With the rapid development of automobile industry in today's society, automobile painting, as an important part of automobile production and maintenance technology, is also developing rapidly in all aspects. But today, with the emphasis on sustainable development, energy conservation and environmental protection have become an important indicator in the painting process. This paper introduces the current operation technology and some new technologies of automobile painting, and analyzes the coating function and materials of automobile painting.
In the 2 1 century when the automobile industry is developing rapidly, the automobile maintenance industry has attracted much attention. In recent years, the technologies, processes, materials and equipment used by automobile maintenance enterprises in automotive sheet metal have made great progress than before, but the basic painting process is still somewhat backward. In particular, there are not many methods of anti-rust measures, and many of them only rely on brushing anti-rust paint. This will often lead to premature corrosion of welded and repaired joints, thus reducing the service life of local body and even affecting the safety of the whole vehicle. As a person engaged in automobile painting, he has his own unique views on automobile painting. It is necessary to have a comprehensive understanding of the future development trend of the industry from pure manual operation to semi-mechanized operation. No matter from the aspects of coating materials, technology, operation technology and coating function, its purpose is to make the appearance of automobile body more artistic and improve its commodity value and service life. Here, from my personal point of view, I will talk about the function, operation technology and development of automotive coating materials.
2 1 century is called the new century facing the environment. Reducing painting pollution, reducing painting cost and improving painting quality has always been the theme of painting technology development. This paper expounds the common sense of automobile painting technology, discusses the standard technological process of automobile painting, and puts forward some matters needing attention in the process of automobile painting.
First, the role of automobile painting
(1 protection-due to the special use environment of the car: wind, sun, rain and stones, the car is required to have certain anti-corrosion performance and service life.
(2) Decorative function-Because cars are constantly shuttling between the expressway and the urban and rural areas, people hope that they can bring colorful life and that cars are beautiful, comfortable and attractive in color. Therefore, modern large-scale intensive production of automobile painting is necessary, which requires a lot of manpower and material resources to build and manage modern large-scale painting production lines.
(3) Special signs-By spraying different paint colors on the car body, people can easily identify what cars with different colors represent. For example, medical vehicles are mainly white with the red cross symbol, while fire engines are painted with full red paint.
(4) Special function-Because the specific purpose of the car is different, we should consider what the car is for when painting. For example, those used to transport grain, oil or milk must be non-toxic; When transporting acid and alkali, corrosion must be prevented.
Second, the car painting process
Automobile painting technology can generally be divided into two parts: one is the surface treatment of metal before painting, also known as spray pretreatment technology; The second is the construction technology of painting. Surface treatment mainly includes removing the oil, dust and rust on the vehicle surface, and removing the old paint layer in the repair work to improve the surface state of the workpiece and lay the foundation for the next operation. Its pretreatment specifically includes mechanical processing and chemical treatment of the surface of the body panel according to the damage of various vehicles. Such as phosphating, oxidation and passivation.
1, surface treatment process Surface treatment is one of the important processes of antirust paint. The quality of antirust coating is closely related to the way and quality of surface treatment. According to relevant data, the service life of the coating is affected by three factors: (a) surface treatment, accounting for 60%; (b) Painting architecture, accounting for 25%; (c) The mass of the coating itself, accounting for 15%. The surface treatment of sheet metal parts is generally chemical surface treatment, and the process flow is: pre-degreasing → degreasing → hot water washing → cold water washing → pickling → cold water washing → neutralization → cold water washing → surface adjustment → phosphating → cold water washing → hot water washing → pure water washing → drying.
The pretreatment process of the above-mentioned sheet metal parts can also be properly adjusted according to the oil and rust conditions of the sheet metal stamping parts, or the pickling process or pre-degreasing process is not needed. Degreasing and phosphating are key processes in chemical treatment process, which directly affect the quality of chemical treatment of workpiece and the quality of antirust coating. In surface treatment, polishing has a great influence on the final quality. Especially in the early traditional operation-manual water grinding, the water left in the plate after water grinding will lead to many paint defects, so now the industry uses dry grinding instead. Dry grinding occupies a great position in today's industry, because it has obvious advantages compared with traditional water mill. For example, the work efficiency can be improved by 40%-60%; Because dry grinding will not produce waste water, the pollution to the environment is obviously lighter than that of water grinding; The labor intensity of employees has also decreased a lot; Repair rate and painting quality of vehicles are better than that of waterwheels. For example, dry grinding will not cause defects such as foaming of paint film, prickly heat, fisheye and rust of substrate due to residual moisture in the plate. Dry grinding technology has been widely promoted in existing 4S shops, so it is an inevitable trend for the industry to promote dry grinding technology. Related process parameters and related auxiliary equipment are also factors that can not be ignored to affect the quality of surface treatment.
2, topcoat spraying process
(1) Automobile maintenance painting: Automobile maintenance painting is the most representative and comprehensive painting process in automobile beauty maintenance construction. The key is to keep the edge moist, and at the same time, to minimize the paint flying on the horizontal surface, so as to prevent the paint mist from depositing in the dry part and causing surface sanding.
In the vehicle painting procedure, the roof is sprayed first, and then the front cover and side of the engine are sprayed. , so that the "wet edge" can always be maintained, and at the same time, the flying paint on the horizontal plane can be minimized, which can prevent the flying paint from falling into the dry area and producing a sand surface. If possible, it is best to choose a downdraft spray booth. At this time, because the airflow flows from the roof to the bottom of the car, the shape of the fog is different.
(a) painting the roof. At the joint of the roof, windshield and rear window, the strip painting method is used for painting. Start spraying near the edge of the painter's car first. As far as possible, keep the spray gun equidistant from the roof surface about 15~20cm, spray from left to right first, and then from right to left, with moderate humidity (spray from the edge of the roof on each floor). Because gravity or siphon spray guns are mostly used in repair construction, the inclination angle of the spray gun is limited due to the influence of the spray gun cup (try to keep the spray gun vertical and not inclined). The overlapping coverage of each layer of sector is 50% or 65%, and it is sprayed from the edge to the center until obvious soft luster can be seen.
(b) Spray the front cover of the engine. Clean the surface with a dusted rag first (note: it is not allowed to use an air gun to remove the surface, so as not to blow the dust on the front cover onto the newly painted roof). Spray the joint between the windshield and the front cover by strip spraying method (it is best not to use strip spraying method at the edge of the front cover), and the width of the sector overlaps by 50% or 65%. Each layer is sprayed from the edge to the center, and the other side is sprayed from the center to the edge. The sector width of each layer covers about 10cm.
(c) spraying the back cover. Wipe the surface with a rag and prepare enough paint to avoid color difference caused by running out of paint in the middle of spraying. Using strip spraying method, spray once along the bottom edge of the rear window glass, covering about two layers of fan width. Then switch to the other side and move from the center to the edge for spraying. During the whole spraying process, the coating should be kept 50% or 65% moist, and the running speed of the spray gun should be fast. The sector coverage area of each layer is about 10cm.
(d) side spraying. And prepare enough paint. Because of the long side of the car, it is necessary to spray it in sections. At a distance suitable for painters to walk with guns, spray a layer vertically and directly by strip spraying to separate it into sections. This section takes two guns from the bottom or top, first from left to right, and then from right to left, and continues by spraying. The sector width between each spray gun covers 50% until the surface of this part is completely covered by spraying. Then proceed to the next paragraph, that is, spray a gun vertically downward with a strip spray method to draw the second paragraph. Repeat the above operation, spray the second section, and so on until the side painting is finished.
(2) Repair painting of the whole panel: When a certain part of the car body, such as the front cover, the door and the rear cover, is damaged, it is necessary to carry out repair painting of the whole panel. Generally, there may be two situations: one is that there is no big deformation or crack on the board surface, and only the whole board surface needs topcoat; The second type is the damage of the board surface, which needs to be renovated before it can be installed on the car body. The former can be painted with closed isolation paint after the car body is cleaned, and then directly painted with topcoat; For the latter, rust removal, anti-corrosion primer coating and putty scraping must be carried out after the car body is cleaned, and the top coat can only be sprayed after the intermediate paint and the closed isolation paint are sprayed.
The whole board repair is different from the whole vehicle repair. When maintaining the whole vehicle, the color of the top coat is not considered, because as long as the color consistency of the whole vehicle is maintained, it can be consistent with the color number specified by the customer. However, the difference between the color of this piece and the original paint color of other parts of the car body must be taken into account when repairing the whole plate. Therefore, before the whole board is repaired, the sample of the repair paint must be strictly compared with other original paint parts on the car body, and the painting can be officially started only after it is correct.
Third, automotive coating materials
Automobile body topcoat is the outermost coating of the vehicle, which directly reflects the external decoration and anti-corrosion of the vehicle. It is generally expected that automotive coatings have excellent gloss. The gloss is not only related to the shape design of the car body and the appearance accuracy of the car body processing (for example, it is generally felt that the gloss of the curved surface or convex surface is better than that of the plane), but also related to the matching process of painting and surface painting. Only careful painting design and good painting environment conditions can make the surface coating have excellent decoration. At the same time, because automobile painting belongs to advanced protective painting, the topcoat film must have excellent corrosion resistance, weather resistance and crack resistance. If you want to get a paint surface with bright colors, good brightness and strong rust prevention ability, the quality of the paint should not be underestimated.
In the 1920s and 1930s, automobile paint was a single variety-nitrocellulose paint. In the mid-1950s, alkyd coatings were used. In the mid-1960 s, foreign thermoplastic dienoic acid resin coatings began to enter the market in large quantities, replacing nitro coatings and becoming the leading products of automobile repair coatings. In the mid-1970s, a series of two-component coatings began to enter the market, such as nitroacrylate isocyanate and acrylate isocyanate. At present, acrylic polyurethane resin coatings and polyester polyurethane coatings have become the leading products of automobile repair at home and abroad. Due to the continuous development of the industry, there are a wide variety of coatings today. What will be the development trend in the future?
In recent years, the appearance of water-based paint has made the automobile painting industry have a new development direction. First of all, what is water-based paint and what are its characteristics? Waterborne coatings are made of water as dispersion medium, special waterborne resin as base material, special additives synthesized by high technology and refined by new technology. Waterborne paint is a revolutionary product in coating industry. Compared with traditional oily coatings, water-based coatings are non-toxic, odorless, nonflammable, and do not need diluent dilution, which is an internationally recognized green product. As a new product in coating industry, it has obvious advantages compared with oily paint:
1. environmental protection: water-based paint is a pollution-free product, and there is no waste residue, waste gas and waste water discharged during production, and there is no environmental pollution. In use, it is non-toxic, odorless and benzene-free, and the content of heavy metals is far below the national environmental protection limit standard, which is harmless to human body. It is a new generation of green products to protect the ecological environment.
2. Economy: the coating area of water-based paint is more than twice that of ordinary paint; Waterborne paint antirust paint can be directly coated on the rust layer (floating paint and oil stains need to be removed).
3. Safety: flame retardant and explosion proof. Waterborne paints can be produced, transported, stored and used at normal temperature and pressure.
4. Fast: the drying speed of waterborne paint film is fast, which is 1/5 of that of ordinary paint at room temperature.
5. Convenience: Water-based paint can be directly diluted with tap water, which is convenient and safe for construction, and the tools and equipment after construction are easy to clean.
To sum up, in the future, automobile painting will continue to improve the corrosion resistance, stone impact resistance and decoration of the coating, and it will also develop in the direction of environmental protection and energy saving. Because of the outstanding performance of dry grinding technology, it is believed that dry grinding will become more and more common in the industry in the future, and its advantages will bring the greatest benefits to the industry. With the intensification of competition in the automobile market and the update of automobile manufacturing and maintenance technology, basic painting technology has attracted great attention of automobile manufacturers and maintenance service personnel. A wide range of coating materials with complete specifications and good functions will undoubtedly further promote the improvement of maintenance quality and prolong the service life of automobiles.