I.T.H. Bits

Down-the-hole or in-the-hole bits have been around for at least two decades now. Early on, the major players were TRW Mission (which is now with Sandvik), Ingersoll-Rand and Atlas Copco. As the popularity of ith driling spread, however, a number of other manufacturers jumped into the fray.

ITH drills can produce low-cost muck from both development and production drilling. The initial capital outlay might discourage some mining companies from adopting ith drills, but manufacturers point to relatively low maintenance and reliable performance as key advantages.

For DTH (or ITH) drill bits, the trend generally is toward smaller holes — 4 1/2 inches as opposed to 6 1/2 inches. The 5 1/2-inch bit is also making inroads. Nowadays, bit manufacturers must have a diverse line to satisfy customers. Not only must the bits fit hammers manufactured by several different companies, but they must also be offered in the different faces that production people require.

Boart Canada of Mississauga, Ont., supplies high-quality down-the-hole bits and hammers to the North American mining and construction industries. Boart says it leads in the European market in the 3 1/2-to-6 1/2-inch range. The key features are quality, price and extensive technical support, the company’s literature states. Recent innovations include the availability of ballistic buttons for difficult conditions.

Recently, Boart Europe field-tested and launched its BH40 DTH hammer into the French market as a precursor to worldwide introduction. Aimed at general surface and undrground mining applications, the BH40 suits pressures from seven to 25 bar and features a backhead/chuck thread designed for ease of decoupling, a piston blow rate optimized for high penetration and reliability, a reversible wear sleeve, valveless operation and variable flushing rates. Boart produces bits to fit hammers made by Atlas Copco, Boart, Bohler, Demag, Ingersoll-Rand, Mission and several other companies.

At Kenroc Tools Corp., of North Bay, Ont. (the only manufacturer in in this country to make drill bits up to 20 inches), design flexibil is a key aspect of manufacturing, says marketing manager Dan Mahoney. Bits are designed on a CAD system and made on numerically controlled CAM machines. Kenroc also incorporates proprietary grades of steel and cold-stamped (as opposed to hot-rolled) forgings in its bit manufacture.

Kenroc offers flat-face, mushroom, drop centre and concave bit face designs. It sells bits to fit Mission, Atlas Copco, Ingersoll-Rand and other manufacturers’ machines.

Brunner Canada, based in Mississauga, Ont., says its claim to fame is that it can design just about any face that a mining company requires. So whether it be crown, centre, flat face or whatever, Brunner can manufacture it. The company sells DTH its that fit Atlas Copco, Mission, Ingersoll-Rand, Bulrock and other hammers.

Atlas Copco’s bits range from eight to 17 1/2 inches in diameter in the cop 8, 10 and 11 models using large-gauge buttons. The bits are ideally suited for fissured and extremely abrasive rock, says the company’s sales literature. Atlas Copco’s concave front bits feature large-gauge buttons, a design that works well in extreme drilling conditions.

Ingersoll-Rand Drilling Equipment offers 33 different bit sizes, from 4 1/8 inch up to 30 inches. Ingersoll-Rand notes that while button bits might look alike, there are differences in strength, hardness and wear characteristics of the bit body; and in the positioning, size and mounting of the buttons. Even the geometry of the bit is a factor in drilling results. The company’s bits range in size from 4 1/8 to 40 inches. Its DuroRock bit is designed for very abrasive conditions.

Sandvik Coromant produces bits with flat-face fronts for hard and abrasive rock, concave fronts for medium-hard ann medium-abrasive rocks, and convex fronts for high penetration in non-abrasive rock. The drill bits fit a variety of hammers, from those of Atlas Copco to those built by Zimmerman.

Sandvik Mission bits come in drop-centre, concave, step-gauge, double-gauge and flat-face designs. They range in size from four to 33 inches.

Secoroc offers several different fronts on its bits — the flat front, convex front -51, drop centre front -52, concave front -53 and ballistic front -61. The first four are commonly used in hard-rock mines.

Secoroc manufactures bits that fit hammers made by Atlas Copco, Ingersoll-Rand, Mission and others.