In machining and manufacturing processes, anti-rust water is widely used for inter-process rust prevention and long-term storage protection. The concentration of anti-rust water is a critical parameter affecting rust prevention effectiveness. Insufficient concentration can lead to workpiece corrosion, while excessive concentration results in cost waste and may leave residues on workpiece surfaces. Therefore, accurate and convenient testing of anti-rust water concentration is an essential part of on-site quality control in the machinery industry.
I. Main Methods for Testing Anti-Rust Water Concentration
1.1 Refractometer Method — First Choice for On-Site Testing
The refractometer method is the most commonly used and convenient approach for on-site testing of anti-rust water concentration in the machinery industry. Its principle is based on the proportional relationship between the refractive index of light passing through a solution and the solution concentration. Effective components in anti-rust water, such as rust inhibitors and corrosion inhibitors, alter the refractive index of the solution, allowing concentration values to be calculated by measuring the refractive index.
1.2 pH Measurement Method — Auxiliary Verification Tool
The pH value of anti-rust water is closely related to its rust prevention performance. Most water-based anti-rust fluids require alkaline conditions with a pH of 8.5–9.5 to achieve optimal rust prevention. Alkaline environments help form stable passive films on metal surfaces while inhibiting microbial growth. When anti-rust water concentration decreases, the pH value typically drops accordingly.
1.3 Chemical Titration Method — Laboratory Precision Testing
When precise determination of specific components in anti-rust water is required, chemical titration can be employed. This method is suitable for anti-rust water with clearly defined formulations and is commonly used for quality acceptance of anti-rust water from suppliers and periodic sampling inspections.
1.4 Electrochemical Method — Advanced Testing and Failure Analysis
The electrochemical method evaluates rust prevention performance and indirectly reflects effective concentration by measuring the influence of anti-rust water on the electrochemical corrosion behavior of metals. National Standard GB/T 26109-2010 "Water-Based Anti-Rust Fluid — Rust Prevention Performance Test — Multi-Electrode Electrochemical Method" specifies the technical requirements for this method.
1.5 Rust Prevention Performance Verification Method — Final Determination of Concentration Compliance
The above methods are all indirect testing approaches. The most reliable way to verify concentration is to directly test the rust prevention performance of the anti-rust water. When refractometer or pH test results are questionable, the following simple method can be used for verification:
Cast Iron Chip Method (Simple On-Site Verification): Spread an appropriate amount of iron chips on filter paper, add the anti-rust water to be tested to fully saturate the chips, place the sample at room temperature for 24–48 hours, and observe the rust condition of the chips and filter paper. If no rust marks are present, the anti-rust concentration meets the standard.
II. Comparison of Testing Methods
Testing Method | Application Scenario | Accuracy | Response Time | Cost | Advantages |
Refractometer Method | Routine on-site monitoring | Medium | Instant | Low | Fast and simple, no reagents needed |
pH Test Paper Method | Rapid on-site screening | Low | Instant | Very Low | Extremely simple operation |
Chemical Titration Method | Laboratory precision testing | Very High | 30–60 minutes | Medium | Quantitatively accurate |
Electrochemical Method | Advanced analysis | Very High | Several hours | High | Comprehensive performance evaluation |
Rust Prevention Verification Method | Confirmation when concentration is questionable | Qualitative | 24–48 hours | Low | Direct effect validation |
III. Selection Recommendations
3.1 Routine Inter-Process Monitoring
Use the refractometer method as the primary approach, with pH test paper as auxiliary verification. Establish a relationship database of "concentration–pH value–rust prevention effect."
3.2 Centralized Fluid Supply Systems
In addition to concentration monitoring, regularly test pH value, water hardness, and microbial content to comprehensively assess the condition of the anti-rust fluid.
3.3 New Fluid Acceptance / Periodic Sampling
Use chemical titration or entrust third-party laboratories for testing.
3.4 Failure Analysis
Employ electrochemical methods combined with rust prevention performance verification.
Conclusion
Testing anti-rust water concentration is a critical link in quality control for inter-process rust prevention in the machinery industry. Using refractometers for rapid on-site control, supplemented by titration for precise calibration, along with normalized testing and management, can prevent rework and scrap caused by rust prevention failure while eliminating waste of concentrated solution.
Ningbo Qianhao Metal Products Co., Ltd. is a professional casting and manufacturing company. Our internally used anti-rust water has established a three-level testing system of "routine inspection + periodic sampling + comprehensive testing," combined with rust prevention performance verification tests to ensure that anti-rust water always remains within the effective concentration range. We systematically conduct quality training annually and keep pace with cutting-edge industry standards, deeply integrating the latest methods into every stage from design to production. By choosing us, you will gain not only a supplier that meets standards but also a reliable partner that views quality as a strategic core and is committed to continuous improvement.
Quality Control Department: Ji Yanxiu