The polyurethane polymer, or urethane, is part of a family of chemical compounds that exhibits features similar to natural rubber; it is both elastic and stretchy. Urethane has benefits beyond those of rubber because it has a high load-bearing capacity, better compressions set, and considerably stronger tear strength. It is also tolerant to grease, oil, and ozone, and has a greater resistance to abrasion. The compound is completely synthetic and can be molded into a very soft or hard material. Urethane bushings are often used in automotive parts and industrial equipment, particularly because of their advtanges over rubber and their ability to be molded into unique designs.
Heavy duty trucks use urethane bushings in their suspensions. The main types of bushings they use are a walking beam end bushing, a walking beam center bushing, and a torque arm bushing. All bushings in this kind of vehicle use a polyurethane polymer. The bushing itself is made up of three layers: an outer bushing piece, an inner bushing piece, and a polyurethane bushing member placed between the outer and inner bushing member, which extends the life of both the bushing piece and the suspension of the truck. Prior to using urethane bushings, heavy duty trucks used a rubber interface, which had a shorter lifespan, in place of the polyurethane bushing.
Another type of urethane bushing is used on the joint connecting a tie rod to a lever arm as part of a vehicle’s steering mechanism. This joint must be constructed so that there is angular deflection and no rigidity in the mechanism. It must also be sturdy against excessive wear if a driver often uses it. Ball joints were once used because they provided the mechanism with good angular deflection, but they were expensive to build and repair. Urethane bushings are more economical, simply constructed, have an extended life, and do not wear as much as ball joints.
Trailer hitches, like steering mechanisms, also once used pivoting joints. These types of joints attached two vehicles, allowing them to swivel at an angle relative to each other when making left and right turns. The joint, however, wore down quickly and any jolts from one vehicle would be transferred to the vehicle attached — for example, from trailer to driver vehicle. A different mechanism that uses urethane bushings reduces the wear of the hitch mechanism, as well as distributes the shock effect over an extended interval of time. This is also known as vibration reduction, which is a benefit to the driver.