GlossaryKind of term: Manufacturing termBlasting
What is blasting?
Blasting treats a surface with abrasive media thrown at high speed, to clean it, roughen it or give it an even matt appearance.
The speed comes from compressed air or a turbine wheel. The media decide the result. Glass bead gives a fine, even matt finish on aluminium and stainless steel and masks light machining marks. Aluminium oxide is sharp and roughens the surface, for example as a key for a coating. Steel grit and shot clean mill scale and rust off steel. Blasting changes roughness and can remove a thin layer of material or deform the surface plastically.
What decides the result of blasting?
The result depends on media type, size and hardness, air pressure or wheel speed, angle, distance, exposure time and the workpiece material. Angular media cut and roughen; round media deform the surface more than they remove material. Thin walls can distort under impact, and media can stay behind in holes and threads. Media previously used on carbon steel can embed iron particles in stainless steel or aluminium, causing rust staining or corrosion; blasters therefore keep media separate per material.
What does the standard say about blasting?
For steel that will be coated, cleanliness after blasting is often stated as an Sa grade to ISO 8501-1, for example Sa 2½. That is a visual assessment against reference photographs, not a measurement. The roughness profile for a coating is specified separately, often with reference to the ISO 8503 series. For a decorative matt finish there is no comparable general class: a sample, a named medium or a roughness value then fixes the requirement.
How does blasting work in practice?
Blasting is often subcontracted and priced per batch or per basket, usually with a minimum charge. Masking fits, threads and sealing faces is handwork that may be charged separately; whether masking is needed depends on medium, tolerance and function. Sequence matters: blasting before anodising gives an even matt anodised surface, and a blasted part that is machined afterwards shows bright patches. When the drawing says ‘blasted and black anodised’, that is two operations.
What is blasting often confused with?
Blasting is not deburring: at most it rounds off fine burrs, and a real burr stays. Shot peening is a related but different process: at a controlled intensity and coverage it introduces compressive stress into the surface to raise fatigue strength. Its purpose is strength, not appearance or cleanliness.
How do you see blasting in Blake?
In Blake, blasting sits with the part as a finishing proposal from the drawing, for you to confirm or correct. Subcontracted, it becomes its own estimate line from your subcontract library, and the line stays open for as long as the price is missing. More on estimating.
Frequently asked questions
Does blasting change the size of a part?
Slightly, depending on the media: angular media remove a thin layer, round media mainly deform the surface. On ordinary faces that rarely matters, on fits and threads it does; those are therefore often masked.
Why do you blast a part before anodising?
Because blasting gives an even matt base that masks light machining marks and scratches, and the anodic layer follows that look. Without pretreatment, machining marks stay visible; chemical etching is another route to a matt finish.
What does Sa 2½ mean?
A cleanliness grade to ISO 8501-1 for blast-cleaned steel: very thorough blast cleaning, with at most slight stains in the form of spots or stripes. It is a visual assessment against reference photographs, used to prepare steel for coating.