Help with Amperage for Tig Brazing Brass !

[comp-any-2015]

Hello all,

I am new here all though often browse the forum for advice. I am trying to Tig weld or perhaps more specifically Tig braze some brass together and am struggling to get a good result and in desperation and turning to the forum for some help. Any advice / tips are really appreciated.

I am using a Murex Transtig 200-i and there is no foot pedal (which I know is not ideal but just trying to get some tests done) I am particularly struggling with the amperage setting I should be using..?

I am using:
Transtig 200-i Tig Welder
Tig Torch with no.6 Ceramic
Argon shielding Gas

Filler rods I am trying are:
SIFPHOSPHOR BRONZE NO 82
SIFsilcopper No.968 (C9)
Copper Tig Rod (C27)

Brass I am using is:
3/4" x 3/4" x 1/8" Brass Square Tube CZ108
3/4" x 3/4" x 1/8" Brass Angle CZ121

I can get a good weld when doing a test on mild steel at about 60-80amps but when I try the same on the brass it doesn't seem to work so well. The filler rod kind of balls up and doesn't melt properly.

Hope this makes sense?

Thanks in advance for taking the time to read this.

Martin

 

[Chris Stevens]

Why not try silver solder? Brazing brass is pretty difficult.

 

[Richard.]

The very little bits ive done have been best on ac with aluminium bronze. The trick is not to get it too hot and release the zinc. The run should come out gold. Get the small puddle formed then hit it with filler. Remember your brazing not welding so no need to go at it trying to penetrate with loads of current or you'll get it too hot and lose control. It's one instance where I personally like a little more arc length. Not much as your aim is still not to melt across the arc but it's all about getting the filler in. I'm far from an expert at it and as Chris said it's not the easiest.

 

[comp-any-2015]

Hi Chris and Richard, Thanks for your replies.

I need the strength and colour match so am trying to go down the tig brazing route.

Sorry if this is an obvious question but could you explain what you mean by getting the small puddle formed? Is this using the filler rod or melting the base metal a little? I am struggling to get it started!

Do you increase your arc length by simply holding the tungsten a little further back?

Thanks for your help.

Martin

 

[comp-any-2015]

I should add, if I go up to about 130amps I am able to get a decent weld with the brass is it normal that I should need so many more amps for the different base metal?

 

[Richard.]

You count on both hands how many times I've actually done it. So I'm no pro and my meathods are only what I have had semi decent results from.
Yes the pool is formed from the base material and from memory it looks a little scummy. Add the fill as soon as it comes through. The melting point of the filler is lower than the brass so you keep adding fill positively so that you keep the brass from getting too hot. It will release zinc which is the horrible fume and white soot around the braze. The trick is to keep the heat as low as poss to keep that zinc down. I find a slight increase in arc length helps but whether that's the right thing to do I'm not sure as I have only taught myself. I also find its easier on AC with aluminium bronze than on DC with silicon bronze but that's a preference thing I think.
A pedal does help a lot here as it's more crucial to keep control of that little pool. Practicing tig brazing always is a lot easier if you've got decent size lumps of brass to do it on. Expensive practice I know but the little bits get heat soaked so quickly.

 

[WorkshopChris]

The brass will probably want to wick the heat away faster than steel of a similar section. The biggest problem with brass if the boiling out and gassing of the zinc content. Have you had a look on the sif data sheets for rod compatibility.

 

[comp-any-2015]

Thanks for your replies,

Ok, That makes sense Richard ! what do you mean heat soaked ? I am using 150mm (ish) lengths and they are getting bloody hot !!

I wondered if I was 'loosing' the heat due to the brass dissipating it faster therefor me needing more amps? Do you know where I can find the sif data sheets, I have never checked this before? Thanks for this tip!

 

[WorkshopChris]

Try
https://www.google.co.uk/url?sa=t&r...ng.pdf&usg=AFQjCNFNRfuMILaYJNja4vxalWBkyJ3byQ

They are not that easy to find used to be on the weldability site have a good google if you cant find any let me know i have some pdf on my hard drive somewhere will try to dig them out.

 

[hotrodder]

CZ108 melts at around 916°C, CZ121 melts at ~ 875°. They'll be kinda 'averages' somewhere between the solidus and liquidus temps which for cz108 are 905° - 930°C according to the internet

Your pure copper filler melts at 1085°, the C9 silicon copper starts to melt at 910 but has a liquidus temp of 1025°C. The C11 / cusn6 / phosphor bronze has a pretty similar temp range

Zinc boils at 907°C

I'd be thinking oxy fuel, 'regular' brazing wire like sifbronze #1 and flux (or some boric acid powder mixed into a paste with distilled water)... better colour match as the composition is much closer to the brasses being joined (loads more Zn) and a more compatible melting range, 875 - 895°C. A slightly oxidising flame is helpful when welding brasses or brazing instead of the more usual neutral flame used for welding steels etc... it helps reduce porosity by oxidising any zinc that gets volatised instead of letting it boil

 

[WorkshopChris]

Your 968 rod:-
http://www.weldability-sif.com/media/pdfs/info/RO961201.pdf

No 82:-
http://www.weldability-sif.com/media/pdfs/info/RO821601.pdf

 

[WorkshopChris]

There is a guy on youtube in the states Keith Fenner who does quite a bit of brazing, in one video he gas brazes/welds two big sections of brass bar together. Might be worth a search of his channel.

 

[Tigman]

I had some success on a big lump of brass have a look in my photo album ( I think its in there ) , it took a lot of heat but once hot it was very simple , I have tig brased a 100mm copper pipe to a bi metal flange on a water main ( also in Album) again once hot it went well not sure if I used C9 or C11 one for copper to brass , the other for brass to brass !

 

[Chris Stevens]

Hi Chris and Richard, Thanks for your replies.

I need the strength and colour match so am trying to go down the tig brazing route.

Sorry if this is an obvious question but could you explain what you mean by getting the small puddle formed? Is this using the filler rod or melting the base metal a little? I am struggling to get it started!

Do you increase your arc length by simply holding the tungsten a little further back?

Thanks for your help.

Martin

Colour match will be very difficult, but might be worth looking at the linked PDF as Harris suggest they can supply suitable material: www.harrisproductsgroup.com/~/.../GuidetoBrazingandSoldering.pdf

 

[HughF]

I'd be oxy fuel-ing this with flux and a suitable rod. Tig brazing isn't the way to go imho.

 

[zeppelin builder]

use AC current and no8 ceramic plain type ie no gas lens as it it will be fit for the bin when your finished covered in white zinc fume and little bits of brass make sure you got good ventilation for precise stuff silver solder /oxy acetylene the answer

 

[mark501w]

Gave enough heat to start puddle added silica bronze wire on ac with argon.

 

[zeppelin builder]

watch the two edges melt bridge it soon as possible with a dab of filler let the pool sink till its flush or slightly below add more filler to bring the deposit just above flush then move forward ,keep the build up smaller and narrower , if its purely a cosmetic item machine up an internal sleeve and silver solder