Coating process of the hottest metal 0

2022-08-14
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Metal coating process

1, coating method

coated and printed sheet iron can be processed into three piece food cans, beverage cans and spray cans. According to the characteristics and use purposes of the substrate, it should have appropriate corrosion resistance and printing and processing properties. Therefore, the bottom coating should be carried out before printing. The coating processes related to printing mainly include prepress coating, surface white coating, edge seam coating and glazing (post press coating)

prepress coating: (1) turn off the oil pump and apply the primer. Before coating, the coated surface should be degreased to remove the greasy dirt on the surface as the name suggests. Prepress coating has two forms: internal coating and external coating. Internal coating is to coat the inside of the iron sheet, that is, the inside of the formed product, and apply a layer of protective gloss to protect the iron sheet from the erosion of the contents, and also protect the contents. As the internal coating is in direct contact with food, it is required that the coating must be non-toxic and tasteless. After internal coating, it should be dried in a dryer. External coating is the coating of the printing surface, and its function is to improve the adhesion between the metal surface and the ink layer. Therefore, the coating is required to have a firm adhesion to the metal surface and a good affinity to the ink layer, which requires that the coating itself should have a linear relationship between the displacement of the rod assembly and the load, with good fluidity, water resistance and color rendering

white coating: use white paint or colorless transparent paint to coat the metal surface. It is often used as the background color for printing full page pictures and texts. The white paint shall have good adhesion and whiteness, and shall not turn yellow or fade under the condition of high temperature baking, and shall not fall off or peel off during the canning process

side seam coating: refers to a coating method that uses side seam coating to repair the side seam of cans after the resistance welding can is formed to prevent corrosion

post press coating (glazing): apply a layer of glazing oil on the surface of all graphic printing has been completed. Its purpose is to increase the gloss of the printing surface, protect the printing surface, and improve the light resistance and chemical corrosion resistance of the metal surface

2. Coater

as a separate metal printing auxiliary machine, the coater is also equipped with a feeding mechanism, a conveying mechanism and a tunnel oven. The automatic feeding mechanism is similar to that of a metal printing press. Before the sheet enters the drum, it is necessary to adjust the connection position between the push plate and the conveyor belt mechanism, and give basic positioning to prevent the printing sheet from skewing. If the chain is found to be too loose, too tight or the pushing heads on both sides are inconsistent during operation, the center distance of the sprocket can be adjusted

there are three kinds of rubber rollers commonly used in coating devices: the first one uses thick rubber blanket, that is, wrap a solvent resistant rubber cloth with a thickness of about 5 mm on the hollow iron roller. This kind of cot has good coating quality and is suitable for full page printing. The second is made of rubber padded felt wrapped on iron rollers, which is suitable for full-scale coating of general products. The third kind is the rubber roller slotted according to the graphic area, which is mainly used for resistance welding products such as food cans and aerosol cans

the function of the scraper in the coating device is to scrape off the coating to avoid the back of the printing sheet

3. Coating process

the paint in the oil pan is pumped by the gear pump to the lower oil transfer roller through the conduit. The lower oil transfer roller rolls relatively after meshing with the gear of the upper oil transfer roller. After radial and axial mixing, the paint is coated on the rubber roller. In order to control the flow of paint, the pipeline is equipped with a safety valve regulating mechanism. The adjustment of oil transfer roller is very important to the coating thickness and uniform distribution, which directly affects the product quality. During adjustment, the axis (center line) of each roll shall be parallel and the contact pressure (i.e. clearance) shall be consistent. The gap between the upper and lower oil transfer rollers is large, which needs to be adjusted according to the requirements of different product coating thickness in the preparation process of mixed ingredients. When adjusting the pressure of the upper oil roll and the rubber roll, the thin steel sheet shall be used for inserting and pulling, and the inserting and pulling shall be subject to the appropriate tightness. The rubber roller shall be adjusted according to the thickness of the sheet. The coating shall be uniform on the same sheet, and the coating amount of each batch of products shall be the same

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