Abrasive Blasting 101
Updated January 2022: Not all blast cabinets are created equally and abrasive media selection is very much dependent on the application and machine at hand. Whether you’re doing aerospace engineering or cleaning a car part, using the right abrasive in the right machine is key to the success of your project. If you aren’t sure you have the right machine, check out our buying guide to confirm you have the right cabinet.
Glass beads, plastic, soda and steel shot are considered non-cutting abrasives. Glass beads are by far the most used non-cutting abrasive type being that they do not reduce the size of a part and remove only the surface coating be it paint, rust, etc. When used correctly, glass beads can actually make the size of a part appear to grow by making a small crater in the part surface that measures larger unless you are using a profilometer, a measuring instrument used to measure a surface’s profile, in order to quantify its roughness. When used properly, glass beads impact the surface while spinning, making a small indentation in the part surface and sealing the surface. In some cases, depending on the part material, the surface is sealed with a luster. The larger the bead the more luster the part has after blasting.
There are other non-cutting abrasives that have special applications. Plastic abrasive is commonly used for aerospace applications because it can provide chemical-free cleaning without changing the metallurgy of the part. Soda, which cannot be recycled, is another non-cutting abrasive that is capable of cleaning parts that are covered in oil and other deposits. Steel shot is also a non-cutting abrasive, and its weight overcomes most coating adhesions by simply overpowering the coating. The part being blasted must be able to withstand such strong abrasiveness, and many thin parts are distorted by shot peening.
In cases such as hard anodizing, the surface created by glass beads is detrimental. Hard anodizing requires an open part surface for adhesion, which is why cutting abrasives are used. The most used cutting abrasive type is aluminum oxide – it opens surfaces, has great recycling rates, can produce a gloss surface with the correct abrasive mesh size for powder coated surfaces and allows the best possible adhesion for many other critical coatings. Aluminum oxide has many different types but now the most used is brown fused aluminum oxide, which contains a small amount of iron. Being that some applications do not allow for iron, iron-free white aluminum oxide is also available. On the Mohs mineral hardness scale Aluminum Oxide has a hardness of 9.0. Another even harder commonly used cutting abrasive is silicon carbide, which rates at 9.5 on the Mohs scale. To put this into perspective, sand rates about 4.0, and for this reason it’s not used in cabinets, as it would explode on impact under nearly any pressure.
One important factor to always keep in mind is that blasting cabinets use different kinds of abrasive media than portable blast equipment because the latter doesn’t recycle abrasives. For example, softer, much less expensive cutting abrasives like sand, slag and garnet should never be used in cabinets because these abrasives will overload any size dust collector and quickly create a huge mess.
For more information, see our Glass Bead Conversion Chart and our Grit Size Conversion Chart.