Different blasting media for different jobs

Question:

In the July issue the Mechanic on Duty wrote about sandblasting. The August issue did not have a follow-up regarding using baking soda, plastic media or crushed walnut shells. In Aerospace, we’ve played with crushed dry ice too, and it works very well, but is a bit costly. There’s also one floating around using powdered glass for a media, and that sounds just a little too risky.

Answer:

The different blasting media are suited to different purposes. Sand blasting is great for removing rust on bridges and heavy castings, but will thin, warp, peen and harden automotive sheet metal. And in the wrong hands sand can eat through sheet metal in a matter of seconds. Glass beads or garnet are better for removing paint and rust from thinner components. But I only strip precious automotive tin with Automotive and Aircraft paint stripper because there is no risk of damage to the metal with it. Yes, it is messy and toxic, but it won’t damage irreplaceable parts.

Soda blasting is great for big items that will not fit in a blasting cabinet because it does not create the harmful dust and grit that can get into your lungs and cause damage. But soda blasting is only marginally effective for removing more than surface rust. Walnut shell blasting was invented by the aerospace industry because it will remove dirt and rust, but it won’t damage the sheet metal because it is not very aggressive. The aerospace industry likes it because the nutshell dust will not ruin bearings if it gets into them, whereas sand, glass beads or garnet will ruin them in a hurry. Plastic media is similar to walnut shells in the way it behaves.