no residue on a surface to impede the bond of coating require additional 

 investigation. However, study in this area is limited as solvent cleaning is 

 usually used with other surface preparation processes. 



Hand and power-tool cleaning of metal surfaces is widely used; however, 

 this process usually produces some areas of polished metal, which are not 

 conductible to good coating adhesion. Developmental studies are being done 

 in an effort to devise means of removing loose contaminating particles from a 

 structure surface by designing wire tips for brushes that will remove con- 

 taminants and improve brush wear. 



In pickling, acids such as sulfuric, hydrochloric, phosphoric and nitric 

 are used. Inhibitors are added to minimize metal loss. However, acids leave 

 considerable residue on metal surfaces that can cause coating adhesion 

 problems. The elimination of residues by hot-water rinsing helps but rede- 

 posited salts or absorption of atomic hydrogen may cause metal embrittlement. 

 Means to prevent these possibilities must be considered. 



Flame cleaning removes only loose rust particles and grease, therefore it 

 must be followed by wire brushing and coating application while the surface 

 is dry but cool. Because this process has a high cost, it is not used to a 

 great extent and little improvement in its use is being studied. 



Blast cleaning is the most effective method of cleaning metal surfaces. 

 The degree of blast cleaning can be determined by type of blasting material, 

 the pressure used in blasting, and the amount of time of blasting per unit 

 area. The metal surface anchor pattern developed as a result of blast 

 cleaning can be controlled. Certain coating systems may require a deep 

 anchor pattern, others a shallow anchor pattern. Some blasting materials 

 produce a rounded anchor pattern while others a sharp pattern. Because 

 different types of coating primers require different adhesion conditions, 

 surface preparation must be considered as a part of the coating system. 



(b) Coating Application Techniques . Coating application 

 techniques are an integral part of a protective coating system. As new and 

 better coating systems are developed, new application systems must also be 

 created. Application systems presently in use are brush, roller, various 

 spray methods, flow and electrostatic processes. The electrostatic processes 

 came about with the development of plastic resins which are applied in the 

 dry powder form. This application system involves a specific surface prepa- 

 ration process. Still in the development and improvement stage is an im- 

 provement in the process that will produce a required thickness of a near 

 perfect coating, without pinholes or holidays, using a variety of plastic 

 resins. Present electrostatic applications are very good but the adaptability 

 of this procedure to a wider variety of resins or the development of a 

 greater number of coating" resins for use in this process must continue. 



(cl Improved Coating Materials . Asphalt coatings consisting of 

 a dispersion of high molecular weight hydrocarbon compounds (asphaltenes) in 

 heavy residual oils are made into asphalt enamels, hot applied, solvent-reduced 

 asphalt coatings and emulsions. Because the asphalt residue, from which the 

 coatings are made, is used as a raw material for many other products, the cost 

 of such coatings is rising and there is relatively little asphalt coating 

 research and development activity. 



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