5 Must-Have Features in a abrasives for metal

Article Sections

• Introduction
• What makes sandpaper so abrasive?
• Why you should care about the abrasive grain you choose for your project.
• Aluminum Oxide – The Versatile Powerhouse of Abrasives
• Silicon Carbide – Self-Sharpening And Great For Beautiful Finishes And Glass
• Ceramic Alumina – Long Lasting, Great For Metal Finishing
• Alumina-Zirconia – The Grittiest Of Them All           
• Conclusion
• Abrasive Grains Cheat Sheet

Introduction

If you’re looking to create the best version of your woodworking or metal projects, no doubt sanding will be a key part of that process, whether you’re rough sanding to remove jagged edges, de-burr, in preparation for gluing, or if you are in the finishing and polishing stages.

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Each of these steps clearly requires different sandpaper grits to get the best results, but the grain type will also impact your overall results – and believe it or not, it may even be best to change types depending on the material you’re working with and the stage you’re at. So, clearly, choosing the right type of abrasive will be critical, and could mean the difference between a high-quality finished product and an amateurish-looking piece, in addition to increasing the life of your sandpaper, getting the best results for your sanding/polishing/finishing stage, having a faster, cleaner and cooler (reduced heat/friction) sanding job.

But, what to pick? It can certainly be overwhelming to choose, once you start to look into all the types of coated abrasives on the market (not to mention just on our website!), even if you’re an experienced sander. In this article and accompanying materials, we’ll detail the most common abrasive grains we offer and some of the conditions and materials that they work best for. 

And, if you’re more of a visual learner, skip to the bottom of this article and download the infographic with all this information.

(Note that most of these products are fairly versatile, designed in a lab for particular conditions and you may have other factors to consider, such as budget, time and versatility of materials/projects, type of sanding process/machine, product format requirements, so use this only as a guide – don’t take it as gospel.)

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So, wait… If it’s not actually sand, what makes it so abrasive?

If you’re reading this article, it may not come as much of a surprise to you that the term “sandpaper” is actually a misnomer, as the grittiness of sandpaper is not actually made from sand, like at the beach, and this grit is not always even attached to paper.

So, if it’s not actual sand, then what is it? And, what are the differences between the various abrasive materials?

Sandpaper is actually a type of coated abrasive, meaning, it is made from some type of abrasive “grain”, such as the types we are going into in this article, which is affixed to some kind of backing – often paper, cloth, plastic, or even foam sponges or mesh. There may or may not be other added fillers or coatings, such as stearation.

These days, there are several types of abrasive materials used on sandpaper products, including a few natural rocks/minerals and a handful of synthetic substances, manufactured in labs, each with their own advantages and disadvantages.

The most common natural minerals used in abrasives are emery and garnet, while four common manmade types are silicon carbide, aluminum oxide, ceramic alumina and alumina- zirconia. Each varies in longevity, coarseness/aggressiveness, amount of friction required, friability, cost, ideal application, available grit sizes and coating and what formats of products they are available on, such as disks, sheets, or belts.

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Why you should care about the abrasive grain you choose for your project.

Before we discuss each of these grains, it’s important to consider why these characteristics matter. First, and let’s be real, does anyone really enjoy sanding? If you do, let us know!! …But for the rest of us, sanding can be a bit time consuming, boring and even a pain on the hands, so, wouldn’t it be great if we could make the process more efficient, and more effective? Other than making it merely tolerable with some headphones and great music, we can often speed up the process by using the proper type of abrasive product for our application with proper technique, which will save time and resources.

Additionally, using the proper abrasive grain / project material combination, as well as proper technique and pressure, can also help to reduce sanding costs by allowing your products to last longer. One way this happens is thanks to using products that create less friction, and therefore less heat, which causes the abrasives to cut more effectively, not burn your material and clog up less. Furthermore, the friability, or the characteristic that allows grains to break to form new, sharp edges (self-sharpening), allows you to go longer before the sandpaper wears out.

Now that you know why it’s important to choose the right grain for the project, let’s discuss each of the four options we have available.

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Aluminum Oxide – The Versatile Powerhouse of Abrasives

The most versatile of the synthetic abrasive grains, Aluminum Oxide commonly comes in three types: pink, white and brown, or semi-friable. Aluminum oxide is a chemical compound of aluminum and oxygen formed by fusion and then broken down and sorted by grit size through a series of mesh screens (see this video for an example). Each of the types measures at about 9 on the Mohs Hardness Scale, a measurement scale that defines how resistant materials are to scratching. The Mohs scale places common minerals on a scale of one through ten, starting with Talc at the bottom and Diamond at ten. 

Most of the time, the type of aluminum oxide will not be mentioned on our website, however each type is more suitable for different types of sanding.

Aluminum oxide-based coated abrasives can be used in belt sanding, power sanding or for hand sanding applications, and are available on a range of backing materials with both open and closed coatings.

Pink

Pink aluminum oxide is available in coarse through fine grit products on a variety of different backings and in a variety of formats. It generally works well for softer substrates, such as wood, for aggressive sanding.

White

White aluminum oxide is available in coarse through fine grit products on a variety of different backings and in a variety of formats. It generally works well for wood, providing a cooler sanding experience for aggressive sanding on wood and lacquers, as well as for use between coats of finish on your woodworking projects.

Brown/Semi-friable

Brown, or semi-friable, aluminum oxide is the most common type of aluminum oxide, because of its versatility. It is available in coarse through micro grit products, coming affixed to a variety of different backings and in a variety of formats. It generally works well for harder substrates, such as metal (particularly softer metals), fiberglass, drywall, painted/primed surfaces and wood. When used in coarser grits, from 80 to 180, with a medium pressure/tension, this grain works well for wood and metal stock removal, allowing the grains to break and re-sharpen, making the product last longer. When used in finer grits, around 600-800, this material is great for finishing and polishing metal.

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Silicon Carbide – Self-Sharpening And Great For Beautiful Finishes And Glass

Silicon Carbide, another popular grain type, is a semiconductor containing silicon and carbon and is produced through carbothermal reduction. It is the hardest common abrasive grain, other than diamond, and measures at a 9.5 on the Mohs Scale of Hardness.

While silicon carbide tends to wear quicker than aluminum oxide, it is also sharper and more friable, therefore it is still a long-lasting product and is ideal for uses on harder materials, rougher surfaces, and for polishing, due to its hardness and sharpness. It is best for metals (particularly harder metals) and is the only grain that can be used on glass, stone and marble. Silicon carbide is also effective on MDF and cork.

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Silicon carbide is frequently used in wet sanding applications, such as polishing stone and marble, as well as automotive polishing applications. In coarser grits, this abrasive is good for removing rust, deburring metal and glass, refinishing wood flooring (cutting through/removing old finish). Silicon carbide can also be used to sand between finishing coats in woodworking projects, so it is common to use aluminum oxide for rough sanding of raw wood, and switch to silicon carbide when in the finishing stages of the same project.

Being a pretty versatile, and relatively forgiving, abrasive grain, silicon carbide is available on belts, disks, sheets, sponges and for use in power sanding and hand sanding applications.

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Ceramic Alumina – Long Lasting, Great For Metal Finishing

Ceramic alumina is a long-lasting synthetic grain produced directly as a grain through an aqueous dispersion of fine aluminum oxide powder. While it can often be more expensive, it lasts longer and provides a cooler sanding experience than aluminum oxide. Often simply referred to as ceramic, this grain works best on metal, stainless steel in particular, and requires a hard surface/pressure in order to activate the friability. While it can be used on wood, it will be very aggressive ploughing through the wood instead of cutting it.  This could lead to a very uneven scratch pattern which will result in a poor finish.

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Alumina-Zirconia – The Grittiest Of Them All             

Alumina-Zirconia, also referred to as zirc or zirconium, is produced by die-casting and is typically available in only coarser grits, up to 120, on belts and disks for power sanding units. Because this grain is best for heavy stock removal in mills, an initial sanding of raw woods, and removing burrs from very hard metals, it is mostly available on heavy cloth backings with mostly open coats, to provide a sturdy product with space for a lot of material to accumulate. This allows the products to withstand medium to high pressure and avoid clogging too quickly. If you have a lot of rough sanding to do for raw woods, rust or other metal work, choosing zirconia might be the best option, in spite of a potentially higher price, because it will last longer, be more friable, and provide a cooler sanding experience than aluminum oxide.

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Conclusion

As you can see, there are certainly many aspects that will influence which abrasive grain, and therefore, which “sandpaper” will be best for your particular application. While aluminum oxide is the most common, and generally most affordable of our products, choosing another material, or combination of materials and grits, might ultimately be more cost effective, longer lasting and even more effective at the job, even if you only work with one base material. For instance, if you are someone that frequently works with jagged wood, bringing it all the way to a finish, or if you work with reclaimed metal parts for cars, it may make sense to mix, therefore, choosing different grains for coarser applications verses finishing and polishing.

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Abrasive Grains Cheat Sheet

Here is a sample of a great infographic, designed to help make all this information much simpler, and easier to understand.

If you would like further information or assistance, we welcome you to contact our customer service or sales representatives.

abrasive, sharp, hard material used to wear away the surface of softer, less resistant materials. Included within the term are both natural and synthetic substances, ranging from the relatively soft particles used in household cleansers and jeweler’s polish to the hardest known material, the diamond. Abrasives are indispensable to the manufacture of nearly every product made today.

Abrasives are used in the form of grinding wheels, sandpapers, honing stones, polishes, cutoff wheels, tumbling and vibratory mass-finishing media, sandblasting, pulpstones, ball mills, and still other tools and products. Only through the use of abrasives is industry able to produce the highly precise components and ultrasmooth surfaces required in the manufacture of automobiles, airplanes and space vehicles, mechanical and electrical appliances, and machine tools.

This article surveys the principal materials used in abrasives, the properties of those materials, and their processing into industrial products. Most abrasive products are made of ceramics, which include some of the hardest materials known. The origins of hardness (and other properties) in ceramic materials are described in the article ceramic composition and properties.

History

The use of abrasives goes back to earliest man’s rubbing of one hard stone against another to shape a weapon or a tool. The Bible mentions a stone called shamir that was very probably emery, a natural abrasive still in use today. Ancient Egyptian drawings show abrasives being used to polish jewelry and vases. A statue of a Scythian slave, called “The Grinder,” in the Uffizi Gallery in Florence, shows an irregularly shaped natural sharpening stone used to whet a knife.

Sand and pieces of flexible hide were early man’s sandpaper. Later, craftsmen tried to fix abrasive grains to flexible backings with crude adhesives. A 13th-century Chinese document describes the use of natural gums to fix bits of seashell to parchment. About two centuries later, the Swiss began coating crushed glass on a paper backing.

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Early sand and glass abrasives lacked sharpness, and by the 19th century early abrasive products like the natural sandstone that had been formed into the “grinding wheel” no longer met the needs of developing industry. In Swen Pulson, working in the Norton and Hancock Pottery Company, Worcester, Mass., U.S., won a jug of beer by betting that he could make a grinding wheel by combining emery with potter’s clay and firing them in a kiln. Pulson succeeded on his third try; this incident signaled the end of unsatisfactory glue-and-silicate bonded products and the birth of the vitrified grinding wheel.

Just before the beginning of the 20th century, when the natural abrasives emery, corundum, and garnet were falling short of industry’s demands, the American inventor Edward G. Acheson discovered a method of making silicon carbide in electric furnaces, and scientists at the Ampere Electro-Chemical Company in Ampere, N.J., U.S., developed alumina. In the General Electric Company succeeded in manufacturing synthetic diamonds. Like other man-made abrasives, synthesized diamond proved superior in many applications to the natural product, which had been used in grinding wheels since .

Once used only when precise dimensional accuracy and smooth surfaces were necessary, abrasives have become a widely applied industrial tool. Higher grinding-wheel speeds, more powerful grinding machines, and improved abrasives have steadily augmented their role.

Abrasive materials: their composition and properties

The materials used to make abrasives can be broadly classified as either natural or synthetic. Natural abrasives include diamond, corundum, and emery; they occur in natural deposits and can be mined and processed for use with little alteration. Synthetic abrasives, on the other hand, are the product of considerable processing of raw materials or chemical precursors; they include silicon carbide, synthetic diamond, and alumina (a synthetic form of corundum). Most natural abrasives have been replaced by synthetic materials because nearly all industrial applications demand consistent properties. With the exception of natural diamond, most of nature’s abrasives are too variable in their properties.

One of the most important properties necessary in an abrasive material is hardness. Simply put, the abrasive must be harder than the material it is to grind, polish, or remove. Hardness of the various abrasive materials can be measured on a number of scales, including the Mohs hardness test, the Knoop hardness test, and the Vickers hardness test. The Mohs scale, first described in , measures resistance to indentation as judged by which material will scratch another. This scale, which assigns numbers to natural minerals, has been widely accepted and is used by mineralogists. The Knoop and Vickers hardness tests employ pyramid-shaped diamond indenting devices and measure the indentation made by the diamonds in a given test material. The Vickers test was designed primarily for metals. With the Knoop test, however, the hardness of extremely brittle materials including glass and even diamonds can be measured without harming either the indenter or the test piece.

Toughness or body strength characteristics are also significant to abrasive function. Ideally, a single abrasive particle resharpens itself by the breakdown of its dull cutting or working edge, which exposes another cutting edge within the same particle. In synthetic abrasives it is possible to achieve some degree of control over this property by varying grain shape during the crushing or sizing operation, by making changes in the purity of the abrasive, by alloying abrasives, and by controlling the crystal structure within abrasive grains. Thus abrasives can be developed to meet the operating conditions found in a variety of applications.

Interaction between the abrasive and the material being ground prevents the use of one abrasive as a universal medium. For example, when silicon carbide is used on steel, or alumina on glass, some reaction takes place that has yet to be clearly defined but that results in rapid dulling and inefficient abrasive action. Attrition resistance is the name given to this third, very significant property.

The table lists prominent natural and synthetic abrasive materials. Links are provided from the table to further information on the materials and the hardness scales.

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Hardness of prominent abrasive materialsabrasive materials hardness Mohs scale Vickers scale Knoop scale natural abrasives industrial diamond 10 10,000 8,000 corundum 9 2,200 1,600–2,100 emery 7–9 1,600 800–1,800 garnet 7–8 1,100–1,300 1,300–1,350 flint 7 900–1,100 700–800 quartz 7 1,100 700–800 pumice 5–6 — 430–560 talc 1 — — synthetic abrasives synthetic diamond 10 10,000 8,000–10,000 boron nitride (cubic) 10 7,300–10,000 4,700–10,000 boron carbide 9–10 3,300–4,300 2,200–5,100 silicon carbide 9 2,800–3,300 2,000–3,700 alumina 9 2,200 2,000–2,600