troysmith80

I've been playing with brazing for several weeks. I've made several practice joints and not many have been exactly how i wanted them but most have been strong and reasonably well shaped. There are still plenty of issues though.

For the next step in the learning process i made a rear rack and brazed it permanently to the frame of an old bike i have. I took pictures and video, hoping for some feedback. I'm afraid you can't see much in the video, as is typical in torch or welding operations due to the brightness. I don't think i can do custom exposure in video mode with this camera. Maybe i should have put an extra pair of welding goggles in front of the lens?!

Any advice is much appreciated.

Video is 5 minutes, I braze two joints.






First, i clean the tube, using any combination of filing or sanding with 220 sandpaper or emery cloth

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I brush on the flux

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Brazed jont - why is it mostly so nasty looking? Is this oxidation? Did i get it too hot? (Note, there is brass all the way around, but some of it is covered with that black crap, the nice looking brass is just the last two spots i worked on).

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Brazed jont - why is it mostly so nasty looking? Is this oxidation? Did i get it too hot?

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I assume i have to repeat the entire cleaning process and get rid of all that crap before re-heating this and trying to build up a larger fillet?

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This is a different one, after a lot of cleanup work. Not terrible looking, but a little bit porous. I thought maybe i could put a little heat to it and flow out those pits, but i'm afraid i'll just mess it all up.

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Here is the whole rack

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rellis

Sure looks like too much heat. Keep the flame moving at all times during brazing. Preheat for a longer period. The porosity in the bronze can be from too much heat or from contamination. Clean the surfaces AND the brazing rod to the point that when you wipe them with 91% isopropyl no dirt shows on the paper towel.

unterhausen

remove more paint

yes, you are overheating. You can tell when you see pock marks and copper precipitating out of the bronze. With bronze, you will see a little cruft here and there, but you should be able to flux, pick up the torch and heat the joint again without cleaning on a properly brazed joint. My main thought while watching is that you were concentrating the torch in one location a lot more than I do. When it gets too hot, flick the torch away.

I have to admit I've never watched anyone braze before, even myself. I've been wanting to film myself, but I can't figure out how to talk my camera into wearing glasses.

Here is a bb/seat tube cooling down. As you can see, the bronze is still covered in flux, and I could heat it right back up again and add bronze if I wanted to

jd0g

The one thing I wish I'd learned sooner is that the hot, central blue cone of the flame is for welding only, not brazing. Do not let it hit the work. you're looking for a bright cherry red color on the steel, not yellow or white. The steel is white hot and starting to melt when you hear the popping sound. Heat treated tubing is quite sensitive to overheating, e.g. straw yellow hot.

mudboy

You're not using enough flux, or you're not using the right type of flux.

Cassave

Yep, what those guys said.......

Too much heat. And don't be afraid to lather on the flux.

Try running a richer flame. Adjust for a sizable mediumt blue "feather" outside the hot core.
If you can actually hear the torch, it's probably too lean for brazing.

unterhausen

not sure that he needs more flux, but it is possible it's not the right kind. He still has flux up on the tubes. You can always pull flux in from areas like that if you need more flux. He's definitely charring the flux, I'm pretty sure that's what most of the cruft is. Out of curiosity, I tried using silver flux for bronze after the LWS assured me strongly that it would work. I don't think you can get bronze to stick if you do that, but it's been a while.

With bronze, my experience is that you really don't need that much flux, but it's nice if you want to take pictures.

tuz

I have to admit that looks like silver flux?

Otherwise yes it got too hot. You should preheat more; get the whole area hot by backing off the flame and sticking around until the area becomes close to red-hot. Then move in closer and touch the rod to the work until it flows, then back the flame off a little, repeat around the joint. Something like that.

unterhausen

I don't think it's sliver flux, I remember the silver flux charring almost immediately at bronze temps. Looks like gasflux type b

troysmith80

Thanks for the feedback everyone. I suspected that overheating was part of my problem.

The flux i'm using was sold to me at the LWS along with the filler rod. It's called Stay-Silv by Harris. It says it's white brazing flux for brazing stainless steel, monel nickel, copper, brass, bronze and other ferrous and non-ferrous alloys. Due to the name, "Stay-Silv" i was afraid this flux was for silver brazing and asked the guy at the shop, he assured me this is the stuff for the filler rod he sold me.

Is it brass or bronze that we use for filler? I thought it was brass. My filler is labeled: LFB-BARE, Part # PP1063LFBARET, AWS/SFA A5.8

I've not cleaned my filler rod at all, and only sanded/filed the base metal, no alcohol or solvent or anything wet. I'll start doing that.

I may try gooping on more flux too. And running a little richer on the gas mixture. I've been bringing the blue cone down to a single, sharp cone. I'll let it feather out a bit.

It's hard to tell in the video but i do not get the inner cone very close to the joint at all. I realize that overheats the filler and i've seen the copper come out when that happens. Or at least i guess that's what it's called, when i see areas afterward that are copper colored instead of brass. Occasionally i'll bring the torch in close to quickly flow one spot without melting everything all around it. Is that the technique used to build up large fillets without all the filler flowing away under gravity?

troysmith80

Just after 3:00 in the video, something started popping at me. I said that i've never had that happen before, and i haven't. Any idea what was happening there? I'm wondering if that was heated/expanding air inside the tube escaping out through the molten part of the joint? It kept happening in that same spot and it was popping and spattering tiny little bits of metal out (fortunately they were very small or it would be dangerous).

BHOFM

The splattering is from too much heat. I clean the joint, and preheat, heat the rod a
bit and dip it in the flux, I never put flux on the material, it makes a big mess.

These are much smaller than you are working on, but a sample..

unterhausen

I stand corrected, you are using the wrong flux. Looks like Stay-silv is active a lower temp than you would want for LFB. As I stated above, my LWS told me that Safety-silv would work with LFB. I tried it out of curiosity, and it failed miserably.

So order some Gasflux type b from Henry James or some LFB flux from Cycle Design

when you overheat LFB, some of the alloy will come out of solution. It acts like it's boiling and you get popping/sizzling noises. Seems like that is most likely what happened to you. If you don't vent a tube, you will get some nastiness where the braze allows the hot gasses to vent, so that could be it also. You can drill a vent hole and then fill it really quick once the joints are all done. Use a small drill and don't allow it to go all the way into the tube, just barely break through. The tube should be hot so it doesn't vent.

mudboy

Here's how a pro (not me) applies flux:


IMG_7170 by e-RICHIE, on Flickr

unterhausen

you can have too much flux, but I don't remember the last time it happened to me. That being said, that's a lot of flux, and I'm thinking he's not done. RS is not known for half measures.

I use more flux than I think I need for silver. It's hard to apply more once you've started. I'm generous with flux for bronze, but I've never felt like I was going to run out, even when I was practicing brazing from one end of a 3" long sleeve to the other.

troysmith80

BHOFM, are you saying those joints were not cleaned at all after brazing?

Interesting that you recommend just dipping the rod in flux, that means very little flux in the operation, right?



Man... cleaning all that black crud off after every operation is a major pain in the ass

troysmith80

Hmm, so maybe this is the wrong flux? It would be nice if i tried a different product and this was a bunch easier! Probably wishful thinking.

LWS = Local Welding Shop, right? What is LFB?

BHOFM

Yes, they were cleaned, but it was just a quickie. The brass flows where the flux is placed. I just rub the
hot rod with with flux on it around where I want the brass. Hard to explain, easy to show and do..

A blast cabinet makes easy work of it.......

Live Wire 

Low Fuming Bronze..the stuff you are already using. (edit: I guess you weren't using LFB)

Ain't no maybe about it, you have the wrong flux!

Just watched your video, I'm suprised the flux worked as well as it did, because by the time the metal turns orange like that, silver flux is pretty much cooked.
Your flame is way too aggressive for a joint that small, you shouldn't be able to hear it at all. Adjust the flame until it's quiet and neutral (little to no acetylene feather in the cone) then work in closer with the blue cone almost touching the part. But get the right flux first!

unterhausen

The fact that it seemed to survive fairly well fooled me. Stay-silv rod is mostly copper with 5% silver, so it has a higher liquidus temp than silver. But it still melts 300C below where LFB does

troysmith80

Ordered some flux from Henry James. Lady on the phone was selling me on some filler too. I told her i've got to burn through what i've already got first but she agreed to send me a sample. She was a character, got on my case for not being politically active, lol.

jd0g

@BHOFM,
The sandblasting looks good, what are you building for Barbie?

Live Wire 

Ha, that was Monika, she's the best.
ps, should've bought the rod too.

BHOFM

Thought everyone here had seen these, posted them a few times..

32"X18", 12lbs. 2.2hp.

jd0g

Nice! I like the baby croc.

@Troy: Thanks for posting this, it's an interesting mistake.
BTW the handlebar I posted above was done with the Gasfluxer from Henry James, not paste.

@unterhausen: I've seen a few videos of TIG and brazing now that appear to just use the auto iris on the camera. The flame isn't as bright as the sun, or even reflections of the sun, you should be fine without a filter or Monogoggle