1.How does the Dyne Pen/Dyne Liquid Test work?
Using a series of test liquids (dyne solutions) with varying surface tensions, when the test liquid is applied to a solid surface:
If the liquid forms a continuous film that remains intact for more than two seconds, the surface free energy of the solid is higher than the surface tension of the test liquid.
If the liquid shrinks and breaks into droplets within two seconds, the surface free energy of the solid is lower than the surface tension of the test liquid.
By experimenting with different dyne solutions, a critical value can be determined. This critical value represents the dyne value of the galvanized coil surface, expressed in mN/m (millinewton/meter).
2.What are the advantages and disadvantages of the Dyne Pen/Dyne Liquid test?
Advantages:
Extremely fast, simple, and low-cost.
Ideal for rapid on-site evaluation and quality control.
Disadvantages:
The results are semi-quantitative and somewhat subjective.
Affected by operator technique, ambient temperature, and humidity.
The test fluid evaporates, and concentration may fluctuate, requiring regular calibration.
3.What is the principle of contact angle measurement?
A drop of pure liquid (usually deionized water) with known surface tension is placed on the surface of a galvanized coil. An optical device is used to measure the angle between the droplet and the solid surface at its point of contact, known as the contact angle.
A small contact angle (a widely spread droplet) indicates that the liquid readily wets the surface, indicating high surface free energy.
A large contact angle (a bead-like droplet) indicates that the liquid does not readily wet the surface, indicating low surface free energy.
4.What are the advantages and disadvantages of contact angle measurement?
Advantages:
Accurate, objective, and quantifiable results.
Provides more detailed information on surface energy components.
Disadvantages:
Expensive equipment (contact angle meter).
Complex operation, requiring specialized expertise.
Slow test speed, not suitable for on-site production line use.
5.What are the precautions in practical application?
Surface Cleanliness: Any oil, fingerprints, or dust will significantly reduce the measured dyne value. Ensure the surface is absolutely clean before measurement.
Surface Treatment:
Skin Finishing: After skin-pass milling, galvanized coils have a smoother surface, more active sites, and a higher surface free energy.
Passivation: Galvanized coils are typically treated with a chromate or chromium-free passivation treatment to form a protective film. Different types of passivation films (e.g., chromium-containing and chromium-free) can also affect the surface free energy.
Aging: The surface properties of galvanized coils may change over time, especially if stored in poor conditions, resulting in surface contamination or slight oxidation.