Cutting tools are the single most expensive consumable item in hard rock cutting operations. The cutting tool technology and its development will determine the future of hard rock mechanical excavation. The aim of this study is to identify the factors affecting the life of a particular type of tool, the disc cutter. Another aim of the study is to develop a long-life disc cutter.
It is believed that disc cutter shape affects rock fracture and therefore cutter performance and cutter life. However, the current generation of disc cutters is made of hardened steel and these cutters wear rapidly and consequently they are unable to maintain their original shape in strong and abrasive rock. This wear problem could be reduced if the cutter was made from a harder material. Unfortunately as material hardness increases so does the propensity for brittle failure. In this study, the optimum cutter shapes were identified by laboratory tests with four different cutter shapes and numerical modelling. A new cutter was designed based on this work using a harder material to increase the life.
Laboratory tests were conducted in two different rocks: sandstone and granite. The results showed that the bevel and wedge cutters registered only half the normal force of the flat cutter. Also the force fluctuation of the flat cutter was higher than that of the bevel and wedge cutters. The surface of the rock machined by the flat cutter was rougher than by the bevel and wedge cutters. The results also showed that the rate of wear of the wedge cutter was less than that of the flat cutter.
Numerical modelling to study the crack propagation induced during the cutting operation was carried out using a discrete fracture modelling code FRANC2D. This modelling showed that the bevel and wedge cutters formed chips more easily than the flat and dome cutters under the same loading conditions. In other words, the bevel and wedge cutters required lower forces to form chips than the flat and dome cutters.
The new cutter development included wedge shape optimisation, cutter design and field tests. The field tests showed that the new cutter increased the tool life by a factor of 20. This new technology has led to two CMTE patents.
The research successfully demonstrated that the new cutter with optimum shape and harder materials reduced the cutter cost significantly. The application of this new cutter can be extended to all hard rock cutting machines.