The tapered drill rod is a hexagonal hollow rod with a shank structure. The shank is connected to the rock drilling equipment, and the head of the rod is a taper structure that can be connected with a tapered bit. Although its quality is very much related to the quality of brazing steel and smelting, whether the manufacturing process is reasonable and whether the forging equipment is advanced is also significant. In addition, the heat treatment process of the drill rod directly affects its quality and service life.
What is heat treatment?
Heat treatment is a process of heating, holding, and cooling solid metals or alloys in a medium to change the overall or surface structure to obtain the desired properties. According to the required properties, there are many types of heat treatment, and the process includes heating, heat preservation, and cooling in three stages.
According to different heating and cooling methods, the classification of heat treatment is as follows:
1. General heat treatment, including annealing, normalizing, quenching, and tempering.
2. Surface heat treatment, including induction heating surface quenching, flame heating surface quenching, laser heating surface quenching, and chemical-physical vapor deposition.
3. Chemical heat treatment, including carburizing, nitriding, and multi-component co-carburizing.
The importance of the heat treatment process
The tapered drill rod must withstand significant impact force and torque during operation and endure complex and variable geological conditions. Therefore, its materials must possess high strength, high hardness, and good toughness. The heat treatment process can significantly improve the mechanical properties of the drill rod by altering the material’s internal structure and enhancing its hardness, strength, wear resistance, and fatigue resistance. In turn, extends the drill rod’s service life and improves operational efficiency.
How to choose the heat treatment process of drill rod?
1. The basis for the selection of the heat treatment process of the drill rod is the steel grade. Different steel grades for different types of drill rods. In the production of drill rods, only by selecting the correct steel grade can it be possible to choose a heat treatment process that can give full play to the advantages of the steel grade to ensure the quality and service life of the drill rod. Different steel grades have different options for the best heat treatment process.
2. The selection of the heat treatment process of the drill rod is based on the basic requirements and the failure mechanism of the drill rod. The basic requirements of drill rods vary according to their own. The reasons for the failure of drill rods often include the unreasonable structural design of the drill rod or defects in the processing steps of the drilling process, mistakes in operation during use, etc. However, whether the heat treatment process is appropriate and whether there are quality problems during heat treatment are the essential factors. For the main reason for the failure of the drill rod, after excluding various external factors, select the best heat treatment process to ensure the internal quality.
3. The selection of the heat treatment process of the drill rod should follow the economy, rationality, and feasibility. The biggest feature of the drill rod is the significant limitations of the heat treatment due to it being too long. Often a heat treatment process cannot meet the basic requirements of each part of the drill rod. Only by selecting several heat treatment processes and treating each part separately, can the basic requirements of each part of the rod be guaranteed. So it needs to be considered.
4. The final criterion for the heat treatment process selection is the actual service life of the drill rod. The long service life in the mine rock drilling test is the most important basis for the heat treatment process selection.
To improve the product performance and service life of tapered drill rods, what are its heat treatment processes?
Commonly used heat treatment process for tapered drill rods
Normalizing
Normalizing is heating the drill rod to a temperature above the critical temperature (generally slightly above the A3 point) and then cooling it naturally in the air. It is used to reduce internal stresses, refine the organization, and improve strength and toughness.
The tapered drill rod is thin and long, and if quenched as a whole, it is easy to deform, the most commonly used heat treatment process for it is normalizing, and the most suitable is medium frequency induction normalizing. The normalizing of the tapered drill rod is carried out after forging the collar and sharpening the molding. The purpose of normalizing is mainly to refine the grains, eliminate the stress after forging, obtain high fatigue strength, good damping performance, and relatively uniform structure, as well as lay a good foundation for the shank adapter quenching. It can be seen that normalizing is one of the most important heat treatment processes for tapered drill rods.
Quenching
Quenching is the heat treatment process of heating the steel to a critical temperature (or above), holding heat for a definite time, being austenitized, then, obtaining the martensite by rapid cooling at a cooling rate greater than the critical cooling rate. Because the tapered drill rod shank has to withstand the high-frequency impact of the rock drill piston, and the hardness of the piston is usually in the range of HRC59-HRC62, the shank adapter must be quenching.
Tempering
The drill rod cannot be used directly after quenching and must be tempered. Tempering is a heat treatment process in which the drill rod is heated to a temperature below Ac1, held for a definite time, and then cooled to room temperature to eliminate internal stress. Then we can obtain the required structure and properties after quenching.
Stabilization treatment
It is used to reduce the stress and deformation of the tapered drill rod during use and improve its stability.
Optimization of the heat treatment process
Optimizing the heat treatment process is crucial for enhancing the performance of drill rods. By adjusting heat treatment parameters, upgrading heat treatment equipment, and adopting advanced heat treatment technologies, the performance stability and service life of the drill rod can be further improved. For example, using advanced heat treatment equipment and control technology allows for more precise temperature control and uniform heating effects. Additionally, optimizing cooling methods and tempering processes can further eliminate internal stress, enhancing the toughness and plasticity of the drill rod.
Conclusion
The commonly used heat treatment process for tapered drill rods is crucial for improving their performance and extending their service life. The choice of process is influenced by factors such as the drill rod material, application scenarios, and performance requirements. Therefore, thorough material testing and process design should be conducted before heat treatment. Additionally, selecting the correct heat treatment process and equipment is essential. To ensure the final product meets the expected requirements, drill rod manufacturers must choose an appropriate heat treatment process.
With the continuous advancement of material science and heat treatment technology, we can expect future tapered drill rods to exhibit better performance and greater adaptability to complex and changing engineering needs. For engineers and technicians in related industries, an in-depth understanding and proficiency in these heat treatment processes will undoubtedly provide greater convenience and benefits to their work.
