Reusing abrasive media is a process that can happen in blast cabinets and other contained blast enclosures. For portable sandblasting and outdoor blasting, the used media is too difficult to collect, filter, and reuse, so that media generally gets disposed.
However, if you’re using a blast cabinet for industrial applications, having a process for reusing abrasive media becomes important. Some of the factors you must consider are: how many times can you recycle certain types of blast media? What variables will extend or shorten the life of your media? Are there certain types of media that last longer than others?
Some Factors to Consider
There are several factors when it comes to reusing abrasive media, and what to take account of.
Is the Media Single-Pass or Multiple-Use?
What is the Mohs’ hardness of the blast media? And of the surfaces being blasted?
Is your blast cabinet a siphon system or direct pressure?
Are you using a reclaim unit along with your dust collector?
What force, or PSI, are you blasting with?
What size nozzle and hose are you using with your blast media?
Single-Pass Media vs Multiple-Use Abrasive Media
Some blast media, because it has a low Mohs’ hardness, or because of other factors, is what is known as single-pass media. This means you can only use it one time. Either because of the low hardness of the media, the force with which it is being propelled, the hardness of the surface being blasted, or a combination of each – the blast media disintegrates into particulates that are too small to be reused.
Abrasive media that is higher on the hardness scale tends to have a longer use life. The harder the media, the more passes it takes for it to shatter into smaller and smaller particulates.
Also, in most cases, the larger the screen size of the abrasive media, the more total uses you will get out of your blast media.
Mohs’ Hardness Affects Recycling of Blast Media
The Mohs’ hardness scale is a scale for measuring materials or elements. The lower the number, the softer the substance. Talc is a 1, Diamond is a 10.
Here’s the Mohs’ hardness for some common abrasive media types.
Sodium bicarbonate (for soda blasting) – 2.5
Plastic urea – 3 to 4
Corn cob – 4 to 4.5
Walnut shells – 4 to 5
Crushed Glass – 5 to 6
Glass beads – 5 to 6
Pumice – 6 to 7
Coal slag – 7
Nickel Slag – 7
Copper Slag – 7
Staurolite – 7 to 7.5
Steel shot or grit – 8
Garnet – 7.5 to 8.5
Aluminum oxide – 9
Boron carbide – 9 to 9.5
Silicon carbide – 9 to 9.5
One of the big factors in the re-usability of an abrasive media is how hard is the blasted surface compared to the media itself?
If the object being blasted is several levels harder than the media being used, the recycle rate will be lower.
When you blast an object, the media and the surface impact and push against each other. The harder the surface versus the hardness of the media, the lower the usable lifespan of the blast media.
Direct Pressure vs Siphon Blast at the Same PSI
Another factor to consider is whether you are using a direct pressure blast system or a siphon system blast cabinet.
Direct pressure propels with double the force at the same PSI compared to a siphon system blast cabinet. For example, if you are blasting with glass beads at 75 PSI in a direct pressure blast cabinet, the media will disintegrate on impact. On the other hand, if you are bead blasting at 75 PSI in a siphon blast cabinet, you should get about 30 recycles out of the glass bead abrasive.
Know the Maximum Impact Velocity of the Abrasive Media
Each type of abrasive blast media has a maximum impact velocity, rated for both direct pressure and siphon blast applications. This is usually measured in PSI.
When you exceed the maximum impact velocity, it chews up your media, as it shatters into small particulates and becomes dust. By staying within the limits of the maximum impact velocity, you will be able to recycle most types of non-soft media.
Use an Abrasive Media Reclaimer for More Efficiency
No doubt, every blast cabinet should have an appropriately-powered dust collector. But by adding a separator reclaimer to your blast cabinet setup, you will be able to recycle your abrasive media more efficiently. While a dust collector gets rid of the dust in the enclosure, the spent media can still be re-circulated in with the good abrasive. A reclaim unit ensures that you will always be blasting with non-contaminated media. Essentially, a reclaim unit helps separate spent media from recyclable media, while helping change the air in the cabinet more quickly.
Using a separator reclaimer alongside your dust collector will also help improve your blasting efficacy. Because the smaller particulates are being filtered out, and the good media is being reused, your blasting is always being done with non-contaminated media, instead of the dull, shattered, and splintered particles.
The Shape of Blast Media Affects Durability
Round media, like glass beads or steel shot used for peening, tend to absorb impact (within the recommended velocity) a bit better than angular media. This is because the impact spreads across the spherical surface more evenly than angular blast media.
Use an Adequate Amount of Abrasive Media
While it’s possible to “stretch” a small amount of abrasive, it’s always a good idea to fill your blast cabinet with media to appropriate levels.
If you are blasting with whatever media is left over in the hopper, that will get used up rather quickly. This means you to have to keep stopping to refill the cabinet with media, which decreases productivity.
How Many Times Can You Recycle Your Blast Media?
Here’s a chart of how many recycles you should be able to get out of each type of media, at specific PSI, if you are blasting a steel surface. If you are blasting objects of a different hardness or composition, the recycle rate might vary.
Final Thoughts on Blast Cabinet Media Recycling
Understand the type of sandblasting media you are using, and stay within the recommended impact velocity for each abrasive. Direct pressure cabinets require less PSI than siphon blast cabinets for similar results.
The harder the media, generally, the longer it will last. Using an abrasive reclaim in conjunction with your dust collector will help you get more mileage out of your blast media.