Purpose of shot blasting

Shot blasting removes rust, scale, old surface contamination and weak oxides while creating a surface profile for subsequent coating or conversion treatment. It is commonly used before zinc flake coating, phosphating, painting or other surface-protection systems.

The objective is not simply to make the part look clean. A suitable profile improves mechanical anchoring, increases effective surface area and supports coating adhesion. Excessive blasting, however, can damage threads, edges, thin sections and dimension-sensitive areas.

Media and contamination control

M.S. shot, S.S. shot, grit or other media choices must match the substrate and final requirement. Carbon-steel media can contaminate stainless steel surfaces and may create later rust staining. Stainless media or glass bead may be more appropriate for stainless parts depending on purpose.

Media cleanliness and segregation matter. Oil-contaminated media, worn media, mixed media or excessive dust can reduce coating adhesion. For quality-sensitive jobs, the process route should identify whether blasting is for cleaning, profiling, cosmetic uniformity or pretreatment.

Geometry and masking limits

Blasting is line-of-sight dominant. Deep recesses, blind holes, internal cavities and hidden faces may not receive the same treatment as exposed surfaces. Thread roots, sharp edges, laser-cut burrs and thin tabs should be reviewed for potential damage.

If areas must remain unblasted, masking or alternative handling needs to be discussed. Rubber plugs, tapes and fixtures can help but may leave transitions or missed areas that require acceptance.

Inspection after blasting

Inspection may include visual cleanliness, profile review, dust removal and surface readiness for the next process. For coating work, parts should not be left exposed for long periods after blasting because freshly prepared steel can flash-rust in humid conditions.

Packaging and transfer after blasting should avoid oily hands, dirty bins, wet floors and mixing with rusty parts. The time between blasting and coating should be controlled where possible.

RFQ and approval checklist

  • Substrate: mild steel, stainless steel, cast iron, forging, casting or fabricated assembly.
  • Purpose: rust removal, profile creation, cleaning before coating, cosmetic matte finish or rework.
  • Media preference and contamination restrictions.
  • Thread/edge/dimensional sensitivity and areas to protect.
  • Follow-up process and maximum acceptable delay before coating.