Brazing Questions

Without knowing your joint configuration, I can only offer the following guidelines:

Apply the proper flux to the joint.

Begin heating the part with the most mass, that is, the part that will soak up the most heat. Try to bring both sides of the joint up to brazing temperature at the same time. Use the flux as a guide. When the flux liquefies, you are at brazing temperature. Keep the flame moving to keep the joint uniformly hot. Apply your brazing filler through the torch flame, using the flame to melt the filler. Apply heat to the joint to allow the filler to completely fill the joint. Do not overheat either the joint or the filler. Keep the joint temperature just at the point that the filler is liquid. That's it in a nutshell. Realize that volumes have been written on the subject. If you're a little gun shy, try to develope your technique on a scrap part. Good luck.

It will be helpful if you could describe what you are trying to braze, in reference to joint design; socket/tube, lap, etc. If a socket, which material is inserted into the other?

When brazing two metals together, whether they are the same material or different material, ideally the temperature of both metals should be the same. Brazing filler metals travel into the joint mainly due to the slight gap between the brass and the copper in your example (capillary attraction). In the case of a copper pipe inserted into a brass fitting, the heating source (flame) would be transferred from the brass to the copper pipe and back again, while heating all around the joint. The time heating the brass or the copper would depend on estimating how much of a heat sink each metal would be. If the joint is heated evenly, the brazing filler metal will penetrate all the way into the joint.

copper being a better conductor is giving heat to the brass...if you sweat the copper the brass will wet easily

If it is, say, a brass flange and copper pipe..............it may be easier to silver solder it...............dependent on the strength of joint that you require.

Watch out for distortion............if this could become a problem.

FYI: Brazing de similar metal you may use the following silver rod:

1. Silver rod: 5 to 15% silver content

2. Silver coated rods: 45% silver

Hope this will help you

Both parts should be heated to reach brazing temperature at the same time. Design the braze joint so it does not contain any trapped gas. The gas will expand while the joint is being heated and force the flux and braze alloy from the joint area. Think about brazing a plug into a counterbore. If neither the plug or the counterbore are vented to atmosphere, the air between the two parts will expand and try to push the plug and the braze materials out of the hole.

when bazing brass to copper it is important to start with a clean joint you would also want to use a flux designed for brazing. you should pre heat the brass but then focus the heat on the copper. good luck

Personal experance has shown me that brazing copper and brass together with brass to be difficult and not too effective. I suggest you go to your local heating and air conditioning parts supply house (Mercone or the such like) and get a few sticks of Stay Sil filler material and flux. Try your local welding supply they should have it. This is a very strong silver solder that requires more heat than a propane torch can provide so you will need an oxy/fuel torch. It is used in industry to braze(silver solder) oxygen lines, air conditioning lines, and has the appearance of a brazed joint. It doesn't look like silver solder at all. Do not use the silver solder you get in the little tube at the hardware store. It's low temp, soft, and not strong.

I think some people here are getting the wording mixed up and are thinking of brazing as using a brass type rod filler metal only. You can get the brass rod with higher silver content and it works well with certain cast iron and bi metal brazing such as steel to cast vacuum lines but it won't work for copper. I have "brazed" or soldered hundreds of brass valves to copper on a/c pipe in large schools and it is done all the time. We too use the flat Sty Silv brand silver solder rods to do this "brazing" or soldering, which ever you decide to call it. When we do this we still call it silver soldering whether it is the right term or not I really don't know. Stay Silv is different than the traditional silver solder in that it is a different base alloy. Also it does not usually contain as much silver and it was developed for the higher pressure a/c lines. Because of less silver content it is also cheaper to use. They make Stay Silv with many different silver contents and for copper to brass I would recommend the 5% or 10% and a good non water soluble acid flux. You can get it in any pipe supply or welding supply as has been previously stated. If you are however sweat soldering a brass valve or fitting onto a copper water line the same acid flux and a solid core roll of solder is all you need and Stay Silv or any other brand of the so called silver solders is overkill IMO.

pipewelder

Agreed Excellent answers.

I have been an HVAC mechanic for 30 years and the only other way that I have bound copper and brass together is with Stay Brite #8, and Flux. However if there are to be fluctuation's in temperature then go with the Silver. The Silver will be strong and dependable for years. As said before the materials need to be the same temp before brazing and the material should melt which ever alloy you decide to use. As Pipewelder said the material used will follow the flame as you move around the joint as the materials are attracted to heat, however I have always liked to feather the flame towards the greater mass so that it sucks more of the brazing material in to the joint rather than just a close to the edge surface joint.

I have soldered numerous brass fittings onto Cu pipe using normal soft solder with no problems.

What you use depends on the final use of the item.

Clean the socket and pipe, spread a paste flux on the pipe and into the socket, heat until above the MP of the solder (an ordinary gas torch will do this) then place the solder on the joint and run it around. The molten solder sucks into the joint and if no strain is placed on the solder before it gets below the softening point, you have a gas and water tight joint.

If any water is present, the steam generated causes a leaky joint. One way to overcome this is to pack the pipe with bread. The bread absorbs the water long enough to set the joint. Running water turns the bread soggy and the mess can be blown out the nearest outlet.

If you are joining anything more demanding than plumbing, you will need to use silver solder or braze the joint, as has been so well described by others.