Coating process

Painting

Painting is an important part of the surface manufacturing process of construction machinery products. Anti-rust, anti-corrosion coating quality is one of the important aspects of the overall quality of the product. The appearance of the product not only reflects the product protection and decorative properties, but also constitutes an important factor in the value of the product.

First, coating process

The anti-rust coating process for construction machinery can generally be divided into the surface treatment process before coating and the anti-rust primer coating process.

1, surface treatment

Surface treatment is one of the important processes for anti-rust coating. The quality of anti-rust coating of construction machinery depends to a large extent on the quality of the surface treatment.

According to the British Imperial Chemical Company, coating life is limited by three factors: Surface treatment, accounting for 60%; Coating construction, accounting for 25%; Coating itself, accounting for 15%.

Construction machinery industry, the surface treatment of different parts.

Mechanical cleaning can effectively remove rust, welding slag and oxide scale on the workpiece, eliminate welding stress, and increase the binding force between the rust-proof coating film and the metal substrate, thereby greatly improving the rust-proof quality of the construction machinery parts. The mechanical cleaning standards require Sa.25, ISO 8501-1:1988. The surface roughness should be 1/3 of the thickness of the anti-rust coating. The steel shots used for spraying and shot blasting should meet the requirements of GB6484.

The surface treatment of sheet stampings is generally referred to as chemical surface treatment. The process flow is:

Pre-degreasing→degreasing→hot water washing→cold washing→pickling→cold washing→neutralization→cold washing→surface conditioning→phosphorization→cold washing→hot water washing→pure washing→drying

The above process can also be appropriately adjusted according to the oil and rust conditions of the sheet stampings, or without the pickling process, or without the pre-degreasing process. Degreasing and phosphating are key processes in the chemical treatment process. These two processes directly affect the quality of the chemical treatment of the workpiece and the quality of the anti-rust coating. The relevant process parameters and related auxiliary equipment are also non-negligible factors affecting the quality of the surface.

2, coating process

Due to the wide range of construction machinery, many specifications, the weight of the whole machine, and large parts, the coating method is generally applied by spraying. Spray tools include air spray guns, high-pressure airless spray guns, air-assisted spray guns, and hand-held electrostatic spray guns. The air spray gun has low spraying efficiency (about 30%), and the high-pressure airless spray gun wastes paint. The common feature of the two is that the environmental pollution is relatively serious. Therefore, it has been replaced by air-assisted spray guns and portable electrostatic spray guns. For example, Caterpillar (CAT) Co., Ltd., the world’s largest engineering machinery company, uses air-assisted spray guns for spraying, and hand-held electrostatic spray guns are used for thin panel covers such as engine hoods. Construction machinery painting equipment generally uses a more advanced water spin booth. Small and medium-sized components can also be used as spray curtain spray booths or pumpless spray booths. The former has advanced performance, while the latter is economical, convenient and practical. Because the whole machine and parts of the construction machinery are heavy and the heat capacity is large, the drying of the anti-rust coating is generally performed by baking a uniform hot air convection. The heat source can be adapted to local conditions. Steam, electricity, light diesel oil, natural gas and liquefied petroleum gas are used.