automotive | Under-the-hood
system, the release must always work safely and reliably even after very long exposure to high tempera- tures or other environmental influences. Grivory HT2VS-3HH is said to be suitable for use at tempera- tures up to 270°C and the material exhibits excellent heat aging over a temperature range from 180 – 220°C with no performance loss over the complete tempera- ture range; it says this is in contrast to other heat- stabilised materials. “Significant cost savings can be achieved compared to previously used PEEK,” the company says. Albert Flepp, product manager for Grivory HT, says
various other close-to-engine projects involving this material are close to commercialisation.
Steering innovations Not all under-the bonnet applications offering potential for conversion to thermoplastics require high heat resistance. In safety-critical systems such as electronic power steering (EPS), for example, the call is for a combination of precision, long-term dimensional stability and overall cost reduction. High performance engineering compounds are quickly replacing diecast aluminium in important components of EPS systems. EPS technology is fast replacing hydraulic power
steering, says Tim Vorage, global innovation manager automotive, at DSM. Close to 60% of all cars now have EPS systems, and growth over the last few years has been in double digits. He predicts that inside five years, electronic systems will account for 80% of the market. Hydraulic systems require a continuously running pump, so replacing hydraulics with electronics has an important effect on CO2
emissions. “We are talking
about a few grams every kilome- tre,” Vorage says. Overall fuel efficiency of the vehicle continues to improve by ongoing weight reductions in EPS systems via metal replacement. This also provides system cost reductions of anywhere from 10 to 30%, he says. The most critical part of an EPS system is the
Right: This column EPS
system features a housing for
the worm gear in DSM’s Arnite XT glass
reinforced PET 16
housing containing the worm screw and wheel, all of which have to meet extremely precise and critical specifications in order to provide the correct feel back through the steering wheel for the driver as well as the required level of safety (if the gear and worm wheel fail to engage, steering is lost). The gears are normally injection moulded in polyamides, but the housing is traditionally made in aluminium. However, it is now increasingly being replaced by engineering thermoplastics, most notably DSM’s Arnite XT,
INJECTION WORLD
a highly glass-filled compound based on PET. “The levels of dimensional accuracy and stability
called for are very high, so the choice of material and the design of the parts is critical,” Vorage says. “It’s a job for specialist materials, product designers and processors.” He says Arnite XT is capable of adhering to the extreme tolerances called for. It has much lower moisture absorption than polyamides and it also has a low and iso- tropic coefficient of linear thermal expansion (CLTE). “In our production for Arnite XT, we have extremely
narrow tolerances,” Vorage says. Batch-to-batch variation in glass fibre content for example is +/-1% on a specification of 35% - he says the minimum margin on competing products is 2%. A similar grade was developed earlier for another safety-critical application, a brake booster. According to Vorage, Arnite is used in something approaching 80% of all brake boosters fitted to cars around the world. There are two types of EPS system at the moment:
column-type designs for A and B category vehicles (that is, smaller) cars fit on the steering column just behind the wheel (see image left); rack types sre used on larger cars. Depending on the system, the weight of Arnite can be between 200 and 500g per unit. Several companies are now producing such EPS systems around the world. “General requirements are quite similar. We are helping these companies move from metal to plastic and we always involve the moulder, which has to be very sophisticated, ” Vorage says. According to Vorage, DSM is virtually alone globally in
supplying material developed specifically for this application together with engineering design support for the application. “We are the only supplier capable of mass producing material with the very high dimension- al stability required for the application,” he claims. DSM is also working on use of its bio-based EcoPaXX polyamide 410 for EPS worm gears. It says it provides excellent tribologi- cal performance, high strength and fatigue properties, and high temperature resistance.
Opportunity in EVs Vehicle weight reduction is an important goal for all car makers, but it takes on an additional importance for electric vehicles (EVs), many of which can travel much shorter distances between recharges than regular cars can between one fuel refill and the next. SABIC highlights the use of its Noryl polystyrene-
modified polyphenylene ether blends to help EV makers cut weight and enhance battery performance.
www.injectionworld.com
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