Bead blast finish vs sandblasting: which media gives a uniform matte surface without eroding edges or tolerances?

What is the real difference between bead blasting and sandblasting?

The difference is particle shape: round beads strike and dimple the surface, while angular grit strikes and cuts it. Round media gives a smooth satin matte with little material removal; angular media gives a sharper, rougher etch and removes metal with every pass.

A spherical glass bead hits the surface, deforms a small crater and bounces off. The metal is pushed around more than it is removed, which is why a bead-blasted aluminum part looks soft and even, and why the surface is slightly cold-worked afterward. An angular particle such as aluminum oxide behaves like a tiny cutting tool. It shears metal off, leaves sharp peaks and valleys, and is the right choice when the goal is to strip scale, paint or rust, or to give a coating something to grip.

Literal silica sand has largely left metal finishing. Breathing respirable crystalline silica causes silicosis, and US federal rules set a permissible exposure limit and control requirements for it in general industry (OSHA 29 CFR 1910.1053), while abrasive blasting enclosures and ventilation have their own requirements (OSHA 29 CFR 1910.94). So when a drawing says “sandblast”, the shop is likely to use whatever angular media it runs, and you will not know which one unless you name it.

How much does blasting change dimensions, edges and threads?

A well-controlled glass bead process removes very little material, but “very little” is not zero, and it concentrates on edges, thin walls and thread crests. Angular grit removes noticeably more, so any feature with a tight size, form or sealing requirement should be masked rather than trusted to the blast.

Blasting is a line-of-sight process with no dimensional control of its own. Exposed corners take hits from two directions, so they round first; a crisp machined edge on a cosmetic face can come back softened, which conflicts with a drawing that also asks for sharp edges. The break sharp edges note and a blast callout need to agree with each other. Thread crests behave the same way: the crests of an external thread and the entry threads of a tapped hole are the most exposed points, and fine-pitch threads can be damaged enough to fail a gauge.

The features that should normally be masked or blasted before final machining are bearing bores and press-fit diameters, O-ring and gasket sealing faces, datum faces used for inspection, tapped holes and external threads, electrical contact surfaces and any face carrying a tighter flatness or roughness requirement than the blast can hold. Soft alloys and thin sections deserve extra care, because high pressure on a thin aluminum wall can also cause slight distortion from the peened skin. If a toleranced feature must be blasted for appearance, measure it after blasting on the first article and put the post-blast value on the inspection report, not the pre-blast one. How to mark masked features on the drawing is covered in masking for anodizing; the same callout logic applies to a blast mask.

What goes wrong when blasting is combined with anodizing, passivation or plating?

Most failures come from media contamination and cleanliness, not from the blast itself. Steel media embedded in aluminum or stainless rusts, glass residue trapped in blind holes contaminates baths, and anodizing amplifies any unevenness in the blast.

Media must be dedicated to the substrate. A cabinet that also runs steel grit leaves iron particles in an aluminum or stainless surface; after anodizing or exposure to humidity those particles show as dark specks or rust bloom. On stainless steel, blasting can also leave the surface with free iron and a disturbed passive film, which is one reason passivation after mechanical finishing is common practice; the acceptance tests are defined per ASTM A967 (ASTM A967/A967M-25), and the passivation guide covers how to call it out.

Anodizing is the most common follow-on for a bead-blasted aluminum part, and it is unforgiving. The oxide grows into the blasted texture and dyes evenly only if the blast was even, so streaks from an operator changing angle or distance show clearly after anodizing even if they were hard to see on bare metal. The Type II vs Type III anodize guide explains why hard anodize changes appearance more than decorative anodize. Blind holes and crevices trap broken media, which then comes out in the tank or in your assembly, so require a cleaning step and inspect those holes.

Finally, light peening from glass bead is not the same as controlled shot peening. If fatigue life depends on compressive residual stress, call out shot peening with intensity and coverage per SAE AMS2430 (SAE AMS2430) instead of relying on a cosmetic bead blast.

How is bead blasting handled on a Saola order?

Bead blasting is not one of the eight finishes on the Saola finishing menu, so a blast callout has to be raised in the RFQ before it is quoted.

The finishes our partner plants apply are listed on the surface finishing page: electroplating, anodizing, gold plating, zinc plating, RoHS-compliant blue trivalent chromate, powder coating, pad printing and oil-dip rust protection, and the quote names where each step is done. If your drawing calls for a bead blast finish ahead of anodizing or powder coat, say so in the RFQ so it is raised before the quote rather than discovered after tooling. For burr removal, the factory page shows parts deburred by hand at the bench and tumbled in a magnetic finisher that reaches burrs inside small holes, followed by an ultrasonic wash; that is deburring and cleaning, not a cosmetic matte texture, and it should not be read as a substitute for a specified blast. Machining itself is done at our lead CNC plant on its CNC milling and turning lines. Send the drawing through the quote form with the finish callout and any approved sample.