1. Attachment
The corrosion resistance 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 will react differently depending on the composition, organization and structure of the steel surface, and the zinc is added and out. The angle and speed of the solution also have a great influence. 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). It is only meaningful to measure the average adhesion weight (g) per unit area (㎡).
There are many methods to measure the adhesion amount, such as destructive slice metallographic observation method, pickling method, non-destructive film thickness measurement method, electrochemical method, and estimation method of weight difference between incoming and outgoing goods. The commonly used methods are the film thickness gauge method and the pickling method.
The film thickness meter 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. Ordinary iron parts use the original iron material Angelica zero base material, which can still get quite accurate numbers, and castings are absolutely inaccurate.
The pickling method is the most accurate method for the formal inspection report, 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 rates 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/iron. Therefore, it is not very reasonable to judge the uniformity by the number of repetitions of a certain immersion time.
Therefore, in 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.
Three, solidity
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. The general inspection methods include hammering, squeezing, rolling, 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. To facilitate the measurement of firmness, two galvanized steels are used to 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 for general formal inspection reports. Relevant specifications.
