Pretreatment section of aluminum coil roll

Before the aluminum coil is rolled, there are some pretreatment sections should be made to ensure that the surface of the aluminum coil is clean. In order to avoid the presence of residual oil and lubricants on the surface, the impact on painting and use. Therefore, the aluminum roll should be pretreated in the following ways before forming.

First, hot water can be used to clean the aluminum trim coil. Hot water cleaning is mainly to clean the degreaser residues on the surface of the substrate, to ensure that these residues can be dissolved in it, in order to prevent these degreasers from causing secondary pollution to the substrate. The way of use is mostly washing and spraying. The water quality is best not too high. Otherwise, minerals in the water will produce mineral patches on the surface of the substrate.

Secondly, due to the fast linear speed of the pre-coating line, the degreaser used is generally of high concentration. Typical degreasers include sodium hydroxide (NaOH), sodium carbonate (Na2Co3), sodium silicate (Na2SiO 3), phosphate and other components. Hot alkali degreasing process is generally divided into two steps to ensure that the surface of painted aluminum coil substrate is cleaned, and spray scrubbing is often used.

Finally, it is passivated. Passivation treatment is to form a conversion film on the surface of the base material by pressure spraying, dipping or roll coating. Pressure spraying is usually used. Sludge produced during the use of passivation liquid often blockages the spraying holes, thus affecting the spraying effect. Although the way of dip coating solves this problem, the consumption of passivation liquid is larger. The above two methods need to wash the excess passivation liquid with water in practical operation, which will lead to the problem of waste water recovery and purification. Roller coating is the best passivation construction method, which has the advantages of uniform coating, economic and practical, and no need for washing. Aluminum sheets are usually treated with chromate/oxide type additives, which contain chromate, chromic acid, phosphoric acid and accelerator fluoride and molybdate. Such agents must be added with phosphoric acid, otherwise they can not be used to treat aluminum plates for food and drink.