Undoing Loctite fixed screws

[rick]

I need to undo 4 x CSK stainless steel screws 3/8x24 UNF These are screwed into 6061 anodized billet aluminium.

Fixed by a Loctite (or similair) 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

[MrCheerful]

I would expect them to snap if you try impact. Heat will break up loctite, but it will be hard to get significant heat to the right point. A T bar driver would be favourite, trying forward and back till they come free. Otherwise drill the heads, remove the fitting and get mole grips on the remains.

[newshound]

IIRC it should soften at something like 150 C, and certainly by 200. Also at temperature, differential thermal expansion will be working your way. These temperatures won't soften the screw and should not affect the anodising. I wouldn't try to heat locally, I would cook the whole thing in an oven (assuming it will fit).

[Andrew Mawson]

Red hot poker (or preferably a copper bar) applied to the screw head. Once the Loctite is close to 100 deg C it will let go and can be undone.

Andrew

[rick]

Drilling not an option ... this is an assembled part - been replaced under warranty - have to send old one back - they have agreed to split it to make package much smaller ... but can't damage anything.

I have a T-bar so will use that .. I can apply heat direct to screw head but concerned aluminium will draw away the heat

[rick]

No this is effectively T shaped .... 48" long bar into a 18" long strut .... mortice & tennon style fits with 4 cross screws. 2 from each side.

[rick]

You think that would be better than a micro flame direct onto screw head (I can do either) Didn't think it would release at 100 thought it would be up around

3-400 at least. So maybe successful then.

I could also apply a heat gun to surrounding aluminium ... or do you think best apply heat only to screw head

[Peter Parry]

Heat works on all thread lockers. At 200 - 250 deg C the thread locker should be soft enough to allow removal of the bolt.

[rick]

Peter - do you know will it soften the ss screw or harm the anodizing that temp ?

From that link ... applying heat direct to screw face with my micro burner ...should be enough ... judging 200C may be more interesting .... time to dig out thermocouple & MM I think

[soup]

There are several grades of thread locker. Colours are for Loctite,if blue the screws should just unscrew with no heat, purple is the lightest grip of the lot only the red stuff should require heat .

Heat gun on the entire area plus your micro torch on the head should allow removal of red whilst the blue stuff should only need more torque (BUT DO NOT USE THE IMPACT GUN) whilst the purple will require more torque but not as much as the blue.

[Peter Parry]

Neither should be affected by that temperature.

Some sources recommend touching a Beeswax rod to the screw head when up to temperature. The wax melts and finds its way into the thread making it easier to remove.

[Robert]

Stainless is a relatively poor conductor of heat - thats why ss teaspoons dont burn you when you stir hot liquids etc. Might be better trying to apply heat to alloy around thread.

[newshound]

I'd go for heat gun to surrounding metal, to get benefit from the thermal expansion too. You don't want to over-heat the polymer to the extent that it turns into a carbonaceous char, with some mechanical strength.

[newshound]

Good point. Also Aluminium is a *good* conductor, so this way you will get the temperature up all the way to the root.

[rick]

I had thought that screws are surrounded by huge chunk of aluminium ...it might soak away heat ... but will heat up both.

[rick]

Unfortunately until I get first one out - don't know what they used ... hoping it's not red. I only normally put blue on screws I need to remove in future.