Blasting Abrasive Comparison - Ceramic Beads and Glass Beads.

Ceramic beads and glass beads are available in two types and in practice can easily be substituted for one another. However, though both can be used as blasting beads or peening beads, when used for shot peening care must be exercised to ensure the beads are used according to the peening specification of the job. Ceramic beads have a number of advantages over glass beads, among them a greater toughness and density. The life of ceramic beads exceeds that of glass beads by at least 30 to 1, if not more.

This toughness feature has several advantages, among them:

In surface finishing – Consistency is the key advantage as ceramic beads will produce a more consistent result over long production runs. When considering products created for consumer consumption, to be able to reproduce this consistent finish is critical. During blasting, the glass beads in the abrasive working mix are constantly breaking down as new beads are added. The fluctuation produced during the process results in a greater chance that the finished surface will not be consistent.
In contrast, ceramic beads have a longer life. So when adding beads to the mix the breakdown is significantly slower, resulting in a smoother, more consistent finished surface.

More consistent peening intensity – The slower breakdown rate is a noticeable factor in choosing ceramic beads over glass in the shot peening process. The objective of shot peening is to extend the life of a part by inducing a layer of residual compressive stress onto its surface. This process prevents the formation of fatigue cracks, which is a cause of part failure.

Shot peening is the process to achieve this and the layer of compressive stress is the result of bombarding the surface with small abrasive spheres. Ideally, each particle of the peening media would be of precisely the same size and have a perfect spherical shape. In practice, this does not happen due to the production of the media and its breakdown during the shot peening process. The size and shape of the media used for peening is a critical variable and needs to be controlled as tightly as possible.
What happens during the shot peening operation is the breakdown of the media will cause fluctuations in the shapes and sizes of the media. The smaller and damaged particles need to be constantly removed and replaced, as broken particles or particles with sharp edges negatively affect the entire process by damaging the surface. The advantage of ceramic beads is once again evident as the breakdown rate of the particles is significantly slower than glass beads. The result is a more consistent spherical particle size throughout the process and an overall higher quality shot peening operation.

Fingerprints and staining – Blasted surfaces are prone to appear imperfect due to fingerprints and handling, especially stainless steel items. The aesthetic value of a perfectly blasted surface finish can be ruined through handling after the blasting process. Because surfaces blasted with ceramic beads are much less likely to be damaged in the handling process, they are a preferred medium when processing items that are likely to be extensively handled. The result will be a surface that retains its finish far longer than with glass beads.

Less waste disposal – Waste disposal is expensive. The reduced breakdown rate of ceramic beads can make a significant difference in waste disposal costs for high volume users. Based on the 30 to 1 advantage of life expectancy, the difference can be measured in tons, disposing of 1 to 2 tons of waste instead of tens of tons.

Finally the bad news for ceramic beads. The purchase price of ceramic beads is significantly higher than glass beads. For the short sighted purchaser, (I'm sure we all know several of them!) that only looks at the purchase price, this will be an obstacle. For the buyer that can see the big picture, this will not be an issue as in the long term ceramic beads have a significant economic advantage.

 

Author: Chris Charlton
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