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What is Sand Blasting?
Sand Blasting is the preparation of a substrate and is carried out at high-velocity to clean or etch a surface.
Swedish Standard SIS 05 5900-1967:
"Life of an anti corrosive coating is dependent on how thoroughly the surface has been prepared prior to coating."
Steel Structures Painting Council SSPC-PA 15213, USA:
"Advance the technology and promote the use of protective coatings to preserve industrial, marine and commercial structures, components and substrates."
Metal spraying and painting have long been regarded as competitive but it is rapidly being realized to as ultimate failure invariably results from rusting of the underlying steel, once barrier protection has certain positive protection by virtue that they are anodic to steel and sacrifice themselves. A combination of paint provides the ideal treatment for long term protection. Maintenance repainting is then only necessary.
Surface Protection: Up to 80% of all coatings failures can be directly attributed to inadequate surface preparation, which affects coating adhesion.
The method of surface preparation depends on the substrate, the environment, and the expected life of the coating system.
Spraying versus Painting: Sprayed metal coatings are applied in a molten state to form a pure metal finish. Solutions which have metal particles in suspension are applied without heating, with the result that it is precisely the same form as in the original solution without forming the fine atomic spray as in spray coatings.
Electrolytic Protection: Protection of ferrous metals against electrolysis by the attachment of sacrificial anodes. Prolonged protection can only be provided by metallic coatings which are the base metal and sacrifice themselves by cathodic action. Scientists have proved that a satisfactory of electrolytic protection from zinc rich paints requires a Zn content of atleast 93% in the film. However, with this percentage, the solutions become very thick and are not easy to apply uniformly either with a brush or by spraying. Moreover the paint loses its binding power at this level and even after continuous sticking practically impossible to ensure that the percentage of Zn at every point will be at the required level.
Costs: Despite various claims to the contrary, an adequate metallic paint system is not cheaper than an Al coating applied by metal spraying. Relevant factors to be considered here include the increased free life obtained by metal spraying compared to the periodic painting required at regular intervals longer downtime required in painting for drying.