Tires : Effect of inflation pressure.

High inflation pressure increases stiffness, which reduces ride comfort and generates vibration. Tire footprint and traction are reduce when tires are over inflated. Over inflation causes the tires to transmit shock loads to the suspension, and reduces the tire ‘ s ability to support the required load for cornerability, breaking and acceleration. The rolling resistance friction coeficient decreases by increasing the inflation pressure. The effect of increasing pressure is equivalent to decreasing normal load.

Under inflation results in cracking and tire component separation. It also increases sidewall flexing and rolling resistance that causes heat and mechanical failure. A tire’s load capacity is largely determined by its inflation pressure. Therefore, under inflation results in an overloaded tire that operates at high deflection with a low fuel economy, and low handling. Proper inflation pressure is necessary for optimum tire performance, safety, and fuel economy (Energy Tires). Correct inflation is especially significant to the endurance and performance of radial tires because it may not be possible to find a 5 psi under inflation in a radial tire just by looking. However, under inflation of 5 psi can reduce up to 25% of the tire performance and life.

Polyurethane in Textile Machinery

The most importhant application to date in the textile field has been the use of polyurethane elastomers for loom pickers. Here the application is vary arduous, the shuttle weighing about 1 lb traversing a 4 ft loom approximately 150 to 200 times a minute. Previously the materials chiefly used were either raw hide or rubber-fabric composition. On the average polyurethane pickers outlast other types of pickers but they do exhibit a number of unexplained early faileres. The life of the picker is very dependent on the correct setting of the picker in relation to the shuttle, and if badly aligned, the picker will fail rapidly. The search for even better pickers is still proceeding, and the most recent design incorporate a wearing block of high density polyethylene inside a resilient body of a hard thermoplastic polyurethane.

Other application in the textile and allied field include falling bars for selector needles on the knitting machines, cot roller covering, and drive couplings for bobbins.

Polyurethane in Paper-making and Printing

Solid polyurethane are being used successfullyfor the top of vacuum boxed on paper-marking machinery. A gauze holding the paper fibers travels across the vacuum box and excess water is removed by vacuum. The polyurethane is less harsh to the guaze than other materials and is itself resistant to wear. This is an example where polyurethanes are used sucessfully in water at a temperature around 50 *C .

Special grades of very soft polyurethane elastomers have been used for many year for printing rollers. The hardness of these materials vary from around 10 to 30 Shore A and the physical properties are poor compared with what is normally expected from polyurethane elastomers. However, solid polyurethane around a hardness of 60 to 70 Shore A are being used for scraper blades on silk-screen printing due to their solvent resistance and low ink pick up.