Theoretical consideration of fatigue strengthening of conical picks for rock cutting

Rock mining is a key process associated with the drilling of tunnels and underground mine roadways and the extraction of useful minerals in mines. Under suitable conditions (rock workability), it is performed through cutting using conical picks. This technique is used not only in tunneling or mining but also in civil engineering—for example, in the construction of underground architectural objects using trenchless, approaches, or in road construction—for example, to renovate asphalt and concrete road surfaces, squares, or runways at airports. Picks experience wear and tear during the cutting process, or even destruction, which can decrease mining efficiency. Thus, it is necessary to replace picks on the working units of mining machines. Body breakage is one of the most severe forms of pick damage. This effect can be ad hoc, or more often fatigue. Fatigue cracking occurs suddenly in the pick bodies, without any clear preceding signs to allow corrective actions to be taken. Such loss of picks significantly affects the mining process, resulting in dynamic overloads of the mining machine, increased vibrations accompanying its operation, high energy consumption during the mining process, and increased exposure to dust. Damage resulting from the loss of picks due to various causes, such as breakage, is usually costly to repair, as it necessitates the replacement of important elements of the cutting system (e.g. cutting heads), which leads to unplanned downtime and expenditure. This article addresses the issue of eliminating such undesirable defects of cutting picks. The mechanism underlying fatigue destruction of conical pick bodies during their operation is described. The paper also defines pick fatigue life and highlights the factors influencing this parameter. Furthermore, this work aimed to propose a new design and technological solution for the conical picks equipped with a compressed reinforcing sleeve. The design requirements for this type of picks were determined with the goal of ensuring efficient strengthening action of the reinforcing sleeve, which in turn can significantly increase the fatigue life of conical picks.