Abrasive grit blasting media

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Abrasive grit blasting was defined in an earlier post as a method of surface modification hy impinging abrasive particles on the surface usually with a force. The abrasive particles are what are termed as the abrasive media. While some abrasive media are easily identifiable, there are some that the average person would not have dreamed of using as one

The most common abrasive grit blasting media are obviously silica, alumina and silicon carbide. However, silica generally creates a lot of dust and is not preferable to use as an abrasive grit blasting media from the stand-point of operator health issues. Continued exposure to silica dust can lead to pulmonary diseases. Alumina, which is basically aluminum oxide can be used either as standard purity or high purity grades. Silicon carbide is a very hard material, but is also relatively more expensive.

Steel grit which is from recycled steel is sometimes used as media for abrasive blasting. A variation of steel grit is the steel shot which is basically a round form of steel grit. Steel shot blasting is sometimes called shot peening, because the rounded steel shots do not generally create a roughened surface for subsequent coating, for example, but create a surface with large compressive stresses. This is sometimes used after heat treating or some coating operations.

All that is fine and okay you may think, but did you know that walnut shells can be used as a blasting media? Or how about ground corn cob? Surprised? Well, these materials ARE ( and have been ) used for quite some time now and offer a bio-degradable blasting media.

When it comes to abrasive media, sometimes grits of different sizes are mixed to produce the perfect surface roughness requirements. For example, a number 80 aluminum oxide grit may produce a very fine surface finish and a number 36 aluminum oxide grit may produce a very coarse surface finish, but a blend of the two in the correct proportion, under the right conditions of pressure, stand-off distance and speed of movement may produce the perfect surface roughness. This is usually determined only by trial and error.

Glass bead material is also used sometimes as an abrasive blasting media. This is generally used as far as I have seen in the finishing operation to produce a nice cosmetically pleasing appearance and not for the purpose of a roughness requirement.