Pre treatment refers to the process of thoroughly cleaning the oxide skin, rust, grease, dust and other dirt on the surface of the workpiece before painting, so that the coating powder can firmly bond with the metal surface, have strong adhesion, and thus achieve high quality of the product, extending its service life. The general process of pre-treatment is: degreasing - water washing - surface adjustment - film coating - water washing (flexible adjustment according to the characteristics of the workpiece). Pre processing is divided into three forms: spray type, submerged type, and submerged groove type. The processing method is selected based on the workpiece and specific production requirements.