I am trying to restore an old cast aluminum bellhousing that has lots of white corrosion. I tried using various grit of glass beads and it does not do what i want. I tried wire brushes but it shines the surface up too much. I want to put the casting in my cabinet and give it a nice dull as cast finish by removing material from the surface but preserving the texture cast finish. I was doing some reading and lots of guys suggested aluminum oxide blast media the question i have is what grit? I see aluminum oxide media offered in 40,80 120; 180; 220 and 320 grit sizes. what grits are safe for cast aluminum? i need to buy a 50lb bag so i do not want to overspend experimenting here so i wanted to ask you guys for suggestions as the bags are pricey to order and ship.
You can buy small quantities on FleaBay and experiment. YMMV due to the variations in blast equipment, volume and pressure of your air supply. I have some 220 I have yet to try, so I'm not the short answer you are looking for. Good luck either way.
I use 80 grit and it works well; aggressive enough to remove rust/corrosion, but not enough to materially change the surface finish. Keep in mind you will end up with a satin finish no matter which grit you use so if the part originally had a 'shiny' as-cast finish that will go away. But you'll have pitting from any corrosion that will show up so don't expect a 'restored' finish in any case. I'd also recommended 'baking' the part for several hours at at least 250 degrees to 'boil' any remaining contaminants out of the casting before blasting, you'd be surprised how much 'stuff' can come out. The 80 grit also leaves a good 'tooth' for good paint/powdercoat adhesion if that's needed.
Most aluminum foundries use steel grit to blast castings after removing gating, risers and grinding parting lines. Probably not practical for a home blasting unit. I have 70 grit aluminum oxide from Harbor Freight in mine and I wouldn’t go any finer then that unless you did a lot of blasting on delicate parts. Most of the time glass beads or crushed glass is a lot cleaner. Your mileage may vary.
I use glas balls. Their size is up to 0,5mm. They should be used with a lower blasting pressure than sand or broken glas to avoid them breaking up. The glas balls clean the cast aluminium very well and due to their round shape, they close the pores so the cast part stays clean a lot longer.
Try wire brushing first to remove the corrosion, then bead blast to give it a dull even finish. Another thought is NAPA (as well as other sources) sells a product called aluminum brightener in a spray bottle. It works well to remove corrosion and deep ground in dirt and grime.
I too have used vapor blasting with good results, mostly on vintage carbs that come out super clean. Nothing quite like it. Two carb pics in my album. Under 28 Special Coupe.
we have a bay at the shop set up for dry ice blasting mainly used for underbody and engine bay detailing (google it) it uses granulated dry ice as a blast media (machine is adjustable for mica grind,flow rate and air pressure) , what i have found is it works amazing on cast aluminum ,, it does not damage or disturb the surface as in it really micro cleans the aluminum but not screw up than natural look as in it does not look sandblasted ,glassbeaded or wire wheeled , i had experimented doing some random engine parts and saw how well it did , as a restorer aluminum casting are a real challenge to make look original or even really clean up with out making them looked boogered . the big one for me was the day i bit the bullet pulled up my big boy pants and took my OG sharp 59a heads for a cleanup they turned out amazing , i had no idea that at some point they had been rattle can cleared , came right off , cleaned chambers , all is great ,, next up my OG navarro race model intake ,, ill hopfully figure out how to do some pics fabricator john miss you dad
I use 80-grit glass beads, after cleaning up in a 600psi pressure wash cabinet. Never use silica containing media. That can mess you up quite badly.
I work in aerospace, and we use the ice blaster for aluminum. Heavy corrosion will always leave a mark, but normal wear and lite corrosion will clean up nice. I wish I could bring my heads and intake into work and blast them, but the company frowns upon that. Another way is to have them acid dipped. The acid will remove all internal corrosion that you could never remove with blasting. It takes an experienced acid dipper to do the right job. It's a delicate process that will destroy the part if done wrong. Acid dipping can also cause porosity. I've been curious to experiment with electrolysis, but don't know enough about it. All normal blasting media will etch the aluminum and open up the pores, resulting in accelerated staining unless coated with a clear or waxes. Soda, walnuts, or plastic media might work well too at lower pressures and finer grits. I've been researching this for awhile, since my Hotton & Sullivan heads are irreplaceable. I can't make any mistakes. Trial and error with trusted professionals is the best bet to restore uncoated aluminum. If your painting the aluminum, any media will work, since your coating the etched surfaces. Good luck with your projects.
I use worn out glass beads in the cabinet, then hit it with high pressure soda blast. The soda evens out the finish. Soda first just shines up whats there and doesn't do much cleaning of the stains, it removes dirt and grime.
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