Original message
| backyard mech
 |  "Brazing Techniques"
, posted Sun 27 Jun 22:37  
Xenos some weeks ago I read a post that I think you wrote that dealt with brazing techniqes. It was about not using too thick of a braze joint. (at least I think it was you) Then a couple of weeks ago I read another post from someone else stressing the importance of brazing with nitrogen-seems like it was in an old lineset or something. So I was thinking it would be neat to have brazing techniques in the knowledge base. As if you don't have enough to do here already.
Maybe we could start a thread that would give ideas for that project. If this is too time consuming I understand. I took welding my senior year in High School but it wasn't specific to the hvac industry, just general welding of different types.
So to start the thread, Why use nitrogen while brazing a new lineset? Doesn't the pressure blow out the braze joints while brazing. What pressure would be applied with the nitrogen. Everyones comments are welcomed. and other information on brazing would be appreciated.
By the way I am addicted to this sight. Everytime I read a post I think about solving it a certain way and then someone else answers and gets me thinking of other solutions. This is a tremendous tool for learning and helping others. I have taught scores of maintenance techs over the last 8 years in a variety of fields. teaching and learning are so rewarding I want to express my appreciation to everyone who contributes here. I have grown to respect many of the mechanics who post here. Keep up the good work!
Absolute Tempcontrol
Aurora Colorado
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| Xenos
Webmaster 
| "Re(1):Brazing Techniques" , posted Sun 27 Jun 22:59
Thank you and that’s and excellent idea.
When ever we solder / weld we get this black flaky stuff. This is due to the pipe oxidizing. This same flakey stuff on the out side of a pipe also forms on the inside of it. Some systems like heat pumps are quite sensitive to this and this can cause the reversing valve to stick as well it can plug up driers or screens quite well. So how do we prevent this oxygenation from occurring in the piping when we weld? Well if we allow a small amount of nitrogen to purge through the system there will be no oxygen in there. So when the joint is complete the copper inside will still be sparkling clean and not black and flakey.
P.S. Yes I would have mentioned about building up on the outside of a joint.
I have another as well, When ever I use silver solder, I always go over it with silfos, The silver acts like a flux for the silfos and strengthens the joint. I have never had to reweld a silver joint doing it this way.
I have heard of plumbers doing the same and mixing soft solders.
Xenos.
The best way to escape a problem is to solve it.
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| | backyard mech
| "Re(2):Brazing Techniques" , posted Sun 27 Jun 23:31
Interesting.
So let me get this straight-I would only introduce nitrogen to the lineset one time not maintaining any pressure, just letting it displace the oxygen? I mostly work with new linesets that are precharged with nitrogen.
Please recomment on the reasons for not building up the braze joints.
I must admit I have never heard of mixing solders other than using alloys that are already mixed. I use Silvaloy 15 excel a 15% silver/phos/copper alloy, it works well especially when filling loose joints. (The melting range is 1190 F.to 1475 F.).
I have also read that the silver in it is not affected by vibration. which I assume is why you are able to "build up" braze joints when using this product.
Absolute Tempcontrol
Aurora Colorado
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| | Xenos
Webmaster
| "Re(3):Brazing Techniques" , posted Mon 28 Jun 16:42
On the nitrogen issue, I have the system open and I allow a small amount of nitrogen to run through the system the whole time I weld. Again it’s just a small amount.
When we solder there is the seal made. This seal is not made out side the joint but inside between the 2 metal surfaces. Therefore any excess solder ( silfos) on the out side is just a waist, it doesn’t add to the seal at all. For my fist 15 years or so in the trade, I always built up silfos on the out side of the joint, this is what I was taught and I never had a leak from doing it or so I thought. A few years ago I went to Niagara Falls on a Dectron Factory training course, during this training we spoke in depth about silfos and welding while there they proved to us that any buildup in silfos on a joint will cause the joint to crack. They had a 2 5/8 piece of copper there and the crack in the pipe was right where the build up of silfos was and not at the actual joint at all. The reason for this is the expansion and contraction rate of the silfos and copper are different. If the silfos is less than 1/32 thick ( between the joint) it will flex however if it’s thicker than this ( buildup out side a joint) it will cause the copper to crack over time as it wont flex when the copper does.
Xenos.
The best way to escape a problem is to solve it.
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| | backyard mech
| "Re(4):Brazing Techniques" , posted Mon 28 Jun 23:25
I wonder if the failure in the braze joint would have been the same if the product I use was used in the test as it is an alloy that has copper in it? Where is a metalurgist when you need one? Anyone know? I was reading a welding manual today about properly roughing up the copper fittings before brazing them (a habit I have been accustomed to probably from years of soft soldering), which got me thinking about deburring the copper pipe after cutting it with a pipe cutter. I am paranoid about getting the copper shards out of the lineset as the potential for damage seems obvious. But on the other hand I don't want to restrict the flow either. Any thoughts or methods to share?
Absolute Tempcontrol
Aurora Colorado
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| | HVAC Doc
| "Re(5):Brazing Techniques" , posted Tue 29 Jun 16:05
This is an interesting thread. I had always "assumed" everyone used Nitrogen while brazing. It does take practice as to how much pressure to put in so you don't blow you flame out or fittings apart. 5 psi or less is about all it takes. One thing I always have noticed is the joints seem "cleaner" and "neater" than ones done without nitrogen. We too clean and deburr copper lines and fittings before brazing (makes a difference as well) but one thing we do before brazing and installing the drier is purge the lineset out from the suction side (leaving liquid line open to blow and debris out. By doing it backwards we "hopefully" do not catch anything in the strainer/orfice/coil and leaving the drier out keeps from filling it with junk right off the bat.I do know some of my guys will take the bottle to the coil and blow the suction line out towards the unit and just hold the hose in and use a rag to "plug" the end up where the hose is stuck in.
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| | OMuilleoir
| "Re(6):Brazing Techniques" , posted Mon 12 Jun 15:28
Can anyone tell me the standard procedure for introducing nitrogen purge to a brazing area? What method is used to deliver nitrogen from a cylinder tank to the braze region?
I am brazing copper tubing to a brass valve fitting for pure oxygen service. Any ideas are greatly appreciated.
OMuilleoir
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