What is the root cause of the "orange peel pattern" in the coating of automobile wheels?

The coating process of automobile wheels is not only related to the beauty of the vehicle, but also an effective protection for the wheel itself. However, in the actual spraying process, many automobile factories will encounter a headache-orange peel pattern. This uneven surface structure seriously affects the overall visual effect of the wheel. So, what is the root cause of the "orange peel pattern" in the coating of automobile wheels?

Ⅰ. Overview of the orange peel pattern phenomenon

Orange peel pattern, also known as poor leveling, is a common defect in wheel spraying. It manifests as the uneven surface of the paint film similar to orange peel, which seriously affects the smoothness and glossiness of the coating. The appearance of orange peel not only reduces the aesthetics of the wheel, but also may affect the durability and anti-corrosion performance of the coating.

Ⅱ. Analysis of the causes of orange peel

1. Improper spray gun adjustment

The adjustment of the spray gun is a key link in the spraying process. If the air pressure, fan angle or distance of the spray gun from the spraying surface is improperly set, the paint atomization will be poor. If the paint is sprayed in a too wide fan shape or the spray gun distance is too large, the paint will be over-dried before reaching the spraying surface. At this time, the mist paint particles will maintain the shape formed by the nozzle unchanged, thus forming a rough surface structure.

2. Improper use of thinner

The thinner plays a vital role in the spraying process. It not only adjusts the viscosity of the paint, but also affects the drying speed of the paint. If inferior thinners are used or the thinner ratio is incorrect, it will directly affect the leveling performance of the paint. Insufficient thinners or the use of fast-evaporating thinners will cause the paint particles to be over-dried before reaching the spraying surface, resulting in orange peel.

3. The ambient temperature is too high

The ambient temperature of the spraying operation has a direct impact on the drying speed of the paint. When the ambient temperature is too high, the paint particles are over-dried when they reach the spraying surface, and they cannot be fully leveled, thus forming orange peel texture. Therefore, the ambient temperature should be strictly controlled during the spraying process to avoid adverse effects of too high or too low temperature on the spraying effect.

4. Improper drying process

Drying is an important part of the spraying process. If the drying is improper, such as forced drying before the paint particles are leveled, the probability of orange peel texture will be greatly increased. In addition, during multiple spraying, if the paint film sprayed previously is over-dried, the solvent in the paint sprayed again will be absorbed by the bottom layer, resulting in the failure of the paint particles sprayed again to level, thus forming orange peel texture.

5. Uneven mixing of paint

The bottom layer of the paint will precipitate after long-term storage. If the paint is not fully stirred before spraying, it will cause uneven drying of the paint parts, resulting in orange peel texture. Therefore, the paint should be fully stirred before spraying to ensure the uniformity and stability of the paint.

III. Remedial measures for orange peel

For the orange peel phenomenon that has already appeared, we can take the following remedial measures:

1. Grinding and polishing

If the orange peel phenomenon is mild, you can use wax of appropriate coarseness and fineness to grind and polish after the paint film is completely dry. If the situation is serious, you can use fine sandpaper to grind the orange peel surface until it is smooth, and then wax and polish it. It should be noted that excessive grinding should be avoided during the grinding process to avoid damaging the paint film.

2. Re-spraying

If the orange peel phenomenon is serious and cannot be solved by grinding and polishing, you can consider re-spraying. Before re-spraying, the wheel hub should be thoroughly cleaned and treated to ensure the flatness and cleanliness of the sprayed surface. At the same time, the spray gun parameters, diluent ratio and drying process should be adjusted to avoid the recurrence of orange peel.

In actual operation, we should analyze and handle it in combination with the specific situation to ensure that the spraying effect of the wheel hub reaches the best state. Consult us now to learn more about coating knowledge!