How not to do Tig brazing

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Over the past few days I've done a little reading and I may have answered my own questions regarding what I did wrong, but I'll show you guys how I did it and how it turned out and you can make suggestions for improvement.This was a repair to the base of a vise which had one of the screw tabs broken off.  I initially thought it was cast iron, but when I put the burr to the broken site, it came out pretty shiny, so this might have been cast steel.  I "buttered" the tab site with bronze as you can see in the first photo.  I was running with a 3/32 thoriated electrode with max amps set to 200 since the area was up to 1/2" thick.  Gas lens with flow set to 11 cu ft/hr.  I initially used some 3/32 gas rod with the blue flux with most of the flux knocked off.  With gas, this flows beautifully over surfaces, but with Tig, it just seemed to form blobs.  I tried aiming the arc adjacent to the lump to heat the cast iron up to almost liquid, but that didn't make the bronze spread.  When I aimed the arc at the bronze lump and really stepped on the pedal, I could get the bronze to melt and flow a little.  Sometimes I was able to stir the puddle with the bronze rod and push it to where I wanted it.  The bronze kept popping and spitting, and in the end I think there was enough spatter that it ruined the screen on my gas lens.  I tried using some Petersons blue flux.  That helped things spread a little.  I finally got it all covered.  The bronze was not golden and shiny like it usually is with the gas torch.  It was blackened and there was a lot of white deposit around the area of the brazing.  I put the new steel tab up to the area for joining and brazed it on with the tig.  More of the same adventures and this time there was a forest of white crystalling material around the area of the brazing.  You can see all of this in the photos.I think my main mistake was using gas rod, not realizing that I should have been using silicon bronze rod.  I probably was using too much amperage although most times I was just using enough to make the bronze melt.  Heating it hotter did help it to spread.OK experienced ones, tell me how to improve my tig brazing. Attached Images
Reply:yikesSilBr tig rod is cheap 1st on WeldingWeb to have a scrolling sig! HTP Invertig 400HTP Invertig 221HTP ProPulse 300HTP ProPulse 200 x2HTP ProPulse 220MTSHTP Inverarc 200TLP HTP Microcut 875SC
Reply:Couple basic things come to mind right away. First off, using copper/zinc fillers is tricky with Tig as its easy to boil the zinc out, causing popping etc. This is why the silicon bronze fillers are popular for electric brazing. Second thing, Tig will have the disadvantage of not being able to "sear" the surface of the casting and consume the graphite, nor does it have the chemical de-oxidation of a flux. Searing with an oxidizing flame, and then cleaning with an acid etch before brazing with silicon bronze would have given you better results.
Reply:I've had similar troubles trying to TIG braze, even when using silicon bronze filler, and I suspect the reasons were what Makoman said, because when I used the same rod (and added some borax powder) and used a gas torch (with neutral or slightly oxidizing flame) instead of TIG, everything worked fine.Now whenever I braze, I use O/A – not TIG.
Reply:Originally Posted by makoman1860Second thing, Tig will have the disadvantage of not being able to "sear" the surface of the casting and consume the graphite, nor does it have the chemical de-oxidation of a flux. Searing with an oxidizing flame, and then cleaning with an acid etch before brazing with silicon bronze would have given you better results.
Reply:RWL, Searing is done prior to many brazing operations on cast iron, reguardless of the heat source used for the actual brazing. It must be done with and oxy/fuel torch flame, set to about 1-2X oxidizing ( quite oxidizing ). Acid etch can be a local phosphoric or hydrocloric followed by a rinse. Actually on cast iron, the torch has many advantages, both chemical and thermal. In general, localized heating of cast iron is more risky than a larger heat input due to thermal stress.
Reply:First off let me say that I've not done a whole lot of TIG brazing. I've tried it on a few things a quickly went back to using the torch. It has it's place but IMHO not on cast iron.   Let's just start by saying that the whole key to doing a good job with cast iron is preheat, maintaining heat in the piece, and slow even cooling of the piece. All of which points towards torch work. TIG is a concentrated heat where you're just heating a small area. This fine even preferred for most welding just not cast iron.   Doing what I do with cast iron (machining it afterwords) dramatically shows the need for all of this heat. If it's not done that way then the cast iron next to the weld will be so hard you can barely scratch it with a carbide tool.   Now to give a example lets say that you're going to weld some high carbon steel. What do you do? You preheat the piece, maintain a proper heat level while welding, and post heat with controlled cool down. Stop and think about this next point. High carbon steel has a maximum of 2% carbon and that's the absolute maximum it can hold nearly all carbon steels in the real world are less than 1% carbon. Many much less. 4140 for example has 0.4% carbon in it.   By definition cast iron always has more carbon. So much in fact that the iron can't hold it all and it's precipitated out into the iron matrix in one of several forms depending on the type and heat treat of the cast iron.   What I'm trying to get across here is the fact that you have to treat cast iron as if it was the highest carbon steel you've ever welded (which it is).   I'm not enough of a expert to try and discuss the details of all the different forms on iron and carbon mixes but I know enough and have experienced enough to know the above is true. Now onto the more practical matters.   First off is proper cleaning and preparation of the joint. This is critical. You may well need to heat the piece and let it cool to get all the excess oil and crap that's soaked into the cast iron over the years. However if you do the burn in like is described above then you will have to redo the surface preparation if you want the brass to flow into the cast iron like it needs to for a good bond. Clean unburned surface is needed for a good bond and there's a few key points to that.  First point is grinding smears the carbon on the surface making it difficult to get a good flow of the brass. This means that some other means is needed for the final surface prep even if you use the grinder for the majority of the removal.   I use one of two methods to do the final prep. I either sand blast the surface to be bonded thoroughly or you need to use a sharp (and I mean sharp) cutting tool of some form. A sharp file can work on simple shapes but my most used method is a sharp carbide burr in a die grinder.   Next point is to not overheat the area you're fixing to braze while bringing the piece up to temperature. If you overheat and burn the area then the brass will not flow properly and you'll be forced to try and burn it into the piece. This can be tricky on some pieces and I'll often flow the brass along the top of the V joint first to prevent this surface burning since the sharp edge has a tendency to overheat while you're working at getting the brass to flow in the bottom of the joint. This is where proper and enough preheat of the overall piece is crucial. It's best to start you're heating by heating beside the joint you're brazing rather than right at the joint. Only once you get enough heat soaked into the piece can you really get to work flowing the brass out.   Another tip is to use a larger tip than you think you need. You need to keep the flame low enough that it doesn't blow the brass away while you're working. As well as you need to heat the larger overall piece rather than a pin point heat. Pin point heat will make for boiling of the zinc out of the brass causing it to not flow properly and creating bubbles in the finished piece. You can switch to a small tip for the final building up and shaping of the brass joint but only after getting a good flow of brass on the overall piece.   If for some reason you accidentally overheat part of the piece and the brass stops flowing on you then you need to let it cool and prepare the the surface again. This is often the case when you're doing both sides of the piece. Getting the first side flowed out will tend to burn the other side making it difficult or impossible to get a good flow. Ideally the whole piece would be covered in flux when you're heating it but it's pretty much impossible to get it all covered without having problems like this. It is something that you should work towards.   That brings up the discussion of flux. I prefer the Peterson brand myself but they make more than one kind. Unfortunately the absolute best flux for cast was there #3 (for cast and malleable at low to medium heat) which was a two part flux. It worked very well even on dirty cast iron. However they don't make it any more. They do make a #2 (for cast and malleable at high heat). It's not as good but sometimes it will let you bond to a piece that won't let you stick in any other way. I usually keep a can of it open and nearby so that I can use it for those small difficult areas that crop up sometimes. It's not the perfect flux though. It tends to bubble the brass while you're working leaving bubbles in the finish work and it doesn't flow as well as the standard #1. Thus there's times when I'll mix the two if the piece is giving me trouble. Sometimes I'm forced to use the #2 for the first pass and then go back over with the #1 for the buildup and flow out of the piece.   There's more that I could write on the subject but I'm totally out of time here. I should of been out in the shop a good while ago. But hopefully some of this will be helpful to some one.Millermatic 252XMT 304'sDynasty 280DXHypertherm PowerMax 1250Miller Trailblazer 302 EFIOptima PulserXR feeder and XR Edge gun and more athttp://members.dslextreme.com/users/waynecook/index.htm
Reply:My first experience with tig brazing actually went fairly well (I was out of oxygen for the torch), it was a hydraulic fitting that had been brazed originally, the joint cracked and failed and the guy needed his machine running before morning to stand up his barn. Anyway, I cleaned everything up really well and used regular OA braze rod with the powdered flux. Heated the rod up with a propane torch, dipped it in the flux and crossed my fingers. Got the part red with the tig and started dipping, everything flowed out nicely and the part was put back in service. It was a really nasty looking mess with the flux residue everywhere but a little water and scrubbing and it looked just fine. The trick was to not use too much heat and boil the zinc out. Whole process didn't take 10 minutes.Cast I can see being more difficult with the carbon inclusions and other things, but a steel line into a steel block worked pretty well.
Reply:Thanks Makoman and Irishfixit.  All good advice from experience.  I'm still open to hearing others experiences, particularly with regard to building up small areas since that's something I'll have to do in the project of building up some gear teeth.
Reply:Ive done a few gear teeth for antique lathes using the torch, with very little post machining needed. You can do VERY delicate work with a torch in this application, tig has no magic here.
Reply:After having watched Keith Fenner braze a lot with a torch I don't think I would attempt it any other way.Miller Diversion 180Hobart Handler 140 (Soon to be replaced with Miller 211?)Miller Spectrum 625 Extreme
Reply:Best way to do iron is fire up the grill. Bring it up hot, pull it off, toss it on the bench and nail it with a Hilco Bronze C. Toss it back on the grill, shut the lid and pull it out in the morning. Give it a glass bead first, if possible.Bubble gumTooth pixDuct tapeBlack glueGBMF hammerScrew gun --bad battery (see above)
Reply:If you're getting the white dust around your braze you are TOO HOT!  Silicon bronze likes the slightest bit of red glow to steel, any more is TOO HOT.  Most people's difficulties brazing stem from working at too high of a temperature.  You really just need heat to heat the part, then concentrate the heat on the rod to melt it onto the part you are repairing.  Don't do like soldering and try to get the part hot enough to melt the filler.  Brazing is an extremely versatile process and give a great deal of control and is easy to do in the field.  It's too bad more people don't know how to do it anymore.  I always keep an oz of 50N brazing alloy around because it can join just about anything (except aluminum) and is very strong (110ksi).
Reply:My experience with helibrazing is limited but I did find it to be quicker and prettier in addition to being a more reliable repair method than OA brazing for my application. The specific application and context was the repair/rework of suction manifold pipes on large hydrogen/helium compressors. The manifolds were constructed of what appeared to be cast iron soil pipe welded to ISO pipe flanges (the compressors were manufactured in the UK). The manifold was hung off the compressor by only one flange with no other support structure, so they would frequently crack where the flange was welded to the pipe (the pipe itself would crack right beside the weld). One of my co-workers attempted to grind out the cracks and MIG weld them, but they would often crack during cooling. Several manifolds were repaired with coated brass brazing rod and the OA torch, but the physical size of the piece required a LOT of preheat and usually used up a set of bottles by the time the repair was finished. During one of my scavenging trips in the basement, I found an old tube of 1/8" aluminum bronze filler rod and decided to try it next time we had a cracked manifold to repair. I rigged up a propane roofing torch for preheat, used an IR temp gun to measure the surface temp and started piling on the filler with the TIG torch once we'd reached 230 degrees F. I don't recall my amperage settings, but I do remember not needing very much pedal travel to get a nice puddle. I did a root and a cap, and as far as I know the piece is still in service, no cracks since. Your mileage may vary!