Explosive spraying equipment

　

Explosive spraying is sprayed by using the high-temperature gas shock wave generated by combustible gas after detonation. A certain proportion of combustible gas (such as acetylene) and combustion-supporting gas (such as oxygen) and spray powder are injected into the barrel of the detonation spray gun, and after mixing, they are ignited by electric sparks to produce a single explosion. The powder suspended in the air flow is heated and accelerated, rushes out of the spray gun, collides with the surface of the workpiece and deposits on the surface to form a coating. Subsequently, a stream of nitrogen gas was injected into the gun to purge the barrel. Then start the next explosion. This process is repeated continuously to form a spray. The detonation and cleaning process is extremely fast, and can be completed 4 to 8 times per second. Each detonation can form a coating circular spot with a diameter of about 25mm and a thickness of about 5-10μ. The coating circular spot of explosive spraying is thin in the middle and thick at the edge. This is because the powder particles after detonation are bound by the gun barrel, and many particles collide with the inner wall of the gun barrel for many times, and then spray out after rebounding. due to.
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The gas explosion pressure in the gun barrel is very high, about 10 atmospheres (about 145psi). The explosion temperature is about 3300°C, the air velocity at the outlet of the spray gun is about 1500m/s, and the velocity of the powder particles is about 600-800 m/s.
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The powder is heated for a very short time during the detonation process, and most of the particles can only be heated and cannot be melted, but they can be ejected from the muzzle at a very high speed and hit the surface of the substrate with high kinetic energy to form a bond. Coating with high strength and low porosity.
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equipment composition
The explosive spraying system is mainly composed of the following equipment:
Gas supply system and pipeline: The gas supply system consists of gas source, pressure reducing valve, flow regulator, flashback preventer and corresponding pipeline. The system needs to be able to deliver gas, oxygen and nitrogen separately.
In order to obtain a stable gas supply, bottled acetylene is generally used. The connection of the gas system is pressure reducing valve (pressure regulation and pressure indication)→regulating needle valve→flow meter→backfire preventer (for gas)→spray gun.
The pressure and flow of oxygen and nitrogen should be continuously adjustable within the parameters specified for the spray gun.
Explosive spray gun: The spray gun is the most critical equipment in the explosive spraying system. The main structure is a cylindrical long barrel. The barrel is provided with inlet valves for gas, oxygen, and nitrogen, and powder inlets, as well as a spark plug for ignition.
Powder feeder: used to deliver powder to the spray gun.
Control system: It has the functions of controlling the switching program and switching time of each electromagnetic valve, as well as ignition.

main feature
Due to the high speed of the sprayed particles, the bonding strength of the coating is high (can be greater than 70MPa), and the porosity is low (can be less than 1%).
The time of each detonation is extremely short, and the time for powder particles to be heated is also extremely short, so the coating material has less carbon loss and less oxidation. When used to spray carbide coatings (such as tungsten carbide), there is very little carbon loss, which can be Get high hardness and high density carbide coating.
Since the powder particles are heated for a very short time, most of the particles are not heated to a molten or semi-molten state, and even fewer particles are completely fused. The thermal stress of the generated coating is small, and there are few thermal cracks. Therefore, the reliability of the coating is good.
Due to the pulse spraying and the cooling effect of a large amount of accompanying carbon dioxide gas, the temperature of the sprayed workpiece will not be overheated. The workpiece needs neither cooling nor preheating.
Not suitable for spraying high melting point materials. The deposition efficiency of general powder spraying is also relatively low.