20 giugno 2016
Headquartered in Chantilly, Virginia, USA, William A. Hazel, Inc. is a premiere total site development contractor. They encountered hard rock while working on infrastructure projects to support a population surge in the Washington, D.C., area. Since their drill bits were not giving them the longevity they desired, the company granted a request by Atlas Copco to field test Powerbit top hammer drill bits.
“We hoped to see something with double the life, but we were getting way more than that from the Powerbits. They have excellent wear characteristics”
Typical patterns for the test consisted of 25 to 30 blastholes, 89-mm (3 ½ in.) in diameter and drilled with T45 to a depth of 3 meters (10 ft). Several feet of soil overburden were left in place as stemming material over diabase rated with a hardness of 275 MPa (40,000 psi). Maintaining hole diameter to the hole bottom is crucial, as booster cartridges are 70 mm (2.75 in.) in diameter, leaving an annulus of only 9.5 mm (⅜ in.) for emulsion-type explosives. Gauge retention during bit life is a priority concern, affecting precise booster placement, consistency in hole charging, and even fracture size and overall effectiveness of the shot. Such shallow drilling requires drillers to be “in and out” of holes in rapid succession. Insufficient time is allowed in the hole for flushing air to cool the drill string, resulting in excessive heat that leads to shortened tool life. Drill rigs used in the test represented several leading manufacturers. Each rig was assigned one 89 mm Powerbit. The Powerbit was not engineered as an improvement on existing designs but instead as a design and research project from scratch, using input from customers at the onset. The bit body steel grade and the button materials were developed with longevity and high quality in mind. William A. Hazel, Inc. sought a bit whose price was comparable to its currently favored, non-Atlas Copco bit but would exceed that bit’s 120 m (400 ft) average service life in the diabase by at least twice the footage: 240 m (800 ft). The Powerbit often tripled the footage of their average bit, exceeding 365 m (1,200 ft), yet effectively maintained its 89-mm gauge in each case. There were no bit failures during the testing period.