Views: 283 Author: Site Editor Publish Time: 2020-11-18 Origin: Site
The common damage forms of construction machinery mainly include the wear and local damage of the friction pair. For the repair of worn parts, traditional repair methods include mechanical processing repair methods, welding repair methods, and electroplating repair methods. Thermal spray repair technology can also be used for components with simple structures. However, for the partial damage of some important parts, the above-mentioned repair methods are often labor-intensive, time-consuming, material-consuming, or even impossible to repair.
For the local damage of hydraulic cylinders, commonly used welding repair methods include repair welding, surfacing welding, brazing, etc. Each welding repair method has its own advantages and disadvantages.
The welding technique that is used to repair local defects of parts is called repair welding. The biggest feature of repair welding is simple construction and low repair cost. During repair welding, appropriate repair welding materials and repair welding processes should be selected according to the type of material.
For ordinary carbon steel, the repair welding method should be determined according to the carbon equivalent of the material. For repair welding of stainless steel, cast iron, aluminum and aluminum alloys, appropriate treatment methods and construction parameters should be selected according to the properties of the material and the use environment of the workpiece.
In order to reduce the soldering temperature during soldering, people use solder with a lower melting point for thermal welding, which is brazing. The biggest difference between repair welding and brazing is that no molten pool is formed on the workpiece during brazing. In the brazing process, only the solder is melted, and the matrix is not really melted. The infiltration effect of the molten solder is used to adhere to the substrate and form a repair layer on the brazed part.
If the brazing filler metal and flux are selected properly, the micro diffusion between the brazing filler metal and the matrix will help to improve the bonding strength between the brazing layer and the matrix. Therefore, compared with fusion welding, the thermal influence of the workpiece during brazing is small, the parts are rarely deformed, and the mechanical properties are not greatly affected.
At present, many people use brazing-electric brush plating composite repair technology to repair pressure pits. After scraping and grinding, a layer of wear-resistant coating is brush-plated to realize the repair of the pressure pit.
Cold welding repair technology is a new type of repair method developed using the principle of resistance welding. When there is a high contact resistance between the base metal and the patch metal, the resistance heat generated by the large current pulse output by the pulse power supply will bond the metal sheet and the base together. The more electric pulses generated per unit area, the more bonding points, and the higher the bonding strength between the metal sheet and the substrate. Since the patch only presents an instant high temperature at the electrode contact part, the workpiece itself will not heat up during the patch process.
The disadvantage of patch repair technology is that when the depth of the pit is much higher than the thickness of the metal sheet, multiple repairs are required, and the construction efficiency is low. Because the patch is locally bonded instead of integrally welded, the bonding strength between the metal sheet and the base is not high, and there are many gaps between the layers.
In addition, since the patch layer and the base cannot be integrated, when the cold-welded workpiece is ground, a smooth transition cannot be formed between the base and the patch. Substrates with good electrical conductivity (copper, aluminum, etc.) cannot be repaired by patch due to their low surface contact resistance.
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