Emre Avunduk

Effects of Different Cutting Patterns and Experimental Conditions on the Performance of a Conical Drag Tool

This study aims at determining the effects of single-, double-, and triple-spiral cutting patterns; the effects of tool cutting speeds on the experimental scale; and the effects of the method of yield estimation on cutting performance by performing a set of full-scale linear cutting tests with a conical cutting tool. The average and maximum normal, cutting and side forces; specific energy; yield; and coarseness index are measured and compared in each cutting pattern at a 25-mm line spacing, at varying depths of cut per revolution, and using two cutting speeds on five different rock samples. The results indicate that the optimum specific energy decreases by approximately 25% with an increasing number of spirals from the single- to the double-spiral cutting pattern for the hard rocks, whereas generally little effect was observed for the soft- and medium-strength rocks. The double-spiral cutting pattern appeared to be more effective than the single- or triple-spiral cutting pattern and had an advantage of lower side forces. The tool cutting speed had no apparent effect on the cutting performance. The estimation of the specific energy by the yield based on the theoretical swept area was not significantly different from that estimated by the yield based on the muck weighing, especially for the double- and triple-spiral cutting patterns and with the optimum ratio of line spacing to depth of cut per revolution. This study also demonstrated that the cutterhead and mechanical miner designs, semi-theoretical deterministic computer simulations and empirical performance predictions and optimization models should be based on realistic experimental simulations. Studies should be continued to obtain more reliable results by creating a larger database of laboratory tests and field performance records for mechanical miners using drag tools.

Predicting Performance of Raise Boring Machines Using Empirical Models

Raise boring machines are used for excavation of shafts and other vertical structures in mining and civil engineering fields for material, human transportation and ventilation purposes. RBM uses a small diameter drill rod, around 230–350 mm to drill a pilot hole down to the required depth. Once the pilot hole has been drilled to the desired depth, a reamer is attached to the drill rod. The reamer is then pulled back up to the upper level, creating a round shape. This continues operation provides a faster advance rate than other methods. The flexibility in different angles and diameters is a great advantage compared to drill and blast excavation method. RBM creates a shaft with smooth walls which usually does not require lining in an appropriate geology. The hole is more stable than a drilled and blasted method and has better air flow, making it ideal for ventilation shafts. The cutting performance of raise bore machine is mainly dependent on geological features of rock, specification and design of the machine, and operational parameters such as force on cutter and rotary speed. Few studies have been published in the literature related to performance prediction of the raise boring machines. Morris (1969) developed a semi-empirical method of predicting the boring rate and cutter life. In his method button penetration index with the other factors was used to predict the machine performance. Lightfoot (1970) founded a good correlation between the performance of raise drill (Model 480) and the result of Morris (1969). Seiler (1972) developed a boreability index by pressing hydraulically a sphero-conical tungsten carbide insert into a flat rock surface. Then by dividing the load to created depth a boreability index was calculated. Calder (1972) stated the empirical model to predict boring rate from drilling studies. His rotary drilling model relates boring rate to uniaxial compressive strength of the rock, thrust force and hole diameter. Pigott (1985) stated some suggestions for faster and cheaper drilling of shafts in soft to medium strength formations. Nishimatsu et al. (1987) tried to improve the boring capacity of the blind raise boring machine using theoretical concepts. Bilgin (1989) and Bilgin et al. (2014) stated that, penetration index obtained from indentation tests could be used to estimate the RBM performance. Elgenklow (2003) investigated Robbins 34RH and 53RH raise bore machine performance at El Teniente mine in Chile. In this investigation utilization time was obtained 29.8 and 40.3 % for 34RH and 53RH machine, respectively. In the present study, borehole samples obtained from Eti Copper Kure Asikoy underground mine were first tested to define some of the basic physical and mechanical properties, and then cutting experiments using a linear cutting test rigs with chisel, conical, and disc type cutting tools were realized with two different cutting depths at unrelieved cutting mode. The linear cutting tests were performed to find out the cuttability properties of samples and to define the cutting performances of different cutters. The results of laboratory and field studies were used to develop empirical models for predicting penetration rates of raise boring machine. Two empirical models are suggested and verified. & Aydin Shaterpour-Mamaghani mamaghani@itu.edu.tr