In the actual salt spray testing process, due to the influence of various factors, there are often some errors, which may cause the test results to deviate from the real situation, and then affect the correct evaluation of materials or products with salt spray test machine. It is necessary to deeply discuss the common errors in salt spray testing and put forward effective ways to avoid them.
Before the salt spray test, if the oil, dust, processing debris and other impurities on the sample surface are not completely removed, these pollutants will affect the contact between the salt spray and the sample surface during the test, so that the test results can not truly reflect the corrosion resistance of the sample itself.
When the sample size is too large, it may exceed the effective spray range of the salt spray chamber; However, samples with special shapes, such as those with deep holes, grooves or complex curved surfaces, are easy to cause uneven distribution of salt spray on their surface, which makes the degree of corrosion in different parts vary greatly.
Salt spray concentration is one of the key parameters of salt spray test. If the salt is not accurately weighed, the solution is not evenly stirred, or the salt spray generating device of the equipment fails during the liquid mixing process, the salt spray concentration may deviate from the set standard.
Salt spray testing has strict requirements for ambient temperature and humidity. Too high or too low temperature will change the physical and chemical properties of salt spray and affect its corrosiveness; High temperature may cause the water in the salt spray to evaporate too quickly, resulting in salt crystallization on the sample surface, affecting the uniformity of corrosion; If the humidity is too low, the salt spray may not be able to fully adhere to the sample surface, reducing the corrosion effect.
The spray method includes spray pressure, angle and quantity. Excessive spray pressure may make the salt spray particles too small, easy to be blown by the air flow, and can not settle uniformly on the sample surface. If the pressure is too small, it may lead to uneven spray, and the local spray amount is too large or too small. An inappropriate spray angle exposes some parts of the sample directly to a strong spray stream, while others are under-sprayed. Too much or too little spray can also mislead test results and fail to accurately simulate the actual corrosion environment.
The length of test time is directly related to the corrosion degree of the sample. If the test time is too short, the sample may not be fully exposed to the salt spray environment, and the corrosion reaction has not reached a stable state. On the contrary, if the test time is too long, the sample may undergo excessive corrosion, resulting in the accumulation of corrosion products, falling off, changing the corrosion shape and rate of the sample surface, and distorting the final test results.
The position of the sample in the salt spray cabinet has a significant effect on the test results. If the sample is placed too close to the spray port, it will be affected by strong salt spray impact force and high concentration salt spray, and the corrosion degree will be more serious than that of other samples. The sample placed in the dead corner of the airflow may be exposed to less salt spray and less corrosion. The inhomogeneity of corrosion caused by location difference will increase the dispersion of test data and reduce the accuracy and reliability of test results.
Frequently opening the salt-spray test chamber door to inspect samples or performing other unnecessary operations during the test may damage the stable environment in the test chamber. The entry of outside air will change the temperature, humidity and salt spray concentration in the chamber, and may introduce new impurity particles that adhere to the surface of the sample and interfere with the normal process of corrosion.
The correct identification of the type of corrosion on the sample surface is the basis for the accurate evaluation of test results. Different corrosion types, such as uniform corrosion, pitting corrosion, crevice corrosion, etc., have different effects on material properties and evaluation methods. If the corrosion type is wrongly judged during the evaluation process, inappropriate rating criteria will be used, resulting in a misjudgment of the corrosion resistance of the sample.
The integrity and accuracy of data record is an important guarantee for the reliability of salt spray test results. During the testing process, if there are data omissions, recording errors, such as inaccurate recorded data such as corrosion area, depth or weight loss, or the use of wrong statistical methods during the data analysis stage, it may lead to the wrong interpretation of the test results.
Select the right cleaning solvents and tools based on the material, surface condition and possible contaminants. During the cleaning process, make sure all surfaces are thoroughly cleaned. At the same time, care should be taken to avoid scratches or other damage to the surface of the sample during the cleaning process, so as not to affect the test results.
When selecting test samples, it is necessary to fully consider the size and spray characteristics of the salt spray test chamber, and try to choose samples with appropriate size, relatively simple shape and representative. For samples with special shapes, appropriate treatment measures can be taken, such as sealing or filling deep holes, dividing complex surfaces into multiple relatively simple planes for testing, and then comprehensively evaluating their corrosion resistance. In addition, in the process of sample preparation, it is necessary to ensure the consistency of the surface roughness of the sample, processing technology and other factors to reduce the interference of the test results due to the difference of the sample itself.
Regular calibration and maintenance of salt spray test equipment is the key to ensure test accuracy. For the salt spray generator, it is necessary to check and calibrate the salt spray concentration regularly in accordance with the equipment operating procedures, and ensure that the salt spray concentration meets the test standards by accurately weighing the salt mass, measuring the solution volume and checking the spray amount. At the same time, the temperature sensor and humidity sensor in the test chamber should be calibrated regularly to ensure that the measurement accuracy is within the allowable range. In addition, the spray system should be maintained to check whether the nozzle is blocked and whether the spray pipe is leaking.
Before the salt spray test, it is necessary to consult the relevant test standards and specifications in detail, such as ASTM B117, ISO 9227, etc., and accurately set the parameters of the test equipment according to the standard requirements, including temperature, humidity, salt spray concentration, spray pressure, spray time, etc.
According to the material of the sample, the use, the expected use environment and the relevant standard requirements, scientifically and reasonably determine the salt spray test time. When determining the test time, you can refer to previous testing experience of similar products, relevant industry standards, or through pre-testing to initially assess the appropriate test duration. In the formal test process, it is necessary to operate strictly in accordance with the set time, and avoid arbitrarily shortening or extending the test time. For some products that need to be exposed to the salt spray environment for a long time, the method of segmented testing can be used to check and evaluate the sample in different time periods to more fully understand the change rule of its corrosion resistance.
When placing samples in the salt spray test chamber, the principle of uniform distribution should be followed to ensure that each sample is fully exposed to the salt spray environment and is not blocked by other samples or the internal structure of the test chamber. At the same time, it is necessary to avoid contact or collision between samples to prevent contact corrosion or friction damage from affecting the test results. The inside of the test chamber should also be cleaned and inspected before placing the sample to ensure that no foreign matter remains.
In order to ensure the stability and accuracy of the salt spray test process, the opening of the test chamber and the handling of the sample during the test should be minimized. Before the test begins, make sure that all test conditions are set, the sample is placed correctly, and the equipment is operating properly. If it is really necessary to check the sample during the test, strict operating procedures should be formulated to minimize the opening time of the cabin door and reduce the impact of the external environment on the cabin environment. During the inspection process, it is necessary to avoid touching the surface of the sample to prevent pollutants such as grease and sweat on the hand from contaminating the sample and interfering with the corrosion process.
The professional quality and experience of corrosion assessors are crucial to accurately judging the results of salt spray tests. Therefore, the relevant personnel should be systematically trained to familiarize themselves with the characteristics, formation mechanism and identification methods of various corrosion types, and master the commonly used corrosion rating standards, such as ASTM G46, ISO 10289, etc. Through training, the evaluator's observation and judgment can be improved to ensure that the corrosion type of the sample surface can be accurately identified during the evaluation process, and the correct rating standard is used for evaluation.
In the process of salt spray testing, a perfect data recording table should be designed to record in detail the test conditions, test time, corrosion appearance description, corrosion area, depth, weight loss and other data of each sample. Through data analysis, not only the corrosion resistance of the sample can be understood, but also the influence of different factors on the corrosion results can be analyzed, which provides a valuable reference for material improvement, product design and quality control.
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