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Old 09-14-2014, 09:27 PM
jayd_2 jayd_2 is offline
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Default Brazing mild steel

I’m new Shop Floor Talk and I’m not sure if is the right place to post these questions.

I learned to braze over 25 years ago but haven't done any in 15+ years and I have a new project that will require some brazing.

My first question is about brazing thin gauge round tubing (1” diameter .083 wall) and back in the day I would have used 1/16” brass rod and powdered flux, it’s been too many years to remember exactly what type flux it was. The tubing is low carbon steel, what type brass rod and flux should I use?

The project I’m working on is modifying a steel bicycle frame to create an early 1900’s board track racer. The frame is made out of low carbon steel and is brazed (brass) together using 1” tubing with a .083 wall, the tubing is inserted into a lug (tube .083 wall) about 3/4” long. I would like to heat the lug and tubing then remove the tubing, is there any possibility to soften the brass enough to remove the tubing without distorting the lug?
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Old 09-14-2014, 09:42 PM
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Shade Tree Welder Shade Tree Welder is offline
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There are different grades of brazing rod some are low melting temps some
are high. If you have low melting heating the joint and removing the tube
should be easy. You should see the braze start to soften and melt at the
exposed end at that point if you are heating some light pulling and twisting
should get the tube out. If it is high temp stuff, the steel tubing will likely be
a red hot state before the braze melts and be much more likely to distort.

Harris Alloys has a good website for more in depth information on brazing
materials.

http://www.harrisproductsgroup.com/
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Old 09-14-2014, 09:43 PM
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And yes this is the correct spot to post this question.
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Old 09-14-2014, 09:50 PM
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Are you sure it is brass not bronze filler? Brass is generally a bright yellow, where bronze is a paler yellow.
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Old 09-14-2014, 09:55 PM
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Quote:
Originally Posted by milomilo View Post
Are you sure it is brass not bronze filler? Brass is generally a bright yellow, where bronze is a paler yellow.
LOL I had to reread his post, I just read it as bronze the first time through,
cause he was talking about brazing... good catch.
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Old 09-14-2014, 10:02 PM
jayd_2 jayd_2 is offline
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Quote:
Originally Posted by milomilo View Post
Are you sure it is brass not bronze filler? Brass is generally a bright yellow, where bronze is a paler yellow.
Not sure yet have not stripped the paint off, but did see a video where the frames were being brazed and its either brass or bronze.

I'm hoping it's brass, if its bronze I doubt I'll be able to separate the parts without damaging the lug. Bronze would probably be a better choice for strength correct?
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Old 09-14-2014, 10:06 PM
jayd_2 jayd_2 is offline
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I just watched the video again and it looks like brass to me.
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Old 09-14-2014, 10:14 PM
jayd_2 jayd_2 is offline
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I need to lengthen the existing tubing by about 4 inches. Would adding a 4" section of tubing with a custom made tube on the inside that extends past the joint at each end be an option? If so should I do a few small plug welds for extra bonding? I would prefer to replace the existing tubing but may have to add a piece instead.
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Old 09-14-2014, 11:12 PM
Toploader Toploader is offline
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I use something like these during roll cage repair or adding tube. The small ridge in the center leaves a nice gap for welding or in your case brazing. And I would plug weld/braze it. Once sanded down, it looks clean and one piece.
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Old 09-19-2014, 09:43 PM
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Quote:
Originally Posted by jayd_2 View Post
The frame is made out of low carbon steel and is brazed (brass) together using 1” tubing with a .083 wall, the tubing is inserted into a lug (tube .083 wall) about 3/4” long. I would like to heat the lug and tubing then remove the tubing, is there any possibility to soften the brass enough to remove the tubing without distorting the lug?
Softening the brazing is not a description I am comfortable with but rather would term it as re melting the brazing metal.

Yes It is possible, but only with a good idea of the geometry of ( if that's the correct word) the path that that the brazing material follows when it is initially used to braze one one tube within another.

If done properly in the first place there should be a degree of capillary action where the final disposition of the brazing filler has flowed between the inner and outer tube.

This means that you have to heat both the areas where you see the brazing externally and where you think it will be as it has crept between the tubes.

It will be necessary to keep both those areas hot enough to maintain the molten state of the filler to allow the separation of the two tubes.

Its easier said than done as you will need to keep the torch moving once the metal becomes molten and keep moving it to maintain the molten state of the brazed filler over both those areas.

One torch might do but two would be better with an operator for each torch in my opinion.

I would have all the equipment ready and have a suitable clamping mechanism to attach to pull the inner tube.
Remember not to over heat the brazed filler as there is only a narrow temperature window between the molten state and the zinc content of the braze material flashing off to a gas.
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