When using pre-painted steel coils, check whether it has quality problems, otherwise it will affect subsequent processing, whether you are producing sandwich panels or processing metal roofing.
Poor bendability (T bend)
Features: When the steel is bent 180 degrees, the coating on the processed part cracks and peels off.
Causes:
1. Too much pre-treatment.
2. The coating thickness is too thick.
3. Over-baking.
4. The manufacturer of the bottom coating is different from that of the top coating, or the thinner is used improperly.
Poor hardness (pencil hardness)
Features: Use a drafting pencil to forcefully scratch the surface of the coating, and a scratch will be left on the surface after wiping it off.
Causes:
1. The furnace temperature is low and the coating is not fully cured.
2. Improper heating conditions.
3. The coating thickness is thicker than specified.
Pit spots
Features: Foreign matter or dust mixed from the outside will protrude like rice grains on part or all of the surface after painting.
Causes:
1. Other types of paint or paint from other companies are mixed into the paint.
2. Foreign matter is mixed into the paint.
3. Poor water washing during pretreatment.
Poor solvent resistance (MEK)
Features: Paint peels off in spots when wiped with butanone.
Causes:
1. The baking temperature does not meet the requirements.
2. There is a problem with the curing of the paint.
3. The pretreatment cleaning is not clean.
Impact failure
Features: After the paint film is impacted, part or all of the paint peels off after being taped.
Causes:
1. Poor pretreatment.
2. Check whether the curing temperature of the topcoat is reasonable.
Orange peel
Features: The dried surface coating is rough and uneven like orange peel.
Causes:
1. The wet film is too thick.
2. When the viscosity of the paint is high.
Shrinkage
Features: The paint film is uneven and the bottom is partially exposed.
Causes:
1. The surface of the steel strip is not clean.
2. The cooling water of the primer is not clean.
3. The viscosity of the paint does not meet the requirements of the machine.
Missing coating
Features: The topcoat is not applied.
Causes:
1. The topcoat on the edge is not applied, the substrate shape is not good or the pressure between the coating roller and the large backing roller is insufficient.
2. The topcoat in the middle of the board surface is not applied, and there is water or other foreign matter on the board surface after the primer is cooled.
Color difference
Features: The color of the same standard board is different.
Causes:
1. The coating thickness is too thick or too thin.
2. It is not a batch of paint.
3. Uneven stirring when the viscosity is diluted.
Poor gloss
Features: The gloss range is abnormal.
Causes:
1. Inappropriate coating thickness.
2. Inappropriate curing conditions.
3. Insufficient stirring.
