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Analysis on the causes of defects in thermal spraying coating!

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Analysis on the causes of defects in thermal spraying coating!



Coating fragmentation

1. When spraying, the spray gun moves too slowly, so that the coating sprayed at one time is too thick, resulting in overheating of the coating

2. The spraying distance is too close to make the coating overheat

3. The shrinkage rate of spraying material is too high or there are many elements (such as sulfur, phosphorus, etc.) that cause hot and cold crushing

4. The current is too high during EFI; During air spraying, the oxidation flame is used, and the coating is over oxidized

5. After spraying, the workpiece is over quenched and cracked

6. There is water vapor and oil mist in the compressed air, which reduces the bonding strength of the coating

7. The rotation center of the workpiece is not accurate, and the spraying spark is slanted on one side, so that the second layer of coating is thick and thin, and the shrinkage is uneven

Coating shelling

1. The surface roughness of the substrate is not enough or there are dirt adsorption such as lime soil, which reduces the adhesion of the coating

2. The workpiece contains grease, and the grease overflows during spraying (especially for Nodular Cast Iron Crankshaft)

3. There is visible oil and water in the compressed air

4. The spray gun is too far away from the workpiece, when the metal particles reach the workpiece, the plasticity decreases, and the adhesion is not enough

5. The time between turning and roughing, roughing and spraying is too long, resulting in surface oxidation

6. Alumina grinding wheel is used in grinding, resulting in local overheating and expansion

7. The spark of the spray gun is not concentrated, and the flame deflects during spraying, so that the metal particles cannot adhere to the tool surface effectively

8. The linear speed of the workpiece and the moving speed of the spray gun are too slow, and the inclusions float on the surface, which reduces the adhesion strength

Coating delamination

1. When intermittent spraying is used, it is not finished at one time. If it stops for too long, the coating will have delamination and spalling during polishing

2. Oil and water from compressed air splashed on the surface of workpiece during spraying

3. The spraying place is not clean, and a large amount of dust adsorbs on the surface of the workpiece after each layer of spraying, so that there are foreign objects isolated or partially isolated between the layers

Spraying is not wear resistant

1. When spraying, the spray gun is too far away from the workpiece, and the metal particles are cooled early. After spraying on the workpiece, it becomes a loose coating. When the metal spraying coating is working, some particles fall off and scratch the friction surface

2. There are a lot of grinding wheel chips embedded in the coating and scratch the surface during grinding

3. The wire feed speed is too fast, and the particles are flaky

4. Unsuitable metal materials, low hardness and wear resistance (such as low carbon content of steel wire and too soft coating)

5. The air pressure is too low and the spraying distance is too far, resulting in the reduction of the bonding strength


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