1.What are the main international and industry standards?
JIS G 3313 / JFS A 3021 (Japanese Industrial Standard)
This is a widely cited standard in the industry, typically using "milligrams per square meter" (mg/m²) as the unit.
It classifies cleanliness into different grades, for example:
Grade A: Extremely clean, very little residue (typically <50 mg/m²), suitable for electroplating and high-requirement coatings.
Grade B: Clean, little residue (e.g., 50-100 mg/m²), suitable for general coatings.
Grade C: Standard cleanliness, with a small amount of residue (e.g., 100-200 mg/m²), suitable for parts requiring simple processing or no surface treatment.
ISO 11126 / ISO 8502 (International Standards)
The ISO 11126 series concerns the surface treatment of steel before painting.
The ISO 8502 series specifically assesses surface cleanliness, such as qualitatively or quantitatively evaluating grease residue through methods like water cracking, cloth wiping, or solvent extraction. It places greater emphasis on on-site assessment before painting.
EN/DIN Standards (European Standards)
European automotive and manufacturing industries have stringent requirements. For example, automakers such as Volkswagen and BMW have their own material standards, with specific regulations on the cleanliness of cold-rolled steel sheets (e.g., residues < 100 mg/m², or even lower), typically requiring third-party testing reports.
2.What are the stipulations in Chinese standards?
GB/T 5213 Cold-rolled low-carbon steel sheet and strip
This is the basic standard for cold-rolled sheets, providing descriptive requirements for surface quality (e.g., "the surface must be free of defects that affect its use"), but it does not provide specific, quantifiable cleanliness levels.
GB/T 9791 Metals and other inorganic coatings - Thermal spraying - Cleaning and treatment of surfaces
This standard covers methods for assessing cleanliness before surface treatment.
Industry and enterprise standards
Large steel companies such as Baosteel and Ansteel have their own "Enterprise Standards" or "Technical Agreements," which clearly specify cleanliness control indicators for different customer needs, usually based on JIS or customer requirements. This is the most critical basis for actual operation.
3.What are the principles and results of solvent extraction-gravimetric method?
Principle: A sample of known area is scrubbed or soaked with a specific solvent (such as acetone or petroleum ether) to extract surface grease and soluble substances. After evaporating the solvent, the weight of the residue is measured.
Result: Expressed directly in mg/m². This is the most objective and comparable quantitative indicator.
4.What are the principles, advantages, and disadvantages of the contact angle measurement method?
Principle: A drop of water is placed on a clean surface, and the contact angle between the water droplet and the surface is measured. Higher cleanliness results in higher surface energy, causing the water droplet to spread more widely and thus a smaller contact angle. Conversely, the presence of oil or dirt leads to a larger contact angle.
Advantages: Fast and non-destructive.
Disadvantages: It is an indirect measurement, easily affected by surface roughness, and is typically used for rapid monitoring on production lines.
5.What are the testing principles and applications of dyne pens/dyne solutions?
Principle: Apply a test liquid with known surface tension to the surface and observe whether it can spread evenly without shrinking within 2 seconds. The highest surface tension value that can be spread is the surface energy (unit: dynes/cm or mN/m).
Application: Commonly used in the printing and coating industries to quickly determine whether a surface meets treatment requirements (e.g., ≥38 dynes).