INCREASING THE EFFICIENCY OF COAL MASS GRINDING BY CHANGING THE GEOMETRY OF THE IMPACT SURFACE OF THE GRINDING WHEEL

In hammer mills, fuel is ground by the impact of the beaters on the coal pieces entering the mill, as well as by the abrasive action of the beaters on the coal in the space between the beaters and the mill body. A disadvantage of hammer mills is the rapid wear of the beaters, requiring their frequent replacement. It is known that the greater the mass of the material being worn, the longer the beater can work, all other things being equal. The mass of the metal being worn can be increased by increasing the mass of the beater itself or the degree of metal utilization. As practice shows, increasing both has its limits. The optimal mass of the beater for medium-capacity mills with a diameter of up to 1,6 m is 8…10 kg, for high-capacity mills with a rotor diameter of
2…2,5 m, the optimal mass of the beater is 12…14 kg. Increasing the mass of the beater beyond these values does not lead to a significant increase in the service life of the beaters, since this reduces the degree of metal utilization. In addition, replacing beaters weighing more than 14 kg significantly increases the labor intensity of beater replacement operations. The paper investigates the dependence of specific beater wear on the angle of impact with the crushed material and shows the sequence of changes in the shape of the working surface of the beaters. The abrasion of the beaters at different angles of attack of abrasive coal particles is considered, the particle ejection velocity from the working element is calculated, and a mathematical model of the forces arising during the working movement of the beaters is compiled. A methodology for designing the geometric shape of the working element of a tangential hammer mill – a beater – has been developed, which allows for ensuring stable mill efficiency due to uniform wear of the striking part of the beater while maintaining its effective working area.

tangential hammermill, grinding wheel, working surface, coal mass, crushing, grinding, abrasive wear, angle of trim, efficiency coefficient