Tribological Testing of Metallurgical Coke: Coefficient of Friction and Relation to Coal Properties

Tribological testing and analysis of metallurgical-grade cokes were conducted to elucidate the nature of the surface of each coke and the influence of the surface on coke abrasion resistance. The coefficient of friction (COF) was contrasted between cokes of different coal origins. The results indicate that the COF increases with (i) parent coal vitrinite content and (ii) decreasing rank of the parent coal. The amount of ultrafine (i.e., <10 mu m at the longest dimension) material produced by coke during continuous rotational tribological testing increased as the rank of the parent coal increased. Above a parent coal mean maximum vitrinite reflectance of 1.37%, the COF began to decrease slightly beyond the first 40-60 s of testing, which can be attributed to the anisotropic, graphitic ultrafines acting as a surface modifier or lubricant. This has implications for the abrasion resistance of coke under blast furnace conditions, in which graphitic ultrafines acting a lubricant would likely reduce the degradation rate of the coke. For the pilot oven coke from the blend examined, the COF at all stages of the experiment was approximately linear with blend composition. The exploratory study described in this paper indicates that the wear characteristics of inertinite maceral derived constituents (IMDC) and reactive maceral derived constituents (RMDC) are different and that the wear behavior of the RMDC is rank dependent, while that of the IMDC is less sensitive to the rank of the initial coal.