What's an abrasive?In short, it's a material with a textured surface used to shape, smooth, contour, clean, prep, or finish a hard surface by rubbing and wearing away imperfections or shaping the surface through friction. Abrasives can also roughen a surface, depending on the abrasive and what it was created for. People use abrasives commonly to remove paint and rust, polish wood, shave down corners and edges, cutting, and more.
Abrasives include: sanding belts, surface conditioning discs, sandpaper, flap discs, diamond blades, sanding sponges, fibre discs, grinding cones, and more. The type you'll need varies on what tool you are using as well, for example: grinder, belt sander, orbital sander, hand sander, etc. We'll discuss this more later in the article.
Choosing the right type of abrasive is important because 1) it will make the task easier, 2) the material you are rubbing is not being damaged, and 3) you will get the right finish.
Types of AbrasivesThere are two types of abrasives: coated and bonded. Coated abrasives are generally soft and flexible (belts, sheets, rolls, discs) compared to bonded abrasives that are solid and made in shapes for specific purposes (grinding wheels, polishing stones, cutting-off wheels).
What are abrasives made of?Abrasives are composed of a variety of materials. We're going to focus on the three most common materials:
- Aluminum oxide
- This is the most common abrasive material. It works great for smoothing wood, drywall, metal, and can be used to remove rust and paint from surfaces. Durability and versatility are other reasons this material is ideal. It comes in a huge range of grits, from extremely coarse to very fine.
- This is a higher, industrial-grade of aluminum oxide. Unlike regular aluminum oxide, ceramics are only available in coarse grits. They are extremely tough and are optimal for heavy metal removal applications.
- Zirconia Alumina Alloy
- This consists of zirconium oxide and aluminum oxide and is used for rough grinding. Ideal for grinding and finishing metals such as stainless steel.
Grit (or Hardness)The grit of an abrasive determines the coarseness or fineness of the abrasive's surface. When using coated abrasives, grit is a better measurement of usefulness for your specific application. For bonded abrasives, it's more about the abrasives' hardness.
|Image from Kemet at http://www.kemet.co.uk/blog/metallography/coated-abrasive-sample-chart|
The grit number is the amount of individual abrasive grains on the abrasive side of the material. The higher the grit number, the smaller and finer the abrasive grains. The lower the grit number, the bigger and more coarse the abrasive grains.
GradeBonded abrasives have a grit number, but the hardness is a better measure of what the bonded abrasive is capable of. This is expressed by the grade: a letter from A to Z (A=soft and Z=hard). This also defines the strength of the bond: the softer the grade, the weaker the bond.
The grade defines the abrasives preferred speed, depth,and which materials they are better for. Softer abrasives are better for harder materials and harder abrasives are better for softer materials. Please note to not use only the grade to determine if the bonded abrasive is the one you need. It also depends on your tool: how fast is it going?
Grades differ from manufacturer to manufacturer.