Pumice, Garnet And Ceramic Blast Media - Choice And Use

Abrasive blast medias

These abrasive blast medias are of a hardness on MOH's scale 6 to 7.5

Pumice Grit

Pumice grit is a natural mineral - volcanic ash formed by the solidification of lava that was permeated with gas bubbles.  Pumice powder  is used for less aggressive operations where the protection of the surface is important. This material is readily available in most countries, however transport costs make this a product that is likely to be not an economic proposition for those of us in non volcanic regions.

Garnets

Garnet blast media can be used in all types of dry and wet blasting machines.  It is of a high quality alluvial garnet and is a natural mineral found in several regions of the world. It is classed as a relatively hard media, fairly brittle.  It has as short media life expectancy and mostly used as an expendable abrasive depending on availability.  Also used as a waterjet cutting agent in steel cutting applications.

Ceramic Media

Zirblast and Zirshot *(are brand names)

Zirblast and Zirshot are high quality fused ceramic beads manufactured from crystalline zirconia and bonded with amorphous silica.  Both products have a very slow breakdown rate and as such are ideal for blast impact finishing operations involving automated machinery, where consistency of finish is important.

Both products are chemically identical.   Quality checks for roundness, surface defects etc., allows Zirshot to be certified to the demanding standards.

Zirshot can be supplied with certification to most aerospace standards should these be required..

Zirblast is designed for all other impact finishing applications and is available at a more economic price.

Applications

Being chemically inert and iron-free products, these ceramic beads can be used for a wide variety of applications such as cleaning without dimensional change, shot peening, stress relieving, deburring, scale removal etc.

Sand

(As a blast media) - It is classed as a health hazard due to the high content of free silica and is banned all over Europe for all sand blasting operational uses.  It is likely to cause early death!

The use of silica sand for blasting can result in the release into the air of free silica that can cause a serious health problem, named silicosis.  It is associated with silicon dioxide (SiO₂), silicon dioxide occurs in many forms in the earth. Ordinary sand is nearly pure silicon dioxide.

As workers inhale the dust it travels through their mouths, down their throats and into their lungs.  Silicon dioxide dust /powder can block the tiny air passages in the lungs through which oxygen and carbon dioxide pass. When this happens, silicosis results.

Silicosis is similar to pneumonia. The person finds it difficult to breathe. The longer one is exposed to silicon dioxide dust, the worse the problem gets. In the worst cases, silicosis results in death because of the inability to breathe properly.

The more commonly used medias are:

• aluminium oxide
• white aluminium oxide
• urea and other plastic abrasives
• corn cob grit
• walnut shell grit
• glass beads
• 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