The basic treatment of car color change is usually because the car owner is not satisfied with the paint film color Satisfied, request to change to other colors. Therefore, for the basic treatment of color change, since the paint film is intact and has strong adhesion, the original paint cannot be removed, and the surface of the original paint can only be polished evenly and smoothly. The first purpose is to polish the smooth original paint film. Uniform fine sand grains to enhance the adhesion of the new paint; second, when the original paint film is too smooth, it is easy to cause quality accidents Therefore, it is necessary to conduct professional grassroots treatment, and then to change the color and spray paint, so that the quality of the coating can be guaranteed.
The basic treatment of color-changing cars is mainly polishing. Polishing can be carried out in different so as to obtain a better treatment effect and ensure that the quality of the painting after color change is excellent. Now, several common polishing methods before changing the color of the paint film are introduced as follows:
(1) Grinding method of alkyd paint layer
Alkyd paint is an ordinary paint, which is mainly used for painting ordinary passenger cars and trucks. This kind of paint film has average hardness, good and is relatively easy to polish. The grinding method is as follows:
① Grinding method of truck base
Grinding the base layer of the truck before changing the color is mainly to polish the front, left and right sides and the surrounding surface of the upper top of the cab. When polishing, use No. 240~280 water sandpaper, spray water and grind each place 8-10 back and forth . Smooth the small orange lines on the surface of the paint film (similar to the fine lines on the surface of orange peel) with water, and then pass the water grinding on each surface in this way . For other minor parts such as the inside and back of the cab and the surface of the trailer, use No. 100-120 emery cloth to lightly polish each surface evenly.
For all kinds of freight cars with logos and font sizes, if it is required to change the color and spray other paints, as long as the original paint film of the car has no cracks, blisters, bumps, crystal lines, rust, etc., tap water or high-pressure paint can be used first. Use a water gun to wash away impurities such as mud and ash in various parts . For parts with thicker and more muddy dirt such as fenders, chassis girders, and wheels, you can spray them with a high-pressure water gun until they are softened, and then use Remove the thick mud with tools such as a scraper, and then rinse it with water repeatedly. When water-grinding the cab of this type of vehicle , first grind off the markings on the doors on both sides, and repeatedly water-grind until the font size is effectively ground, and no traces of the font size can be left. If necessary, the topcoat can be worn through. . Otherwise, the traces of the original font size will be displayed after changing the color and painting, which should be kept in mind.
② Passenger car base grinding method
It should be divided into three methods: light grinding, heavy grinding and water grinding.
a. Light polishing mainly refers to the fact that the new passenger car has not left the factory after being painted. According to the opinions and requirements , it needs to be painted with other colors. For this type of passenger car, as long as the factory logo and ribbon are not sprayed, but only the top coat has been sprayed , use No. 120 emery cloth to lightly polish the outer paint film evenly, and lightly polish the inner paint film. After wiping off the floating residue, the color changing spray paint can be carried out. Because this kind of coating has not yet been effectively dried, it cannot be polished vigorously, let alone polished with water, otherwise it is not only easy to be stained with abrasive cloth when polishing, but also easy to wear through the topcoat and expose the bottom if you don't pay attention. Another point is that the original topcoat is not fully dry, and light sanding will not affect the adhesion of the respray paint.
b. Re-grinding mainly means that the car's topcoat, ribbon, factory logo and font size have all been painted, and the paint film has been effectively dried. In this case, when it is required to change the topcoat and ribbon of other colors, Re-grinding is required for processing. You can first use No. 80-100 emery cloth to repeatedly polish and smooth all parts of the topcoat (that is, fully smooth the orange grain on the surface of the paint film). For the color ribbon and font size, use emery cloth to flatten the wooden block to smooth the outline, and then polish it completely, so as to prevent rework caused by showing the outline of the ribbon and font size after spraying and changing the color paint.
c. Water polishing is mainly suitable for polishing the base layer of passenger cars with large patterns and many outlines of ribbons, which is conducive to improving the quality and work efficiency of polishing. When water grinding, first use 180-220 water sandpaper to dip in water (or pour water) to repeatedly water-grind each outline of the ribbon until it disappears checking, wipe the outline by hand without any blocking feeling, which is qualified. After the color ribbon and font size are all smoothed, use No. 280-320 water sandpaper, and then water-grind the whole car smoothly. Generally speaking, the contour line of the ribbon is difficult to grind, and it needs to be polished many times, that is, after water grinding once, wipe off the water stains, dry the water, check along the light or hand-wiping inspection, if there are traces, it should be water-grinded again Repeat this many times until it is fully ground.
(2) Grinding method of amino drying paint layer
The coating of amino baking varnish is hard, has strong adhesion, and is more difficult to sand than the base layer of alkyd paint. When grinding, different methods should be used according to the type in order to obtain a better grinding effect.
① Ordinary car paint polishing method
It mainly refers to the polishing of the amino drying paint layer of ordinary passenger cars and trucks.
a. Use No. 120-150 water sandpaper for rough grinding, and water to grind the orange lines on the surface of each paint film (referring to the external surfaces) repeatedly . Grinding with water 8-10 times back and forth can smooth the orange grain. For parts with larger orange patterns (rough orange patterns) and the outline of passenger car ribbons, at least 15-20 rounds of water grinding are required to smooth the base layer. Therefore, during the grinding process, it should be checked while grinding until the paint film of each main part is qualified by water grinding.
b. After the original paint layer of each car is finely ground, there are still obvious coarse sand marks on the surface. It is necessary to use fine grinding to eliminate the sand marks and make the surface smooth, so as to improve the coating after color change. quality. If you do not use the rough grinding method , it will not only take a lot of effort, labor and sandpaper, but also it is not easy to smooth the rough orange lines (including the outline of the ribbon), and the expected polishing effect will not be achieved. For fine grinding, use No. 240-280 water sandpaper to basically smooth the coarse sand marks, and then use No. 320-360 water sand paper to effectively grind the coarse marks until they are smooth and smooth. Wipe off the water marks and dry the water effectively After that, you can carry out color-changing spray painting.
② Mid-range car paint polishing method
Sleeper buses, ordinary cars, etc., are often called mid-range cars. The original paint of mid-range cars mostly uses amino polyester drying paint, and the quality indicators such as the flatness, smoothness, and gloss of the painted film after painting are correspondingly ordinary cars, because the original paint of ordinary cars often uses amino Alkyd drying paint coating. The surface of the mid-range car paint film has small orange lines and few impurities, so it saves labor and labor when polishing. However, water grinding must be carried out in two steps to smooth the base layer of the original paint.
a. Use 280-320 water sandpaper for the first water grinding, 8-10 back and forth for each part; 15-20 back and forth for each part of the passenger car ribbon; 3-5 back and forth for each part such as the edge.
b . For the second time, water grind No. 360-400 water sandpaper, and water grind 6-8 back and forth for each part of the plane; 8-10 back and forth for each part of to smooth the outline.
(3) Grinding method of nitro lacquer base
Nitro paint is tough and wear-resistant, but the paint film is thinner than that of amino drying paint and alkyd paint. Do not use coarse water sandpaper to prevent the metal substrate from being worn through the paint film or rough marks. Affects the quality of color-changing coatings. When water grinding, it can be ground at one time with No. 360-400 water sandpaper.
Before grinding the base layer of nitro paint with water, first use a high-pressure water gun to wash away the floating dust and other impurities on the surface. If you do not have a high-pressure water gun tool, you can fix the rubber hose or plastic hose on the faucet, and rinse the impurities repeatedly with tap water , to prevent impurities from scratching the paint film and producing groove marks during water grinding. If there is oil stain on the surface of the base layer, first use cotton gauze dipped in gasoline to wash off the oil stain, then use a high-pressure water gun or tap water to rinse the surface of the paint film, and then carry out water grinding. Generally speaking, 10-15 rounds of water grinding at each place can fully smooth the orange grain and small particles of impurities on the surface of the paint film. After all the parts of the car have passed the water grinding process , use tap water to repeatedly rinse off the wear stains, wipe off the water marks, and effectively dry the water, then conduct a comprehensive inspection , and then carry out color-changing coating after confirming that they are qualified.
(4) Polyurethane paint base grinding method
The coating of polyurethane paint has strong adhesion, is tough and wear-resistant, and is more difficult to polish Moreover, in the color change of automobiles, such as high-end luxury large and medium-sized buses, mid-to-high-end cars, etc., its The original paint is mostly polyurethane topcoat or acrylic polyurethane topcoat. Therefore, the water grinding of the base layer of the polyurethane paint should usually be carried out three times, so that the impurities such as orange lines on the surface of the original paint film (except the base layer of the polished paint) can be fully ground. The water grinding method is as follows:
①The first water mill
The main content of the first water grinding is that the main parts such as the engine cover, the fenders of the front and rear wheels, and the doors on both sides should be water-grinded on the base of the car; The outline part and the part below the windshield of the front wall, including the door, are repeatedly and meticulously water-polished until the orange pattern disappears completely, and the abrasion is cleaned.
When water-grinding the base of the car, first use 360-400 water sandpaper, and then water-grind along the direction of the surface of the object longitudinally and back and forth (water- grind along the length, do not grind horizontally). In order to prevent chaotic sand marks. In the process of water grinding , the grinding surface should be checked by hand while water grinding, so as to prevent leaking or abrasion (grinding) of the paint film. When water-grinding the base layer of a luxury passenger car, first use 240-280 water sandpaper to reciprocate and vigorously water-grind the ribbon and the outline until the polished surface has an unstoppable feel (horizontal touch). After the water grinding of these parts is qualified, use the old No. 240-280 water sandpaper to polish all parts of the topcoat
The surface water is smoothed (including the ribbon part) until it feels unstoppable. After each part has passed the water mill inspection, rinse off the ground dirt and wait for the second water mill.
②The second water mill
The main content of the second water grinding is to remove the corners missed in the first water grinding, the parts where the orange grain is not fully ground, the joint parts, the small face parts and the remaining edges of each surface (the unground edges) And so on, followed by careful water grinding qualified.
③The third water mill
基层经过两次水磨后，表面已达到平整光滑，但漆膜表面还留有砂纸磨痕，尤其是乱砂痕，需要将其水磨消失。所以，第三次水磨要用更细的水砂纸，将明显的砂痕水磨至完全消失，使表面达到非常平整光滑，为改色喷漆打好质量基础。但这次水磨，需要顺物面纵行直磨，不能横磨或斜磨，以防再次出现乱砂痕而造成返工。如水磨轿车，可用500-600号水砂纸，顺物面长向纵行往返来回水磨，对前后盖罩和车门的外部，由于物面较大较平，可用水砂纸包20毫米厚、50-60毫米宽、80-100毫米长的橡胶块进行水磨，这样更容易磨平乱砂痕。对豪华客车，可改用360-400号水砂纸，包橡胶块水磨，其他面手压水砂纸水磨，依次将全车各主要饰面水磨至非常光滑即可。
（5）金属漆基层打磨法
金属漆基层包括银粉漆（如粗银、中银、细银、特细银等）、银粉闪光漆、珠光漆（珍珠漆）等，多为丙烯酸聚氨酯类，漆膜较薄，主要靠罩光清漆保护。所以，打磨这类原装漆的基层时，主要是将罩光清漆表面的细小桔纹及少量的小颗粒杂质水磨平整即可，故不能用粗水砂纸打磨，以防磨穿清漆涂层或产生粗痕。如打磨轿车基层，可用 400-500号水砂纸每处用力轻而均匀地往返水磨 8-10个来回，即可将清漆涂层磨平滑。对喷涂有标志字号的轿车基层，可先用360-400号水砂纸，用力将标志字号水磨干净，再用500号水砂纸进行全面水磨。
When polishing the base layer of luxury passenger cars, because the original paint ribbons of luxury passenger cars are mostly colored (2-3 or 3-4 colors ) acrylic polyurethane paint coating, it is laborious and labor-intensive to grind with water. In order to improve the grinding efficiency, you can first use Grinding machine pad cover 150-180 emery cloth, dry-grind the outline of the ribbon pattern evenly, and then use 360-400 water sandpaper for comprehensive water grinding.
