Radial-ply tire

Before the 1960s, the bias-ply tire exemplified standard construction. It had a typical rolling resistance coefficient of 0.015 on hard pavement. Since then, the radial-ply tire has emerged, offering a coefficient closer to 0.010. Coefficients as low as 0.008 to 0.009 have been claimed in tires suitable for use on passenger cars. Cutting the coefficient from 0.015 to 0.008 offers the opportunity for about a 10 percent reduction in fuel consumption. 

FIGURE 26.28 Side force coefficient and self-aligning torque of a radial ply tire 175 R 14 on two wet road surfaces of different friction coefficient, at three slip angles and loads as function of the quantity c (Equation 26.17c) aU on log scales. The sohd hnes correspond to the brush model. (From Schallamach, A. and Grosch, K.A., Mechanics of Pneumatic Tires, S.K. Clark (ed.). The US Department of Transportation, National Highway Safety Administration, Washington DV.)... 

The effect can be seen in Figure 26.75 which shows the results obtained with the two-wheeled trailer discussed above. Tire group A was a re-treaded bias tire group B a commercial steel-belted radial ply tire. When one tire of each group was mounted on the axle of the trailer for equal set slip angles, the direction of the tow bar adjusted itself in such a way that the tires run under the same... 

FIGURE 26.75 Comparing the rate of wear of a retread bias tire with a commercial radial ply tire (a) one tire each mounted on the trailer axle (equal force comparison) and (b) two tires of each group mounted and run consecutively (equal slip). 

Being cut from tires, the rubber samples in this work cannot always be studied using standard test procedures. The specific techniques used to measure rubber aging have been described in detail elsewhere and are summarized below [2]. The same techniques have been used to evaluate rubber aging in both field and the laboratory oven-aging studies. For reference. Figure 34.2 shows a diagram of the internal components of a radial-ply tire. 

The balance between natural rubber and SBR is a delicate one. Natural rubber has made a comeback and reversed its downward trend. Developments of rubber farming have raised the yield from 500 Ib/acre/yr to 2,000-3,000. Petrochemical shortages and price increases have hurt SBR. Finally, the trend toward radial-ply tires, which contain a higher proportion of natural rubber, favors this comeback. Fig 18.1 shows the U.S. natural rubber consumption trends vs. U.S. SBR production, where this bounceback of the natural rubber market is very evident from 1980 to the present. The competitive price structure for these two elastomers through the years has been very evident, and their prices are never too far apart. 

The most important single trend in the U.S. tire market is the switch from cross-ply and belted bias-ply to radial-ply tires. Radials held only 8% of the... 

Figure 2.75 shows the constructions of a standard bias (diagonal) ply tire and a radial ply tire. The major components of a tire are bead, carcass, sidewall, and tread. In terms of material composition, a tire on an average contains nearly 50% of its weight in actual rubber for oil extended rubbers (typically containing 25 parts of aromatic or cycloparafiBnic oils to 75 parts of rubber), it is less. The remainder included carbon black, textile cord, and other compounding ingredients plus the beads. 

In the radial-ply tire, one or two plies are set at an angle of 90° from the center line and a breaker or belt or rubber-coated wire or textile is added under the tread. This construction gives a different tread-road interaction, resulting in a decreased rate of wear. The sidewall is thin and very flexible. The riding and steering qualities are noticeably different from those of a bias-ply tire and require different suspension systems. 

In the tire industry which faces the most difficult mixing problems, this type of mixer is still practically the only accepted mixing device. The tire industry has accepted the fact that the batch type mixer will not be replaced by a continuous mixing device in the near future, especially since the radial ply tire came into being, because this tire requires very tough types of rubber. The same is not the case as far as the plastics industry is concerned. In fact, predictions made several years ago that the batch type mixer will disappear and be replaced by continuous mixing equipment has come true in the filled polymers industry. Some of the continuous mixing devices are discussed below. 

The carcass ply/pHes coat compouad fuactioas are basically the same as the steel breaker compouad. Normally ia the steel belted PCT the ply is textile cord of polyester or rayoa fabrics which are soft and flexible. The tmck radial steel tire normally uses a steel cord ply. Earthmover tires are of two basic constmctions, ie, radial usiag steel and bias usiag textiles (see Tire cords). 

Silica. The main uses of silica are in the treads of off-the-road tires for improved chunking and tear resistance and as a component of the bonding system for brass and zinc-plated steel cord. These are commonly used in radial passenger and truck tire belt skim stock. In addition the body plies of steel radial truck tires, hoses and belts, and footwear use significant volumes of silica as a reinforcing filler. 

There are certain technical limitations in the devulcanization of rubbers, and vulcanization is, in fact, not truly reversible (Pryweller, 1999). The partial devulcanization of scrap rubber will result in a degradation of physical properties. In many cases, this may limit the amount of substitution levels in high-tech applications such as passenger tires. But it can provide the compounder of less stringent products with an excellent low-cost rubber that can be used as the prime rubber or at very high substitution levels. According to Franta (1989), reclaim cannot be used for tread compounds in tires because every addition may decrease their resistance to wear. However, this statement has not been checked in case rubber devulcanized without an addition of chemicals. Considerable amounts of reclaim are consumed for carcasses of bias ply tires for cars if the compounds are of NR for carcasses of radial tires no reclaim is added. On the other hand, reclaim is added to compounds for bead wires and it may also be added to sidewalls. Within the framework of direct recycling options a number of applications for GRT outside the rubber industry have been proposed. Such applications include the use as a tiller in asphalt for the surface treatment of roads and as a rubberized surface for sport facilities. 

During the manufacture of tires (typically radial ply construction for passenger cars), the polyester tire core is subjected to drastic hydrolytic conditions. The rubber is molded into the basic tire shape and rubber vulcanization uses various accelerators, some of which cause severe aminolysis of the polyester chain. The process is run at 175°C in the presence of steam. While PET is fairly resistant to strong aqueous ionic base at moderate temperatures, nonpolar bases like ammonia, hydrazine, and simple aliphatic amines can easily diffuse into the PET structure and cause aminolytic breakdown [55]. 

The wide adoption of radial tires during the decades of the 1970s and 1980s caused a major contraction in demand for blacks for tire use as the expected life of an automobile tire moved from 20,000 miles with bias ply tires to over 40,000 miles with radial tires. This brought about considerable consolidation in the carbon black industry, particularly in North America and Europe. 

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