Synthetic corundum: aluminum oxide
The mineral most widely used in the production of flexible abrasives.
It is a synthetic aluminum oxide (Al2O3, the same mineral that rubies and sapphires are made of) obtained by high-temperature fusion (3000 °C) of bauxite.
It is a particularly hard mineral (9 on the Mohs scale) but also resistant to impact and wear, characteristics that make it still the most widely used mineral in the manufacture of abrasive belts, flap wheels, flap wheels with shank, abrasive rings, and many others.
Silicon carbide
Another synthetic mineral, a mix of carbon and silicon (SiC) created at the end of the 1800s in an attempt to find a more performant mineral compared to aluminum oxide. It is indeed an extremely hard mineral (9.5 on the Mohs scale, therefore very close to diamond), but also very brittle.
This brittleness makes it suitable only for working materials more fragile than itself (glass, ceramics, plastics, cast iron, and bronze), while for the manufacture of abrasive belts to be used on most metals, corundum remains by far the best choice.
Zirconium
This is an evolution of corundum. Also obtained by very high-temperature fusion, a certain percentage (around 25-30%) of zirconium oxide (ZrO2) is mixed with the aluminum oxide (Al2O3).
The result is a mineral slightly less hard than corundum, but decidedly tougher. This greater toughness makes it more performant than corundum in the processing (with abrasive belts or flap wheels) of difficult materials such as stainless steels. This performance difference decreases with finer grits.
Ceramic abrasives
The most performant abrasive grain available. Here too we are looking at an evolution of corundum, which is reduced to a very fine powder (on the order of a thousandth of a millimeter) and then recompacted and subjected to a sintering process (at approximately 1300 °C).
The resulting solid is then crushed to obtain abrasive grain of the desired size. The result is a mineral of hardness comparable to the corundum from which it was derived, but with a very uniform internal structure that allows it to wear optimally during the abrasion process, making it the best choice for working on difficult materials (stainless and alloy steels), and for heavy stock removal.
La consiglio abrasivi produces a wide range of tools with ceramic abrasive: abrasive belts, flap wheels, flap wheels with shank, reinforced rings, flap discs, Velcro discs, and much more.
Wasn't it called sandpaper?
Traditionally in woodworking, glass, sand, or powdered cuttlefish bones were used as abrasives, with which surfaces were smoothed through the so-called "seppiatura" (cuttlebone sanding).
