Abrasive Grit Blasting Inspection

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Abrasive grit blasting processes are coming under increased scrutiny in situations where it is used as a precursor to more elaborate coatings such as plasma sprayed coatings. This is because the abrasive grit surface preparation techniques form an integral part of the final coating quality. A poorly grit blasted surface will produce a bad quality coated surface and hence increased importance is being placed not only on the abrasive grit blasting process itself but also on the inspection steps that provide quality assurance after the process.

Now what are the steps involved in abrasive grit blast inspection is the main thrust of this post. The first criteria is proper grit blast coverage. It is essential to check for proper and complete grit blast coverage of the required areas as well as ensuring that masking for grit blast to prevent grit blasting on not allowed areas is properly followed through.

Associated with this requirement is the inspection for uniform grit blast coverage. What this means is that the grit blasted finish must be uniform throughout the required area. This can be a problem sometimes when using manual techniques, because in such cases, sometimes the gun movement may be non-uniform in certain areas or the stand off distance may be different in some areas resulting in some areas having a different finish than other areas. This non-uniform coverage must be avoided and the inspector needs to watch for this during inspection.

Surface finish must be considered a key inspection criterion. While the best way to ensure accurate surface finish value is by the use of a profilometer, at the very least, visual grit blast surface finish standards need to be established and the inspector can visually inspect as to which standard matches closest to the component at hand. It is preferable that inspection of grit blast surfaces by comparison to visual standards be performed at least at a 10X magnification level.