I’m a Mechanical Engineer who gets excited about material properties, and today, I’m sharing one of my favorite words: friability.
Friability measures how well a piece of material holds up under duress. All solid substances in the world experience friability, to varying degrees, meaning that all solids eventually break into smaller pieces upon impact.
Here’s an example from the blasting booth: if we’re blasting steel substrate with crushed glass, the glass will degrade faster than the steel during the blasting interaction. Crushed glass is highly friable compared to steel – it fractures, breaks, and turns to dust. The steel remains unaffected.
Steel grit, on the other hand, is a low-friability blast medium that’s very effective on steel substrates. Steel grit can withstand up to 2,000 impacts, making it possible for us to recycle it many times before it turns to dust.
Kaser stocks 3 blast media (steel grit, crushed glass, and aluminum oxide), but there are hundreds of options on the market. The words “shot” or “bead,” for instance, mean the blast medium is rounded. Rounded blast media is designed primarily for peening. Grit, on the other hand, is angular or pointed, making it better at removing material (i.e., rust or old coatings). Coal slag, garnet, soda, walnuts, corn cobs, even sand, though it has fallen out of favor for environmental reasons – with all of these options, how do you choose?
Start by comparing friability.
Let’s say you’re blasting a thin piece of aluminum (which is softer – and more friable – than steel). Steel grit has a lower friability than aluminum, and crushed glass has a higher friability than aluminum. Which do you choose? If the blast medium has lower friability than your substrate, steer clear: it’s likely to cause damage, warping, and even holes. Stick with blast media that are more friable than your substrate (in this example, go with the crushed glass).
It should go without saying that we never want to damage the substrate during blasting. However, we have to weigh that against our desire to keep pricing reasonable. Yes, the blast medium should have higher friability than the substrate, but it should also have a good rate of removal, otherwise we’re wasting our time. The line is fine: get results, but do no harm.
Trying a new blast medium is always a bit nerve-wracking, but there’s no need to fly completely blind. Check the friability before you order – compare that to the friability of our substrate, and the friability of media you’ve used in the past. This should help you anticipate its performance.