1.What are the core testing standards and methods?
International Standards:
ISO 11143:2020 "Determination of residual oil content on the surface of cold-rolled steel sheet-gravimetric method" or ISO 16055:2020. This is currently the most widely accepted and authoritative method internationally.
ASTM D3815 "Standard Test Method for Determination of Unwashed Gum in Aviation Fuel by Solvent Extraction and Infrared Spectroscopy" (sometimes used for oil extraction).
Chinese National Standards:
The appendix to GB/T 2518-2019 "Continuously Hot-Dip Galvanized and Zinc Alloy Coated Steel Sheets and Strips" typically specifies the requirements for residual oil or iron content on the surface of galvanized substrates (i.e., cold-rolled coils), and uses the gravimetric method for testing.
GB/T 4333.10-2019 "Ferrosilicon-Determination of Carbon Content-Gravimetric Method" and other standards share the same gravimetric principle.
Japanese Industrial Standards:
Standards such as JIS G3313 "Cold-Rolled Electro-Galvanized Steel Sheets and Strips" specify residual oil content.
2.What are the standard tests for qualitative/semi-quantitative analysis?
Water Break Test:
Principle: Clean surfaces are hydrophilic, and water droplets will spread evenly on them; oil-contaminated surfaces are hydrophobic, and water droplets will shrink into beads. This is the most classic and rapid testing method.
Surface tension testing pen/solution:
Principle: A test solution with a known surface tension value (such as dyne solution) is applied to the surface of a steel plate. Whether the surface tension meets the standard is determined by whether the liquid contracts within 2-3 seconds. For example, if a surface tension ≥ 38 dynes/cm is required, a test solution with a surface tension of 38 dynes/cm is used.
Fluorescence/Ultraviolet (UV) Detection:
Principle: Some rolling oils contain fluorescent agents that fluoresce under ultraviolet light. By comparing the fluorescence intensity or area, the distribution of oil contaminants can be semi-quantitatively assessed.
FTIR (Fully Spectroradiography):
Principle: By analyzing extracts using infrared spectroscopy or directly performing ATR (Attenuated Total Reflectance) detection on the surface, not only can the types of oil be quantitatively analyzed, but also qualitatively identified.
3.What are the common limits for oil pollution control?
General Purpose (CQ, Commercial Quality):
Requirements are relatively lenient. Residual oil levels may be 200-500 mg/m² or even higher, primarily for rust prevention.
Stamping/Deep Drawing (DQ, DDQ, EDDQ):
Requirements are stringent. Residual oil levels are typically controlled at around 100-300 mg/m². The oil film must be uniform, ensuring lubrication for stamping without affecting welding and cleaning.
Appliance Panels, High-End Housings:
Requirements are high. Residual oil levels are generally < 150 mg/m² to ensure adhesion of subsequent coatings.
Automotive Exterior Panels (O5 Surface):
Requirements are the most stringent. Residual oil levels are typically required to be < 50 mg/m², or even < 30 mg/m² (e.g., high-end brands like BMW and Mercedes-Benz). Precise monitoring using gravimetric methods is mandatory, and the oil composition is also important (low silica, easy to clean).
4.How to select and implement standards?
Contract Priority: We prioritize adherence to the testing methods and limit standards explicitly stipulated in the technical agreement signed with the client.
No Contractual Provisions:
For situations requiring precise control and quality arbitration, we employ ISO 11143 or an equivalent gravimetric method.
For rapid on-site monitoring, we use hydrophilic film rupture testing or surface tension testing.
Establish Internal Control Standards: Steel production companies develop internal process control standards that are more stringent than customer standards to ensure 100% product qualification upon leaving the factory.
5.What are the advantages and disadvantages of solvent extraction-gravimetric method?
Accurate, objective, and arbitrable
Time-consuming, requires laboratory equipment, and is costly