What are the Quality Problems of Rock Drill Bits?

Table of Contents

Rock drill bits are commonly used drilling tools in engineering construction, and their quality directly affects the efficiency and safety of drilling operations. However, during actual use, various quality problems may occur with rock drill bits, which will not only affect their service life but may also cause safety accidents. This article will analyze the possible quality problems of rock drill bits and help you better understand and deal with these problems.

rock drill bits

Possible quality problems with rock drill bits

Fracture and fall-off of cemented carbides

The fracture and fall-off of cemented carbides are the main form of drill bit failure, which is related to welding residual stress in the drill bit, lack of welding, low brazing strength, and other reasons. There are sometimes stresses in the weld or cemented carbide after welding, and the existence of these stresses has a great impact on the quality after welding. When there are occasional defects at the sharp corners of the cemented carbide or in the inner layer near the surface, it will also cause local thermal stress concentration, and the thermal stress at this time will be magnified by 2 to 3 times. In use, it will often cause the carbides to break, so it should be paid attention to.

rock drill bit

Low brazing strength

The brazing strength of rock drill bit is an important criterion to measure the quality of welding, and the factors affecting it are mainly the weld gap. During the welding process, if the gap between the weld seam is too small, carbides and steel body in some places will even be in close contact, so that the solder cannot spread to the entire welding surface after melting, reducing the strength of the joint; when the gap is too large, the support of the base body to the weld after welding is weakened, as well as the large gap in the solder is columnar casting organization, coarse grain, loose organization, strength, and toughness is poor, resulting in a decrease in the strength of the joint.

The cause of residual stress

Residual stress caused by difference in thermal expansion coefficient

The thermal expansion coefficient of cemented carbide and steel bodies is very different. In the brazing temperature range, the coefficient of thermal expansion of carbide is about half that of the steel body. The difference in shrinkage during post-weld cooling will generate enormous stresses in the weld and carbide and steel body on both sides of the weld. When this welding stress is serious, it can crack the cemented carbide and the weld, causing rock drill bit to fall off and break when it is working.

Residual stress caused by uneven temperature

During the brazing process, because of the phenomenon of thermal expansion and cold contraction, the temperature difference between the various parts of the solid material will cause thermal stress inside the material, the size of this thermal stress is related to the material’s elastic modulus thermal expansion coefficient material temperature difference. As the temperature difference increases, the thermal stress also increases, because the carbide has good mechanical properties, the temperature difference is large, and it is not enough to cause cracks in the carbide. However, during welding, the carbide will be integrated with the drill bit through the solder, and the thermal stress of the shell is also added to the carbide blade. In this case, the thermal stress of carbide blade is twice that of the unwelded state. In addition, if the local heating of drill bit is too fast or too high during welding, or the local cooling is too fast, it is possible to make the carbide have too much thermal stress locally.

rock drill bit

Measures to reduce stress

1. Control the heating and cooling speed to avoid excessive temperature differences. It is very important to control the cooling speed after welding during brazing.

2. Take necessary measures when heating and cooling to prevent local overheating or rapid cooling.

3. Strive for uniform heating, shorten the solder liquefaction process as much as possible, avoid volatilization of low melting point, produce weak tissue and slag inclusion in pores, and reduce oxidation of the brazing surface.

4. Appropriately increasing the weld gap can reduce the stress added to the cemented carbide.

Uneven hardness

The hardness of a rock drill bit has an essential impact on its drilling ability and wear resistance. If the hardness of the drill bit is uneven, it will lead to uneven stress during drilling operations, which may easily lead to drilling deflection, cutting-edge cracking, etc. It will not only affect the drilling quality but also shorten the service life of the drill bit.

Poor heat treatment

Heat treatment is a critical link to improve the hardness and durability of rock drill bits. Improper heat treatment will result in insufficient or excessive hardness of drill bit, making it prone to brittle fracture or premature wear. It will not only affect the service life of the drill bit but may also cause safety accidents.

Poor material quality

The material quality of a rock drill bit significantly influences its performance. If low-quality materials are employed in its construction, the drill bit’s hardness, strength, and durability may be inadequate, making it susceptible to breakage or premature wear. It not only hampers project progress but also poses a potential threat to the safety of operators.

Poor surface quality

The surface quality of rock drill bits significantly impacts drilling operations. Defects like pores and slag inclusions on the drill bit’s surface diminish its wear and impact resistance, affecting its overall service life. Additionally, these defects can lead to stress concentration, heightening the risk of drill bit brittleness.

Dimensional accuracy does not meet the requirements

The dimensional accuracy of a rock drill bit is crucial to its performance. If the diameter, length, and other parameters of the drill bit deviate from the design requirements, it will lead to problems such as inaccurate drilling size and reduced drilling efficiency. Failing to meet dimensional accuracy requirements can also lead to increased friction and impact between the drill bit and rocks or hard materials, heightening the risk of wear and brittleness of the cutting edge.

Factors affecting the quality of rock drill bits

Material quality

High-quality materials can provide better strength, toughness, and wear resistance, improving performance and service life of rock drill bits. Therefore, selecting high-quality raw materials and reasonable manufacturing processes are important measures to improve the quality of rock drill bits.

Machining precision

High-precision machining can ensure the accuracy and consistency of the dimensions of each part of the drill bit, thereby reducing friction and impact during use and extending its service life. Therefore, improving processing accuracy is also an important measure to improve the quality of rock drill bits.

Heat treatment process

A reasonable heat treatment process can improve the microstructure and mechanical properties of the material, thereby improving the wear resistance, toughness, and impact resistance of rock drill bits. Therefore, optimizing the heat treatment process is also an effective way to improve the quality of rock drill bits.

Storage and usage environment

Storing and using rock drill bits in unfavorable environments, such as high humidity and elevated temperatures, can readily lead to issues like rust and corrosion. These problems can adversely impact the performance and service life of the drill bits. Therefore, maintaining a dry and clean storage environment and avoiding unfavorable environments such as high temperature and humidity are also important measures to improve the quality of rock drill bits.

How to improve the quality of rock drill bits

Choose quality materials

Selecting high-quality materials is crucial for enhancing the quality of rock drill bits. Opting for materials characterized by high strength, wear resistance, and toughness, such as high carbon steel and alloy steel can significantly improve the performance and service life of the rock drill bit. Additionally, it is essential to pay attention to the internal quality of the material to prevent defects such as pores and slag inclusions.

Improve machining accuracy

The use of advanced processing equipment and techniques, such as CNC machine tools and laser cutting can ensure the accuracy and consistency of the dimensions of each part of the rock drill bit and reduce errors and defects. At the same time, strengthening quality inspection and control during processing is also an important measure to improve processing accuracy.

Optimize the heat treatment process

A reasonable heat treatment process can improve the mechanical properties and microstructure of the material, thereby improving the wear resistance, toughness, and impact resistance of rock drill bits. The best treatment effect can be obtained through continuous testing and optimization of heat treatment process parameters, such as quenching temperature and tempering time. At the same time, the staff should pay attention to quality control and temperature control in the heat treatment process to avoid overcooking, decarburization, and other problems.

Strengthen storage and usage management

Good storage and usage management can extend the service life of rock drill bits. Maintain a dry and clean storage environment to avoid damage to rock drill bits caused by moisture, rain, high temperature, and other unfavorable environments. During use, personnel should handle the equipment with care, avoiding collisions and falls to prevent damage and deformation. At the same time, regular inspection and maintenance can also detect and deal with it in time.

The necessity and significance of studying the quality issues of rock drill bits


  • Improve engineering efficiency: as a critical component in drilling and mining operations, the quality of rock drill bits affects operating efficiency. If the rock drill bit has quality problems, it may lead to reduced drilling speed, unstable drilling quality, and even interruptions in operations, seriously affecting the project’s progress. Therefore, studying the quality issues of rock drill bits is an inevitable requirement to improve engineering efficiency.
  • Ensure operation safety: the unstable quality of rock drill bits may cause a series of safety problems, such as bit breakage and falling off, which not only pose a threat to the personal safety of operators but may also cause damage to equipment. Therefore, an in-depth study of the quality issues of rock drill bits is of great significance for preventing safety accidents and ensuring operating safety.
  • Reduce economic costs: quality problems with rock drill bits may lead to frequent replacement and repair, which not only increases operating costs but may also affect the overall economic benefits of the project. Studying the quality problems of rock drill bits, identifying the root causes, and proposing valid solutions can extend the bit’s service life, reduce replacement and maintenance costs, and enhance the project’s economic benefits.


  • Promote technological progress: research on the quality issues of rock drill bits will promote technological innovation and progress in related fields. By optimizing material selection, refining manufacturing processes, and enhancing structural design, the performance and quality of rock drill bits can be continuously improved, thereby advancing drilling and mining technology.
  • Improve industry competitiveness: high-quality rock drill bits are a key factor in improving project efficiency, ensuring operating safety, and reducing economic costs. Studying and resolving quality issues with rock drill bits can enhance the competitiveness of related enterprises and industries, enabling them to capture more market share.
  • Promote sustainable development: as society increasingly prioritizes environmental protection and sustainable development, the standards for drilling and mining operations are also rising. Studying the quality issues of rock drill bits will help improve operating efficiency and quality and also help reduce energy consumption and environmental pollution, promoting the sustainable development of the drilling and mining industry.


Quality issues with rock drill bits can impact their proper operation and performance. Therefore, it is essential to strengthen quality inspection and maintenance during actual use. At the same time, to improve the quality and performance of rock drill bits, it is recommended to choose reliable suppliers for procurement and strengthen training and technical explanation of operators to ensure that they use and maintain the bits correctly.

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