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surface-conditioning-material

Abrasive Grains – Choosing The Right Abrasive For Your Application

With so many products now available in the surface finishing market, it is important to choose the most effective type of grain for your application, both to reduce costs and maximise efficiency. All abrasive products will do the job to some extent, however the key is using the ones which will do it in the shortest time and achieve the best result. As such we have broken down each type of abrasive grain into how they are structured, how they perform and the applications for which we recommend they are used.

Aluminium Oxide

The least expensive of all the available types of grain, aluminium oxide is a general purpose option and one of the most widely used. It is durable with sharp cutting edges and requires little pressure to remove material, however it dulls during use and so its performance reduces over time.

With metalworking in particular, aluminium oxide is only recommended for use on softer substrates such as aluminium in the coarser stock removal stages (i.e. up to P120.) However, as the operator works through the finer grades they will be aiming to improve the finish rather than take off material and should therefore apply less pressure, and as such it is suitable at this stage to use on almost all metals. For this reason it is often available in a wider range of grits than other grains, in some cases up to P1000.

aluminium-oxide-abrasive
As aluminium oxide performs best on softer materials it is also suited to woodworking. Often 100% of the surface of a sanding product will be covered in abrasive grain (known as ‘closed-coat’); this provides the most aggressive form of sanding action and is ideal for hard woods. However, there are also semi-open or open coat alternatives, where only 75% or 50% respectively of the surface of the abrasive will be covered in abrasive grain. The benefit of this is that due to the larger gaps between the grains it will trap less sanding residue, which is ideal for softer, more resinous woods such as pine that are more prone to loading on to the abrasive.

Zirconia

zirconia-abrasive
The second most common type of grain, zirconia lasts considerably longer and cuts more quickly than aluminium oxide. This is due to its self-sharpening grain which exposes sharp, fresh grit as it breaks down, however in order for this to be effective it does need to be used at higher pressures to break the grain down or it will just “glaze” over the workpiece and not actually cut. As such zirconia is best used on high pressure grinding/machining applications.

Due to the very aggressive and fast-cutting nature of the grain, zirconia is generally only available in the coarse to medium grit range (often no finer than P120.) For finer finishing stock removal is not the priority so less pressure is likely to be applied and zirconia would not therefore be suitable. It can be supplied in some materials with an open coat for use on soft materials such as rubber and leather, and so such products are prominent in the shoe repair industry.

A common feature of zirconia is a “topsize” (also known as “top coat”, or “supersize layer”.) This is a coating which is sprayed on to the grit to act as a coolant when working on heat-sensitive metals such as stainless steel and exotic alloys, and therefore reduce discoloration or burning. It can however also act as a lubricant to help reduce loading (where stock removed from the workpiece builds up on the abrasive and makes it less effective) on softer metals such as aluminium. The presence of a topsize does reduce the aggressiveness of the grain however, and so it is best not to have one if discoloration will not be an issue, for example when working on mild/carbon or structural steel.

Ceramic

Ceramic lasts the longest of all coated abrasives, as well as being the fastest cutting. This is due to the micro-crystalline grain which self-sharpens and fractures more uniformly to give more consistent performance, and works well in medium to high pressure applications and even the most demanding requirements where productivity and fast stock removal are key.

Ceramic is often supplied with a top-size to offer cooler grinding on heat-sensitive metals such as stainless steel, similarly to zirconia. This is however sprayed as an additional layer on top of the abrasive grain which therefore reduces its aggressiveness, and so it is best to use an abrasive without a top-size on metals such as mild steel which do not suffer from burning.

ceramic-abrasive

Silicon Carbide

silicon-carbide-abrasive
A more specialised material, silicon carbide grains are sharper and harder than aluminium oxide but less durable due to their brittle nature and more narrow shape.

The grain macro-fractures during use, which means that it breaks down into smaller pieces that act to re-sharpen it before it goes dull. This does however happen relatively quickly compared to other materials and so silicon carbide offers the best life & performance on substrates such as plastics, glass and brass, that require little to no pressure to be applied while the razor-sharp grains offer a very fast cut and leave a bright, consistent finish.

Agglomerate

A specialist material consisting of aluminium oxide grains which are compacted to form larger, more uniform granulates. This provides a much more even and consistent finish throughout the life of the abrasive (which is also extended due to the structured grain wearing more slowly.)

A uniform scratch depth and pattern is achieved with the worn/dull grain being shed and fresh grain being exposed from underneath. The consistent performance and finish is particularly suited to satin finishing stainless steel surfaces.

At first glance the surface of the abrasive appears deceptively coarse for its equivalent grades in other materials, due to the grains being clustered together. However the surface finish which it achieves is much finer than its appearance would suggest.

agglomerate-abrasive

Surface Conditioning Material

surface-conditioning-material
Made from a non-woven nylon web impregnated with fine aluminium oxide abrasive grains, surface conditioning material offers limited stock removal capabilities while its open structure resists clogging and delivers consistent results when finishing, blending, polishing, graining and cleaning on metals and plastics.

With a flexible backing this also maximises performance on curved and contoured workpieces such as tubes and pipes, as well as other hard to reach areas. Gaps between the fibres prevent the build-up of swarf, ensuring that it does not clog up the abrasive and maximises its service life. The benefit of non-woven materials is that the fibres will not leave fine splinters on the workpiece, as is a common occurrence with steel wool that is an alternative product for similar applications.

Trizact

Designed for intermediate finishing and fine polishing, the abrasive grain of Trizact is formed into tiny three-dimensional pyramid structures, ensuring that fresh, sharp mineral is continually exposed as these wear down. This produces a consistent cut and a uniform finish.

Performing best at medium pressures makes Trizact ideal for polishing applications on metals such as carbon steel, as well as stainless steel for which it features a grinding aid to reduce surface temperatures when grinding and therefore minimises discoloration.

The benefit of Trizact is that it stays sharp from start to finish, ensuring a consistent, predictable finish throughout its service life. It can therefore last up to five times as long as conventional abrasives, which naturally see a decline in performance and cut over time as the grain dulls.

trizact-abrasive

Felt

yellow-felt
Rather deceptively felt materials can not be considered to be ‘abrasives’ at all as they have no abrasive or stock removal properties whatsoever. These are designed for polishing once the surface has been prepared for final finishing, and are used in conjunction with compounds to clean and polish substrates such as stainless steel and glass.

Felt has good absorption properties, with its open structure allowing it to soak up particles of dirt when cleaning, and absorb the polishing media to apply it consistently across the surface.