China’s surfacing industry status
The development history of surfacing
Surfacing is a process in which a layer of wear-resistant or corrosion-resistant metal is applied to the surface of a part by welding to improve the surface hardness of the workpiece or to repair an old part that is unqualified. China’s surfacing technology originated in the late 1950s. In the early stage of development, it was mainly used to repair the shape and size of parts. In the 1960s, the shape and shape were combined with surface strengthening and surface modification. The application field of surfacing technology was further expanded after the reform and opening up. The surfacing technology has expanded from the repair industry to the manufacturing industry. The application and development of flux-cored wire in the 1990s enabled some high-alloy and high-hardness surfacing materials to be made into a wide range of automated production welding wires, greatly improving surfacing. The level of automation.
The common surfacing industry
(1) Roll industry
Rolls are important parts of a rolling mill’s rolling mill. Rolling steel by the pressure generated when one or a group of rolls are rolled is an important consumable part that determines the efficiency of the rolling mill and the quality of the rolled material. Fast roll wear In order to obtain a good service life, a surfacing method was used in the 1970s to improve the surface hardness of the roll and obtain a higher service life. Rolling not only uses surfacing in production to obtain high performance, but also can be used to repair rolls when the working time of the rolls is long, resulting in irregular surface or oversize, which prolongs the service life of the rolls. And reduce manufacturing costs.
The surfacing methods of the rolls include submerged arc automatic welding, electroslag welding, gas shielded welding, etc. Among them, submerged arc automatic welding is the most widely used. Depending on the working conditions of the rolls, the choice of surfacing methods is different, and the selected surfacing materials are not the same. In addition to ensuring the surface hardness, wear resistance, corrosion resistance, impact resistance and the like are also considered. For example, the cold rolled roll (9Cr2Mo material) has a flux-cored wire hardness ≥HRC62 or higher, and the hot-rolled backup roll has an average hardness of HSD74 (converted to Rockwell hardness of HRC55).
(2) Valve industry
With the development of modern technology, more and more valves work in high temperature, high pressure, high corrosion, high wear resistance, etc. In order to improve the wear resistance, high temperature resistance and corrosion resistance of the valve, the factory generally uses surfacing. Technology to increase the hardness of the valve housing or internals to improve the wear resistance and service life of the valve.
Commonly used valve surfacing techniques are aerobic-acetylene flame surfacing, manual arc welding and plasma arc welding. Surfacing materials are iron-based, nickel-based, cobalt-based, nickel-based and other surfacing materials. If you want to obtain the valve surfacing surface that meets the design and application requirements, it must be strictly in accordance with the development of operating instructions and operational requirements. Select the appropriate welding material according to the base metal (work material) and welding method. For example, the oxygen-acetylene flame surfacing technique is used, and the hardness of the cobalt-based alloy Stellite 12 after surfacing is HRC48. If the tungsten carbide surfacing electrode is used for surfacing, the hardness can reach above HRC60.
(3) Petroleum industry
With the emergence of ultra-deep wells, high-angle wells and offshore oil rigs. The ensuing problem is that the drilling time is greatly extended, and the lateral force of the drill pipe acting on the casing is continuously increased, which causes the wear problem of the drill pipe and the casing to be more prominent. The oil drill pipe joint is a key component in the oil drilling process, and with the continuous development of modern drilling technology, the requirements for the wear resistance of the drill pipe joint are continuously improved.Surfacing welding is often used to improve the wear resistance and service life of oil drill pipe joints.
The welding method commonly used in oil drill pipe joints is the open-arc welding flux-cored wire, plasma spray-welded alloy wire, etc. If the arc-welded flux-cored wire is used, the hardness is generally around HRC60.
How to process the workpiece after surfacing
The workpiece after surfacing is generally uneven, there are weld defects such as pores and slag inclusions, and the hardness of most workpieces after surfacing is above HRC45. The commonly used processing methods are grinding and turning.
Grinding method: According to different workpieces, choose the appropriate grinding machine for grinding. The unilateral margin of the workpiece is generally 2-3mm. The processing efficiency of the grinding machine is too low. Generally, the grinding allowance is 0.2-0.3mm. The artifact between. And for large surfacing parts due to the large size, exceeding the processing range of the grinding machine, the grinding machine can only process small piles of weldments and can obtain good precision.
Turning method: Turning is the most common way of processing surfacing parts. Since most of the surfacing parts are uneven, it is easy to vibrate during the process, so the tool must be selected with excellent impact resistance and wear resistance. High efficiency and low cost can only be achieved by choosing the right tool material.
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