Before the aluminum coil is rolled, some pretreatment sections are needed to ensure that the surface of the aluminum coil is clean. In order to avoid the existence of residual grease and lubricant on its surface, which will affect the coating and use. Therefore, aluminum roll in the following aspects of the amount of pre-treatment.
1、 The aluminum coil can be cleaned with hot water. Hot water cleaning is mainly to clean the residual degreasing agent on the surface of the substrate, so as to ensure that these residues can be dissolved, so as to prevent the secondary pollution of the substrate caused by these degreasers. The usage is mostly immersion and spray brushing. The best water quality should not be too high hardness, otherwise, minerals in water will form mineral spots on the surface of the substrate.
2、 Due to the fast linear speed of precoating line, the degreasing agent used in hot alkali degreasing is generally high. The typical degreasing agent contains sodium hydroxide (NaOH), sodium carbonate (Na2CO3), sodium silicate (Na2SiO3), phosphate and other components. The hot alkali degreasing process is generally divided into two steps to ensure that the surface of aluminum coil substrate is clean, and spray brushing is often used.
3、 It is passivated. Passivation treatment is to form conversion film on the surface of substrate by pressure spray, dip coating or roller coating. Generally, pressurized spray is used. Sludge produced in the process of passivation liquid often blocks the spray hole, thus affecting the spray effect. Although dip coating can solve this problem, the consumption of passivation solution is large. The above two methods need to wash the excess passivation liquid with water in actual operation, which will lead to the problem of wastewater recovery and purification. Roller coating is the best passivation construction method, which has the advantages of uniform coating, economic and practical, and no need of washing. Generally, chromate / oxide type treatment agent is used for aluminum plate, which contains chromate, chromic acid, phosphoric acid and accelerant fluoride and molybdate. Phosphoric acid must be added to this kind of treatment agent, otherwise it can not be used to treat aluminum plate for food and beverage.