Severe galling. Stainless in Aluminum

[GordMay]

Originally Posted by Don C L

What Gord recommends is also called an "Easy Out;" a reverse thread screw that would go into the head of the screw there after you drill it out a bit...

Originally Posted by GordMay

...
I’d try using a reverse twist [left handed] drill bit, just smaller than the bolt diameter, and counter-clockwise [reverse] drilling; and most of the time, the S/S bolt will come out, while drilling [like with a tapered screw extractor].

Actually, I was recommending a conventional drill bit, except with a reverse twist, and smaller than the fastener.
An "Easy Out" is a brand of tapered screw extractor.

[Don C L]

Originally Posted by GordMay

Actually, I was recommending a conventional drill bit, except with a reverse twist, and smaller than the fastener.
An "Easy Out" is a brand of tapered screw extractor.

Ah, my mistake, thanks.

[NorthCoastJoe]

I would use this and if it fails go to cutting and drilling.

https://www.jbtools.com/lisle-30750-...8aAtUuEALw_wcB

[jeanathon]

Originally Posted by thinwater

The other thing I have found very helpful, if you have more time and if the threads do not have grease or penetrating oil in them, is a weak acid, such as lactic acid (CLR). A long soak will dissolve the corrosion products. I think it actually works better in many cases, but it takes a day or so to penetrate. If it does not work, let it dry and use penetrating oil. But if you have used oil this won't work. It has to be first.

I started wondering if CLR would dissolve the oxide, and tested it on some. It dissolved it well, and I plan on using it on two screws that are still in the mast that I left proud.

Originally Posted by Bowdrie

A friend had to replace the mounting saddle of his vang, it was curved-to-fit the mast and fastened by eight 1/4-20 hex head machine screws.
Four of the screws came out, the other four broke their heads off.
Thus, with the mount removed there were four "studs" of machine screws sticking out of the mast with little chance of success of removal.
We went to plan "B".
Took a 12V battery and jumper cables, one cable went on the mast step, the other was touched to the "stud".
When the stud started to "glow" the current was stopped and vice-grips were applied, the broken machine screws then came out with little force needed.
Caution: should you try this, completely enclose the battery in a soaking wet beach towel/blanket, a procedure as this has caused battery explosions on occasion.

That sir is just gangster!


Now for the rest of the story. The two screws holding the motor on did not have near as bad corrosion from being on the inside of the mast as the 4 screws on the outside. I believe the penetrating oil helped remove friction from where the shoulder of the screw contacted the motor flange. I put an allen wrench in the screw head then clamped vise grips on the head so tightly you could not remove the wrench. It may have been the first time I did not round out the head of the damn things. Thanks all for your suggestions.

[barnakiel]

soak soak soak


there is a special liquid for softening SS bolts in alloy plates, but I found people use soda or dilluted hydrochloric with good results


the engine possibly just needs new brushes ? or maybe a basic rewinding job ? both easily done by your local garage


mind what holds the screws may be not the deposits (aka white death) but rather ill-applied loctite


if you destroy the threads in the alloy part (this is likely) you will have to have the plate re-threaded and new, bigger bolts/screws for the engine - you may be able to find monel fasteners and you may use the Boeing or the duralac paste to avoid further corrosion on the SS alloy front


b.

[Norman_E]

Stainless steel screws in aluminium are bad news unless they were put in with a coating like Duralac. If seized in place penetrating oil has little effect. I have had success by immersing the part in boiling water. Mild acids, e.g. citric acid may help, and I have even seen Coco Cola suggested. If all else fails you just have to drill the bolt out. At least socket head screws help you to centre the drill.

[sinnerman]

All of the above, plus use a heat gun to heat the screw.

[frank huybers]

the best thing you could do to remove stainless steel bolts out of an aluminium mast is welding an nut on top of the blocked screw take a nut from where you could wld from the inside M8 M10 or M12 if your welding rot get stuck on the nut leave it for a few seconds the passing current will heat up the blocked treat and and you will be able to anticlockwise the nut with the bold you even will not damage the original treat in the aluminium keep welding on the nut until she is red hot i did many repairs like this on mast equipment
good luck water sailing">Blue water sailing

Originally Posted by SailingHarmonie

Just to be clear, this is NOT "galling". Stainless threads in aluminum do not "gall". It really DOES matter what is happening here, because the approach to repair is very different.

"Galling" usually happens on a boat when stainless threads run on stainless threads under very heavy load. The chromium oxide layer is rubbed off, and the pure metal is directly in contact on the male and female threads under very high pressure, and with friction generating high local temperatures. The two pieces of metal "cold weld" together. They essentially become one piece. This happens only during assembly, and not over time. There is NO fixing this. No amount of magic mystery oil or any other technique will un-weld the parts. They need to be cut, or drilled to separate. This can be easily prevented by using a good thread lubricant.

The locking together of stainless and aluminum is a completely different thing and is due to galvanic corrosion of the aluminum that is in contact with the stainless steel. This occurs over time, and in contact with slat water. The resulting aluminum oxide is very hard, and occupies more space than the original metal, making removal extremely difficult.

I have never found the application of any oils to be very helpful in this case. If possible, repeated heating (VERY HOT) and cooling of the parts can usually break free the grip. Almost always, if you can unscrew the stainless fastener, the aluminum threads will have corroded to the point that they are no longer suitable for load bearing fasteners, so a heilcoil is going to be needed no matter what.

When you reassemble, do use TefGel or similar product. When installed this way, I have always been able to easily remove stainless fasteners in aluminum with hand tools after 15 years of salt water exposure.

[Monte Cresto]

Food for thought: When reinstalling stainless screws into aluminum I
use "Alumalast" on the threads and haven't had corrosion problem for
over 30 years. I periodically recoat screws for accessibility.

[sinnerman]

Originally Posted by frank huybers

the best thing you could do to remove stainless steel bolts out of an aluminium mast is welding an nut on top of the blocked screw take a nut from where you could weld from the inside M8 M10 or M12 if your welding rot get stuck on the nut leave it for a few seconds the passing current will heat up the blocked treat and and you will be able to anticlockwise the nut with the bold you even will not damage the original treat in the aluminium keep welding on the nut until she is red hot i did many repairs like this on mast equipment
good luck Blue water sailing

This is exactly how mechanics remove broken bolts/studs on automobile engine blocks, exhaust systems, suspension components etc..

cheers

[gregjm]

Jean....machinist here and this method works almost all the time.
I use a jewelers oxy-acetylene torch and heat around the bolt area but not the bolt. That causes the parent metal to swell very quickly. Propane and butane torches do NOT generate enough heat fast enough. Speed is the key. Next, the aluminum corroded granules get locked in the threads so you need to take advantage of the heat and slowly loosen and tighten the fastener a little at a time....like 1mm. You will notice with more heat that your distance moved will slowly increase as you break up the corrosion into dust where it will get into the thread grooves but can still be turned. Every boat should have this small inexpensive torch on the vessel. It heats to 5,000 F. so things get done quick. Cutting, soaking, manhandling and drilling is just a waste of time. https://www.amazon.com/Oxygen-Acetyl...s%2C174&sr=8-3

[Lee Jerry]

Originally Posted by gregjm

Jean....machinist here and this method works almost all the time.
I use a jewelers oxy-acetylene torch and heat around the bolt area but not the bolt. That causes the parent metal to swell very quickly. Propane and butane torches do NOT generate enough heat fast enough. Speed is the key. Next, the aluminum corroded granules get locked in the threads so you need to take advantage of the heat and slowly loosen and tighten the fastener a little at a time....like 1mm. You will notice with more heat that your distance moved will slowly increase as you break up the corrosion into dust where it will get into the thread grooves but can still be turned. Every boat should have this small inexpensive torch on the vessel. It heats to 5,000 F. so things get done quick. Cutting, soaking, manhandling and drilling is just a waste of time. https://www.amazon.com/Oxygen-Acetyl...s%2C174&sr=8-3

This sends up red flags to me. Maybe it's OK, but I'm not sure.

First, aluminum melts around 1200 degF, so that is a concern. Especially in a thin-walled mast.

Second, not sure what alloy the mast is, but it's likely a 6000 series. Heat-treatable alloys, like the 6000s, lose ~1/3 of their strength in the heat affected zone during welding. Why wouldn't that apply here?

[Disailor]

I've always had success with the following: Soak with PBlaster. Sometime keeping it wet over 3 or 4 days. Helps if you can apply the PBlaster to the threads on the back side. I use a propane torch on hi and Heat the aluminum (it will take while). I also use a tool to alternately tighten and loosen the screw. Once movement is about 1/4 turn gradually increase pressure to unscrew.

[Rucksta]

This is a tip I picked up from a welder building plate boats.
Technique was used for localised stress relief in MIG welded panels.
He believed the alloy was still self annealing using this process.

Soot the work with a low oxygen flame.
Heat with a clean flame until the soot starts to burn off.

If continued heat is applied the burnt off soot will reveal clean alloy with a light straw colour.

The alloy is about to turn into a blob.

[gregjm]

Lee Jerry....

Aluminum also has a high heat coefficient and the heat dissipates out quickly which is why it requires a lot of heat quickly. Extruded masts are not generally heat treated and having owned a machine shop and doing this work for years I know what works. It is quite easy to do a ball rebound test on the material if it concerns anyone to check the hardness. You're making far too big a deal out of this without a doubt which is generally why I don't get involved in these type of discussions on forums. Go do some experimental R&D to satisfy your doubts. We did this stuff for almost 50 years and a lot with U.S. Navy scrutiny. The original poster can do what he wants, I studied the setup problem and it would resolve quickly. Amateurs have a much harder time drilling stainless out than what I propose.