It is difficult to remove them once these bits are stuck.
Glass bead cleaning is still used in many applications and is OK for some items. Plastic media has replaced glass beads as a blast media due to it's more inert nature.
Glass beading is not going to remove the stress built into the cast part.
Glass bead or similar blast media is not the same or close to shot peening.. The goal of shot peening is to create a controlled compressed layer which effectively "pre-loads" the surface of the part and helps strengthen it.
Both castings and rolled stock has built-in stressed from their manufacturing process. If a deep enough section of the surface layer is removed, these stresses relax of change which causing the part to change dimension. Examples of this would be cast iron machine tool foundations are stress relieved (also applies to cast iron engine blocks) by aging or very controlled heat treating to relieve built in stress before any machine work is done. This prevents the part from changing dimension after machining..
For those who do machine work, ever notice a part can stress relax after or during the machining process and ruins your whole day?
Bernice
PaulD said:
I have heard two schools of thought on glass bead blasting aluminum castings such as heads, manifolds and transmission cases.
One is that you reduce strength by abrading the outer layer of the casting which has stress characteristics from the casting process. The other point is that no mater how much you clean it, some abrasive glass particles will remain inside.
Other folks think it works fine, do it on a regular basis, and the plus is that it looks wonderful.
What are your experiences?
Paul Davock
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Castings are generally porous, this is where tiny bits of glass bead (silica contamination) can get trapped and might cause problems later.It is difficult to remove them once these bits are stuck.Glass bead cleaning is still used in many applications and is OK for some items. Plastic media has replaced glass beads as a blast media due to it's more inert nature.Glass beading is not going to remove the stress built into the cast part.Glass bead or similar blast media is not the same or close to shot peening.. The goal of shot peening is to create a controlled compressed layer which effectively "pre-loads" the surface of the part and helps strengthen it.Both castings and rolled stock has built-in stressed from their manufacturing process. If a deep enough section of the surface layer is removed, these stresses relax of change which causing the part to change dimension. Examples of this would be cast iron machine tool foundations are stress relieved (also applies to cast iron engine blocks) by aging or very controlled heat treating to relieve built in stress before any machine work is done. This prevents the part from changing dimension after machining..For those who do machine work, ever notice a part can stress relax after or during the machining process and ruins your whole day?Bernice