Bare Bronze vs. Flux Coated Brazing Rods

Utility of braze welding

Whether you are a HVAC technicial, a plumber, or a metal artist, braze welding is a very useful and versatile method for making metal joints. The utility of braze welding lies in the fact that different alloys and metals can be joined together. Whats more is that the heat required is significantly lower than that used for welding so heat distortion is minimized. The braze welding alloy is much more fluid that steel filler metal and actually flows into the braze welding joint by capillary action.
In order for a solid braze welded joint to form and the bronze filler rod to be able to flow, a flux is needed. Flux is a chemical mixture that actively dissolves oxidation naturally present on metal surfaces and also provides a shield against the oxygen of the air during heating so the filler metal can flow into the joint.

What is brazing exactly?

Brazing practiceBrazing is a process where two metals being joined are heated and a filler meta,l which usually melts at a lower temperature, is added to flow into between workpieces creating a bond. The most common brazing alloys used are bronze or brass. Sometimes it is necessary to use silver bearing brazing alloy. Most metals can be brazed except aluminum, magnesium, or titanium. Another benefit to brazing is that dissimular metals can be joined. For example, you can braze steel and copper together with bronze brazing rod.

Flux coated rod

Flux Coated RodsOne product line available to the braze welder is the flux coated brazing filler rod. These come in various compositions for joining different alloys. The main benefit is the flux is already on the rods and does not need to be pruchased separately.  The disadvantages outweigh the benefits and the convenience in my honest opinion. First, if you are working with new metal or at least relatively clean metal, you would need to scrape as much as 3/4 of the flux off the flux coated rod. The flux is tanacious and somewhat glassy due to the high level of borates. If you overheat the joint and use to much flux, it will form an incredibly hard black mineral glass that is next to impossibly to remove. Flux residue removal is essential if any painting or surface finish is going to be done. What happens if any flux is not removed, the flux will effloresce causing it to “bloom” into a crystaline crust. This will lift and rupture any paint or lacquer exposing the joint to further corrosion and moisture from the air.

Bare bronze brazing rods

Brazing FluxAn alternative to flux coated brazing rods is to use bare bronze rods with a paste flux. This involves less work because their is no flux to scrape off when brazing clean metal. With paste flux, you can use as little or as much is needed. This is important as different alloys need different amounts of flux. For instance, stainless steel needs a little more flux due to the tough oxide coating. The flux paste I use is used for all commonly brazed alloys. It has borates like on the flux coated rods but with a little fluoride. This facilitates easier removal of flux residues with a wire brush and hot water. The fluoride fumes are corrosive and toxic so you must be mindful of ventilation.

Starburst Sculpture created by braze welding

StarburstThis is a great examply of what I do with braze welding. I make home decor. Notice how the bronze joint not only is functional but decorative due to the contrast with the grey steel. For more photos and information please visit this link to the listing in my Etsy Shop.
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One thought on “Bare Bronze vs. Flux Coated Brazing Rods

  1. Brazing Rods says:

    Awesome article,
    I like the valuable info, you have provided in your article. Thank you for sharing with us.

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