Abrasion loss

Consistent with historical results, the loss modulus at high strain correlates well with laboratory abrasion results. The best correlations occur at high strains, i.e., on the order of 50%-125%. Abrasion losses are considered to be predominantly high-strain events. Thus, the ability of a compound to dissipate energy at high strain will improve the toughness or abrasion resistance of the compound. However, it is important in the tire industry that this increase in hysteresis at high... 

A more basic approach is to consider the dependence of the abrasion loss not on pressure but the energy dissipation W caused by the frictional force F. For sliding experiments this is... 

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.)... 

FIGURE 26.44 Abrasion loss as function of pressure for four different compounds. A SBR + 50 HAF black, B NR + 50 HAF black, C NR + 50 thermal black, D NR + 50 activated CaCOs. (From Schallamach, A. and Grosch, K.A., The Mechanics of Pneumatic Tires, S.K. Clark (ed.), The US Department of Transportation, National Highway Safety Administration, Washington DV, p. 407.)... 

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. 

Champ et al. [47] devised a simple abrasion experiment by measuring the abrasion loss caused by a razor blade scraping under load across a mbber surface. For this an Akron abrader sample wheel was used. They used soft unfilled noncrystallizing mbber compounds based on different polymers. Under these conditions strong abrasion pattern develop. 

FIGURE 26.56 Log Abrasion loss by a blade (solid lines) and log cut growth rate (dashed hnes) of noncrystallizing rubber compounds as function of log frictional and log tearing energy, respectively isomerized natural rubber (NR), 2 styrene-butadiene rubber (SBR), and 3 acrylate-butadiene rubber (ABR). (From Champ, D.H., Southern, E., and Thomas, A.G., Advances in Polymer Friction and Wear, Lieng Huang Lee (ed.), Plenum, New York/London, 1974, p. 134.)... 

The results are shown in Figure 26.58 for two blunt surfaces Knurled aluminum and knurled steel. Aluminum produces a lower abrasion loss than steel. On both surfaces, however, the abrasion was much higher when MgO was used as an absorbing powder than with the mixture of Fuller s earth and alumina. The two compounds examined were an NR compound without antioxidant and one with two parts of Nonox ZA. There is a very clear difference between the two compounds indicating that oxygen plays an important role. 

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 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. 

The abrasion loss as log (abrasion) of log (energy) and log (speed) is best presented either in tabular form filling out the table of Figure 26.67 or as a three-dimensional graph [52] as shown in Figure 26.68. Notice that the abrasion between the mildest condition (upper left) and the most severe condition (lower right) differs by a factor of about 1000. More important for practical use is the relative rating of an experimental compound to a standard reference compound. 

Road wear is force controlled. This is a fundamental difference to slip-controlled laboratory abrasion test machines or wear tests with a trailer as described above. In force-controlled events the abrasion loss is inversely proportional to the stiffness of the tire whilst under slip control the abrasion is proportional to its stiffness (see Equations 26.18a and 26.19a). 

FIGURE 26.78 Theoretical acceleration (force) distribution function in a computer simulation, the resulting energy dissipation multiphed by the frequency of occurrence and the expected abrasion loss, using Equation 26.18 with parameter for a passenger tread compound. 

Having calculated the force for a particular event the slip is calculated using the bush model and hence the energy dissipation is obtained. Using the factors of the abrasion equation, determined with the LAT 100 on an alumina surface the abrasion loss for each event is calculated. The forces are different for a driven and a nondriven axle and accordingly different abrasion rates will result. 

Extensive product trials using the LCBM technique in standard tire recipes have proved that the tensile strength and modulus, elongation at break, compound hardness, abrasion loss, and hot air aging properties have improved substantially compared to mixes prepared using conventional technique. 

Microdeval abrasion loss (%) Magnesium sulfate soundness loss (%) Friction angle (°)... 

Fig. 6. Abrasion loss versus reinforcement factor low oil SBR, 50 phr black 201...

If abrasion loss is measured as a function of test parameters such as speed, temperature, degree of slip, contact pressure etc, it may be possible to combine the results in some way to produce a composite measure of abrasion resistance. Obtaining data as a function of test parameters is impossible, or at least very tedious, with most apparatus, but can be achieved automatically with the LAT system (see Section 2.6). 

---