Dent removal method for tubing

[Guest]

Today I am working on straightening round and streamline tubing pieces.

As I worked I recalled that a few weeks ago someone, I am told it was Tim, made a post regarding fixing dented oil sumps by pressuring the sump with air and heating the dents.

Well I tried that on tubing, both small streamline (about 1.5") and some 1.5" round as well.

Simply amazing!

The round had a dent near a cluster - 95% gone now.

The streamline had a 15 degree bend and a dent - straight now and no dent.

Amazing!

In hindsight I can see it would have been easier if I had a helper apply the air because I applied it with my right hand using a blow gun to a close fitting hole and duct tape of course while I heated with a torch in my left hand.

Or I could have made a nice set up with some fittings and clamps but what I did worked.

Thanks Tim!

My dilemma now is whether I should sleeve what I fixed. There is no dent but I did straighten.

I plan to try a lift strut later today or tomorrow.


Dave R

[PA1195]

Re: Dent removal method for tubing

I may have mentioned this elsewhere, but when I helped restore my former PA-11 I applied full compressor air to the bare fuselage. Was looking for tubing leaks and areas weakened due to corrosion. Found same right now! Weak spots simply blew away metal and could then be repaired. Eventually it held at least 90 PSI. Never knew that heat could be applied to un-dent a section.

Most fuselages have rear drain holes so I stuck the compressor's air gun to them rubber tipped to seal air leak. After sealed we pumped anticorrosion Stits Tubeseal into the fuselage here and there.

Gary

[Nefj40]

Re: Dent removal method for tubing

That was Tim and oil tanks.

[Hank Jarrett]

Re: Dent removal method for tubing

Be VERY careful not to damage the heat treat of high strength materials with this method! You probably won't have too much problem with welded assemblies since they are designed to tolerate heat affected areas around welds, but it is NOT a good idea for machined parts without considering strength loss in the heat zones. I have used it with great success for parts like Oil kidney tanks and their service tubes but the heat will REALLY screw up the flange if it gets to it. You need to bolt the flange to a heavy plate to keep it straight and may need to torch anneal it after straightening the tank. A good solid plate will suck up most of the heat and keep it from warping.
If I was getting a dent out of a strut I would check the hardness after repair to see if strength was lost. I doubt it will loose any, but a hardness test is easy and cheap to do. Also keep the pressure as low as possible (it only takes a few pounds!). A kidney tank can become a bomb with pressure from a shop compressor in it and a torch making a hot spot! After fixing my kidney tank I was thinking a tile gun might provide enough heat, but haven't tried it. On aluminum parts I know 300*F is PLENTY of heat, steel I don't know, I would need to check my materials book.
Just be careful! Compressed air can cause parts to burst. On my fuel tank I only used a few pounds. CERTAINLY not 20 or 30! I actually used a condom over the fill hole to KEEP from over pressurizing my fuel tank for leak checks.

Hank

Yes, it DID get a lot of funny looks during the test!

[Hank Jarrett]

Re: Dent removal method for tubing

Be VERY careful not to damage the heat treat of high strength materials with this method! You probably won't have too much problem with welded assemblies since they are designed to tolerate heat affected areas around welds, but it is NOT a good idea for machined parts without considering strength loss in the heat zones. I have used it with great success for parts like Oil kidney tanks and their service tubes but the heat will REALLY screw up the flange if it gets to it. You need to bolt the flange to a heavy plate to keep it straight and may need to torch anneal it after straightening the tank. A good solid plate will suck up most of the heat and keep it from warping.
If I was getting a dent out of a strut I would check the hardness after repair to see if strength was lost. I doubt it will loose any, but a hardness test is easy and cheap to do. Also keep the pressure as low as possible (it only takes a few pounds!). A kidney tank can become a bomb with pressure from a shop compressor in it and a torch making a hot spot! After fixing my kidney tank I was thinking a tile gun might provide enough heat, but haven't tried it. On aluminum parts I know 300*F is PLENTY of heat, steel I don't know, I would need to check my materials book.
Just be careful! Compressed air can cause parts to burst. On my fuel tank I only used a few pounds. CERTAINLY not 20 or 30! I actually used a condom over the fill hole to KEEP from over pressurizing my fuel tank for leak checks.

Hank

Yes, it DID get a lot of funny looks during the test!

[PA1195]

Re: Dent removal method for tubing

Condoms...I wondered why there's no new Taylorcrafts.

Gary

[Guest]

Re: Dent removal method for tubing

condoms...i wondered why there's no new taylorcrafts.

Gary

lol!

[Guest]

Re: Dent removal method for tubing

I did two struts, it worked well.

This time I attached fittings so I could connect the air hose to it and free my hands.

Regulator set at 80-90 psi but with leaks I bet the strut was at 50 or 60.

One strut came out better I think because I started on it fresh with this method whereas the other had previously been worked on by another method that left some residual unevenness.

One must be careful, patient and thoughtful when doing this because you could blow a hole thru just like when you weld an unvented tube and it pops.

Struts get welded fittings on the ends and middle so heat is not an issue also struts get sleeves welded on so heat is not issue. The steel in normalized not hardened.

Dave R

[Guest]

Re: Dent removal method for tubing

That was Tim and oil tanks.

Thanks Dave, I corrected my initial post.

[Guest]

Re: Dent removal method for tubing

I should have thought to add this earlier but didn't.

Some may find it to be intuitive but others may not so it should be pointed out.

The danger in doing this is not to the steel but to the persons doing the work.

Basically you are creating a pressure vessel (a small one) then tempting it to fail by heating spot on it to the plastic region of the metal.

1) So when you heat a spot heat watch what you are doing from the side, making your line of sight approximately parallel to the surface that you are heating so that if it pops thru the molten metal is moving away from you. If you look directly at the spot you heat (ie. line of sight perpendicular to the surface) then if it pops the molten metal is coming directly at your face.

2) Wear eye protection.

3) Use the cone of the flame in a position parallel to the surface as well as perpendicular to the surface when you heat the metal so as to heat a spot that is sufficiently big or small and the correct shape that is needed (round, oval, stripe...) for the shape of dent that you are working on.

4) After the initial heat a big dent becomes a bunch of little dents that have to be removed. When you watch what you are doing from the side you can watch the metal move and remove heat at the right moment. If it goes to far you can remove the air pressure, re-heat the spot then tap it back with a small hammer.

I hope I didn't forget anything but probably did.

Dave R

[Hank Jarrett]

Re: Dent removal method for tubing

I was mostly referring to machined steel parts and aluminum and other heat treated parts. I agree completely that normalized steel should be no problem except for the danger of a blow out if you get the heat or pressure too high. Always better to start with way too LITTLE heat and pressure and bump the heat up a little at a time until the steel starts to move. It is kind of like bumping aluminum. Better to use LITTLE steps and hits, NOT one hard hit. I start repairing dents in aluminum with a spoon pushing from the back side. Hammers and blocks are the last resort. I am going to try the tile gun and a little heat on some scrap aluminum damage and see if it works easier.

Hank

Struts get welded fittings on the ends and middle so heat is not an issue also struts get sleeves welded on so heat is not issue. The steel in normalized not hardened.

Dave R

[Guest]

Re: Dent removal method for tubing

I was mostly referring to machined steel parts and aluminum and other heat treated parts. I agree completely that normalized steel should be no problem except for the danger of a blow out if you get the heat or pressure too high. Always better to start with way too LITTLE heat and pressure and bump the heat up a little at a time until the steel starts to move. It is kind of like bumping aluminum. Better to use LITTLE steps and hits, NOT one hard hit. I start repairing dents in aluminum with a spoon pushing from the back side. Hammers and blocks are the last resort. I am going to try the tile gun and a little heat on some scrap aluminum damage and see if it works easier.

Hank

I should have been more specific, by struts I meant wing lift struts. There are many kinds of struts. Good point about going little steps. Dave R

[astjp2]

Re: Dent removal method for tubing

Actually streamlined tubing used in lift struts is magnafluxed for cracks, that is why its so expensive. Just an FYI..and Dave, that tail wheel is boxed up but I need to still drop it in the mail. Tim

[astjp2]

Re: Dent removal method for tubing

Forgot to mention that Sikorsky main rotor blades are pressurized with nitrogen and if they get a crack, the BIM indicator will go red when the aircraft is preflighted..lost a skycrane because the mechanic didn't take the indicator seriously...and it tossed a blade in flight...

[Guest]

Re: Dent removal method for tubing

Actually streamlined tubing used in lift struts is magnafluxed for cracks, that is why its so expensive. Just an FYI..and Dave, that tail wheel is boxed up but I need to still drop it in the mail. Tim

My guess is that the magnaflux check is important on streamline tube because it is manufactured by rolling (longitudinally) a round tube into the streamline shape and a defect could result.