Dry Film Thickness: The Pillar of Anti-Corrosion Protection and a Challenge for Fasteners

Corrosion is a silent and persistent enemy that compromises the durability and integrity of metallic structures. To combat it, anti-corrosion paints form an essential protective barrier, but their effectiveness does not depend solely on the coating’s formulation. A factor often neglected, yet absolutely critical, is the dry film thickness (DFT). This parameter is the basis of anti-corrosion performance, and when it is outside the specification, it can lead to premature failures, rework, and high maintenance costs.

Why is Dry Film Thickness so Important?

DFT represents the final thickness of the paint film after it has completely dried, i.e., after all solvents have evaporated. It defines the physical barrier against corrosive agents such as moisture, oxygen, and industrial pollutants. A correct thickness allows the paint to perform its essential functions:

• Barrier protection: It prevents the metal from coming into contact with the aggressive environment.
• Corrosion inhibition: Through pigments or inhibitors incorporated into the formula.
• Durability and adhesion: An adequate DFT ensures good adhesion and mechanical resistance of the coating.

When this thickness is below the specified level, protection is compromised. On the other hand, an excess of paint can lead to failures such as cracking, detachment, incomplete drying, and material waste—without proportional gains in durability.

The Critical Case of Fasteners: Low-Thickness Coatings

DFT control is fundamental in any application, but it becomes especially challenging when it comes to fasteners (bolts, nuts, washers, etc.). These components require high dimensional precision and tight tolerances to ensure efficient assembly.

Anti-corrosion coatings for fasteners are typically applied with reduced thicknesses, ranging from a few to a few dozen micrometers. In this scenario, small variations can compromise functionality:

• Assembly interference: A slightly thicker layer can increase the diameter of the fastener, making installation difficult and even damaging parts.
• Loss of dimensional tolerance: In assemblies with minimal clearance, excess paint can prevent a proper fit.
• Impact on torque and functionality: Changes in thickness alter the coefficient of friction of the threads, resulting in imprecise torques and risks of loose or overly tight joints.

Measuring DFT: An Unavoidable Quality Control

Given this scenario, rigorous control of the dry film thickness on fasteners is indispensable. Tools such as magnetic or eddy current gauges are essential to verify that the coating is within the range specified by the project.

Advantages of Precise DFT Control on Fasteners:

• Ensures assemblability: prevents rework, breakages, and production delays.
• Preserves mechanical performance: maintains the torque and load properties of the fasteners.
• Reduces waste: of paint, rejected parts, and time.
• Ensures compliance: with technical standards and customer requirements.

Conclusion

Dry film thickness is much more than a technical number—it is a direct indicator of the quality and effectiveness of anti-corrosion protection. In the case of fasteners, the challenge is even greater, requiring precise and constant monitoring. Investing in measuring technology and rigorous control protocols is not just a good practice: it is an essential strategy to ensure reliable assembly, cost reduction, and the longevity of metallic components.

Protection begins with the right thickness.