Tinplate (commonly known as tinplate) refers to a steel plate with a thin layer of metal tin plated on the surface. Tin plate is made of low-carbon steel rolled into a steel plate with a thickness of about 2mm. After pickling, cold rolling, electrolytic cleaning annealing, smoothing, trimming, and then cleaning, electroplating, reflowing, passivation, and oiling Cut into tin-plated sheet finished products. The tin-plated tin plate is high-purity tin (Sn>99.8%). The tin layer can also be coated by hot-dip plating. The tin plate obtained by this method is thicker, and the amount of tin used is large, and no purification treatment is required after tin plating.
It combines the hardness and strength of steel with the solderability, corrosion resistance and bright appearance of tin. Tin plate has the advantages of odorless, non-toxic, light weight, easy to process and shape. Printing different patterns can also beautify products, so it has been widely used in the food canning industry, electronic devices, chemical paint and other industries. In the production process of tin plate, after the strip steel is tin plated and reflowed, in order to prevent the tin layer from oxidizing and yellowing when the tin plate is stored or the paint is baked, and at the same time to improve the sulfur resistance of the tin plate, it is necessary to The tin plate is passivated.
The tin plate is composed of five parts, from the inside to the outside are the steel substrate, the tin-iron alloy layer, the tin layer, the oxide film and the oil film.
The production process of tin plate mainly includes tin electroplating, reflow, cathode passivation and oiling process. The tin plating process deposits a layer of metallic tin on the cold-rolled plate. The reflow process makes a very thin tin-iron alloy layer formed between the cold-rolled substrate and the pure tin layer. The cathode passivation treatment and the oil coating process respectively form a passivation Chemical film and oil film.
- Equal-thickness tin plate: cold-rolled tin plate with the same amount of tin plating on both sides.
- Different thickness tin plate: cold-rolled tin plate with different tin plating on both sides.
- First-class tin plate: the electroplated tin plate that has undergone online inspection, under normal storage conditions, is suitable for conventional painting and printing on the surface of the entire steel plate, and must not have the following defects: ①Pinholes penetrating the thickness of the steel plate; ②The thickness exceeds the deviation specified in the standard; ③Surface defects such as scars, pits, wrinkles, rusts that affect the use; ④Shape defects that affect the use.
- Second-level tin plate: The surface quality is lower than that of the first-level tin plate. Small areas such as inclusions, wrinkles, scratches, oil marks, indentations, burrs, burning spots, etc., are allowed to have obvious surface defects or shape defects. Ensure that the entire steel plate can be conventionally painted and printed.
Tin plate is generally manufactured according to the following procedures:
- Hot rolling: On a continuous hot strip mill, the slab is hot rolled at a higher rolling temperature to produce sheared hot rolled steel plates and continuous coils;
- Pickling: The pickling line is used to remove scale on the surface of strip steel before cold rolling. This kind of large reduction cold rolling is required for the production of thin tin plate required by the market. A good pickling effect will also help improve the surface quality and cleanliness of the steel plate to meet the needs of the subsequent tin electroplating process;
- Cold rolling: The pickled coils are cold rolled on a cold rolling mill to reach the specified thickness. In order to ensure product quality during the cold rolling process, it is important to ensure that the cold rolled strip has a uniform thickness, obtain a good surface quality, and meet the flatness requirements. These quality characteristics will be reflected in the final product quality of the tin plate;
- Annealing: Cold rolling will elongate the grain structure of the strip along the direction of cold rolling, making the strip hard and brittle. However, during the annealing process, the cold-rolled steel strip is reheated and kept at a certain temperature in a reducing atmosphere for a period of time to form new non-deformed grains so that the material properties meet the specified requirements for use. There are two annealing methods: bell annealing (batch annealing) and continuous;
- Smooth rolling or secondary rolling: Smooth rolling or secondary rolling is usually the final processing. This rolling process can produce a slight cold work hardening phenomenon for the strip steel, and at the same time can increase some toughness and eliminate the yield platform phenomenon. Moreover, cold rolling and or secondary rolling can also make the strip meet the required surface finish requirements, and improve the quality and flatness of the strip.
New production technology
(1) Clean with high-density current. Different types of high-density current electrolytic cleaning sections are selected according to the speed of the unit, and two-stage electrolytic cleaning is used for the unit using secondary cold-rolled plates as raw materials. There is a spray cleaning section in the middle to replace the scrubbing section, reducing maintenance.
(2) Use stretch straightening machine. The stretch straightening machine is used to improve the shape of the strip steel plate so that the height of the wave shape does not exceed 1.5mm, and the steepness does not exceed 0.6%.
(3) Use insoluble anodes. Japan’s Nippon Steel Corporation first developed the insoluble anode technology, which uses platinum-plated titanium anodes. Because the anode is an insoluble material, it eliminates the uneven distribution of the tin layer caused by the change in the distance between the anode and the anode due to the dissolution of the electrode plate; the anode life is at least 10 months, thus eliminating the need for frequent replacement and casting of the tin anode; in addition, due to The distance between the strip and the anode is correspondingly reduced, thus reducing power consumption and facilitating the installation of a plating tank waste gas collection system. The two tinning lines of Baosteel 1420 Cold Rolling Plant and the Yichang sheet tinning line under construction all use insoluble tin anodes.
(4) Adopt adjustable edge cover. Match with the width of the strip to prevent thickening of the coating at the edges and ensure a more uniform coating.
(5) Electroplating solution concentration control. With the insoluble anode technology, the X-fluorescence analyzer is used to measure the metal tin content from the sampler, and the actual content is compared with the given content to obtain the concentration replenishment amount. The oxygen blowing amount is controlled to control the dissolution rate of the tin and make the plating solution The concentration is stable.
(6) Mix and heat to reflow. Using resistance heating and high frequency induction (frequency up to 100 ~ 200kHz) mixed heating reflow.
(7) Online small defect detection. Using laser surface inspection and magnetic flux leakage micro-inclusion detection, 90% of surface defects can be detected; internal micro-inclusions can be detected when the strip is running at high speed.
(8) Develop extremely thin alloy tin-plated plates. Many countries in the world are developing ultra-thin alloy tin-coated steel plates with a coating thickness of 0.5 to 0.89 grams per square meter, or even thinner. This kind of ultra-thin plated plate has good weldability, high corrosion resistance and excellent adhesion to paint. The most representative ones are iron-nickel-tin alloy coated sheets, iron-tin alloy tinned steel sheets and zinc-tin alloy coated sheets.
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