Q:What effect does insufficient substrate surface cleanliness have on corrosion resistance?
A:If there is residual grease, salt or rust on the substrate, a "corrosion cell" will be formed, causing the coating to bubble and peel from the inside, and the corrosion will spread to the substrate.
For example: If the steel structure is painted without thorough rust removal, the rust is highly hygroscopic, which may cause bubbling of the coating and shorten the anti-corrosion life.
Q:What is the impact of insufficient roughness on corrosion resistance? How to solve it?
A:Risk: A surface that is too smooth will reduce the mechanical bite force between the coating and the substrate, resulting in poor adhesion and easy penetration by corrosive media.
Solution: Control the surface roughness (such as Rz 40~80μm) through sandblasting, increase the contact area between the coating and the substrate, and form an "anchor chain effect".
Q:What are the advantages and disadvantages of different coating methods?
A:1. Brush coating / roller coating
Advantages: Suitable for complex structures or small-area construction, low cost.
Risks: Easy to produce brush marks and bubbles, uneven coating thickness, and insufficient local film thickness may become a corrosion breakthrough.
2. Spraying (air spraying / airless spraying)
Advantages: High efficiency, uniform coating, controllable film thickness, suitable for large-area construction.
Risks: Air spraying is easy to inhale air to form bubbles, and the air compressor moisture needs to be discharged regularly;
If the pressure of airless spraying is insufficient (such as <150bar), it may cause poor atomization, too thick coating or sagging.
3. Dip coating / shower coating
Applicable scenarios: small workpieces or batch production (such as hardware, automotive parts).
Risks: Insufficient dipping time or incomplete draining leads to too thin coating or sagging;
If the coating viscosity is improper during shower coating (such as too high viscosity), uneven thickness or accumulation is likely to occur.
Q:What are the consequences of improper coating thickness selection?
A:Insufficient film thickness
Risk: The coating cannot effectively prevent water, oxygen, salt spray and other corrosive media from penetrating into the substrate, leading to early corrosion.
Standard reference: The total thickness of the anti-corrosion coating for steel structures is usually required to be ≥150μm (ISO 12944), and ≥300μm for marine environments;
Excessive film thickness
Risk: Incomplete drying of the coating (especially thick paste coatings), residual solvents inside, pinholes or cracks, and accelerated corrosion.
Q:How do improper drying conditions affect corrosion resistance?
A:Too low temperature:
Effects: paint dries slowly, solvent residue increases, coating density is poor, easy to absorb water and cause corrosion.
Too low temperature: Effects: paint dries slowly, solvent residue increases, coating density is poor, easy to absorb water and cause corrosion.
Solution:
Choose a paint that matches the ambient temperature (such as low-temperature curing epoxy);
Control the construction environment humidity ≤80%, and use dehumidification equipment when necessary.