Need help separating corroded aluminum parts

[skipmac]

Originally Posted by roverhi

If you can't use a torch because of location, adjacent materials you can do the following to apply heat.

Jumper cable trick.
Hook jumper cables up to the battery as you normally would. On the other end put a bolt (1/4" x 2" bolt works fine) in the postive lead clamp of the jumper cable. Clamp the negative lead as close to the offending bolt as possible. Touch the bolt in the positive lead clamp to the head of the fastener. You set up what is essentially an arc welder. Will heat the fastener to a cherry red if left in contact long enough. It also gets the fastener way hotter than you can with a MAPP torch. It works really well as it only heat up the area of the fastener and not burning up the surrounding country side like you do with a torch. It is really the only way to get serious heat to a fastener if there is painted surfaces or plastics close by. Quench the heated fastener with penetrating oil. Try to remove the fastener with an impact driver, either manual or power. Repeat the process till you break the fastener loose. Other than using the trick to remove all the fasteners on a 44 year old mast, used it to get corrosion welded bolts out that passed through substantial aluminum castings on my self steering vane.

Having said the above, the hardest fastener to remove is not one that is threaded into aluminum but one that simply passes through an aluminum casting like cleats, etc. Getting the bolts out of the self steering casting took something north of 25 iterations, heating with the jumper cable and quenching with penetrating oil over many days. A good idea to coat the shaft of any fastener in aluminum cleats or castings with Lanocote.

I tried the jumper cable trick a couple of years ago on the SS bolts corroded into the frame of a cast aluminum hatch. Maybe didn't try enough iterations but heating the bolts to glowing but not cherry red at least 8-10 times, dowsing with PB Blaster in between as you suggested and got nothing. If I have to do this again I'll give it a few more rounds. I do worry about screwing up the aluminum if that part got too hot.

[kryg]

I have an Aluminum sail boat over the last year and a half I have had the hull deck mast and chain plates and gear totally stripped and rebuild. the boat as is 30 + years old. the only thing that can separate components is LOTS of heat and more heat with a blow torch keep the leg base cold with a very wet rag and heat the part you want to remove with lots of heat when you think that is enough keep going with more heat than try to remove it here in Australia we have a blow torch called Hot Devil by Trade MAP Gas, the tanks re yellow and come with a blow torch attainment as a kit,
Here is Hot Devil by Trade MAP Gas, link for a reference. https://www.nationalwelding.com.au/t...CABEgLEIPD_BwE
good luck with it,




Kryg. SV Skoiern IV

Originally Posted by Beach View

Hello CF,

I hope you can help me separate my anodized aluminum cockpit table legs from their anodized aluminum bases. The bases are bolted & bonded to the deck so I have to work on them in place. I have new legs, but I have to save the bases.

The legs are tapered at each end to fit into the tapered holes in the bases. Over the years they have corroded themselves together. I’ve tried soaking them in penetrating oil, and I McGyver’d an adapter to be able to use a 2 ½ ton bottle jack to pull the legs up while beating on them, but no joy.

Does anyone know of any way to separate them or something (acid?) that would dissolve the corrosion?

My last resort is to cut the legs off as close to the bases as I can, make cuts from the inside of the stumps to the bases (the hard part), then bang the pieces out with a hammer.

Thanks in advance,

Bill

[Reefmagnet]

If using a fuel gas, here's an old trick for telling when aluminium is reaching the maximum temperature it can bear before it starts to melt. This is important because aluminium melts at about 1/3 the temperature that it's oxide does and doesn't bother glowing red prior to turning to liquid. The trick is to turn the oxygen off on the torch and "paint" the aluminium being heated with the carbon from the flame. Proceed to heat the aluminium with the torch and the correct amount of heat is reached when the carbon starts to disappear off the surface.


Sometimes, the oxide will turn to sand if heated to high enough temperature and release it's grip. Best way to remove bolts corroded into aluminium is to heat the ferrous bolt until it's just about ready to melt as this will turn the oxide to sand. Heating can be done with an oxy fueled gas torch or even by welding on the remains of the bolt/stud to heat it. For those using welding/battery current in an attempt to heat the oxide junction, be aware that aluminium oxide acts as a diode of sorts so it may be worth experimenting with changing the polarity of the leads across the junction to improve the localized heating as you'd certainly want the "sacrificial" side of the frozen joint to receive the most heat.

[Beach View]

Hello CF,


Thank you for all of your advice. In the end brute force won the day. I ended up cutting the legs off as close to the bases as possible, and since I’m under COVID-19 quarantine in Italy I have nothing but time (and a crappy hacksaw) on my hands I cut two slots from the inside of the stumps, then knocked the pieces out with a hammer. No damage to the bases, but lots of hard white corrosion on both parts. I chipped out & sanded as much corrosion in the bases as possible (while trying to avoid damage to the remaining anodizing), then I applied a little silicone grease.


Honestly, I don’t think there was another solution to this one. In the future this will be on my PM list….


Ciao,


Bill

[dennismenace111]

An angle grinder with a 4" cutoff wheel works wonders and are very inexpensive at Harbor Freight.

Its a sure thing to separate the aluminum pieces...

[JDanielBryant]

You might want to try the other end of the pH scale to see if you have any luck. I have a PhD in Metallurgy and just retired from Alcoa (the aluminum company) two years ago, and I can say that Al is only stable in a narrow pH band, about pH 4 (Coke) to pH 9 (milk of magnesia). We would etch aluminum (convert Al into Al2O3 oxide and its hydrates, the white corrosion product you see on it) with acids or caustics. It’s hard to say whether drops of diluted drain cleaner (potassium hydroxide or sodium hydroxide) would work, but it might be worth a try. Obviously wear safety glasses and gloves and have plenty of water to flush it off. Personally I would prefer to lean on the fact that alumina is good thermal insulator. Wrap the tubes is cold damp towels and rapidly heat the base with a heat gun to expand it around the tubes and whack them to loosen them up. My two cents.

[George DuBose]

Acetic acid (vinegar) comes in various strengths. I would try the strongest I could find. Nothing is going to replace the aluminum lost to corrosion.

[Ken Fry]

It looks like problem solved -- but thought I'd throw this in for future reference:

For these pieces, this would not make sense (unless you have a tig weldeer sitting around), but if things are expensive, and there is an internal round part stuck in a external round part, run a weld bead around the inside of the internal part (being sure you do not penetrate to the external part). The when it all cools, the internal part shrinks away from the external.

Sometimes...

Almost all the time when the internal part is steel. (I've used this technique to remove a pressed-in bearing race from an aluminum engine case, for example, where the usual heating of the whole assembly did not help.)

You need plenty of wet rags around to keep adjoining things cool, preventing fires, etc.

[bstreep]

I'm late to the party, but I'll jump in. My father was a corrosion engineer. When I posed a similar problem to him (aluminum on a roller furler), I went through all of my attempts. Many of which can be read on this thread, including PB Blaster, acid, Calcium Hydroxide, Hot/Cold. I tried them all.



He knew the ONLY solution to this problem: "Son, don't you own a hacksaw?" Unlike steel, there is no other solution.

[JeanF73]

Heat on the outside
Ice or dry ice on the inside