Metal surface pretreatment is an essential link in metal material anti-corrosion engineering. The purpose is to remove the rust layer, scaling, dirt, and oxide scale on the surface of the material so that the anti-corrosion coating and the metal surface can be better bonded together to prevent the corrosion of the metal material by corrosive substances and prolong the life of the metal substrate.
Currently, metal surface pretreatment methods mainly include cleaning, tool rust removal, and sandblasting rust removal. Among them, the open dry sandblasting technology is the most common application. The dry sandblasting process produces a large amount of sand, rust, and harmful dust, which seriously pollutes the environment and causes great harm to the human body.
High-pressure water jet pure rust removal is more accepted and valued by people because of its advantages of environmental protection, simplicity, high quality, safety, and low cost. This article mainly introduces the application of domestic ultra-high pressure cleaners in rust removal.
The ultra-high pressure cleaning machine pressurizes the ordinary water to an ultra-high pressure of 170-250 MPa through a high-pressure oil pump and a supercharger and then sprays it quickly through the nozzle. The water jet forms a high concentration of energy, the speed is nearly three times the speed of sound, and it impacts and grinds the cleaned metal surface like a water arrow. The rust layer and scale are primarily distributed in layers or porous. Once the scale layer is penetrated, the ultra-high pressure water jet is inserted between the scale layer and the metal surface in a wedge shape. When the impact energy and wedge splitting force are more significant than the ultimate adhesion strength of the scale layer and the base metal, the rust and scale layer will be removed.
When the ultimate strength is reached, the rust and scale layer will be removed. Different water jet pressures can be selected for further rust and scaling. The relationship between rust removal grade and water pressure is shown in the table below.
| Rust removal grade | Water pressure M/ Pa |
| Sa1 | 150 ～ 170 |
| Sa2 | 170 ～ 190 |
| Sa2.5 | 190 ～ 220 |
| Sa3 | 220 ～ 250 |
The high pressure water cleaning machine mainly consists of three parts:
It mainly comprises a power device (diesel engine and its auxiliary devices), an oil pump, an oil-water supercharger, and an accumulator. The diesel engine is a Cummins six-cylinder engine with a power of 132-176kW, a maximum working pressure of 250MPa, a maximum working flow of 40L/min, and can work continuously between 140-230MPa. The ultra-high pressure water pressurized by the supercharger enters the integral hydraulic multi-gun distribution valve through the accumulator. For the same host, one machine with a single gun, one device with two guns, and one with three can be selected according to different applications and requirements: a Gun or one machine with four guns in various configurations.
It is mainly composed of a safety valve, pressure regulating valve, hydraulic control check valve, directional control valve, multi-gun distribution valve, and electrical control part; double safety valves control the pressure regulating system, and the multi-gun distribution valve is an integral hydraulic control distribution valve. The electrical control is PLC control.
It mainly comprises a high-pressure hose, spray gun, gun barrel, spray head, and nozzle. The high-pressure water delivery hose has two configurations: an imported hose and a domestic hose. The maximum working pressure of the imported hose is 250MPa, and the maximum working pressure of the domestic hose is 200MPa.
1) According to different use occasions, select the appropriate pressure level, high-pressure water jet rust removal can meet the requirements of metal coating surface pretreatment without damaging the treated metal substrate.
2) High-pressure water jet cleaning will not cause secondary pollution. Secondary cleaning treatment is not required if there are no special requirements after treatment.
3) High-pressure water can remove the surface of objects with complex shapes and structures and can perform cleaning and rust removal operations in narrow spaces or harsh environments. 4) High-pressure water rust removal has a high degree of mechanization, high cleaning efficiency, strong descaling ability, and low cost.
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