The thickness determination method of color coating plate is studied

0 Introduction
Color coating plate as a widely used in construction, home appliances, transportation and other industries composite materials, both the mechanical strength of metal and easy to mold and other advantages, but also organic coating decoration and corrosion resistance advantages. The coating thickness of the color coating plate will directly affect its processing and use performance. The coating is too thin, and it is easy to scratch the coating when processing, which in turn affects the decorative and corrosion resistance of the color coating plate
the
. For thin coatings, the aging and corrosion resistance are greatly reduced when used, even if they are not damaged during processing. However, too thick a coating can lead to an increase in the production cost of color coating plates, and this is also a waste caused by excessive product quality. Therefore, for color coating plate manufacturers, it is very important to accurately determine and strictly control the coating thickness of color coating board. In this paper, the current international, domestic and on-use test methods to determine the thickness of the coating carried out a study, for different types of color coating plate proposed the most suitable coating thickness measurement method.
a comparison of 1 GB/T 13448-2006 method
1.1 4 coating thickness detection methods
in GB/T 13448-2006 Colored Coated Steel Plates and Four kinds of color coating coating thickness test methods are introduced in the steel belt test method: magnetic thickness meter method, thousand-scale method, gold phase microscope method and drilling destructive microscope method, in which the gold phase microscope regulations as the arbitration method. Regardless of the method used to determine the coating thickness of the color coating plate, the substrate and coating of the color coating plate will directly affect the measurement results. Based on Baosteel's many years of testing experience, the comparison of the scope of application, detection accuracy and advantages and disadvantages of these four methods is shown in Table 1.
present, China's color coating plate production enterprises more use the thousand-microsecond method to determine the thickness of the coating, while European and American enterprises are more using drilling destructive micro-observation method. The main reason for this difference is that, in addition to the domestic labor costs are lower than in Europe and the United States, the limitations of various testing methods themselves are also the main reasons.
1.2 substrates
Colored coated substrates typically include cold-rolled steel plates, galvanized steel plates, hot galvanized steel plates, and hot-plated aluminum-plated zinc plates. Cold-rolled substrate because there is no coating, and the production process determines the thickness of the substrate itself and surface roughness of the uniformity is better, so no matter which test method is used, the thickness of the coating is less than other substrate detection error. Fluctuations in the thickness and surface roughness of the plated substrate determine that the determination results will be greatly affected by the use of the magnetic thickness meter method and the kilometer method in the national standard. Because the magnetic thickness meter method first to determine the total thickness of coating coating, and then to determine the thickness of coating, and the thousand-scale method to determine the total thickness of the coating plate, and then determine the thickness of the substrate, the two methods of two separate thickness determination operation can not ensure that the location of the determination is at the same point, so will be affected by the substrate and coating fluctuations, resulting in fluctuations in the measurement results, and thickness measurement results of fluctuations and substrate fluctuations. Although the gold phase microscope and DJH method can ensure that the measurement position remains the same, but because of the fluctuations of the substrate will make the detection interface difficult to divide clearly, which will also affect the accuracy of the single point of determination results. The national standard stipulates that each specimen shall be measured by an average of 3 points, but because of the fluctuation of the single point measurement result itself, the measurement error cannot be eliminated by means of a mean. According to Baosteel's
testing experience, the discreteness of coating thickness determination results is directly related to the size of substrate fluctuations.
1.3 Effect of coating performance
The roughness of the coating surface of the color coating plate will also affect the accuracy of the four detection methods in the national standard, while the elasticity of the coating itself will affect the accuracy of the magnetic thickness meter method and the thousand-scale method. Both methods use a detection probe, which affects the thickness of each measurement and thus the measurement results by the degree to which the probe is pressed against the coating or substrate. With the continuous enrichment of color coating plate product varieties, the coating surface is no longer a single smooth surface effect, the appearance of the surface has different texture effects of the product, such products with magnetic thickness meter method and the thousand-scale method simply can not determine the thickness of the coating. Because the depth of its texture can reach at least 5 to 10 m, magnetic thickness meter and thousand-meter method when the depth of the texture is counted as the thickness of the coating, resulting in a large system error. The gold phase microscope and DJH method can be used to determine such products, but due to irregular fluctuations in texture, the measurement interface is greatly influenced by human factors, and the measurement results fluctuate greatly.
1.4 measurement area
the larger the detection area, the better the representativeness of its test results, the better the detection accuracy. The detection probe diameter of the magnetic thickness gauge is generally 1.5 mm, the detection probe diameter of the micrometer is 6.3 mm, the measuring length of the gold phase microscope method is generally not more than 1 mm, and the measurement diameter of the DJH method is generally about 1 mm. Therefore, under the same conditions, the results of the thousand-square-foot method of these four detection methods fluctuate the least.
1.5 Measurement Accuracy and Analysis of Its Advantages and Disadvantages
Through the long-term accumulation of measurement results and operational experience of these four methods, we analyze the accuracy and advantages and disadvantages of the 4 methods, as shown in Table 2, using the results of the 90 g hot galvanized substrate as an example.
the above reasons, more domestic detection accuracy and faster thousand-scale method as a color coating coating thickness detection method. Because the substrate fluctuation is small, the determination fluctuation of DJH method is small, so more DJH method is used which is influenced by human factors.
2 International and domestic methods
Other international and domestic measurement methods of coating thickness include wedge cutting, thickness difference measurement, weighing, X-ray fluorescence, β-ray reflection, magnetic measurement and eddy current measurement. The magnetic thickness gauge in the national standard of the color coating plate is a magnetic measurement method, a thousand-micrometer French thickness difference measurement method, a drilling destructive microscope method belongs to the wedge-cutting method, and the gold phase microscope method is an arbitration test method. Weighing is cumbersome and not suitable for fast-paced factory laboratories, and X-ray fluorescence and β-ray reflection are used to calculate coating thickness by measuring the content of a characteristic element in the coating, which is not applicable to samples where the coating formulation is not fixed. After the investigation and test operation of the vortex measurement method, it is found that the most accurate and simple way to determine the coating thickness of the color coating plate is a kind of equipment that combines the magnetic measurement method with the vortex measurement method, and the coating thickness is calculated by combining the probe to determine the total thickness and coating thickness of the coating layer at the same time. This method of determination, because the total thickness of coating and coating thickness of the same point is measured, thus avoiding the influence of the magnetic thickness meter method on the coating fluctuations, the accuracy of the measurement results has been significantly improved. For samples with less plate fluctuations, the higher the detection accuracy, for example, for color coating plates of cold-rolled plates and galvanized substrates, the coating thickness detection accuracy can be as high as 0.5 m.
3 Conclusion
(1) For the current situation of substrate fluctuations in domestic color coating board, the thousand-scale method is the best method, with the advantages of cheap equipment, simple operation and high detection accuracy. The disadvantages are: the operator's skill requirements are high, the coating surface textured effect of the product can not be detected, the test results can only be accurate to the integer.
(2) For color coating plates with textured effects on the surface, DJH method is the best method, which has the advantages of easy operation, fast and clear interface determination. The disadvantages are: the equipment procurement and operation cost is high, the test results are subjectively influenced by the test personnel, the measurement results are affected by the fluctuation of the substrate, can not be used to detect the cold-rolled substrate color coating plate.
(3) Magnetic-vortex phase measurement coating thickness method is also a good method, with reasonable equipment cost, simple operation, fast, high precision of single-point determination (can be accurate to 0.5 m). The disadvantage is that it is greatly affected by the flatness and uniformity of the substrate surface.