For systems operating at 350 degrees or higher, braze-welding copper pipe fuses two or more pieces together to create extra maximum joint strength.
Brazing is a tried-and-true way to join two pieces of metal for connecting systems of refrigeration, gas distribution, and HVAC (heating, ventilation, and air conditioning) equipment.
But how to braze copper with the minimum amount of hassle?
Understanding The Brazing Process
Before you buy your brazing tools, it’s important to understand exactly what brazing is and how it works.
Sometimes used for plumbing, the brazing process is a way to join metals together by melting them, then flowing the molten metal through a filler material. The filler material acts as a “braze” that holds the two pieces together while they cool and solidify.
What Is Brazing?
Brazing is a process used to join two or more pieces of metal by heating them together and applying pressure. It typically involves heating a filler material to a melting temperature between 3620 and 6330 degrees Fahrenheit before inserting it into the joint.
Once the filler metal melts and flows, it bonds with the surrounding metal to form a solid bond that can last for decades.
Brazing can be done with either gas or electric heat sources. Electric brazing uses an argon torch to melt the filler, while gas brazing uses a blowtorch that applies heat by burning the torch’s fuel in an oxygen-rich environment.
- Electric brazing is generally more efficient at producing high-strength joints due to its smaller heating element, though it’s also more dangerous since it requires constant eye contact and proximity to the oxidizing flame
- Gas brazing has a much lower risk of fire and explosion because there’s no ignition source in close proximity to the work area. However, gas welding also requires special skill, so electric welding may be preferred for beginners
During the brazing process, temperatures can get very hot (840ºF) so a filler metal must be used to help cut a path and mold the joints together. This filler metal is called a blazing rod.
Rods designed for brazing have a lower melting point than the base metal so that it does not melt during the brazing process.
A brazing rod, known as a filler, is a short length of the metal bar used for joining processes or sealing an end or joint in a pipe, tube, or other metallic structure. It can be made from various materials such as steel, aluminum, brass, and titanium.
There are a few different types of fillers on the market. For example, there are some that contain copper-phosphorus which means they are self-fluxing, (including brazing alloys) removing the need to apply any flux on the pipe.
There are others that are not self-fluxing which means a flux chemical mixture needs to be applied manually.
Flux Reduces Damage To The Copper Pipe
Flux is a substance that can be used as a solder to join metals. It flows easily between two surfaces and creates a strong bond when heated.
Flux is often used on a brazed joint because it melts copper and copper alloy quickly and evenly, making it easy to join them together.
Flux also prevents oxidation, which is where oxygen reacts with iron oxides and causes corrosion. In addition, fluxing also protects the surface from other elements like oxygen and water that can cause oxidation.
What Is Flux Made Of?
Flux is made of an alloy of silver, tin, and other metals that react with each other when they are heated. It’s commonly made by heating metals at high temperatures in a kiln or furnace.
Flux is available commercially in different forms such as paste, powder, liquid, and granular form.
Brazing uses a combination of heat, flux, and a metal rod that melts at a lower temperature than the pieces being joined.
The metal rod becomes a “solder” between the pieces, but the solder joints are not melted until the torch flame reaches a temperature above the brazing temperature of the metal.
The brazing temperature is below the melting point of the braze metal being joined, so it is less likely to damage or distort the joint than a fusion process such as soldering or welding.
However, a brazing job is not as strong as a fusion weld. For this reason, brazing is often used to join materials that are too thick or too brittle for fusion welding.
Brazing copper pipes requires a neutral flame torch that can cut through metals without causing any damage due to their high temperatures.
They consist of a torch handle, a tank with a pressure regulator, and a towing cable. The fire generated by the torch is fed through the tank which supplies it with oxygen.
The best torches for brazing copper are:
- Propane torch for pipes 1-inch pipes in diameter or smaller- (melting point- 3620F/1995C)
- Oxy-acetylene torch for 1-inch pipes in diameter or larger- (melting point 6330F/3500C)
Step By Step Brazing Method
Now that you know how the brazing process works, let’s take a look at a step-by-step method to ensure a safe and durable fitting.
Step 1: Clean all the pipe surfaces as well as the inside of the joint fittings thoroughly with a wire brush or abrasive pad.
Step 2: Sand down the outside tip of the pipes with an abrasive material of your choice.
Don’t skip this step as preparation is 90% of the job.
Step 3: If your copper pipe is phosphorus, apply the flux with a flux brush to the end of the pipe.
For beginners, try using thinning flux because it provides better coverage and melting form. It’s not a good idea to apply too much flux because if you do, the flux will run down the copper tube.
Step 5: Heat the fitting’s hub after the pipe has been heated while keeping the flame moving at all times.
Step 6: The rod can be used to determine if the pipe is hot enough by touching the edges. The edge won’t budge if the temperature isn’t hot enough. The temperature is reached only when it melts. A red pipe is another sign that indicates that the pipe has reached the required temperature.
Step 7: Once the pipes are fully heated, with the flame still concentrated on the pipe, you can begin smoothing the rod over the edges of the pipe, ensuring there are no gaps between the pipe and the fittings.
Step 8: Once your joint has been properly brazed, allow it to cool naturally. Applying a wet rag too soon might compromise the joint.
Step 9: Remove any excess debris or grease from the pipe surface with a wire brush or cloth once the joint has cooled down.
Step 10: Make sure your joint is free of holes, voids, and gaps by inspecting it all around. Use a mirror if you’re working in an awkward position.
When To Use Copper Braze Instead Of Bronze Or Copper Joining?
In some cases, it may be advisable to use bronze, rather than copper, for the joint. Bronze is more easily shaped than copper, and it is also less likely to be damaged by bending during installation.
In other cases, it may be advisable to use a copper joint, rather than a bronze one. For example, a copper joint is often needed for a fitting that will be subjected to high pressure. Copper can resist higher pressures than bronze.
You should also use copper if the connection must be made with a silver soldering wire.
Brazing Problems And How To Avoid Them
There are a few things you should do to make sure your brazing setup is a safe and successful process. First, make sure you are wearing the proper safety equipment, including gloves and safety glasses.
Be sure to clean your work area thoroughly before you start. This will help prevent any contaminants from getting on your pieces, which can cause problems later on down the road.
Because of this, you need to take care not to damage your piece when removing it from the brazing rod holder. And last but not least, keep an eye on the temperature of your brazing rod and flux as you go along.
If it gets too hot, it could melt your brazing rod holder or flux, which could lead to an unsafe situation for everyone involved.
Braze welding is a common method of joining copper and other metals. This process uses heat, flux, and solder to create a strong braze joint that resists corrosion.
Braze welding is a good alternative to fusion welding because it is not as likely to distort the metal being joined.
There are many types of joints that you can make using copper pipe and a torch. Select the type of joint that best suits your application, and then follow the directions on this page, and comment if you have any questions, for the best possible results.