Naturally Mined Grains

Naturally Mined Grains are not as durable as their synthetic counter parts but they do have a few advantages.  Products using naturally mined grains are usually lower in cost than products made with synthetic grains.  Secondly, due to their ease of friability, naturally mined grains are good for polishing and hand operations.  Although life is lessened when using naturally mined grain, depending on the application, these products have their place.  The four main types of naturally mined grains are.

• Garnet – Moderately durable and sharp.  Suited for soft wood sanding.
• Emery – This grain is best suited for polishing metals
• Crocus – Made of iron oxide this grain is extremely soft and very fine.  Limited to fine polishing applications such as gold.
• Flint – This is actually not flint but nonconductive quartz.  It is ideal for paint removal and electric motor sanding.

The Structure of Coated Abrasives

Coated abrasives are manufactured with the following components.

• Backing or Substrate – Carrier for which the abrasive grain is adhered to.
• Base or Make Coat – The initial adhesive that holds the grain onto the backing.
• Grain – The type of abrasive mineral used for the particular material being produced.
• Size Coat – A bonding agent that gives the grain retention.
• Grinding Aid – This is an optional additive placed over the size coat to reduce heat and add lubricity.

Grinding Aid

(Fig. 4C)

Using figure 4C above, you can consider this schematic a cross section of a closed- coat material.  Which means the abrasive grain is close together.  Now picture the same schematic above but with every other grain missing.  This would be considered an open-coat material. Closed coat materials are generally used for ferrous metals whereas open-coat products are generally used for non-ferrous materials.