Galvanized steel pipe, is generally called cold plating pipe, choose electroplating, only in the steel surface galvanized, steel pipe cavity without galvanized.
Hot-dip galvanized steel pipe, the general selection is hot-dip galvanizing process, steel pipe inside, the surface is a zinc layer.
The difference between galvanized pipe and hot galvanized pipe:
1, processing technology is different, one is organic chemistry solution, a is physics solution; Hot-dip galvanised coating is firm and not easy to fall off.
2, hot-dip galvanizing coating is thick, so it has strong anti-corrosion ability. And galvanizing (electroplating process) coating symmetry, process performance is good, coating thin thickness is generally in the middle of 1 μm to more than 10 μm.
3, hot-dip galvanizing is an organic chemical solution, belonging to electrochemical corrosion. Galvanizing is a physical solution, just brush a layer of zinc on the surface, there is no galvanizing inside, so the zinc layer is easy to fall off. Hot dip galvanizing is used in construction engineering.
4, hot-dip galvanizing steel pipe is to make the molten metal material and the iron base material reflect and cause the aluminum alloy layer, and then make the base material and coating both closely together.
Electroplating zinc, commonly known as cold galvanizing, is the use of electrochemical methods, zinc ingots as the anode, After the zinc atom loses the electron to become the ion state to dissolve in the electrolyte, but the steel strip serves as the cathode, the zinc ion gets the electron reduction on the steel belt to the zinc atoms deposition to the steel surface, forms the coating.
There is a big difference between the galvanizing quantity of the hot dip galvanized sheet and the electrolytic galvanized sheet. The galvanizing amount of hot-dip galvanizing can not be too small, generally the minimum is 50 ~ 60g / m2 on both sides and the maximum can reach 600g / m 2. The galvanizing layer of electrolytic galvanized sheet can be very thin, and the minimum is 15g / m2. However, if the coating is thick, the production line speed is very slow and does not meet the characteristics of the modern process, the general maximum is about 100g / m2. Just because of this, the production of electrolytic galvanized sheet is very limited.
Hot dip galvanized sheet and electrolytic galvanized sheet are fundamentally different in the microstructure of the coating. There is a brittle compound layer between the pure zinc coating and the steel strip substrate on hot-dip galvanizing plate. Zinc flowers are formed when the pure Zn coating crystallizes and the coating is uniform and void. The zinc atoms in the zinc layer only precipitates on the surface of the steel strip, and is attached to the surface by physical action, there are many holes to dry, easy to cause pitting corrosion due to corrosive media, so hot dip galvanized sheet than electrolytic galvanized sheet more corrosion resistance.
Hot dip galvanizing and electrolytic galvanized sheet heat treatment process is also completely different, hot dip galvanized sheet generally hard plate as the raw material. Continuous annealing and hot dip galvanizing on the galvanizing line, the steel strip is heated and cooled in a short time, so the strength and plasticity are affected to some extent, and its stamping performance is worse than the cold rolled plate after degreasing annealing in the same professional production line. Electrolytic galvanized sheet, which is made of cold-rolled steel, has the same processability as the cold-rolled sheet. However, the complicated process flow of the electrolytic galvanizing sheet increases the cost of production. In short, the production cost of hot-dip galvanizing plate is lower, the application range is wider, and it has become the main variety of galvanized plate market.
Zinc plating is through the electrode reaction, for galvanizing, and hot-dip galvanizing is dipping raw materials into the zinc pot for galvanization, it is metal reaction and physical reaction.
When hot-dip galvanizing, the raw material surface is a layer of intermetallic compound, then zinc, while the surface of zinc plating is zinc, there is no intermediate layer.
Electroplated zinc zinc layer is thinner, and hot-dip zinc coating is thicker
Zinc plating can not be mass produced, low yield, and hot-dip galvanizing can be mass production, high yield.
The surface state and corrosion resistance of electroplating is better than hot-dipped zinc
Zinc plating is better than hot-dip galvanizing, so it is expensive
Zinc plating costs high, so the price is high. Hot galvanizing zinc aluminum alloy with high prices when more than 4W / ton……
Zinc plating and hot-dip galvanizing corrosion protection principle is the same. It’s just that the processes are different.
After electroplating zinc – the surface is clean. Bright appearance. But because the zinc layer is attached, it will fall off over time.
Hot dip galvanizing – some not as beautiful as electroplating. But zinc layer has penetration, use time is longer than electroplating.
1, hot-dip galvanizing plate general zinc layer is thicker, about 10 um above, corrosion resistance is stronger. So is a usually used galvanizing process. And electroplating zinc is very thin, About 3-5 um, hot plating surface rough, bright, serious cases with zinc flowers, plating is smooth, gray (hair pollution).
Galvanized steel sheet made by electroplating has good processability. But the coating is thinner and less resistant to corrosion than hot-dipped galvanized sheet. Cold galvanized sheet is electroplated zinc, The amount of galvanizing is very small, only on the outer wall of the galvanized (hot-dip galvanizing – both inside and outside), only 10-50g / m2, its own corrosion resistance than hot-dip galvanized sheet tube is much different.
2, chemical industry generally more zinc plating, suitable for small parts; Hot-dip galvanized sheet is generally used for power equipment and components, suitable for large components and equipment.
Zinc plating is commonly known as cold galvanizing plate, is the use of electrochemical way, the zinc ingot as an anode, After the zinc atom loses the electron to become the ion state to dissolve in the electrolyte, but the steel strip serves as the cathode, the zinc ion gets the electron reduction on the steel belt to the zinc atoms deposition to the steel surface, forms the coating.
In order to remove the iron oxide on the surface of the steel pipe, the hot-dip galvanized steel sheet is washed by ammonium chloride or zinc chloride solution or ammonium chloride and zinc chloride mixed aqueous solution tank after pickling, and then sent to the hot dip plating tank.
3, hot dip galvanized sheet and electrolytic galvanized sheet have a big difference in galvanizing quantity. The galvanizing amount of hot galvanizing plate can not be too small, generally the minimum is 50 ~ 60g / m2 on both sides, the maximum can be up to 600g / m2. The galvanizing layer of an electrolytic galvanized sheet can be very thin, with a minimum of 15g / m2, but the production line speed is very slow if the requirements of thick coating are not suitable for the characteristics of the modern process, the general maximum is about 1O0g / m2. Just because of this, the production of electrolytic galvanized sheet is very limited.
4, hot dip galvanized sheet and electrolytic galvanized sheet are fundamentally different in the microstructure of the coating. There is a slightly brittle compound layer between the pure zinc coating on the plate and the base of the steel strip. The pure Zn coating usually forms zinc sparkle when it crystallizes, and the coating is uniform without porosity. The zinc atoms in the zinc layer only precipitates on the surface of the steel strip, and is attached to the surface by physical action, there are many holes to dry, easy to cause pitting corrosion due to corrosive media, so hot galvanized sheet than electrolytic galvanized sheet more corrosion resistance.
5, hot dip galvanized sheet and electrolytic galvanized sheet heat treatment process is also completely different, the hot dip galvanizing sheet with cold hard plate as the raw material, in the galvanizing line continuously annealing and hot galvanized sheet, The steel strip is heated in a short time and then cooled, so the strength and plasticity are affected to a certain extent. Its stamping performance is worse than the same cold plate after degreasing annealing by professional production line. Electrolytic galvanized sheet, which is made of cold-rolled steel, has the same processability as the cold-rolled sheet. However, the complicated process flow of the electrolytic galvanizing sheet increases the cost of production. In short, the production cost of hot-dip galvanizing plate is lower, the application scope is wider, and it has become the main variety of galvanized plate market.
6, hot-dip galvanizing sheet pipe is to make the molten metal and iron matrix reaction and produce alloy layer, so that the matrix and coating two combination. Hot-dip galvanized sheet has the advantages of uniform coating, strong adhesion and long service life. Formal galvanized pipe manufacturers, in order to ensure quality, most do not use electroplating zinc (cold plating). Only those small, equipment old small enterprises use zinc plating, of course, their prices are relatively cheap. The Ministry of Construction has formally below, the elimination of backward technology cold galvanized pipe, is not allowed to use cold galvanized steel pipe for water, gas pipe.
The galvanizing plate that is commonly used now is hot-dip galvanization plate, and the electric line that uses the groove and so on uses is cold galvanize plate, color has certain difference.
Hot-dip galvanizing and cold galvanizing how to distinguish difference and discrimination?
First, the difference between processes is:
Hot-dip galvanizing is to remove oil, pickling, dipping, drying after immersion in molten zinc for a certain time, can be lifted out.
Cold galvanizing is also called galvanizing, it is to use electrolysis equipment to put the workpiece into the solution of zinc salt after deoiling, pickling, and connect the anode of electrolysis equipment. A zinc plate is placed on the opposite side of the workpiece and connected to the cathode of the electrolysis equipment. The power supply is switched on, and a layer of zinc is deposited on the workpiece by the directional movement of current from the cathode to the anode.
Difference in appearance: electroplated zinc appearance is relatively smooth, bright, using color passivation process electroplated layer is also yellow-green color, was colorful. The electroplating layer of white passivation process is bluish white or white is green light, and the coating of white passive process is slightly colorful under a certain angle with sunlight. In the corner of complex workpiece is easy to produce “electric burning” and become gray, this part zinc layer is thicker. Low current gray area is easily formed in the negative corner, which has thin zinc layer. The workpiece as a whole no zinc tumor, caking and other phenomena. The appearance of hot-dip galvanizing is slightly rougher than zinc plating, and is silver-white. It is easy to produce process water lines and a little drip, especially on the end of the workpiece. But the zinc layer of hot-dip galvanizing is dozens of times thicker than zinc plating, and the corrosion resistance is tens of times.
The difference between galvanized finished products:
- Hot-dip galvanized steel pipe is galvanized inside and outside, but cold-galvanized steel only outside.
- The cold coating is uniform and thin. The thermal coating is thick and the thickness is not uniform.
- Cold plating appearance is bright, hot plating color is dark.
- Because of the thin layer, the corrosion resistance is poor. The hot coating is several times thicker than cold galvanizing, and it forms an infiltration layer with the base metal, and has good corrosion resistance.
- Cold galvanized steel pipe looks bright surface, smooth and flat; Hot-dip galvanizing surface is not cold galvanizing fine and bright, hot-dip galvanized steel tube surface seems to have some uneven bumps, and the surface does not shine, not too reflective.