August 8, 2020
Baolida galvanized pipe classification and process description
Galvanized pipe, has the dual advantages of corrosion resistance and long service life, and the price is relatively low, so now its use rate is higher and higher. The following introduces the classification and process of galvanized pipe.
Classification of galvanized pipe: galvanized steel pipe is divided into cold-plated pipe and hot-plated pipe.
1. Hot dip galvanized pipe
Hot dip galvanized pipe is to make molten metal and iron matrix reaction to produce an alloy layer so that the matrix and coating are combined. Hot dip galvanized steel pipe is first pickled, in order to remove iron oxide on the surface of the steel pipe, after pickling, through ammonium chloride or zinc chloride aqueous solution or ammonium chloride and zinc chloride mixed aqueous solution tank for cleaning, and then into the hot dip plating tank. Hot dip galvanizing has the advantages of uniform coating, strong adhesion and long service life.
2, cold galvanized pipe
Cold galvanized is electric galvanized, the galvanized amount is very little, only 10-50g/m2, and its own corrosion resistance is much different than hot galvanized pipe. Regular galvanized pipe manufacturers, for quality, do not use galvanized (cold plating). Only those small enterprises with obsolete equipment use electro galvanizing, of course, their price is relatively cheaper. At present, the Ministry of Construction has officially below, eliminated cold galvanized pipe technology behind, the future is not allowed to use cold galvanized pipe for water, or gas pipe.
3. Hot-dip galvanized steel pipe
Complex physical and chemical reactions occur between the steel tube matrix and the molten bath, forming the corrosion-resistant zinc-iron alloy layer with a close structure. The alloy layer is integrated with the pure zinc layer and the steel tube matrix. Therefore, its corrosion resistance is strong.
4, cold galvanized steel pipe
The zinc layer is an electroless coating, which is independently layered with the steel tube matrix. The zinc layer is thin, and the zinc layer is simply attached to the steel tube matrix and easy to fall off. Therefore, its corrosion resistance is poor. In new residential buildings, it is forbidden to use cold galvanized steel pipes as water supply pipes.
Steel pipe before zinc plating treatment:
That is, pickling, cleaning, washing, dipping solvent, and drying. The welded pipe is lifted from the crane to the pickling tank for pickling (about 2 tons per lift). About 26% hydrochloric acid solution was pickling. In order to prevent excessive pickling and acid fog volatilization, 0.5~1.0g/L corrosion inhibitor and fog inhibitor were added to the acid washing solution, pickling was carried out at room temperature, and the pickling time was generally 30~60 minutes. In order to make the steel pipe pickle evenly, the steel pipe was lifted 2~3 times by crane during pickling. To improve the pickling effect. When the acid concentration drops to 100g/L, it should be supplemented or replaced, and the iron content reaches 220~260g/L as waste acid discharge. After pickling, the steel pipe is lifted from the crane to the cleaning tank for cleaning to remove the residual acid and iron salts accumulated on the surface of the steel pipe after pickling. Then, it is lifted to the washing platform and washed with 0.7-0.8mpa water. After the water drops dry, the steel pipe is lifted to the solvent tank for dipping and coating for about one minute. The solvent was 600~650g/L zinc chloride, 80~100g/L ammonium chloride, and 1~2g/L OP-10 surfactant. In order to improve the preplating effect of the steel pipe in the solvent, the solvent is always kept weak alkaline, and then hoisted from the truck to the drying furnace into the drying furnace to dry, the drying temperature is 100~130 degrees, the time is generally 6~10 minutes.
The advantages of the optimized sulfate galvanized pipe is as high current efficiency and fast deposition rate, which is incomparable to other galvanized processes.
The optimization of sulfate galvanized pipe:
Because the coating crystallization is not fine enough, the dispersion ability and deep plating ability are poor, so it is only suitable for the plating of pipe and wire with simple geometric shapes. The sulfate electro-galvanizing iron alloy process is optimized to the traditional sulfate galvanizing process, only the main salt zinc sulfate is retained, and other components are discarded. An appropriate amount of iron salt was added in the new process to make the original single metal coating form zinc-iron alloy coating.
The recombination of the process not only carries forward the advantages of high current efficiency and fast deposition rate of the original process, but also makes the dispersion ability and deep plating ability greatly improved. Complex parts can not be plated in the past, but now simple and complex parts can be plated, and the protection performance is increased by 3 ~ 5 times more than that of a single metal. The PRODUCTION PRACTICE SHOWS THAT THE GRAIN OF THE COATING IS FINER AND BRIGHTER THAN THE ORIGINAL ONE, AND THE DEPOSITION rate is faster. The coating thickness reaches the requirement within 2 ~ 3 min.
The scope of use of galvanized pipe:
Galvanized steel pipe is divided into hot dip galvanized and electric galvanized two, hot dip galvanized layers thick, with uniform coating, strong adhesion, long service life, and other advantages. The cost of galvanizing is low, the surface is not very smooth, and its corrosion resistance is much different than that of hot-dip galvanized pipe.
In order to improve the corrosion resistance of steel pipe, the general steel pipe is galvanized. Galvanized steel pipe is divided into hot dip galvanized and electric galvanized two, hot dip galvanized layer is thick, the electric galvanized cost is low, and the surface is not very smooth.
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