The DTH drill bit is an essential part of the DTH hammer as a direct tool to break the rock of the DTH hammer. If the DTH drill bit fails, it will directly affect the progress of the project and increase the cost of the enterprise at the same time. Therefore, understanding the failure mode of the DTH drill bit can help us extend its service life and drill better.
The failure mode of the DTH drill bit includes the failure of the main body of the drill bit and carbides. The failure modes of the main body include impact end face damage, shrinkage of the drill bit body, and spline failure at the end of a drill bit. The main failure modes of carbides of the drill head include carbide wear, carbide loss, and broken carbide.
Failure mode of DTH drill bit body
Impact end face damage
The damage of the impact end face is reflected in the formation of a crater on the end face. The impact end face of the drill bit completes rock breaking under the high-frequency impact of the piston. Under the continuous reciprocating impact, the impact face will produce fatigue damage, fine cracks, and plastic deformation. As the cracks expand and the plastic deformation range expands, a crater is formed, eventually leading to the failure of the impact face of the drill bit.
Shrinkage of the drill bit body
During the drilling process, the DTH drill bit is also continuously rotated by the torque transmitted by the spline, and the gauge button will be worn under the simultaneous action of impact load and torsional torque. After a long period of use, the wear of the gauge button becomes more and more serious, which will eventually cause the end face of the drill bit head to direct contact with the rock and then wear the drill bit body, resulting in a decrease in the outer diameter of the drill bit and a shrinkage phenomenon. This shrinkage can cause bit irregularities, affecting run-in efficiency and hole size.
Spline failure at the end of the drill bit
The DTH hammer transmits torque through the spline at the end of the drill bit to complete the rotary drilling during rock breaking. During the working process, the spline is affected by the reverse torque and impact vibration of the rock at the same time, the force is relatively complicated, and stress concentration is prone to occur, resulting in plastic deformation. After a long time of use, the spline will fail. The failure of a single spline will increase the force on the other remaining splines, and finally, the overall spline will not work, and the drill bit will not be able to rotate normally, which will affect the regular drilling work.
Failure mode of carbides of DTH drill bit
Abrasion
When the DTH hammer works, the carbide is a direct rock-breaking component that rotates and scrapes the rock to crush through the impact force and torque transmitted by the drill bit. In actual use, carbides are also the most easily damaged and failed parts.
In the process of contacting with the rock, the broken rock particles are abraded in the impact and torsion, and when the gauge button encounters large or sharp rock particles, scraping and abrasion will occur, which eventually leads to the failure of the gauge button.
Broken button
During the working process, the DTH drill bit bears drilling pressure, torsional moment, impact load, and rock reaction force, while the carbide inlaid in the head is a brittle material. When drilling in hard strata, the rock reaction force increases, which is easy to form stress concentration. After being used for some time, cracks will appear on the surface of the carbide, and the cracks will continue to expand as the drilling progresses, and when they reach a certain level, a brittle fracture will occur.
Button loss
The drill bit body is worn
The surface wear of the drill bit reduces the contact surface between the gauge button and the drill bit, and the holding force provided by the drill bit to the gauge button decreases, resulting in the gauge button falling off.
Plastic deformation of tooth hole
During the impact rock-breaking process, the drill bit is subjected to the positive pressure of the rock against the drill bit in the axial direction. The axial and circumferential forces on the drill bit act on the tooth hole of the drill bit through the button. The farther the tooth hole is from the center of the drill bit, the greater the torsional shear stress on the tooth hole. The material of the drill body is softer than the button, prone to plastic deformation under the repeated action of higher impact and shear loads. With the increase in the number of impacts, the plastic deformation value of the upper end of the tooth hole wall continues to expand, forming a flare in the upper semicircular surface of the hole wall, weakening the tightening force of the hole on the button, loosening the button and causing the gauge button to fall off.
Damage to the hole wall in the process of pressing the teeth
There are mainly three methods of tooth pressing for DTH hammers: brazing fixed teeth, heat-inserted teeth, and cold-pressed fixed teeth. Among them, the effect of brazing fixed teeth and thermally inserted teeth are good, and the stress generated in the pressing teeth is small, which is suitable for small-diameter drill bits.
Insufficient interference of carbide assembly
The friction between the drill bit and the alloy teeth is mainly generated by the interference amount, therefore, the selection of interference is important for the tooth-fixing process. If the interference is too small, the friction force will be insufficient. During the rock-breaking process of the drill bit, the carbide and the tooth hole will slide relative to each other, which will eventually cause the carbide to fall off, and the drill bit failing. If the interference is too large, it will lead to the failure of the drill bit. Therefore, to effectively improve the ability to fix the teeth, the carbide should have the optimal interference amount with the tooth hole to achieve a rational fit.
Measures to prevent DTH drill bit failure
Use high-quality materials
Choosing materials with good wear-resistant, high temperature-resistant, and impact-resistant performance to make DTH drill bits can improve their service life and stability.
Reasonable design of drill bit structure
Optimize the structural design of the drill bit to improve its bearing capacity and fracture resistance. Additionally, ensuring effective cooling and slag discharge is also prioritized.
Standardized operations
During usage, drilling operations must strictly adhere to the operating procedures to prevent damage to the drill bit due to improper handling.
Control drilling parameters
According to the geological conditions and engineering needs, set the drilling parameters reasonably to avoid damage to the drill bit caused by excessive drilling pressure and rotation speed.
Regular inspection and replacement of drill bits
Regularly inspecting the wear and damage of drill bits and promptly replacing severely worn ones are crucial measures to prevent failures. Additionally, during the drilling process, operators should attentively monitor the drill bit’s working condition and address any abnormalities promptly upon detection.
Development trends of DTH drill bit technology
With the advancement of science and technology and the improvement of engineering needs, DTH drill bit technology is also constantly developing. In the future, DTH drill bits will pay more attention to material selection and structure optimization to improve their wear resistance, impact resistance, and stability. At the same time, the development of intelligent and automated technology will also provide new means and methods for the maintenance and management of DTH drill bits.
Conclusion
The failure modes of DTH drill bits vary. But with a thorough understanding of the reasons behind their failures and the implementation of effective preventive measures, we can prolong their service life and enhance engineering efficiency. Additionally, with the continuous advancement of technology, the performance and stability of DTH drill bits will further improve. We expect that in the future engineering construction, DTH drill bits will play an even greater role and contribute significantly to human progress and development.
