METHODS OF APPLICATION 1-19 5 METHODS OF APPLICATION Paints may be applied on a work with a spatula, brush, roller, spray, etc., or by immersing the work in a paint bath. Spraying and immersion are the two most frequently used methods in the auto industry. 1. SPRAYING Spraying can be done by air spraying, airless spraying or electrostatic painting. All these three methods are based on a common principle; the paint is atomized and is adhered to the surface by the energy of injection to form a coat on the work. Spraying has the following merits and demerits: 0 Since the paint is sprayed by atomization, it is applied efficiently and a beautiful finish is ensured.
0 The paint can be applied in a large area regardless of the shape or material of the work. 0 A large paint mist occurs during atomization resulting in a relatively large loss of paint. II 0 The paint must be kept at an appropriate viscosity for atomization using a large amount of thin- ner that does not contribute to the formation of a coat itself. (1) AIR SPRAYING Air spraying is based on the same principle as atomization. When compressed air is supplied from an air nozzle in an air cap, it creates negative pressure at the tip of the paint nozzle. The paint is sucked up as a result.
The sucked paint is smashed into · tiny mist-like particles by the compressed air, and then adheres to the surface of the object. Since the paint is scattered in a mist, there results a large loss of paint. This is a major defect of the air spraying method. But this method can be applied to virtually all kinds of paint with relatively simple equipment and ensures a beautiful finish. By properly adjusting the air pressure and pattern width of the spraying gun, this method can be used to spray paint over complex shapes. Therefore, air spraying is most suitable for repainting of automobiles hav- ing diverse surfaces and requiring quality finish.
PRINCIPLE OF ATOMIZATION Air Cap Spraying guns may be divided into the gra- vity feed type, suction feed type and the compressor type depending on the method used to supply the paint. (See Section 4-8 for detailed explanation of individual types.) PROMCIPLE OF AIR SPRAY -21-