Plastic automotive wheel rims may be getting closer to prime time. And the payoff could be big in overall vehicle weight savings.
BASF this month was awarded a U.S. patent for a new concept that overcomes problems with previously developed plastic wheels.
From the patent: “It is already known from DE-U 297 06 229 to produce rims for a motor vehicle from a fiber-reinforced plastic. However, on account of the great forces that are transmitted at the rim, the plastic of the rim does have a tendency to creep, which leads to deforming of the rim.”
Too much fiber loading creates cracks in the rim, which may lead to rupturing.
One of the keys in the new approach is the use of an adaptor for fastening the rim to the wheel mounting. The goal of the design is to transmit force directly from the wheel mounting to the adapter, avoiding formation of damaging stress peaks in the plastic. In the BASF invention, “The force is transmitted to the plastic more uniformly, whereby the risk of damage to the plastic, in particular crack formation, is minimized.”
The rim could be made of any of a number of plastic compounds. The preferential compound comprises a blend of at least two types of polyamides and a high loading of random long glass fibers (45 to 65 percent by weight). One candidate is already commercially available: BASF’s Ultramid Structure, which consists of PA6 and PA66 grades as well as specialty polymers with long glass fiber-reinforcement of 40 to 65 percent.
The adaptor, which could be insert molded, could be titanium, ceramic or some other material. The preferred production method is injection molding or casting.
BASF’s first public venture into plastic wheels was in 2011 when smart and BASF exhibited the first all-plastic wheel rim in the smart forvision, a concept vehicle. The wheel was shown at the International Motor Show (IAA) in Frankfurt/Main and at the plastics trade fair Fakuma in Germany.
The smart all-plastic wheel rim was said to be over 30 percent lighter than a standard production aluminum wheel. Savings are even greater compared to a steel wheel