Abrasive Media
Non Ferrous medias are of a hardness on MOH’s scale 6
It should be noted that any abrasive described as 6 and over on the MOH scale is classed as abrasive
Aluminium
Depending on the make up chemistry of the aluminium or aluminium alloy, extreme care must be taken if employing this blast media. The fine dust is very combustable and can in some circumstances explode. Normal Co2 fire attenuation is not an option. Fire can burn uncontrollably if specialist fire protection is unavailable. Maintenance on a turbine machine that has any aluminium or magnesium alloy dust in crevises and blind areas is a big problem, especially when hot remedial work is necessary. BE WARNED!
Aluminium grit is the more popular if it is an absolute necessary choice and specification.
The method of delivery can be delivered by either suction / venturie air blast or a pressure delivery system.
It is harder to control the flow in a turbine or wheel blast machine as the mass and density of the aluminium blast media is very light. (Results are variable according to your component hardness).
Zinc Cut Wire Shot
Zinc shot is a soft metallic shot used with preference in the diecasting and gravity casting industries for deburring and deflashing of aluminum and zinc alloy castings. Zinc shot is an ideal abrasive for blasting corrosion resistant steels and non ferrous products where the risk of ferrous contamination to the surface is not acceptable. Zinc shot is manufactured from virtually pure zinc, this enables it to be used in applications where there is a high risk of explosion if an aluminum shot were to be used.
This risk is typically manifested when deflashing aluminum components with aluminum shot or grit. The dust generated can lead to an explosive atmosphere as the aluminum blast media are about 10 times more explosive than zinc shot, therefore the use of zinc shot greatly reduces the risk of explosion. Also, zinc shot is about 2.5 times denser than aluminum shot making it a far superior media for deflashing or deburring of components that would ordinarily not be deflashed or deburred adequately with aluminum shot. Its high density enables it to remove burrs up to 40% in size of the shot’s diameter. Zinc shot removes burrs 0.5mm thick whilst an equivalently sized aluminum shot will remove a burr only 0.3 mm thick.
Brass
Brass media can be used but it is somewhat expensive. Clean brass swalf or Nerlings from a cutting / machine tool process have been know to be used for cleaning brass stampings or forgeing to remove graphite lubricants from the surface and provide a clean brass finish.
The more commonly used medias are:
- aluminium oxide
- white aluminium oxide
- urea and other plastic abrasives
- corn cob grit
- walnut shell grit
- glass beads
- pumice
- crushed glass grit
- silicon carbide
- steel grit
- steel shot
- chilled iron grit
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Post written by
Haydn Kitchen
Shot Blasting Technical Manager