As the power of hydraulic rock drills continues to increase, the diameter of the drilled hole also increases, and the usage of shoulder impact drilling tools and tubular drilling tools is also gradually expanding. At the same time, with the continuous maturity of friction welding technology, the friction welding process in the processing of long rod parts and parts with different performance requirements has more and more advantages.
What is Friction Welding?
Friction welding is an advanced material connection technology and manufacturing technology, is that use of the relative rotation between the welded parts while applying the appropriate axial pressure friction pressure for friction and the heat generated so that the weld contact surface near the high-temperature plastic zone, the friction surface of the plastic deformation of metal and flow, prevent the oxidation of metal, promote the mutual diffusion of welded metal atoms. When the temperature reaches the welding temperature, the relative rotation between the weldments stops quickly, the axial pressure is increased to the upsetting pressure, and the pressure is kept for some time appropriately so that the two weldments are welded to each other firmly. It is a solid-state connection technology, and its welding zone is a forged structure, so it is also known as “forging welding”.
Features of friction welding process
1. High quality. The friction welding zone is a forged structure, which can obtain a joint that is as strong as the base metal or even stronger than the base metal.
2. High efficiency. The welding time of each piece is counted in seconds, generally only tens of seconds, which is incomparable with other welding methods such as fusion welding and brazing.
3. Energy saving, material saving, and low consumption. No welding rod, flux, brazing filler metal, shielding gas, metal filling, or electrode consumption is required.
4. Good weldability and stable quality. It is especially suitable for the welding of dissimilar materials. Compared with other welding methods, friction welding has unique advantages, such as friction welding of steel and copper, steel and aluminum, steel and brass, etc.
5. Environmental protection, no pollution. The welding process does not produce fumes or harmful gases, no spatter, no arc, and sparks, no radiation.
Combined with its characteristics, the drill rod processed by friction welding technology reduces the difficulty of processing the threads at both ends, improves the quality of processing the threads at both ends and uses different materials and heat treatment processes for different parts of a component to improve the service life of drill rod and reduce costs.
Function of Friction Welding Technology in Drill Rod
The production of heavy drill rods requires a high geometry of the raw hollow steel, so it is selected separately before each production run. Before friction welding, hollow steel with too deviated core holes could not be produced as heavy drill rods and is recycled as scrap steel. Even if the selected hollow steel is qualified, it will produce out-of-size short material during the undercutting process and will only be recycled as scrap. Using the friction welding process can make use of them all.
The main form of failure of the heavy drill rod is the fatigue crack fracture at the root of the thread after the thread wears, while the rod body generally does not fracture after wear, and the strength requirement for the rod body is not high. Therefore, we can use partial core material for the rod body and hollow steel with more positive holes to process the threads, and finally weld them together by friction welding, and then after subsequent heat treatment to meet the requirements of the heavy drill rod production process, thus reducing the production cost and improving the rate of hollow steel into the material.
Application of Friction Welding Technology in Drill Rod
Application in heavy-duty MF rods
The failure of heavy-duty MF rods is mainly due to wear and fatigue fracture at the root of the thread, and only a small part of the drill rods are fatigue fractured from the thread or the rod body. Therefore, to improve the service life and rock drilling efficiency of the heavy-duty MF rod, the structure, and process of the heavy-duty MF rod must be designed: the rod body is made of 22CrNi3Mo hollow steel, and the threads at both ends are made of 22CrNi3Mo solid bar material. The threads at both ends are machined in short pieces to increase the spindle speed and feed rate of machining to obtain high machining efficiency and surface finish. The rod body is machined with the structure of a storage slot and finally welded together by friction.
Application in the guide rod
The guide rod requires a design structure with small center holes at both ends of the drill rod and a large center hole in the rod body. This center hole reducer structure is difficult to achieve by forming with a conventional hollow steel rolling process, and the friction welding process is the most reasonable way to weld the two end joints and the rod body together.
