Open-Pit Forum ? Range Mechanization Progresses

ON the Minnesota Ranges, 600 million tons of material have been moved in the past three years to produce 172 million tons of direct-shipping iron ore. Increasing wage rates and cost of equipment and supplies, coupled with the larger amount of waste material to be moved in comparison with the quantity of ore make it imperative that tile industry adopt all practices and methods which will enable it to move earth at progressively lower costs. Drilling. Prior to and during the war practically all blastholes drilled were 6-in. in diameter and put down by drills using strings of tools weighing from 2000 to 3000 lb. Present trends indicate that heavier drilling equipment making 9-in. holes wit11 3000 to 6000 lb tools will be more economical. Holes up to 12 in. diameter will be made with this equipment. Forging and hardening practices for bits to increase footage is receiving attention. One manufacturer expects to market 9-in. bits having sintered carbide inserts in the reaming and cutting edges. Oxygen and oil to burn holes in the rock are being tested for making blastholes at a considerably greater speed than can be obtained with a blasthole drill on the same size hole. To dale, however, the cost has been prohibitive.