Flux and brazing

[kay86]

Hello everyone,

Apologies for revisiting a beginner's topic, but I'm still in the process of learning how to achieve decent copper-to-copper brazing joints. Previously, I attempted using 30% flux-coated silver rods, but the outcomes were less than satisfactory, mainly due to my inability to properly control the heat, affecting the effectiveness of the flux.

Recently, I tried using Harris ECO Smart flux, applying it directly onto the joints and using a 40% bare silver rod for brazing. While the results showed some improvement (pic attached), they were still not the best. I believe the issue may still lie with the type of flux I'm using. The Harris ECO Smart flux is marketed as a "color change" flux, designed to indicate the correct brazing temperature. However, I find this feature somewhat redundant, as conventional wisdom suggests brazing should occur when the copper reaches its characteristic cherry red hue, which typically precedes the melting point of the rod. Surprisingly, I sometimes achieve better joints without using any flux, which shouldn't ideally be the case.

I acknowledge that I need to further refine my skills, particularly in managing the correct type of flame, as well as improving my dexterity and heat control. Nonetheless, I am committed to enhancing the quality of my brazing joints.

Could you all recommend a type of flux that could facilitate my practice and help improve my results?

Thank you!

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[monkey spanners]

I generally use Johnson Matthey Easyflo flux powder. I usually use the flux coated rods but have the powdered flux open and ready if I feel I need more on a joint.
If using uncoated rods, warm them with the flame then dip them in the flux, wait a bit and then remove to get the rod coated, if not enough has stuck repeat the process to get the rod coated sufficiently to make your brazed joint. As you use the rod you can top up the coating by repeating he dipping process, or top up precoated rods if needed also.

If you are doing copper to copper joints you don't need to use such high silver content rods, you can get easier results with 2% or 5% rods, they are self fluxing so don't need separate flux. They are not so runny when melted so are easier to use for joints with bigger gaps.

You only really need high silver content rods when joining copper to other metals such as steel or brass.

[kay86]

Hi monkey, by self fluxing you mean they have phosphorus in them?

[martinw58]

if joining copper to copper pipe you do not need fluxed rods

[kay86]

I don't need flux at all?

[RANGER1]

Copper to copper 15% silver, no flux required.
If using 2% not strong enough, that would be for plumber & water.
45% silver solder need flux, that is for copper to brass or steel.
Each area % this may alter slightly.

[kay86]

Copper to copper 15% silver, no flux required.
If using 2% not strong enough, that would be for plumber & water.
45% silver solder need flux, that is for copper to brass or steel.
Each area % this may alter slightly.

thank you!