8-1 Major Components of Shearers [1]

Although there are many models, the shearer has several common basic components. A double-ended ranging-drum shearer [2], for example, consists of four major components: electric motors[3], gearheads [4], haulage unit��power pack��[5], and cutting drums [6].

The electric motor ranging from 300 to 1000 horsepower��223��750kw�� is the power source for the shearer. It provides to run the hydraulic pumps [7] in the haulage and the gearheads for cutting drum. The large capacity shearers are generally equipped with two electric motors: one for the haulage unit and one gearhead and the other for the other gearhead and other ancillary equipment [8]. The motor can be remotely controlled.

There are two gearheads, one on the left-hand side and the other on the right- of the shearer. Each gearhead consists of a gearhead gearbox [9] and a ranging arm.

The cutting drum is laced with spiral vanes [10] on which the cutting bits are mounted. It diameter ranges from 0.86��1.83m with rotational speeds [11] from30 to 195 rpm. The drums are also equipped with power cowls [12] to increase the coal loading efficiency. The power cowl is usually located behind the cutting drum. For that reason, it can be rotated a full 180º.

The electric motor, haulage unit, and gearhead boxes combine to form the shearer��s body, which is mounted on the underframe [13]. The underframe has four sliding shoes [14]. The face-side shoes are fitted and ride on the face-side top guide of the face conveyor pan [15], and the other two gob-side sliding shoes are fitted on a guide tube to prevent derailment. The haulage speed of the shearer ranges from 5.8��14.0 m/min.

In addition, the shearer is equipped with auxiliary hydraulic pumps and control valves [16] for operating the ranging arms and power cowls, water spraying devices [17], cable [18], chain anchorage [19] and tensioners [20], and so on.

8-2 Types of Modern Shearers

Single-ended fixed-drum shearer [21]is an earlier model. A single drum is mounted on the shearer��s body and cannot be adjusted for height. Therefore, it is not suitable for areas where there are constant changes in seam thickness and floor undulation [22]. Thus the single-ended fixed-drum shearer is used mostly for thin seams.

This is a single-ended ranging-drum shearer [23]. The cutting drum is mounted at the end of the ranging arm . The ranging arm can be raised up and lowered down by hydraulic control to accommodate the changing seam thickness and floor undulation. But when the seam exceeds a certain thickness, the single drum shearer cannot cut the entire height in one cut, and a return cutting trip [24] is necessary to complete a full web cut [25]. Furthermore, since the drum is located on the headentry [26] side, it generally requires a niche in the tailentry [27] side. A niche [28] is a precut face end, one web deep and a shearer��s length long. With a niche at

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