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Loctite on shafts

How to break the bond

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mike robinson 207/12/2009 12:25:46
38 forum posts
32 photos
I am making a fabricated mill engine crankshaft using silver steel for the crankshaft and big end with mild steel for the crank webs. The Loctite I have used is very strong and sets very quickly. Too strong and too quickly!!! It bonded before I could get the webs in the correct position.
Before I really mess it up whats the best way to destroy the bond so I can disassemble and try again. Need to make sure I dont heat treat the silver steel,,,,, is a domestic oven ok ? Whats the minimum heat? I dont want to use a blowtorch if I can help it. Is there another way ?
Thansk for the help
Mike
keithmart07/12/2009 13:08:50
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165 forum posts

Hi heat is the answer, or you might try acetone (nail varnish remover).


The amount of heat required should not worry the silver steel. 


You could also email the locktite site, as they are normally very helpfull





mike robinson 207/12/2009 13:15:33
38 forum posts
32 photos
Hi thanks for the confidence boosting comments - will try it tonight
D.C.Clark07/12/2009 13:27:48
16 forum posts
8 photos
What flavor Loctite?  They make many different types of adhesives.  Some will release at fairly low temps: < 450F ( 230C ) others will not.
 
Does it say "Threadlocker" on the label?  Loctite red or green Threadlocker will release with heat.  Blue should break pretty easily with a wrench.
 
All the info is available at http://www.loctiteproducts.com/  They are also very helpful and responsive to inquiries, in my experience.
 
A counter-top toaster oven is a handy thing to have in the shop.  I use one to release adhesives, melt machinable wax and cerro alloys.  Coat mild steel parts with motor oil and bake, for a nice rust resistant patina.  Dry things.
 
Give your wife a new one for Christmas, and take the old one. ( Nota Bene:  It is important to perform these steps in the given order. )
 
One of those little palm-sized refillable butane torches is also useful for releasing adhesives when you just want a quick, point application of heat.
 
It is vital to have excellent  ventilation.  Heating cyano-acrylates, especially,  is risky business how ever you do it.  I take it outdoors and stay upwind of the work.
 
 David Clark in Southern Maryland, USA
mike robinson 207/12/2009 14:26:10
38 forum posts
32 photos
Its 648 retaining compound. The clearence on my parts are minimal (transition fit) and the lower clearance speeds the cure time. Great if your fast enough. Lesson learned. I will try some a la carte cooking tonight with the windows open. Appreciate the advice 
Martin W07/12/2009 18:38:02
940 forum posts
30 photos
Hi Mike
 
Just been on the Loctite site re 648 retaining compound. The data sheet says heat parts to about 250C then dissemble when hot. Then if required clean by soaking in Loctite solvent and use a wire brush to remove any residue, presumably a brass brush would do and it shouldn't mark the steel.
 
This compound is not a cyanoacrylate based material but a Urethane Methacrylate based product. Even so its probably best not to take a chance by breathing the fumes giving of during heating.
 
Hope this helps and good luck.
 
 
 
Martin
Martin W07/12/2009 22:56:17
940 forum posts
30 photos
Mike
 
Looked at the data sheet again and should you decide to give it a second try with Loctite 648 you can delay the setting time by cooling the parts to be joined. The graph indicates that at 22C the bond reaches 5% of full strength in 5 minutes whereas at 5C the bond reaches 5% of full strength after 1 hour, these figures are for steel/steel joints and the time taken to reach 100% bond strength of other metals/finishes vary. These figures are based on a 0.05mm gap.
 
Looks like the way to go would be cool, assemble, adjust and then warm.
 
Cheers
 
 
Martin
Tony Martyr08/12/2009 09:26:30
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226 forum posts
45 photos
Mike
I agree with Martin - when I built a camshaft where each lobe was loctited with 648 onto the shaft I always put the shaft in the freezer overnight. Not only does it give you greater adjustment time but it gives you a greater initial clearance, so long as the male part has been left at ambient temperature of course!
Tony
mike robinson 208/12/2009 21:00:05
38 forum posts
32 photos
Success, the crankshaft components are now apart without damage and cleaning up was quite easy. After some chef style work in the kitchen it soon became blowlamp time. I am really impressed with this 648 stuff, its so strong. Appreciate the idea about cooling down in the freezer, time to get my jigs sorted and practice a few dry runs agaist the clock. Thanks to all for the welcome suggestions. Mike  

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