brazing flux paste

[bambuko]

When I decided to learn brazing (or more specifically fillet brazing, sometimes called bronze welding) I started with Sifbronze No1 rod and Sifbronze brazing flux.
Unfortunately Sifbronze brazing flux was a big disappointment - I wanted to use it as a paste to spread on the tubes I was brazing so I mixed it into something like a paste, but it was lumpy and either too runny or too dry and it didn't stick to where I wanted it to be.
Afterwards there was a business of removing... well it's crap

Did a bit of googling and found LFB Bronze Paste Flux (from Cycle Design USA) - it's creamy, smooth, sticks exactly where you want it and afterwards half an hour in hot water and it's gone. The only drawback is that it is about 50% more expensive than Sifbronze flux.

Not a problem if you pass this cost to your customer, but for a diy type (on a meagre pension) it soon adds up, so my question is:
How?where do I get creamy smooth brazing flux paste that's easy to clean afterwards, and is no more expensive than regular Sifbronze flux?

Chris

 

[Rrunnach]

How about flux coated rods, no idea of cost though?

 

[weldequip]

Afterwards there was a business of removing... well it's crap

Hard, black glaze? Too much heat

 

[hotrodder]

If you want to try cheap buy some boric acid powder from the chemists and mix into a paste with some filtered/boiled/deionised water. I know several VERY well respected framebuilders that use nothing more exotic. Doesn't take much to get the residue off with some hot water, smoothness/creaminess/stickyness is down to how you mix it though

 

[bambuko]

thanks guys,

@weldequip - no it's not black, just hard and totally insoluble in water. The other stuff I mention simply washes away after brazing, so I am convinced that it's not me just the nature of the beast (which doesn't mean I couldn't improve my brazing )

@Rrunnach - coated rods are an option if it works for you, but I want to use flux paste

@hotrodder - mixing my own boric acid powder sounds very interesting. Will definitely investigate it.

Sounds like I also made a mistake in just using tap water to prepare my own paste? There are also some suggestion about adding a drop of washing up liquid?

 

[Rrunnach]

thanks guys,

@Rrunnach - coated rods are an option if it works for you, but I want to use flux paste

I'm not asking the question, merely offering another option for you to try.

 

[GrahamGKD]

Hi Chris,
Not sure what kit you have to hand but if you use TIG to braze you don't use flux. You need to use different filler rods though (so far I've used SIFBronze No 8 but I've just taken delivery of a pack of these ones - not tried yet). The rods are expensive but, not having bought any gas brazing rods, I don't know how they compare?

 

[bambuko]

Sorry Rrunnach for the confusion I seem to have caused? I understand that you are offering another option, but...

I prefer flux paste to coated rods, simply want to find cheap flux paste which is easy to remove afterwards.
Chris

ps for clarity - I am using oxy propane gas kit (see http://www.weldequip.com/oxy-propane-brazing.htm)

 

[pedrobedro]

Oxy acetylene brazing I used to heat the rod tip and dip it in the flux powder, never had that much that I had to clean it back off. Try dipping your rod in the cream flux and weld with it that way. I used to do quite a bit and never actually tried spreading the flux on the work.

 

[bambuko]

@pedrobedro - thanks for your suggestion. I am familiar with this technique and I appreciate you suggesting alternative, but my googling various frame building boards seems to suggest they all agree that the best method for fillet brazing of bicycle frames is un-coated rod and paste flux painted on frame tubes.

I am mainly interested why Sifbronze flux is such a pig to use when compared to the other flux I have tried and whether there is any other flux option?

Chris

 

[the artfull-codger]

When I decided to learn brazing (or more specifically fillet brazing, sometimes called bronze welding) I started with Sifbronze No1 rod and Sifbronze brazing flux.
Unfortunately Sifbronze brazing flux was a big disappointment - I wanted to use it as a paste to spread on the tubes I was brazing so I mixed it into something like a paste, but it was lumpy and either too runny or too dry and it didn't stick to where I wanted it to be.
Afterwards there was a business of removing... well it's crap

Did a bit of googling and found LFB Bronze Paste Flux (from Cycle Design USA) - it's creamy, smooth, sticks exactly where you want it and afterwards half an hour in hot water and it's gone. The only drawback is that it is about 50% more expensive than Sifbronze flux.

Not a problem if you pass this cost to your customer, but for a diy type (on a meagre pension) it soon adds up, so my question is:
How?where do I get creamy smooth brazing flux paste that's easy to clean afterwards, and is no more expensive than regular Sifbronze flux?

Chris

I use sifbronze flux myself & allways mix it to a cream & add a little fairy liquid to it, if it's too lumpy/runny/dry then your mixing is at fault,it does vitrify but citric acid removes it, I use sulphuric myself to remove it, even silver brazing flux glazes over, tenacity no5 for higher melting/longer heating & easy flow for lower melting/shorter heating, also don't let it soak too long in the heat do it as quick as you can.

slan go fol

 

[bambuko]

Thanks the artfull-codger,
I have suspected that my flux mixing could improve, I am also guessing that using de-ionise/boiled water and a drop of fairy liquid might help?
I will try all this and report.
Good advice about technique (avoid over heating etc) - I am sure this will get better as I practice, practice, practice, etc

I am still curious as to why the American flux I have is so much nicer to use? and why when using exactly the same brazing technique it is so much easier to remove afterwards.

What I am saying, is that regardless how crappy my brazing is, it is the same for both Sifbronze flux and LFB Bronze Paste Flux and one is a pig and the other dead easy

Chris

ps Tenacity no5 is for silver brazing which not the same as bronze brazing - I am assuming that it would not be good idea to use it with Sifbronze?

 

[Tiggy_dorset]

Oxy acetylene brazing I used to heat the rod tip and dip it in the flux powder, never had that much that I had to clean it back off. Try dipping your rod in the cream flux and weld with it that way. I used to do quite a bit and never actually tried spreading the flux on the work.

I do similar. Heat the rod end, dip into the flux powder. I then spread the flux around the joint on the heated job before the brazing operation. I pickle most work that I do which cleans off any flux residue left behind.

 

[bambuko]

It's great that dipping works for you guys and I guess it's clear now that Sifbronze flux requires something stronger (and acidic) than just warm water to get rid of it after brazing.

Chris

 

[Tiggy_dorset]

It's great that dipping works for you guys and I guess it's clear now that Sifbronze flux requires something stronger (and acidic) than just warm water to get rid of it after brazing.

Chris

Hot water alone should take the flux off, but you will have to leave the item soaked for a little while (maybe 30 minutes). It should turn milky white when left in hot water, then can be wiped off. Although my experience of this is with a Sif flux I use with silver solder. I would expect the reaction to be the same with the flux you are using, but could be wrong.

 

[hotrodder]

I am still curious as to why the American flux I have is so much nicer to use? and why when using exactly the same brazing technique it is so much easier to remove afterwards.

What I am saying, is that regardless how crappy my brazing is, it is the same for both Sifbronze flux and LFB Bronze Paste Flux and one is a pig and the other dead easy

Chris

It's probably down to the composition, if you could find the MSDS sheet (i tried and failed) there may be some clues in it. Borax and boric acid are two of the usual suspects but other stuff is added to imrove things- action, consistancy, tenacity of residue etc

ps Tenacity no5 is for silver brazing which not the same as bronze brazing - I am assuming that it would not be good idea to use it with Sifbronze?

Different temps... good resource and general info here albeit not really specific to the work you're doing http://www.cupalloys.co.uk/fluxes-c59.html and another http://www.jm-metaljoining.com/products-pages.asp?pageid=63&sectionid=3 with a list of the various ingredients here... http://www.lamberts.co.uk/profile/sections/pipeline/coshh/sol-sds-eff.pdf

 

[bambuko]

@hotrodder
- no, I can't find MSDS for I guess fairly obvious reasons
and even those I can find quote components at +/-50%

- you are absolutely correct about borax and boric acid being the usual main components. That's why I was going to ask you about your comment earlier on, that "...buy some boric acid powder..." - are you saying that these "...VERY well respected framebuilders that use nothing more exotic..." use only boric acid and nothing else? or do they also have some secret witches brew of their own?

- I know the difference and am familiar with Cup Alloys and Johnson Matthey (have been using their stuff for more years than I care to remember), just didn't know how to politely tell the guys straying into silver soldering that they are off topic and off tangent - I have precisely described what the topic of the discussion is, but such is the nature of interweb and forums and I am sure they offered in good faith so I am OK

- there are brazing fluxes that claim not use borax or boric acid and I suspect possibly that might be a clue to "...residues are readily soluble in warm water perhaps with the help of a soft nylon brush..."
Some on the other hand (like Sif Bronze brazing flux) tend to go very glassy and are a real pig.

Possibly this is not a big issue for majority of user because they just dip the rod in the flux and are therefore very sparing in their use of flux?

 

[Tiggy_dorset]

just didn't know how to politely tell the guys straying into silver soldering that they are off topic and off tangent

You just did

Ill go and sit back down and start paying more attention to the class

 

[hotrodder]

are you saying that these "...VERY well respected framebuilders that use nothing more exotic..." use only boric acid and nothing else? or do they also have some secret witches brew of their own?

No witches brew... the various jobs i did in exchange for framebuilding lessons from Ron Cooper (RIP, he passed away a few days ago) included going to the Chemists round the corner to buy boric acid powder, mixing it up with nothing other than water (probably got berated for mixing it too thin or too lumpy) and cleaning up/finishing frames. As i was obviously the tea boy as well i probably spent more time boiling the kettle than i did reaming this and facing that.

 

[bambuko]

Thanks for this hotrodder. Nothing better than first hand experience and advice.
I will follow your recommendations!
BTW, while we talking brazing experience - what tip sizes?
I started far too small with No1 and No3. Now I am happy with No5 and No7, just need to be careful not to overcook (not too much of a problem on the mild steel, but might as well learn good habits).
Most of the advice on the interweb about brazing bike frames quotes US torches and nozzles, so I am interested in confirming UK equivalents?