Galvanized channel steel
Corrosion resistance is mainly determined by the thickness of galvanized layer. Therefore, the thickness of galvanized layer is often the main basis for determining the quality of galvanized layer. The galvanized layer has different reactions depending on the composition, structure and structure of channel steel. In addition, the angle and speed of entering and leaving galvanized solution also have a great influence. Therefore, it is impossible to have a uniform zinc layer thickness in practice. Therefore, it is absolutely impossible to determine the attachment quantity by a single point (position), and it is necessary to measure the uniform attachment zinc weight (g) per unit area ().
There are many methods to measure adhesion, such as destructive slice metallographic observation, acid pickling, non-destructive film thickness gauge, electrochemical method, weight difference between incoming and outgoing, etc. Commonly used are measuring method and pickling method. Coating thickness gauge is the most common and easy way to measure the thickness of zinc layer by magnetic field induction. Its basic condition is that the appearance of channel steel must be smooth and intact so that more accurate figures can be obtained. Therefore, it is impossible to get a precise figure at the edge and corner of channel steel or rough, angular steel castings or castings. Ordinary iron castings are made of raw iron, Angelica sinensis and zero base material. Quite accurate figures can be obtained, and the castings are absolutely inaccurate.
The acid pickling method is the most accurate method for the formal inspection report. Only when slicing, we must pay attention to the fair choice of the upper and lower parts to obtain the accurate figures. However, it also has some drawbacks, such as time-consuming, difficult to obtain the area of complex channel steel, too large parts can not be pickled as a whole, and so on. Therefore, it is sufficient to use thickness gauge to control the on-site process, and acid pickling method to do the final detection.
Hot dip galvanized trough steel is still the thinnest center of zinc layer, so it is necessary to test whether the thinnest part of galvanized trough steel conforms to the specification.
The homogeneity test method is usually copper sulphate test, but this method is very problematic for the test of zinc coatings and alloy coatings. Because the dissolution rate of zinc layer and alloy layer in copper sulfate solution is different, the ratio of zinc to iron in alloy layer is also different. Therefore, it is not reasonable to judge the average by the repetition times of a certain soaking time.
Therefore, in recent European and American specifications and JIS, there has been a tendency to abolish this experimental method, replacing homogeneity with dispersion, focusing on visual or tactile sensation, and checking the dispersion status with film thickness gauge when necessary.
Because the area measurement of small components with complex shape is not easy, it is not easy to obtain uniform film thickness. Sometimes the copper sulfate experiment method has to be used as a reference, but the copper sulfate experiment can never replace the purpose of adhesion measurement.
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