Pre-treatment For Aluminum Trim Coil Production

To guarantee the cleanness of aluminum trim coil surface, some pre-treatment steps are necessary to remove remains grease and lubricants on the coil surface. Generally speaking, the pre-treatment entails three steps.

　　First, wash the raw aluminum coil stock in hot water. The main purpose of hot water cleaning is to eliminate the degreaser residue on the surface by having them dissolved in water therein, which further prevents secondary decontamination of the substrate by the degreaser. Common methods are soaking and spray scrubbing. The hardness of water should not be too high. Otherwise, minerals in the water will form mineral spots on the surface of the substrate.

　　Secondly, due to the high line speed of the pre-coated line, the degreasers used are generally high in concentration. Typical degreasers include sodium hydroxide (NaOH), sodium carbonate (Na2CO3), sodium silicate (Na2SiO3), phosphates, and other ingredients. The hot alkaline degreasing process is generally carried out in two steps to clean the surface of the aluminum trim coil substrate and often employs a spray wash.

　　Thirdly, the aluminum trim coil gets passivated. The passivation treatment is to form a conversion film on the surface of the substrate by pressure spraying, dipping or roll coating of aluminum coil coating. Pressure spraying is usually used. The sludge generated during the use of the passivation solution often blocks the orifice and affects the orifice. Although the impregnation method solves this problem, the passivation solution is consumed in a large amount. The above two methods require water to wash too much passivation solution in actual operation, which will lead to problems of waste water recovery and purification. Roll coating is a good passivation construction method, which has the advantages of uniform coating, economical use, and no need for cleaning. Aluminum trim coil rolls are typically treated with a chromate or chromic oxide type of additive comprising chromate, chromic acid, phosphoric acid and extender fluoride and molybdate. Such a treatment agent needs to be added with phosphoric acid, otherwise it cannot be used for the treatment of aluminum coil rolls for foods and beverages.

Reprinted from http://haomei-aluminium.com/en/News/Knowledge/aluminum-trim-coil-pretreatment.html