chassis welding or brazing?

[Chris B.]

Does any one know if a 1990 chassis is welded or brazed? I have broken the small tube that clamps the wing support bracket, which is definitely brazed to the chassis.

[Big Brother]

AFAIK.....

 

Brazed if its a Caterham

Welded if its a Westfield

 

Steve

Se7en-Up!

 

It'S NOT Green!, its the colour of an unripe MANGO

[jackb_ms]

What is the difference?

And which is best?

 

Jack

 

Emily, The Very Yellow 21

[Sheds Moderator]

Brazing aka bronze welding is the joining of 2 bits of steel using molten brass or bronze alloys. Because brass/bronze melt before steel the parent metal is not melted. Welding involves the joining of steel (say) using a steel filler rod *and involves melting the parent metal*. Consequently the join is the same metal as the parent metal.

 

Which is best? Ooh, call a metallurgist. Brazing isn't a continuous join, you rely on the filler sticking to each side of the joint. Welding is continuous so *should* be better, all other things being equal. However, they aren't equal. Welding may introduce more distortion, as the heat is greater, and there is a heat affected zone near a weld, where the parent metal becomes brittle owing to the heat/cool cycle. This may cause cracking in later life.

 

The ideal is to weld everything then place the workpiece in a kiln and heat it to a preset temperature then cool it under controlled conditions. This way you take out all the heat induced stress. Obviously this is impractical unless you are making small spaceage components at huge cost.

 

If I were repairing a 7 chassis I'd braze it for choice. That said I own a welder or two but not brazing gear so it would get, as a mate of mine used to say, BluTacked. Bzzzz....

[Joe 90]

It's bronze welded, which isn't exactly the same as brazing. I would braze a little bracket rather than weld.

 

SEP field working, not spotted in 102,900 miles. Some photos on webshots, updated 21 Sept

[ECR]

Oliver

 

What's the difference between brazing and bronze welding.....

🤔

[caterhamnut]

Some piccies of the Caterham chassis brazing here

 

HUGE UPDATE ALMOST WITH VIDEO

here

70,000miles in 3 years

[Westfield]

 

 

Angus

 

Fantastic site, just spent a good half hour on there!

[Rob Walker]

Roger,

 

Brazing is heating of the parent metal and rod until the brass brazing rod melts onto the heated area, usually using oxygen and acetaline, very slow puts a lot of heat into the area being brazed and the borax flux used needs removing before any painting/powder coating. Bronze welding as per the caterham chassis is welding by electric arc providing the heat source, very quick and causes only the minamum of heating of the parent metal. Result a strong , ductile joint with minamum distortion. It also looks neat as the the bronze flows readily arount the joint.

[xflow7]

Rob, thanks for the explanation. I take it that the parent metal does not beome molten in Bronze Welding? Or if it does, only very superficially?

 

Thanks,

 

Dave

[Sheds Moderator]

Parent metal is not melted at brazing temps, not even a bit. Copper alloys like bronze and brass melt at 7/800°C, steels 1000/1100°C. In this respect brazing is like soldering and silver soldering.

[xflow7]

BOSS, thanks, but, I was actually asking about Bronze Welding, as Rob points out there are significant differences in the heating profile between brazing and bronze welding. However, I wasn't clear whether the difference was just spatial extent of the heated area, or whether, locally to the joint, there is significantly more heating of the parent metal in Bronze Welding vs. brazing.

 

Cheers,

 

Dave

[ECR]

Thanks Rob

 

So bronze welding is essentialy similar to TIG welding but with a bronze filler rod ?

 

All repairs that Arch have carried out for me have been done with oxy/acetylene and a gas fluxer. Are you sure that they bronze weld ?

[caterhamnut]

Larger close-up pic in higher res of a Caterham joint here where you can see the heat patterns etc

Incidently, this is the top front suspension mount - the chassis is stacked upside down ontop of another - you can see the bracket ready for the nose cone Dzus fastener.

 

HUGE UPDATE ALMOST WITH VIDEO

here

70,000miles in 3 years

 

Edited by - angus&tessa on 17 Nov 2004 15:20:17

[Barry]

from Chris Flavell

[xflow7]

Great link, Barry. Thanks.

[ECR]

Thanks Barry... and Chris !

[caterhamnut]

Must remember to check other areas of this site more often

 

HUGE UPDATE ALMOST WITH VIDEO

here

70,000miles in 3 years

[Rob Walker]

Roger

 

Yes Arch use the bronze arc welding technique on the new chassis and yes its similar to tig welding but with a nickle/brass wire. It may be that when making any repairs its less of a risk of damaging electronic equipment such as ecu`s and data logging?instrements that they play safe and use gas on some repairs. Horses for courses

[MikeR]

The other thing to bear in mind is that brazing is less forgiving when it comes to tollerences. The two bits of steel have to be a very very close fit, where as (mig) welding you get bits to withing a mill or two or three. In fact with Mig a little bit of a gap can be an advantage as it encourages penetration (the bonding) of the two bits of steel - hence the reason lots of chassis are mig'd today, its arguably about as strong and easier.

 

It should also be noted that the Gov messed up the MOT car repair regulation. A chassis has to be repaired using the same sort of joint that made it, which sounds a good idea....... so a mig'd chassis can't be brazed but for some strange reason a brazed chassis can be mig'd ! Don't ask, i don't understand why.

 

[Sheds Moderator]

I think it's because seam welding has always been assumed to be the strongest means of attaching 2 bits of metal (which it may not be). The evidence for this is that in the event of a subsequent failure the weld never breaks, it's the metal just next door. This is the result of the embrittlement of the heat affected zone, see earlier.

[Joe 90]

Bronze welding doesn't need the close gaps that brazing needs, which is pretty handy during manufacture. It's not too difficult to change a design from welding to bronze welding, but if you want to braze it you have to change the tolerances on your tube ends.

 

SEP field working, not spotted in 102,900 miles. Some photos on webshots, updated 21 Sept

[Rob Walker]

The main problem when brazing using gas is that it is a totally uncontrolled process you direct the flame onto the joint and what temperature the joint gets to could be anything up to and above the melting point of the parent metal when its only necessary to heat the joint enough as to melt the brass filler rod at around 550C. The extra heat if appied causes the brass to oxidize and the steel becomes brittle in the joint area, you get a dirty joint with holes/bubbles in the brass filler.

[Sheds Moderator]

Which isn't to say Rob that an unskilled operator can't make a mess of any joint. I know that some of my early attempts at MIG were awful. Equally learning to solder aged 16 was pretty painful. A skilled operator OTOH can make an equally good joint in steel by brazing or a variety of welding techniques. You have to be a bit of a numpty to get the joint to steel melting temps when there is a filler rod going in at half that temp.

 

 

[Joe 90]

Agree with BOSS, if you don't know what you are doing you can get any technique wrong. In general, the lower the melting temperature of the filler, the smaller the heat affected zone. On the other hand, low melting point fillers have lower strengths.

 

SEP field working, not spotted in 102,900 miles. Some photos on webshots, updated 21 Sept