1 -20 BASIC KNOWLEDGE ABOUT PAINTS AND PAINTING Hose Water Mist Spray Gun . , (2) AIRLESS SPRAYING When we squeeze the tip of a hose with our fingers while the water is running through it, water is scattered in all direc- tions in a mist-like condition. In airless spraying, the paint is injected from a nozzle under a high pressure and speed to break it into small particles. Unlike the air spraying method, only a small amount of air is mix- ed with the paint in the airless spraying method. For this reason, there is only a small loss of paint which leads to a high adhering efficiency. This method can be used with paints having high viscosity levels.
But it does not permit the pattern width adjustment and its finish is not as good as that of air spraying. Therefore, this method is used for painting the skirt and lower sections of a car and not on the external panels that require quality paint- ing. I Paint (Under High Pressure) PRINCIPLE OF AIRLESS SPRAYING Electric Field PRINCIPLE OF ELECTROSTATIC PAINTING (3) ELECTROSTATIC PAINTING Electrostatic painting is a method based on the principle that the positive and negative electrical charges attract each other while electrical charges of the same polarity repel each other. The paint is charged negatively in a high voltage generator while the body is charged positively as it is grounded.
Since paint particles from the paint applicator are charged negatively, they repel each other and are atomized. These negatively-charged particles are attracted by the positively-charged body and adhere to it. Electrostatic painting has the following merits and demerits: 0 The paint is attracted by an electrically attracting force and the paint loss is less than by spray- ing methods. 0 Since atomization is promoted by an electrically repelling force, this method ensures a beautiful finish. Metallic paints applied by this method result in a "metallic" finish that is not found in ordinary spraying methods. 0 The coating efficiency is very high and ensures a high work speed.
0 Paints do not stick to recessed areas very well because the electric potential is low in those areas. Corrective painting is required there. 0 This method cannot be used with non-conductors (glass, plastics, wood, etc.) unless they are given conductive treatment. An automatic electrostatic painting machine is used in new vehicle production lines to apply the sur- facer (second coat) and the top coat. A hand-held electrostatic painting machine is designed for total painting in repainting. But such a device is rarely used because there is only a small demand for total painting and it takes much time to prepare it for use and to clean it after use. -22-