Hard-Facing Technology
Hardfacing materials are hard, wear-resistant materials applied on a worn or new component surface by hard-facing technologies such as built-up welding (PTA, laser cladding, oxyacetylene surfacing), spray&fuse welding, infiltration and thermal spraying to reduce wear. These products not only significantly enhance the wear resistance, corrosion resistance, heat resistance, impact resistance and other properties of the component surface, but also serve special functional coatings such as sealing, insulation and heat insulation. It can extend the service life of the components significantly, reduce consumption & production costs, and improve work efficiency.
Oxyacetylene Flame Welding
Oxyacetylene flame welding is the most common method of build-up welding. This process can melt the welding-rod by oxyacetylene flame and coat it onto the surface of the workpiece to form a hard layer. Oxygen, acetylene and flame gun are needed for this method. It also requires that the surface of the workpiece must be cleaned up and the workpiece must be preheated to an appropriate temperature before welding. In addition, it’s important to minimize the weld pool during surfacing, so as to avoid the deposition of tungsten carbide particles to the bottom of the weld layer. Furthermore, if the welding pool is too large, it is easy for the welding layer to have pores.
Plasma Transfer Arc Welding
Plasma transfer arc welding (PTA) can be used for processing special valves, drill bits, mining parts, mold, shaft, and others. Although this built-up welding equipment is relatively complex and the cost is relatively high, the thickness of the welding layer can be controlled, and the grains of the welding layer are uniform and neat. Adjusting and controlling the welding parameters can be complex, so the operator must have high operation skills.
High Velocity Oxygen Fuel (HVOF)
High Velocity Oxygen Fuel (HVOF) coating is a thermal spray coating process, which is used to improve or restore a component's surface (properties or geometry). This surface engineering technique better enables life extension of equipment by increasing erosion and wear resistance, and corrosion protection. HVOF spraying works by mixing fluid fuel and oxygen, which is fed into a combustion chamber and ignited. The resultant gas has an extremely high temperature and pressure, which is ejected through a nozzle at supersonic speeds. To the high velocity gas stream, powder is injected, which partially melts. The stream of hot gas and powder is directed towards the surface to be coated. The resulting dense coating has low porosity and high bond strength [1], providing many benefits such as corrosion resistance.