During the drilling, the drill rod not only bears the tension, compression, bending, and torsional cyclic stresses imposed by the hydraulic rock drill with high frequency and impact energy but also to huge impact load. In addition, the service conditions of drill rods are very harsh, and there are differences in the production process of drill rod manufacturers, so its service life is uneven. Improving the service life of drill rods can both improve rock drilling production efficiency and help enterprises save costs. Therefore, enterprises need to understand the factors that affect the quality stability of drill rods.

The factors affecting the quality stability of drill rods are mainly materials, processes, and equipment.

1. Materials

Drill rod is a tool working under dynamic load conditions and must have high fatigue resistance, wear resistance, and impact resistance, and these properties are related to the steel type, steel purity, and organizational uniformity. Therefore, the quality of steel for drill rod is directly related to the service life of drill rod.

2. Equipment

The equipment required to produce drill rods includes straightening machines, lathes, upsetting machines, friction welding, milling machines, thread lathes, well carburizing furnaces, well tempering furnaces, internal and external shot blasting machines, air-cooled quenching equipment, anti-corrosion treatment equipment.

① There are many manufacturers of straightening machines, lathes, upsetting machines, friction welding, milling machines, and internal and external shot blasting machines, and the equipment is relatively mature. As long as the process is reasonable and the personnel is skilled in operation, there are no problems.

②The quality of thread processing has a greater impact on the drill rod. The use of imported lathes to process threads with better finish and standardized thread shape has a certain effect on quality improvement.

③Rock drilling tools’ anti-corrosion treatment is also very effective in improving the quality of drill rods. The smoothness of circulation in the well-carburizing furnace directly affects the depth of the carbon layer, the surface carbon content, and the uniformity of the metallographic organization of drill rod, which is very critical to the quality of drill rod. The uniformity of drill rods in the furnace and the uniformity of different drill rods at the same height in the furnace also have a direct influence on the quenching of rods later.

3. Process factors

Processes that have a greater impact on the quality uniformity of drill rods include the carburizing process and the secondary quenching process.

①    Carburizing process

For deep well type carburizing furnace, only by ensuring the uniformity of temperature and carbon potential in the furnace can the uniformity of the carbon layer depth and surface carbon concentration of drill rod be guaranteed.

② Secondary quenching treatment

The drill rod after high-temperature tempering is placed in an 8-meter well-type carburizing furnace for secondary heating and quenching, protected by methanol and propane atmosphere, to ensure that the temperature and carbon potential in the furnace is controlled within a reasonable range. After the carbon potential is reached, keep it warm for 1 hour and put it in an air-cooled quenching device for quenching. After it is released from the furnace, it is quickly hoisted into the air-cooled tower with adjusted wind speed by a crane, and the temperature is measured inside and outside the drill rod with a temperature measuring gun and an induction thermocouple to ensure the cooling rate of drill rod. After the temperature is reached, adjust the frequency of the variable frequency centrifugal fan immediately, and measure the temperature inside and outside the drill rod with a temperature measuring gun and an induction thermocouple to ensure that the drill rod cools to room temperature at a cooling rate of ≥3°C/s. After tempering, the organization is tested, the hardness of the drill rod surface and the heart can be controlled in 1HRC, and the upper middle and lower metallographic organization is uniform to achieve the uniformity of the hardness and metallographic organization of the second quenching drill rod.