Alumina (also known as corundum or bauxite) is an inorganic compound composed of aluminum and oxygen with the chemical formula Al2O3. It occurs naturally in corundum crystals but can also be synthesized for industrial use via the Bayer process or nitrogen plasma synthesis. During the manufacturing process, aluminum oxide is melted into a crystalline structure of irregularly shaped particles/grit that can then be incorporated into a variety of abrasive products.
Key Properties of Alumina
Hardness:
With a Mohs hardness of 9, AO is one of the toughest and most durable abrasives available, second only to diamond. This hardness helps it retain its sharpness and also makes aluminum oxide suitable for use on a variety of materials, including hard steels, alloys, and certain ceramics.
Toughness:
The toughness of an abrasive is determined by its ability to withstand impact and resist fracture during normal use, which eventually causes it to break. Aluminum oxide is an intermediate toughness abrasive, being tougher than silicon carbide but more brittle than zirconium oxide or ceramics. In many applications, its toughness falls somewhere in between. It is tough enough to handle high-pressure grinding and sanding tasks on most materials, while its brittleness is reflected in its brittleness.
Friability:
Fragility is a property of an abrasive grain that refers to its tendency to break into smaller particles. While this may sound a bit negative, it is an advantage for some abrasives, such as aluminum oxide. Instead of becoming dull with use, the sharp surface of the abrasive breaks under pressure, exposing a sharp cutting edge. This self-sharpening property has many benefits, including helping to maintain consistent cutting speeds and reducing heat buildup in the workpiece.
Common Products Containing Aluminum Oxide
Aluminum oxide is versatile and affordable, and is used in nearly all types of consumer abrasive products. Here is a list of some commonly used aluminum oxide product forms and types.
Abrasive Belts: Used in belt sanders for stock removal, blending, and finishing.
Abrasive Discs: Used in angle grinders and other tools for grinding, grinding, and polishing surfaces.
Grinding Wheels: Used in stationary machines and portable grinders for deburring, deburring, and shaping metal, wood, and other materials.
Cutting Discs: Used in angle grinders, die grinders, and cut-off saws for cutting metal, masonry, concrete, and other materials.
Sandpaper Sheets: Used by hand or by machine, offering flexibility and precision.
Nonwovens: Often found in various forms, sometimes with aluminum oxide embedded in nylon, used for surface preparation, light deburring, and cleaning.
Abrasive Sizes and Applications
Aluminum oxide grit/particles range in size from very coarse (16 grit) to extremely fine (1200+ grit), with each size serving a specific purpose:
Coarse grit (16-60) for heavy-duty deburring, shaping, and deburring of metal/wood
Medium grit (80-180) is great for measuring, cleaning, and descaling metal
Fine grit (220-600) for finishing sanding, polishing, and surface prep
Ultra-fine grit (800-1200+) for ultra-smooth, polished surfaces on metal/wood
Compared to Other Abrasives
Aluminum oxide isn't the only abrasive. While it's versatile, there are other options you should consider depending on the application and material. Here's a quick comparison of aluminum oxide with other common abrasives:
Silicon Carbide
Harder and runs hotter than aluminum oxide, better for aggressive stock removal
More brittle, cuts faster, but has a shorter lifespan
Great for ceramics, stone, glass, and hardened steel
Can be used for wet sanding
Zirconium Corundum
Harder and sharper than standard aluminum oxide
Excellent damage resistance and heat dissipation properties
Best for tough metals like stainless steel and titanium
Ceramic Aluminum Oxide
Advanced aluminum oxide grain, higher purity/density, higher cost
Retains its shape better than standard aluminum oxide
Provides a cooler cut, better for heat-sensitive applications
Can be used for wet sanding
Why Choose Aluminum Oxide?
Aluminum oxide has many advantages over other abrasives, including:
Cost-effectiveness: It's generally less expensive than most other abrasive grains, especially specialized abrasive grains like ceramic aluminum oxide.
Versatility: One of aluminum oxide's greatest strengths is its versatility. It can be used on a variety of surfaces, from metal to wood, and is suitable for different processes such as grinding, deburring, and finishing.
Durability: Aluminum oxide is a tough material that doesn't wear easily. Aluminum oxide abrasives generally last longer than softer materials.
Performance: Aluminum oxide is known for its durable properties and can hold a sharp cutting edge longer than many other abrasives.
Availability: As one of the most common abrasive grains, aluminum oxide products are widely available in many forms and most grit sizes.
Common Uses for Aluminum Oxide
In industries such as metalworking, welding and fabrication, toolmaking, and woodworking, aluminum oxide is an essential abrasive for everything from initial cutting and grinding to final sanding and polishing. Some common applications include:
Grinding Metal: Aluminum oxide grinding wheels are often used for aggressive material removal and are frequently used to grind welds, shape metal parts, and sharpen tools.
Surface Preparation: Aluminum oxide sandpaper and polishing discs are used in everything from woodworking to auto body repair to achieve a fine surface finish.
Deburring: Burrs formed on metal parts can be removed using aluminum oxide grinding discs or belts after machining operations.
Polishing: Aluminum oxide is often added to polishing and buffing compounds or used in buffing wheels to polish metal and wood surfaces to a high sheen.
Sandblasting: It is also a popular choice of media for sandblasting operations.
