Frame Repairs

[ianashdown]

Hi,

I have a Lola T-202 that needs a little repair in the area of the 'horns' that hold the front radiator. The chassis was built using nickel-bronze technique as was typical in England at the time. My welder claims he can repair this using silicone-bronze rod and a TIG welder. It would use low heat and would still basically be a brazed joint, just using the TIG as the heat source.

Has anyone any experience of this process?

I had planned to build a Gas-Fluxer and repair it in the same way as it would have been built, but this sounds like a really good method and I don't have to build the gas-fluxer!

Any comments appreciated.

Ian

[R. Pare]

No way on the silicone bronze - it is way too weak - about half the strength of mild steel.

Nickel-bronze, acetylene torch, and a can of flux will do the job very nicely.

[S Lathrop]

Ian;

Richard is correct. I would repair the frame using the original low temperature welding process. TIG will not tolerate the nickel-bronze. That is from personal experience.

A gas fluxer is great but you can use bare rod with flux. I recommend using canned flux vs the coated rods as you have better control of the flux.

Steve

[kea]

I agree too.
I'm lucky to have an inline fluxer (that I bought used at a welding supply a long time ago), so I too use bare rod. I've tried the coated rod, from the same brazing rod supplier and really didn't like it as well.

[Brian]

The nickle-bronze rod is most likely Sifbronze no. 2, and mostly you have to mail order it from England, it's not really distributed in North America - at least I couldn't find it. I have used an Allstate silver-bronze coated rod, which is about as strong as nickle-bronze at 85Kpsi, but is more eutectic so it's hard to get the fillet right. Plus getting the flux off seems to be a multi-year process, for me anyway...

Brian

[old 59]

Richard, Steve and Keith;

What diameter bare nickel-bronze rod do you recommend for most chassis repairs?

Thanks

[R. Pare]

Rod size will depend on how big the desired fillets are to be, so it could be all over the map.

Been 20 years since I last looked at rod specs, but I remember that what we bought from the local supplier had a tensile spec of 115kpsi. A quick google search came up with rods ranging from 65kpsi up to 95kpsi, so with a bit more time spent, the higher spec rod could be found as well.

I would imagine that there are differences from one makers rod to another in how the rod flows as well as how well it sticks, so that should be researched as well.

i know that there are also spray fluxes out there, but I don't know their suitability for brazing.

Flux removal: most can be removed by wrapping a wet rag around the joint to dissolve the flux, or it can be scraped or blasted off.

The biggest problem (that I am aware of, anyway) in trying to TIG braze is that it is way to easy to boil the filler, which will separate the alloying components and severely weaken the fillet. Not that it can't be done and done well, but oxy/acetelyne is much easier to control.

[kea]

I use Sif-Bronze #2, 2.4mm dia most of the time.

[old 59]

Thank you Richard and Keith.

[ianashdown]

Hi,

I've not been able to find Sifbronze #2 Rod in the US but the UK web site shows the rod having a Ultimate tensile strength of 540 N/mm2 (78.3kpsi) It has 9% nickel.

Have also forund another rod that has 15% nickel and has a UTS of 100kpsi. It also in the UK so I'm not sure how easy it would be tpo get here in teh US.

What would be an ideal UTS number for an old space frame made presumably of Mild steel tubing?

Thanks,

Ian

[Roland V. Johnson]

PM sent

[Brian]

"What would be an ideal UTS number for an old space frame made presumably of Mild steel tubing?"

Mild steel tube has a tensile strength in the 65 Kpsi range. The cross section area of the steel is less than the cross section of the fillet, if you do it right, so the braze fillet has the potential to be stronger than the tube even if the braze material is less strong than the mild steel. The rods we have been talking about are all 75 Kpsi or stronger, so from some points of view overkill - the joint is stronger than the tube.

The trick to brazing race car frames is getting the heat right and the prep right so the fillet is formed correctly and the braze bonds to the parent metal correctly. You need what I call a very soft flame, low pressures on the gases. I do it so infrequently I tend to get good at it just as I am finishing the last joint...

Brian

Brian

[Rick Iverson]

Nickel Bronze 2mm diameter Sifbronze 101 with flux. I have some in MN, but no way to access it until next spring. I bought 2kg of rods as well as flux from the UK, and sold most on Apex at cost, so there is plenty out there. Go to General classified and place a wanted add, and remark I can replenish their stock when we return from FL.

VR

Iverson

[LFFR]

Ian,

Check out old thread; http://www.apexspeed.com/forums/showthread.php?t=39654

John Mihalich, Jr.

[stephen wilson]

I would also strongly recommend testing some sample pieces to failure. It's easy to get a pretty good looking fillet that's not fully bonded to the parent metal, creating a very weak joint.