In the manufacture of metal facilities, hot-dip galvanizing and cold-dip galvanizing are two commonly used manufacturing processes. As a metal anti-corrosion method, hot-dip galvanizing usually puts the steel structure to be derusted into the molten zinc at about 500 °C, so that the zinc layer adheres to the surface of the steel structure. Cold galvanization makes a metal film attached to the surface of metal and other materials through electrolysis, so that the surface of the material has a uniform texture, anti-corrosion and wear-resistant, and a more beautiful appearance. After the above preliminary understanding, the following Tuba Rabbit editor will introduce the difference between hot-dip galvanizing and cold-dip galvanizing in detail.
Hot-dip galvanizing is also known as hot-dip galvanizing. Hot-dip galvanizing is a surface treatment method that improves the rust resistance of steel parts. Hot-dip galvanizing is to degrease steel parts in lye, and then remove rust in acid (hydrochloric acid or sulfuric acid of a certain composition) to expose a clean metal surface, and then immerse themselves in a molten galvanizing pot, so as to cover the parts with a uniform and complete zinc layer, which greatly improves the anti-rust ability of steel parts and prolongs their service life. For example, the common highway guardrails, transmission towers, etc. are hot-dip galvanized, and these equipment can be used for ten or even twenty or thirty years without rusting.
Cold galvanization is to hang the workpiece that has also undergone degreasing and rust removal to show no dirt and wetting into the cathode in the electroplating tank specially prepared with electrolyte, and the anode is zinc. When the DC power supply is turned on, the zinc ions on the anode migrate to the cathode, and the discharge is discharged on the cathode, so that the workpiece is coated with a layer of zinc layer.
The hot-dip galvanized coating is thicker, generally 30-60 microns, and the coating has a high anti-corrosion ability. Long-term rust prevention of steel parts suitable for outdoor work, such as highway fences, power towers, large-size fasteners and other relatively “coarse” workpieces. Older iron water pipes were also hot-dip galvanized.
Electro-galvanized, the surface of the workpiece is smooth and flat, but because the coating is relatively thin, generally within 5-30 microns, the anti-corrosion time will be relatively short. They are used to prevent rust in indoor parts, such as chassis bottoms, panels, small size fasteners, etc.
The difference between the principle of hot-dip galvanizing and cold-dip galvanizing
Hot-dip galvanizing uses the principle of zinc resistance to atmospheric corrosion to electrochemically protect steel and other materials, and the zinc carbonate protective film on the surface can slow down the speed of zinc corrosion, and even if it is destroyed, it will form a zinc film layer.
Cold galvanizing is the use of chemical methods to separate zinc alloys into zinc ions, which have been attached to the surface of steel, and the new layer formed in this way is generally thinner, and steel is prone to rust under normal circumstances.
The difference between the appearance of hot-dip galvanizing and cold-dip galvanizing
The outer surface of cold galvanized is relatively smooth and bright, the electroplating layer of the color passivation process will be yellow-green, and the electroplating layer of the white passivation process will be blue-white, and there is only a small amount of zinc layer at both ends of the cold galvanized steel pipe, and there is no galvanized layer in the middle.The outer surface of hot-dip galvanizing is rough, dark, and generally silvery-white, because the production process causes some water lines and drops on the surface, and the surface does not shine or reflect. Hot-dip galvanized steel pipes have a complete galvanized coating inside and out.
The source and function difference between cold galvanizing and hot galvanizing
Hot-dip galvanizing originated in the cold-rolled strip industry more than 100 years ago, and is a relatively ancient hot-dip method, which is mainly used in metal structure facilities in various industries.
As a new type of electroplating, cold galvanizing is the best material to replace hot-dip galvanizing, and most of the cold galvanizing solvents do not contain toxic solvents and heavy metals such as toluene and ketones. Cold galvanized as a thick film material, has good thixotropy, after full stirring, add a small amount of diluent, you can carry out coating construction, generally in the room temperature environment for operation. Cold galvanizing construction projects can reduce the emission of waste water and waste gas, reduce energy consumption, have a greater guarantee for the personal safety of construction personnel, are conducive to environmental protection, and have high social benefits.
The production process of hot-dip galvanizing and cold-dip galvanizing is completely different, the thickness and price of hot-dip galvanizing far exceed that of cold-dip galvanizing, and the adhesion of cold-dip galvanizing is not as good as hot-dip galvanizing, therefore, the corrosion resistance of hot-dip galvanizing is dozens of times that of cold-dip galvanizing. Cold galvanizing can be plated on only one side, while hot-dip galvanizing must be fully plated.
