Removing Loctite fixed screws

I need to undo 4 x CSK stainless steel screws 3/8x24 UNF
These are screwed into 7000 series anodized billet aluminium.
Fixed by a Loctite (or similar) thread lock
The heads are imperial allen socket.
From past experience I know that even non-Loctite ones can be difficult
to remove, the screws being stainless are relatively soft and they will
round out easily.
Any thoughts over best approach .... I could leave a soak in Plus-gas
penetrating oil, but unsure if that will help .... or I could apply heat.
If the latter then how much to help break Loctite, without damaging
anodized finish or softening screw. .... I have a micro propane torch so
could apply localised heat ...
I also have a pneumatic impact wrench .. I could also use that rather
than just allen socket in ratchet handle
Reply to
rick
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I don't know how much heat to apply - rather, I don't know the temperature that is required, but heat it has to be, unless they've found something new.
IIRC Loctite is acrylic.
I think the drill (NO! Not the drill!) is to heat it and then use the impact wrench *lightly* if that can be done with the pneumatic version. Make sure the hexagon bits are correct for the job: even a loosely-fitting hexagon drive can make a mess of the contact areas.
Reply to
RustyHinge
Maybe I need to buy a new hex bit ..
Reply to
rick
Once cured loctite anaerobic adhesives won't dissolve in any of the usual solvents. The permanent stuff must be heated to 450F to break down enough for the fastener to be removed. That's probably too hot for your 7075, you don't want it to lose any of its temper. What I would do is try penetrating oil and heating the aluminum as hot as possible without risking the los of temper. The aluminum will expand away from the steel fastener and this may allow the penetrating oil to wick in and break the bond. Eric
Reply to
etpm
What temp is it safe to go to without affecting temper (or anodized finish)
I had thought about just heating the face of the screw to such a temp.
Reply to
rick
I'm not an expert on heat treating aluminium but I was recently asked about filling some dings in an aluminium bicycle frame made of 7005 and the maker mentioned that was artificially aged to strengthen the frame after welding at 315C (600F). It's not like steel where heating above certain limits will temper the alloy, rather it has to be heated much higher to put various elements into solution then quenched to keep them there leaving it in a soft state, the artificial aging allows those elements to precipitate out and harden the alloy. The thought on the bicycle frame was to use a low temperature solder to fill the dings before powder coating as none of the powder coaters were confident the powder coat fillers would work in the application.
Regarding heating the fastener to soften the loctite, earlier I looked up the technical data on 603 regarding fits but noted it mentions heating to 250C for dismantling and doing so while hot.
Reply to
David Billington
snipped-for-privacy@whidbey.com on Tue, 06 Dec 2016 09:26:28 -0800 typed in uk.rec.models.engineering the following:
The trick is to have the heat expand the aluminum 'faster' than it does the steel screw. Or, to figure a way to chill the steel screw enough to break the loctite. Thermal expansion is a tricky ting to work with.
Reply to
pyotr filipivich
Back in the day I had a similar dismantling problem, spoke to Douglas Kane ( Loctite Agents ) and was told they use a hair drier as it softens/weakens the loctite enough without risking damage to componants. Loctite show graphs of temp versus strenth at different temps. Even boiling water will lower strength by 30 to 60 % depending on grade.
Regards Colin
Reply to
Colin Docherty
I suppose I could put heat on aluminium with heat gun ... directly over where it is threaded - and then spray freeze spray onto screw face
Reply to
rick
OK I have an electric heat gun .... so this might be better approach
Reply to
rick
rick on Wed, 7 Dec 2016 12:38:01 +0000 typed >> snipped-for-privacy@whidbey.com on Tue, 06 Dec 2016 09:26:28 -0800 typed in
Might work. "Try it and report back to the class." :)
Reply to
pyotr filipivich
Make sure that you use a good quality allen key, such as either an Unbrako or Bondhaus make. I would use a T handle allen key as it will allow you to apply downward pressure to keep the key in the socket. Even a slightly slac k key will start to round out a soft stainless screw.
As for heating could you get the item in a domestic oven?
John H
Reply to
John H
Why not try connecting a variable voltage power supply to the screw and bil let and slowly increase the voltage so that the screw temperature increases (if there is some resistive continuity). Make a handle so that a torque c an be applied during the heating process.
Reply to
lordgord1
Unfortunately you will be expanding the screw into the aluminium, making it a tighter fit - however, it might have broken the Loctite sufficiently to let it move once it cools.
Now if you had a tiny liquid nitrogen dispenser...
Reply to
RustyHinge

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