1. Attachment amount
Corrosion resistance is mainly determined by the thickness of the galvanized layer. Therefore, the measurement thickness is often the basis for determining the quality of galvanizing. The galvanized layer reacts differently depending on the composition, structure and structure of the steel surface. The angle and speed of the solution also have a great influence. Therefore, it is practically impossible to obtain a completely uniform coating thickness. Therefore, it is absolutely impossible to measure the amount of adhesion by a single point (part). It is necessary to measure the average attached zinc weight (g) per unit area (m2).
There are many methods for measuring the amount of adhesion, such as destructive slice metallographic observation, acid washing, non-destructive film thickness meter, electrochemical method, and weight difference estimation method. Commonly used are the film thickness method and the pickling method.
The film thickness gauge (coating thickness gauge) is the most common 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 before accurate numbers can be obtained. Therefore, at the corners of the steel or rough, angled steel or castings, etc., an accurate number is unlikely. Ordinary iron parts with the original iron material Angelica zero substrate, can still get quite accurate figures, castings are absolutely inaccurate.
The pickling method is the most accurate method for formal inspection reports. However, it is necessary to pay attention to the fair choice of the upper and lower parts when slicing, in order to obtain accurate figures. However, it also has shortcomings, such as a lot of time, complex steel area is not easy to find, too large pieces can not be soaked. Therefore, it is sufficient to make full use of the film thickness gauge to control the on-site process, and the acid picking method for the final test is sufficient.
The most rustable part of hot dip galvanized steel is still the thinnest part of the zinc layer, so it is necessary to measure whether the thinnest part meets the standard.
The test method for uniformity is generally tested with copper sulfate, but this method is problematic for the test of the galvanized layer 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 is different, and the alloy layer also differs due to the difference in the ratio of zinc/iron. Therefore, it is not very reasonable to determine 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, and the uniformity is replaced by distribution, and the visual or tactile sensation is dominant. When necessary, the film thickness gauge is used to check the distribution state.
The small-sized components are difficult to measure due to the area measurement, and it is difficult to obtain the average film thickness. Sometimes, the copper sulfate test method has to be used as a reference, but the purpose of measuring the adhesion amount cannot be replaced by the copper sulfate test.
The so-called solidity is the adhesion between the galvanized layer and the steel. It is mainly required that the galvanized component has the property of not being peeled off during finishing, transportation, storage and use. The general inspection methods include hammering, squeezing, and winding. .
The hammering method is to hammer the test piece and check the state of the surface of the plating film. Fix the test piece so that the height and level of the hammer support table are the same. The hammer is centered on the support table, and the vertical position of the handle weight is naturally dropped. The hammer is struck at 5 points in parallel at 4 mm intervals to observe whether the film is peeled off or not. However, within 10mm of the distance or end, this test shall not be carried out, and the same place shall not be struck more than 2 times. This method is the most common and is suitable for solid testing of zinc, aluminum and other films. Others such as the squeezing method and the winding method are rarely used, so they are not mentioned for the time being.
The average person often has a misconception. Often, in order to measure the solidity, two galvanized steel materials are used, and the corners are knocked on each other to observe the corner peeling. If there are just a few thicker zinc particles at the corners. If it is not handled well in the operation, it will be peeled off with a strong tap. Therefore, this method cannot be used to determine the adhesion of a normal galvanized coating to an iron base.
Adhesion, uniformity and firmness are the items that define the hot dip galvanizing quality inspection for general specifications. Is also the standard for general formal inspection reports