Shaft

(in engineering), a rotating machine part (usually mounted in bearings) that transmits a torque moment. The shaft is one of the basic parts of almost all machines and mechanisms. According to their design, a distinction is made among straight shafts (smooth, stepped, or splined camshafts), crankshafts, flexible shafts, and so on.

The most common shafts are the straight stepped shafts, in which the retaining steps prevent axial displacement of the parts located on the shaft, and the transitional steps mark the boundaries of sections with different diameters and tolerances. The design criteria for shafts include strength, stiffness, and resistance to vibration.

a vertical or inclined mining excavation having an opening from the earth’s surface and designed to open mineral deposits and service underground workings.

A distinction is made between main and auxiliary shafts. The main shaft is located in the central mining area and is principally designed to hoist coal, ore, and other useful minerals to the surface; the auxiliary shaft is used to transport personnel, gangue, equipment, and materials. In addition, the auxiliary shaft can be used for ventilating the shaft and supplying it with fresh air (an intake shaft) or for expelling exhaust; shafts of this kind are located in the central industrial area and on the flanks (flanking shafts) of the mining area. Shafts are equipped with skips, cages, rail or conveyor transportation, and—during the construction stage—buckets.

The upper portion of the shaft has an opening from the earth’s surface called the mouth or collar; the lower portion, below the level of the pit bottom, is called the sump. The shafts usually have a round cross section, although rectangular and, less frequently, elliptic shafts are also found. Vertical shafts can be as much as 9 m in diameter and 3 or 3.5 km deep. Inclined shafts can be rectangular, arched, or round. The shaft walls are reinforced with concrete, reinforced concrete, and metal or reinforced-con-crete tubing; in hard and firm rock, spray concrete is used. The reinforcement of the shaft usually includes metal horizontal components (buntons) and vertical components (conductors) to ensure the smooth operation of skips and cages. Shafts are constructed by blasthole drilling, boring equipment, and shaft-sinking machinery.

A variant of the mine shaft is the blind shaft. A blind shaft is a vertical mining excavation not having a direct opening from the surface and constructed mainly to hoist useful minerals from lower levels of the mine to higher ones.