Materials Performance

DEC 2014

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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49 NACE INTERNATIONAL: VOL. 53, NO. 12 MATERIALS PERFORMANCE DECEMBER 2014 Continued on page 50 Dust contamination on blasted surface Q: We have the problem of dust con- tamination on an autoblasted surface. I have also observed some black dust (not dry but a bit wet and very fine) on substrates that seems to be difficult to clean well by means of air blow. Can you recommend a method of proper cleaning of such dust and the acceptance criteria? Is it possible to get a dust-free surface on substrate blasted by an autoblast machine? A: Dust on the surface can cause serious problems if not removed after the blast process. Te most common way to remove the dust is with air blowing. You must frst check that the air to be used to blow down the material is free from oil and water. Te easiest way to check air cleanliness is with white paper or a white rag. Blow low-pressure air onto the paper or rag to see if you accumulate any oil, grease, or moisture. A: We have observed black-colored dust contamination on blasted steel surfaces when the abrasive (steel grit or steel shot) was not controlled for screen size. In our experience, this dust residue is produced by breakdown of the steel abrasive. Abrasive blast profle prevents removal of the dust contamina- tion by compressed air. We were success- ful in removing the residue by reblasting with fresh abrasive. We observed coating adhesion failure when the dust is left on the surface. Someone coined the term " backside contamination" when observ- ing the dust attached to the backside of failed coatings. A: Te dust contamination observed on autoblasted steel surfaces is a mixture of mill scale, rust, and other contamination on the steel itself, along with degraded abrasive and an important but least considered contamination— dust produced by impact of abrasives on rubber curtains at the ends of the autoblast machine. Te last one makes the dust sticky on the blasted surface and very difcult to remove. Te problem encountered can be referred to the machine supplier, who can recommend a better dust collection system. We are operating an autoblast machine in our facility with trouble-free blasting. We have observed black-colored dust contamination on blasted steel surfaces when the abrasive (steel grit or steel shot) was not controlled for screen size.

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