UNDER THE HOOD | AUTOMOTIVE
of thermal expansion. The Pocan XHR series has an elongation at break of up to 4.7% (ISO 527-1,-2), which counteracts the formation of stress cracks. Moreover, the improved long-term temperature stability and hydrolysis resistance reduce susceptibility to stress cracks. Stress crack resistance is tested under extremely harsh conditions in heat shock tests. This involves subjecting the overmoulded components to abrupt changes in temperature from -40°C to 125°C and back in several hundred cycles and keeping them at the various temperatures for extended periods (30 minutes). Lanxess says in heat shock tests, components with Pocan XHR metal overmoulding exhibit no stress cracks or, if they do, the cracks do not appear until after many multiples of the usual number of test cycles. That makes the XHR products well suited to overmoulding metal parts, such as bus bars, connectors, power strips and main supporting frames. The melt viscosity of all Pocan XHR variants remains constant for a long time at the injection
moulding temperatures customary for PBT. The materials can therefore be injection moulded stably within a wide processing window. The improved flowability relative to comparable standard PBT
materials makes it possible to imple- ment thin-walled geometries. Furthermore, overmoulding of metal parts can take place
at lower filling pressures, which means that the metal inserts are not distorted or pushed out of position in the tool by the molten material. Pocan XHR also offers good resistance to strong
alkalis. This reduces elongation at break by around only 40% when the material is stored at 55°C in 1-molar sodium hydroxide solution for 100 hours. This is a significant improvement over standard PBT. On vehicle underbodies in particular, a combination of road salt, cast iron, and moisture can cause a mildly alkaline environment to build up. Lanxess says that XHR compounds are there- fore ideal for electrical and electronic components such as sensors, housings and connectors. The company is also introducing flame-retardant
Left: One of the potential applications of Pocan XHR from Lanxess is housings for automatic parking brakes
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IMAGE: LANXESS
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