Coated abrasives come in a variety of grain choices. Each grain’s characteristics such as heat dispersal, friability, and work piece interaction are all important when choosing the right product for the application. Other considerations when picking a coated abrasive product should be the amount of material being removed and the desired finish required balanced with minimal cycle time.
* Friability or Fracturing – The tendency of the individual abrasive grains to fracture under pressure.
Abrasives are either manufactured or naturally mined.
Manufactured Grains
I – Aluminum Oxide: There are four main types of aluminum oxide: white, pink, blue, and brown. The main ingredients of which is bauxite, coal, scrap iron, and chromium oxide. White is a pure version of aluminum oxide. This grain is mainly used in grinding applications where a more friable grain is desired. Pink is aluminum oxide with chromium oxide. This grain is tougher than its white counterpart, used in grinding applications. Blue fired aluminum oxide grain is heat treated adding friability for aggressive cutting action and continually sharp grain. Brown has a mixture of bauxite, coal, and scrap iron. This is the most common aluminum oxide and due to its toughness is considered the workhorse of abrasive grains. (See Fig. 1C)
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| (Fig 1 C) |
II – Silicon Carbide: This grain is black in color. It is the most pure grain because there is no extraneous metals in it. Silicon is the ideal choice when grinding titanium. Titanium is usually contaminated by other metals and the purity of silicon carbide eliminates this issue. Silicon carbide is harder but more brittle than aluminum oxide. The grain penetrates the work piece and cuts faster under light pressure more than any other grain. However, its longevity is short lived due to its friability. Silicon is used on low tensile strength materials along with non-metallic materials such as rubber, glass, plastics, and wood. This grain is also good for non-ferrous metals such as brass, aluminum, and bronze.
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