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NEW HEAT-SHIELD OF DUPONT ZYTEL HTN PROTECTS MERCEDES BEAUTY-COVER
Powerful modern diesel motors generate a lot of heat in the tightly packed motor compartment. The conventional, relatively inexpensive, nylons which are used under the bonnet for large covers soon meet their thermal tolerance limits. That is why DaimlerChrysler chose an efficient and cost-effective solution for its new three-litre 6-cylinder diesel motors: a heat-shield of DuPont Zytel HTN high-performance nylon to protect the multi-functional beauty-cover made of glass- and mineral-reinforced nylon from local overheating. Woco Industrietechnik GmbH, of Bad Soden-Salmünster, a Tier-1 supplier, developed these parts and supplies them to DaimlerChrysler. Jürgen Weigel, product group leader in Woco's development department for acoustic components, comments: "When the engine is running, temperatures directly above the turbo-charger 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 dispersion. Thanks to the very good surface characteristics of parts moulded from Zytel HTN, we have no difficulty in meeting aesthetic requirements without any additional painting." Together with DuPont, Woco selected Zytel HTN51G35 for the heat shield: this is a 35 % glass-fibre reinforced grade from the 51 series, which provides the lowest water absorption and highest glass transition temperature of the HTN range. Says Weigel: "The high glass-fibre content and the optimised arrangement of the attachment points provides 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 discolouration or other degradation effects, despite the high temperatures, on the visible areas of the class-A surface." 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 processability. High resistance to brake fluids, lubricants and fuels, as well as to aggressive cleaning liquids, makes Zytel HTN an ideal material for under-the-bonnet applications. Thanks to its low thermal expansion coefficient, parts made from it have high dimensional stability and low warpage. Weigel concludes: "Since Woco first used DuPont Zytel HTN in the engine compartment of a DaimlerChrysler four-cylinder in-line diesel, over ten 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, which 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 4500 employees around the world, 390 of whom work in R&D, achieved a turnover of about €630 million.
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