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How much do you know about the coating knowledge of castings?

Issuing time:2020-09-04 12:50Author:momo

六格展示coating.jpgAfter cleaning and inspection, castings are usually painted on the surface for rust prevention or aesthetics.


There are several coating methods commonly used in production, how are they applied?


A.The spraying method is a coating method in which the paint is sprayed on to the surface of the casting by means of compressed air.


The spraying device is mainly composed of spraying gun, compressed air source, air tank, rubber tube, spraying room,ventilation device and so on.There are many types of spray guns, such as suction type, gravity type, pressure feed type and long rod type.


Before spraying, the paint should be diluted with a suitable diluent and evenly stirred until the viscosity is moderate. If there are coarse agglomerated pigment particles in the paint, usea copper wire screen with an aperture of Φ120-Φ140mm or 2-3 layers of overlapping gauze to filter.The surface of the casting should be cleaned with a cleaning solution (such as a 0.2% sodium nitrite aqueous solution) at a temperature of 80-90℃for 1-10 minutes. If necessary, it can be washed again with a neutralizer.After cleaning, the surface of the casting should be blown dry or natural dry.When spraying, the distance between the spray gun and the surface of the casting should be controlled within 150-200mm. The spray gun should be perpendicular to the surface of the casting and move up and down or left and right at a constant speed. The moving speed should not be too fast or too slow, usually 10-20m/min.Each spraying should not be too thick to avoid defects such as pinholes andmicro-wrinkles.


After spraying, the casting can beself-dried or dried; the spray gun must be cleaned with thinner, but it is not allowed to disassemble and clean the nozzle and other parts, otherwise it will affect the spraying effect. If there is excess paint in the paint bucket, it must be sealed.


Pay attention to labor protection and fire prevention when spraying. The work site must be ventilated and exhausted to keep the air unblocked. Ignition and smoking are strictly prohibited.Operators should wear work clothes and protective devices. Face and hands should be coated with protective ointment. If you feel unwell during operation,you should leave the work site immediately.


B. The dip coating method is a coating method in which the casting is directly immersed in the paint solution to stick a layer of paint film.


The dip coating device is mainly composed of a dip coating tank and a dip coating hook. In mass production, the dipping process often adopts pipeline operation, and the assembly line is mainly composed of washing machine, dipping tank, drying chamber and suspended conveyor chain.


Pour the paint solution into the dipping tank before dipping, and the surface of the paint is about 200mm away from the top of the dipping tank. Add appropriate amount of thinner according to the viscosity of the paint solution, and stir evenly with a wooden stick. The paint in the dip tank should be stirred frequently to keep the consistency of the paint uniform. The castings can be self-dried or dried after dipping. After the dip coating operation is completed, the residual paint on the edge of the dip coating tank should be cleaned up, and the dip coating tank should be covered with a lid.


In order to ensure the normal operation of dipping and the quality of dipping, the dipping tank should be thoroughly washed at regular intervals to remove impurities brought in by the casting. In order to prevent the surface of the paint pool from being skinned, a proper amount of thinner can be sprayed into the paint pool during the dipping processto isolate the paint pool surface from the air.


C. The electrophoretic coating method is a coating method that uses the principle of electroplating to make the negatively charged paintcolloidal particles move to the casting connected to the positive electrode under the action of a DC electric field, and attach to the surface of the casting to form a paint film.


The electrophoretic coating device ismainly composed of a DC power supply, an electrophoresis tank, and a paintmixing device. The electrophoretic coating device is matched with conductivehook, flusher and drying room.


Before electrophoresis coating, use compressed air to blow out the dust and residual iron shots on the inner and outer surfaces of the cleaned castings. Mount the blown castings on the conductive hooks, and pay attention to the concave surface of the castings to be immersed in the electrophoresis tank. No air is trapped in the electrophoresis tank, and paint is not trapped in the electrophoresis tank. The mounted castings should be rinsed with water before being immersed in the electrophoresis tank. The rinsed castings should be cleaned of water in the inner cavity and immediately immersed in the electrophoresis tank for electrophoretic coating . When castings are immersed in the electrophoresis tank, care should be taken not to touch the wall of the electrophoresis tank to avoid short circuits.


The process parameters of electrophoretic coating should be selected according to the electrophoretic primer used. During electrophoresis, the stirring pump should be activated to stir the paint solution so that the solid content in the paint solution is uniform without precipitation. After electrophoretic coating, use high-pressure water or tapwater to wash away the paint, foam and variegation, to prevent the remaining paint from re-dissolving the formed paint film. After rinsing, send the castings to the drying room for drying. After painting, cover the paint tankwith canvas.


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