1-26 BASIC KNOWLEDGE ABOUT PAINTS AND PAINTING (1) CHEMICAL PRETREATMENT STAGE This is the stage in which stains, fats and greases adhering to the inner and outer body panels are removed completely. At the same time, a zinc phosphate film is formed to improve corrosion resis- tance of the steel metal and increase adhesion of the undercoat. Chemical pretreatment can be done in one of two ways. In the spray method, chemicals are sprayed from a nozzle. In the full-dip method, the vehicle body is completely immersed in a chemical bath. The full-dip method is used at Toyota because it ensures greater rust preventive effects.
G) Washing Stains and fats and greases are removed from the body prior to chemical pretreatment. HOT BATH 1 HOT BATH 2 DEGREASING RINSING Stains adhering to the body are washed off in a hot bath (40- 50°C). Rust preventing oil from the stamping process is removed using a low alkaline degreasing agent. Degreasing agent is washed off. ® Chemical pretreatment SURFACE ADJUSTMENT ZINC PHOSPHATE TREATMENT The body is dipped in titanium phosphate colloidal The zinc phosphate coat is promoted in a solution to raise the crystallization point in treatment solution (primary zinc phosphate order to get a precise zinc phosphate coat. + phosphoric acid + accelerator).
®Washing and drying WASHING WASHING BY PURE WATER DRYING Treatment solution is removed by washing (about 3 times). The body is washed again using pure water. The body is dried in a tem- perature of 1 00 to 140°C. -28-