Automotive Coating Treatment System

The automotive coating treatment system is one of the longest processes, with the highest technical complexity and the strictest environmental requirements in modern automobile manufacturing. It not only determines the aesthetic quality of the vehicle (color, gloss) but also serves as the first line of defense against corrosion (rust) for automobiles.
A complete automotive coating system typically consists of core processes such as pretreatment, electrophoresis, adhesive application, primer, topcoat, clear coat, and inspection, along with the following six major systems: body transport system, pretreatment electrophoresis system, grinding and sealing system, spraying system, drying oven system, and exhaust gas environmental treatment system.

Pretreatment System

The purpose of the pretreatment system is to obtain a clean metal surface with appropriate roughness.

Pre-cleaning/Degreasing: High-pressure water and alkaline degreasing agents are used to remove stamping oil, rust-proof oil, and dust from the vehicle body.

Phosphating/Silane Treatment:

Traditional Phosphating: A dense zinc phosphate crystalline film is formed on the surface of the vehicle body, enhancing the adhesion and corrosion resistance of the electrophoretic layer.

New Film Technology: Such as zirconium salt silane treatment, which is more environmentally friendly, produces less residue, and can be performed at room temperature.

Electrophoresis System

The electrophoresis system is a key process that ensures the vehicle body has rust resistance for over 10 years.

Cathodic Electrophoresis: The vehicle body is immersed in the electrophoresis bath and a direct current is applied. Positively charged paint particles (epoxy resin) deposit on the negatively charged surface of the vehicle body, forming a uniform primer layer.

UF Cleaning: After electrophoresis, ultrafiltration liquid is used for cleaning, recovering the paint that has been removed and preventing pinholes in the paint film.

Drying Oven Equipment

Solvent Evaporation and Moisture Evaporation: During the initial heating phase, the organic solvents or water (for water-based paint) in the coating first evaporate.

Leveling and Melting: As the temperature rises, resin particles begin to melt and flow, reducing the surface tension of the paint film, thus leveling it and eliminating orange peel and brush marks.

Crosslinking Reaction: Upon reaching a specific temperature (e.g., 180°C for electrophoretic paint, 140-160°C for clear coat), the functional groups in the resin undergo a chemical crosslinking reaction (polymerization), forming a three-dimensional network molecular structure. This process is irreversible and imparts the final hardness, weather resistance, chemical resistance, and adhesion to the paint film.

Transport System

The transport system is responsible for accurately and stably transferring the white body between various process stations (pretreatment tank, spray booth, drying oven, grinding area, etc.).

The coating transport system has evolved from ground chains to swing arms, sleds, and multifunctional shuttles.

Swing Arm Chain/Swing Arm Conveyor: The vehicle body is hung on the swing arm by a fixture, and the swing arm can swing up and down.

Multifunctional Shuttle: An automatic, independently operating transport cart.

Rodip System (Rotating Dipping): The vehicle body can rotate 360 degrees after being clamped.

Spraying System

The spraying system is the most core and precise part of the automotive coating workshop, directly determining the final color effect, gloss, brightness, and paint utilization rate of the vehicle body.

If the transport system is the artery and the drying oven is the internal organ, then the spraying system is the pair of dexterous hands. The spraying system in modern automotive coating is fully dominated by robotic automatic spraying, supplemented by a small amount of manual touch-up.

A complete automatic spraying system typically consists of the following subsystems: paint supply and mixing system, spraying execution mechanism (spraying robot), atomizer responsible for turning liquid paint into tiny droplets, spraying booth environment control system, and overspray mist treatment system (wet venturi/dry curtain separation system).

Exhaust Gas Treatment System

In the automotive coating system, RTO (Regenerative Thermal Oxidizer) is the core environmental protection equipment for treating painting exhaust gases (VOCs). Since the painting workshop (especially the spray booth and drying oven) generates a large amount of exhaust gas containing organic solvents such as benzene, toluene, and xylene, these gases cannot be directly discharged into the atmosphere, and RTO purifies them through high-temperature combustion.

The exhaust gas is heated to a high temperature of 760°C - 850°C in the combustion chamber. At this temperature, the molecules of organic exhaust gas (VOCs) undergo oxidation and decomposition reactions, converting into harmless carbon dioxide and water vapor. The purification efficiency of this process is usually over 99%.

The high-temperature clean flue gas generated by combustion passes through a heat storage chamber equipped with a ceramic heat storage medium before being discharged. The heat is absorbed and stored by the heat storage medium, and the flue gas is released after cooling down.

The low-temperature exhaust gas on the other side passes through the preheated ceramic heat storage medium before entering the combustion chamber, absorbing its stored heat, so that the exhaust gas is preheated to near combustion temperature before entering the combustion chamber.