Automobile maintenance is so different from other fields. For example, brush coating, roller coating, dip coating, flow coating and high-pressure airless spraying are generally not used here, and compressed air atomization spraying is used in most cases. If the vehicle to be repaired is metal flash paint, it is also necessary to know whether electrostatic spraying is used in the construction of the last primer when spraying the top coat in the automobile assembly plant. If this is the case, electrostatic spraying should also be used to repair the container, otherwise the color difference may occur because the arrangement direction of aluminum powder in the repair coating is different from that of the original coating.
The painting of automobile maintenance is different from the painting production line of automobile manufacturers. Although it can't be said that the requirements for painting process are lower, it also has its particularity, simple operation, convenient color change, large or small spraying area, and intermittent operation most of the time. Therefore, it seems easier to meet the requirements of most automobile maintenance and construction with traditional spray guns.
With the rapid growth of metallic flash paint and pearlescent paint in recent years, cars are becoming more and more luxurious, and the performance of automotive repair paint is also constantly improving, so the requirements for spraying construction have to be improved accordingly. Therefore, spraying light metal flash paint is much more demanding in construction than spraying dark metal flash paint. There are some difficulties in the quality control of light metal flash paint, such as construction stability and color difference, especially the so-called different angles and colors are much more sensitive than dark paint. Therefore, when spraying light metal flash paint, the painting conditions and technology should be strictly controlled according to the construction essentials of the automobile repair paint adopted.
2. Dressing skills in automobile painting.
The so-called edge closing operation should be carried out by the painter in the process of repairing spots or grinding the edges of newly sprayed and old coatings. Edge closing means that the trigger is not locked when the gun goes off, which means that the paint supply is very small at this time. With the movement of the spray gun, the supply of paint gradually increased, and the trigger was not released until the end of the gun operation, which greatly reduced the supply of paint, thus obtaining a special transitional effect operation. The specific operation method is as follows:
(1) Move the spray gun smoothly until it is close to the surface of the substrate to be sprayed, and gradually pull the trigger to spray. Then suddenly but steadily release the trigger and the spray gun continues to move. This is from the outside to the inside.
(2) Place the spray gun above the surface of the substrate to be sprayed, lock the spray gun and pull the spray gun for spraying. Then move the spray gun outward smoothly, and once the spray gun approaches the edge sealing area, slowly release the trigger. Smooth operation, and then continue to move the spray gun. This is sprayed from the inside out.
3. Technical points of automobile repair spraying technology
(1) Take the gun. The spray gun is held by the palm, thumb, little finger and ring finger, and the middle finger and forefinger are used to pull the trigger. Some painters have been working for a long time, so they change the way of holding a gun from time to time. Sometimes they only use their thumb and palm to cooperate with the little finger, sometimes they use their ring finger to cooperate with the gun, and their middle finger and forefinger are used to pull the trigger. This can relieve fatigue and improve labor efficiency.
(2) the direction of the spray gun relative to the surface of the substrate. The spray gun should be perpendicular to the surface of the substrate, or as vertical as possible. If the spray gun is a little skewed, the result will inevitably cause the spray belt to flow to one side, while the other side will be very thin and lack of paint, which is very likely to cause striped coating.
(3) The distance between the spray gun and the leakage surface of the substrate. For siphon spray gun, the best working distance is 15~20cm. If the distance is too close, it may flow, and the color may even be inconsistent with the expectation when spraying metallic flash paint or pearlescent paint. If the distance is too far, exceeding 20cm, it may lead to dry spraying and overspray, which will make the leveling of the coating worse. If metal flash paint is sprayed, it may also change color. The pressure spray gun may be remote from the substrate. Generally, the best distance is about 20~30cm. These are the basic principles that spraying construction must follow.
(4) The moving speed of the spray gun. When spraying, the moving speed of the spray gun has a great influence on the spraying effect. If the spray gun moves too fast, the surface appears thin, poor leveling and rough; If the spray gun moves too slowly, the coating formed is too thick, which is very likely to cause sagging. The ideal moving speed of the spray gun should be that after spraying once, the newly sprayed layer looks full and moist, neither thin nor barren, nor excessively piled up. In a word, the moving speed of the spray gun depends on the specific situation of the construction site. Generally speaking, if it is only a relative comparison, the moving speed of the pressure-fed spray gun is faster than that of other types of spray guns.
(5) Control of the trigger. The spray gun is controlled by a trigger. The deeper the trigger is pulled, the greater the liquid flow rate. In the process of traditional gun walking, the trigger is always locked, not semi-locked. In order to avoid the accumulation of sprayed paint at the end of each gun run, experienced painters should loosen the trigger slightly to reduce the supply of paint.
4. Matters needing attention in spraying construction during automobile maintenance
(1) spraying sequence of full spraying truck. For vehicles with full spraying, the spraying sequence should be planned before full spraying. Whether the spraying sequence is reasonable or not has a great influence on the quality and luster of the paint film.
1. Firstly, spray the parts that are difficult to reach during spraying, such as the inside and edge of the hood, the trunk, the gap, the inner layer of the door, etc. When spraying the door frame, keep the door slightly open to avoid dust flying outside the car and damaging the paint surface outside.
2. The direction of air circulation in the painting room is from top to bottom along both sides of the car. So the painting sequence should be from the roof to the open door, then around the body and back to the door. This can solve the phenomenon of "paint loss" caused by "gun flower" at the gun joint of sequential spraying; Continuous spraying can eliminate overlapping seam marks on the vertical plane.
(2) Spray metal flash primer. When repairing a car, it is generally required that the color of the coating film must be consistent after spraying metal flash primer, and the overlapping width of each spraying must reach 3/4, and the moving speed should be uniform, and gun jumping and gun leakage are not allowed. After spraying, it is necessary to check whether the color of the whole vehicle is uneven. If the color is uneven, the uneven part can be corrected by viscosity reduction and spray painting fog. In order to avoid the uneven phenomenon of metal flash primer in spraying construction, attention should be paid to:
1. Before spraying, the spraying surface must be sealed with two layers of primer to prevent color difference;
2. Before spraying, the prepared paint should be stirred to prevent the metal color from sinking;
3, spraying construction, paint spray method must be adopted, paint layer can't spray too thick;
4. The thinner should use quick-drying solvent to reduce the leveling property of the paint film before it is wet;
5. Generally, about 2~3 layers are sprayed, which shall be subject to full coverage and uniform color, with a long interval between each layer;
6. Be sure to use a spray gun with uniform paint mist to prevent the phenomenon of "gun jumping".
(3) buses and vans are painted with ribbons. Bus and van bodies generally use 3~4 colors, and both sides and front and rear of the body are designed with streamlined straight outline and wedge-shaped geometry.