DTH drill bits include high-pressure, medium-pressure, and low-pressure DTH drill bits according to the working air pressure. High-pressure DTH drill bits are mainly used in high-pressure DTH rock drilling projects and are the main consumable parts. Therefore, the manufacturer’s analysis of the cause of the failure of the high-pressure DTH drill bits can effectively prolong the service life of the products and help the enterprise reduce rock drilling costs.
The DTH drill bit consists of carbides, exhaust holes, head, splines, and impact end faces. Among them, the failure reasons of carbides and exhaust holes are very simple and will not be repeated.
Failure of the impact end face
The impact end face is mainly bearing the periodic repeated severe impact of the piston, and its failure forms are pitting, spalling, and collapsing and the failure type is impact fatigue damage. The reason is that the carburized layer on the surface of the drill bit has high hardness and brittleness. The impact force of the drill bit is great when it is working, and brittle cracks are easily formed. The hardness of the base material of the drill bit is low, and it is easy to undergo plastic deformation under the action of the impact force. Repeated plastic deformation can easily lead to crack initiation and pitting, and an increase in the number of pitting develops into pockmarks, pockmarks expand into local shallow exfoliation, and finally, the end face continuously peels off and sinks until it collapses.
Spline failure
Spline connects the drill bit to the DTH hammer and rotates together downhole, and also serves as a track for the downward movement of the drill bit. When the drill bit is working, the force on the spline is relatively complicated, and the lateral side is subjected to pulsating compressive stress caused by the shear reaction force of the rock change during rotation. At the same time, the high-frequency impact of the drill bit brings certain vibrations and friction, which is prone to stress concentration. And lead to plastic deformation, resulting in spline failure.
Head failure
The forms of drill head failure are collapse and tooth loss, the fractures are all brittle, and the crack source is located in the radial direction of the cemented carbide column tooth hole. The reason is that the carburized layer on the surface of the drill bit is hard and brittle, and the impact force is great when the drill bit is working, so it is easy to produce cracks. In addition, the carbide column carbide hole has been carburized, the hardness is very high after quenching, and the carbide column carbide button is pressed into the hole for an interference fit, and the tangential tensile stress of the tooth hole is generated, so it is easy to crack along the radial direction of the tooth hole and produce brittle cracks when working.
To sum up, the failure mode of the high-pressure DTH drill bit is collapse and crack, while wear is the second failure mode. The main reason for drill bit collapse and cracks is the unreasonable carburizing process and other factors. Therefore, manufacturers can solve the problem of failure of high-pressure DTH drill bits during use by improving the carburizing process and many other means.
In addition to wear failure, high-pressure DTH drill bits can also fail due to impact loads, erosion by corrosive media, material issues, and improper operation by personnel. In response to this, we can take the following solutions and suggestions:
- Select high-quality materials and reasonable heat treatment processes to improve the rock drill bits’ wear resistance and service life.
- Optimize the structural design of the drill bit, select appropriate parameters according to actual working conditions and use requirements, and improve the drilling efficiency and stability of the drill bit.
- Select the model of the high-pressure down-the-hole drill bit based on the actual project conditions and the properties of the rock.
- Strengthen the training and management of operators, improve their operating skills and safety awareness, and avoid drill bit failure caused by improper operation.
- Conduct regular inspections to ensure the drill bit’s optimal performance and extend its service life.
- Choose high-quality products produced by regular manufacturers to ensure the quality and use effect of the drill bit.
Conclusion
The reasons for the failure of high-pressure down-the-hole drill bits are varied, but by improving material properties, optimizing structural design, strengthening maintenance, enhancing operating skills, and reasonably selecting use conditions, the risk of drill bit failure can be effectively reduced and its service life extended. For engineers, understanding and mastering these failure causes and solutions is crucial for improving engineering efficiency and quality.
