Help with Brazing

[onebullet]

keep in mind you were overheating everything, if your added material is just globbed on top its not doing anything to add strength.

I cant speak on the silver solder as ive never used it but i have experience as a welder and the principles are still the same.

also keep in mind that you are probably fatiguing the joint to break it (unless it just snaps off) which will break pretty much anything that bends.

 

[hotwheels000]

The joints were weak due to the plumbers solder being used. If you have sweat copper joints before you will get this no problem. Heat control was involved in copper, same here.

As you are heating the material to braze, keep in mind the bronze will flow the the warmest area, fillers always follow the heat and the tightest joint ( capillary action) When you feel the joint is warm enough introduce the coated bronze rod. The flux will melt off and flow onto you joint, shortly after your filler rod will,start to melt. Use you tourch to pull the molten filler to the area you want. You will get a much better joint if the material flows verses just filling the joint with large amounts of rod. If it isnt flowing it will be just like a cold solder joint when making electrical conections.

Make sure the entire area around the joint is sufficiently warm so that area doesnt act as a heat sink. Also dont braze directly on a steel suface as it will become a heat sink also and steel all the heat you are trying to intrduce to the joint. I like to set things up so as I am brazing the joint suspended. Not always possible so the next best is a kiln brick or fire rated stone to set the parts on. Never braze or introduce heat to a standard brick as it has the potential to explode.

 

[onebullet]

The joints were weak due to the plumbers solder being used. If you have sweat copper joints before you will get this no problem. Heat control was involved in copper, same here.

As you are heating the material to braze, keep in mind the bronze will flow the the warmest area, fillers always follow the heat and the tightest joint ( capillary action) When you feel the joint is warm enough introduce the coated bronze rod. The flux will melt off and flow onto you joint, shortly after your filler rod will,start to melt. Use you tourch to pull the molten filler to the area you want. You will get a much better joint if the material flows verses just filling the joint with large amounts of rod. If it isnt flowing it will be just like a cold solder joint when making electrical conections.

Make sure the entire area around the joint is sufficiently warm so that area doesnt act as a heat sink. Also dont braze directly on a steel suface as it will become a heat sink also and steel all the heat you are trying to intrduce to the joint. I like to set things up so as I am brazing the joint suspended. Not always possible so the next best is a kiln brick or fire rated stone to set the parts on. Never braze or introduce heat to a standard brick as it has the potential to explode.

not sure why you would need to heat up the whole thing, you just said yourself that the material goes to the hottest point. The material being used isnt big enough or thick enough to wick away enough heat and considering its all connected anyway its going to warm up while the work area is being warmed. Pre heat is used on thick material for fusion welding (which this is not) to get more penetration.

Yes heat will disperse through the material but not enough to effect the joint in a negative way. If anything it would make the structure weaker due to heat cycling.


EDIT: not saying you are wrong, just wondering the logic/theory used

 

[hotwheels000]

General guidlines used for all types of brazing, ie tubing,solid stock, flat plate, etc... Maybe I could have been a bit more clear. Having been a plumber makeing navy spec brazeing joints at the shipmyards in copper and copper nickle, you learn to preheat the work evenly before introducing the filler. When a joint is cut open for inspection you can clearly tell if the part was pre heated and the filler flowed properly.

I use a micro torch for most of my work now, the heat is so pin point you must heat the entire joint before filler is aplied or it will become a cold joint. Same can happen with the mapp torches, just not as likely since they disperse a wide pattern of heat. I usually heat the part of the joint facing me, then the backside and introduce the filler on the front side. If the front wasnt pre heated first, you would introduce more heat than needed to melt the filler. More heat can cuase the problems you mentioned.

Its a good habit to get into when brazing almost any medium of any size.

I didnt mean heat the whole project, just the area of the joint in this small scale.

 

[onebullet]

ah, misunderstood you. Thought you wanted him to heat the entire thing haha.

thanks for clarifying

 

[Cr00zah]

I'd also suggest using a flux with acid in it (I got mine at the local welding shop). Once you clean the material, apply the flux; when you heat the acid-based flux, it too cleans, and it becomes very very obvious when to apply your filler.

 

[BadWagon]

Wow great info in this thread. Subscribed.

 

[murdock]

I'm not sure if this was covered yet( don't have time to read every post atm) but from the look of your pics you didn't clean the brakeline, yeah its galvanized. So you'll want to sand around the area you are heating up. or you can use sulfuric acid, the acid will take the galvanized coating right off of it. JUST BE SURE TO RINSE IT OFF before heating with a torch. It will make some gnarly vapors.

Galvanized gives off some pretty bad vapors on its own so make sure you're brazing with a good amount of fresh air. Hope this helps you!