28 replies to this topic

[Greg Locock]

Inside tubes of steel spaceframes. Aircraft industry practice is linseed.

[desmo]

Bicyclists have used any number of products for just that forever. Proprietary stuff like Boeshield and JP Weigle Frame Saver. It all seems to do the trick to some degree.

[Siddley]

Do they coat the tubes before welding and just accept that the oil will be burnt away from the area near the welds, or squirt it in afterwards somehow ?
If it's a case of squirting it in afterwards I'd assume holes would need to be drilled in each run of tubing ?

[Greg Locock]

In some industries access ports are provided, and replenishing the fluid is part of scheduled maintenance.

[Siddley]

That's interesting. I know the ( magnesium alloy ? )  spaceframe on the Porsche 917 was pressurized with nitrogen and the driver had a gauge in the cockpit so he would know if it had cracked. That was also a feature of some aerobatic planes, in the case of the wing spar.

 

When I was a race mechanic ( unpaid, for a one man club level team which never really amounted to anything ) I would always gravitate to the historic sidecar outfits and look at the brazing on the frames. They were unpainted so a crack was easier to detect and were brazed from Reynolds or similar tubing. I loved that brazing and aspired to being able to do the same myself. I did get pretty good at it.

 

[bigleagueslider]

Aircraft practice with steel tube spaceframe weldments is usually to take no further action regarding corrosion protection in the enclosed volumes of tube weldments. Prior to welding (typically a TIG process) both the inner and outer tube surfaces are thoroughly cleaned of corrosion or surface contaminants such as oil/grease. During welding, the internal volumes of the tubes are purged with an inert gas to prevent oxididation on the back side of the welds. After welding, there is usually no moisture trapped inside the enclosed tube volumes due to the inert gas purge used during welding. So internal corrosion is not usually a problem.

[gruntguru]

I would use this stuff.

 

http://www.royalpurp...rvative-oil-10/

 

[Kelpiecross]

When I built my one-and-only spaceframe I used one inch square sixteen gauge galvanised tubing. Nobody else seems to use gal tubing - I don't know if there is a reason not to use gal. I also found that gal tubing was a little easier to nickel-bronze weld. For the areas where the gal was burnt off my intention is to slosh thinned Killrust paint through the tubing and then drain it. Could get a little messy though.

[bigleagueslider]

Brazing is not the same as fusion (TIG) welding. TIG welding alloy steel requires that the steel surfaces at the weld be totally clean and corrosion-free. If you are attempting to make a weld repair of a tube structure, and there is oil present on the inner surface of the tubes, then the weld will always end up contaminated by the oil.

[Lee Nicolle]

When I built my one-and-only spaceframe I used one inch square sixteen gauge galvanised tubing. Nobody else seems to use gal tubing - I don't know if there is a reason not to use gal. I also found that gal tubing was a little easier to nickel-bronze weld. For the areas where the gal was burnt off my intention is to slosh thinned Killrust paint through the tubing and then drain it. Could get a little messy though.

Galv or zinc? both are reputed to make the steel more brittle. As does chrome too. 

My experience with zinc and galv is that it spits everywhere when oxy welding and is even worse when arc welded. And forget MIG, It just will not weld. Even after grinding the plating off.

As for fish oil, or any oil inside the tubing it will burn, in fact has the potential to explode when welding. And whatever will spoil any weld

Edited by Lee Nicolle, 08 April 2014 - 08:59.

[John Brundage]

Some transit buses use Dinitrol Penetrant LT on the inside of the frame tubes, other use PPG Cora Tube.

[Siddley]

 I don't know if there is a reason not to use gal. I also found that gal tubing was a little easier to nickel-bronze weld.

 

I don't know either, but I reckon you should find out before adding wheels and an engine 

I found that the key to good brazing ( bronze welding, whatever you want to call it ) was absolute cleanliness of the joint, together with proper fit etc, obviously.

What effect the zinc could have had on the joint would be worrying me. It might be nothing, but then again it might not...

Just out of interest I have managed to MIG weld galvanised steel using flux cored wire, that was a workbench though.

[kikiturbo2]

galvanized tubing is a real pain to weld using mig as it emits noxious fumes..

[Siddley]

galvanized tubing is a real pain to weld using mig as it emits noxious fumes..

It's OK if you do it outside and try not to inhale...

But looking at your avatar picture I reckon you know a lot more about welding than I do....

[Lee Nicolle]

galvanized tubing is a real pain to weld using mig as it emits noxious fumes..

It does with stick too. Do it outside. We once built about 300 feet of tubular fencing.  fence rails and galv Hills Hoist beams. After trying the MIG which was useless we then got out the arc. Which did actually attach everything together. But after about one it was gloves, overalls and leather boots. Even doing it outside we were both a bit loopy from the fumes after. Fence is still there near 20 years later. 

[Kelpiecross]

Galv or zinc? both are reputed to make the steel more brittle. As does chrome too. 
My experience with zinc and galv is that it spits everywhere when oxy welding and is even worse when arc welded. And forget MIG, It just will not weld. Even after grinding the plating off.
As for fish oil, or any oil inside the tubing it will burn, in fact has the potential to explode when welding. And whatever will spoil any weld

I only use oxy/LPG. I found that for an amateur welder oxy/acetylene gets too hot too fast and I was inclined to suddenly melt holes through the steel. Oxy/LPG doesn't quite reach steel's melting point so is more "foolproof" for a beginner. I like nickel-bronze as you can see it "wet" the steel and flow when you make a good joint. And N-B joints appear to me to very good joints - almost unbreakable.

I am about to buy a gasless MIG welder so it is useful to know that gal welding by electrical means is tricky. It would be handy to know if gal does actually cause brittleness.

[Lee Nicolle]

I only use oxy/LPG. I found that for an amateur welder oxy/acetylene gets too hot too fast and I was inclined to suddenly melt holes through the steel. Oxy/LPG doesn't quite reach steel's melting point so is more "foolproof" for a beginner. I like nickel-bronze as you can see it "wet" the steel and flow when you make a good joint. And N-B joints appear to me to very good joints - almost unbreakable.

I am about to buy a gasless MIG welder so it is useful to know that gal welding by electrical means is tricky. It would be handy to know if gal does actually cause brittleness.

Nickel bronze does too. A very strong joint but sometimes will crack right alongside the weld. Bicycles are a good case as is very old offroad buggies which many were nickel bronzed. Though so were countless tube chassis racing cars too. And I have seen a few of those cracked [or break] too. 

All welding has its weakness, personally I feel MIG is the best. TIG is prettier but not as strong for structural stuff. TIG though beats anything else with sheet metal, especially were viabration is at play, sumps and the like. Bronze cracks,, as I have just rebronzed an old one today.

These days though bronze is good, I can still see it!

[Magoo]

A few years back, a race team here in our little industrial park pranged up their nice new big-name dirt sprint car chassis. The frame sat outside their back door for maybe a year when they decided it wasn't as bad as it looked, and they repaired it and put it back on the racetrack. However, they soon encountered odd things falling off and falling apart on the car, clearly the result of corrosion from the inside out. Not sure what the solution is except maybe don't leave race cars out in the snow. 

[bigleagueslider]

I only use oxy/LPG. I found that for an amateur welder oxy/acetylene gets too hot too fast and I was inclined to suddenly melt holes through the steel. Oxy/LPG doesn't quite reach steel's melting point so is more "foolproof" for a beginner. I like nickel-bronze as you can see it "wet" the steel and flow when you make a good joint. And N-B joints appear to me to very good joints - almost unbreakable.

I am about to buy a gasless MIG welder so it is useful to know that gal welding by electrical means is tricky. It would be handy to know if gal does actually cause brittleness.

The term welding implies a fusion of the base materials. Fusion of the base metals requires them to be heated sufficiently to locally transition the metals from a solid to a liquid state. The term brazing implies joining the base metals by melting a filler metal over the joint that has melting temperature below that of the base metals, and during the brazing process the base metals are never heated to the point where they transition from solid to liquid. There are many processes used to braze alloy steel tube structures, including gas torch brazing or even brazing using nickel-bronze filler and a TIG torch.

 

[Kelpiecross]

I did realize that the process should correctly be called "brazing". However it does seem to be fairly common practice to refer to the process as "nickel-bronze welding" or just "bronze welding". I suspect it is called "welding" to distinguish it from the much lower strength types of brass brazing. (I presume the term "braze" means "with brass").

I use it because it makes a very strong joint and I can actually successfully make a joint - which is more than I can say about fusion welding.

[Greg Locock]

It was the method of choice (pre MIG) for getting russty British cars through their annual inspection. reason was that the braze soaked through all the rust and restored some sort of integrity. Welding would have just blown more holes in the rust.

 

However the next point of failure was just where the braze ended, this super stiff thick compound of brass and rust met with the rusty steel next to it, nice stress raiser.

 

I don't think you are allowed it any more.

 

The main disadvantage compared with MiG welding sis that you are putting a lot more heat into the base metal, so distortion is a bigger issue. 

[Lee Nicolle]

A few years back, a race team here in our little industrial park pranged up their nice new big-name dirt sprint car chassis. The frame sat outside their back door for maybe a year when they decided it wasn't as bad as it looked, and they repaired it and put it back on the racetrack. However, they soon encountered odd things falling off and falling apart on the car, clearly the result of corrosion from the inside out. Not sure what the solution is except maybe don't leave race cars out in the snow. 

We have rescued 40 y/o Super mods and Midgets from out in the weather. Sometimes some of the lower bars need to be replaced but they have generally lived ok. Modern chrome moly cars should never rust like that, even in the snow.

What usually causes the rust is the track dirt, stabilised with lime or gypsum. or in the old days dolomite surfaces. Even then if they are welded up properly the should be airtught. The old chassis generally had a multitude of things riveted, screwed  to the chassis unlike these days where that is illegal and everything is tagged.

[Lee Nicolle]

The term welding implies a fusion of the base materials. Fusion of the base metals requires them to be heated sufficiently to locally transition the metals from a solid to a liquid state. The term brazing implies joining the base metals by melting a filler metal over the joint that has melting temperature below that of the base metals, and during the brazing process the base metals are never heated to the point where they transition from solid to liquid. There are many processes used to braze alloy steel tube structures, including gas torch brazing or even brazing using nickel-bronze filler and a TIG torch.

 

I have heard about brazing with a TIG but never seen it before

[Lee Nicolle]

It was the method of choice (pre MIG) for getting russty British cars through their annual inspection. reason was that the braze soaked through all the rust and restored some sort of integrity. Welding would have just blown more holes in the rust.

 

However the next point of failure was just where the braze ended, this super stiff thick compound of brass and rust met with the rusty steel next to it, nice stress raiser.

 

I don't think you are allowed it any more.

 

The main disadvantage compared with MiG welding sis that you are putting a lot more heat into the base metal, so distortion is a bigger issue. 

Far less distortion MIG welding than oxy or even brazing. Especially on thin metal. Though TIG is even better.The other advantage is that you can paint straight over it wheras the flux from bronze requires a good deal of cleaning off. Or the paint / bog, powder coat peels off fairly quickly.

[bigleagueslider]

I have heard about brazing with a TIG but never seen it before

You can braze with a TIG torch because the TIG torch only provides a source of heat similar to a conventional gas torch. The TIG torch also provides some shield gas flow, but this is not required for most brazing alloys. With a MIG torch, the heat is provided by current flow through the filler wire which melts as a result.

 

TIG brazing is an excellent way to join tubes made of high-strength alloy steels like 4130. With brazing, the tube is not heated sufficiently to produce a phase change (solid to liquid to solid) in the material, so the tube material in the HAZ retains most of the metallurgical properties it had as manufactured. This is not true with fusion welding processes.

 

More importantly, as the picture clearly shows, a tube chassis TIG brazed by a professional just looks awesome.

[Kelpiecross]

It was the method of choice (pre MIG) for getting russty British cars through their annual inspection. reason was that the braze soaked through all the rust and restored some sort of integrity. Welding would have just blown more holes in the rust.
 
However the next point of failure was just where the braze ended, this super stiff thick compound of brass and rust met with the rusty steel next to it, nice stress raiser.
 
I don't think you are allowed it any more.
 
The main disadvantage compared with MiG welding sis that you are putting a lot more heat into the base metal, so distortion is a bigger issue.

As the owner of a slightly rusty (well, very rusty actually) ancient Pommy car I might find the brass trick very useful.

[Greg Locock]

I don't think you are allowed it any more. Seriously, check with the MOT book. It's not a very good repair, doubler plates back to good metal is much better, and obviously wholesale resectioning is best. I saw the front of the chassis of a series 1 landrover fall off once, due to a combination of brazing and lost of underseal to cover it up.

[Kelpiecross]

I was intending to use brazing on the many minor rust areas on the car - not for really big areas. As well as this my old bomb (a '49 Mk.5 Jag) has a separate chassis - this was not going to get any brazing - just the separate body shell. I wouldn't be surprised if brazing was "legal" on the body of a separate chassis car.

I have to admit in my younger days I got away with some diabolical liberties to get cars past rego - rust holes backed with cardboard and then painted - almost entire sills sculpted from Polyfilla (not even proper car polyester filler - too expensive). And I wasn't the only one doing such things.

[MatsNorway]

Rumor has it one guy at work got a complaint on the sound.. from a section on his car. He filled it with concrete. Showed it and suppedly passed. I might need to double check that one because its funny as hell.