Welcome to Shandong Zhishang Steel Co., Ltd.
Welcome to Shandong Zhishang Steel Co., Ltd.
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Hot-dip galvanized pipe is a special steel pipe, its surface is covered with a layer of galvanized layer, which is mainly to improve the corrosion resistance of the steel pipe. This steel pipe is mainly divided into two types: hot dip galvanized and electric galvanized. Among them, the coating of hot galvanizing is thicker, and the cost of electric galvanizing is lower, but the surface may not be as smooth as hot galvanizing.
The production process of hot-dip galvanized pipe involves the reaction of molten metal with iron matrix to form an alloy layer. In this way, the substrate and the coating can be tightly bonded together. Specifically, the process of hot dip galvanizing begins with pickling the steel pipe to remove the iron oxide on the surface of the steel pipe. After pickling, the steel pipe is washed in an aqueous solution containing ammonium chloride or zinc chloride before being fed into a hot dip bath. The advantages of hot dip galvanizing lie in its uniform coating, strong adhesion and long service life. In this process, the steel tube matrix and the molten bath will undergo complex physical and chemical reactions to form a corrosion-resistant zinc-iron alloy layer. This alloy layer is closely combined with the pure zinc layer and the steel tube matrix, and therefore has strong corrosion resistance.
In practical applications, the iron pipes commonly used in gas, greenhouses and heating systems are also galvanized. However, when the galvanized pipe is used as a water pipe, a large amount of rust and scale may be produced in the pipe. This will not only contaminate the sanitary ware, but also may breed bacteria because the tube walls are not smooth. In addition, rust may also lead to high levels of heavy metals in water, posing a serious threat to human health. Therefore, from the 1960s and 1970s, developed countries in the world began to develop new pipes and gradually banned the use of galvanized pipes. China's Ministry of Construction and other relevant departments also issued a clear document in 2000, prohibiting the use of galvanized pipes. Now, the cold water pipe in the new community has rarely used galvanized pipe, but the hot water pipe in some communities still uses galvanized pipe.
Hot galvanized sheet is hot rolled galvanized sheet, cold galvanized sheet is cold rolled galvanized sheet. From the material point of view, the composition of the two galvanized sheets are basically similar, the difference is that the cold galvanized sheet is thinner than the hot galvanized sheet, the surface quality is better, the process is more complex, and the price is higher. From the process point of view, the steel is rolled by hot rolling, rolled into a certain thickness of the plate, such as the thickness of 10mm or so, if the user has no higher requirements for the surface of the plate, thickness, mechanical strength, it can be processed as a finished product, such as galvanized, sold directly, is a hot plate. If there are higher requirements for the plate, then the hot-rolled plate is sent to the cold rolling line for re-processing, after pickling, annealing, re-rolling and other processes, to get a thinner, smooth surface and better mechanical properties of the cold-rolled plate.
"Galvanized sheet 275g/㎡" means that the sum of the double-sided galvanized amount of the galvanized sheet per square meter area is 275 grams. The zinc flowers of hot dip galvanized steel plate are larger and more obvious, called "zinc flowers", and the zinc flowers are not fine enough, called "no zinc flowers".
What does having flowers and no flowers mean which is more expensive?
The zinc flowers of hot dip galvanized steel plate are larger and more obvious, called "zinc flowers", and the zinc flowers are finer and less obvious, called "no zinc flowers".
The hot plate substrate is generally made of zinc flowers, the cold plate substrate is generally made of no zinc flowers, and the cold plate is made of no zinc flowers, the surface is more smooth and smooth, the hardness is low, the elongation is high, the directional consistency is good, and the price is more expensive.
Galvanized sheet flowers and flowers are differentiated according to the surface state of galvanized sheet, generally weak eye will know, the surface has a pattern is flowers, there is no flowers. Flowers and no flowers have nothing to do with the material. The material depends on the substrate used for galvanizing, such as Q195, Q345, SPCC and so on. There is also no relationship between thickness and presence of zinc flowers.
There is a galvanized sheet, that is, the surface of the galvanized sheet is printed with a pattern, the appearance looks very bright, beautiful, and is generally used to make home appliance shells, buckets, and so on. There is no pattern on the surface of the flowerless galvanized sheet, which looks not as bright as the flowered galvanized sheet, dark color, and cold plate. There is no difference in performance, mainly in appearance.
There is a flower is the surface of the board has a pattern like a leaf, but also divided into small zinc flowers with large zinc flowers, no flowers is like aluminum plate, flat what pattern is not there
Hot-dip galvanized channel steel, also known as hot-dip zinc channel steel and hot-dip galvanized channel steel, is an effective way to prevent metal corrosion. It is to immerse the channel steel after rust removal into the melting zinc liquid about 440~460℃, so that the surface of the channel steel is attached to the zinc layer, so as to play the purpose of anti-corrosion.
With the continuous expansion of the use of hot galvanized sheet, the following purposes can be achieved by polishing the strip steel in the modern continuous hot dip galvanizing unit:
(1) Improve the flatness and flatness of the sheet, but also the surface of the zinc particle flattening, so that the surface of the strip smooth, which is especially advantageous for later deep drawing and other occasions with higher precision;
② The polishing roll used has been pre-shot peening, so the surface of the plating plate has a certain roughness after polishing. It can improve the adhesion of the coating, but also can store a certain amount of grease, in the deep drawing process, the lubrication of the die is beneficial;
③ For the plating plate after painting treatment, although the surface is controlled into small zinc flowers, small zinc flowers can still be exposed through the paint layer. Therefore, for some high requirements of galvanized sheet, small zinc flower surface needs to go through polishing treatment. This can make the galvanized sheet obtain a more uniform silver appearance;
(4) By finishing, the lower yield point can be reduced to make the yield platform disappear or less obvious, which can prevent the slip line in the future drawing or deep drawing, and improve the possibility of deep drawing.
The coating thickness formula is: Dz = Gz (Sz*dz), where: Dz -- coating thickness mm, Gz -- per square meter coating weight g, Sz -- coating area mm2, dz -- zinc specific gravity, the above formula can be simplified as: Dz = 0.000139Gz
The causes of white rust are: hot dip galvanizing and other acid, alkali, salt and other corrosive media together; Passivation film or anti-film is destroyed; Passivation or oiling effect is not good; The storage warehouse is not well ventilated and damp; Galvanized sheet in the transport of water; Transported at low temperature and stored at high temperature, condensate is formed.
When the hot galvanized sheet is in the humid air, especially when the air contains SiO2, CO2, NO2 and NO and other acidic substances, the surface of the galvanized layer will soon produce loose white rust. The main components of white rust are ZnO and Zn (OH) 2. This kind of white rust not only affects the appearance, but also brings great difficulties to the future use.
There are three ways to test the corrosion resistance of hot-galvanized sheet: salt spray test; Wet test; Erosion test.
Chromate passivation treatment of galvanized sheet can form passivation film, its chemical reaction formula is as follows: Zn+H2GrO4-ZnGrO2=H2
The trivalent chromium in solution passivation group is insoluble in water, and its chemical properties are not active, which plays the skeleton role, while the hexavalent chromium is easily soluble in water, which can play the role of re-passivation when the passivation film scratches, and has the healing effect of passivation film. Therefore, within a certain limit, passivation film can prevent steam or moist air directly erosion galvanized sheet, zinc layer plays a protective role.
large zinc flower is normal zinc flower, according to the normal production process can produce large zinc flower, its crystal core diameter is not less than 0.2mm; The diameter of the crystalline nucleus less than 0.2mm is called small zinc flower, which is generally not identifiable by the naked eye.
Dark spots are formed by further oxidation of white rust. The main causes of white rust are:
Poor passivation, passivation film thickness is not enough or uneven; No oil on the surface or residual water on the strip surface; The surface of the strip contains water when it is rolled up. Passivation not completely dried; Getting wet or rain-soaked during transportation or storage; The storage time of finished products is too long; Galvanized sheet and other acid and alkali and other corrosive media contact or stored together.
The main reasons for zinc layer shedding are: Surface oxidation, silicon compounds, cold bound emulsion is too dirty, NOF section oxidation atmosphere and protective gas dew point is too high, air fuel ratio is unreasonable, hydrogen flow rate is low, furnace aerobic infiltration, strip into the pot temperature is low, RWP section furnace pressure is low and door suction, NOF section furnace temperature is low, Grease evaporation is not enough, zinc pot aluminum content is low, unit speed is too fast, insufficient reduction, zinc liquid residence time is too short, coating thickness.
Known: the production specification is 0.75×1050mm, and the coil weight is 5 tons. What is the length of the coil? (The specific gravity of galvanized sheet is 7.85g/cm3)
Solution: L = G/ (h×b×p) = (5×1000)/(0.785×1.050×7.5) = 808.816m
Answer: The coil is 808.816m long.
Mainly: peeling, scratches, passivation spots, zinc particles, thick edge, air knife stripes, air knife scratches, exposed steel, inclusion, mechanical damage, poor steel base performance, wave edge, ladling bend, inappropriate size, embossing, zinc layer thickness, roll printing, etc.
There are two kinds: air-cooled and water-cooled.
There are three kinds of vertical, horizontal and vertical annealing furnaces.
Product categories: General coil (CQ), structural galvanized sheet (HSLA), deep drawing hot galvanized sheet (DDQ), baking and hardening hot galvanized sheet (BH), duplex steel (DP), TRIP steel (Phase change induced plastic steel), etc.
It can be divided into two types of in-line annealing and out-of-line annealing, which are also called protective gas method and flux method.
There are three types of electrogalvanizing, hot-dip galvanizing and coating galvanizing.
