Zinc Coating Standard of Steel Wire and Wire Products

Zinc Coating Standard of Steel Wire and Wire Products

Attached: BS EN 10244-2-2001.PDF

As a professional manufacturer, we are very strict in the selection of raw materials. The amount of zinc applied to all hot-dip galvanized wires must comply with the BS EN 10244-2-2001 standard, and the materials need to be tested separately when entering and leaving the warehouse. Only materials that pass the inspection can be used for product production.

BRIEFLY:

Hot-dip galvanizing is to make the molten metal react with the iron matrix to produce an alloy layer, so that the matrix and the coating are combined. Hot-dip galvanizing is to pickle the steel parts first. In order to remove the iron oxide on the surface of the steel parts, after pickling, it is cleaned in a tank of ammonium chloride or zinc chloride aqueous solution or a mixed aqueous solution of ammonium chloride and zinc chloride , and then sent to the hot dip coating tank. Hot-dip galvanizing has the advantages of uniform coating, strong adhesion and long service life.

The most widely used steel materials in the industry will corrode to varying degrees when used in environments such as atmosphere, seawater, soil and building materials. According to statistics, the world's annual loss of steel materials due to corrosion accounts for about 1/3 of its total production. In order to ensure the normal use of steel products and prolong their service life, the anti-corrosion protection technology of steel has always received widespread attention.

Hot-dip galvanizing is one of the most effective means to delay the environmental corrosion of iron and steel materials. It is to immerse the iron and steel products whose surfaces have been cleaned and activated in molten zinc solution. The surface is coated with a zinc alloy coating with good adhesion. Compared with other metal protection methods, the hot-dip galvanizing process has the protection characteristics of the combination of the physical barrier and electrochemical protection of the coating, the bonding strength of the coating and the substrate, the compactness, durability, maintenance-free and economical of the coating. It has unparalleled advantages in terms of flexibility and adaptability to the shape and size of products. At present, hot-dip galvanized products mainly include steel plates, steel strips, steel wires, and steel pipes.

PROCESS INTRODUCTION:

The principle of hot dip galvanizing (hot dipped galvanizing), simply put, is to immerse the cleaned iron parts in a zinc bath through the wetting effect of the flux, so that the steel reacts with molten zinc to form an alloyed alloy. skin. In a good hot dip galvanizing operation, each process should be under strict control, and the function of the process should be fully exerted. And if the operation of the previous process is not good, it will cause a chain reaction of adverse reactions in the subsequent process, which will greatly increase the operating cost or cause poor hot-dip galvanized products. If the pretreatment is not good, the molten zinc cannot react completely with the steel to form the most perfect galvanized film structure. If the post-treatment is not good, the appearance of the galvanized film will be damaged, and the commodity value will be reduced.

ADVANTAGE:

1. The entire steel surface is protected, no matter in the inside of the pipe fitting in the depression, or any other corner where the coating is difficult to enter, the molten zinc is easy to cover evenly.

2. The hardness value of galvanized layer is larger than that of steel. The uppermost Eta layer has only 70 DPN hardness, so it is easy to be dented by collision, but the lower Zeta layer and delta layer have 179 DPN and 211 DPN respectively, which is higher than the 159 DPN hardness of iron, so its impact resistance and Abrasion resistance is quite good.

3. In the corner area, the zinc layer is often thicker than other places, and has good toughness and wear resistance. Other coatings are often the thinnest, the most difficult to construct, and the most vulnerable place at this corner, so maintenance is often required.

4. Even due to great mechanical damage or other reasons. A small part of the zinc layer will fall off and the iron base will be exposed. At this time, the surrounding zinc layer will function as a sacrificial anode to protect the steel here from corrosion. The opposite is true for other coatings, where rust builds up immediately and spreads rapidly under the coating, causing the coating to peel.

5. The consumption of the zinc layer in the atmosphere is very slow, about 1/17 to 1/18 of the corrosion rate of steel, and it is predictable. Its lifespan far exceeds that of any other coating.

6. The life of the coating depends on the thickness of the coating in a specific environment. The thickness of the coating is determined by the thickness of the steel, that is, the thicker the steel is, the thicker the coating is, so the thicker steel part of the same steel structure must also get the thicker coating to ensure a longer life.

7. The galvanized layer can be painted with duplex system due to its beauty, art, or when it is used in a specific severe corrosive environment. As long as the paint system is selected correctly and the construction is easy, its anti-corrosion effect is better than that of single painting and hot-dip galvanizing. The lifespan is 1.5~2.5 times better.

8. To protect steel with a zinc layer, there are several other methods besides hot-dip galvanizing. Generally, the hot-dip galvanizing method is the most widely used, the best anti-corrosion effect and the best economic benefit.

JUDGMENT CRITERIA AND REASONS:

Coating Weight:

The corrosion resistance is mainly determined by the thickness of the galvanized layer, so the measurement of the thickness is often the main basis for judging the quality of the galvanized layer. 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, the measurement of the adhesion amount can never be judged by a single point (location). It is only meaningful to measure the average adhesion zinc weight (g) per unit area (㎡). 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, estimation method of weight difference between incoming and outgoing goods, etc. The commonly used methods are the film thickness gauge method and the pickling method.

The film thickness gauge is the most common and trouble-free method to measure 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, at the corners of the steel or rough, angled steel or castings, etc., it is unlikely that an accurate number will be obtained. Ordinary iron parts use the original iron material as the base material of Angelica zero, and quite accurate figures can still be obtained, but the castings are absolutely inaccurate.

The pickling method is the most accurate method for formal inspection reports, but it is necessary to pay attention to the fairness of the upper and lower parts when slicing, so that accurate numbers can be obtained. However, it also has disadvantages, such as time-consuming, difficult to obtain the area of ​​complex steel, too large pieces cannot be pickled and so on. Therefore, it is sufficient to make full use of the film thickness gauge to control the on-site process, and to use the pickling method for the final inspection.

Uniformity

The most rust-prone part of hot-dip galvanized steel is still the place with the thinnest zinc layer, so it is necessary to test whether the thinnest part meets the standard.

The test method for uniformity is generally copper sulfate test, but this method is very problematic for the test of zinc coating composed of zinc layer and 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 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 and replace uniformity with distribution. In addition, small components with complex shapes are difficult to measure due to 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 measuring the adhesion amount.

Solidity

The so-called solidity is the adhesion between the galvanized layer and the steel, which mainly requires the galvanized components to have the property of not peeling off during the finishing, transportation, storage and use. The general inspection methods include hammering method, extrusion method, coiling method, etc.

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 that the hammer support platform is of the same height and level. The hammer is centered on the support platform, so that the shank weight falls naturally in the vertical position, and strikes 5 points in parallel at an interval of 4mm, and observes whether the film peels off to judge. 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 the most common and is suitable for the solidity 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 be peeled off when 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 that define the quality inspection of hot-dip galvanizing for general specifications. It is also the standard for general formal inspection reports. about specifications.