Boart Longyear offers a wide selection of bits for the inner drill string of overburden drilling systems for a variety of ground conditions that drillers face every day. Inner drill string bits are primarily designed for rotary percussive drilling, but in some situations perform well in mixed drilling or pure rotary drilling. In addition to standard designs, Boart Longyear offers several specialty designs for unique drilling situations and can also design custom bits upon request.

Construction

The bit bodies are constructed of high-strength quenched-and-tempered steel. The high-quality tungsten carbide inserts are induction brazed into the steel bodies, ensuring a permanent fit without overheating issues associated with flame brazing. Strict machining control of the carbide seats prevents premature loss of carbide inserts.

Gauge Protection

Boart Longyear offers tungsten carbide gauge protection on some designs. Gauge protection will prevent excessive wear on the bit’s outer diameter in abrasive ground conditions.

Shrink Fit Carbides

Shrink-fitting installation of all hemispherical, ballistic, and two-step tungsten carbide inserts instead of the standard induction brazing is available. This very precise construction method is often used when drilling in extremely hard ground conditions, enhancing bit performance.

Advantages

• Computer-controlled inductive brazing of tungsten carbide inserts for superior process control and overheating prevention, common with flame brazing 

• High-grade body construction with quenched and tempered steels 

• Optional gauge wear protection, tungsten carbides available