Common defects and prevention measures in the process of steel drum painting
Common defects and prevention measures in the process of steel drum painting
Qi Guoliang
First, the coating film sag: the paint is sprayed on the surface of the steel drum, under the action of gravity, part of the paint flows evenly downward, so that the coating film is uneven and thick, forming tear marks. In severe cases, the phenomenon of drooping like a curtain is called sag. .
1, the cause:
(1) The coating viscosity is too low and the coating film is too thick;
(2) The nozzle diameter of the spray gun is too large, the spray pressure is too small, the spray nozzle is too close to the surface of the steel drum, and the paint sprayed out in a certain period of time is excessive.
(3) The coating itself is slow in drying, the solvent is volatilized slowly, and the fluidity is large during the film formation process.
(4) The steel drum before the spraying is not well treated, the surface is oily or watery, and the coating has poor adhesion to the surface of the steel drum.
(5) There are many heavy pigments in the paint, which are easy to precipitate during storage. If the construction is not fully stirred, it is easy to sag.
(6) At present, the steel drum is generally sprayed with dry paint. After spraying, it should be sent to the baking oven for baking. It should not stay too long.
2. Prevention measures:
(1) Adjust the application viscosity of the coating. The coating film does not need to be coated too thick, as long as the specified requirements are met. If a thick coating film is required, two or more sprayings may be selected.
(2) The nozzle and spray pressure, the distance of the spray gun, the angle of the spray gun and the steel drum, and the travel speed should be adjusted to the appropriate parameters according to the operation requirements and paint performance.
(3) Select the matching diluent to adjust the balance between the evaporation rate of the diluent and the dryness of the coating.
(4) Do the pre-treatment of steel drum spraying to prevent oil and water from adhering to the surface of the steel drum and improve the adhesion of the coating.
(5) The paint should be thoroughly stirred before use, and the paint with a long storage time will precipitate.
(6) After spraying with dry paint, the steel drum should be sent to the oven for baking in a timely manner within the specified time, otherwise it will easily cause sagging.
Second, the loss of light: the paint film is full and shiny after painting, but after a period of time, the phenomenon of gloss gradually disappears, called loss of light.
1, the cause:
(1) The surface of the steel drum is rough and porous.
(2) The surface temperature of the steel drum before the coating is applied is too high.
(3) The quality of the coating itself is poor.
(4) Add too much thinner to the coating.
(5) The baking temperature after coating is too high and the time is too long.
2. Prevention measures:
(1) The surface of the steel drum is not smooth. If the rust is not treated, the phosphating film is too rough and the surface is dirty, oil or water.
(2) Reduce the surface temperature of the steel drum before spraying, otherwise it will affect the gloss of the coating.
(3) Purchase good quality coatings.
(4) The amount of drying type coating thinner should not be too large.
(5) The coated steel drum should be exposed to the air for a period of time before being sent to the oven, so that the paint has its own leveling time.
Third, back sticking: After the coating is dried, the phenomenon of sticking after a period of time is called back tack.
1, the cause:
(1) The problem of the coating itself, the thinner of the volatility is added to the paint, and the drier is improperly formulated or used insufficiently.
(2) The coating is too thick, the primer does not have a chance to dry, and the coating is only dry.
(3) Baking type paint baking time is too short, baking paint to dry, need to be baked according to the process, whether it is baking time or baking temperature should be guaranteed.
(4) The steel drum after spraying has a bad storage environment, such as cold, rain, acid, alkali, salt, and smoke.
(5) Applying a new coating on the old coating, due to the presence of atmospheric contaminants such as sulfides on the old coating, affecting the normal drying of the new coating, a back stick phenomenon may occur.
2. Prevention measures:
(1) The coating should be made of a moderate diluent, adjust the amount of drier, and use less or less dry resin.
(2) The coating film should not be too thick. If it is sprayed twice, the first coating must be completely dried before it can be sprayed twice.
(3) Bake in strict accordance with the provisions of the construction process to ensure the baking time and baking temperature.
(4) Have a good storage environment.
(5) The old coating must be cleaned before applying a new coating, such as rust removal, sanding, degreasing, etc.
4. Shedding: The coating film loses its proper adhesion to the substrate, so that the phenomenon of being separated into small pieces (or whole pieces) away from the object surface is called shedding.
1, the cause:
(1) Improper pre-treatment, the surface of the steel drum is oily, watery, rust, dust or chemicals.
(2) The baking time of the paint film is too long or the baking temperature is too high, so that the hardness of the paint film is high and the phenomenon is brittle.
(3) The coating itself has poor adhesion or excessive diluent is added during spraying.
(4) The coating is too thick, the coating is not dry, the coating is dry and the bottom layer is not dry, causing the topcoat to shrink during the drying process and causing the coating to fall off.
(5) The coating is stored in a chemical environment such as high humidity, acid, alkali or salt to damage the coating film.
2, prevention measures
(1) The pre-treatment of the steel drum is very important, and the surface of the steel drum must be cleaned.
(2) Strictly follow the construction process of the coating.
(3) Purchase good quality coatings, and paints and thinners should be matched properly.
(4) The coating should not be too thick during construction to ensure that the coating is dry.
(5) The coating should be kept in a good environment.
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