Tread compound

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. 

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

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 Use of oil-extended natural mbber treads, found to have excellent traction on ice and snow, superseded studded synthetic mbber treads when studs were banned in certain countries and states owing to the damage they cause to partially cleared roads.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. 

Blends of halogenated butyl mbber are used in tire sidewalls and tread compounds (97). In sidewalls, ozone resistance, crack cut growth, and... 

Friction Properties of Tread Compounds at Higher Speeds.698... 

On the dusted track the diminished adhesion friction component is clearly apparent for all three rabbers when comparing them with the master curves on the clean track The friction plateau observed for the rubbers filled with 50 pphr black which is typical for tire tread compounds is observed for most rubbers, as shown in Figure 26.5. 

Friction Coefficients and Relative Ratings of Four Tire Tread Compounds at 4.5°C Ice Surface Temperature and a Speed of 0.5 km/h... 

Figure 26.33 shows the side force coefficient as function of log speed for different temperatures at a constant load and slip angle for a tire tread compound based on 3,4 cw-poly-isoprene, a polymer... 

Laboratory measurements are primarily concerned with tread compound traction properties. Tread pattern and other tire parameters like cornering and longitudinal slip stiffness require still tests with tires on either large indoor machines or direct proving ground measurements. 

FIGURE 26.35 Master curve of the side force coefficient of two tread compounds with different glass transition temperatures on wet Alumina 180 A 3,4 IR Tg = —21°C and OESBR Tg = —46°C. Two spot measurements at two different water temperatures show that the ranking if the two compounds reverses. (From Grosch, K.A., Kautschuk, Gummi, Kunststojfe, 6 m, 432, 1996.)... 

FIGURE 26.36 The side force coefficient of an OESBR black-fiUed tire tread compound on wet blunt Alumina 180 as function of log a v obtained at three speeds and five temperatures (black open squares) with a quadratic equation fitted to the data (black solid line). The red marked points were obtained at one speed for five temperatures with the dotted red line the best fitting quadratic equation, indicating the risk of extrapolation with a limited set of data. 

FIGURE 26.43 Abrasion loss as function of pressure for a butadiene rubber (BR) tread compound on four different abrasive surfaces. O tarmac, Akron abrasive disk, A concrete I, A concrete II. (From Grosch, K.A. and Schallamach, A., Kautschuk, Gummi und Kunststojfe, 22, 288, 1969.)... 

Experiments carried out at a constant speed over a range of temperatures showed, however, that for tire tread compounds the temperature dependence of abrasion, although smaller reaches in this case, too, a minimum at a particular temperature as shown in Figure 26.51 and rises sharply with a further decrease in temperature. 

Experiments measuring the energy density at a high rate of extension over a range of temperatures showed that the abrasion-temperature function for tread compounds had a similar shape as the inverse of the energy density at break temperature curve. This is also shown in Figure 26.51... 

This is about 2000 indicating that the energy required to remove unit volume of mbber even by the very sharp abrasive track is an inefficient process. A surprising result is that the tread compounds have a much higher abrasion loss than the gum mbbers, as shown in Figure 26.52. This shows the abrasion as function of temperature for three mbbers (A) SBR, (B) ABR, and (C) NR, the sohd fines are for the gum mbbers, the dotted one for the same polymer, filled with 50 HAF black. The reason will become apparent when examining the appearance of the abraded surfaces. 

FIGURE 26.52 Sliding abrasion of three different tread compounds as function of temperature at a sliding speed of 0.01 m/s (a) styrene-butadiene rubber (SBR), (b) ANR, (c) NR,-tread compound, —gum compound. 

FIGURE 26.55 Abrasion surface appearance of a natural rubber (NR) black-fiUed tire tread compound for sliding abrasion at different temperatures. 

FIGURE 26.58 Abrasion of two natural rubber (NR) tread compounds, one unprotected, the other with two parts Nonox ZA on a knurled Aluminum and a knurled steel surface, respectively, in the presence of (a) magnesium oxide (MgO) powder and (b) a dust mix of Fuller s earth and alumina powder. (Deduced from Schallamach, A.,Appl. Pol. Sci., 12, 281, 1968.)... 

FIGURE 26.59 Time record of the abrasion loss on a standard Akron grinding wheel in nitrogen and air of a natural mbber (NR) tread compound (a) unprotected and (h) protected with an antioxidant. (From Schallamach, A., Appl. Pol. ScL, 12, 281, 1968.)... 

Figure 26.61 shows the abrasion of an OESBR tread compound as function of load for different slip angles on a sharp Alumina 60 surface. Because of the wide range of abrasion rates for different slip angles the abrasion data were plotted on a log scale. It is seen that at the small slip angle the dependence on load is small and becomes more pronounced as the slip angle is increased. This is expected from the bmsh model. At small slip angle the side force is independent of the load and hence it is expected that the abrasion behave in a similar way. 

FIGURE 26.61 Log (abrasion) of an OESBR and a natural rubber (NR) tire tread compound as function of load at different slip angles at a speed of 19.2 km/h. left Abrasion loss of the OESBR compound as function of load. Right the relative wear resistance rating of natural rubber (NR) to the OESBR as function of load for different slip angles. 

Also shown is the relative rating between the OESBR compound and an NR + black tire tread compound. At the smallest slip angle the rating of the NR is better than the OEBR but decreases with the load. As the slip angle is increased the rating reverses. 

FIGURE 26.64 Log (abrasion) for two tread compounds natural rubber (NR) + black and styrene-butadiene rubber (SBR) + black on two surfaces of different sharpness Alumina 60 and Alumina 180 blunt as function of log (energy dissipation). (From Grosch, K.A. and Heinz, M., Proc. IRC 2000, Helsinki, 2000, paper 48.)... 

FIGURE 26.65 Log (abrasion) as function of log (energy dissipation) for a commercial tire tread compound at three different speeds. Surface Alumina 60. 

FIGURE 26.68 Log abrasion as function of log energy and log speed for a tire tread compound. 

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