Rock drilling tools are necessary for mining, energy construction, foundation engineering construction, traffic road development, and other construction engineering fields. It has many types, and the drill rod, as one of its main products, is a key component of rock drilling equipment. Although the drill rod is a slender rod, it is subjected to various cyclic stresses imposed by high-frequency and high-impact power rock drills under conditions of severe wear and tear and with corrosive media. Therefore, the service life of drill rods is often short, and how to improve the service life of drill rods has become an essential issue for efficient and low-consumption rock drilling.
Many factors affect the service life of the drill rod, such as material, heat treatment process, environment, and other factors. The failure forms of the drill rod caused by them are also different. Among them, the fracture of the drill rod is the most prominent factor that affects the service life of the drill rod.
The main factors leading to the breakage of the drill rod
Fatigue damage
Fatigue damage generally begins at cracks, defects, or the lowest hardness. Although these cracks or other defects are too small to be observed with the naked eye, they suddenly break along the fatigue section under the long-term action of cyclic repeated loads until the remaining section is insufficient to support the load.
In addition, the internal defects of the drill rod in steel type, smelting, rolling, geometric structure and its parameters, forging, machining, heat treatment, etc., as well as additional bending stress, mechanical wear, acid water corrosion, and unfavorable rock drilling models and lithology, inferior drill bit, incorrect operation, etc., will aggravate this fracture.
Forging and heat treatment defects
When the drill bit and shank adapter are forged and heat treated, a transition zone is formed between the heated part and the unheated drill rod. This zone is the lowest hardness and strength, so it is also the easiest to break.
The problem of rock drill steel
The rock drill steel is cast into ingots from the steel furnace, then formed in the rolling mill, which may produce more or fewer defects, and even produce a decarburized layer with lower hardness. Another indicator of the quality of rock drill steel is its heat treatment state. After being formed, the rock drill steel grain is coarser, organization disorder, and there is high residual stress. Therefore, making it into a drill rod will inevitably affect its strength and life.
To fundamentally solve the factors that affect the service life of the drill rod is inseparable from the research on these factors. In most cases, these factors are related to the internal and external factors of the drill rod, and we can improve the service life of the rod accordingly.
How to improve the service life of the drill rod?
Choose the suitable material
The material selection of drill rods is very important. High-quality materials can provide better strength and corrosion resistance, thereby extending the service life of drill rods.
Control the processing quality
The machining quality of the drill rod is crucial to its service life. Ensure that machining accuracy and surface quality are strictly controlled in manufacturing to avoid defects and cracks. Fine processing can improve the strength and fatigue resistance of the drill rod and reduce the risk of failure.
Proper heat treatment
Heat treatment can improve the organization and performance of the drill rod. Heat treatment methods such as quenching, tempering, and surface treatment can increase the drill rods’ hardness and wear resistance and improve their bearing capacity and fatigue resistance.
Regular maintenance and lubrication
Regular maintenance and lubrication of drill rods is the key to maintaining their proper operation and extending their service life. Clean the surface of the drill rod from dust and dirt and inspect it periodically for wear or corrosion. The use of proper lubricants can reduce friction and wear and improve the working efficiency and service life of the drill rod.
Reasonable design and use
Factors such as working loads, stress concentrations, and vibration need to be considered when designing and using drill rods. Proper design can reduce stress concentration and vibration, thus reducing fatigue damage to the drill rod. At the same time, avoid overloading the drill rod and ensure that it operates within the rated working range.
Avoid over-tightening
Avoid overtightening when installing and tightening drill rods. Overtightening can lead to stress concentrations and deformation, increasing the risk of fatigue failure of the drill rod. Avoid this by using the correct fastening force and fastening method.
Pay attention to environmental factors
Environmental factors will also have an impact on the service life of the drill rod. Avoid exposure to moisture, corrosion, or high temperatures, which may accelerate the failure of the drill rod. Use materials with better corrosion resistance or take appropriate protective measures in harsh environments.
How to maximize the service life of drill rods?
Of course, if we want to maximize the service life of the drill rod, we must adapt the drill rod to the properties of the drill bit, rock drill, and rock. The specific methods are as follows.
Select the rock drill and drill rod according to the type of rock
To ensure long enough service life when drilling hard rock, the drill rod must be made of alloy hollow steel with high fatigue strength. The type of rock drill also has an important influence on the service life of the drill rod. A light rock drill with a high impact frequency should be used to drill hard rock. Rock drill with low frequency and high impact power should be used for rock drilling with high wear resistance. In addition, it is also necessary to avoid the use of a small section drill rod that is unfit for the type of drill, to avoid excessive bending and early fracture of the drill rod.
Select the drill rod with the appropriate length according to the blast hole depth
When drilling deep blast holes, avoid using the same long drill rod from opening to end. Because, when a long drill rod is used to open the hole, the unsupported part of the drill rod is long, easy to bend, and bending stress is also larger.
Select the appropriate drill bit and pay attention to the wear degree of the drill bit
Do not select the drill bits with a large section that is not suitable for the drill rod. Otherwise, the drill rod will be overstressed and easily broken early.
The worn rock drill sleeves must be replaced in time
When using the worn drill sleeve, the gap between the shank adapter and the drill sleeve increases, and the shank adapter is skewed, making the impact of the piston an inclined impact, resulting in an eccentric load, causing additional stress, which does not only reduce the drilling speed but also reduces the drill rod service life.
To maintain proper thrust
When the rock is hard, the drilling speed is slow and the thrust is often insufficient. When the thrust is too large, it will cause large bending stress. Therefore, too large or too small thrusts can accelerate the fatigue failure process of the drill rod.
Precautions for using air leg rock drill
It is necessary to prevent the axis of the rock drill and the drill rod from being inconsistent due to improper operation, causing eccentricity, resulting in increased bending stress on the drill rod and accelerated drill rod fatigue; After opening the hole, let the rock drill hang on the drill rod for a while, to aovid the drill rod to bend.
Avoid scratches and rust on the surface of the drill rod, resulting in early fracture of the drill rod.
In the process of use, whether it is replacing the drill bit or when the drill is stuck, it is necessary to avoid the trauma caused by hitting the drill rod;
To avoid corrosion on the surface of the drill rod and the inner wall, the drill rod should be placed in a relatively dry room;
The drill rod that is not used immediately should be avoided in the well;
The inner and outer surfaces of the wet drill rod should be blown to dry completely after use.
Straighten the bent drill rod in time
Hammering should be avoided when correcting, and a hydraulic straightening machine can be used.
Conclusion
Improving the service life of drill rods requires overall consideration of factors such as material selection, processing quality, heat treatment, maintenance and lubrication, rational design, and use. Through reasonable measures and methods, the service life of drill rods can be extended to the maximum extent, and the reliability and efficiency of equipment can be improved, thus improving the economic benefits of enterprises.
