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This post was last edited by B0SS on 2018-8-30 at 18:10. Mine hydraulic props are support components widely used in coal mines today; in large and medium-sized coal mining enterprises in China, the usage rate of hydraulic props in coal mining faces has exceeded 50%. However, due to the harsh underground conditions, severe corrosion and wear on the surface of the hydraulic props occur, leading to their failure. Currently, hydraulic struts achieve surface corrosion protection through chromium plating. Due to its poor wear resistance, the lifespan of the chromium plating is only 1.0–1.5 years; it tends to peel and flake off, which affects the performance of hydraulic struts. Additionally, the chromium plating process causes significant environmental pollution. Therefore, research on surface strengthening techniques for hydraulic struts is receiving increasing attention. Surface strengthening of hydraulic struts is usually achieved through cold welding, composite electrodeposition, and electrospraying. In recent years, great progress has been made in plasma powder surfacing technology in our country. This technology is a surface treatment method used to improve the properties of a substrate; alloy powder is applied to the surface of the substrate using various filling methods. Under the action of a plasma beam, the applied powder is rapidly heated and melted, and after rapid solidification, it forms a metallurgical surface coating with properties such as corrosion resistance, wear resistance, and heat resistance. 1. Principle of plasma powder surfacing: Plasma powder surfacing uses a plasma arc as the heat source; the high temperature generated by this arc is used to rapidly heat the alloy powder and the surface of the base material, causing them to melt, mix, diffuse, and solidify together. After the plasma beam moves away, self-cooling occurs, resulting in the formation of a high-performance alloy layer that enhances the strength and hardness of the part’s surface. Due to the high arc temperature, high heat transfer rate, good stability, and strong controllability over the depth of melting of the plasma arc, it is possible to freely adjust the thickness, width, and hardness of the surfaced layer by adjusting the relevant surfacing parameters. After plasma powder surfacing, a fused interface is formed between the base material and the surfacing material, resulting in high bonding strength ； The surfacing layer has a dense structure, offering good corrosion and wear resistance ； The dilution of the base material and the surfacing material is reduced, resulting in minimal changes in the material properties ； Using powder as a surfacing material enhances the selectivity in alloy design, particularly enabling the seamless surfacing of refractory materials and improving the wear resistance, high-temperature resistance, and corrosion resistance of the workpiece. 2. Advantages of plasma powder cladding: Compared with traditional surface modification techniques such as thermal spraying, electroless plating, plasma spraying, and vapor deposition, plasma powder cladding technology has the following advantages: 2.1 It can be applied to a wide range of material systems, and is particularly suitable for cladding high-melting-point alloys on the surfaces of low-melting-point metals to produce a dense metallurgically bonded coating ； 2.2 The heat-affected zone is small, the workpiece is less prone to deformation, and the yield rate of surfacing operations is high ； 2.3 The plasma surfacing alloy coating features stable surface properties, controllable composition and thickness, as well as a flexible process that facilitates automated production ； 2.4 Local areas on the surface of the formed workpiece can be surfaced by welding ； 2.5 The surface strengthening layer has a dense structure, high hardness, excellent quality, and a smooth surface; it also possesses high toughness, strength, wear resistance, and corrosion resistance ； 2.6 Plasma surfacing technology falls under the category of green remanufacturing; the processing process is pollution-free and the working conditions are favorable ； 2.7 Plasma surfacing has a fast deposition speed and a low dilution rate; the dilution rate in plasma surfacing can be controlled at 5%-10%, or even lower. 3 Surface surfacing repair process for columns 3.1 The processing equipment used is the DML-V03BD plasma powder surfacing system to repair the surface of hydraulic columns. This device is mainly composed of a plasma generator, a surfacing gun, powder feeding control, a machining machine tool, and other components; it is easy to operate and greatly improves production efficiency. 3.2 Preliminary preparations include understanding the operating conditions to determine the cause of pillar failure, knowing the material of the workpiece, as well as the dimensions and shape of the area to be repaired; additionally, it involves understanding the repair techniques and the required performance standards. There are many ways in which hydraulics can cause the failure of pillars, primarily due to various types of wear, such as abrasive wear, corrosive wear, and fatigue wear. On this basis, the repair plan is determined, including the surface treatment of the workpiece before repair (degreasing, rust removal), the selection of alloy materials, the surfacing welding current, the powder feeding speed, the spindle rotation speed, the ion gas flow rate, etc. In this experiment, nickel-based self-dissolving alloy powder with grade NI45 was used as the plasma surfacing material. These powder series are suitable for workpieces that require local wear resistance, corrosion resistance, and fatigue resistance. They enable the formation of a nickel-based coating with a dense structure, free from pores, inclusions, or cracks, and possessing high hardness; this coating is metallurgically bonded to the substrate. 3.3 Repair process: The plasma surfacing equipment uses high-purity argon as both the ionizing gas and the shielding gas. To ensure operation over extended periods of time, the equipment is equipped with a chiller unit; distilled water is generally used as the cooling fluid to remove the heat generated by the plasma generator during operation, thereby ensuring the stable functioning of the surfacing gun. During the repair process, continuously monitor the conditions of the surfacing, including the thickness of the surfacing layer, its flatness, and the overlap rate. The DML-V03BD surfacing equipment allows for the adjustment of current and powder feeding speed at any time during the surfacing process, thereby controlling the thickness of the surfaced layer and the quality of the surfacing result. The process parameters for surfacing welding are as follows: welding current (A): 120~130 ； Ion gas flow rate (NL/min): 1.5–1.8 Shield gas flow rate (NL/min): 5–10 ； Welding speed (m/min): 0.9–1.1. After the surfacing process is completed, it is necessary to inspect the appearance quality of the surfaced layer for any defects such as cracks or pores. A portable hardness tester is used to initially determine the hardness of the surfaced layer, and the dimensional accuracy and positional accuracy of the workpiece are also checked. Once the requirements are met, the pillars are processed, including turning and grinding, to achieve the final dimensions and precision of the workpiece. 3.5 Welding results: Tests have shown that the plasma welding technique enables the surface hardness of the alloy reinforcement layer applied to mining hydraulic props to reach HRC 40, thereby significantly improving the corrosion resistance, wear resistance, and other mechanical properties of these props. 4 Conclusion Through testing and customer feedback, plasma powder surfacing technology has achieved great success in the hydraulic strut repair industry. Since plasma powder cladding is a pollution-free process that takes place in an atmospheric environment and is simple to operate, it results in a significant improvement in the quality of the parts after cladding. This allows for reduced replacement times for hydraulic struts, thereby ensuring higher production efficiency and saving substantial amounts of money, which holds great significance for fostering a society focused on conservation.