Bead blasting is a technique whereby fine glass beads (on their own or mixed with other non-abrasive media) are directed under high pressure at a stainless steel substrate to remove surface deposits without damaging the surface. Bead blasting gives what can be described as a soft, smooth and even finish. The resulting uniform, matt finish has low reflectivity. Often used on stainless steel after partial coating of a component to remove or even out the discolouration uncoated stainless steel exhibits after heating.
Comparison of grit blasting and bead blasting.
In grit blasting, the impacting coarse silica grit cuts the metal surface, removing small amounts of metal. The resulting surface finish will have a relatively rough or jagged finish which is ideal for assisting a subsequent coating to bond to it.
In contrast, bead blasting a surface with a glass bead mixture does not remove metal from the surface. The impact of the beads results in small, smooth edged rounded craters in the surface, giving a dimpled appearance as metal is pushed aside. Cleanliness of the bead mixture is important in maintaining the desired decorative effect.
During bead blasting of some stainless steels, the surface is work hardened and surface compressive stresses are induced. These surface property changes can give improved stress corrosion cracking resistance, improved fatigue resistance and an increased surface hardness. Care must be taken though to avoid distortion. So bead blasting ought not be applied to stainless steel thinner than say 0.4 mm.
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