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17

2019

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11

The correct use of cold-rolled coils is popularized

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The corrosion resistance is mainly determined by the thickness of the galvanized layer of the cold-rolled coil, so the thickness measurement is often the main basis for judging the quality of the galvanized sheet. The galvanized layer has different reactions depending on the composition, structure and structure of the steel surface. In addition, the angle and speed of the zinc solution in and out also have a great influence, so it is actually impossible to obtain a uniform coating thickness.

The uniformity test method generally uses the acid copper test, but this method is very problematic for the test of the zinc coating composed of the zinc layer and the alloy layer. This is because the dissolution rates of the zinc layer and the alloy layer in the acid copper test solution are different, and the alloy layer is also different due to the difference in the ratio of zinc/iron. Therefore, it is not very reasonable to judge the uniformity by the number of repetitions of the immersion time.

Fix the test piece so that the hammer support platform is of the same height and level. The hammer is used as the support platform, so that the shank weight falls naturally in the vertical position, and strikes 5 points in parallel at 4mm intervals to observe whether the film is peeled off for judgment. However, this test shall not be performed within 10mm from the corner or end, and the same place shall not be struck more than twice. This method is widely used and is suitable for the solid test of zinc, aluminum and other films. Others such as squeezing method and wrapping method are rarely used, so they will not be mentioned for the time being.

Ordinary people often have a misconception. For the convenience of measuring the firmness, they take two galvanized steel materials, tap each other with the corners, and observe the peeling of the corners to judge. If there are just a few thicker zinc particles at the corners. If it is not handled properly during the operation, the thick zinc particles will peel off when it is knocked hard. Therefore, this method cannot be used to determine the adhesion between the normal galvanized film and the iron base.

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