Posted on 03/12/2017 9:53:29 PM PDT by Windflier
It appears that's going to be the key to getting these bolts out.
My plan is to soak the bolts with a high grade penetrating oil overnight, then gently warm the aluminum rods they're screwed into while applying cold to the bolts themselves, just before I try to turn them out.
Along the way I'll try the tapping trick to try and break the corrosion bonds.
I'll get some pics up in a follow-up post, so folks can see the project. I'll scan back through here and ping everyone who offered their advice.
Much appreciated!
At 81 years I use a gray beard, it doesn’t work for these body.
;^}}
Um, yeah, I was inaccurate there. It’s not a true chemical bond of aluminum to steel. But is there not some adhesion of the corrosion products to both substrates? I can think of few cases of corrosion I’ve seen, where removal to “bare metal” does not involve force / scraping / sanding. It usually doesn’t just rub off to bare metal with one’s (unaided) finger...
There is also a frictional effect too, no? That is, the surfaces become pitted, so one has to shear the corrosion products to break free. It would be somewhat similar (but not exactly so) to the effect of fine grit in the threads.
My other question is, does the penetrant actually break down the corrosion products? I would think not, but I could be wrong.
There may be a wedging effect and seizure taking place from the tapered bolt being squeezed/tightened down into the softer aluminum seat, something like the seizing effect that occurs on a tie rod end getting stuck in its seat. Modest heat applied to the aluminum around the bolt should address this issue.
Ping me too when it’s solved. I’ve been lurking but am interested. Thanks
Some of the corrosion products usually adhere pretty tightly to the base metal: i.e. Aluminum Oxide to Aluminum, and Iron Oxide to Iron. They do not cross-adhere.
Increased volume is the major effect, but the surfaces become less smooth and there is an increase in friction.
The third question is an ambiguous one. The penetrant does not chemically break down the corrosion products, but it does promote a physical breakdown.
With steel in contact to aluminum, the aluminum will preferentially corrode, acting as a sacrificial anode for the steel.
Will do, Mom.
Right. In that case, is the aluminum corrosion product aluminum oxide? That's pretty hard stuff, or at least the particles of it are....
Thank you, corporal Hicks. BTW i mention this as an option for Detroit quite often.
CC
I have experienced this often while working on motorcycles.
The best results I have gotten is by using penetrating oil then using an impact driver with a heavy dead blow hammer.
I have never done that, What I do know is that if I have a rusty steel surface, most lubricants will help the rust break down into smaller particles if I apply some shear forces. Both this effect and the lubrication is what makes penetrating oils work.
I can think of several potential mechanisms. The study of surfaces interacting, wear and lubrication is called Tribology. The boys who study that can probably give you a better answer.
Use the acetone/ATF mix instead of PB Blaster. The results are superior.
...is the aluminum corrosion product aluminum oxide? That's pretty hard stuff, or at least the particles of it are...
You are correct. Aluminum oxide is the corrosion product and it is very hard. Aluminum oxide particles are commonly used as an abrasive. Corundum is one common name for the abrasive. Hardness does not necessarily mean high friction. Small aluminum oxide spheres are a standard item of commerce and I have used them as ball bearings and as spacers in various mechanisms. For mechanical uses, specify "synthetic ruby spheres". The red color makes them more visible and easier to assemble. Clear ones are known as "synthetic sapphire" are water white and crystal clear. If optical properties are important, they are the ones to use.
In any event, the material makes great ball bearings in the right application. So hardness is not necessarily a bad thing.
bkmrk
Right - I have heard of ruby and sapphire bearings, but never used any in anything I built myself. My experience with Al203 is in abrasives apps, and in a few cases of undesired corrosion that went far past the usual protective surface layer on aluminum.
I would certainly expect that very hard “grit” that has “grown” in the threads doesn’t help matters, if one wants a machine screw or bolt to come out...
Tribology, eh? If someone had run that word by me, prior to your post, I’d have figured it was the study of small, furry, fictional creatures from the future. (Just kidding!)
Thanks for the heads up on the acetone/ATF mix. I have an application, as soon as the weather gets a little better!
Also thanks to all for the info. on this thread. It encourages me to ask similar questions here in the future.
Thank you for the suggestion. I can’t get to my project this weekend, but I’m blocking out next weekend to get ‘er dun.
Well, most Freepers never do tell how these “help me thread” problems are resolved. No matter how many times they say they will.
I figure their wives must fix it for them and they don’t want to tell...
(Someone bumped that other thread.)
I fell you, if I'd resolved my problem, I surely would have posted that resolution to the thread.
In a nutshell, I tried about half a dozen of the best suggestions on the thread, and still was not able to free the bolts frozen in my machine. I even reached out to the manufacturer for help. Their chief machine tech told me that I'd already done everything he would recommend.
The consensus opinion at this point, is to pull the entire rear exit assembly and replace it with a new one. That's a repair that I absolutely CAN do.
Thanks for following up with me.
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