In order to determine which sandpaper product may be most suitable for a particular sanding application, it is important to understand the different abrasive grains that are available and their respective properties. The ideal abrasive grain offers maximum resistance to wear but also has the ability to fracture before serious dulling occurs. These properties satisfy the requirements of efficient stock removal, finishing and polishing. The selection of a suitable abrasive grain is critical to ensuring the greatest productivity of the sandpaper product. Some common types of abrasive grains and their properties are outlined below.
Silicon carbide is the hardest, sharpest, and most durable of the minerals commonly used in coated abrasives. The natural mineral form of silicon carbide is long, thin, and extremely sharp. This mineral is synthetically produced in electric furnaces to produce a glossy black color and a high degree of hardness. This mineral is made by combining pure white silica sand and coke, a by-product of coal production. Silicon carbide grains are shaped like icicles with extremely sharp points and narrow grain bodies. Its hardness is second only to diamond. Due to its narrow grain body and brittle characteristics, when pressure is applied to the tip of this grain it fractures. This means it breaks into smaller sharp pieces with cutting edges that act to re-sharpen it before it goes dull, resulting in a similar surface finish from the start to the end of its sanding life. This characteristic is referred to as friability. The benefit of friability is that a sharp edge is always against your workpiece providing extremely consistent finishing ability. Silicon carbide is superior to any other abrasive in its ability to penetrate and cut faster under light pressure.
Silicon carbide is ideal for applications involving glass, plastic, rubber, paint, wood, and titanium alloys. It is also recommended for finishing nonferrous metals such as brass, bronze, copper, and aluminum. Silicon carbide products often have waterproof backings, allowing them to be used for wet and dry sanding. Wet sanding helps to reduce scratches and prevent clogging. Our Wet & Dry Sanding Sheets have a silicon carbide grain.
Aluminium oxide is the most popular abrasive grain used in sanding applications. It is considered the most versatile grain in terms of its numerous applications. Aluminium oxide is an abrasive grain that is made through the fusion of the mineral bauxite. This grain type is usually a brown or red colour and is suitable for most woodworking and general metalworking applications. It is available in an extensive range of grits which is a major reason for its popularity.
Aluminium oxide is specifically useful for applications on high tensile materials including the sanding of wood, carbon steel, alloy steel, composites, and solid surfaces. The durability of aluminium oxide makes it an ideal choice for a variety of sanding applications. The use of this grain mineral facilitates the penetration of tough materials without excess fracturing or shedding, which may be experienced with other types of abrasive grains. Where ‘toughness’ or the ability to resist fracturing, is a major consideration, aluminium oxide is likely to outperform other coated abrasive grains.
Aluminium oxide material is available on a variety of backings including paper, cloth, mesh, fibre, hook & loop, film, and more. Aluminium oxide grain is found in an extensive range of our sandpaper products including sanding sponges, dry rub sheets, wet and dry sheets, rolls, discs, flap wheels, belts for portable sanders, edge sanders, linishers, stroke sanders, wide belt sanders, and more.
Zirconia alumina grain is commonly referred to as zirconia. This mineral is a mixture of zirconium oxide dissolved in aluminum oxide at molten temperatures. Similar to Aluminium Oxide, the main ingredient of zirconia is bauxite. Coated abrasives use a micro-crystalline structure form of zirconia that is characterised as sharp, hard, and extremely tough. Due to the structure and extreme toughness, smaller particles of zirconia grain break off in use and at a much slower rate than with aluminium oxide. Zirconia produces superior sanding performance on a wide variety of materials of both high and low tensile strength. Typical applications include grinding of carbon steel, stainless steel, tough bronzes, a wide variety of stainless steel and exotic alloys, grey malleable, ductile and nodular cast iron, aluminum, titanium, and more. Zirconia’s heavier grain promotes extensive durability, without any adverse effects from high temperatures. Zirconia performs extremely well when subjected to high grinding pressure applications and is often equally effective at lower grinding pressure levels.
Zirconia is commonly used in circumstances where high removal rates and time are critical factors. Zirconia is ideal for heavy grinding of metals, high stock removal applications, and planing of wood, because the controlled fracturing of the grain continuously produces sharp, new abrading points. This ability of zirconia to self-sharpen as it is used is one of its most popular features. Sandpaper with zirconia grain is available in grits ranging from 24 to 120, and is typically blue in colour. Zirconia is usually mounted on heavier paper or cloth backings and the grain itself can be 15%-40% more expensive to produce when compared to aluminium oxide. The advantage of zirconia over aluminium oxide is its increased durability and performance under high heat and pressure applications. Many of our sanding belts and discs feature a zirconia grain.
Whilst there are several types of ceramic materials, ceramic aluminium oxide is arguably the most popular. Ceramic is manufactured by combining bauxite, just like regular aluminium oxide, with other materials in a chemical bonding process. This chemical bonding results in raw grain that is very porous and coral-like in appearance. Ceramic aluminium oxide is a long-lasting, tough, dense abrasive due to its microstructure. The extremely small micron size particles break off during grinding, producing multiple new cutting edges. As it stays sharp, especially when used in medium and high-pressure operations, it cuts at a higher rate than other abrasives. It is recommended for use on forged and carbon steels, high nickel, and cobalt alloys. Ceramics were created for rough grinding on metal, but have crossed over into many other areas and applications. Ceramic grain produces a fine and consistent scratch pattern and due to this, it is fast becoming the grain of choice for many wood sanding applications.
Ultimately, the selection of a suitable abrasive grain is vital to the productivity of the sandpaper and its effectiveness in an application. Whilst we have outlined some common types of abrasive grains, many types have not been discussed and may similarly be used for a range of applications. It is important to understand the properties of the common types of abrasive grains in order to select the most suitable sandpaper product for an application.
It is also worth noting that abrasive grains, like all things, are available in different qualities. If an abrasive product manufacturer uses a higher quality of grain, in a greater percentage, when coating their product, it will perform better. RMN Abrasives, as a leading abrasives manufacturer in China, uses the most advanced equipment to manufacture high-quality custom sanding belts and abrasive belts.