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jvo
04-22-2005, 12:28 PM
Join Date: Feb 2004
Location: Lethbridge AB Canada
Posts: 190

In-line flux attachment for brazing.

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The fender is now repaired, and given back to its owner, thanks for the replies. Will, I've been told that paint doesn't stick too well to brazing, and I've never done any brazing myself. This is a topic I'd like to explore, though, a topic I'd really like for someone to elaborate on. I have a friend in Calgary, who's a mechanical engineer by trade, that raced a couple formula Fords for nine seasons. He used to, and still does, braze all his tubing joints, with what he calls an in-line flux torch attachment. It resembles a tig welded joint, and he claims it is extremely strong, as it doesn't change the parent metal's characteristics at all, i.e. no stress points. He claims the parent material beside the brazed joint will always break first. The finished joints really look nice, not like the brazing that local farmers have used for the past hundred years, before mig welders became popular. I've asked about this in-line flux attachment at the local welding stores, and they look at me like I grew another ear. Anyone done this before? Perhaps I should post this as a new topic. John V.O.
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Last edited by jvo : 04-22-2005 at 11:21 AM. Reason: Post as a new topic, please. This was originally in a post called Welding a cracked in fender. This is nothing I really plan on doing,(this in-line flux brazing thing), but my friend claims this is the best way to attach tubing joints, and he now builds high-end bicycle frames also, using this technique. I've merely been wondering about this for quite a few years, but have never seen anything else about it anywhere else. John V.O.

metalchomper
04-22-2005, 02:23 PM
I've brazed the trim holes on a car I did 15 years ago. It's sitting in the garage waiting on another restoration. The paint my be faded, but it's still adhering to the brass just fine. It's real important to clean the flux off of it. I used a cheapie sand blaster to clean them.

Gene_Olson
04-22-2005, 03:01 PM
I used a cheapie sand blaster to clean them.
That may have been the trick. Copper is notoriously difficult to get paint to stick to, especially if it's smooth. Giving something tooth so the paint can grip and a good coat of primer goes a long ways.

G.

Don Thorne
04-22-2005, 03:16 PM
Hi John:

J.W. Harris at one time carried a “Speed Flux Dispenser” a quick call to them today and found out they no longer handle it, and don’t know where one could be obtained. So I guess they have just evaporated.



Don

jvo
04-23-2005, 11:12 AM
I guess next time I am able to, I'll take some pics of his work. The way he brazes his joints, are really pretty. It looks like really fine tig welding. Surprises me that more of you folks haven't seen this. As I stated above, I have no intention of doing this myself, just that my friend Steve Scott from Calgary really feels this is the answer. Perhaps some members from the area know him as well. He's been a friend since high school, but I only see him once or twice a year. He's fairly well known in the track racing scene in the area, I think. Still builds formula Ford motors. I'll make an effort to take some pics and post them sometime this year. John V.O.

Kevbo
04-25-2005, 04:09 PM
The biggest trick to high quality brazing is perfect fit-up.

Bronze filler is strong...around 90 ksi vs. 70 ksi for the best steel filler.

The catch is that it's fatigue life sucks. That is why fitup is so critical.

The steel parts must be in contact or nearly so (few thousands clearance) so that when the filler shrinks, it pulls the steel parts tight and produces a tension preload in the filler.

Like a well engineered bolted joint, the filler then only sees this preload regardless of the service loads. The joint must be such that the filler never flexes, or stretches under load.