Galvanised steel sheets are coated with a layer of metallic zinc to prevent corrosion on the surface of the steel and to prolong its service life, this galvanised steel sheet is called galvanised steel.
① Hot dipped galvanised steel sheet. The thin steel sheet is dipped into a molten zinc bath so that a thin steel sheet with a layer of zinc adheres to the surface. Currently mainly produced using the continuous galvanising process, whereby the rolled steel plate is continuously dipped into a galvanising bath containing a zinc solution to make galvanised steel sheets.
② Alloy galvanised steel sheet. This steel sheet is also manufactured using the hot dipping method, but is heated to approximately 500°C immediately after discharge from the tank to form an alloyed film of zinc and iron. This type of galvanised steel has good coating adhesion and weldability.
(iii) Electro-galvanised steel sheet. Galvanised steel sheets produced by the electroplating method have good processing properties. However, the coating is thinner and less resistant to corrosion than hot-dipped galvanised sheets.
④ Single-sided and double-sided differential galvanised steel sheets. Single-sided galvanised steel sheet is a product that is galvanised on one side only. It has better adaptability than double-sided galvanised sheet in terms of welding, painting, rust-proof treatment and processing. To overcome the disadvantage of one side not being galvanised, there is another layer of galvanised sheet on the other side, i.e. double-sided differential galvanised sheet.
⑤ Alloy and composite galvanised sheet steel. It is made from zinc and other metals such as aluminium, lead and zinc and is used to manufacture alloy or even composite coated steel sheets. This type of steel sheet has not only excellent rust protection properties but also good coating properties.
In addition to the five types mentioned above, there are also coloured galvanised steel sheets, printed and coated galvanised steel sheets, PVC laminated galvanised steel sheets, etc., but the most commonly used at present is still hot-dipped galvanised steel sheets.
(1) During the entire service life of the galvanized sheet, the first corrosion that occurs is the oxidation of the galvanized layer on the surface, resulting in white rust. After a longer period of time, the white rust on the surface will further react with carbon dioxide and other impurity gases in the moist air to form black spots. When the galvanized sheet is used for a long time and the galvanized layer corrodes more severely, the steel base loses the sacrificial anti-corrosion effect of zinc and begins to oxidize to form red rust. Once the steel base begins to oxidize, the corrosion rate becomes very fast, and the galvanized sheet ends its life.
(2) In addition, there are two special corrosion conditions of galvanized sheet called blackening. One is that after the galvanized sheet is used for a period of time, due to the influence of elements such as lead in the galvanized layer, the matte part of the spangle will be blackened, and the blackened galvanized layer still has a protective effect on the steel base. It only has a certain impact on life span. This situation has been greatly improved after the current stop using lead and switching to antimony to promote the formation of spangles. Another situation is that the galvanized sheet is transported. Due to the low coiling tension and the looseness between the steel strip layers, the parts of the steel coil contacting the skid will rub against each other and cause oxidation. After the white oxide is rubbed off, the plating Black spots are produced on the surface of the zinc sheet. This situation will destroy the passivation film, thin the galvanized layer, greatly reduce the life of the galvanized sheet, and the appearance will also be affected.
(3) The corrosion resistance of the galvanized sheet in a dry environment or a pollution-free environment is very superior. However, in a contaminated environment, the life span will be greatly shortened, and it must be pre-coated into a colored plate before use.
(4) In general, the corrosion of galvanized sheet is not caused by all the galvanized layers on the surface being uniformly corroded, but the coating is corroded first where the coating and the substrate are poorly bonded, resulting in severe local corrosion and loss of use Performance. From this point of view, the adhesion of the galvanized layer, especially the overall adhesion, is more important than the thickness of the galvanized layer. If the local adhesion of the galvanized layer is not good, even if the galvanized layer is thicker, it will start to rust from the poor adhesion. This is similar to the principle of the bucket, and it is a problem that the galvanizing production technicians must understand.
The biggest difference between galvanised sheet and galvanised sheet is the difference in the coating. Galvanised sheets have a uniformly distributed layer of zinc material on the surface, which acts as an anodic protection for the substrate, i.e. alternative corrosion protection for the zinc material. In addition to the base material used, the internal base material can only be damaged if the zinc corrodes completely.
The surface coating of aluminised zinc sheets consists of 55% aluminium, 43.5% zinc and a small amount of other elements. Under the microscope, the surface of the aluminised zinc coating has a honeycomb structure. The “honeycomb” made of aluminium contains zinc. In this case, although the aluminium-zinc coating also acts as an anodic protection, on the one hand the zinc content is reduced and on the other hand the zinc material is encapsulated in the aluminium and is not easily electrolysed, so the anodic protection is greatly reduced. As a result, the cut edges will rust very quickly once the Alu-Zinc sheet has been electroplated, at which point the cut edges are essentially lost and protected. For this reason, aluminium and zinc plated sheets should be cut as little as possible. After cutting, the edges should be protected with rust-proof paint or zinc-rich paint to ensure the longevity of the sheet. Extension
Galvanised sheets have a more attractive surface than galvanised sheets and are more expensive than galvanised sheets. Small lace is more expensive than large lace.
Galvanised sheet steel has a uniquely smooth, flat and ornate surface. The base colour is silvery white and has excellent corrosion resistance. The normal service life of Aluzinc sheeting is up to 25a. It has good heat resistance and can be used at temperatures up to 315°C. Good adhesion between the coating and the paint film. It has good processing properties. It can be punched, cut, welded, etc. The surface conductivity is very good. Good
The composition of the coating consists of 55% aluminium, 43.4% zinc and 1.6% silicon by weight respectively. The production process of galvanised steel is very similar to that of galvanised steel, which is a continuous melt coating process. The colour coated product has excellent adhesion and flexibility.
Galvanised aluminium sheet has twice the heat reflectivity of galvanised steel. We can use it as an insulating material. Alu-Zn sheet also has good heat resistance, withstanding temperatures above 300 degrees Celsius, very similar to the high temperature oxidation resistance of aluminised steel, and is commonly used in chimneys, ovens, lamps and fluorescent light covers. As 55% AL-Zn is less dense than Zn, it has the same weight and thickness as gold plating.
(1)The packaging is divided into two types: galvanized steel sheets cut to length and galvanized steel sheets in coils. General tinplate packaging, lined with moisture-proof paper, and tied with iron waist outside. The binding is firm to prevent the galvanized steel plate of the inner window from rubbing against each other
(2)Specifications, models, specifications and related product implementation standards (described below) all indicate the thickness, length, total width and allowable errors of the galvanized steel sheet strongly recommended. In addition, the total width and length of the board and the total width of the roll can also be specified according to the customer’s requirements.
(3) Appearance of the surface layer: the galvanized steel sheet has different surface conditions due to the different treatment processes in the coating process, such as general spangles, fine spangles, flattened spangles, zinc-free flowers and pickling and phosphating The surface layer and so on. Galvanized steel sheets and galvanized coils that are cut to length should not have the disadvantages of hazardous applications (described in detail below), but steel coils are allowed to have multiple abnormal parts such as electric welding and welding positions.
(4) Hot-dip galvanizing quantity Index value of hot-dip galvanizing quantity: Hot-dip galvanizing quantity is a reasonable way to express the thickness of zinc layer of galvanized steel sheet. There are two types of double-sided hot-dip galvanizing with the same amount (ie equal-thickness hot-dip galvanizing) and different double-sided hot-dip galvanizing (ie, differential thickness hot-dip galvanizing). The company’s hot-dip galvanizing capacity is g/m2.
(5) Physical properties ① Compressive strength test: Generally speaking, only galvanized steel sheets for construction, drawing and deep drawing can have their compressive strength characteristics. ② Tensile test: It is a key new item to consider the performance of sheet metal. However, the regulations of various galvanized steel sheets in various countries in the world are not consistent. It is generally stipulated that after the galvanized steel sheet is bent 180o, the zinc layer on both sides of the surface must not be removed, and the plate base must not be cracked or broken.
(6)The organic chemical composition of the hot-dip galvanized steel sheet is regulated by the standards of various countries in the world. If Japan does not require it, the United Kingdom does. Generally, no finished product inspection is done.
(7)Board shape considerations There are 2 index values for the pros and cons of the board shape, namely verticality and long-knife curve. The verticality of the plate and the larger control value of the long-knife curve have certain requirements.
(1) There are many kinds of coils on the market. When choosing and buying, you must first observe the surface of the plate, and choose the plate that looks very smooth and uniform, and there are no obvious scratches and particles to avoid these problematic plates.
(2)The surface of the board is uniform, the texture is clear and regular. With these characteristics, the raw materials used in the board are high-quality materials. The pattern of the board surface is chaotic and irregular, indicating that uneven heating has occurred during the processing, so do not buy this.
When purchasing, avoid problems such as scratches, particles, and uneven pattern distribution on the surface. Choose a regular large company for selection, which can avoid some quality problems.
(1) Improving the surface flatness of galvanised sheet. After smoothing, the flatness of the galvanised sheet is improved to a certain extent and the waveform of the galvanised sheet is partially eliminated. At the same time, slag particles or other uneven spots on the surface can be flattened to make the surface smooth.
(2) Adjusting the surface roughness of the galvanised sheet. By controlling the surface roughness of the finishing machine’s work rollers, the original uneven roughness of the galvanised sheet surface can be unified to within a certain range. This improves the paintability of the product and the lubricity of the process.
(3) Improving the surface colour of galvanised sheet. For both shiny and non-shiny products, smoothing allows the galvanised sheet to achieve a more uniform glossy surface. For some private companies using large flake products as colour coated sheets, the flake bumps and different gloss levels formed by the large flake crystallisation can be smoothed and unified and the flake will become blurred, facilitating the covering of the flake in the painting process.
(4) Improve the processing performance of galvanised sheet. Through the smoothing process, the yield plateau of the galvanised sheet can disappear or become inconspicuous, thus preventing metal slip lines from appearing in subsequent processing.