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Principle and process of galvanizing

Update:16-06-2019
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1、The meaning of fastener galvanizing Zinc plating refe […]

1、The meaning of fastener galvanizing

Zinc plating refers to a surface treatment technique that coats a layer of zinc on the surface of a metal, alloy or other material for aesthetics, rust prevention, and the like. The main method used is hot-dip galvanizing.

Zinc coating is an anodic coating, which is mainly used to prevent corrosion of steel. Its protective performance has a great relationship with the thickness of the coating. After passivation, dyeing or coating of the photoresist, the zinc coating can significantly improve its protection and decorative properties. With the development of the galvanizing process, the use of high-performance galvanizing brighteners, galvanizing has entered the protective-decorative application from purely protective purposes.

2、The principle

In the plating tank containing the galvanizing solution, the parts to be plated which have been cleaned and specially pretreated are used as the cathode, and the anode is made of the plated metal, and the two poles are respectively connected with the positive electrode and the negative electrode of the direct current power source. When galvanizing, the quality of the anode material, the composition of the galvanizing bath, the temperature, the current density, the energization time, the stirring strength, the precipitated impurities, the waveform of the power supply, etc. all affect the quality of the coating and need to be controlled at the right time.

3、Category

Galvanizing is divided into cold galvanizing, mechanical galvanizing, hot galvanizing and electrogalvanizing. The main method used for galvanizing the surface of steel sheets is hot-dip galvanizing. The production process of hot-dip galvanized sheet mainly includes: preparation of original board → pre-plating treatment → hot dip plating → post-plating treatment → finished product inspection. The performance characteristics of electro-galvanizing are thick zinc coating, fine crystal, uniform and non-porous, and good corrosion resistance; the zinc layer obtained by electroplating is relatively pure, and the corrosion in acid, alkali and other mists is slow, which can effectively protect the fastener matrix. The galvanized layer is passivated by chromic acid to form white, color, military green, etc. It is beautiful and has certain decorative properties. Because the galvanized layer has good ductility, it can be cold-rolled, rolled, bent, etc. Forming without damaging the coating. The fields involved in electro-galvanizing are more and more extensive. The application of fastener products has been of great significance in the national economy, such as mechanical manufacturing, galvanized hook-and-loop chain, electronics, precision instruments, chemicals, transportation, and aerospace.

4、The process

The galvanizing process mainly includes two types of hot-dip galvanizing and cold-galvanizing. Cold galvanizing is also known as electroplating. Here we mainly discuss electroplating zinc. There are many kinds of electroplated zinc, which are varied. However, from the pH value of the galvanizing bath, there are mainly two categories: alkaline galvanizing and acid galvanizing. The alkaline galvanizing process means that the pH of the plating solution is alkaline. Although this process is not as stable and detailed as the cyanide galvanizing process. But its biggest advantage is that it is cyanide free. The harm to the environment is much smaller. The pH of the acid galvanizing bath is 4-6. The coating obtained from this plating solution is fine and has a good dispersing ability. The plating solution is less toxic. However, the main disadvantage is that the plating solution is unstable, and the emitted ammonium chloride gas is highly corrosive to the plating equipment. Current efficiency is also low. Strong sensitivity to impurities. The potassium chloride (or sodium chloride) galvanizing process is a new cyanide-free galvanizing process developed in the 1980s. Its main component is: zinc chloride main salt, generally used in the content of 70-90g / L. The biggest advantage of sulphate galvanizing is the large current density (1-5A/dm2), which is fast. However, the disadvantage is that the dispersion ability of the plating solution is very poor, and it is not suitable for plating more complicated workpieces. Due to its particularity, sulphate galvanizing is mainly used in industries such as iron-plated wire, steel strip and steel plate, which are simple in shape and continuous in production.

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