Boart Longyear

Inner String Bits

We offer a selection of bits for the inner drill string of overburden drilling systems to serve the wide variety of ground conditions that drillers face every day. The inner drill string bits are primarily designed for rotary-percussive drilling but in some situations can perform well in mixed drilling or pure rotary drilling. In addition to the common designs, Boart Longyear™ offers several specialty designs for unique drilling situations and can also design custom bits on 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 insuring a permanent fit without overheating issues associated with flame brazing. Strict machining control of the carbide seats prevent premature loss of carbide inserts.

Gauge Protection
We offer tungsten carbide gauge protection on some designs. Gauge protection will prevent excessive wear on the outer diameter of the bit in abrasive grounds.

Shrink Fit Carbides
Boart Longyear can, on request, shrink fitting installation of all hemispherical, ballistic, and two-step tungsten carbide inserts instead of the standard induction brazing. This very precise construction method is often utilized when drilling in extremely hard ground conditions giving the bits enhanced performance.

Advantages
• Computer controlled inductive brazing of tungsten carbide inserts provides superior process control and prevents overheating common with flame brazing.
• High grade body construction with quenched and tempered steels.
• Optional gauge wear protection tungsten carbides available to assist.