Tread

The tread is probably the most critical component of the tyre determining the final performance. It is also the thickest component of the tyre and it contributes most of the energy losses that in turn will cause a rise in the tyre s running temperature and an increase in fuel consumption for the vehicle. Tread is also responsible for the safety component of the tyre and its surface is designed to provide good grip in all conditions of dry. 

A typical formulation for a radial tyre tmck tread is shown in Table 35. For improving heat resistance, the use of Perkalink 900 is recommended (289). The recommended loading for this cure system is 0.5 phr. 

A typical formulation for a bias tyre truck tread is shown in Table 36. 

A typical formulation for a passenger tyre tread is shown in Table 37. To raise the curing temperature, the use of antireversion chemical, Perkalink 900 has been recommended (119). 

Silica as a reinforcing filler is being used more extensively in the tyre industry to provide improved tear resistance and decreased rolling resistance. In 

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Cracks depth measurement in pipe - lines, boilers, rotor duct, on turbines blades, in tread rings, welds etc. 

Thus if Amontons law is obeyed, the initial velocity is determined entirely by the coefficient of friction and the length of the skid marks. The mass of the vehicle is not involved, neither is the size or width of the tire treads, nor how hard the brakes were applied, so long as the application is sufficient to maintain skidding. 

As might be expected, this simple picture does not hold perfectly. The coefficient of friction tends to increase with increasing velocity and also is smaller if the pavement is wet [14]. On a wet road, /x may be as small as 0.2, and, in fact, one of the principal reasons for patterning the tread and sides of the tire is to prevent the confinement of a water layer between the tire and the road surface. Similarly, the texture of the road surface is important to the wet friction behavior. Properly applied, however, measurements of skid length provide a conservative estimate of the speed of the vehicle when the brakes are first applied, and it has become a routine matter for data of this kind to be obtained at the scene of a serious accident. 

Because of the large difference in tp between successive molecular layers, each layer becomes complete at a relative pressure (plp°)g which is determined by the value of rp/kT for that layer, viz integral values). Each layer will therefore give rise to a step, such that the riser corresponds to the cooperative build-up of the layer and the tread to the transition between the layer and the next higher one. 

The ICI Treading Concept Methanol (LCM) process incorporating a GHR and oxygen blown secondary reformer is shown schematically in Figure 4. This process was commercialized in AustraUa in 1994 (14). 

The avadabihty of prompt iadustrial scrap is directiy related to the level of iadustrial activity. Producers geaeraHy do aot accumulate prompt iadustrial scrap because of storage requiremeats and iaventory control costs. Thus, it is rapidly available to the scrap consumer or the ferrous scrap iadustry. Prompt iadustrial scrap comes from imported steel as well as domestic steel mill products. Obsolete scrap, also known as old or post-coasumer scrap, is widely used. Treads ia aew steelmaking capacity and the reduced proportions of premium scrap iadicate that use of obsolete scrap should be expected to iacrease. 

Guanidines. Guanidines (10) were one of the first aniline derivatives used as accelerators. They are formed by reaction of two moles of an aromatic amine with one mole of cyanogen chloride. Diphenylguanidine (DPG) has enjoyed a resurgence ia demand as an activator for sulfenamides and a co-accelerator ia tire tread compounds which employ siUca fillers for low rolling resistance. Guanidines alone show too Htde activity to be extensively used as primary accelerators. There were no U.S. producers as of mid-1996. 

Silica. The main uses of siUca are in the treads of off-the-road tines for improved chunking and tear resistance and as a component of the bonding system for brass and 2inc-plated steel cord. These are commonly used in radial passenger and tmck tire belt skim stock. In addition the body pHes of steel radial tmck tires, hoses and belts, and footwear use significant volumes of siUca as a reinforcing filler. 

The paeumatic tire coasists of two basic areas the tread area which is respoasible for grouad coatact, and the casiag which is responsible for supporting load and transmitting power to the tread area. Each of these areas has several components with markedly divergent properties which serve specific and unique functions, and all of which must iateract with iategrity for maximum performance. 

The tread is desigaed and compounded for abrasion resistance, traction, low rolling resistance, and protection of the carcass. It often is divided iato two subcomponents to maximize performance the outer tread for surface contact, and the undertread for tying iato the carcass while reduciag tire rolling resistance through decreased hysteresis. 

The steel belt, which provides strength and protection for the ply or pHes, is encased ia a compouad that must possess adhesioa to the steel which provides stress transfer from the very rigid steel to the many times more flexible tread, sidewall, and textile carcass components. The wedge compound is formulated to reduce belt-edge sheer stresses while tying the belt to the carcass and reduciag hysteresis. 

Tke compounds contain the following generalized ingredients in the approximate proportions noted. Industry practice is to formulate starting with 100 parts by weight of the mbber (phr). Table 17 offers examples for various treads. 

Table 17. Typical Tread Compound Formula and Ranges of Materials...

Tread Sidewal 1 Wire breaker Ply coat Apex Chafer Bead Liner... 

In tires, carbon black is important because of the high flex fatigue and tear strength requirements of this product. Poor dispersion can result in premature cracking in both treads and sidewalls. In off-the-road tires poor dispersion results in excessive chip/chunk causing a significant loss in treadwear in addition to tread lug cracking which can lead to loss of an entire lug (radial tread bar). 

Overcuring is encountered to some degree in all compounds of any thickness because of the slow conductance of heat through mbber. Earthmover tires may have tire shoulder gauges in excess of 0.3 m (- 12 in.). The outside/inside are overcured to effect a satisfactory state-of-cure in the tread mbber. 

Of course, the above appHes when staying within a given tread design and at equivalent tread stiffness. Tire designs that allow water to be channeled out of the tread mbber/road contact area are significantly superior to those that do not, even when more contact area is available. Tread element stiffness plays an important role in traction capabiUties as softer treads have less column stiffness and reduce tread void areas, ie, there is more mbber on the road but this is offset if water channeling is significantly reduced. 

Snow and wet traction are highly dependent on the tread pattern. Although the tread pattern overwhelms the compound properties in significance, the latter can play a role in optimizing snow traction. Compounds using polymers with low glass-transition temperature, T (—40 to —OS " C), remain more flexible at low temperatures. Tread compounds with low complex modulus at 0—20°C have better snow traction. 

Natural mbber was also used extensively in its oil-extended form in winter tires in the 1970s (57). Use of oil-extended natural mbber treads, found to have excellent traction on ice and snow, superseded studded synthetic mbber treads when studs were banned in certain countries and states owing to the damage they cause to partially cleared roads. This concept has been extended into aH-season tires, which account for over 75% of original equipment and replacement tires in the United States. It has been shown (58) that part replacement of styrene—butadiene mbber (SBR) in the formulation of aH-season tire tread compounds with oil-extended natural mbber increases ice and snow traction, reduces rolling resistance, and has no effect on normal wet grip. Also, there is only a minor trade-off in wear performance, because below a tire surface temperature of approximately 32°C, the wear of natural mbber is superior to SBR, whereas above this temperature the reverse is tme (59). Thus, wear of an aH-season tire ultimately depends on the surface temperature of the tread over its annual cycle of temperatures. 

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