The DTH drill bit is a critical component that is in direct contact with the rock during the rock-breaking process of the DTH hammer. The structure and material selection of the DTH drill bit is directly related to the rock drilling efficiency and the service life of the DTH hammer. The DTH drill bit has two main structures: a drill edge structure and an end face structure. The end structure contains the end shape and geometric structure, which can include many components. What are the important geometric structures of the end face of the DTH drill bit?

1.    Exhaust holes

The wear of DTH drill bits and carbides during drilling is related to the material properties of the skirt body and carbides and the size and flow velocity of cuttings at the bottom of the hole. The wear rate of carbides directly determines the service life of the DTH drill bit. Additionally, cuttings movement at the hole’s bottom primarily relies on high-pressure gas inside the vent hole to blow them to the ground. Consequently, designing an exhaust hole should consider factors such as DTH drill bit strength, venting resistance, and rock chip-blowing performance.

2. Slag discharge tank

The slag discharge tank is related to the end face of the vent hole, and the jet flows through the vent hole to the bottom of the hole to sweep the cuttings at the bottom of the hole, and the debris is exhausted from the bottom of the hole to the ground through the slag discharge tank. Therefore, to prevent drill sticking and reduce the wear of the drill bit and carbides, it is necessary to increase the slag discharge groove as much as possible while ensuring the strength of the DTH drill bit. It will allow the cuttings to move more smoothly.

3. Anti-jamming angle

In the process of drilling, to prevent the jamming phenomenon, it is necessary to reduce the contact area between the drill bit and the hole wall should be reduced by setting an inwardly inclined step at the outer circle of the drill bit’s head. The step height is determined by the height of exposed teeth of carbide, generally set at 20mm, and the anti-seize angle is 10°. The setting of an anti-seize angle can avoid the phenomenon of a stuck drill, ensure the regular drilling of the drill bit, and prolong its service life.

4. Spline

The DTH drill bit both impacts and rotates to break rock. Additionally, the drill pipe provides a torsional moment through the spline set at the end of the drill bit. However, these splines are subject to back-torque from the rock at the bottom of the hole as well as the vibration and friction brought by high-frequency impact during the process of impact rotation of the drill bit to break the rock, which is prone to plastic deformation after long time use and eventually leads to spline failure. Spline failure will lead to the inability of the drill bit to rotate and the impactor to operate normally.

The main reason for the failure of the spline is the irrational fit clearance between the spline and the front joint. In the actual assembly process, to ensure a smooth reciprocating impact process between the piston and the drill bit, there is a matching gap between the spline of the drill bit and the internal groove of the front joint of the DTH hammer. Too small a fit clearance will lead to increased friction between the spline and the inner groove of the front joint, intensifying spline wear; too large a fit clearance will lead to insufficient stability in the reciprocating motion of the drill bit, resulting in plastic deformation of the spline after repeated collisions.