The wear and tear on the expensive underground equipment used by the mining industry is very considerable indeed, particularly at the coal face where mammoth automatic cutters have taken over from the miner.
An example of wear on the machinery is provided by the main drive head shafts of the coal rippers. One end of the shaft carries the drive, and the other end carries the 1.524m (5ft) diameter cutting head which rips into the coal seam at the face. The drive shaft is keyed to accept the cutting head mechanism and it is at this point that the wear is most severe. The photograph shows the size and position of the keyway clearly. Wear takes place around the bearing circumference and particularly at the keyway edges (which carry the full weight and impact shock of the cutting heads). In the metal spraying rectification of these shafts, any wear of the actual keyway is repaired first of all by re-welding and re-cutting to standard size. The surfaces of a number of such shafts have been reclaimed. A deposit of S2 1.5mm (0.060”) thickness has been applied using the Metallisation Arc Spray system.