What Is Abrasive Blasting?
A stream of abrasive material is propelled at high speed at a surface using air pressure and the purpose of the blasting is to remove substances such as rust, scale, paint and graffiti from a surface.
Abrasive blasting both cleans a surface and roughens it. This roughness is called anchorprofile. A top quality coating put on a marginally prepared surface will perform no better than a cheap coating applied to a squeaky clean surface. Surface preparation is an important step that affects the life of a coating. The life of any powder coating system is longer on a blast-cleaned surface than on a hand-cleaned surface.
Why Is Surface Preparation Important?
Surface preparation is the most important part of a coating system because it affects the performance of the coating more than any other variable. If the surface preparation is poor, coating performance is usually going to be sub-standard. If surface preparation is good, then the coating applied over it is likely to perform well. Abrasive blasting creates a foundation in two important ways:
- In a mechanical way, by providing an anchor for the coating; and
- In a chemical way, by allowing intimate contact of coating material molecules with the steel (or other material) surface.
Why Abrasive Blasting?
When a surface is very smooth, coatings have a difficult time adhering strongly. A light scrape easily removes a coating on glass. On the other hand, it is difficult to remove a coating on a rough surface like sandpaper. Steel, when it is abrasive blasted, has a surface that is rough, with a series of tiny peaks and valleys called surface profile. Coatings anchor themselves to the valleys of the profile, and the peaks are like teeth. This is why surface profile created by blasting is sometimes called an "anchor pattern" or "mechanical tooth."
Abrasive blasting also removes contaminants such as rust/paint/scale etc. When contaminants such as these are painted, they interfere with the mechanical and chemical adhesion of the coating to the substrate so that the coating is likely to fail. On the other hand, when all soils are removed, the coating can achieve complete and continuous contact with the substrate, thus assuring the best possible adhesion. When a coating adheres well, it is likely to be an effective barrier. The coating can minimise or prevent moisture (the electrolyte in the corrosion process) from reaching the substrate.