sand blasting 1

[kagadpencil]

can some one tell me why metal turns white when it is sand blasted? - I was just curious since I was quite amazed to see it.

 

[metengr]

Typically, sand or grit blasting to remove oxides or coatings with abrasive media results in a very thin layer of metal removed, leaving behind a "rough" surface texture that consists of microscopic peaks and valleys. I believe the visual appearance of "white metal" is actually very fine (micro) particulate from the abrasive that is embedded in the valleys on the surface of the metal.

 

[kagadpencil]

so is the very fine (micro) particulate matter always white? Is all abrasive material always white? is it true that the surface will always look white irrespective of the type of the abrasive material that you use.

 

[metengr]

No, not always. If alumina or silica grit is used, they typically tend to produce a "white" appearance on metal surfaces.

Metal shot for blasting will tend to produce a light gray or silver looking color because of the reflection of light off the roughened metal surface. If glass bead, walnut shells, or dry ice is used as a medium for blasting, you will tend to develop more of a matte surface finish that is not really white metal.

 

[EdStainless]

It is an optical effect from the light scattering off of the surface. If you grit blast copper it turns a light orange or pink, depending on the grit.
The sharper the grit, the whiter the surface. It is not a function of grit residue. You get the same effect blasting with SiC or slag which are black.

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Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[notnats]

It is the same optical effect that gives a white head to beer.

Cheers,
Jeff