Heating prop shaft to remove key

[kalanka]

I am trying to remove a very stubborn 1/4 inch brass key in the keyway of a 1 inch stainless steel propeller shaft.

So far it has resisted repeated applications of penetrating oil, tapping with a drift, pliers, ice and heating fairly gently with a blow lamp.

I feel that the next step is to heat it more strongly. Am I likely to damage the heat treatment of the shaft if I heat the key to dull red?

Any other ideas?

Thanks

 

[JumbleDuck]

I am trying to remove a very stubborn 1/4 inch brass key in the keyway of a 1 inch stainless steel propeller shaft.

So far it has resisted repeated applications of penetrating oil, tapping with a drift, pliers, ice and heating fairly gently with a blow lamp.

Brass has a higher coefficient of thermal expansion (~18.7) than stainless (~17.3 for 304, ~16 for 306) so heating will be making it tighter. Suggest you try freezing - dry ice is surprisingly cheap. I use www.dryice.co.uk.

The greater expansion of brass than steel when heated was crucial to the conviction of Arthur Rouse: https://en.wikipedia.org/wiki/Alfred_Rouse#Murder

 

[vyv_cox]

I agree with JumbleDuck's post but to answer your question, 300 series stainless steels cannot be hardened by heat treatment, only by work hardening. Most shafts are in the normalised condition, implying no work hardening (unlike many fittings that are cold stamped) so heating will not harm them.

 

[colhel]

Two ideas spring to mind either drill and tap say about M5 and use a screw to give more purchase. Or if you're replacing the key anyway just drill a long it's late a few holes to weaken it allowing the key to crush.

 

[fisherman]

Drill and tap right through, one end, drive it off with a bolt. Mine are supplied like this.

 

[GrahamM376]

Hacksaw a slot in one end against the shaft, just wide enough to insert screwdriver. You should then be able to lever it up with a spacer under the screwdriver

 

[PlankWalker]

Hacksaw a slot in one end against the shaft, just wide enough to insert screwdriver. You should then be able to lever it up with a spacer under the screwdriver

This is exactly what I did this winter plus boiling water and rags, IT WORKED!

Plank

 

[Poignard]

Hacksaw a slot in one end against the shaft, just wide enough to insert screwdriver. You should then be able to lever it up with a spacer under the screwdriver

+1

 

[dom]

Brass has a higher coefficient of thermal expansion (~18.7) than stainless (~17.3 for 304, ~16 for 306) so heating will be making it tighter. Suggest you try freezing - dry ice is surprisingly cheap. I use www.dryice.co.uk.

The greater expansion of brass than steel when heated was crucial to the conviction of Arthur Rouse: https://en.wikipedia.org/wiki/Alfred_Rouse#Murder

Interesting; and two quick questions if I may:

1. I know oil doesn't freeze as such but becomes steadily less viscous as it cools. Is it possible that at circa dry ice temps any residual oil on the bolt will become less viscous to the point of a tar like consistency which could jam the bolt?

2. Is there any risk of cracking a housing or something using this technique?
​

 

[Heckler]

I am trying to remove a very stubborn 1/4 inch brass key in the keyway of a 1 inch stainless steel propeller shaft.

So far it has resisted repeated applications of penetrating oil, tapping with a drift, pliers, ice and heating fairly gently with a blow lamp.

I feel that the next step is to heat it more strongly. Am I likely to damage the heat treatment of the shaft if I heat the key to dull red?

Any other ideas?

Thanks

A pair of wire side cutters to grip and lever or a screwy to tap and lever it out.
Stu

 

[JumbleDuck]

Interesting; and two quick questions if I may:

1. I know oil doesn't freeze as such but becomes steadily less viscous as it cools. Is it possible that at circa dry ice temps any residual oil on the bolt will become less viscous to the point of a tar like consistency which could jam the bolt?

2. Is there any risk of cracking a housing or something using this technique?
​

1. That might be a risk, but I don't know if oil becomes adhesive as well as viscous. I used to do a lot of work with stuff a LOT colder than dry ice, and we never oiled or greased anything for those conditions.

2. Wouldn't have thought so. Dry ice is only 100^oC below room temperature, so it will only cause the same sort of strains and stresses as you'd get 100^oC above room temperature, but with tension and compression reversed.

 

[vyv_cox]

2. Is there any risk of cracking a housing or something using this technique?

300 series stainless steels are ductile down to cryogenic temperatures. Everything in LNG production equipment is made from them, pipework, valves, compressors and tanks, for this reason.

 

[JumbleDuck]

300 series stainless steels are ductile down to cryogenic temperatures. Everything in LNG production equipment is made from them, pipework, valves, compressors and tanks, for this reason.

At proper low temperatures some stainless undergoes a shear transition to martensite which bumps its strength up by (iirc) 30% or so, which is why the tensile and bend test rigs I designed for use in liquid nitrogen were made of stainless, and why I was using them to test stainless clad copper wires for cryogenic use. I can't remember which grade of stainless now - it was a long time ago.

Thread drift - dontcha love it?

 

[dom]

Thread drift - dontcha love it?

True, then again thanks to you and Vyv for such detailed answers

...it really helps one to laterally think about how to go about solving a problem like this.

 

[vyv_cox]

At proper low temperatures some stainless undergoes a shear transition to martensite which bumps its strength up by (iirc) 30% or so, which is why the tensile and bend test rigs I designed for use in liquid nitrogen were made of stainless, and why I was using them to test stainless clad copper wires for cryogenic use. I can't remember which grade of stainless now - it was a long time ago.

Thread drift - dontcha love it?

Not sure whether the difference of 30 degrees C between N2 and LNG boiling points is significant but I never saw any evidence of brittleness in any LNG equipment. The oldest ones, in Brunei in our case, must be 40 years old by now. (Just to drift the thread even further )

 

[JumbleDuck]

Not sure whether the difference of 30 degrees C between N2 and LNG boiling points is significant but I never saw any evidence of brittleness in any LNG equipment. The oldest ones, in Brunei in our case, must be 40 years old by now. (Just to drift the thread even further )

It might have been just a jump in yield stress, which was all I cared about. Memo to self: find and reread notes.

 

[CAPTAIN FANTASTIC]

Drill and tap method is the best, then insert a machine screw to lift the key out; actually, many keys come with a threaded hole for that purpose.