How to guarantee the coating quality of the drum surface (2)

Common defects

Causes

Improvements

1Sag, vertical flow and flow mark

This kind of defect causes the paint film to produce uneven streaks and flow marks due to the abnormal flow of the paint on the vertical surface. 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.

1 The solvent evaporates slowly. The temperature is too low, almost no air changes, and the ambient air contains high levels of solvent vapors.

2 The coating formulation viscosity is too low.

3 thickness is too thick. The spraying distance is too close, the spraying angle is not proper, and the spray pattern is so large that the overlap is too much.

1 strictly control the temperature, appropriate ventilation, in line with the requirements of the process standards.

2 Strictly control the construction viscosity of the paint and deploy it according to the standard.

(3) Control spraying distance and effective spray width, and move the spray gun and the surface of the steel barrel to move in parallel so that the spraying thickness is uniform and it is better to control it at 20-25 microns.

2 Coarse grain, 疙瘩

The defect is the formation of protrusions on the dry paint film, which are distributed in a granular form on the partial surface of the steel drum.

1 There is dust in the painting room and the air in the drying room is not clean.

2 The paint is not well filtered, the paint that is easily precipitated is not well stirred, the paint skin is mixed in the paint or the deteriorated paint is used.

1 The dust in the painting room should be sufficient, and the air in the drying room should be strictly filtered and purified.

2 The preparation of the paint must meet the technical requirements, carefully filter, fully stir, and prevent the mixing of the paint and other materials.

3 exposed, poor coverage

This kind of defect mainly refers to the phenomenon of leaking or painting too thin and bottoming out.

1 The spray gun has an effective spray pattern that is too small to leak the spray at the center of the top and bottom lids of the drum.

2 Coating viscosity is too thin and the coating is too thin. The paint is not mixed well enough for mixing. The precipitation is put into use without stirring.

1 Reasonably adjust the effective spray gun spray.

2 According to the process requirements of the deployment of paint, paint must first stir the precipitate and put into use.

4 pinhole

A pinhole is a small hole like a pinhole or a leather-like pore on a paint film, with an aperture of about 100

1 Coatings: The surface tension of the coating is too high, the flowability is poor, flatness is poor, and the release of air bubbles is also poor.

2 Coating: Drum paint before bad treatment, surface residual water, oil and other debris; paint intense stirring for a long time, mixed with air to generate numerous bubbles, and the viscosity is too high; spray air pressure is too high, destroy the solvent balance; The drying solvent volatilizes too fast and the heating rate is too fast.

An effective way to prevent pinholes from drying on the surface of the paint film is to eliminate the aforementioned reasons. In the actual production, strictly controlling the viscosity of the construction, reducing the viscosity and controlling the parameters of the coating process can effectively eliminate the large number of pinholes.

5 orange peel

When spraying, it can't form a smooth dry film, but the degree of orange-like roughness is about 3

1 coating viscosity is too large, poor leveling.

2 Insufficient spray pressure, poor atomization; spray distance too far, spray gun running too fast, spray thickness is not enough.

3 The drying temperature is too high, or it enters the high temperature zone prematurely, and the flux evaporates too quickly.

1Adjust the paint construction viscosity.

2Control the compressed air pressure to achieve good atomization;Adjust the spraying distance and the speed of the gun so that the spraying thickness is not less than 20

3 Control drying specifications to meet the requirements of the process standards.

6 wrinkles

The phenomenon of wrinkle-like streaks in the film during drying is called wrinkling.

1 The film is too thick and exceeds normal.

2 The coating has too high viscosity.

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

4 The solvent evaporates too quickly and the coating tends to wrinkle.

1 strictly control the spray thickness.

2 According to the process requirements of the deployment of paint, so that the viscosity meets the requirements.

3 In accordance with the drying technical specifications to develop a gradual warming baking drying process conditions

4 Control solvent evaporation rate.

7 poor drying

After the coating is dried according to the drying specifications specified by the technology, but the paint film is not completely cured, the film is wet, the hardness is low or the surface dryness is not dry, which all belong to poor drying.

1 Drum surface residual water or oil.

2 Sprayed compressed air contains oil.

3 Spray layer is too thick.

4 dry drying room bad ventilation, low temperature, high humidity, short drying time.

1 Strengthen the surface treatment before the paint, remove the oil and water in the compressed air.

2 Control spray thickness.

3 Ensure that the technical status of the drying room is good.

8 rusty

Shortly after the coating of the steel drums, red lines or rust spots appear through the paint film under the paint film.

1 There is a problem with the pre-paint treatment of steel drums. The surface quality is poor, there is rust on its own, and there is no net removal.

2 The coating is incomplete. If there are defects such as pinholes, missing coating, etc., the corrosion resistance of the paint film is poor.

3 Damage to the paint film during stacking, and the humidity and temperature of the storage air are too high.

1 The surface must be cleaned before painting, and it may be best to perform phosphating.

2 Ensure coating integrity.

3 When stacking, do not cut the coating and do not roll on the site. Storehouses must be ventilated and must not be stored in open air.

9 becomes brittle

The phenomenon of loss of elasticity or elasticity of the paint film is called brittleness, and it is a prelude to the cracking or peeling of the paint film.

1 overheating drying, drying temperature is too high, drying time is too long to make the film become brittle.

2 paint expired, poor spraying paint film is also easy to become brittle.

3 The film is used under too low temperature conditions.

1 Dry according to the recommended drying conditions for the process or technical conditions. If the drying room takes a long time to repair due to a fault, the drying temperature in the drying room should be reduced or the steel drums dried in the drying room should be taken out in time.

2 Use good quality paint, pay attention to the expiration date.

3 Steel drums used under conditions of excessively low temperatures must be coated with the special paints that are used in conjunction with them.

Third, the steel drum surface coating requirements of the environment

Another important factor to ensure the quality of steel drum surface coating is to have a suitable coating environment, which includes the following:

1, spray drying indoor lighting, and uniform brightness

Appropriate brightness should be provided in the drum surface coating operation area (spraying room), but direct sunlight and strong light should be avoided to facilitate operation.

2. The temperature and humidity in the spraying room are moderate

The temperature and humidity of the air have a great influence on the surface coating performance of steel drums. If they are not properly mastered, they will cause various defects in the coating on the drum surface. Due to their different volatility and workability, different coatings require different temperatures and humidity during coating. The following are the environmental temperature and humidity requirements for some paint applications.

Paint name

Temperature (°C)

Relative humidity%

Note

Alkyd resin coating

Nitro coating

Modified amine curing epoxy coating

Polyamide curing ring coating

Polyurethane coating

10~30

15~20

10~30

15~30

5~30

≤85

≤70

≤85

≤85

≤70

Good temperature

Over temperature and humidity is not good

Good temperature

Good temperature

Bad humidity

3, spraying the indoor air should be cleaned when the drum surface coating

Spraying room air on the drum surface should be kept dry, clean, with little or no dust. Because the dust in the spraying chamber adheres to the paint film on the surface of the steel drum during spraying, it not only affects the appearance quality of the steel drum, but also reduces the coating performance and durability of the steel drum. Therefore, the spraying of indoor air should be strictly controlled during the production process. Cleanliness of circulation.

4, spraying drying room should be well ventilated, suitable for ventilation

The air in the spray drying room should continue to flow. On the one hand, it can speed up the coating drying, so as to dilute the concentration of harmful substances in the spray drying room and improve the sanitary conditions in the workshop.

5, spray drying indoor should be fire and explosion

During the coating process of steel drums, a large amount of solvent vapor will be volatilized. These solvent vapors and air are mixed to form explosive gas at any time. If exposed to fire, they are prone to explosion and combustion. Therefore, in the flammable liquid volatile areas are not allowed to use open flame, electrical equipment all use explosion-proof type, must be configured with a sufficient number of fire extinguishers to ensure safe production.