Metal Can Container Raw Material – Performance of Tinplate
1. Material properties
(1) The degree of quenching and tempering (expressed by surface Rockwell hardness HR30T) represents the mechanical properties of the material with the degree of quenching and tempering. Under the same manufacturing conditions, it better represents the material properties, but in the annealing process (continuous annealing or bell type When annealing) is different, the same tempering degree shows different strength and elongation. The thickness of the substrate is different, and due to the anvil effect, there is a certain difference between the measured value and the actual value. Due to aging reasons, the tempering degree will also change.
(2) Formability In addition to the harsh deformation of the material during drawing and other processing, general can and lid processing can withstand tinplate. Uniform performance is required, and the grain size of the material is suitable (tin plate is generally 7#~9#). With the acceleration of can making speed, it is required to have small fluctuations in material properties, small fluctuations in thickness, and good plate shape, otherwise defects such as cans will be easily caused. In order to prevent ridges in can making and tensile strain during stamping, the strain aging of the tinplate is required to be small.
(3) Direction In addition to the strict requirements for anisotropy of DI materials, the requirements for direction are not too strict in general can-making processing, but for secondary cold-rolled tinplate, the longitudinal and transverse properties differ greatly (horizontal sb Large, low elongation), the circumferential direction of the can body is required to be consistent with the rolling direction. When the primary cold-rolled tinplate has tensile deformation of expanding diameter or changing from circle to square, it is better to make the circumferential direction of the can body consistent with the rolling direction, which can reduce the occurrence of defects such as cracking and local deformation.
2. Size and shape
Thickness: The thickness tolerance is required to be small, the standard is 8.5% of soil, and the actual requirement is much lower.
Width and length: the tolerance is required to be small, the standard is -0/ten 3mm, and the actual requirement is much smaller.
Flatness: large warping, middle waves, and side waves will affect iron printing and can making, and the requirement is within 3mm.
Pinhole: During the production process of tinplate, it is detected by a pinhole instrument. The leak detection device on the canning line is also very important to avoid leaking cans from the factory.
3. Surface properties
(1) Surface roughness The surface roughness of the substrate is obtained when it is flat. In addition to having an important impact on the drawing process of DI materials, the roughness is appropriately rough, which can improve the adhesion of the tin-plated layer and the painted layer; Increased roughness, not easy to scratch, scrape.
(2) Tin coating amount The thicker the tin coating, the less pores and the higher the corrosion resistance. In order to study how to obtain a tin coating with good continuity and high corrosion resistance with a relatively small amount of tin plating, in addition to requiring the surface of the original plate to be clean, the electroplating process must be well controlled, and the process parameters must be stable to reduce fluctuations.
(3) The tin-iron alloy layer is obtained by reflowing to obtain the required tin-iron alloy layer, which improves the adhesion of the tin-plated layer and improves the corrosion resistance of the tin-plated plate. The K plate requires a higher alloy layer; the alloy layer is hard and brittle , too thick will reduce the welding performance, but also easy to fall off. Efforts should be made to control the continuity and density of the alloy layer to produce tinplate with high corrosion resistance. The key to the reflow process is to complete the heating according to the desired reflow heating curve. The combination of resistance heating and induction heating provides good conditions for the control of reflow.
(4) The passivation layer is obtained by chromate passivation treatment, which can effectively inhibit the oxidation of tin, improve the finish and corrosion resistance of the tinplate, and effectively prevent the generation of sulfur spots. According to the purpose and different contents, different passivation layers are required, such as orange, cherry, pineapple, pear and peach and other food cans and 18L bamboo shoot cans, which require high power for passivation.
(5) The oiled surface is coated with a layer of DOS oil, which acts as a lubricant to prevent scratches, abrasions, abrasions, and also has an anti-rust effect. However, when the oil is applied too much or the oil is uneven, it is easy to cause the “eye hole” defect of the coating film.
4. Corrosion resistance
(1) Corrosion resistance of plain canned foods such as oranges and pineapples, use plain iron to maintain the flavor and color of the food in the can. Most of these foods are acidic and require canned food to have high corrosion resistance. The main factors related to corrosion are the tinplate material for canning, the type of content, canning conditions, storage conditions, etc. From the perspective of tinplate materials, in an acidic environment without oxygen, tin is firstly corroded and dissolved to protect iron. In order to improve the corrosion resistance of tinplate, strict production control is required, and high corrosion-resistant plates (ie K plates) are provided to users.
(2) Corrosion resistance of painted cans In order to reduce costs and save precious tin resources, people no longer use the method of increasing tin plating to improve corrosion resistance, but use lower tin plating to paint to improve cans The life span; painting can also prevent sulfur-containing protein foods from sulfide blackening; flavors such as beverages and beer are sensitive to the presence of a small amount of dissolved metals, so painted cans are used. It is necessary to ensure that the coating film is complete and free of defects. Cans no longer rely on the dissolution of tin to prevent corrosion of the substrate, and the paint layer has become the first line of defense. Some people have done experiments: the shelf life of cans with defective coatings is much shorter than that of unpainted ones, so it is necessary to prevent scratches on the coatings, damage to the flanging parts, or peeling off of the coatings produced during the stamping process of the can lids, etc. . In order to ensure the quality of the coating film, it is sometimes painted multiple times; for strong acid beverages, it must be sprayed inside after the can is made to prevent rapid corrosion and even leaking cans.
Most tinplates need to be coated, and the quality of the coating will directly affect the corrosion resistance of the metal cans; some also need to be color printed. Finishing properties include wettability and adhesion.
(1) The wetting paint is not wet or has holes, and the corrosion is concentrated at the defect site. Compared with the non-painting, pitting corrosion is more likely to occur. There are many factors affecting wettability, including coating, finishing conditions and tinplate.
The main causes caused by tinplate are as follows:
① Excessive oiling or uneven oiling.
② There is foreign matter attached to the surface. Machine oil, silicone resin, fine powder, moisture, etc.
③Surface state, aging, storage temperature, etc.
(2) Adhesion When the adhesion of the coating film is not good, cracks, peeling or peeling will occur during processing deformation.
Adhesion is also related to paint and painting process, and the factors related to tinplate are as follows:
①Through passivation treatment, the oxidation of tin is inhibited and the adhesion of paint is improved. But the storage time and the number of repeated heating and baking
② Influence of surface roughness.
③ The influence of tin layer thickness.
The body of the three-piece tank and various barrels must be welded, so the quality of the weld seam is very important. It is required to adjust the welding parameters reasonably to obtain a smooth, uniform weld seam to prevent concentrated corrosion and even tank leakage. Most of the substrates of tinplate are low-carbon aluminum-killed steel, and the welding performance is good. With the acceleration of can making speed, stable welding performance is required. In terms of tinplate, the relevant performance must be guaranteed, mainly in the following points:
①The steel is pure, the thickness and dimension deviation is small, and the hardness is uniform.
②The surface is clean, free of dust and garbage.
③Appropriate surface roughness.
④The lower the tin plating layer, the better the soldering performance. When the tin plating layer is low, control the tin-iron alloy layer to ensure a certain pure tin layer.
⑤ The welding parameters of the tin-plated plate with IF steel as the substrate should be carefully controlled.
More: Jiujiang Yixin Technology Co., Ltd. Provides Good Quality Tin Can Machinery To Clients In Domestic And Overseas.