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Old 07-03-2015, 16:19   #1
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Removal of stainless screws from aluminum and corrosion

The stainless screws cause the aluminum to corrode and the screws seize up. Sometimes they come out with a bit of patience, drips of penetrating oil and a wait and maybe a tap with an impact driver. Sometimes they need drilling out. That's not fun.

I now have an aluminium window to re-bed with 15 stainless screws holding it down, many of which I can see are corroded. Before I go at it and turn it into a dog's dinner I thought I should ask how best to get the screws out. Would a cordless impact driver help? What is the best way to do it?
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Old 07-03-2015, 16:25   #2
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Re: Removal of stainless screws from aluminum and corrosion

An impact driver will certainly help. Use after using penetrating oil for a couple of days if you have the time. A large soldering iron or soldering gun used to heat the screw before you use the impact driver can help as well. There are a number of other threads on here with lots of ideas. A google custom search should turn them up.
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Old 07-03-2015, 18:53   #3
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Re: Removal of stainless screws from aluminum and corrosion

Start soaking them with penetrating oil for a while in advance. Like daily, or several times a day for a week+ before you go near them with tools, if you can. Well, other than perhaps giving them a light tap with a mallet, to assist the penetrant in getting into the threads more effectively.

When it comes to tools, & pulling out seized screws in aluminum, I prefer the non powered variety. That way you can feel when you're on the edge of too much resistance/about to tear the head off of the fastener. Even if it means going to vice grips on the head of the screw or bolt, to get a better grip than a screwdriver alone will provide.

Also, of course, leaning on top of the handle of the screwdriver while turning it (or trying to) helps. As does doing anything you can to relieve pressure on the fastener/metal interface. Ditto on sometimes seeing if you can tighten a frozen one 1/8th of a turn @ first, prior to trying to extract it.

I've even used blocks of dry ice, or set stubborn parts in big freezers, in order to get the stuck metal bits to contract a bit. Just watch the bare skin on metal thing, if you go this route.

Also, given that you're talking about removing fasteners around a window, is there something heavy which you can lean up against it, so as to reduce the pressure of it's gasket against the frame & fasteners?

Plus when undoing screws or bolts on the perimeter of something like this, at the outset especially, you only want to loosen each one only a little. As if you totally pull one, a lot of it's load is taken up by it's nearby neighbors... making them even tougher to pull.
And if you can undo the fasteners in something resembling an X pattern, that'll generally help to mitigate this kind of issue also.
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Old 07-03-2015, 18:58   #4
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Re: Removal of stainless screws from aluminum and corrosion

I have had a lot better results using a manual impact driver rather then the cordless/electric kind. They are able to deliver far more downward force/holding power/shock then the electric kind ever can. Along with oil and heat as mentioned above, I would say thats your best bet.
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Old 07-03-2015, 19:01   #5
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Re: Removal of stainless screws from aluminum and corrosion

Heat!
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Old 07-03-2015, 20:38   #6
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Re: Removal of stainless screws from aluminum and corrosion

CorrossionX instead of penetrating oil.
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Old 07-03-2015, 21:28   #7
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Re: Removal of stainless screws from aluminum and corrosion

You might try the jumper cable trick. Hook the jumper cables up to a battery in the normal way. On the other end, put a bolt in the postive lead clamp. Clamp the negative (black) as close to the offending bolt as possible. Touch the bolt in the positive lead to the head of the fastener. You are essentially setting up an arc welder. It will heat the fastener to a cherry red if left in contact long enough. It works really well as you are heating just the area of the fastener and not burning up the surrounding area plus getting the fastener way hotter than you can with a MAPP torch. Used it to remove all the fasteners that wouldn't come out with the battery powered impact tool on my 40 year old mast. Worked a charm and also used used it to get corrosion welded bolt out that passed through substantial aluminum castings on the self steering vane.

Having said the above, the hardest fastener to remove is not one that is threaded into aluminum but one 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. Have a couple of bolts in aluminum cleats that I've been trying to remove for a couple of years without success. The cleats were through bolted so I got them off the boat by removing the nuts but can't get the bolts out of the cleats.

The best thing other than the jumper cable trick was a battery powered impact driver. Used a small 12v Hitachi but most are 18v marketed in a package with a drill these days. They will get out many fasteners that won't yield to a simple screw driver. Biggest issue with mine was shattering the flat bits after only a few fasteners. Went through quite a few of the bits.
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Old 08-03-2015, 01:45   #8
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Re: Removal of stainless screws from aluminum and corrosion

[QUOTE=roverhi;1768504]You might try the jumper cable trick. Hook the jumper cables up to a battery in the normal way. On the other end, put a bolt in the postive lead clamp. Clamp the negative (black) as close to the offending bolt as possible. Touch the bolt in the positive lead to the head of the fastener. You are essentially setting up an arc welder. It will heat the fastener to a cherry red if left in contact long enough. It works really well as you are heating just the area of the fastener and not burning up the surrounding area plus getting the fastener way hotter than you can with a MAPP torch. Used it to remove all the fasteners that wouldn't come out with the battery powered impact tool on my 40 year old mast. Worked a charm and also used used it to get corrosion welded bolt out that passed through substantial aluminum castings on the self steering vane.

Having said the above, the hardest fastener to remove is not one that is threaded into aluminum but one 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. Have a couple of bolts in aluminum cleats that I've been trying to remove for a couple of years without success. The cleats were through bolted so I got them off the boat by removing the nuts but can't get the bolts out of the cleats.
QUOTE]

Sounds like a handy trick, albeit one I'd be cautious in using until I had a good feel for using it. Though the same idea works well to help to extract stuck wires used in stitch & glue construction.

Not that the cleats or bolts are worth much by now, or removing at this point, but you might try the Coca-Cola or Vinegar trick. Meaning, use a mild strength, semi-wicking, acid, to penetrate the area(s) built up by salts, & corrosion (oxides & mineral deposits).

It works with varying degrees of success to clean up the corrosion on & in battery cables, still hooked onto the terminals. Or at least once or twice, anyway. As much past that, I'm not sure how much of your battery cables you'd be dissolving.
And no, I'm not brave nor foolish enough to try & flush out such a brew with fresh water. I don't care to be a human ground wire. If we unhook the terminals, then that's another story.

But Vinegar might be a good bet on the cleats, were it not for aluminums abysmal location on the galvanic scale, & thus as an educated guess, it's less than stellar resistance to being gobbled up by the vinegar (Acetic Acid).
Still, given that you could throw the whole mess into a clear jar or bowl & thus observe the proceedings, with frequent hands on checks for progress, it'd be an interesting experiment.

And if someone wants to do a test run of vinegar vs. aluminum, it might help the OP figure out if such might be a viable tool to use in the fasteners conundrum.
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Old 08-03-2015, 01:46   #9
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Re: Removal of stainless screws from aluminum and corrosion

If the screw heads are proud, as in pan heads, you can carefully grind the heads off and remove the outer ring, then you'll have the screw shanks to vise grip out, with some penetrant.
If they are flush head screws, drilling is best.
Be nice to see what your working with.


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Old 08-03-2015, 05:24   #10
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Re: Removal of stainless screws from aluminum and corrosion

I am facing removing 2 screw holding a broken line stopper/rope clutch to a mast. Can't get at the fasteners easily to apply any liquids or BP blaster. I will probably simply drill them out and re drill new holes offset for the new ones if whats left of the screws can't be removed with a screw remover. That usually doesn't work.
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Old 08-03-2015, 05:46   #11
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Re: Removal of stainless screws from aluminum and corrosion

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Originally Posted by Sandero View Post
I am facing removing 2 screw holding a broken line stopper/rope clutch to a mast. Can't get at the fasteners easily to apply any liquids or BP blaster. I will probably simply drill them out and re drill new holes offset for the new ones if whats left of the screws can't be removed with a screw remover. That usually doesn't work.
I had a cleat that had the same problem. I drilled out the old screws and added helicoils.

As for the OP, the only thing that is guaranteed to work is heat. heated hot enough the oxide turns into sand and falls away. Heating is not always practical however. I've read that a 50/50 mix of acetone and auto transmission fluid makes an excellent corrosion release. I've had mixed results with stainless steel and aluminium corrosion however a cordless impact driver will be much better than a static load as it will have less tendency to shear the screw. I own an 18 V impact driver and a 10.8 V unit and, not surprisingly, the smaller unit is much more effective on screws and small bolts than the larger.
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Old 08-03-2015, 06:54   #12
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Re: Removal of stainless screws from aluminum and corrosion

Thanks people for the useful replies here.

As to the heat suggestion I was wondering why it would work as both metals would heat up and expand and it might be better to chill the screw and heat up the aluminium, but I checked and the thermal coefficients of expansion of aluminium is twice that of steel. So heating the area should open the join a little. That may explain why it works.

The screws are small and countersunk, so some options are not available to me like gripping it.

I have a manual impact driver, but with the screws being located next to a glass window I am hesitant to use it.
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Old 08-03-2015, 10:06   #13
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Re: Removal of stainless screws from aluminum and corrosion

Quote:
Originally Posted by poiu View Post
The stainless screws cause the aluminum to corrode and the screws seize up. Sometimes they come out with a bit of patience, drips of penetrating oil and a wait and maybe a tap with an impact driver. Sometimes they need drilling out. That's not fun.

I now have an aluminium window to re-bed with 15 stainless screws holding it down, many of which I can see are corroded. Before I go at it and turn it into a dog's dinner I thought I should ask how best to get the screws out. Would a cordless impact driver help? What is the best way to do it?
It usually is the aluminum that is corroded. Using a penetrant is a good idea. You are dealing with small screws in small holes and I suppose the port is still installed and you are trying to remove it. Most of the screws will probably turn out if you use the right sized screwdriver. Otherwise, try to grab the head with a good ViseGrip that still has sharp teeth.

When I reinstalled my ports and had to screw the retaining frames from the inside. I went with a size larger screw and used blue Loctite to reduce future corrosion from starting.

Using an impact wrench, manual or otherwise, might cause more damage, like breaking the glass.

Patience...is the key.
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Old 08-03-2015, 10:16   #14
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Re: Removal of stainless screws from aluminum and corrosion

I watched an outboard mechanic deal with stainless screws stuck in aluminum many times. He would use a torch to heat the aluminum and the screws came out with no problem. Yes the aluminum expands much more than the stainless.

When he reassembled it, he would coat the screws with Permatex 3. If the engines came back again, the screws would come right out with no corrosion.
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Old 08-03-2015, 11:57   #15
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Re: Removal of stainless screws from aluminum and corrosion

I use all the expletives and macho death threats I can come up with. Doesn't always work but I get the last word and feel better about my efforts. when they do come out use a tap or thread chaser to clean the female threads and recoat with teffgel or similar.
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