Clean, Roughen & Strengthen

What happens on metal surface while shot blasting ?

A blast wheel rotates and throws steel shot or angular steel grit toward the workpiece, finally proper surface finish is achieved for further painting, coating or other process.

It seems simple, but 3 actions are happening on metal surface at same time while shot blasting.

Clean

Cleaning is priority task of shot blasting.

Including, but not limited to following on metal surface will be removed – rust, mill scale, oxide, oil, grease, dirt, paint, coating, foreign matter, impuritiy, lumps, bumps, imperfection, older or damaged materials, contaminant, casting sand, corrosion, detritus, debris…

Rust Grades & Blast-cleaning Grades can be helpful to understand cleaning.

Roughen

Roughening is important for painting or coating, or sometimes just to get a certain rough appearance of aesthetic. Roughening degree is determined by painting or coating coverage requirement, or surface finish requirement. Compared to steel shot, steel grit can impact higher peak-to-valley depth on metal surface.

Strengthen

Shot peening is happening together with cleaning and roughening, no matter wanting or not. For some workpieces, proper shot peening is useful, building up compressive stress to enhance fatigue strength and increase service life and load capacity. For some workpieces, that is harmful, causing to bend or wrap. Compressive stress can be controlled by abrasive type, exposure time, as well as velocity and volume of abrasive being thrown.