Suggestions for Selecting Different Rock Types and DTH Drill Bits

Table of Contents

In rock drilling projects, choosing the right down-the-hole drill bit is crucial. Different types of rock have different hardness, compressive strength, and mineral composition, so different types of down-the-hole drill bits are required for drilling operations. This article will introduce different rock types and suggestions for selecting down-the-hole drill bits to help engineers better complete rock-crushing projects.

Rock types and their characteristics

In rock-crushing projects, common rock types include soft rock, medium hard rock, and hard rock. Each rock type has its unique characteristics and difficulty of breaking.

  • Soft rock: soft rock is a rock with a compressive strength of less than 20MPa, such as shale or clay rock. This type of rock has low hardness and is prone to breakage, but it can easily cause the drill bit to become clogged.
  • Medium hard rock: medium hard rock is a rock with a compressive strength of 20-40MPa, such as sandstone or limestone. This type of rock has moderate hardness and difficulty in breaking. It is somewhat challenging.
  • Hard rock: hard rock is a rock with a compressive strength greater than 40MPa, such as granite or basalt. This type of rock has higher hardness and is more difficult to break, requiring a high-hardness drill bit and higher impact energy.

Recommendations for the selection of down-the-hole drill bit

DTH drill bit

DTH (Down-the-Hole) drill bits are tools utilized in tandem with DTH hammers to bore holes in rock formations. Depending on the specific rock formations, the head of the DTH drill bit has many different face configurations. When drilling, it is necessary to select the appropriate surface structure and carbide button shape according to the rock conditions of the formation, etc., to achieve twice the result with half the effort.

Flat face drill bit

This type of face is more common and is suitable for drilling very hard rock formations and corrosive rock formations at high wind pressure. It features fast drilling speed and low wear of the drill body.

Convex face drill bit

This shape is suitable for drilling soft rock and medium-hard rock formations under low and medium-pressure conditions. The drill bit skirt body is not easy to corrode. It is characterized by the low load-bearing of the gauge button, slow wear, and fast drilling speed.

Concave face drill bit

This shape applies to almost all rock formations, especially in medium-hard and uniform rock formations, and has the best effect. It has the characteristics of a wide application range, minimum blast hole deviation, and good slag discharge effect.

Double gauge face drill bit

This shape head is suitable for drilling very hard rocks under high wind pressure. The double gauge buttons can effectively reduce the wear of the skirt body. It has the characteristics of fast drilling speed and low wear of the drill bit skirt body.

Rocket bit

This type of drill bit was introduced by Sandvik and is suitable for soft rock. The specific surface structure enables the drill bit to have an excellent slag discharge effect and has the characteristics of fast drilling speed.

In summary, for hard rocks with higher abrasiveness, it is recommended to use flat-face drill bits to extend service life. In the case of medium-hard rocks with developed joints and numerous fissures, concave face drill bits are more suitable and can reduce the probability of hole deflection.


Different rock types have various requirements for the selection and use of down-the-hole drill bits. Engineers should fully understand the characteristics and crushing difficulties of diverse rock types. When selecting a down-the-hole drill bit, comprehensive considerations need to be made based on the actual situation to achieve the best drilling effect and extend the service life of the drill bit. At the same time, to better complete the rock-crushing project, it is also necessary to pay attention to the correct use and maintenance of down-the-hole drill bits to avoid excessive wear and damage.

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