Surface Treatment Knowledge Hall: Construction Machinery Painting

Coating is an important part of surface manufacturing technology of construction machinery products. The quality of anti-rust and anti-corrosion coating is one of the important aspects of the overall quality of products. The appearance quality of products not only reflects the protective and decorative properties of products, but also is an important factor that constitutes the value of products.

I. coating technology

The anti-rust coating technology of construction machinery can be generally divided into pre-coating surface treatment process and anti-rust primer coating process.

1, pre-processing

Pretreatment is one of the important processes of rust-proof coating. The quality of rust-proof coating for construction machinery depends largely on the way of pretreatment.

According to Imperial Chemicals, coating life is limited by three factors: pretreatment accounts for 60%, coating construction accounts for 25%, and coating quality accounts for 15%.

Pretreatment methods of different parts in construction machinery industry.

Mechanical cleaning can effectively remove rust, welding slag and oxide scale on the workpiece, eliminate welding stress, increase the bonding force between rust-proof coating and metal matrix, thus greatly improving the rust-proof quality of construction machinery parts. The mechanical cleaning standard meets the requirements of ISO8501-1:1988 Sa2.5 level. The surface roughness should reach 1/3 of the thickness of the anti-rust coating. The steel shot used for shot peening and shot peening should meet the requirements of GB6484.

The pretreatment of sheet stamping parts is generally called chemical pretreatment. The technological process is:

Pre-degreasing degreasing hot water washing cold water washing acid washing cold water washing neutralization cold water washing surface adjustment phosphating cold water washing hot water washing pure water washing drying

The above process can also be adjusted according to the oil and rust condition of sheet metal stamping parts, or no acid pickling process or pre-degreasing process is needed. Degreasing and phosphating are the key processes in chemical treatment process, which directly affect the quality of chemical treatment and anti-rust coating. Relevant process parameters and related auxiliary equipment are also important factors affecting the physical quality of the surface.

2. Coating process

Because of the wide range of construction machinery, many specifications, heavy machine and large parts, spraying is generally used for painting. Spraying tools include air spraying gun, high-pressure airless spraying gun, Air-assisted Spraying Gun and portable electrostatic spraying gun. Air spraying gun has low spraying efficiency (about 30%) and high-pressure airless gun wastes paint. The common feature of both is that the environment is polluted seriously, so they have been and are being replaced by Air-assisted Spraying Gun and portable electrostatic spraying gun. For example, Caterpillar (CAT), the world's first construction machinery company, uses Air-assisted Spraying Gun for spraying, and portable electrostatic spraying gun for thin panel panels such as engine hood. Coating equipment for construction machinery generally adopts more advanced water rotary spraying room. Small and medium-sized components can also use water curtain spraying room or pump-free spraying room, the former has advanced performance, the latter is economical, convenient and practical. Because the whole machine and parts of construction machinery are heavy and the heat capacity is large, the drying method of the rust-proof coating is usually hot air convection with uniform baking. Heat sources can be adapted to local conditions, such as steam, electricity, light diesel, natural gas and liquefied petroleum gas.