MAPP gas and aluminum: danger of melting?

[bill good]

Mouse Milk. Leave over night & then unscrew.

Regards

[Mikado]

Originally Posted by zstine

I think that vinegar is something to try and heating with electric is another option. In fact, there are induction heaters on the market for this purpose if the battery arc welder method scares you. If you are worried about melting the AL with MAPP, use a cheap propane torch as it is cooler and probably impossible to melt the AL. Another thing to alleviate your fear is to hold some Lead against the AL as Lead melts at just over 600F, way below AL's melting point.
good luck

2nd this. Go purchase a $20.00 propane torch and work the heat/WD40 for a while before going to the drill and tap option.

[Mikado]

And when you put it back together use anti-seize !

[hsi88]

I see people recommending WD40. WD40 repels water but is not a penetrating solvent. It will work sometimes, but will not touch the penetrating capabilities of PB Blaster or Kroil (or even straight acetone). I restore old motorcycles (mainly Brit bikes like Nortons, Triumphs). And steel screws set into aluminum engine cases are often fused after a few seasons of sitting outside. I end up drilling out at least 2-3 screws with carbide drill bits on every motor.

I have used just about everything there is. Freeze sprays, etc. For screws, I prefer Kroil and a hammer driven impact driver (the one I still have from the 70's is my favorite). I have also used a tool from Japan called Vampliers. Look it up on Amazon. Vice Grips can sometimes be used, but there has to be enough screw head to get on. If everything else fails, buy a small set of carbide drill bits (you will dull regular drill bits) and some "easy outs". Tools of last resort.

[Jim Cate]

I notice several folks have suggested various combinations of heat/cool/impact for removing these screws. When in similar situations, I've always attempted the extraction while the assembly is still hot... as soon after applying the torch as I can get going. It has usually been successful if I could get it hot enough.

I don't see the advantage of letting it cool down before extraction... that way you loose the advantage of dissimilar coefficients of expansion. Have I got this wrong?

Jim

[Wotname]

Originally Posted by Jim Cate

I notice several folks have suggested various combinations of heat/cool/impact for removing these screws. When in similar situations, I've always attempted the extraction while the assembly is still hot... as soon after applying the torch as I can get going. It has usually been successful if I could get it hot enough.

I don't see the advantage of letting it cool down before extraction... that way you loose the advantage of dissimilar coefficients of expansion. Have I got this wrong?

Jim

I don't reckon you get too much wrong Jim

I believe (but don't know) that cycling the heat/cold method helps separate the corrosion bond. Especially if you can apply heat to the body and then shock cool the faster thus using the dissimilar coefficients of expansion to your advantage.

Then apply the penetrating fluid of choice which now has a chance to move into the hopefully newly created void.

Then apply heat again to body immediately prior to trying the extraction - as your method suggests and for the reasons you mention.

Once again I plug the benefits of Reducteur H 72. I duuno whats in it but I suspect it has a chemical effect of the corrosion bond - I do know that it works remarkably well. I have used it as a last resort on steel fasters in aircraft Al structures where applying heat is just not an option . While others are reaching for the drill, I'll reach for H 72. In the past Mouse Milk was all you could try but the H 72 is a quantum leap forward.

[captlloyd]

Originally Posted by Jim Cate

I notice several folks have suggested various combinations of heat/cool/impact for removing these screws. When in similar situations, I've always attempted the extraction while the assembly is still hot... as soon after applying the torch as I can get going. It has usually been successful if I could get it hot enough.

I don't see the advantage of letting it cool down before extraction... that way you loose the advantage of dissimilar coefficients of expansion. Have I got this wrong?

Jim

Well, there is no right or wrong. In this case of dissimilar metals your approach might work best. Steel on steel, maybe heat-cool is better. I don't think anyone has mentioned the forces of impact, in combination with various fluids mentioned. Sometimes a few raps with say a small drift or punch will go a long ways in helping to break the bond.

[roverhi]

Originally Posted by Jim Cate

I notice several folks have suggested various combinations of heat/cool/impact for removing these screws. When in similar situations, I've always attempted the extraction while the assembly is still hot... as soon after applying the torch as I can get going. It has usually been successful if I could get it hot enough.

I don't see the advantage of letting it cool down before extraction... that way you loose the advantage of dissimilar coefficients of expansion. Have I got this wrong?

Jim

If there is considerable difference in thermal expansion characteristics of fastener and what it's frozen in, tackling removal while still hot has merit. Using a cooling fluid to selectively cool one metal over the other probably has more effect. The reasoning behind letting things cool off is the heating and cooling may break the corrosion bond and/or allow penetrating lubricant to wick into the material interface.

[Jim Cate]

Originally Posted by roverhi

If there is considerable difference in thermal expansion characteristics of fastener and what it's frozen in, tackling removal while still hot has merit. Using a cooling fluid to selectively cool one metal over the other probably has more effect. The reasoning behind letting things cool off is the heating and cooling may break the corrosion bond and/or allow penetrating lubricant to wick into the material interface.

Peter (and others), the subject was s/s fasteners in an aluminium base, and in this situation there is a large differential in expansion coefficients, and thus my ideas. I agree that the combination of heating the base metal and then cold-blasting the screw might well add to the differential... I'd like to try that next time I'm frustrated by a frozen screw.

And re the Reducteur stuff: I've used it successfullly on rusted steel/steel interfaces. It is supposed to attack the iron oxides in the rust chemically, and seems to do so. I'm thus surprised to hear that it works on the Aluminium oxides and hydroxides involved in the subject cases. I've got a can and will give it go... hoping for a pleasant surprise!

What I really hope is that eventually I will have some form of anti-seize on every damn s/s screw on the boat, and that I can retire my impact wrench!

Jim