oxy-acetylene brazing question

**Bluesman** · 05-23-2011, 07:44 PM

I know in stick welding, mig, tig, and even oxy-acetylene fusion welding there is some blending of the base metals and other than just oxy-fusion welding there is some blending of filler rod to strengthen the bond and cause a weld to "hold" and actually be stronger than the base metals. I use brazing a lot on my farm. I've told stan (sic fab) about me brazing feed augers back together when they break cause they are spring steel and if you "weld" them the heat changes the "spring" in the steel and it will make it brittle and break again. Although I don't consider myself an expert at ANYTHING, I am a pretty damn good fella when it comes to brazing repairs/applications and have often brazed stuff back together that other folks said would be impossible cause it was "too thin.". I even repaired a broken electrical switch on the farm the other day that was not only thin, but was difficult because of the braze being right next to the wires and plastic housing of the switch.

My brazing is VERY strong and often while trying to test how strong the braze is, I break or tear the base metal. What I'm curious about is that if there is NO PENETRATION on a braze and it is only surface adhesion like glue, then how the heck can it be so strong that the bond will fail and the base metal rips/breaks? The brazing rods are basically brass alloy and are very flexible and stuff so how can they make a bond so strong? Is it chemical? Or physical or what?

I hate to sound ignorant but seriously, it is basically the equivalent of a hot glue gun being able to create a bond between two pieces that is stronger than the original material. I mean gorilla glue and duct tape aint even capable of that

**SICFabrications** · 05-23-2011, 07:47 PM

oxy/fuel brazing is very very similar to the tig process.... small haz n all.... this is a question that i dont know the answer to, i would be willing to bet that welding wookie would know tho...

**Bluesman** · 05-23-2011, 08:03 PM

Nice to hear from you ol friend! Been a awhile and last time I talked you were neck deep in a BIG job! Glad to have you back. It has been kinda quite without ya.

**Tritium** · 05-23-2011, 08:23 PM

I believe that brazing creates a molecular bonding that is only 1 step shy of the fusion of welding. I used to work with precision optics and when two optical surfaces were lapped incredibly flat they would bond at a molecular level when joined requiring no glue and were impossible to separate without destroying the element surfaces. Just a guess about brazing, I could be wrong.

Thurmond

**oneeyedmac** · 05-23-2011, 10:10 PM

Awesome question...

**WookieWelding** · 05-23-2011, 11:04 PM

ok with brazing you can join dissimilar alloys including non metals to each other neither base metal/material are brought above melting temperature thru capillary action the flux and filler are drawn into the joint holding on to the molecules of the the material being brazed

**Bluesman** · 05-24-2011, 04:45 AM

So it is a molecular bond with the filler? The reason the brazing works so well on the flexible auger is because it doesn't get as hot as arc welding and doesn't comprimise the "spring" of the metal so it is still flexible everywhere except for the inch or so I overlap it. This molecular bond can be broken by reheating to the melting temp of the filler rod and pulling the two pieces apart BUT you can only "wash" so much of the filler off and even though you get the two pieces pulled apart there is still a super thin layer of filler on both sections of base metal. That must be that molecular bond thing still working. I've only had to disjoin a braze a few times and it is usually when I'm making another repair an notice a previous repair "wearing thin" or if it moves a little bit during the repair process and needs to be repositioned. I just know that after a repair, I've not had a break anywhere within a braze, but I've had breaks close to a repair. Most of the time it is from metal fatigue and the new break has nothing to do with the previous repair job. Now there are some hands around these parts that can't manage to get the repair. Right and their braze either fails from not getting a good "stick" or because they overheat the base metals and destroy the spring qualities of the steel and it becomes brittle near their welds.

So, when their augers break they just go buy another one. They say they can't be repaired and it isn't worth it. Me, I'm poor and can't afford to buy another whole piece of flighting every time one breaks so I fix mine. I been telling them other hands to just give me their broke augers and I will get rid of them for em.

Gives me an endless supply of material that I can add to mine when they get too short from being repaired multiple times or when I have a section that needs to be replaced because it wears thin from use.

**Tritium** · 05-24-2011, 11:43 AM

I thought molecular bonding sounded correct. There are some adhesives that provide molecular bonding as well (the parent material will tear before the glue bond gives up). Bluesman, I know what you mean about having to repair what you have instead of running out to "buy" another. Repair it any way possible was the way I was raised. I can also braze pretty well because I was taught that at a fairly young age on the farm. Also Oxy / Acetylene welding (which I also was taught but haven't practiced in years) looks to be almost identical to tig welding to me (just a different torch with a cleaner "flame").

Thurmond

**Bluesman** · 05-24-2011, 04:42 PM

Originally Posted by Tritium

I thought molecular bonding sounded correct. There are some adhesives that provide molecular bonding as well (the parent material will tear before the glue bond gives up). Bluesman, I know what you mean about having to repair what you have instead of running out to "buy" another. Repair it any way possible was the way I was raised. I can also braze pretty well because I was taught that at a fairly young age on the farm. Also Oxy / Acetylene welding (which I also was taught but haven't practiced in years) looks to be almost identical to tig welding to me (just a different torch with a cleaner "flame").

Thurmond

Damn skippy! If it aint broke, don't fix it and if it is, see if duct tape or a braze will work!

**Tritium** · 05-24-2011, 04:49 PM

Duct tape is a "modern" convenience. We used bailing wire for most everything that was not brazed or welded and used bailing wire many times for filler wire for welding. Can't find bailing wire any more here though. Everyone has gone to poly twine (I hate that stuff).

Thurmond