First, the methods of galvanizing steel pipes are different.
1. Cold plating of galvanized steel pipes: It is a process that uses electrochemical principles to perform anti-corrosion treatment on the surface of workpieces.
2. Hot-dip galvanizing of steel pipes: Also called hot-dip galvanizing, it is a method in which steel components are immersed in molten zinc to obtain a metal coating.
Second, the principles are different
1. Cold plating of galvanized steel pipes: Use electrolysis equipment to degrease and pickle the pipe fittings and put them into a solution composed of zinc salts. Connect the negative electrode of the electrolysis equipment. Place a zinc plate opposite the pipe fittings and connect it to the electrolysis equipment. When the positive pole is connected to the power supply, a layer of zinc will be deposited on the pipe fittings by using the directional movement of current from the positive pole to the negative pole. Cold-plated pipe fittings are processed first and then galvanized.
2. Hot-dip galvanizing of steel pipes: When the iron workpiece is immersed in the molten zinc liquid, a solid solution of zinc and α-iron (body center) is first formed on the interface. This is a crystal formed by dissolving zinc atoms in the base metal iron in a solid state. The two metal atoms are fused, and the gravitational force between the atoms is relatively small. Therefore, when zinc reaches saturation in the solid solution, atoms of zinc and iron diffuse into each other, and the zinc atoms that diffuse into (or penetrate) the iron matrix migrate in the matrix lattice and gradually form an alloy with iron.
Additional notes:
1. The entire steel surface is protected. No matter inside the recessed pipe fittings or any other corner where the coating is difficult to enter, the molten zinc can be easily and evenly covered.
2. The hardness of the galvanized layer is greater than that of steel. The uppermost Eta layer only has a hardness of 70 DPN, so it is easily dented by collisions, but the lower Zeta layer and delta layer have hardness values of 179 and 211 DPN respectively, which are higher than the 159 DPN hardness of iron, so they are impact-resistant and The wear resistance is quite good.
3. In the corner areas, the zinc layer is often thicker than in other places and has good toughness and wear resistance. The corners of other coatings are often the thinnest, most difficult to apply, and most vulnerable to damage, so they often need to be maintained.
4. Even if it suffers heavy mechanical damage or other reasons. A small part of the zinc layer will fall off, exposing the iron base. At this time, the surrounding zinc layer will function as a sacrificial anode to protect the steel here from corrosion. On the other hand, the opposite is true for other coatings. Rust will form immediately and quickly spread underneath the coating, causing the coating to peel off.
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 is far longer than any other coating.
6. The coating life span 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, the easier it is to get a thicker coating. Therefore, the thicker steel parts in the same steel structure must also get a thicker coating to ensure a longer life.
7. For aesthetics, art, or when used in specific severely corrosive environments, the galvanized layer can be painted with a duplex system. As long as the paint system is correctly selected and the construction is easy, the anti-corrosion effect is better than that of separate painting and hot-dip galvanizing. The total lifespan is 1.5~2.5 times better.
8. In addition to hot-dip galvanizing, there are several other methods to protect steel with a zinc layer. Generally, the most widely used, anti-corrosion effect and economical method is hot-dip galvanizing.
Post time: Mar-20-2024