The car body surface coating refers to the coating film applied to the outermost layer of the workpiece. It is the only visible part of the coating combination and plays the role of decoration, marking and protecting the substrate. It is in direct contact with various climatic conditions (such as rain, sunshine, snow, cold, heat, etc.) and harmful substances (such as acid, alkali, salt, carbon dioxide, hydrogen sulfide). It is the first layer to block these erosions. It cooperates with other coatings The layer serves to protect the substrate. Of course, different automotive coating qualities will have different emphasis on the decorative and protective properties of the top coating due to factors such as grade requirements and usage environment. For example, cars have high decorative requirements: trucks carrying oil, acid, and alkali chemicals Trucks have very high chemical requirements for surface coatings such as oil resistance, acid resistance, alkali resistance, etc., and decoration is placed second. Therefore, in order to meet various needs, the coating industry also produces topcoats with various properties, which can be mainly divided into the following categories. \x0d\\x0d\1. Used for high-end decorative coatings (limousine car bodies) \x0d\\x0d\ It belongs to high-end decorative coatings. The coating requires excellent decorative properties, weather resistance and water resistance. It is suitable for in various climatic conditions. The appearance of the coating film must be smooth and flat, without particles, as bright as a mirror, and with a gloss of not less than 90%. \x0d\\x0d\2. Used for mid-level decorative coatings (mid-level cars) \x0d\\x0d\ It is a high-quality decorative protective coating that requires excellent decorative properties, weather resistance and water resistance. The decorative requirements are only Less than premium decorative coatings. Mechanical strength is superior to advanced decorative coatings. Suitable for various climate conditions. \x0d\\x0d\3. Used for general decorative coatings (automobile bodies) \x0d\\x0d\The coating film has good gloss. It has good hardness, impact strength, flexibility, weather resistance and adhesion, as well as good gloss and color retention, but poor water resistance. Baking above 100℃ can improve its water resistance and adhesion. \x0d\\x0d\4. Used for certain decorative and protective coatings (cars used in hot and humid areas) \x0d\\x0d\This type of coating has a bright coating. It dries quickly and can be sanded and polished. Good weather resistance, moisture resistance and aging resistance. It also has certain properties against heat and humidity, salt spray and mold, and has excellent chemical resistance. However, it has poor adhesion and cannot be used for a long time at temperatures above 60%. \x0d\\x0d\5. Coatings with characteristic requirements \x0d\\x0d\ For example: acid-resistant coating, polyurethane paint, chlorinated rubber paint, epoxy paint, etc.; heat-resistant coating. Silicone paint, acrylic paint (thermosetting), etc.; Wear-resistant coating, polyurethane paint, phenolic paint, etc.; Solvent-resistant coating, polyurethane paint, epoxy paint, etc.; Insulating coating, asphalt paint, alkyd paint, etc. , epoxy paint, etc. \x0d\\x0d\ When selecting automotive coatings, we must pay attention to both protective and decorative properties; we must pay attention to the coating of steel substrates, but also consider the coating of substrates such as aluminum, zinc, plastics, and wood. Since the surface materials and adsorption capacities of various coated objects are different, the coatings suitable for them will also be different; therefore, it is necessary to comprehensively consider various factors and select appropriate coatings according to the properties and actual requirements of various coatings. \x0d\\x0d\ The call to protect the global environment and reduce air pollution has attracted more and more people's attention. Environmental issues also strongly influence the development of automobiles and related industries. Therefore, high solidification, water-based, and powdering have been the basic principles and guiding principles for developing new products in the world's coatings industry since the late 1960s. They have become a reality in Western developed countries and continue to develop and improve. \x0d\\x0d\Water-based coatings use water as the solvent, only a small amount of alcohol and ether as additives, and are formulated with different water-based resins. Water-based paints are prone to disadvantages during painting, and their use is limited. Water has high surface tension and poor color dispersion, making it difficult to obtain coatings with high decorative properties and good corrosion resistance; water has a large specific heat capacity and is difficult to volatilize, requiring the temperature and humidity of the coating environment to be strictly controlled within specified ranges, which generally cannot be achieved. Use drying chamber only with solvent-based coatings. \x0d\\x0d\The basic principles for selecting topcoat are: \x0d\\x0d\(1) It has certain decorative and protective properties and meets product requirements. \x0d\\x0d\(2) Topcoat and primer have good compatibility. \x0d\\x0d\(3) It must be suitable for construction conditions. \x0d\\x0d\(4) It is helpful to reduce costs and facilitate construction. \x0d\\x0d\(5) Comply with labor protection regulations and protect the health of workers.
\x0d\\x0d\ 1. Top coating classification \x0d\\x0d\ The construction of automobile body surface coatings is generally operated by dedicated personnel. There are many classification methods for top coatings. According to the color effect, it can be divided into solid color paint, metallic paint and pearl paint; according to the type of film-forming substance, it can be divided into nitrocellulose paint, alkyd paint and acrylic paint; according to the curing mechanism, it can be divided into solvent volatile type. , oxidation type and cross-linking reaction type, etc. \x0d\\x0d\In addition, the construction of top coating can also be divided into single process, double process and three process according to the construction process. The boundaries between each classification method are not absolute and can cross each other. \x0d\\x0d\Single-process top coating refers to spraying the same paint to form a complete top coat. \x0d\\x0d\Dual-process surface coating refers to spraying two different coatings to form a complete topcoat. Usually, the color paint is sprayed first, and then the varnish is sprayed. The two coatings are combined together to form a complete topcoat. Creates a quality guaranteed complete topcoat. \x0d\\x0d\The three-process process is more complicated. For example, the three-process pearl paint usually sprays a layer of base paint first, then sprays a layer of pearl paint, and finally sprays the varnish. The three coatings can be combined to form a complete topcoat. Generally, the color of single-process topcoat is relatively monotonous, while the effect of three-process topcoat is richer. However, the more processes there are, the more complicated the construction and repairs will be. \x0d\\x0d\1. Construction of single-process topcoat \x0d\\x0d\The single-process topcoat commonly used in automobile repair is mainly two-component solid color paint. \x0d\\x0d\The spraying of two-component solid color paint is currently the most popular type used in the automotive repair industry. \x0d\\x0d\Preparation of the surface to be coated before spraying: \x0d\\x0d\(1) Car body surface requirements\x0d\\x0d\The basic work of the primer primer has been completed on the car body surface to be flat and smooth There are no defects, and the surface contour line is clear and accurate. After dry grinding with P400-P500 sandpaper, it meets the allowable roughness for painting. The unpainted parts should be carefully sealed with special sealing paper and tape. The coated substrate should be degreased and waxed with a special degreaser, and the entire coated surface should be lightly wiped with a sticky cloth to remove floating dust. \x0d\\x0d\(2) Inspection and preparation of spraying environment, tools, and equipment\x0d\\x0d\Two-component paint dries slowly and is easy to collect dust, so the construction environment is required to be clean, and spraying work must be done in an exhaust It is carried out in the spray booth of the wind equipment. The curing agent isocyanate is extremely sensitive to water and oil, so the air compressor is required to provide pure and dry compressed air. The spray flow from the spray gun should be uniform. Pay attention to choosing a spray gun with a suitable caliber. Excessive caliber will cause a large amount of paint, which will cause sagging and orange peel on the paint film on the surface to be coated. A special filter should be used before spraying. Filter the paint to ensure that there are no visible particles on the paint film after spraying. \x0d\\x0d\Two-component paint can generally achieve the required thickness by spraying 2 layers. If the color has poor covering power, you need to spray 3 to 4 layers until it is fully covered. \x0d\\x0d\In spraying construction, it should be sealed with a mid-coat primer to prevent mismatch between the new and old paint films and provide good durability. And pay attention to determine the properties of the old paint film to ensure that the old paint film and the new spray paint on the whole car will not bite, absorb light, wrinkle, etc. If the surface is partially sprayed with primer, a thin layer of primer should be sprayed on the surface of the partial spray primer before the first topcoat is sprayed to reduce the color difference between the primer and the old surface. , laying the foundation for future spraying operations. \x0d\\x0d\ When spraying the first layer, spray a thin layer with a spray pressure of 0.35~0.45MPa and medium humidity, and check the coating surface to confirm whether there are shrinkage holes. Generally, if there is oil or wax on the coated surface, shrinkage holes will appear immediately after the first layer is sprayed. If the bottom coating surface does not match the newly sprayed paint, it will also cause bites and cracks. At this time, the construction should be stopped immediately and some measures should be taken. Corresponding remedial measures or rework. During the construction of two-component coatings, shrinkage cavities are more common. This is mainly because the isocyanates in the paint are extremely sensitive to oil, wax, and water. If there are slight shrinkage cavities in secondary parts, wait until the solvent evaporates and part of the coated surface is slightly dry, then spray the shrinkage cavities 2 to 3 times. The shrinkage cavities will disappear during the second layer of spraying. If the main coating surface or the shrinkage cavity is widely distributed, the construction should be stopped. After drying, sand it with sandpaper or scrape putty according to the specific situation, and then spray again. When slight shrinkage occurs, a small amount of anti-fisheye agent can be added to the primer or topcoat to solve the problem, but the fundamental solution is to do a good job of surface pretreatment of the substrate.
\x0d\\x0d\After spraying the first layer, if there is no problem, it should be left for a while before spraying the second layer. The waiting time will vary depending on the ambient temperature and the type of paint. Generally, it is the best time to spray the second layer of paint when the painted surface is free of dust. To grasp the specific dimensions, you can use your fingers to gently touch the paint film that is sealed with tape. If the wet paint film no longer sticks to your hands, you can spray the second layer. Generally, the spraying work ends after the second layer of spraying. This layer of spraying requires the coating surface to be smooth and bright, without flow marks or orange peel. Therefore, when preparing the paint, the viscosity should be slightly lower than that of the first layer of paint, the spray gun moving speed should also be slightly slower, and the spray pressure can be increased by 0.02 to 0.03 MPa to make the paint particles atomize finer to obtain a satisfactory smooth coating. \x0d\\x0d\ Precautions during construction: \x0d\\x0d\1. How much of the two-component paint should be used, and it should be used now. The prepared paint should be used up within the usage time provided by the supplier. . \x0d\\x0d\2. When opening the front door to spray the rear door, the inside of the front door must be sealed with special masking paper and tape to prevent paint dust generated during spraying from flying into the car and causing pollution. \x0d\\x0d\3. When spraying the roof and front cover from the edge to the center, be careful that the work clothes do not touch the painted parts of the edge to avoid unnecessary rework. \x0d\\x0d\4. The masking paper should be carefully removed immediately after spraying. Be careful not to touch the wet coating surface with your hands and work clothes. If it is forced drying, it should be removed in time when the coating surface is still slightly wet; if the paint film is completely dry, the tape will be more difficult to remove. First, it is easy to leave sticky spots, and second, the paint film may be lifted up by the tape. \x0d\\x0d\5. The isocyanate paint dust in two-component paint is harmful to the human body. When spraying, it should be carried out in a well-ventilated environment, and personal safety protection should be taken, such as wearing work clothes and gas masks. \x0d\\x0d\6. The spraying tools should be cleaned immediately after spraying to avoid cementation. \x0d\\x0d\7. The two-component paint can dry by itself after spraying, or it can be forced dried by baking at low temperature. Generally, it can be put into use after 16h (overnight) at 20℃, and after 30min at 60℃ (metal temperature). It can be put into use after baking and cooling, but it will take a week for complete curing. Specific products must strictly refer to the supplier's requirements. \x0d\\x0d\ 2. Spraying of dual-process topcoat \x0d\\x0d\The following points should be noted when spraying dual-process metallic paint. \x0d\\x0d\1 Before spraying, the preparation of the surface to be painted and the inspection and requirements of the spraying environment, tools, and equipment refer to the two-component solid color paint. \x0d\\x0d\2 The metallic paint must be stirred evenly before spraying. Add the curing agent and diluent according to the specified proportion of the paint. Generally, adjust the viscosity of the paint to 15 to 17 seconds (apply -4 cups, 20°C), filter and then spray. Use slow-drying hardeners and thinners with caution. \x0d\\x0d\3 Metallic paint is generally sprayed in 2 to 3 layers, subject to uniform coverage, with an interval of 10 to 15 minutes between each layer, spraying pressure of 0.4 to 0.5MPa, and even spraying at medium humidity. Metal particles tend to settle at the bottom of the spray gun tank. Pay attention to stirring evenly every time you add materials, and shake the spray gun frequently during spraying to prevent silver powder particles from settling. \x0d\\x0d\4 The last layer of spraying can appropriately reduce the viscosity of the paint, slightly increase the spraying air pressure, and spray it thinly and evenly to facilitate the uniform distribution of silver powder particles and improve the gloss of the coating surface. \x0d\\x0d\5 After spraying, the masking paper and tape cannot be removed immediately. They should wait until they are dried (usually 30 minutes at 60°C. For specific drying conditions, please refer to the paint supplier's product manual). Remove before cooling. \x0d\\x0d\The above data are for reference only, please refer to the supplier's requirements for specific products. \x0d\\x0d\Three-step pearl paint spraying\x0d\\x0d\Three-step pearl paint spraying requires spraying three different types, pure base paint, pure pearl paint, and varnish, which is called three-step pearl paint spraying. Please refer to the paint supplier's information for the paint mixing ratio of each process. \x0d\\x0d\1 Blow dust before spraying, protect it, use degreaser to clean the spray area and take safety measures. \x0d\\x0d\2 Spray three layers of pure base paint to cover the primer. The spray gun distance is 20cm and the air pressure is 0.3-0.6MPa. At the interval between each layer of spraying, a sticky cloth needs to be used to clean the paint dust of each layer. When using a tack cloth, each coat of pure basecoat needs to be dry and dry spraying avoided. \x0d\\x0d\4 Make sure that the base paint dries for about 30 minutes.
Then spray 3 to 4 layers of pure pearl paint, depending on the color of the car body. The spray gun distance is 20cm and the air pressure is 0.3 to 0.6MPa. During the interval between each layer of spraying, use a sticky cloth to clean the paint dust of each layer. When using tack cloth, dry coal each coat of pure base paint and avoid dry spraying. \x0d\\x0d\4After spraying multiple layers of pure color paint and pure pearl paint, the thickness of the paint film increases. As a result, the evaporation of the solvent slows down, so the waiting time for spraying varnish is extended, ensuring that the pearl paint dries for about 30-60 minutes, depending on the weather temperature. Cold and dry weather lasts longer. \x0d\\x0d\ 2. Examples of body painting \x0d\\x0d\ Automobile body painting is a complete process. The following examples illustrate the process of body painting repair. \x0d\\x0d\ Standard coating construction process: soapy water cleaning, degreasing, old coating stripping and cleaning, preparing and filling putty, sanding (repeated several times according to surface conditions), surface cleaning and topcoat preparation, surface Coating, polishing, waxing. \x0d\\x0d\1 Polish and modify the feathered edges. Attention should be paid to the grinding of the feathered edges, as shown in Figure 1. Whether the curvature of these parts and the coating slope of the damaged parts of the coating are appropriate will directly affect the fullness, gloss, refraction, etc. of the coating after the coating is completed. This is also the main operating method of the coating personnel. \x0d\\x0d\2 During the work of polishing the feathered edges, you should also check whether there are any obvious protruding points on the recessed plane of the car body. As shown in Figure 2, or defects that cannot be eliminated by painting, if found, the body sheet metal repair personnel should be asked to reshape or repair these defects. \x0d\\x0d\3 The surface of the car body that has been polished with feathered edges must be a surface that cannot have any defects after painting. The range of polished feathered edges is much larger than the damage range of the door, and the slope cannot be touched by hand. The difference in height is too obvious, as shown in Figure 3. \x0d\\x0d\4 Car body cleaning, use degreaser to thoroughly remove stains from damaged parts of the door, and check and evaluate the degree of damage and coating type of the coated object. Apply an organic solvent for degreasing and wax removal. The damaged part of the door has a simple structure and a smooth curved surface, making it easier to clean. \x0d\\x0d\5 After cleaning, the primer can be applied. The function of the primer is mainly to provide adhesion and prevent corrosion. The bottom layer generally does not have the ability to fill the surface defects of the car body, and it is relatively easy to smooth the curvature of the door. \x0d\\x0d\Deploy putty. First, mix the main agent in the tank evenly so that the bottom surface has the same viscosity to facilitate scraping and curing. To use the curing agent, first open the tube cap to squeeze out the air, then screw on the tube cap and rub the outside of the tube with your palms to make the curing agent even. When mixing, use a scraper to spread the main agent on the pallet, and add the curing agent at a proportion of 1% to 3% of the main agent (refer to the instructions for using the paint). A hard scraper should be used to scrape the putty. The first layer of putty is mainly used to fill up the dents in the car door. Do not scrape repeatedly during the operation. Each layer can be thinner. The damage to this door is not very serious, as shown in Figure 4. \x0d\\x0d\6 Scrape the second layer of putty. The car body door is still scraped with a hard scraper because it is a flat surface. This layer of putty is still mainly for filling. The thickness of this layer of putty should be slightly thinner than the first layer, and the area when partially scraped should be slightly larger than the area of ??the first layer of putty. When scraping, pay attention to the straightness of the edge putty, and the interface with the previous layer of putty should be staggered, that is, do not make the interfaces of each layer of putty at the same location to avoid defects, as shown in Figure 5. It should follow the streamlined direction (horizontal direction of the car shape) and follow the principles from top to bottom and from right to left. When scraping, stretch it as much as possible to reduce the scraping interface. Pay attention to the thickness of the putty layer and the original coating. The surface datum points are flush. As the scope of the scraping putty layer gradually expands, the adjacent scraping putty layers can be connected into one piece when scraping the second or third layer of putty layer depending on the actual situation, so as to reduce the edge of the putty layer and facilitate polishing. \x0d\ \x0d\7 There is a reinforced rib on the lower edge of the door. Pay special attention to the putty here and choose a soft scraper. The putty should be scraped evenly along the arc of the door rib, as shown in Figure 6. \x0d\\x0d\8 When the car body is scratched and damaged, it is often the case that the two pieces are not connected together during the painting operation. It should be noted that the two pieces should be painted at the same time when doing the first step, and each subsequent process should be carried out at the same time, as shown in Figure 7. \x0d\\x0d\9 Polish the putty. After the putty layer is completely dry, you can polish it. For specific drying conditions, please refer to the precautions for using putty.
When polishing putty, be careful to only dry-sand, not water-sand, because the putty is highly water-absorbent, and when the residual water from water-sanding cannot evaporate well, it will cause blistering, "heat rash", peeling, and corrosion of the metal substrate, etc. in the paint film. The main purpose of sanding the putty layer is to obtain a flat and smooth surface. The putty layer can be polished by manual or mechanical dry polishing. Mechanical polishing is suitable for repairing large areas and flat substrates, which can reduce labor intensity and improve work efficiency, as shown in Figure 8. Manual grinding is suitable for substrates with complex shapes, such as corners, folds, contour lines, arcs, concave parts, etc. The two methods can be combined during grinding. \x0d\\x0d\10 The grinding of the putty layer is basically to eliminate all the tiny pits and sand holes on the substrate, so that it is flat and smooth, with no defects, no sand holes, no joints at the edges of the local scraped putty, and the appearance of the graphics is restored. As is, as shown in Figure 9. If the arc of the lower rib of the body door is small, it is better to grind it by hand, which is beneficial to the correction of the arc surface. It is advisable to use P120 ~ P240 sandpaper. Grinding is mainly done in the horizontal direction of the body's streamlined shape. Pay attention to the straightness of the protruding fold lines and contour lines of the substrate. Generally, do not grind in the vertical or diagonal direction. If the substrate needs to be polished in the vertical direction due to specific circumstances, the final polishing should be in the direction of the body. Streamlined horizontal grinding and trimming to prevent vertical grinding marks. The horizontal traces of the streamline are consistent with the streamline direction of the car body, and their organic combination is not easy to detect with the naked eye; while the vertical traces are just the opposite, and the slightest trace of sanding will be clearly displayed. For arcs and concave corners of the base material that are not suitable for sanding by hand, you can hold the sandpaper with your thumbs, press flatly on the base material with four fingers, and then repair and polish evenly back and forth. \x0d\\x0d\11 Dust removal/cleaning/masking, use detergent to clean the oil stains and stains on the coated object, and use masking paper. And use reverse adhesive to cover the parts of the object that do not need to be sprayed, as shown in Figure 10. \x0d\\x0d\ Since the air pressure used to spray the primer is lower than the air pressure used to spray the topcoat (to minimize the spray escape), the masking process on the surface of the workpiece is relatively simple. Reverse masking is often used to prevent spray steps. The so-called reverse masking method means that the masking paper is applied with the inside facing out, so a thin layer of paint mist sticks along the border. This method is used to minimize the steps and make the borders less noticeable, as shown in Figure 11. \x0d\\x0d\12 When spraying the intermediate coating, mix the paint and curing agent according to the proportion specified in the instructions, let it sit for 5-10 minutes and then spray. If the spray viscosity needs to be adjusted, a matching diluent should be added. The construction viscosity should be adjusted to 18~21s (-4 cups of paint, 20°C), a fast-drying or slow-drying thinner that is suitable for the spraying environment temperature should be used, and the spraying operation should be carried out in accordance with the requirements of the technical specifications, as shown in Figure 12. \x0d\\x0d\13 Two-component paint generally requires 2 layers of spraying to achieve the required thickness. If the color has poor covering power, you need to spray 3-4 layers until it is fully covered, as shown in Figure 13. \x0d\\x0d\ When the surface is partially sprayed with primer, a thin layer of primer should be sprayed on the surface where the primer is partially sprayed before the first topcoat is sprayed, so as to reduce the amount of primer and old paint in the process. The color difference between the surfaces lays the foundation for future spraying. \x0d\\x0d\ When spraying the first layer, spray a thin layer with a spray pressure of 0.35~0.45MPa and medium humidity. Check the coating surface to confirm whether there are shrinkage holes or other defects before continuing the construction. \x0d\\x0d\After spraying the first layer, if there is no problem, you should let it sit for a while before spraying the second layer. The resting time depends on the ambient temperature. Generally, spray the second layer when the coated surface is free of dust. To determine the best timing for painting, you can use your fingers to gently touch the paint film that is sealed with tape. If the wet paint film no longer sticks to your hands, you can spray the second layer, as shown in Figure 14. Generally, the spraying work ends after the second layer of spraying. This layer of spraying requires the coating surface to be smooth and bright, without flow marks or orange peel. Therefore, when preparing the paint, the viscosity should be slightly lower than that of the first layer of paint, the spray gun moving speed should also be slightly slower, and the spray pressure can be increased by 0.02 to 0.03 MPa to make the paint particles atomize finer to obtain a satisfactory smooth coating. \x0d\\x0d\14 The spraying of the medium coating is a very careful operation. The use of the spray gun must be controlled during operation. Inexperienced operators can test the spray gun first. After adjusting various parameters (viscosity, air pressure, etc.). Then perform the actual operation, as shown in Figure 15.
\x0d\\x0d\15 The gravity spray gun can be used for medium coating spraying, which can better control various spraying parameters, as shown in Figure 16. The characteristics of the gravity spray gun are that it can use low air pressure and high flow rate, and can fill and cover some small defects on the surface. \x0d\\x0d\16 The lower edge of the car door is a place that requires special attention. There are uneven surfaces such as ribs on the lower edge of the door. During operation, special attention should be paid to the occurrence of defects such as ripples and flowers, as shown in Figure 17. . \x0d\\x0d\17 After the coating is dry, the middle coating needs to be polished, which can be done with 400-grit sandpaper. After cleaning and dust removal, the top coat can be sprayed, as shown in Figure 18. The number of times the top coat should be sprayed can be determined based on the coverage of the coating until complete coverage is achieved. The spraying of the topcoat is the last process of the painting operation, so all repair shops attach great importance to it and often use dedicated personnel to do the work, as shown in Figure 19. There are also many problems that arise during spraying operations. If you do not have an accurate grasp of the spraying tools and operating technical parameters (air pressure, paint viscosity, color, etc.), you should spray a small sample and obtain the technical parameters before proceeding with large-area painting operations. \x0d\\x0d\18 The spray painting of the car door should be controlled to match the color of the original car body, as shown in Figure 20. There should be no color difference after the coating dries. Spray a test sample first to adjust the color difference, and then spray a large area on the car body after determining the color. \x0d\\x0d\After the body surface coating is baked and cooled. Check, if necessary, use P1500~P2000 sandpaper and wet sanding. If dry sanding is used, use P1000~P1200 sandpaper with a dry grinder; then the polishing process can be carried out. \x0d\\x0d\After the painting is completed, it should be submitted to the inspector and main maintenance personnel for further inspection. The main inspection content is whether there is any color difference between the newly repaired coating and the original coating. Check whether the repair surface is flat, without obvious particles or run-offs, whether the coating surface is plump, whether there is flying paint on the surface of other components, etc., as shown in Figure 21. If there are no defects, it can be handed over to the customer for acceptance.