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Thread: Silicon bronze help

  1. #1
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    Silicon bronze help

    I decided to make my second set of pipes for my bike (shovelhead). I'm doing it out of stainless 304. I plan on tigging it with 316 filler. When you get to the flange which bolts to the head it's a different story. After much research and a lot of reading I found that most of the pros who build headers use a mild steel flange and tig braze it to the stainless pipe using silicon bronze rod. The reason for this from what I understand is mild steel distorts less under heat than does stainless. Also silicon bronze melts at a lower temp than does steel so you are using less amps to weld it hence less heat affect zone. Although it is not as strong as a weld it is supposed to be plenty strong in this application. I looked into this because I had a set of stainless flanges that I tig welded to the stainless pipe and it distorted so much I had to shape it back to get it strait.

    I also watched a lot of videos on silicon bronze tig brazing and still cannot figure out what exactly I am doing wrong. I even watched that guy mr. Tig and he welded the same exact mild steel flange to 16 gauge stainless pipe I'm trying to do and I can't for the life of me get it to look the same. He never says what size tungsten, filler or amps he's using.

    Here's what I got:
    -Dynasty 200dx, 1/16 red tungsten, 7 cup with gas lense, 1/16 ERCuSi-A silicoln bronze rod, 60 amps, argon 12 cfh.

    -16 gauge ss 304 pipe to 1/4" cold rolled steel plate. I cleaned the steel with a flap disc and acetone. The fit up is tight, no gaps.

    I cannot for the life of me get a small smooth bead below 60 amps. I know a lot of people say use low amps (30-40), I'm not sure if that applies to this application but as soon as I cranked the amps up to 60 I felt that I could make a smaller, smoother and faster bead. At a lower heat it was big, ugly and got hotter cause I was taking such a long time. You can see that it looks like I am using too high of heat still because there is some sugaring on the inside. I feel like I can almost dip 316 filler wire in at that heat but I have not tried.

    I also tried .045 silbrz rod and I end up feeding in so much just to get it to work for me that 1/16 works out better.

    I'm relatively new at tig so bare with me. Thanks. -Ray
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  2. #2
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    Re: Silicon bronze help

    Twas me I would crank your amp up as high as your machine will let you. Strike an arc hard and right before the base metal melts, jam the filler in. Being it is braze filler it should flow outward, so then move forward like you are welding. When you are done it should look like a weld with beads.

    Looks like you are babying the puddle and eventually it overheats and gets muddy. Push your argon up over 15cfh to 17cfh. and move up to 3/32 dia tungsten.

    Good luck.
    Weld like a "WELDOR", not a wel-"DERR"
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  3. #3
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    Re: Silicon bronze help

    Try getting your sibr settings on an easier joint than a round. I honestly can't even recall settings I use, the machine is usually set hot and I'm just peddling the needed amps.


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  4. #4
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    Re: Silicon bronze help

    Work that pedal and pump and feed. Name:  get-attachment.jpg
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  5. #5
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    Re: Silicon bronze help

    Practice with longer tube pieces and walk the cup. You can get very a short arc length that way. Which should keep the heat where you want it. And prettier welds it works for me maybe it will for you too
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  6. #6
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    Re: Silicon bronze help

    the plate is 4 times thicker than the tubibg. concentrate the arc on the plate..when it starts to shine and makes a puddle, feed a little sibr in and wash it over to the tubing. move and do another one. dont baby the puddle, nail the peddle, get it ,back off a little, feed and move..

  7. #7
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    Re: Silicon bronze help

    Damn you guys lay some nice beads!! I never thought about pumping. It give it a shot.

    Shovelon what are you saying, like 200 amps?

  8. #8
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    Re: Silicon bronze help

    Quote Originally Posted by 66mynd View Post
    Damn you guys lay some nice beads!! I never thought about pumping. It give it a shot.

    Shovelon what are you saying, like 200 amps?
    Yes, and work that pedal like said. concentrate on the plate side. Nice thing is that the bronze flows fast, so you can go fast.
    Weld like a "WELDOR", not a wel-"DERR"
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  9. #9
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    Re: Silicon bronze help

    Silicon bronze will not take the heat of an exhaust system. It's nearly fluid by 1200 degrees F and at full power your exhaust system may reach that temp. It's totally weak by around 600F too which is less than just cruising on the freeway.

    If you want to join stainless to mild steel use 309L stainless filler and weld it. I am a brazing fanatic but an exhaust system is not the right place to use it.

  10. #10
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    Re: Silicon bronze help

    I built a complete exhaust, mufflers and all years ago for my first bike, a TZ750. Used 1 1\4 x .065 304 as tube. Buddy of mine made the four individual flanges where it fits into the head that I welded on to the ends of the tube, sold it 2 years later and it was still holding together....Mike

  11. #11
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    Re: Silicon bronze help

    Quote Originally Posted by 76GMC1500 View Post
    Silicon bronze will not take the heat of an exhaust system. It's nearly fluid by 1200 degrees F and at full power your exhaust system may reach that temp. It's totally weak by around 600F too which is less than just cruising on the freeway.

    If you want to join stainless to mild steel use 309L stainless filler and weld it. I am a brazing fanatic but an exhaust system is not the right place to use it.
    I see where your coming from and I see your logic but don't you at least find it intriguing that there is all this literature stating that silicon bronze is the preffered method of welding flanges to the tube? I mean I wasn't just reading some guy in a forum say what he does, there's actual step by step guides that go through every step of header building and that's the info I'm getting.

  12. #12
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    Re: Silicon bronze help

    Quote Originally Posted by 76GMC1500 View Post
    Silicon bronze will not take the heat of an exhaust system. It's nearly fluid by 1200 degrees F and at full power your exhaust system may reach that temp. It's totally weak by around 600F too which is less than just cruising on the freeway.
    I thought the melting point was considerably higher. Although not as high as stainless steel.
    Weld like a "WELDOR", not a wel-"DERR"
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  13. #13
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    Re: Silicon bronze help

    Melting temps for alloys differ. This reference lists the melting temp as being between 1590F and 1790F. Certainly strength is very low anywhere above 1500F. Probably fine for an engine exhaust.

    http://www.atlasmetal.com/silicon-bronze-everdur.php

    Certainly strength is very low anywhere above 1500F. Probably fine for an engine exhaust. There is plenty of empirical success out there to justify using it in this situation.



    Quote Originally Posted by 76GMC1500 View Post
    Silicon bronze will not take the heat of an exhaust system. It's nearly fluid by 1200 degrees F and at full power your exhaust system may reach that temp. It's totally weak by around 600F too which is less than just cruising on the freeway.

    If you want to join stainless to mild steel use 309L stainless filler and weld it. I am a brazing fanatic but an exhaust system is not the right place to use it.
    Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector

  14. #14
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    Re: Silicon bronze help

    I have worked on many older British race cars that have the header primaries brazed to the head flange. some of the cars are 40+ years old and I have never seen a problem with the brazing melting. Just because the exhaust temperature is 1200+ degrees doesn't mean the flange will be getting that hot. Remember that it is bolted up to a large heat sink (the cylinder head).

    I have found that TIG brazing with silicon bronze you should treat it more like regular welding than brazing. Start feeding rod just before the puddle forms and get moving!

  15. #15
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    Re: Silicon bronze help

    I have never seen an exhaust done in silicon bronze. I use it all of the time for attaching fittings to flat plates because it distorts the plate less than welding which means you don't need to face it in the lathe afterwards. I have just never seen it used for an exhaust. And as I typed that I remember I have seen it used on an exhaust. The spring loops on 2-stroke dirt bike expansion chambers are brazed on with silicon bronze. While 2-strokes see less heat than 4-strokes the spring loops are close to the head which is the hottest part of the pipe. So, maybe silicon bronze is practical. Sil-braze is certainly not, though... especially at 5-10x the price.

  16. #16
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    Re: Silicon bronze help

    i am a great fan of sibr. and i feel as you , Duke , that it is by no means a brazing process, i've never ever seen it wick into a gap..it acts 100% like er70s for me..

  17. #17
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    Re: Silicon bronze help

    I am having better luck. I did as many of you said and turned the heat up and did my best to move faster. I'll take some pictures when I'm done. Thanks

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