A bead-blasted part comes back with a matte finish that looks right and a surface that is wrong: the media embedded in the soft aluminum, or the aggressive grit cut the surface deeper than the finish required. Blasting is not one process with one result — the media type, the size, the pressure, and the distance set the finish, and the media choice is an engineering decision with consequences for the surface integrity, the finish, and the part’s service. The media reference is what turns “bead blast it” into a specification the shop can hit.
What media selection changes: texture, embedment, and surface integrity
The media sets three results. The texture — the roughness and the appearance of the blasted surface — follows the media type and size. The embedment — media particles driven into the surface — depends on the media hardness relative to the part and the blast parameters, and embedded media can contaminate the surface and affect the finish or the service. The surface integrity — whether the blast removes material, stresses the surface, or damages thin features — follows the media’s aggressiveness. A media that is too soft for the job leaves an inconsistent finish; one that is too hard for the substrate embeds or cuts too deep. The selection starts with the part material, the finish target, and the surface that the blast must preserve.
The media size and the blast parameters are part of the specification: the same media at a different pressure or distance produces a different result, and the process should be set for the part, not run at a default.
Glass bead vs ceramic vs aluminum oxide vs steel shot
The common media serve different roles. Glass beads are round and relatively soft, producing a smooth, satin finish with minimal material removal; they are the standard for cosmetic matte finishes on metals. Ceramic media are harder than glass, cutting faster and producing a more aggressive finish with a longer media life. Aluminum oxide is the sharp, aggressive abrasive, used for removing coatings, scale, and heavy oxidation, and it cuts the surface more deeply. Steel shot is heavy and durable, used for peening and heavy cleaning, and it can alter the surface stress. The choice follows the goal: glass for a clean satin finish, ceramic where a harder, longer-life media is needed, aluminum oxide for aggressive removal, and steel for peening or heavy work. The media reference table is the starting map for the selection.
The media hardness relative to the part is the critical check: a media that is much harder than the substrate embeds or cuts, and a media that is softer wears out quickly without doing the work.
Material compatibility and when blasting is risky
Blasting is risky on some materials and features. Soft metals like aluminum and brass can embed media and deform under aggressive blasting; thin sections can warp or erode; threaded features can round or fill with embedded media; and precision surfaces can lose their tolerance. The compatibility review should consider the part material, the features, and the finish that must survive. When blasting is risky, the alternatives — chemical stripping, hand finishing, or a gentler media — should be evaluated against the cost and the result. The blast specification should state which surfaces are blasted and which are protected, so the process does not damage the features the part depends on.
The risk also includes the contamination: media embedded in a part destined for a clean or a coated application can cause finish and adhesion failures, and the cleaning after blasting is part of the process.
Achievable finishes and roughness expectations
The blasted finish can be described by appearance or by roughness, and the specification should use the measure that the application needs. Appearance classes — satin, matte, or coarse — are judged against a sample; roughness values give a numeric target where the surface is functional. The roughness result depends on the media, the size, the pressure, and the part material, so the achievable range should be confirmed with the blaster on a sample. A finish that is specified by appearance should have a sample; one that is specified by roughness should have the measurement method. The blasted finish is a process result, and the sample and the measurement together make it a specification.
The finish also affects the next step: a blasted surface is often the preparation for coating or anodizing, and the roughness that promotes adhesion may differ from the cosmetic finish.
Specifying blast finish and masking on drawings
The blast note on the drawing should carry the media, the size, the finish class or roughness, and the surfaces that are blasted. The masked surfaces — the threads, the precision bores, and the faces that must stay unblasted — are listed, and the masking method is part of the process. The sample is the acceptance reference for the appearance, and the inspection checks the blasted surfaces and the protected surfaces. A blast note that says “bead blast” without the media and the masking leaves the process to the shop; one that carries the media, the size, the finish, and the masking is a specification the shop can quote and the part can be inspected against.
The bead-blasting service page covers the process; this page is the media-level engineering reference. When the media, the parameters, and the masking are specified together, the blasted finish is a controlled result — and the part comes back looking and behaving as the drawing intended.
Qualifying the blast process on samples
The blast process should be qualified on samples before the production parts are run. The sample panels establish the media, the pressure, the distance, and the duration that produce the target finish on the actual material, and they confirm that the blast does not embed, warp, or over-cut the part. The qualification samples are the acceptance reference for the production parts, and they should be kept with the specification so the process is reproducible across orders. The qualification should also cover the masked features: a sample with the masked threads and bores confirms that the masking protects them and that the removal is clean. A blast process that is qualified on the sample is a process the production run can repeat; one that is set from a generic recipe carries the variation into every part.
The production control follows the qualification: the media is checked for the wear that changes the finish, the pressure and the nozzle are monitored, and the finished parts are compared against the sample at the interval that catches the drift. The cleaning after blasting is part of the process, especially for the parts that will be coated or anodized, because the embedded media and the residue affect the adhesion. When the blast process is qualified and controlled, the blasted finish is a repeatable result — and the surface that the sample approved is the surface the production parts deliver.
The blast process should also be reviewed against the part’s function and its next steps. A blasted surface is often the preparation for a coating or an anodize, and the roughness that the next step needs may differ from the cosmetic finish; the media choice should serve the next process as well as the appearance. The blasted part that will be coated needs the surface profile for the adhesion, while the blasted part that is the final finish needs the cosmetic class; the same media rarely optimizes both, and the specification should state which result the part needs. The blast also changes the part’s surface stress and its fatigue behavior, which matters for the parts that carry load; a peening-grade blast can improve the fatigue life, while an aggressive removal blast can damage it. The blast review should consider the part’s function and its service, because the media choice is not only a finish decision. When the blast is specified for the part’s full requirement — the appearance, the preparation, and the service — the process serves the part rather than the default recipe, and the blasted surface delivers what the drawing and the next process need.
Keep the blast sample and the specification with the part, so the finish is reproducible across the orders and the suppliers. The record is the reference for the inspection and the re-qualification when the media or the process changes.
Confirm the blast operator’s process capability with a trial panel before the production run, and keep the trial result with the part specification. The trial turns the media choice from a description into a measured, repeatable process.
The blast spec is complete when the media, the size, the finish, and the masking are named, and the sample and the measurement close the loop with the delivered part.
If you are specifying a blasted finish and want the media, the roughness, and the masking plan reviewed, the 6CProto surface finishing team can work from your material and finish target to the blast specification.