How to determine the cleanliness of color coated substrates after degreasing

The determination of cleanliness can be measured by laboratory instruments measurement and simple on-site determination measurement. Instruments measurement is mainly used in the condition that there’s extra high requirement on the color coated substrates cleanliness and coating mechanical properties. Most of them stay in the scope of laboratory research now.

The determination of color coated substrates cleanliness mainly adopts the following several on-site measurements:

1. Wipe method.
Use gauze, cotton, filter paper to wipe the surface of the strip. And then observe the degree of dirt attached to gauze, cotton and filter paper. To determine the cleanliness of the strip surface.

2. Water drop method.
It is an application that uses contact angles to evaluate cleanliness. Under certain conditions, the larger the diameter of the water drop (a certain volume) drops on the surface, the smaller the contact angle and the higher the cleanliness. That is, use the diameter and shape of the formed water drop on the surface as the basis for the comparison of cleanliness.

3. Infiltration method
The clean metal surface is hydrophilic. So it can be completely wetted with water. When the surface of the strip stained with dirt or oil, there will appear “water loss zone”. That will not be infiltrated by water. However, since the metal oxide film is also hydrophilic, the infiltration method can not detect whether the oxide film can be removed.

4. Breathing method
Breath out to the steel strip after degreasing and drying. If the sample surface is clean, the surface will form a uniform continuous misty water. When the cleanliness is high, the fog spot is uniform. While there is no foggy water in the areas with oil stains.

5. Water cut method
Immersed the cleaned sample into water to make the sample is perpendicular to the water surface and then removed from the water surface. From the direction of the inclined angle of 45 ° to observe whether there is hanging bead or no water area on the the specimen surface after leaving the water surface, if any, there is dirt on the surface of the strip.

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