How to Select the Right DTH Drill Bit?
DTH drill bit, full name - down the hole bit, is a rock drilling tool that is usually equipped on the DTH hammer and operated directly into the bottom of the hole to drill rock.
DTH drill bit is widely used in urban construction, railway, highway, well and other applications and anchor holes, blasting holes and other drilling constructions. According to different application occasions and rock conditions, need to choose different DTH drill bit: different face shape, different carbide button shape, different applicable air pressure ranges .
DTH drill bit Face Shape Selection
There are five main shapes of DTH drill bit face: drop center, concave face, convex face, flat face, double gauge.
Drop Center
The drop center face type is suitable for soft, hard and fractured rock formations with low and medium pressure drilling to obtain fast drilling speed and less hole slope.
Concave Face
The concave face is suitable for all rock formations, especially in the medium hard and uniform rock formations. The hole deviation control is small, and the slag discharge effect is good.
Convex Face
For high penetration rates in soft to medium-hard with low to medium air pressures, convex face is the most resistance to steel wash, and could reduce the load and wear on the gauge buttons, but the hole deviation control is poor.
Flat Face
The flat face shape is suitable for very hard and abrasive rock formations in applications with high air pressures. DTH drill bit of flat face of drilling rate is faster and the DTH drill bit body is less abrasive.
Double Gauge Face
Double gauge face is adapted to drill through very hard rock formations at high wind pressure. At this time, the drilling rate of DTH drill bit is fast and the DTH drill bit body wear is not serious.
DTH drill bit Carbide Button Shape Selection
There are five main shapes of DTH drill bit carbide button: domed buttons (or spherical button), parabolic buttons (or Semi-Ballistic Buttons), ballistic button, sharp button, flat buttons .
Domed/Spherical Button
Domed buttons or spherical buttons are usually used as gauge buttons of DTH Bits, which is suitable for very abrasive and very hard formations.
Parabolic/Semi-Ballistic Button
Parabolic buttons or Semi-Ballistic Buttons are usually used as gauge buttons and middle buttons, which is suitable for medium abrasive and hard formations.
Ballistic Button
Ballistic buttons are usually used as middle buttons of the DTH drill bit, which is suitable for medium abrasive and medium hard formations. Ballistic buttons can also be used as gauge buttons if the rock is soft.
Sharp Button
Sharp Buttons are mainly used as the middle buttons of the DTH drill bit, which is suitable for the soft rock formation with high drilling rate and low tooth breakage rate.
Flat Button
Flat buttons are mainly used as the side protection buttons of the DTH drill bit to reduce the wear of DTH drill bit body surface.
Commonly Used Face Button Collocation
Flat Front Spherical
Flat DTH drill bit is usually paired with spherical button, which use the wear resistance of the spherical button to adapt to extremely hard rock formations (such as Limestone and basalt) and extend the DTH drill bit life.
Flat Front Spherical+Ballistic
Flat Front Spherical+Ballistic DTH drill bit belongs to the compound collocation: the outer ring of the DTH drill bit is the spherical button to prevent wear; The inner ring is the ballistic button, which is used to break rock. So the DTH drill bit can achieve wear resistance and efficiency.
Concave Front Spherical
Concave front spherical DTH drill bit is suitable for soft rock to medium hard rock (such as shale, sandstone), fracture development rock.It is generally used to deal with high-precision blasting holes and loose formation anti-deflection, with high powder discharge efficiency and excellent straightness of holes.
Convex Front Spherical+Ballistic
Convex front spherical+ballistic DTH drill bit is used to balance edge wear and center rock breaking efficiency. The DTH drill bit is suitable for medium hard and hard abrasive rock, such as iron. It has strong comprehensive performance and can adapt to complex working conditions.
Convex Front Ballistic
Convex front ballistic DTH drill bit is usually used for fast drilling in shallow holes. It has the fastest drilling speed, low cost and is suitable for short-term projects.
Matched Air Pressure of Selection
When DTH drill bit is used for drilling shallow holes, loose formations or small projects, the drill rig usually has a low working air pressure. So the side exhaust DTH drill bit with simple structure and low cost should be selected to avoid excessive wear.
When the drill is used to drill deep holes, very hard rock or large mining, the drill rig usually has a high working air pressure. So the DTH drill bit should choose a strengthened alloy tooth layout (radial symmetry) and center exhaust design to adapt to the high-frequency impact of the DTH hammer.
