Study on the guarantee measures of steel drum coating quality (4)

Study on the guarantee measures of steel drum coating quality (4)

(5) Disposal of defects in surface coating of steel drums in a timely manner

The defects detected during the coating process and the final coating performance should be dealt with in a timely manner, and corresponding measures should be taken to remedy the surface coating quality of the steel drum to achieve the purpose of coating.

In the process of coating steel drum, or after coating, the film defects are generally related to the surface condition of the steel drum before painting, the coating process, the coating quality, the coating method and operation, the coating equipment and the environment. Related factors, common defects and causes and improvement measures are mainly the following:

1, sag, sag and flow marks

Such defects cause uneven coating and flow marks on the coating film due to abnormal flow of the paint on the cylindrical surface of the steel drum. Sagging is generally proportional to the specific gravity of the coating, inversely proportional to the viscosity, and proportional to the cube of the thickness of the coating.

The reasons for this defect:

(1) The solvent volatilizes slowly. The temperature is too low, almost no ventilation (poor ventilation), and the solvent evaporation in the surrounding air is high.

(2) The viscosity of the paint preparation is too low.

(3) The thickness is too thick. The spray distance is too close, the spray angle is not appropriate, and the spray width is too large to overlap too much.

Improvements:

(1) Strictly control the temperature, properly ventilate (good ventilation), and meet the requirements of the process standard.

(2) Strictly control the construction viscosity of the paint and mix it according to the standard.

(3) Control the spraying distance and the effective spray width. The walking spray gun (spray disc) moves parallel to the surface of the steel drum to make the spraying thickness uniform, and the coating film thickness should be controlled at 20~25 microns.

2, coarse grain, 疙疸

This defect is caused by the formation of protrusions on the dried coating film, which are distributed in a granular form on the partial surface of the steel drum. Usually large is called 疙疸, small is called "scorpion", and some are finely distributed.

Causes:

(1) There is dust in the painting room (spraying room), and the air in the drying room is not clean.

(2), the paint is not well filtered, the paint that is easy to precipitate is not well stirred, the skin is mixed in the paint or the modified paint is used.

Improvements:

(1) The dust removal in the painting room should be sufficient, and the indoor air should be strictly filtered and purified.

(2), the paint preparation must meet the process requirements, carefully filter, fully stirred, to prevent the paint, impurities mixed.

3, exposed, poor coverage

This kind of defect mainly refers to the phenomenon that the surface of the steel drum is leaky or painted too thin to bottom out.

Causes:

(1) The effective spray width of the leaf gun is too small to cause leakage at the center of the top and bottom of the steel drum.

(2) The viscosity of the coating is too thin, the coating is too thin; the mixing and mixing of the coating is insufficient, and the precipitate is put into use without being evenly stirred.

Improvements:

(1) Reasonably adjust the effective spray width of the spray gun.

(2), according to the process requirements of the paint, the paint must first stir up the precipitate, mix and then put into use.

4, pinhole

The pinhole refers to a small hole having a needle-like small hole or a pore like a leather on the coating film, and has a pore diameter of about 100 μm.

Causes:

(1) Coatings: The surface tension of the coating is too high, the fluidity is poor, the flattening property is poor, and the bubble release is also poor.

(2) Painting: The steel drum is not well treated before painting, and there are residual water, oil and other impurities on the surface; the paint is stirred vigorously for a long time, mixed with air to generate numerous bubbles, and the viscosity is too high; the air pressure during spraying is too high. Destroy the solvent balance; the drying solvent evaporates too quickly and the heating rate is too fast.

Improvements:

An effective way to prevent pinholes from being formed on the surface of the dried coating film is to eliminate the above reasons. In the actual production, the construction viscosity should be strictly controlled, the viscosity should be lowered and the parameters of the coating process should be controlled, that is, the large number of pinholes can be effectively eliminated.

5, orange peel

When spraying, a smooth dry coating film cannot be formed, and the uneven phenomenon of orange peel is called orange peel, and the unevenness is about 3 μm.

Causes:

(1) The viscosity of the coating is too large and the leveling property is poor.

(2) The spraying pressure is insufficient, the atomization is bad; the spraying distance is too far, the spray gun running speed is too fast, and the spraying thickness is not enough.

(3) If the drying temperature is too high, or enter the high temperature zone too early, the solvent evaporates too quickly.

Improvements:

(1) Adjust the coating viscosity.

(2) Control the compressed air pressure to achieve good atomization; adjust the spray distance and the spray gun running speed so that the spray thickness is not less than 20 microns.

(3) Control the drying specifications and meet the requirements of the process standards.

6. The phenomenon that the wrinkle coating film produces wrinkles like streaks during the drying process is called wrinkling.

Causes:

(1) The coating film is too thick and is beyond the routine.

(2) The viscosity of the paint preparation is too large.

(3), sudden high temperature accelerated baking and drying, the coating film will have a greater tendency to wrinkle.

(4) The solvent evaporates too quickly and the coating is easy to wrinkle.

Improvements:

(1) Strictly control the thickness of the spray coating film.

(2), according to the process requirements of the coating, so that the viscosity meets the requirements.

(3) According to the drying technical specifications, formulate the process conditions of gradual heating and baking.

(4) Control the evaporation rate of the solvent.