Polyurethane elastomer in Aircraft Industry

One problem specific to the aircraft industry is the protection of leading surfaces against rain, dust and stone damage. The main surfaces in question are propellers and helicopter bladed, although leading edges of the mainplane and even the taiplane and fin are now being protected. On propellers de-icing mats are used to prevent icing up, and these are generally covered with a thin sheet of polyurethane. This protects the outer layer of nitrile rubber on the mat from stone and dust damage when landing or taking off and also against rain erosion during flight.

Helicopter blades can be made from either a special alumenium alloy or stainless steel, both of which at high speeds aer susceptible to damage, espectively in desert condition. One report indicates the the lift of the rotor blade increased from 40 to 1,000 hours after installation of protective polyurethane mats. This result in a very considerable saving in cost for replacement and also increases the operational life between changes.

Polyurethane lining : Pulleys

In both coal-mining and quarrying, belt conveyors are used to convey the coal or rock from one location to another. One type of conveyor used is a continuous belt to which a steel rope is attached at either side. This rope runs on pulleys and provided the motive power for belt itself. When using metal pulleys two problem arise, wear on the pulley and wear on the steel rope. The latter problem may prove to be more important, since repair or replacement involves considerable maintenance time and the rope itself is very expensive. Lining the faces of the pulley with polyurethane has a twofold advancetage. Wear on the rope is significantly reduced with a resultant saving on the rope cost. Breakdown time is also less, and since output rates of up to 1,000 tph. Another factor is that the pulley life is increased and there is a very marked drop in noise level, which is very real advantage in coal mines.

Another application for polyurethane lining is on the pulleys employed in the installation of overhead electrical transmission lines. The aluminium sheated transmission line are atthached to a relatively small diameter steel rope during the installation and the pulley has to be capable of taking the high unit load from the steel rope and yet be soft enough not to damage the alumenium sheathing.

Figure 1 Pulley (Polyurethane lining) http://www.indiamart.com

Why use polyurethane tires(PU). (2)

To date most polyurethane tires are used for load-carrying wheels where their advantages are immediately obvious. A more recent development is use of softer polyurethane for cushion tires on indrustial trucks. Polyurethane of approximately 75 to 80 shore A hardness are used for this application and give a degree of cushioning together with increased traction.

In all types of solid tires the constant deflection of the tread cause heat build-up in the mass of rubber materials. The higher the speed of the truck the higher is the frequency of deflection and the higher is the consequent heat build-up in the tires.Tires are normally rated at 10 mph and for higher speeds the loading rate has to be reduced, although by careful consideration of wheel size, tread thickness and tread profile higher speeds can be obtain and polyurethane solid tires are operating in certain application up to 30 mph.

In this instance rubber solid tires would not have been capable of carrying the load and still provide the required manoeuvrability. Steel or hard plastic wheels on the other hand would not have had the required traction and would have damage the pile-cap surface. This is possibly an extream example but it does illustrate how polyurethane can permit completely new design approaches.