Flux-coated brazing rods are a great tool to have on hand when you are attempting to fuse two pieces of metal. Having a flux coating over your brazing rod will assist in the formation of the bond and ensure your joint is strong and durable when it hardens.
When utilizing flux-coated brazing rods, you must understand that not all rods are compatible with all applications.
Use the guide below to help make the most appropriate choice when picking out a flux brazing rod for all types of projects and materials.
What Are Flux-Coated Brazing Rods?
A brazing rod is used during brazing applications. These rods create a bond between two pieces of metal with a higher burn temperature than the rod itself. As the blazing rod melts, it flows into the joint and hardens.
A flux-coated brazing rod is made to do the same job, bonding two pieces of material together with a metal filler. However, flux coating is added to the brazing rod for a smoother application and better adherence.
Flux-coating is made from a mixture of chemicals that coats the outside of the filler metal. The filler metal designed to create the bond is protected as the flux cools and hardens. The flux is then removed once the joint is secure.
The best way to utilize flux coating to optimize brazing applications is to clearly understand the different types of flux-coating brazing rods available and when to use them.
Types of Brazing Rods
There are a few different types of brazing rods available for brazing applications.
- Ag-based brazing filler metal: This is the most widely used brazing filler metal. And can be used on various materials.
- W-based filler metal: Used to weld various metals.
- CU-based filler metal- Copper: Used for brazing carbon steel and low alloy steel. Copper zinc is used for brazing various metals, and copper phosphorus is used for brazing copper and copper alloys.
- AI-based filler metal: Used for brazing aluminum and aluminum alloys.
A flux coating can be added to enhance the brazing rod's performance and further secure your joint.
Types of Flux-Coated Brazing Rods
The type of rod you use when brazing depends on the base metals you are attempting to create a joint for. The rod must have a melting point higher than the base material; this allows the melted liquid to form a bond without melting the parts you are trying to connect as it hardens.
The flux on the rod is just as critical; this chemical mixture will improve the wetting and spreading of the filler material.
With that said, it is also crucial to point out that some chemicals in the flux coating can have negative reactions with the base metal.
- Aluminum brazing flux: Used with aluminum brazing alloy or filler
- White flux: Used with brass, copper, mild steel, steel, and nickel brazing alloy or filler
- Black flux: Used with stainless steel brazing alloy or filler
- Bronze flux: Used with bronze brazing alloy or filler
Flux Selection Based on Temperature
The brazing temperature will help you choose the best type of flux for the job. When working with a soft metal with a low melting point, you want to ensure you are using a low-temperature flux.
Aluminum and magnesium are both great examples of low temp brazing rods. Chromium and titanium are both examples of high temp brazing rods.
Photo credit vacaero.com
You are good to go if your brazing rod and flux have a lower melting temperature than the base metal.
How to Use a Flux-Coated Brazing Rod
When using flux coating alone, apply the chemical mixture (typically a paste) directly to your base metal. By doing this, the flux will stick securely to the joint, keeping it protected.
A flux-coating on a brazing rod eliminates the step of brazing described above. Instead of adding the flux before brazing, the coating on the rod will melt off before the filler metal, thus making its way into the joint to prevent air from entering it. This step ensures you get a strong bond and no oxidation formation.
Tips for Brazing with Flux Coating Rods
Remember these tips and tricks to ensure the process goes smoothly when brazing with flux-coated rods.
Clean the Base Surfaces
Although flux coating works great for removing oxides from the surfaces of your base metals, you should still clean them off as much as possible, eliminating contaminants like grease and oils. This will help ensure you get a good bond and no adverse reactions.
Heat Your Brazing Joint
It is essential to heat your base metals when brazing. Heating the brazing joining even to the brazing temperature will assist in the smooth flowing flux.
The Brazing Rod and Flux Should Not Be Melted By Direct Contact
Your brazing rod and flux should never come in direct contact with a torch flame. The filler metal should be melted by the heat of the two base materials you are bonding.
You always want to use a high-intensity flame torch to get your joining metals hot enough to melt the rod and flux.
Keep the Area Well Ventilated
Although this tip doesn’t help with the brazing process directly, it is imperative to remember. Heating metals and chemicals always have the potential to turn dangerous. The fumes that come from this interaction can cause serious health problems. Ensuring the room is well-ventilated will keep you and others safe.
What are the benefits of using flux coating on brazing rods?
The flux coating on brazing rods prevents air from getting into the joints. Flux also removes oxides from your base materials, allowing the filler metal to flow freely. Lastly, flux promotes wetting which assists in the filler metal spreading smoothly and in a thin layer.
What is the most common type of flux coating used on brazing rods?
There are various types of flux coatings for different applications. However, the most common option is white flux.
Do you have to use flux when brazing?
Technically you don’t HAVE to use flux when brazing. However, without it, you will risk air entering the joint and compromising your bond.
Flux brazing rods come in a variety of materials and chemical coatings. These rods save you time during brazing and ensure you get the perfect bond during every application.
To ensure you use the right flux coating for your upcoming project, review the article and decide based on the tips and information provided.