Photo: DuPont
Because of their ability to retain their good properties at very high temperatures, low-friction DuPont™ Vespel® SP-21 guide bushings assist the long-term precision functioning of wastegate actuators, which must control the pressure of the exhaust gas flowing into the turbocharger, even on exposure to aggressive gases.
Geneva/Switzerland, January 2015 -- A leading global supplier of innovative turbocharging systems has chosen DuPont™ Vespel® bushings to improve the reliability and durability of its pneumatic wastegate actuators used in many turbocharger applications. The manufacturer selected this solution because the Vespel® bushings provide consistent friction and low wear over the entire life of the turbocharger, in a hot, dirty environment – even without lubrication, and thus assist the precise functioning of the control systems over the entire lifetime of the vehicle.
Small turbocharged engines allow significant reductions in fuel consumption and exhaust gas emissions. Modern turbochargers are designed in such a way that they generate a high boost pressure even at low engine speeds and thus avoid any undesirable start-up weaknesses ("turbo lag"). Wastegate actuators control the pressure of the exhaust gases entering the turbocharger on increasing engine speed, and controlling them exactly according to the particular driving situation. The Vespel® guide bushings ensure smooth, consistent operation of the connecting rod with minimum hysteresis to ensure accurate control of the turbocharger at all boost pressures and engine speeds in a non-lubricated environment all operating conditions.
The actuator is situated close to the turbine of the turbocharger where exhaust gas temperatures – which can reach as high as 1050°C – as well as limited packaging space result in very high actuator temperatures of more than 220°C. As the turbocharger producer reports, extensive tests had shown that alternative material solutions such as bushings made of engineering thermoplastics failed at these high temperatures. The most suitable solution came in the form of Vespel® SP-21. It has a heat deflection temperature of 360 °C, has no melting point and retains its properties under the long-term effect of heat, even in contact with aggressive exhaust gases. As it was established in the subsequent course of the tests, the Vespel® SP-21 bushings ensured that the operation of the sliding shaft remained consistent during the entire test cycle. And, thanks to the material's high impact strength and excellent mechanical properties, they also allow for a robust assembly processes.
Guide bushings are a typical example for tailor-madeVespel® parts, which are produced by DuPont. Such parts can comply with high specifications regarding dimensional tolerances without any post-finishing work, and are thus suitable for cost-efficient large-volume production. Beyond bushings, other standard applications of Vespel® include all kinds of bearings, thrust washers and mechanical seals, for example in automatic transmissions for cars and utility vehicles. DuPont also provides Vespel® in the form of shapes, such as rods, tubes, plaques, rings, discs or bars, which can be machined to meet customer specific needs.
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