longwall mining




cutting machines - shearers



Cutting Machines - Shearers

Shearers are by far the most commonly used cutting machines, both in Australia and overseas. A shearer consists of a machine body containing electric motors, hydraulic equipment and controls which is mounted over the AFC. Horizontal cutting drums are mounted on the face side of the machine, laced with cutting picks and rotating in a plane parallel to the face. If the AFC is pushed towards the face as the cutting drums are rotated and the shearer travels along the face, it is able to cut into the face for the full web width, moving along a snake in the AFC. This is known as "sumping in". Once fully into the web, the shearer can advance the full length of the face cutting out the web. The snake can also be reversed to cut the wedge shaped portion of coal left while sumping in.

 Courtesy: The first shearers had a single drum rigidly attached to the body of the machine and so had a fixed cutting height and had to be able to get the body of the machine past the edge of the face at one end to cut the full length. Further developments saw the cutting drum being mounted on a hydraulically operated arm to vary the possible cutting height and a second cutting drum being fitted to provide a drum at both ends of the machine. Such machines were originally known as "Double Ended Ranging Drum Shearers or DERDS" but being almost the only type of shearer now used, the term "shearer" is generally understood to refer to this configuration.

The double ended ranging drum arrangement also allows smaller drums to be fitted while still cutting the required height, either cutting part of the seam with each drum in one pass or as two separate passes. The ranging arms allow much easier grading or changes in cutting height where required.

Shearers are mounted onto AFC's using either steel rollers or sliders running on the two edges of the AFC structure, either trapped or sufficiently guided by flanges to ensure derailing will not occur. The clearance between the bottom of the shearer body and the AFC base is an important design consideration as all coal cut on the tailgate side of the shearer has to pass under the shearer body on its way to the maingate. Any severe restriction at this point can cause problems, either causing coal to build up and spill over the AFC back plate or causing the AFC to jam. This is particularly the case where coal frequently comes off the face as large blocks or where roof stone has fallen on the AFC. In some instances a small coal breaker is fitted under the shearer at the low point to prevent blockages occurring.

Most shearers use radio control for normal operations although they are also fitted with manual and/or pendant controls for use in emergency conditions.