With no governing body to oversee its standards, purchasing garnet can be a gamble. What’s more, most suppliers don’t guarantee the quality of their garnet. Because of this there are a few things that abrasive water jet users should know.
- The size distribution of garnet particles can vary greatly. These particles can range from useless dust that clogs the feed system producing inconsistent cuts; or overly large containments that will plug the nozzle.
- The hardness of the garnet will vary depending on the location from where it was mined. Garnet is rated between 7.5 and 8.5 on the Mohs scale. (Used in classifying minerals, the scale runs from 1 to 10. The position on the scale depends on the ability to scratch lower rated minerals.) That’s a 13% spread in the hardness. A softer garnet requires a slower cut than harder garnet.
- Garnet purity
- To extend their supply, some garnet producers blend it with other minerals, such as staurolite. This mixture does not cut well in a waterjet as staurolite is approximately 1/3 the hardness of garnet and has a lower mass. Because of this it breaks up much easier and cannot grind away as much material per grain.
- Poor cleaning and separation techniques at the mine can leave contaminates mixed in with the garnet as well as lots of dust.
- Because it contains sharper edges, crushed garnet will cut faster than alluvial. To achieve comparable cut quality of crushed garnet, with alluvial garnet, cutting speed should be reduced by at least 5%. For thicker harder materials the cut rate should be slowed by 20%.
Know What You’re Getting
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