How is the coating process carried out on bicycle coating lines? And what's the quality like?

Degreasing: Organic solvents, alkaline solutions, etc. are used to remove oil, grease and dirt from the surface of bicycle frames to ensure the adhesion of subsequent coatings. For example, the frames can be treated by spraying or immersion in degreasing agents.
Rust Removal: Methods such as acid pickling and shot blasting are employed to remove rust and oxide scale from the surface of the frames. Acid pickling involves soaking the frames in an acidic solution to dissolve the rust, while shot blasting uses high-speed projectiles to impact the surface of the frames to remove rust.
Phosphating: A phosphate chemical conversion film is formed on the surface of the frames to enhance the bonding strength and corrosion resistance between the coating and the metal surface. Generally, the frames are soaked in a phosphating solution and a phosphating film is formed after a certain reaction time.

Primer Spraying: Methods like air spraying and electrostatic spraying are adopted to evenly spray the primer onto the surface of the frames that have undergone pretreatment. In air spraying, compressed air is used to atomize the primer and spray it onto the frames; in electrostatic spraying, the primer particles are charged and adsorbed onto the surface of the frames under the action of an electric field. The primer serves to provide good adhesion and anti-rust properties.
Drying: The frames with the sprayed primer are sent into a drying chamber and dried and cured under certain temperature and time conditions. Generally, the drying temperature is between 120 °C and 150 °C, and the drying time is 20 to 30 minutes.

Color Mixing: According to the design requirements, the colored paint and solvents are mixed in a certain proportion to prepare the desired color.
Topcoat Spraying: Again, air spraying or electrostatic spraying methods are used to spray the mixed topcoat onto the surface of the primer to form a decorative and weather-resistant coating. The color and glossiness of the topcoat directly affect the appearance of the bicycle.
Leveling and Drying: The sprayed topcoat needs a certain leveling time to make the coating surface smoother, and then it is sent into the drying chamber for drying and curing. The drying conditions are similar to those for the primer drying, but the temperature and time may vary depending on the type of topcoat.

Clear Coat Spraying: To improve the glossiness, hardness and scratch resistance of the bicycle coating, a layer of clear coat is sprayed on the surface of the topcoat. The clear coat is usually a varnish with good transparency and protective properties.
Curing: Through appropriate drying in an oven or natural curing, the clear coat forms a hard and wear-resistant protective film.

Color Uniformity: Visual inspection and color measuring instruments are used to ensure that the color of each part of the bicycle is consistent with the standard color card, that the color deviation is within the allowable range, and that there is no obvious color difference.
Glossiness: A gloss meter is used to measure the glossiness of the coating to meet the product design requirements. Generally, for high-gloss coatings, the glossiness value is required to be above 80 (measured at a 60° angle), while semi-gloss and matte coatings have corresponding lower glossiness standards.
Surface Smoothness: Through visual observation and touching the coating surface, there should be no sagging, orange peel, blistering, pinholes or other defects, and the surface should be smooth.

Adhesion: The adhesion between the coating and the frame surface is tested by the cross-cut method or the pull-off method. It is required that the coating adhesion reaches the level 1 or level 2 standard, that is, there is no peeling or very little peeling of the coating after cross-cutting or pulling off.
Hardness: A pencil hardness tester or other hardness testing equipment is used to detect the hardness of the coating. Generally, it is required to reach H or 2H or above to ensure that the coating is not easily scratched during use.
Corrosion Resistance: Methods such as salt spray test and humidity-heat test are used to examine the corrosion resistance of the coating. For example, in the salt spray test, under certain salt spray concentration and test time conditions (such as 5% sodium chloride solution, 96 hours), there should be no obvious rusting, blistering, peeling or other phenomena on the coating.
Weather Resistance: Artificial accelerated aging test equipment is used to simulate the light, temperature, humidity and other conditions in the natural environment to conduct the weather resistance test on the coating. After a certain period of testing, there should be no obvious discoloration, powdering, cracking or other phenomena on the coating to ensure that the coating has a long service life under outdoor use conditions.