and are difficult to spray. However, there are considerable advantages to 

 the use of airless spray. One major factor is the almost complete absence 

 of overspray. There is less tendency for material to bounce, thereby, 

 providing less air contamination and coating porosity. It is ideal for 

 large flat areas such as tanks and walls, where speed is an asset and good 

 coverage is required. 



The maneuverability and convenience of this equipment, especially when 

 working in confined areas, is another plus. Where heavy coating thickness 

 is needed, airless is the desired tool. Table 50 shows comparable material 

 losses for various application methods. 



Table 50. Estimated loss of coating materials during application. 



Method 



Loss 





(pet) 



Conventional Air 



20 to 40 



Hot air spray 



15 to 30 



Airless spray 



5 to 20 



Electrostatic spray 



5 to 15 



Brush and roller 



4 to 8 



(5) Dip. Coating work can be accomplished by dipping. Most 

 galvanizing is by dipping. Parts which have a high surface area to weight 

 ratio and which are relatively small can be dip coated in coating baths. 

 This would include items such as gratings, ladders, and fence. The quality 

 of a dip coating depends on the surface preparation and the application. 

 The surface of the part being coated must be clean, free of contamination, 

 and have the right profile for the coating being applied. Most coating 

 systems can be applied by dip. These include alkyds, coating systems which 

 cure by evaporation (e.g., vinyls and acrylics) and coating systems which 

 cure by reaction (e.g., epoxies and urethanes) . 



As stated above, the qual 

 surface preparation, but also 

 properly and continuously sti 

 other coating components are 

 ture of the part and of the b 

 range recommended by the coat 

 reaction have a limited appli 

 temperature. The higher the 

 be exercised not to apply coa 

 application life. 



ity of dip coatings depends not only on the 



on the application. The dip bath must be 

 rred and agitated, so that the pigments and 

 uniformly dispersed in the bath. The tempera- 

 ath should be controlled to lie within the 

 ing manufacturer. Coatings which cure by 

 cation life. This life is dependent upon the 

 temperature, the shorter the life. Care must 

 tings which have exceeded their effective 



Care must also be exercised in the application of coatings which cure 

 by evaporation. Solvent must be added from time to time to make up for the 

 solvent lost to the atmosphere by evaporation. Dipping work should be 

 stopped during the application of solvents, and it should not be commenced 

 again until the added solvent is thoroughly and uniformly dispersed. Parts 

 which are dipped are often "turned" while curing, in order to avoid drips 

 and runoff "strings" from the bottom edges. Heat and air movement may be 

 used to increase the cure rate (to shorten the cure time). 



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