What is galvanized sheet metal?
Galvanized sheet refers to steel sheet with a layer of zinc on its surface.
Galvanizing is a frequently used economical and effective rust prevention method.
Around half of the world's zinc production is used in this process.
Galvanized sheet is used to prevent corrosion of the steel sheet surface and extend its service life.
Due to the different treatment methods in the coating process, the surface state of the galvanized sheet is also different, such as ordinary zinc bloom, fine zinc bloom, flat zinc bloom, zinc-free bloom and phosphated surface.
The German standard also specifies the surface grade.
The galvanized sheet must have a good appearance and not present defects that are harmful to the use of the product, such as lack of plating, holes, cracks, slags, excessive plating thickness, scratches, chromic acid dirt, white rust, etc.
Classification of galvanized sheet
Galvanized sheet can be divided into the following categories according to production and processing methods:
① Hot-dip galvanized steel plate
The steel plate is immersed in the molten zinc bath and a layer of zinc adheres to its surface.
At present, the continuous galvanizing process is mainly used for production, that is, the rolled steel sheet is continuously immersed in the zinc melting bath to make galvanized steel sheet;
② Bonded galvanized steel sheet
This type of steel plate is also made by the hot-dip method, but it is heated to about 500℃ immediately after being grooved to form a zinc and iron alloy film.
This galvanized sheet has good coating adhesion and weldability;
③ Electro-galvanized steel sheet
The galvanized steel sheet produced by electroplating has good processability.
However, the coating is thin and the corrosion resistance is not as good as that of hot-dip galvanized sheet;
④ Single side plated and double side difference galvanized steel sheet
Single-sided galvanized steel sheet, i.e. products galvanized on one side only.
It has better adaptability than double-sided galvanized sheets in welding, coating, rust prevention treatment and processing.
To overcome the disadvantage of one side not coated with zinc, there is also a galvanized sheet coated with a thin layer of zinc on the other side, that is, a double-sided difference galvanized sheet;
⑤ Alloy and composite galvanized steel sheet
It is a steel plate made from zinc and other metals such as aluminum, lead and zinc, and even composite coating.
This type of steel plate not only has excellent rust prevention performance, but also has good coating performance;
In addition to the above five types, there are color galvanized steel sheet, printed galvanized steel sheet, PVC laminated galvanized steel sheet, etc.
But at present, the most commonly used is still hot-dip galvanized sheet.
Basic uses of galvanized sheet
1. Cold and hot dipped galvanized sheet is mainly used in agricultural machinery, grain storage, high-speed guardrail and other life industries.
Its main characteristic is low cost and high added value.
2. Galvanized sheet is also used in building materials, household appliances, automobiles and other industries, because these industries are more or less involved in supporting metal structures.
The emergence of galvanized sheet solves this problem in an intelligent way. I believe its demand will continue to increase in the future.
3. In addition to being widely used in industrial production, galvanized sheet also plays an important role in modern buildings, factories, space structures, transportation energy, etc.
The application of galvanized sheets in these areas mainly plays the role of a protective film, which weakens the corrosive effect of the outside world on objects.
What is the material of galvanized sheet?
As the name implies, galvanized steel sheet is coated with a layer of zinc on the surface of the steel sheet, which can play an anti-corrosion role to a certain extent.
This production method can also reduce zinc consumption in the world.
Galvanized sheet material and application:
1. Non-alloy hot galvanized steel strip
D C 5 XD Series:
Can be used for general purpose, deep drawing and biting.
The higher the zinc content on the surface, the better the anti-corrosion performance;
The smaller the amount of zinc on the surface, the better the processing performance.
S XXXGD Series:
It can be used as a structure and has good processing performance and corrosion resistance.
HXXXPD+Z Series:
It includes low-alloy steel, phosphorus-containing steel and hardened steel, which have excellent processing properties and corrosion resistance.
2. Bonded hot galvanized steel strip
DCXXD+ZF Series:
It can be used for structure, stamping and cold forming.
The galvanized sheet of this material has better welding and coating performance, but it is very easy to peel off in the processing process.
Which is better, galvanized sheet metal or stainless steel?
Galvanized sheet is rust-proof and stainless steel is resistant to weak corrosive media such as air, steam and water.
The differences between stainless steel and galvanized steel are as follows:
1. Different concepts
Galvanization refers to the coating of a layer of metallic zinc on the surface of the steel sheet to prevent corrosion on the surface of the steel sheet and extend its service life.
This zinc-coated thin steel plate is called galvanized plate.
Stainless steel refers to steel that is resistant to weak corrosive media such as air, steam and water, and chemical corrosive media such as acid, alkali and salt, also known as acid-resistant stainless steel.
2. Different processing technologies
Galvanizing mainly consists of coating a layer of dense zinc on the surface of the steel.
Stainless steel is the addition of other metallic elements within the steel.
It is the internal structural change that prevents the product from rusting.
3. Different fields of application
Galvanized steel strip products are mainly used in construction, light industry, automobile, agriculture, animal husbandry, fishing, trade and other industries.
Such as for the construction of roof panels, roof rails, etc.;
Kitchen utensils, etc.;
Storage and transportation of materials, packaging equipment, etc.
Stainless steel is mainly used in the construction field, which is one of the highest strength metal building materials.
It is also used in food processing, catering, brewery, chemical industry and other areas with high sanitary requirements.
In comparison, stainless steel is better.
Firstly, galvanized pipes are rarely used. China has banned galvanized pipes since 2000.
At present, galvanized pipes are rarely used for cold water pipelines in new residential areas, and galvanized pipes are used for hot water pipelines in some residential areas.
Galvanized pipes are used as water pipes. After several years, a large amount of rust and scale will be generated in the pipes.
The flowing yellow water will not only pollute the sanitary ware, but also be mixed with bacteria growing on the uneven inner wall.
Rust will cause the heavy metal content in water to be very high, which will seriously harm human health.
What is the difference between galvanized sheet and aluminized zinc sheet?
Galvanized sheet refers to steel sheet with a layer of zinc on its surface.
Galvanizing is a frequently used economical and effective anti-corrosion method.
About half of the world's zinc production is used in this process.
The surface of the aluminized zinc steel plate is smooth, flat and beautiful, and the primary color is silvery white.
The special structure of the coating provides excellent corrosion resistance.
The normal service life of aluminized zinc plate can reach 25 years, and the heat resistance is very good.
Can be used in 315℃ high temperature environment;
The coating has good adhesion to the paint film and good processing performance, and can be used for stamping, shearing, welding, etc.;
The surface conductivity is very good.
The coating is composed of 55% aluminum, 43.4% zinc and 1.6% silicon by weight.
The production process of aluminized zinc steel sheet is similar to that of galvanized rigid sheet and aluminized sheet, which is a continuous fusion galvanizing process.
Zinc-plated steel sheet with 55% aluminum zinc alloy coating has better corrosion resistance than galvanized steel sheet with the same thickness when both sides are exposed to the same environment.
The aluminum-zinc steel plate coated with 55% aluminum zinc alloy not only has good corrosion resistance, but also has excellent adhesion and flexibility.
The difference between galvanized sheet and aluminized zinc sheet lies mainly in the difference in coating.
A layer of zinc material is evenly distributed on the surface of the galvanized sheet, which plays an anodic protection role for the base metal.
In other words, the alternative corrosion of the zinc material protects the use of the base metal.
Only when the zinc is completely corroded can the internal base metal be damaged.
The surface coating of the aluminized zinc plate is composed of 55% aluminum, 43.5% zinc and a small amount of other elements.
The surface of the aluminized zinc coating presents a honeycomb structure under the microscope, and the aluminum composite “honeycomb” contains zinc.
In this case, although the aluminum and zinc coating also plays the role of anodic protection, on the one hand, because of the reduction of zinc content, and on the other hand, because the zinc material is wrapped in aluminum and is not easy to electrolysis , the role of anodic protection is greatly reduced.
Therefore, once the zinc plated aluminum plate is cut, it will soon rust when the cut edge is basically unprotected.
Therefore, the aluminized zinc sheet should be cut as little as possible.
Once cut, the edges must be protected with anti-rust paint or zinc-rich paint, to extend the useful life of the plate.
The surface of aluminized zinc sheet is more beautiful than that of galvanized sheet.
At the same time, the cost of aluminized zinc plate is higher than that of galvanized plate, and the cost of small zinc flower is higher than that of large zinc flower.
In cities with humid air and heavy rain, once a certain spot on the zinc-plated aluminum plate rusts, if measures are not taken in time, the rusty spot will slowly become bigger and bigger, and eventually even the entire surface of the plate ;
The corrosion of galvanized sheet metal will not spread even if there is corrosion at a certain point.
What is the density of galvanized sheet metal?
The thickest zinc coating is 80 grams per square meter, which means 160 grams on both sides.
The most common is 50 grams, which means 100 grams on both sides.
In this way, we can know a simple relationship.
The density of the galvanized sheet is 7.85 tons/m³, that is, the weight of the 1.0 mm sheet per square meter is 7.85 kg and the weight of the 0.75 mm sheet per square meter is 5.8875 kg.
Galvanized sheet density calculation method
Zinc plate density calculation method = weight of iron plate + weight of zinc coating
For example:
Galvanized sheet with a thickness of 1 mm, the weight of the sheet is 7.85 kg, and the weight of the galvanized layer is 2 × 0.05 kg, the weight per square meter is 7.95 kg, and other specifications are also calculated in the same way form.
The weight of galvanized sheet is slightly greater than that of ordinary iron sheet, and the increase in coating thickness is different.
The price should be different for different coating thickness.
What is the function of galvanization?
The function of galvanizing is to prevent steel from rusting, which rusts easily in the natural atmosphere.
Although zinc is not easy to change in dry air, in a humid environment, a dense zinc carbonate protective film will form on the surface, which can effectively protect the steel.
What are the galvanizing processes?
Generally, there are three types of galvanizing processes and methods: mechanical galvanizing, hot galvanizing and cold galvanizing:
Mechanical galvanizing
The mechanical zinc plating process is a more traditional zinc plating process, which causes zinc powder to adhere to galvanized parts through mechanical collision and chemical adsorption to form a coating.
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Hot galvanizing
It is also called hot dip galvanizing.
First, the plated part is pickled to remove the oxide layer on the surface of the plated part, so as to provide conditions for the plating layer to be firmly fixed.
After cleaning with ammonium chloride or zinc chloride, the impurities on the surface of the coated part are removed, and then put into the zinc solution of the hot dipping tank to make the zinc solution adhere evenly and firmly to the plated part through immersion to form a plating layer.
Cold galvanizing
It is also called electroplating.
After removing the dirt and oil dust from the surface, pickling and cleaning to remove the surface impurities of the galvanized parts, the galvanized parts are placed in the zinc salt solution. At the same time, the zinc plate is placed on the opposite side of the galvanized parts, and then the galvanized parts are connected to the negative electrode of the electrolytic equipment.
The zinc plate is connected to the positive electrode of the electrolytic equipment and the power is connected.
Through the electrolytic reaction, the zinc layer is fixed to the galvanized parts.
With the continued maturity of new processes, mechanical coating has been eliminated.
Commonly used processes are hot-dip galvanizing and cold galvanizing.
Countries that mainly produce galvanized steel sheets:
The main producers of galvanized steel sheets are China, Japan, Germany, Russia, France, South Korea, etc.
Common defects, characteristics and causes of galvanized sheet
| Defects | Characteristics | Causes |
| Exposed steel (lack of coating) | If there are black spots or black blocks on the galvanized steel strip that expose the original steel, it is called exposed steel. These black spots or blocks are not coated with zinc and vary in shape and size. Sometimes they are spread across the entire top and bottom surfaces of the steel strip. |
1. Due to the corrosion of the original plate, the yellow rust cannot be fully reduced after entering the annealing furnace; 2. There are defects on the surface of the original board, such as pressed iron oxide scale, severe corrosion, inclusions, etc.; 3. The steel strip enters the preheating section of the annealing furnace for reoxidation, and then enters the reduction section for reduction; 4.The shielding gas is impure, with a high dew point and low hydrogen content (<15%=, the steel strip is oxidized again); 5. Furnace tubes are broken and leaking; 6. insufficient pickling; 7. The composition of the galvanizing aid is not qualified;8. Overcooking of plating aid. |
| Zinc layer falling off | When the mechanical bite or ball impact test is performed on the galvanized sample, the serious separation between the zinc layer and the substrate on the surface is called zinc layer falling off. It can also be seen directly on the production line that the zinc layer is locally separated from the blocky substrate and the zinc layer falls off. |
1. Low oven temperature; 2. The annealing furnace leaks air, water or the reduction conditions are not good, leaving oxides on the surface of the steel strip that have not been reduced well; 3. The original board has a high silicon content; 4. Poor operating conditions such as high galvanizing temperature, long galvanizing time and inadequate control of aluminum content; 5. The original coil is seriously rusted. |
| Zinc particle (zinc scar) | The surface is raised in points and blocks, of different sizes. The particles are like sesame grains and rice, and the surface is rough and uneven. It is called zinc granule in granular form and zinc scar in massive form on the surface. | 1. The bottom slag is too much and is stirred and floated, accompanying the zinc liquid adhering to the surface of the galvanized steel strip or being pressed onto the surface of the steel strip by the submerged roller; 2. The temperature of molten zinc is too high (>470 ℃) to make the bottom slag float; 3. The high aluminum content in molten zinc reduces the solubility of iron in molten zinc, resulting in more foam. |
| Poor zinc flower | The size of the zinc flower is irregular and there is no zinc flower. | Poor temperature rise in the oven area. |
| Gray Coated Zinc Bump | The surface is matte and gray without galvanized layer. | 1. Slow cooling of the original board; 2. Scrape in a semi-solidified state. |
| Air knife range (range) | The galvanized steel strip has a dendritic band or convex band along the rolling direction. | 1. The zinc is too thick and the zinc temperature is low; 2. High aluminum content increases the melting point; 3. Low air knife position or pressure; 4. The air knife gap is partially blocked; 5. Local notch or damage to the air knife; 6. Bad form. |
| Edge thickness (default) | The zinc layer on the edge of the galvanized steel strip is thicker than the zinc layer in the middle or other parts, which is called the edge thickness. Generally, the border has a stripe pattern. | 1. Poor adjustment of the air knife angle; 2. Fast edge cooling; 3. When the speed of the steel strip is less than 30m/min, part of the airflow at both ends of the nozzle is dissipated outwards, which reduces the airflow momentum at the edge, resulting in less zinc scraping at the edge than in the middle; 4. The shape of the original board is not good and there is wave on the edge; 5. The edge of the original plate is seriously rusted. |
| Zinc ripple (zinc wave) | Wavy pattern | 1. High temperature molten zinc; 2. Zinc silk, less aluminum. |
| Shell pattern | Shell pattern, zinc ripple. | High aluminum content and low temperature. |
| Water mark | White band-shaped groove or dot-shaped pit on the surface of a small zinc flower plate. | The cooling water droplets are too large or the water flow surges, causing holes in the unsolidified zinc flowers. |
| Hesitation sequence | Periodic stripes on the surface. | 1. Sinking roller slag and shaft corrosion; 2. The finishing roller is worn out. |
| Finishing and engraving (flower) | There are zinc particles or marks after finishing. | 1. Zinc glued to the finishing roll; 2. Mechanical wear of the finishing machine. |
| C poor handling | The surface is yellowish. | The extrusion drying effect of post-treatment is weak and chromium liquid remains. |
| bell bottom | The steel coil has a bell-mouth shape. | The air knife is blocked, the edge of the steel strip is galvanized, and a bell-shaped mouth is generated during winding. |
| Scratch | scratch | 1. Scrape the original plate; 2. The dip roller is in poor working condition. |
| Side wave and medium wave | The side or central part is wavy. | 1. The original board is bad; 2. The stabilizing roller is in poor working condition. |
| White rust | 1. The surface is white to different degrees; The surface of Zn(OH) 2 shows white oxide powder and precipitate, which is mainly composed of zinc oxide ZnO and zinc hydroxide Zn(OH) 2 . | 1. Poor oil coating and passivation; 2. Bad workshop environment; 3. Contaminated with galvanizing aid and fly ash; 4. Smoke plating auxiliary; 5. Poor oil coating and passivation on the surface; 6. Storage and transportation time is too long in humid conditions; 7. Immersion in rain (sea water) during storage and transportation; 8. The temperature of the storage warehouse is lower than the dew point temperature, and condensed water appears, corroding the surface of the plate; 9. Contact or store with other corrosive media such as acid, alkali and salt. |
| Stratification | Layered inspection is not qualified. | The steel plate has inclusions. |
| The coating is very thin | The amount of zinc plating is less than the specified standard. | 1. Poor adjustment of the air knife; 2. The temperature of molten zinc is too high and the speed is too slow (too fast when using the air knife). |
| Uneven coating | The copper sulfate test is not qualified. | 1. Improper adjustment of both sides of the air knife; 2. The plating roller is eccentric; 3. Severe deformation. |
| The folding performance is unqualified. | The bending test is not qualified and the zinc layer falls off. | 1. The temperature of the molten zinc is too high; 2. The aluminum content is too high or too low; 3. Zinc immersion time is too long (shutdown). |
| Scratch | The coil is scratched. | Poor lifting and damaged package. |
| Black spot on the surface | There are black spots and dark spots on the surface. | Friction of the board surface during storage and transportation. |
| black rust | Black rust stains on the surface. | 1. Prolonged storage; 2. Poor oil coverage and passivation; 3. Coating aid with adhesion dye; 4. Immersion in water (sea water) during storage and transportation; 5. Long-term contact with the industrial atmosphere. |
