November 04th, 2021
From cutting sheet metal to polishing optics, abrasive materials play critical roles in a vast range of industrial applications. Industrial abrasives typically consist of grains of a hard manufactured material such as brown fused alumina. This material can either be “coated” – adhered to a backing material such as paper or cloth – or “bonded”, where it is dispersed throughout a matrix made from a material such as ceramic, glass or rubber.
Coated ceramics are commonly used for power tools such as orbital or belt sanders, while bonded ceramics can be shaped for applications, including grinding/cutting wheels and rotary tool heads. Abrasives are also suspended in liquid, paste or wax such as in polishing agents for lenses; or used in conjunction with compressed gas for sandblasting.
Whether abrasives are used for grinding, cutting, honing, drilling or buffing, the mechanism of action is much the same. On the microscale, abrasives consist of small, sharp tips. These tips make very small cuts in the workpiece, which gradually results in the removal of material. However, the forces applied between these cutting tips and the workpiece go both ways: over sustained use, pieces of the abrasive material are worn away by friction. This happens particularly quickly in commodity abrasives, while higher performance abrasive grains are able to retain sharpness as they wear.
Moderately hard materials such as garnet use are some of the most common abrasives: while they aren’t particularly efficient, these materials are naturally occurring and very inexpensive, lending them to general-purpose coated applications.
The next step up from these materials is fused aluminum oxide (also known as fused alumina). Alumina abrasives most commonly take the form of Brown Fused Alumina (BFA), which is produced by the fusion of naturally occurring bauxites in electric arc furnaces. BFA offers high hardness and durability, making it suitable for use with metals such as iron, steel and bronze. Versatility and high performance at a relatively low price point mean that BFA is a very popular commodity abrasive.
The hardness of an abrasive material is not the only determining factor in its performance, however. As abrasives are gradually worn over time, even very hard materials will eventually be “smoothed” by the abrasive process. This is why abrasives are typically prepared as grains for bonded applications: over continued use, old, smoothed grains are removed and new, sharper grains are revealed. However, while this process prolongs the usable life of bonded abrasives, they are still prone to inevitable wear over time, which means their abrasive performance will never be as good as new.
The huge scope of applications and the consumable nature of abrasives means that, on an industrial scale, the sustainability of abrasive materials can have a real impact. The demand for a sustainable high-performance abrasive grain inspired the development of Targa ceramic alumina grains from Saint-Gobain Abrasive Materials.
While made from alumina, Targa grains offer radically improved performance compared to commodity-fused alumina grains such as BFA. Targa ceramic alumina grains, also known as Cerpass TGE®, are produced via the seeded gel process, which was first developed in 1984 by Saint-Gobain Abrasive Materials.1
The seeded gel process enables the production of highly uniform alumina particles with special abrasive properties.2 The process starts with a colloidal dispersion of sub-micron (<100 nm) particles of Al2O3 or other “seeding agent” compounds (such as
Adding seeding agents to this gel produces a huge number of available nucleation sites to form Al2O3 crystals.3 This results in the eventual formation of small (<400 nm) Al2O3 crystals exhibiting high uniformity and very narrow size distribution.
Targa grains produced via this method exhibit unique abrasive characteristics thanks to their engineered friability and nanoscale structure. When subjected to shear stresses, Targa grains will fracture, thus exposing new, sharp cutting edges as required. This “microfracturing”, which occurs at a rate that maintains productivity, means that Targa grains are effectively self-sharpening: they remain good-as-new even as they wear away. This mechanism of micro-fracturing is qualitatively different to that of conventional fused-alumina ceramics, which become dull by the formation of worn flat surfaces over sustained use and also wear via larger scale macro-fracturing.
The ability of Targa alumina grains to renew the cutting surface under stress is a quality known as engineered friability. Perhaps surprisingly, this doesn’t shorten the life of these abrasives; it actually increases their life while offering superior material removal rates. Seeded gel alumina oxide abrasives have been shown to exhibit an increased grinding ratio compared to conventional abrasives.4 As a result, Targa grains offer a 3 to 5 times improvement in grinding speed compared to commodity grains. Also, for a given grinding operation the required energy for Targa grains can be 4 times to 5 times lower than for brown fused alumina.
Targa ceramic grains offer radically lower carbon emissions than commodity-fused alumina grains. Often, choosing the “sustainable” option involves a trade-off in performance. However, this isn’t the case with Targa abrasive grains. Targa grains are significantly faster, offer a dramatically longer lifetime, and grind with much less power than BFA.
Choosing a high-performance ceramic grain allows manufacturers to reduce their carbon footprint and waste and save space, energy, and equipment — the result is fewer resources required and more sustainable operations.
Saint-Gobain Abrasive Materials can support your company in transitioning to more sustainable abrasive solutions. To find out more about Targa grains and other sustainable high-performance abrasive solutions, get in touch with a member of the Saint-Gobain team.
References and Further Reading
1. Ceramic Grains | Abrasive Ceramics | Ceramic Abrasive. https://www.abrasivematerials.saint-gobain.com/products/cerpass-ceramic-....
2. Lindsay, R. P. The Performance of Seeded Gel Abrasives in the Laboratory and at Customer Test Sites. Aircraft Eng & Aerospace Tech 61, 20–26 (1989).
3. Jackson, M. J. Recent advances in ultraprecision abrasive machining processes. SN Appl. Sci. 2, 1172 (2020).
4. Eranki, J., Xiao, G. & Malkin, S. Evaluating the performance of “seeded gel” grinding wheels. Journal of Materials Processing Technology 32, 609–625 (1992).