1. Poor bending (T-bend)
Features:
During the 180-degree bending test of the steel, cracks and peeling of the coating occurred in the processed parts.
Cause:
1. The amount of pre-processing required is too much.
2. The coating thickness is too thick.
3. Over-baking.
4. The manufacturer of the lower coating is different from that of the upper coating, or the thinner is used improperly.
2. Poor hardness (pencil hardness)
Features:
Use a drafting pencil to draw a line firmly on the surface of the coating and wipe it off, leaving a scratch on the surface.
Cause:
1. The furnace temperature is low, and the coating is not fully cured.
2. The heating conditions are inappropriate.
3. The coating thickness is thicker than specified.
3. Bumps
Features:
Due to the external impact of the steel strip, protrusions or depressions appear on the surface of the plate, some with a certain spacing and some without.
Cause:
1. Foreign matter is mixed on the roller during painting.
2. Puncture marks when bundling thin plate products.
3. Received external impact when rewinding.
4. Edge bubbles
Features:
There is paint on both sides and after drying, bubbles appear.
Cause:
The raw material has burrs, a lot of paint, and gaps on both sides.
5. Pockets
Features:
Foreign matter or dust mixed in from the outside will cause rice grain-like protrusions on part or all of the surface after painting.
Cause:
1. Other types or paints from other companies are mixed into the paint.
2. Caused by foreign matter mixed in the paint.
3. Poor washing during pre-treatment.
6. Orange peel
Features:
The dried surface coating is as rough and uneven as orange peel.
Cause:
1. The wet film is too thick.
2. When the viscosity of the paint is high.
7. Poor solvent resistance (MEK)
Features:
Use MEK to wipe off the paint in spots.
Cause:
1. The baking temperature does not meet the requirements.
2. There is a problem with the curing of the paint.
3. The pre-treatment is not clean.
8. Unqualified impact
Features:
After the paint film is impacted, some or all of the paint will peel off after taping.
Cause:
1. Poor pre-processing.
2. Check whether the curing temperature of the topcoat is reasonable.
9. Shrinkage holes
Features:
The paint film is uneven and partially exposed.
Cause:
1. The surface of the steel strip is unclean.
2. The primer cooling water is unclean.
3. The viscosity of the paint did not meet the machine’s requirements.
10. Missing coating
Features:
A topcoat is not applied.
Cause:
1. The edge topcoat is not applied, the substrate shape is not good, or the pressure between the coating roller and the large back roller is insufficient.
2. The middle topcoat on the board surface is not applied, and there is water or other foreign matter on the board surface after the primer cools down.
11. Color difference
Features:
The color of the standard plate is different.
Cause:
1. The coating thickness is too thick or too thin.
2. Not a batch of paint.
3. Uneven stirring when viscosity is diluted.
12. Poor gloss
Features:
The range of gloss is abnormal.
Cause:
1. The coating thickness is inappropriate.
2. Improper curing conditions.
3. Insufficient stirring.
Thirteen collapsed scroll
Features:
The inner diameter of the steel coil deforms when it is stored in the warehouse after being coiled.
Cause:
1. The steel coil is affected by external forces after being coiled.
2. The winding tension is incorrect.
3. Uneven load.
14. Anti-adhesion
Features:
There is slight peeling when uncoiling, millet-like particles will appear when the primer is applied back, and the surface is uneven after applying the topcoat.
Cause:
1. Insufficient cooling before coiling.
2. Insufficient baking.
3. Part of the load is too large.
15. Crushing
Features:
Pits after application.
Cause:
1. The raw material roll is bruised.
2. Crush with various rollers before coating.
3. Crushing with the paint after application.
I hope these sharings can help you. It is very necessary to choose a stable supplier. If you have any demand for color-coated steel coils, please contact us.