Metallic Spraying Repair Technology For Diesel Generator Set Parts

The metal spraying of the diesel generator set uses a heat source to heat and melt the metal powder or the linear material, atomizes it into small metal particles by high-pressure, high-speed airflow, and sprays it onto the surface of the prepared part at a high speed of 100~300 m/s. A metal coating is formed. The sprayed coating is only mechanically adsorbed onto the substrate, while the base metal does not melt. Spraying is divided into oxygen-acetylene flame spraying, arc spraying, plasma spraying and explosive spraying according to the heat source used. The thickness of the spraying layer is generally 0.05~2mm, and if necessary, it can reach 10mm or more. The following is an introduction to the operation method of oxygen-acetylene flame powder spraying and oxygen-acetylene flame wire spraying in metal spraying of diesel generator set parts.

1. Oxygen-Acetylene Flame Powder Coating

It uses an oxygen-acetylene flame as a heat source, and the sprayed metal, alloy or alumina powder to be used is transported to the flame zone by means of a gas stream, and is heated to a molten state and is directed to the surface of the workpiece at a certain speed to form a coating. Figure 2-24 shows the schematic of this spray. The sprayed powder is fed from the upper hopper through the feed port 1 into the conveying powder gas (oxygen) passage 2, and is heated while being exposed to the oxygen-acetylene combustion gas flow at the outlet of the nozzle 3, while being sprayed onto the surface of the workpiece 6. In the figure, 4 is a flame, 5 is a sprayed layer, 8 is a gas inlet for conveying powder, and 7 is an oxygen-acetylene inlet. Oxygen-acetylene flame powder coating is mainly equipped with a spray gun, oxygen and acetylene supply device, compressed air and control device. This method of spraying is suitable for pre-protecting or repairing parts that have been finished or not deformed, such as shafts and bushings.

2. Oxygen-Acetylene Flame Wire Spraying

The linear metal material used for spraying is continuously fed into the flame zone where the gas is strongly burned. The ends of the wire are continuously heated and melted, and the molten metal is atomized into particles by means of compressed air, which is sprayed onto a clean, rough surface to form a coating. Oxygen-ethyl wire spraying is mainly provided with a suction-type gas metal spraying gun (referred to as a gas spray gun), an oxygen and acetylene supply device, a compressed air and drying device, a filtering device, a control device, a wire feeding device, and the like. This spraying method is widely used, for example, in the wear parts of crankshafts, machine tool spindles, plungers, roll journals, machine tool guides, etc.; in bridges, high-voltage towers, steel gates, carbonization towers, and chemical and fertilizer plants. Spray aluminum on the steel facilities, spray zinc and anti-corrosion; spray copper on the bearing bush, spray babbitt alloy; spray tin on the food container.

The operation method of oxygen-acetylene flame powder spraying and oxygen-acetylene flame wire spraying in metal spraying of diesel generator set parts has been introduced. The following describes the operation techniques of arc spraying, plasma spraying and explosive spraying.

1. Arc Spraying

The process of arc spraying is shown in Figure 2-25.

The two wires 2 serve as two consumable electrodes, and are fed forward by the motor at a constant speed through the variable speed drive. When the nozzles of the nozzles 3 intersect, an arc is generated due to the short circuit. The wire is continuously melted by the arc, and then compressed by the compressed air into fine particles, which are sprayed at a high speed toward the workpiece 5, and deposited as a coating 4 on the surface of the clean and rough workpiece. 1 in the figure is a wire feed wheel.

The main equipment for metal arc spraying is DC welding machine, control box, air compressor and air supply, wire feeding device, arc spray gun and other auxiliary equipment.

This method is widely used in the repair of crankshafts, general shafts, load shafts, and in the preparation of various functional coatings. Due to its high production efficiency, low cost of use, and relatively simple equipment and processes, this technology has been rapidly developed and used as one of the most common spray methods.

2. Plasma Spraying

Plasma spraying uses plasma generated by arc discharge as a high-temperature heat source to rapidly heat the sprayed material to a molten or molten state, obtain a high velocity under the acceleration of the plasma jet, and spray it onto the surface of the pretreated part to form a coating.

The main equipment for plasma spraying includes power supply, control cabinet, powder feeder, plasma spray gun, etc. The auxiliary parts of the equipment include sand blasting machine, air compressor, oil water separator, cleaning device, spray cabinet and heating equipment.

Due to the high temperature of the plasma spraying flame, the coating material is not limited by the melting point, the flame flow speed is large, the coating is finer, the quality is better, and the coating can be formed on the common material with wear resistance, corrosion resistance, electrical conductivity and insulation. Layers, parts can be improved by 1-8 times, this method can spray a variety of metals, non-metal, plastic and high melting point materials. It is mainly used for spraying wear-resistant layer, and has achieved good results in repairing the wear parts of valves, valve seats and valves in power machinery.

3. Explosive Spraying

Explosive spraying is to send a strictly quantitative mixture of oxygen and acetylene to the water-cooled combustion cylinder of the spray gun, and then use a nitrogen gas to flow a certain amount of spray powder to suspend in the mixed gas, and ignite oxygen and acetylene through the spark plug to generate a blast. The explosion heats the molten powder and, under the acceleration of the explosive force, the molten particles are sprayed onto the workpiece at a very high speed to form a coating. Since the spray energy of the explosion spray is large and the density is high, the bonding strength between the coating and the substrate is high. It can spray ceramic powder materials with melting point and high hardness to make excellent anti-wear layer for steam turbine blades, tools and molds. Although the explosive spray is extremely high in bonding strength, the cost is extremely high, the deposition speed is slow, and the application is less.