Do you know the process of car body painting?
For the car body painting, you may see the car's partial spraying in the car repair shop, including sheet metal processing, putty, painting, etc., when you encounter bumps and other accidents that cause your car to be repaired. I believe many people. Not strangers. However, have you seen the overall spraying process of the car body? Do you know how the car body is sprayed in industrial spraying? What process needs to go through? I will give you a detailed introduction below!
The painting process of the automobile itself belongs to the decorative and protective multi-layer coating, and is a coating process with many processes and high coating quality requirements in automobile painting. The commonly used coating process system can be divided into two coating systems (primer + topcoat) according to the coating; three coating system (primer + intermediate coating + topcoat or metallic glitter paint / clear varnish); Coating system (primer + middle coat + top coat + clear varnish, suitable for luxury cars with higher requirements for painting).
Generally, the three-coat system is the most common. The three-coat system is generally used for the car body, the bus and the body of the coach, and the cab of the truck. According to the drying conditions, it can be divided into drying system and self-drying system. The drying system is suitable for automotive coating production in large-scale production lines; the self-drying system is suitable for automotive coating of small batch production and body painting of large special vehicles.
In the industry, the general spraying process of passenger cars and wagon bodies is as follows:
Pre-treatment (de-oiling, descaling, cleaning, surface adjustment) ⇒ Phosphate ⇒ cleaning and drying ⇒ primer ⇒ drying ⇒ putty rough scraping (drying, grinding, wiping) ⇒ putty fine scraping (drying, grinding, wiping) ⇒ lacquer (dry, polished, wiped) ⇒ trim (quick dry, dry, polished, wiped) ⇒ topcoat (dry or shaded) ⇒ color separation (dry)
1. the surface treatment process before painting
In order to obtain a high-quality coating, the pre-treatment of the surface of the object to be coated before painting is called the pre-paint surface treatment. The pre-paint surface treatment is the basis of the coating process, which has a great influence on the quality of the entire coating, including surface cleaning (deoiling, descaling, dust removal, etc.) and phosphating.
There are several ways to clean the surface:
(1) Washing with hot alkali solution and scrubbing with organic solvent to remove oil stain; firstly grinding the surface of glass fiber reinforced plastic with 320-400 mesh sandpaper, then washing with organic solvent to remove the release agent; yellow rust on the surface of the vehicle body using phosphoric acid prepared cleaning solution Scrubbing to ensure excellent corrosion resistance of the coating and good adhesion of the coating to the surface of the coated object.
(2) Various chemical treatments are applied to the surface of the cleaned metal parts to improve the adhesion and corrosion resistance of the paint film. Special chemical treatment of steel parts to improve the bonding force between the paint film and the substrate.
(3) Mechanical removal of the machining defects of the coated object and the roughness required to create the coating film. Phosphating treatments include integral spray and integral immersion. Rapid phosphating with a thin film zinc salt, the quality of the phosphating film is 1-3 g/m, the film thickness is 1-2 μm, and the crystal grain size is 1-10 μm. Phosphating can be carried out at a low temperature of 25-35 ° C or a medium temperature of 50-70 ° C.
2. the putty putty
The purpose of the putty is to eliminate the unevenness of the object to be coated. The putty should be scraped on the dry primer layer. The thickness of the scratch is generally less than 0.5mm. A new large-area scraping putty method should be used. This method is easy to form a large area of flatness. Under the premise of not affecting the production process, it is proposed that each putty should be dried and smoothed, then scraped off the putty again. The putty should be scraped 2-3 times. Scratch and then scrape, which enhances the strength of the putty layer and further improves the flatness. The machine uses a method of polishing putty, and the sandpaper is selected from 180-240 mesh.
3. spray primer
The primer coating is the basis of the entire coating, and the bonding and corrosion resistance of the automotive coating to the metal is mainly achieved by it. The primer should be strong in anti-rust performance (salt mist ≥ 500h), strong adhesion to the substrate (can adapt to a variety of substrates at the same time), good adhesion to the middle coating or topcoat, good mechanical properties of the coating (impact ≥ A coating of 50 cm, toughness ≤ 1 mm, hardness ≥ 0.5) is used as a primer.
The method of air spraying (also optional high-pressure airless spraying) can be used to spray the primer. It can be sprayed twice by wet-on-wet method. The viscosity of the application is 20-30s, each interval is 5-10min, and after spraying, it is flashed 5- 10min into the drying room, the primer dry film thickness 40-50μm.
4. spray coating
Electrostatic spraying or air spraying, spray coating, can improve the stone resistance of the coating, improve the adhesion with the primer, improve the flatness and smoothness of the surface of the coated object, to improve the fullness of the topcoat and Bright.
The medium coating is generally wet-sprayed and sprayed continuously for two times. The construction viscosity is 18-24s, each interval is 5-10min. After spraying, it is flashed for 5-10min into the drying room. The dry film thickness of the medium coating is 40-50μm.
5. spray topcoat
Electrostatic spraying or air spraying, sprayed automotive topcoat, can form a paint film with excellent weather resistance, vividness and gloss. Due to the wide range of construction machinery, many specifications, heavy machine parts and large parts, it is generally painted by spraying. Spraying tools include air spray guns, high pressure airless spray guns, air assisted spray guns and portable 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 both is that the environmental pollution is serious, so it has been replaced by air-assisted spray guns and portable electrostatic spray guns. The spray production line designed by Guangdong Chuangzhi uses air-assisted spray guns for spraying. For thin-plate covers such as engine covers, portable electrostatic spray guns are used. Painting equipment for construction machinery generally uses a more advanced water spray paint booth.
Small and medium-sized parts can also be used in the water curtain spray booth or the pumpless paint booth. The former has advanced performance, and the latter is economical, convenient and practical. Due to the heavy heat capacity of the whole machine and parts of the engineering machinery, the drying of the anti-rust coating generally adopts a drying method of uniform hot air convection. The heat source can be adapted to local conditions, such as steam, electricity, light diesel oil, natural gas and liquefied petroleum gas.
The automotive painting process has its own characteristics and focus depending on the type of vehicle: the main painting part of the truck is the front cab, which has the highest coating requirements; other parts such as the carriage and frame are lower than the cab. .
The painting of passenger cars is quite different from that of trucks. The bus body includes the girders, the skeleton, the interior of the carriage, and the outer surface of the vehicle body, wherein the outer surface of the passenger body is required to be high. The outer surface of the body is not only required to have good protection and decoration, but also has a large spray area and a large plane. There are two or more colors, and sometimes a car ribbon. Therefore, the construction period is longer than that of the truck, the construction requirements are higher than that of the truck, and the construction process is more complicated than the truck.
Cars and small wagons have higher requirements for surface decoration or underlying protection than for large passenger cars and trucks. Its surface coating is a first-class decorative precision, with a beautiful appearance, bright as a mirror or smooth surface, no fine impurities, scratches, cracks, wrinkles, blistering and visible defects, and should have enough Mechanical strength. The undercoat layer is an excellent protective layer. It should have excellent rust and corrosion resistance and strong adhesion. Partial or all of the putty with good adhesion and high mechanical strength will not rust or be used for several years. Shedding and other phenomena.
The above is the industrial spraying process of the automotive industry. If you need to know more about the automotive spraying process and spraying production line, please visit Guangdong Chuangzhi for consultation. Guangdong Chuangzhi Intelligent Equipment Co., Ltd. is a comprehensive enterprise integrating R&D, design, manufacture, installation, commissioning and after-sales service. It has 25 years of experience in coating production line and provides various non-standard coatings for customers. The overall solutions such as production lines, painting equipment and environmental protection equipment have been widely recognized in the auto parts industry, furniture industry, musical instrument industry, cookware industry, home appliance industry, hardware industry, etc., and have been Honda, BYD, Wuzhoulong, Lizhong Wheel, Meishan Zhongche, Zhujiang Piano, Cotton Tree Guitar, Midea Group, Supor Electric, Foshan Lighting, Changjiang Furniture, Federal Home and many other well-known enterprises provide total solutions for non-standard spraying production lines.