Bead Blasting Aluminum - Need something better!

[oneoldbanjo]

I have seen engine cases, cylinders, etc. that people have bead blasted to get them cleaned up and they look pretty good at first. The problem I have is that the original casting is fairly shiny (shiney?) and the surface is pretty smooth when it was as originally cast - then after bead blasting the surface is much more porous and holds onto stains and oxidizes much faster and is harder to keep clean. It also has a very flat appearance and does not have the dull gloss of the original casting.

Does anyone know of anything that can bring back the shine to aluminum afer it has been bead blasted? I have tried bead blasting with Walnut Shells and that doesn't do a thing to erase the dull appearance left by glass beads. Has anyone tried tumbling a cylinder in Walnut Shells, Corn Cobs, etc.? I don't want a bright shiny polished finish - just something that more naturally matches the original aluminum finish. (Specifically I am talking about a cylinder where it is impossible to get back into the fin area and polish or buff by any mechanical means).

 

[motoroilmccall]

What you did was expose the aluminum to anything around. Aluminum is usually "stainless" from the factory because it has been allowed to oxidize in a controlled environment. Aluminum Oxide is an excellent sealer for metals, in fact, when you Anodize an Aluminum part, your simply coating it with aluminum oxide (often with minute amounts of other elements for color, such as Copper for green, Boron for Blue, Sulfur for Yellow, etc etc). Now that you removed its sealer, there's not much you can do. I have HEARD that freezing bare parts makes aluminum parts oxidize faster (which sounds backwards to me, heat should promote oxidizing), personally, I'd get off the staining with whatever you have available, then put it in the oven on low to heat the part and allow it to cool completely before you remove it. Don't heat the snot out of it or you'll run the risk of warping it.