Sandblasting
Sandblasting is method used for many different things.
For one you can use it to effectivlly prepare surface for painting. You can also use sandblasting for restoration purpose, like old rims, wood or for restoring old brick wall. Sandblasting really is used basically just everywhere, from metallurgy, toolmaking, foundry, restoation, glass industy all the way to aviatic and automotive industry.
But how does it work? You have sandblasting machine, sandblasting equipemnt and sandblasting sand. You put sandblasting sand in sandblasting machine, then connect machine with other equipment and start sandblasting. Sandblasting is using air-powered pressure to clean and abrade a surface which is typically metal. Pressure is making sandblasting sand to flow from canister towards surface which abrades it which removes previus color, make it look newer and makes is less smooth which helps for newer paint to be more compact and eventualy last on surface longer.
Most of sandblasters use two hoses, one conencted to bottom of barrel and one connected to top of it. Main reason for this is that when pressure is made one hose is sucking used sand back to sandblaster. This used sandblasting sand is then refiltered and can be used again.