(V) Dealing with the defects of the drum surface coating in time
The defects found during the inspection of the coating process and the final coating performance shall be promptly dealt with, and corresponding measures shall be taken to remedy the defects so as to ensure the surface coating quality of the steel drum and achieve the purpose of paint coating.
During the coating process of steel drums, or after coating, the coating film defects generally relate 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. Factors such as the following, common defects and the causes and improvement measures are mainly the following:
1, sag, vertical flow and flow marks
This type of defect results in uneven coating and flow marks on the coating due to the abnormal flow of the coating on the cylindrical surface of the drum. Sinking is generally proportional to the specific gravity of the paint, inversely proportional to the viscosity, and proportional to the third power of the coating thickness.
The reason for this defect:
(1) Slow evaporation of solvent. The temperature is too low, almost no ventilation (bad ventilation), and the content of solvent evaporation in the surrounding air is high.
(2) The viscosity of the coating formulation is too low.
(3) The thickness is too thick. The spraying distance is too close, the spray angle is not proper, and the spray pattern is so large that there is too much overlap.
Improvements:
(1) Strict temperature control, proper ventilation (good ventilation), and compliance with process standards.
(2) Strictly control the construction viscosity of the coating and deploy it according to the standard.
(3) Control spraying distance and effective spray width, and the walking spray gun (spray plate) moves in parallel with the surface of the steel drum so that the spraying thickness is uniform, and the thickness of the coating film should be controlled at 20-25 microns.
2, coarse grain,
This kind of defect is produced on the dry coating film and is distributed in the form of particles on the partial surface of the steel drum. It is usually referred to as a cockroach, and the small one is often referred to as a cockroach, and some are finely distributed.
Causes:
(1) There is dust in the painting room (spray room), and the air in the drying room is not clean.
(2) The paint is not well filtered, the easily precipitated paint is not well stirred, the skin is mixed in the paint or the deteriorated paint is used.
Improvements:
(1) Dust removal in the painting room should be sufficient, and the air in the drying room should be strictly filtered and purified.
(2), the deployment of paint must meet the process requirements, carefully filtered, fully stirred, prevent paint and sundries mixed.
3, exposed, poor coverage
This kind of defect mainly refers to the phenomenon that the surface of the steel drum is leaked or painted too thin and bottomed out.
Causes:
(1) The effective spray of the leaf gun is too small to leak the spray at the center of the top and bottom cover of the drum.
(2), paint viscosity is too thin, the coating is too thin; coating mixing is not sufficient, the precipitation is put into use without stirring.
Improvements:
(1) Reasonably adjust the effective spray gun spray rate.
(2) According to the process requirements of the deployment of paint, paint must first stir the precipitate, mixed and put into use.
4, pinhole
Pinholes are pinholes or pores like leather pores in the coating film. The pore size is about 100 microns.
Causes:
(1) Coatings: The surface tension of the coating is too high, the fluidity is poor, flatness is poor, and the release of air bubbles is also poor.
(2) Painting: Difficult handling before steel drum painting, residual water, oil and other debris on the surface; intense stirring of the paint for a long time, mixing into the air to generate numerous bubbles, and the viscosity is too high; the air pressure during spraying is too high, Destruction of solvent balance; drying solvent volatilization speed too fast, heating rate is too fast.
Improvements:
An effective way to prevent pinholes from drying on the film surface is to eliminate the above reasons. In actual production, the construction viscosity should be strictly controlled, the viscosity should be reduced, and the parameters of the coating process should be controlled. This can effectively eliminate the large number of pinholes.
5, orange peel
When spraying, a smooth, dry film cannot be formed, and the orange-skin-like irregularity is called orange peel, and the degree of irregularity is about 3 μm.
Causes:
(1), paint viscosity is too large, poor leveling.
(2) Insufficient spray pressure and poor atomization; spraying distance too far, spray gun running too fast, spraying thickness is not enough.
(3) The drying temperature is too high, or it enters the high temperature zone prematurely and the solvent evaporates too quickly.
Improvements:
(1) Adjust the viscosity of the paint application.
(2) Control the compressed air pressure to achieve good atomization; adjust the spraying distance and the speed of the gun so that the spray thickness is not less than 20 microns.
(3) Control the drying specifications to meet the requirements of the process standards.
6, wrinkle coating film in the drying process resulting wrinkle-like phenomenon is called wrinkling.
Causes:
(1) The film is too thick and exceeds the normal.
(2) The viscosity of the coating is too high.
(3) Sudden high-temperature accelerated baking drying, the coating will have a greater tendency to wrinkle.
(4) The solvent evaporates too quickly and the coating tends to wrinkle.
Improvements:
(1) Strictly control the thickness of spray coating film.
(2) According to the process requirements, the paint is formulated so that the viscosity meets the requirements.
(3) In accordance with the drying technical specifications, formulate the process conditions for gradual heating, baking and drying.
(4) Control solvent evaporation rate.
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