Polyurethane tires are used on rotary screen plant

Polyurethane tires are used on rotary screen plant. Rotary screen plant is used extensively in the washing and grading of gravel and sand and also for heat drying of road stones. Other user include the preparation of natural and artificial fertilizers. Where the drum loading and temperature are such that the natural rubber can be used the substitution of polyurethane gives the expected advantages of higher load capacity and longer life. In many case however steel rollers have been in the past used in place of natural rubber due to the high loading required. In these case because of the highly abrasive environment, severe wear can take place both on the steel roller and the steel track on the drum itself. This wear leads to increased vibration in the plant which in turn can result in fractures of welds and rivets. To avoid serious damage the drum tracks have to be remachined at intervals during which the plant is inoperable. More recently these steel rollers have been successfully replaced by polyurethane tires in a number of cases. Taking a typical plant, for example, having an output of 50 to 60 tons per hour of washed gravel the weekly output is equivalent in value to ten times the cost of a set of polyurethane tires to replace the steel tires. The use of polyurethane tires reduces the vibration considerably and substantially reduces the maintenance time required. It also considerably reduces the noise level. In certain case the rotation of the drum can be carried out using polyurethane tires, with a further reduction in vibration.

Polyurethane tires : Overhead cranes

Polyurethane tires are being successfully used on overhead cranes. In these instances the conventional flanged wheel and rail can be replaced by a polyurethane tires which runs directly on the top girder or structure to which the rail would previously be fixed. A polyurethane side rollers is used at the same time to prevent undue sideways movement. The crane is driven by power transmitted througth the tires and the overall result is a noticeable reduction in noise and vibration. Noise elimination is an important factor in modern workshop, and reduction of vibration result in saving on maintenance cost.

A similar use for polyurethane tires is on sewang plant settling tanks. The conventional method is the use of steel wheels running on the circular track, both wheels being driven by a fairly complicate drive mechanism. The substitution of polyurethane tires for the steel tires gives greatly increased traction and allows the replacement of the normal drive mechanism by a single motor on one wheel. This still gives better traction than by driving the two steel wheels separately, especially when the plant is operating in wet condition.

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.

Why use polyurethane tires(PU). (1)

One of the most successful applications for polyurethane elastomer is that of tires for industrial truck. A list of the important advantages that the use of polyurethane tires can offer over rubber tires or steel tires is given below.

1. Polyurethane tires have higher load bearing capacities than similar size rubber tires. In all these case quoted from a 6 inch to a 22 inch diameter tires, the polyurethanes are rate approximately 600% higher than the corresponding natural rubber. When truck are designed specifically for polyurethane tires it is more customary to reduce both the width of the tread and also the overall diameter. Example it will be seen that a 10 x 3 x 6 1/4 (10 inch OD , 3 inch width , 6 1/4 inch metal OD) polyurethane tires has a higher load-bearing capacity than a 22 x 8 x 16 natural rubber tyre. The reduce in overall diameter of the tire can prove very advantageous in warehouse and factories where the floor space is at a premium . In general where the full advantage can be taken of the higher load-bearing capacity of polyurethane, its use can result in considerable cost savings.
2. The general life of a polyurethane truck tires even at higher load is noticeably longer than that of a natural rubber tires due to the substantial improvement in resistance to cutting and abrasion.
3. Industial truck tires have to operate over widely different terrain including rough factory yard , smooth warehouse pass-ages and oil-soaked machine shop. The good oil resistance of polyurethane can be a contributory factor in giving longer life when compare with rubber tires. Compare with steel tires the use of polyurethane tires can give improved traction and does much to eliminate damage to concrete and vinyl floor. Although rubber tires cannot break up the floor surface as can steel, the carbon black filler present can mark the floor surface.
4. Polyurethane tires have considerably lower rolling resistance than rubber tires, mainly as a consequence of the different hardness of two materials employed. In electrically propelled truck this result in a reduction in frequency of battery recharging with a resultant improvment in truck utilization.
5. Many industial trucks are used at sub-zero temperatures in cold storage rooms. The hard polyurethane tires are capable of cutting through the ice formed at these temperature and thus improving the traction. Furthermore the resilience-temperature characteristic are such that polyurethane tires have lower power consumption than rubber tires at these temperature, an important consideration in cold storage rooms.

Figure 1 Polyurethane Tires