Aluminum Sheet Metal Coil

Before the aluminum sheet metal coil is rolled, some pretreatment sections are required to ensure that the surface of the aluminum coil is clean. Avoid the residual grease and smoothing agent on the surface, which will affect the coating and application. Therefore, the aluminum sheet coil must be pre-treated in the following aspects before it is formed.

First, use hot water to wash the aluminum sheet metal. If the hot water scrubbing agent cleans the remaining degreaser on the surface of the aluminum substrate, ensure that these residues can be dissolved in order to prevent the degreaser from causing secondary pollution to the substrate. Most of the application methods are dipping and spraying. The hardness of the water used should not be high, otherwise, the minerals in the water will form mineral spots on the surface of the aluminum substrate.

Secondly, hot alkali degreasing because the pre-coating line speed is faster, so the degreasing agent used usually has a higher concentration. The typical degreasing agent contains sodium hydroxide (NaOH), sodium carbonate (Na2Co3), water glass (Na2SiO3), and phosphate. Equal components. The hot alkaline degreasing process is usually divided into two steps to ensure that the surface of the aluminum coil substrate is cleaned, and spray scrubbing is often used.

Again, passivate the aluminum sheet metal coil. Passivation treatment is to make the passivating agent form a conversion film on the surface of the substrate through pressure spraying, dip coating or roll coating. Usually pressurized spray is used, and the sludge generated during the use of the passivation fluid tends to congest the spray hole, thereby affecting the efficiency of the spray. Although the dipping method has dealt with this problem, the amount of passivation liquid is relatively large.

The above two methods require water to clean the excess passivation liquid in the essential operation, and the recovery and purification of wastewater will occur. Roll coating is a good passivation construction method. It has average coating, economical application, and no need to rinse. And other advantages. Aluminum sheet metal coil usually chooses chromate/oxide type treatment agent, this type of treatment agent contains chromate, chromic acid, phosphoric acid and promoter fluoride and molybdate. Phosphoric acid must be added to this type of treatment agent, otherwise it cannot be used to treat aluminum sheet metal for food and beverages.