What Is Hot Dip Galvanized Steel?

Hot-dip galvanizing is the reaction of molten metal with an iron substrate to produce an alloy layer, thereby combining both the substrate and the plating layer. Hot-dip galvanizing is to pickle iron and steel parts first. In order to remove iron oxide on the surface of iron and steel parts, after pickling, it is cleaned in an ammonium chloride or zinc chloride aqueous solution or a mixed solution of ammonium chloride and zinc chloride. , And then sent to the hot-dip plating bath. Hot-dip galvanizing has the advantages of uniform coating, strong adhesion, and long service life.

The most widely used steel materials in industry, when used in the atmosphere, sea water, soil, and building materials, corrosion will occur to varying degrees. According to statistics, the world's annual loss of steel materials due to corrosion can account for about 1/3 of its total output. In order to ensure the normal use of steel products and prolong their service life, the anti-corrosion protection technology of steel has been widely valued by people.

Hot-dip galvanizing is one of the most effective means to delay the environmental corrosion of steel materials. It is to immerse the steel products after the surface has been cleaned and activated in molten zinc solution. Zinc alloy coating with good surface adhesion. Compared with other metal protection methods, the hot-dip galvanizing process has the protective characteristics of the physical barrier and electrochemical protection of the coating.

The principle of hot dipped galvanizing is simply to clean the

1. The entire steel surface is protected. No matter the inside of the pipe, or any other corner where the coating is difficult to enter, the molten zinc is easily and uniformly covered.

Hot dip galvanized adhesion

The corrosion resistance is mainly determined by the thickness of the galvanized layer. Therefore, measuring the thickness is often the basis for determining the quality of the galvanized layer. The galvanized layer has different reactions depending on the composition, structure and structure of the steel surface. The angle and speed of the solution also have a great effect. Therefore, it is practically impossible to obtain a completely uniform coating thickness. Therefore, the measurement of the amount of adhesion cannot be judged by a single point (part), and it is necessary to measure the average zinc weight (g) per unit area ().

Hot dip galvanized

There are many methods to measure the adhesion amount, such as destructive section metallographic observation method, pickling method, non-destructive film thickness meter method, electrochemical method, and method of estimating the difference between incoming and outgoing weight. Generally used are the film thickness meter 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 using magnetic field induction. The basic condition is that the surface of the steel must be smooth and complete to obtain a more accurate figure. Therefore, it is unlikely to be an accurate figure at the corners of steel or rough, angled steel or castings. Ordinary iron parts use the original iron angelica zero base material, and quite accurate figures can still be obtained, and the casting is absolutely inaccurate.

The pickling method is the most accurate method for formal inspection reports. Only accurate care must be taken when slicing the upper and lower parts to obtain accurate figures. However, it also has disadvantages, such as it takes a lot of time, the area of complex steel is not easy to obtain, and too large pieces cannot be pickled. Therefore, it is sufficient to make full use of the film thickness meter to control the on-site process, and use the pickling method for the final detection. ^[1]

Hot Dip Galvanized Uniformity

The hot-dip galvanized steel is the easiest part to rust, which is still the thinnest 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 galvanized layer coating test consisting of a zinc layer and an 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 is also different due to the difference in the zinc / iron ratio. 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. Instead of uniformity, the distribution is mainly visual or tactile. When necessary, check the distribution state with a film thickness meter.

Hot dip galvanized

Due to the difficulty in measuring the area of small components with complex shapes, it is difficult to obtain the average film thickness, and sometimes the copper sulfate test method has to be used as a reference. However, the copper sulfate test cannot be used instead of the purpose of measuring the amount of adhesion. ^[1]

Hot Dip Galvanized Solidity

The so-called solidness is the closeness of the galvanized layer to the steel. It is mainly required that the galvanized components have the property of not being peeled off during the finishing, transportation, storage and use. The general inspection methods include hammering, squeezing, and winding .

The hammering method is to hit the test piece with a hammer to check the state of the surface of the coating film. Fix the test piece so as not to be level and horizontal due to the hammer support table. The hammer is centered on the support table, so that the vertical position of the handle will fall naturally, and 5 points are struck in parallel at 4mm intervals. However, within 10mm of the distance angle or end, this test shall not be performed, and the same place shall not be hit more than 2 times. This method is the most common and is suitable for solid testing of zinc, aluminum and other films. Other methods, such as squeezing and winding, are rarely used, so I won't mention them for the time being.

Most people often have a misconception, often in order to facilitate the measurement of solidity, take two galvanized steel, knock each other at the corners, observe the peeling of the corners to judge. If there are just a few thick zinc particles in the corners. If it is not handled well in the operation, the thick zinc particles will definitely peel off when struck hard. Therefore, this method cannot be used to determine the adhesion between the normal galvanized film and the iron base.

The amount of adhesion, uniformity and solidity are the items that define the quality inspection of hot-dip galvanizing for general specifications. It is also the standard for general formal inspection reports. Relevant specifications. ^[1]