February 04th, 2021
Natural abrasive materials have been used as rudimentary tools since before records began, and we still utilise minerals today that were in use during pre-historical times. The discovery that some minerals are harder than others and are thus more durable predates the earliest accepted hardness scale by millennia.
Early Abrasives—All About Hardness
We know, for instance, that specific natural minerals, like emery were purposefully chosen for polishing, shaping, and sharpening other objects. With a Mohs hardness of 8, there were few readily available materials better suited to early tooling applications. This is because the central working principle of abrasives is the use of a hard substance to abrade the surface of a less wear-resistant material.
Although emery has largely been replaced by synthetic minerals in industrial finishing applications, it is still used today where its hardness promotes long-lasting traction in non-slip floors, pavements, and stair treads, where a fine hard-wearing grit is bonded to a substrate to promote greater wear-resistance. The same rules largely apply to modern abrasive materials.
With Grains Like These, Who Needs Emery?
Ceramic grain technology is the latest in a long line of abrasive innovations, succeeding the likes of brown fused alumina (BFA) derived from bauxite ore. The demands of the industrial era rapidly exceeded the capabilities of natural abrasives like emery. Despite its exceptional hardness, sustained stress would cause emery grains to fracture across a few distinct planes, causing tools to degrade and dull over time. Engineered grains based on BFA exhibited far superior fracture toughness coupled with the natural hardness associated with mineral alumina. This enabled a superior cutting action for extended periods, even when finishing more challenging work surfaces.
Until the generation of precision-made ceramic grains, abrasive performance was primarily driven by hardness, toughness, and grit size. The size of the grit refers either to the average particle size or the overall particle size distribution (PSD), with large and coarse grains typically corresponding to rapid material removal rates with a relatively poor surface finish. A fine yet strong microstructure, and tailored macrostructure, are subsequently critical to better grain performance.
As engineering capabilities have expanded, manufacturers have understood more about the importance of finely-tuned macrostructural properties, including the affect of grain shape. Continued sharpness was typically assured using high friability grains which artificially fracture to yield more cutting facets over time—usually using some form of chemical dopant. Today, engineers can maintain tight control over grain chemistry to specifically modify crystal boundaries and impart optimised grain performance for highest productivity and superior surface finish.
Want to learn more? Read about The Three Pillars of Ceramic Abrasive Grain Performance
This article serves as a brief introduction to some of the key factors determining abrasive material performance. If you are looking for a specific solution, or want to find out more about the proprietary engineering techniques we deploy at Saint-Gobain, simply contact a member of the team today.