Appearance inspection
Flatness: The surface of high-quality high-temperature resistant coatings should be relatively flat and smooth, without obvious defects such as orange peel, sagging, pinholes, bubbles, etc. For example, by observing the coating surface with the naked eye or using a low-power magnifying glass, if there is sagging phenomenon, it indicates that the viscosity control of the coating during construction is improper or the brushing method is unreasonable; If there are pinholes or bubbles, it may be due to impurities mixed in the coating during the preparation process or insufficient drying or curing. Such coatings are prone to damage in subsequent use, affecting their high temperature resistance and protective performance.
Color uniformity: The color of the coating should be uniform and consistent, without any color spots, color differences, or other issues. If the color is uneven, it may indicate uneven mixing of the coating, inconsistent coating thickness, or uneven external factors during the curing process, which may also indirectly reflect problems in process control and quality assurance.
Performance testing
Adhesion test:
This is a key indicator for measuring the degree of adhesion between the coating and the substrate material. The commonly used methods include grid drawing and opening. For example, the grid cutting method involves using a specialized tool to cut grids on the surface of the coating, then applying tape and quickly tearing it off. Observe the peeling of the coating inside the grid, and the smaller the peeling area, the stronger the adhesion and the better the coating quality; If a large amount of coating falls off after tearing off the tape, it indicates that the coating is easily peeled off from the substrate. In high temperature environments and under external forces, it cannot effectively protect the substrate and cannot meet the requirements for use.
For some high temperature resistant coatings with higher requirements, such as those used in the aerospace industry, more accurate tensile testing equipment will be used for pull-out testing to accurately determine the bonding force between the coating and the substrate.
Thickness detection:
The appropriate coating thickness is crucial for its high temperature resistance and protective function. Coating thickness gauges can be used to measure, and different types of high-temperature resistant coatings have their corresponding reasonable thickness ranges. For example, zinc rich primer coatings generally have a dry film thickness within the specified range. Thin coatings may not provide sufficient anti-corrosion and high-temperature resistance, while thick coatings may easily cause cracking and other problems.
Moreover, the coating thickness should be uniform. If the thickness difference is too large, it is easy to cause local coating failure due to different thermal stresses in high temperature environments, which in turn affects the overall protective effect.
High temperature resistance performance test:
By using professional high-temperature testing equipment to simulate the actual high-temperature environment, observe the changes in the state of the coating at the set high temperature, such as discoloration, softening, peeling, cracking, etc. For example, placing a sample coated with a high-temperature resistant coating into a high-temperature furnace, heating it continuously at the expected operating temperature for a certain period of time, and then taking it out for observation. A high-quality coating can maintain its intact form and performance at the specified high temperature, still firmly adhering to the substrate and playing an effective protective role; Poor quality coatings may quickly experience peeling, detachment, and other phenomena, making them unable to withstand the corresponding high temperatures.
It is also possible to detect changes in some performance indicators of the coating after high temperature, such as hardness, wear resistance, etc., to see if it can still meet the requirements for use. High quality coatings have a relatively small decrease in relevant performance indicators after high temperature exposure.
Corrosion resistance test:
If there are corrosive media in the application environment of high-temperature resistant coatings, their corrosion resistance should be tested. Common methods include immersion test, salt spray test, etc. In the immersion test, the coated sample is immersed in corresponding corrosive solutions such as acid, alkali, salt, etc. for a period of time, and the surface of the coating is checked for corrosion marks, bubbles, peeling, etc. Coatings with good corrosion resistance can effectively resist the erosion of corrosive media.
The salt spray test is to simulate the atmospheric corrosion environment containing salt such as marine climate, place the sample in the salt spray box, and observe the coating changes after the specified spray. The high-quality coating can be kept intact in the salt spray environment for a long time to protect the substrate from corrosion.
Wear resistance test:
For high-temperature resistant coatings used in environments with wear risks, such as those used in mechanical processing, mining, and other fields, their quality should be evaluated through wear resistance tests. Common wear resistance test methods include Taber wear test, sand drop wear test, etc.
In the Taber wear test, the wear amount of the coating is measured by rotating and rubbing a specific grinding wheel on the coating surface for a certain number of turns. Coatings with lower wear indicate better wear resistance and more reliable quality; The sand drop and wear test uses sand particles of a certain size to fall from a height and impact the surface of the coating to determine its wear resistance. High quality coatings can withstand multiple sand particle impacts with minimal surface wear.
Stability assessment
Thermal cycling stability: In practical use, many high-temperature resistant coatings undergo multiple temperature changes, known as thermal cycling processes. Perform multiple high and low temperature alternating cycle tests on the coated samples to observe whether the coating will crack or peel off due to changes in thermal stress. High quality coatings can maintain good integrity and performance after multiple thermal cycles, ensuring long-term stability in high temperature resistance and protective effects.
Chemical stability: Investigate the performance changes of coatings after long-term storage in different chemical environments. In addition to the common acid, alkali, and salt solutions involved in corrosion resistance testing mentioned earlier, for some special application scenarios, such as contact with special organic solvents in chemical production, it is also necessary to test whether the coating will react with these chemicals, leading to performance degradation. Coatings with good chemical stability can maintain long-term performance stability in complex chemical environments.
Product related certifications and reputation
Certification status: Check whether the coating products have passed relevant industry standard certifications, such as strict aviation standard certifications in the aerospace field and corresponding national standard certifications in the industrial anti-corrosion field. Products that have obtained formal and authoritative certification indicate that they have met the corresponding requirements in various performance indicators, and their quality is more guaranteed.
User reputation: Understand feedback from other users who have used the brand or type of coating, obtain information through consulting peers, viewing online reviews, and other methods. If the majority of users provide feedback that the use effect is good and the coating performs stably and reliably in practical applications, then its quality is relatively more trustworthy.

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