Before the aluminum coil sheet is rolled, some pretreatment sections need to be done to ensure the cleanness of the surface of the aluminum coil. In order to avoid residual grease and smoothing agent on the surface, which will affect the coating and application. Therefore, the aluminum coil should be pretreated in the following aspects before forming.
First of all, you might as well use hot water to wash the aluminum roll. Hot water washing is mainly used to wash the degreasing agent remaining on the surface of the substrate to ensure that these residues can be dissolved, so as to prevent these degreasing agents from secondary pollution to the substrate. The application methods are mostly immersion washing and spray brushing. The hardness of the water used should not be very high, otherwise the minerals in the water will form mineral spots on the surface of the substrate.
Secondly, due to the fast line speed of precoating, the degreaser used for hot alkali degreasing normally has a high concentration. The conventional degreaser contains sodium hydroxide (NaOH), sodium carbonate (Na2CO3), sodium silicate (Na2SiO3), phosphate and other components. The hot alkali degreasing process is normally divided into two steps to ensure that the surface of aluminum coil substrate is cleaned, and spray brushing is frequently used.
Thirdly, I passed it. Passivation treatment is to form a conversion film on the surface of the substrate by means of pressurized spraying, dip coating or roll coating. Generally, pressurized spraying is used, and the sludge generated during the application of passivation solution frequently congests the spray hole, thus affecting the spraying effect. Although the dip coating method solves this problem, the amount of passivation solution is enormous. The above two methods require water to clean the surplus passive solution in the essential operation, which will lead to the recovery and purification of wastewater. Roller coating is a good passivation construction method, which has the advantages of average coating, economic applicability and no leaching. Chromate/oxide type treatment agent is usually selected for aluminum plate, which contains chromate, chromic acid, phosphoric acid and promoter fluoride and molybdate. This kind of treatment agent must be added with phosphoric acid, otherwise it can not be used to treat aluminum plates for food and beverages.