Painting process system used
01
The common coating process system can be divided according to the coating, two coating system (primer + top coat); three coating system (primer + medium coating + top coat or metal flash paint / cover light varnish); four coating system (primer + medium coating + top coat + cover light varnish, suitable for luxury cars with higher coating requirements).
Generally, the most common is the three-coating system, the decorative requirements of high car body, bus and tourist car body, truck cab generally use the three-coating system.
According to the drying conditions, it can be divided into drying system and self-drying system. The drying system is suitable for mass assembly line production; the self-drying system is suitable for small batch production of automobile painting and large special automobile body painting.
The general coating process of large bus and station wagon body is as follows:
Pre-treatment (oil removal, rust removal, cleaning, table adjustment) phosphating cleaning dry primer dry putty coarse scraping (dry, grinding, wipe) putty fine scraping (dry, grinding, wipe) in the coating (dry, grinding, wipe) dressing (quick drying, dry, grinding, wipe) top paint (dry or cover) color separation (drying)
Front surface treatment process
02
In order to obtain a high quality coating, the pretreatment of the coating surface before painting is called the paint surface treatment. The front surface treatment is the basis of the coating process, which has a great impact on the quality of the whole coating, mainly including surface cleaning (oil removal, rust removal, dust removal, etc.) and phosphating treatment.
There are several methods for surface cleaning:
(1) Clean with hot lye and scrub with organic solvent to remove oil; polish with 320-400 sandpaper on the surface of FRP, and then clean with organic solvent to remove film remover; yellow rust on the surface of the car body shall be cleaned with phosphoric acid to ensure the coating has excellent corrosion resistance and good adhesion to the surface of the coating.
(2) Various chemical treatment of the cleaned surface of the coated metal parts to improve the adhesion and corrosion resistance of the paint film. Special chemical treatment of steel plate parts to improve the combination force of paint film and substrate.
(3) Use mechanical methods to remove the machining defects of the coating material and the roughness required to create the coating film. Phosphate treatment has integral injection and integral immersion. Thin film zinc salt rapid phospholation treatment, phospholated membrane mass is 1-3g / m, membrane is 1-2 μ m thick, crystal size is 1-10 μ m, can be phospholated by low temperature 25-35℃ or medium temperature 50-70℃.
Application
03
1. Spray primer
Primer coating is the basis of the whole coating, and the combination force and corrosion prevention of automobile coating and metal are mainly achieved by it. Primer should be selected with strong rust resistance (salt spray 500h), strong adhesion with the substrate (can adapt to a variety of substrate materials at the same time), good combination with medium coating or topcoat, good coating mechanical properties (impact 50cm, toughness 1mm, hardness 0.5) coating as primer.
Using air spraying method (can also choose high pressure without gas spraying) spraying priming, can use wet touch wet method even spray two channels, construction viscosity 20-30s, each interval of 5-10min, after spraying flash 5-10min into the oven, primer dry film thickness 40-50 μ m.
2. Scratch putty
The purpose of scraping the putty is to eliminate the irregularity of the coating material.
Puputty should be scraped on the dry primer layer, the thickness of a coating generally does not exceed 0.5mm, the new large area scraping putty method should be used. This method is easy to form a large area of putty, under the premise of not affecting the production process, it is proposed that every scraping putty should be dried and polished flat, and then scrape the next putty, putty to scrape 2-3 times is good, first thick scraping and then thin scraping, so as to enhance the strength of the putty layer and further improve the flatness.
Using the method of machine grinding putty, sandpaper selection of 180-240 mesh.
3. Apply in spray
Using static spraying or air spraying method, spraying in the coating, can improve the stone resistance of the coating, improve the adhesion with the primer, improve the flatness and smoothness of the coated surface, to improve the fullness and fresh reflection of the top paint.
Medium coating general wet wet continuous spraying two, the construction viscosity is 18-24s, each interval of 5-10min, flash 5-10min into the oven, the thickness of medium coating dry film thickness is 40-50 μ m.
4. Spray paint
Using static spraying or air spraying method, spraying the car top paint, can form a weather resistance, fresh reflection and luster of excellent paint film.
Due to the wide range of construction machinery, specifications, the whole machine weight, large parts, generally using spraying method for painting.
Spray tools include air spray gun, high pressure airless spray gun, air auxiliary spray gun and portable static spray gun. The air spray gun spraying efficiency of the air spray gun is low (about 30%), the high pressure air spray gun wastes the paint, the common characteristic of the two environmental pollution is more serious, so it has been and is being replaced by the air assisted spray gun and portable electrostatic injection gun.
For example, the world’s first construction machinery company ——— Caterpillar American company uses air-assisted spray gun for spraying, and the hood and other thin plate cover parts are using portable static spray gun. Painting equipment for construction machinery generally adopts the more advanced water spin spray painting room.
Small and medium parts can also use water curtain painting room or no pump painting room, the former has advanced performance, the latter is economical, convenient and practical. Due to the large heat capacity of the whole engineering machinery and parts, the drying of its anti-rust coating generally adopts the drying method of uniform baking and hot air convection. Heat source can be adapted to local conditions, choose steam, electricity, light diesel oil, natural gas and liquefied petroleum gas.
Automobile coating process has its own characteristics and emphasis according to different automobile types:
(1) The main coating part of the truck is the front cab with the highest coating requirements; other parts, such as carriage and frame, are lower than the cab.
(2) There are great differences between the painting of bus and truck. The bus body includes the girder, the skeleton, the interior of the car and the outer surface of the body, among which the outer surface of the body is higher. The outer surface of the car body not only requires good protection and decoration, but also has a large spraying area, many plane, more than two colors, and sometimes the car ribbon. Therefore, the construction period is longer than the truck, the construction requirements are higher than the truck, and the construction process is more complex than the truck.
(3) Cars and small station wagons, whether in the surface decorative or bottom protection are higher than large buses and truck requirements. Its surface coating belongs to the first level of decorative precision, with a beautiful appearance, bright as a mirror or smooth surface, no fine impurities, abrasions, cracks, wrinkles, foaming and visible defects, and should have sufficient mechanical strength.
The bottom coating is an excellent protective layer, which should have excellent rust and corrosion resistance and strong adhesion; partial or all putty with good adhesion and high mechanical strength will not rust or fall off for several years.
Post time: Jan-03-2023
