanks to its low thermal expansion coefficient, parts made from it have high dimensional stability and low warpage.

Weigel concluded: "Since Woco first used DuPont Zytel HTN in the engine compartment of a DaimlerChrysler four-cylinder in-line diesel, over 10 years ago, we have continued to be impressed by this material. The use of Zytel HTN for a heat shield for thermoplastics with lower thermal resistance is an innovative design solution, which is attractive both in terms of cost and performance. Woco has not just used this material for covers, we have also specified it for many other applications. One example is the resonator situated below the heat shield described here; it mutes airflow sounds around the turbocharger intake."

Woco Industrietechnik GmbH stands for innovative automotive technology, especially in vibration technologies, acoustics and vehicle comfort. With production sites in Europe, America, Asia and South Africa, Woco has become a global leader in developing acoustic and vibration solutions for all aspects of the vehicle. During 2004, Woco, with 4,500 employees around the world, 390 of whom work in R&D – achieved a turnover of about $760 million. For additional information, visit www.wocogroup.com on the web.

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