Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/883641
20 AGGREGATES MANAGER / October 2017 EQUIPMENT MANAGEMENT to Europe. Bottom line: If you can read this, read your manual to be safe and productive. 2) Use sharp bits. How quickly a bit will dull varies on its application. In hard, abrasive rock, an operator can get as little as 200 feet out of a bit — compared to the experience of a top-hammer drill operator in Oklahoma who told Hissem he once got 50,000 feet out of one. How do you know when to change out a bit? Hissem advises doing so when the diameter of the fl at area of a worn button on a bit exceeds one third of the base diameter of the button. He compares a fl attened button to a pair of fl at shoes, which spread the weight of the wearer across the bottom of the shoe. Whereas, a rounded button is like a pair of stiletto high heels, which trans- fer the weight to the surface in a very small area. The smaller the button area touching the surface, the greater the psi and rock-breaking stress brought to bear upon the rock surface. "You never get 100 percent of the energy applied to the bit into the rock. The best you can get is 95 percent, with 5 percent bouncing back," he says. The point is, the sharper the bit, the less energy refl ection you will get, and the faster the bit will cut the rock. 3) Balance feed, rotation, and percussion. These forces are the key variables, and optimizing them can be helped by watching for such things as the size of cuttings coming out of the hole. The chips should be as large as possible, While smart drills offer onboard intelligence, it's important that the driller monitor things such as the flushing action, pitch changes in the drill string, and movements that indicate a change in rock pressure.