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The primer of the workpiece to be scratched must be dry; There shall be no oil, dust and other dirt. These three items are the minimum requirements for coated and scraped workpieces.

 

If the primer is not dry enough, the solvent in the primer cannot continue to volatilize after scraping the atomic ash and curing, and is sealed under the atomic ash layer. In case of high temperature, bubbles are easy to peel off. If there is oil and dust, the adhesion between the atomic ash layer and the primer will be affected, and the atomic ash layer will fall off seriously.

 

2. Preparation and conventional coating of atomic ash

 

Preparation of atomic ash: it shall be prepared according to the requirements in the product operation manual. The main ash and curing agent must be mixed evenly before use.

 

The ratio of curing agent to main ash is generally 2:100, but it can also be adjusted within the range of (1.5 ~ 3): 100 according to the temperature and actual operation. Too much or too little curing agent may cause adverse effects.

 

Scraping and coating atomic ash is a link with high technical requirements in the coating process. It is required that the surface of the workpiece after coating and scraping shall be as flat as possible, and the coating and scraping defects - sand holes, scratches, wild paste and other defects shall be minimized. Generally, atomic ash shall be coated and scraped for 3 ~ 4 times. The following is a brief description of the operation requirements of each pass.

 

Apply the first coat of atomic ash

 

The purpose of the first layer of atomic ash is to fill and scrape large pits. It is painted and scraped with a wide hard scraper, only for leveling, not for smoothness. It is not allowed to scrape back and forth many times during operation, so that the pores in the atomic ash are stuck, which will cause long-term non drying and affect the construction. When applying and scraping, the scraper shall form an angle of 60 ° with the surface of the coated object, and apply and scrape slightly in an arc. Grind after drying, remove the floating ash, and then carry out the second layer of atomic ash.

 

Apply the second layer of atomic ash

 

The purpose of the second layer of atomic ash is still to fill the low recesses. The coating thickness shall be less than that of the first layer. A hard scraper shall be used for the plane, and a rubber scraper can be used for the round bend. When applying and scraping, pay attention to the horizontal direction of the car shape; From right to left, from top to bottom; In order to reduce the coating and scraping interface, the coating and scraping shall be lengthened as much as possible, and the construction requirements shall mainly level the low part.

 

Grind after drying, remove the floating ash, and then carry out the third layer of atomic ash.

 

Apply the third layer of atomic ash

 

The purpose of the third layer of atomic ash is mainly to scrape the pores, sandpaper marks and small depressions left by the previous layer of atomic ash. Smooth and smooth during coating and scraping. Scrapers with good elasticity shall be used during construction, and certain pressure shall be applied to make the scraped atomic ash layer smooth and less pores. Grind smooth after drying, and conduct the fourth layer of atomic ash after cleaning the surface.

 

Apply the fourth layer of atomic ash

 

The role of the fourth atomic ash is basically the same as that of the third atomic ash. It can also be called "fine scraping atomic ash". It is required to dilute the atomic ash and fully apply it once, so that the outer surface of the whole vehicle body can be thinly, smoothly and evenly coated with a layer of atomic ash.

 

Only the workpiece qualified by the above treatment can enter the next process - intermediate coating.

 

Coating defects caused by improper use of atomic ash

 

The finishing coat is the last process in the automobile coating process.

 

If there is a problem after finishing, it is the most troublesome. The following is a brief introduction according to the problems in production.

 

（1） The top coat foams after baking

 

Scrape off the bubbles after the bubbles in the finish coat, and see which layer the bubbles are on. If the bubbles appear in the primer layer, the atomic ash is well combined with the primer, and the substrate treatment may not be in place; After blowing off the bubbles, it is found that there is a layer of primer on the atomic ash and the substrate, then the primer may be too thick or the primer may not be completely dry.

 

（2） Pinholes and depressions appear after baking the finish paint

 

First, consider whether the atomic ash itself causes pinhole quality problems.

 

Secondly, if pinholes appear when the quality of atomic ash is qualified, it is generally because the atomic ash scraping and grinding technology is poor and the sand holes are not handled well.

 

In addition, during the scraping process, if the scraping tool is improperly selected, it will also cause pinholes.

 

（3） "Prickle" after baking the finish coat

 

First, the climate is too humid and the water absorption of atomic ash is too large. The polished atomic ash adsorbs a considerable amount of water. The finish paint is sprayed before the water volatilizes. A small amount of water is sealed under the paint film. Once heated, the water volume expands sharply, breaking through the paint film to form "prickly heat".

 

Second, the water absorption of atomic ash is qualified. After hot air drying, spray the finish coat, and "prickly heat" appears after baking. Then it may enter the drying room before the solvent volatilizes fully after spraying the finish coat. In this way, due to the rapid closure of the finish coat surface, the residual solvent has to break through the paint film to form "prickly heat". Of course, it may also be the quality problem of the topcoat, or the "prickly heat" caused by the mismatch between the polarity of the solvent and the topcoat.