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OK, we had a thread on polishing aluminum earlier. Here's my experiences on using different abrasive blasting media, along with one type of chemical cleaning.
What I started with were engine cases that were very heavily oxidized: white powdery aluminum corrosion:
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I began with the least abrasive - walnut shells - in the blaster. My blaster is the least expensive Harbor Freight floor standing model. My compressor does not deliver enough air for continuous use. I have to pause every few minutes to let it catch up. 45 seconds of blasting, 1 minute for the compressor to pump up.
The walnut shells would remove SOME of the corrosion, but not all of it. Didn't really 'clean' the aluminum, either.
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Next, I had been told of a product called Aluminum Jelly. I guess it's just like Naval Jelly, only for aluminum. Picked up this bottle at my local Ace Hardware for $4.
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You brush it on, leave it sit for 5 minutes and hose it off. Repeat as needed for more cleaning. Don't leave it on for more than 5 minutes per application or it can discolor the aluminum black. Contains phosphoric acid, according to the bottle.
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I think it did a really good job, considering how bad the corrosion was to begin with, and how easy the stuff is to use. Not 100%, though, but by the 3rd application, it had done a really nice job. This would work great, IMO, on things like wheel hubs that you don't want to de-spoke or are too large to get into a blast cabinet.
Here's a look after 3 applications:
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And, just as an experiment, I went back over the Jelly'd area with walnut shells again. This time, it DID remove the last bits of corrosion. A very nice, satin finish:
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But, pretty labor intensive between 3 app's of Jelly AND a trip thru the walnut shells. So, the next experiment was to use glass beads in the blast cabinet. IMHO, this worked great! One time thru, and very good results, without being as 'rough' as using sand.
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To me, this was the best choice for the cases, and I wound up doing the whole job with glass beads. Using about 80 psi in the blaster.
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The only downside was that bead blasting goes kinda slow compared to using sand, but it gives you a more satin, OEM look. Like pressure washing your driveway with 1000 psi washer vs. the big 3500 psi jobbies. You've got to hold the nozzle closer and go back over it to make the finish uniform. I've done sandblasting many times, and it goes much faster, but leaves a roughened surface on aluminum. It's perfect for many rougher cases, cylinder fins and cylinder heads. Also, it's great for prepping for painting, if you're going that route, but not for eventual polishing. Sand roughens the surface, making it VERY time consuming to polish to brightness later on. Here's a look at a previous job done using $3 bag of Home Depot play sand in the blaster at 100 psi. This goes very quickly and removes paint, rust, corrosion, blemishes, etc. And, because it does such a good job stripping, it is much easier to get a uniform result.
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And finally, just in an effort to find something that walnut shells do well, I tried it on very heavily sun-damaged plastic side covers. As you see, the covers were VERY badly sun damaged. The kind of oxidation that scrapes off on your fingers.
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Wow, did that work great! IMO, it saved these otherwise ready-for-the-trash pieces. This was done at about 50 psi:
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So, there you have it. Nothing fancy, just a quick overview of some experimenting I did one day. You're experiences may vary!
Kirk
What I started with were engine cases that were very heavily oxidized: white powdery aluminum corrosion:
I began with the least abrasive - walnut shells - in the blaster. My blaster is the least expensive Harbor Freight floor standing model. My compressor does not deliver enough air for continuous use. I have to pause every few minutes to let it catch up. 45 seconds of blasting, 1 minute for the compressor to pump up.
The walnut shells would remove SOME of the corrosion, but not all of it. Didn't really 'clean' the aluminum, either.
Next, I had been told of a product called Aluminum Jelly. I guess it's just like Naval Jelly, only for aluminum. Picked up this bottle at my local Ace Hardware for $4.
You brush it on, leave it sit for 5 minutes and hose it off. Repeat as needed for more cleaning. Don't leave it on for more than 5 minutes per application or it can discolor the aluminum black. Contains phosphoric acid, according to the bottle.
I think it did a really good job, considering how bad the corrosion was to begin with, and how easy the stuff is to use. Not 100%, though, but by the 3rd application, it had done a really nice job. This would work great, IMO, on things like wheel hubs that you don't want to de-spoke or are too large to get into a blast cabinet.
Here's a look after 3 applications:
And, just as an experiment, I went back over the Jelly'd area with walnut shells again. This time, it DID remove the last bits of corrosion. A very nice, satin finish:
But, pretty labor intensive between 3 app's of Jelly AND a trip thru the walnut shells. So, the next experiment was to use glass beads in the blast cabinet. IMHO, this worked great! One time thru, and very good results, without being as 'rough' as using sand.
To me, this was the best choice for the cases, and I wound up doing the whole job with glass beads. Using about 80 psi in the blaster.
The only downside was that bead blasting goes kinda slow compared to using sand, but it gives you a more satin, OEM look. Like pressure washing your driveway with 1000 psi washer vs. the big 3500 psi jobbies. You've got to hold the nozzle closer and go back over it to make the finish uniform. I've done sandblasting many times, and it goes much faster, but leaves a roughened surface on aluminum. It's perfect for many rougher cases, cylinder fins and cylinder heads. Also, it's great for prepping for painting, if you're going that route, but not for eventual polishing. Sand roughens the surface, making it VERY time consuming to polish to brightness later on. Here's a look at a previous job done using $3 bag of Home Depot play sand in the blaster at 100 psi. This goes very quickly and removes paint, rust, corrosion, blemishes, etc. And, because it does such a good job stripping, it is much easier to get a uniform result.
And finally, just in an effort to find something that walnut shells do well, I tried it on very heavily sun-damaged plastic side covers. As you see, the covers were VERY badly sun damaged. The kind of oxidation that scrapes off on your fingers.
Wow, did that work great! IMO, it saved these otherwise ready-for-the-trash pieces. This was done at about 50 psi:
So, there you have it. Nothing fancy, just a quick overview of some experimenting I did one day. You're experiences may vary!
Kirk
