In the longwall mining of coal, a shearing machine has cutter drum attached to it. The cutter drum is rotated and moved by the shearing machine into the wall by a desired distance depending on the characteristics of the particular coal being mined. The rotating drum is then moved along the wall. As the mined coal falls, it is picked up by a conveyor, which carries it to a location for hauling from the mine.
Cutter drums generally include a hub, which is attached to the shearing machine. The hub carries several helical vanes, and a sump ring is attached to the end of the hub. Cutting bits are attached to the vanes and to the sump ring for engaging and cutting the coal as the cutter drum rotates.
In the typical prior art cutter drum, pockets are flame cut into the vanes to provide seats for bit blocks. The bit blocks are placed in the seats at predetermined angles and then welded to the vanes. Cutting bits are attached to the sump ring in the same fashion.
Another method for attaching bit blocks is to weld the bit block directly to the vanes and the sump ring, without first making a seat, and then bridging the area between adjacent bit blocks with gussets to strengthen the arrangement. In either construction, knock-out holes are generally provided to facilitate removal of a used bit.
These prior art constructions result in cutting drums having very jagged surfaces because the bit blocks and gussets create numerous irregular and uneven surfaces. Falling pieces of coal that have been cut from the coal seam by the cutting bits crash into these jagged and irregular surfaces on the rotating drum. This creates particles of coal and coal dust and distributes them throughout the region surrounding the cutting drum. Such is very dangerous to those working in the mines and reduces the efficiency of the entire longwall mining operation.