Medium and high wind pressure DTH drilling tools are a kind of rock drilling tools used in construction sites such as open-pit and underground mines, quarries, hydropower projects, water well drilling, mineral exploration, rock anchoring hole drilling, geothermal drilling, and subway engineering excavation and pile support. The DTH drill bit is the main consumable part of the medium and high wind-pressure DTH drilling tools. Therefore, a reasonable design of the DTH drill bit is very beneficial to improve rock drilling efficiency, and the design of the DTH drill bit is inseparable from the selection of materials.
Selection of materials for DTH drill bit
Harsh working environment puts high demands on the hardness, strength, toughness, impact resistance, wear resistance, and fatigue resistance of the DTH drill bit. Considering the performance requirements of each part, the material selection of the DTH drill bit can refer to the following points.
- Higher surface hardness to enhance wear resistance, better toughness in the heart to enhance impact resistance, and to avoid brittle fracture and fatigue fracture, the material needs to have good fracture toughness, fatigue strength, and fracture strength.
- High hardenability. To meet the different requirements of the performance of each part of the DTH drill bit, it is beneficial to increase the surface yield strength and improve the cementing force of the tooth hole to the carbides, and it can also improve the yield strength and toughness of the heart.
- It can resist certain corrosion when encountering gas and liquid in downhole rock formations.
- The material hardness remains stable and does not soften under certain high temperatures.
- Good process performance, such as good forge ability and small residual stress after heat treatment.
- High metallurgical quality, good structure uniformity, fewer impurities, especially low phosphorus content, and uniform carbides.
In addition to material selection, the rational design of DTH drill bits is also inseparable from the design of end faces, splines, and carbides.
End Face Design of DTH Drill Bits
There are four main types of end faces for DTH drill bits: convex, flat, concave and deep-concave center type.
| End face | Description |
| convex | It can maintain a high drilling rate when drilling medium-hard and hard abrasive rocks, but the straightness of the borehole is poor, and it is not suitable for rock drilling projects with high requirements for the straightness of blast hole. |
| flat | It is suitable for drilling hard and very hard rocks, and it is also suitable also for drilling medium hard rocks and soft rocks where the straightness of blast hole is not required. |
| concave | It has Good powder discharge, fast drilling speed, and more used in the market. |
| deep-concave center | It is only suitable for drilling soft and medium hard rocks. |
It can be seen from the above table that different end faces of DTH drill bits apply to different rock formations, and the failure mode of the end face is mainly impact fatigue. Therefore, the manufacturer can improve the design of the end face for upgrading in this regard.
The available methods are as follows:
- Reduce surface roughness and improve contact accuracy to reduce local stress concentration and stress peaks during impact.
- Reasonably match the hardness relationship between the piston and the impact end face. Priority should be given to improving the service life of the piston and changing the status quo of replacing the drill bit while also needing to replace the piston.
- Surface treatment, such as shot peening or rolling, can effectively improve fatigue strength and fatigue life.
Spline design
- Process in strict accordance with the design requirements to ensure proper clearance and uniformity of spline.
- The surface is carburized and quenched to increase the hardness of the surface layer and achieve the ability to resist plastic deformation and impact fatigue.
- Reduce surface roughness and improve contact accuracy.
- Increasing the spline cross-sectional area can improve the strength of rock drill bit.
Selection of carbides
To improve the service life of the rock drill bit, three requirements should be considered when selecting carbide grades:
1. According to the drilling technical parameters
Carbides with high molybdenum content should be used for high-frequency small-impact drilling, while carbides with higher bonding agent content should be used for low-frequency large-impact drilling to improve toughness.
2. According to the lithology of different rock formations
For the general rock formation, choose the carbide with lower cobalt content to enhance the wear resistance and impact effect. For the hard rock formation, choose the carbide with higher cobalt content to improve the impact toughness and avoid brittle breakage.
3. According to the working characteristics of carbides in different positions
Because of the different forces on the edge button and the front gauge, the edge button contains lower cobalt content to enhance wear resistance. The front gauge contains higher cobalt content to improve impact resistance.
If the user wants to obtain the best rock drilling effect, it is not enough to focus only on the reasonable design of the DTH drill bit, and the correct selection of the DTH drill bit is equally important. After all, the drilling situation is influenced by the rock conditions and the type of drilling machine, and different forms of carbides and arrangement of buttons are suitable for different rock drilling. Choosing the right DTH drill bit is the precondition for achieving the minimum rock-chipping effect.
