Compared with other rock drilling tools, threaded extension rods have many varieties, complete specifications, large quantities, and good economic benefits. They are widely used in rock drilling projects. Therefore, making high-quality threaded extension rods can ensure reliability, durability, and safety.
Basic requirements for threaded extension rods
The combination of high fatigue strength and fracture toughness
The fracture of threaded extension rods is mainly fatigue fracture. The main reason is that the drill rods have to bear the high-frequency impact force and axial thrust of the rock drill. Moreover, the threaded extension rod is a long and thin rod, the drill rods often sustain bending stress in oblique rock drilling and horizontal rock drilling, because of the influence of the self-weight of the drill tool group. Therefore, the material of the threaded extension rods must have high fatigue strength and fracture toughness.
Good elasticity and wear resistance
The drill rod often works under different bending states, the process of rock drilling, whether it is horizontal, vertical, or oblique operations, due to the change of the rock drill thrust, the inhomogeneity of the rock, or the existence of cracks, holes, and incorrect operation. If the bending condition is severe or the drill rods’ elasticity is not good, it will cause the drill rods to bend and break. Cause early failure. Therefore, the drill rods must have good elasticity.
The threaded structure of the two ends of the threaded extension rods is an important part of connecting the whole set of rock drill tools and transmitting the rock drilling stress. The threaded part is the most important part of the failure of the threaded extension rods, and its failure mechanism is the result of fretting wear and impact wear successively. Therefore, the wear resistance of the threaded part is often the determining factor for the life of the threaded extension rod.
Good corrosion resistance
The main factor of fatigue fracture in drill rods is inner hole corrosion of threaded extension rods due to the combined action of high frequency and high stress and water (often acidic water). Therefore, the threaded extension rods must have good waterproof corrosion resistance.
High straightness and rigidity
The straightness and rigidity of the threaded extension rod are important guarantees for high rock drilling efficiency. In rock drilling, the drill rod should work under the rotating state of 250r/min. If the straightness is low or the rigidity is insufficient, the drill rods will work under the eccentric blow, and part of the rock drilling energy is lost. While bending stress is produced, which increases the probability of the drill rods’ fatigue failure. The higher the straightness and the better the rigidity of the drill rod, the higher the efficiency of transferring the rock drilling stress, the faster speed of the rock drilling .
Good structural design
The threaded extension rods are high-frequency and high-stress transfer rods, the section change of the component can cause stress change and stress concentration, the greater the section change, the lower the efficiency of stress transmission and the greater the failure stress. Therefore, the principle of designing is avoiding or reducing excessive section changes as much as possible to guarantee good structure.
Thread design and lubrication
The design of threaded connections should comply with standard specifications, such as ISO standards. Thread parameters include pitch, thread angle, radial clearance, etc. Reasonable design of these parameters can ensure the tightness and load-bearing capacity of the connection. During assembly, proper use of lubricants reduces thread friction, helps make assembly easier and protects the threads from damage.
Regular maintenance
Threaded extension rods require regular maintenance and inspection to ensure their performance and safety. Check threads for wear and corrosion and replace or repair them if necessary.
Other requirements
- Continuously improve the structure of rock drilling machinery to reduce the destructive stress acting on the drill rod.
- Improve the comprehensive mechanical properties of the drill rod material and the production process level of hollow steel, and reduce the internal and external defects of the drill rod.
- Correct operation and management during rock drilling, good cooperation between drilling tools, and their respective processing accuracy.
A complex stress state and harsh working conditions affect the service life of threaded extension rods. Therefore, to improve the service life of the threaded extension rod, a series of requirements and steps need to be strictly followed when making them to ensure the quality, reliability, and durability of its connection. Whether it is material selection, processing technology, or quality control, a high degree of expertise and rigorous operations are required to meet the needs of the engineering and manufacturing fields.
