Talking about the thermal spraying construction method of hydraulic steel gate

       Among the commonly used anti-corrosion methods for hydraulic steel gates, the most commonly used anti-corrosion method is the coating layer. The coating anti-corrosion methods mainly include coating anti-corrosion and thermal spraying anti-corrosion. According to the practical experience of steel gate production, the construction method of thermal spraying of hydraulic steel gate is introduced.



    1. Surface treatment of steel gate



    Before thermal spraying on the surface of the steel gate, the rust, oxide scale, oil, welding slag, dust, moisture and other contaminants on the metal surface of the gate should be removed to make it all show the gray-white metal color, and keep it dry and have a certain roughness. , to ensure good adhesion between the thermal spray coating and the substrate. The specific method is as follows:



    (1) Construction requirements for sandblasting treatment



    The method of removing debris should be jetting or projecting, generally jetting, that is, sandblasting and rust removal.



    Sandblasting machine is a sandblasting treatment equipment. Selecting appropriate abrasives under certain pressure conditions can achieve high-quality surface treatment effects. The air operating pressure for sand blasting is less than 0.5MPa, and it is equipped with a 6m3/Sr air compressor. When using a mobile air compressor, the displacement is 6m3/s, the rated pressure is 0.8MPa, and the power is 37kw. The compressed air used for sandblasting must be processed by cooling device and oil-water separator to ensure dry and oil-free compressed air. The oil-water separator must be cleaned regularly. The size of the nozzle during sandblasting is 6-8mm. During use, the nozzle should be replaced when the diameter of the orifice increases by 25% due to wear and tear. The distance between the nozzle and the base metal surface should be kept 100-300mm. The angle between the spraying direction and the normal to the surface of the base metal is preferably 15° to 30°. There are many kinds of abrasives for sandblasting with different properties. Generally, quartz sand with higher strength is selected. The abrasive must be dried before use, and the water content should not be greater than 1%, otherwise it must be fried or dried. There are also requirements for the material diameter of the abrasive, and its value is between 0.75 and 3.0 mm.



    (2) Precautions for sandblasting construction



    1. Sandblasting is not allowed on wet metal surfaces. Necessary rain and moisture-proof measures should be taken for open-air operations.



    2. Pay attention to the temperature of the workpiece and the humidity of the air environment. When the air humidity is high or the temperature of the metal surface is lower than the dew point, sandblasting should be stopped.



    3. The metal surface that has been sandblasted and passed the inspection should be kept clean before transportation or anti-corrosion construction to avoid contamination with water or oil impurities, and should not directly touch the metal surface with hands to prevent local rust; it has been contaminated with oil. The metal surface must be treated with the corresponding organic solvent, or re-blasted after degreasing.



    4. When the air humidity is high or there is chemical gas pollution on the metal surface after sandblasting, the next process construction should be carried out within 4 hours, and in a dry and clean environment, the next process should be carried out within 24 hours. Process construction



    5. Sandblasters should wear protective equipment to protect the body from splashing abrasives; clean work clothes must be worn when carrying out anticorrosion construction in large components after sandblasting.



    2. Thermal spray zinc



    (1) Main equipment



    Compressed air system, oxygen, acetylene system, metal air spray gun and hose, etc.



    (2) Working principle



    With the compressed air in the spray gun as the driving force, driven by the driving device, the zinc wire passes through the nozzle and becomes a molten body under the heating of the oxygen-acetylene flame, which is atomized into particles by the compressed air and sprayed onto the workpiece to form thermal spraying. Zinc protective layer. Due to the uneven surface of the substrate after sandblasting, the metal coating after heat dissipation and shrinkage can be firmly attached to the surface of the workpiece. (3) Spraying requirements



    1. The purity of zinc wire for metal spraying shall not be lower than 99.99%.



    2. The zinc wire should be smooth, rust-free, oil-free and crease-free, with a diameter of 2.0-3.0mm.



    (4) Spraying process requirements



    1. The compressed air used for spraying should be clean and dry, and the pressure should not be lower than 0.4MPa.



    2. The spraying distance is 100-200mm, and the spray gun should be at right angles to the surface of the substrate as much as possible, and should not be lower than 45°.



    3. The moving speed of the spray gun should be 25-80μm thick at one time.



    4. There should be 1/3 of the width overlapping between the spraying belts, and the thickness should be as uniform as possible.



    5. The direction of the spray guns between the spraying layers should be perpendicular to each other for cross coverage.



    6. When the surface temperature of the coating drops below 70°C, the next layer of spraying is carried out.



    (5) Precautions for spraying construction



    During construction, the sandblasting schedule should be well coordinated with the thermal spray zinc construction schedule. If the sandblasted workpiece exceeds the allowable exposure under the climatic conditions at that time, it is easy to rust.