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1. The corrosion resistance of the adhesion is mainly determined by the thickness of the galvanized layer, so measuring the thickness is often the main basis for judging the quality of the galvanized layer. The galvanized layer has different reactions due to the composition, organization and structure of the steel surface. , The angle and speed of entering and exiting the zinc solution also have a great impact. Therefore, it is actually impossible to predict a completely uniform coating thickness. Therefore, the measurement of the adhesion amount must not be judged by a single point (location), and it is only meaningful to measure the average adhesion weight (g) per unit area (㎡).
There are many methods for measuring adhesion, such as destructive slice metallographic observation method, pickling method, non-destructive film thickness measurement method, electrochemical method, and weight difference estimation method. The commonly used methods are the film thickness gauge method and the pickling method.
The film thickness gauge (coating thickness gauge) is the most common and trouble-free method for measuring the thickness of the zinc layer by magnetic field induction. The basic condition is that the steel surface must be smooth and complete to obtain more accurate numbers. Therefore, it is impossible to get an accurate figure at the corners of the steel or rough, angled steel or castings. For ordinary iron parts, the original iron material Angelica sinensis has zero base material, and quite accurate numbers can be obtained, but castings are absolutely inaccurate.
The pickling method is the most accurate method for formal inspection reports, but you must pay attention to the fair selection of the upper and lower parts when slicing, in order to obtain accurate numbers. But it also has shortcomings, such as time-consuming, complicated steel area is not easy to obtain, too large pieces can not be pickled. Therefore, it is sufficient to make full use of the film thickness gauge to control the on-site manufacturing process, and to use the pickling method for the final inspection.
2. Uniformity The
most rusty part of hot-dip galvanized steel is still the thinnest part of the zinc layer, so it is necessary to test whether the thinnest part meets the standard.
The uniformity test method generally uses copper sulfate test, but this method is very problematic for the test of the zinc coating film composed of the zinc layer and the alloy layer. This is because the dissolution rate of the zinc layer and the alloy layer in the copper sulfate test solution are different, and the alloy layer is also different due to the difference in the ratio of zinc to iron. Therefore, it is not very reasonable to judge the uniformity by the number of repetitions of a certain immersion time.
Therefore, in the recent European and American standards and JIS, there is a tendency to abolish this test method, replacing uniformity with distribution, focusing on visual or touch, and checking the distribution with a film thickness gauge when necessary.
For small components with complicated shapes, it is not easy to measure the area, and it is not easy to obtain the average film thickness. Sometimes the copper sulfate test method has to be used as a reference, but the copper sulfate test must not be used to replace the purpose of the adhesion measurement.
3. Firmness The
so-called firmness is the adhesion between the galvanized layer and the steel. The galvanized components are mainly required to be non-peelable during finishing, transportation, storage and use. General inspection methods include hammering, squeezing, and Volume attachment method, etc.
The hammering method is to hit the test piece with a hammer to check the surface of the coating film. Fix the test piece so that the hammer support table is not high and level. The hammer is centered on the support table, so that the handle weight will fall naturally. Hit 5 points in parallel at 4mm intervals and observe whether the film peels off for judgment. However, within 10mm from the corner or end, this test is not allowed, and the same place cannot be hit more than twice. This method is the most common and is suitable for testing the firmness of zinc and aluminum films. Others such as squeeze and roll are rarely used, so I won’t mention them for now.
Most people often have a misconception. In order to facilitate the measurement of firmness, they take two galvanized steels and knock each other at the corners, and observe the peeling of the corners for judgment. If there are just a few thick zinc particles at the corners. If it is not handled properly during the operation, the thick zinc particles will surely peel off as soon as it is hit hard. Therefore, this method cannot be used to determine the adhesion between the normal galvanized film and the iron base.
Adhesion, uniformity and firmness are the items defined by the general specifications for quality inspection of hot-dip galvanizing. It is also the standard of general formal inspection report