Polyurethane is applied to automotive industry . The ball joints for steering linkages and front suspension mechanisms of cars have to be protected from wear otherwise play rapidly occurs, which is reflected back to the steering wheel with a resultant loss in steering control. The conventional method of protection is by packing the joint with grease and containing the grease with a flexible gaiter. These gaiters are subjected to the effect of the grease inside and the effect of moisture on the outside and have to operate over serveral years without deterioration. To operate satisfactority they also have to resist the damage caused by small stones thrown up by the tires. The high tear strength of polyurethane is an obvious advantage here, but another equally important advantage is that in the environment of grease, water, ozone and general exposure to weathering the polyurethane elastomers or nitriles. Initially these gaiters were made from millable types of polyurethanes and were two to three times the cost of similar gaiters made in neoprene. Even so the practical advantage gained dictated fairly widespread use, although it is considered that further material improvements are still required and injection-moulded gaiters are already replacing some millable types.
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