Spring element made of low-emission DuPont™ Delrin® acts as buffer during steering column adjustment
Buffer-stops made of the low-emission grade DuPont™ Delrin® 100PE acetal resin cushion the impact when mechanically adjustable steering columns, from ThyssenKrupp Presta of Eschen, Liechtenstein, reach full horizontal adjustment.
Decisive factors in its specification were the material's compliance with stringent emission levels demanded by some of Germany's automotive OEMs for interior applications and its steel-like springiness. The material also is characterized by its vibration damping effect, its high notched impact strength and very good sliding properties.
The buffer-stop, injection-molded in Delrin® 100PE, takes up very little installation space with its 14 mm x 9 mm x 6 mm dimensions. Held by a rivet, it slides during adjustment of the steering column on metal guide rails until they reach their limit at the end of the adjustment range. Although the associated jolt may in some cases be hard, two small springs on either side of the buffer-stop are enough—thanks to the high stiffness and elasticity of the material—to cushion the impact both mechanically and acoustically. Moreover, as a direct benefit of the excellent sliding properties of Delrin® acetal resin, the buffer-stop will continue to move easily, softly and virtually inaudibly on the guide rails for the entire lifetime of the vehicle.
According to Ingo Weise, project manager at ThyssenKrupp Presta: "Acetal is an established material for damping elements used in steering columns. At ThyssenKrupp Presta we have often used Delrin® 100P for similar parts in earlier designs where it met our requirements. In this particular case, however, we needed to meet especially strict emission levels. We therefore worked with DuPont Performance Polymers (DuPont) on finding an alternative, including carrying out required testing. This ultimately resulted in us specifying Delrin® 100PE."
Martin Elmer, marketing manager for injection molding at Huber+Suhner, the Swiss-based supplier of the buffer-stops, adds: "We produce these high-precision parts that are characterized by their variable wall thicknesses, in 16-cavity hot runner molds and keep within a tolerance of just ±0.05 mm. Because the processing requirements of the new, low-emission Delrin® 100PE are almost identical to those of the 100P grade, we were able to adapt our production in the shortest amount of time and without compromising quality, all with the help of the experienced application technicians from DuPont."
Based on the direct and simple changeover in production, as well as the very positive experience to date during serial production, ThyssenKrupp Presta is planning to use Delrin® 100PE for further automotive applications of a similar nature.
The combination of high elasticity and stiffness as well as excellent sliding properties make Delrin® acetal homopolymers a material of choice for applications requiring low weight and where elements are required to absorb high forces, levels of deformation and impact, as well as to continuously move both smoothly and quietly. According to Hans-Hermann Kirner, material development leader for vehicle interiors at DuPont, "Gears and adjustment mechanisms are ideal applications for Delrin®. In view of the strict limits with regard to the emission of volatile particles, Delrin® 100PE is a very suitable application located within the vehicle's interior. It is able to meet the demands of the global automotive industry with regard to emissions of volatile substances during both processing and use. The same applies to the higher flow grades Delrin® 300PE and 500PE. Tests conducted by SGS Institut Fresenius of Taunusstein, Germany, in accordance with VDA 275, revealed emissions of below 2 mg/kg for all three grades, whereas their strength, stiffness, impact resistance and resistance to creep and fatigue are the same as standard grades." DuPont also has recently introduced Delrin® 127UVE, 327UVE and 527UVE, which are all UV-stabilized versions of its low-emission acetal resin for automotive interior applications.
ThyssenKrupp Presta, Steering Division, is one of the world's largest producers of steering columns and steering systems, ranging from non-adjustable models to manually-operated height- and distance-adjustment systems for mid-class vehicles in Europe, America and Asia and electronically-adjustable models for top-range vehicles. At the end of 2007, the company gained a series production order for the supply of steering columns for the BMW 1, 3 and X3 series, as well as the development order for the steering control of other model ranges.
HUBER+SUHNER Gruppe, headquartered in Switzerland and with 24 companies and numerous authorized agents in over 60 countries around the world, is an internationally-leading supplier of components and systems for electrical and optical connectivity for the telecommunications, industrial applications and transportation industries.