Besides powder coating, paint spraying is another commonly used surface treatment process.
The process is to put the paint into the container, spray the paint on the product in the form of mist after pressurized by the machine equipment, and form a layer of paint film to protect the product or semi-finished product and prevent it from rusting. Corrosion, and play a decorative role.The painting process is widely used in ships, locomotives, bridges, machinery and other fields.
Before painting, the workpiece should also be treated with pre-treatment steps such as rust removal, oil removal, water washing, and drying to clean the surface, so that the paint layer will be more firm.Spraying paint can be directly sprayed with a layer of paint, or it can be sprayed 2-3 times repeatedly in order to obtain a dense and firm paint layer.In paint application, a single coat is rarely used because a uniform, non-porous coating cannot be achieved.Usually, a primer layer plus a topcoat layer is used, and an intermediate layer and a finishing layer outside the closed topcoat layer can also be added as needed.The primer layer must have good adhesion to the workpiece to be coated, and the opposite paint layer must have good adhesion and anti-rust ability.The supporting principles of primer layer and topcoat layer are as follows:
It is best to match the drying primer layer with the drying topcoat; the self-drying primer and the self-drying topcoat; the primer of the same base paint and the topcoat.
When using a strong solvent topcoat, such as: nitro paint, perchlorethylene paint, etc., the primer layer must be able to withstand strong solvents without being bitten, such as alkyd paint, epoxy paint, etc.
The primer and topcoat should have roughly similar hardness and stretchability.
When the play-type paint is matched with the curing-type primer, the heat resistance is poor.
The oil degree of the primer is shorter than that of the topcoat, otherwise the weather resistance of the topcoat is poor, and the drying shrinkage of the primer and topcoat is different, which may easily cause cracks in each layer.When using multi-layer heterogeneous coatings, the middle layer is often used to make the paint base transition and achieve a good combination of the bottom layer and the surface layer.
Ferrous metals are suitable for almost all types of primers, while magnesium-aluminum parts and their alloys usually use a passivating primer based on zinc chromate.It is best to carry out effective pretreatment on the surface of the workpiece to form a layer of phosphating film or oxide film to improve the bonding force between the substrate and the primer.Then choose a primer with strong adhesion.For aluminum parts and galvanized parts, the primer of red lead pigment must not be used, otherwise it will cause electrochemical action and reduce the adhesion.