Brazing Copper to Brass with Sil-Fos®

Brazing Copper to Brass with Sil-Fos®

Welcome! Today, Lucas-Milhaupt is going to demonstrate brazing copper tubing to braze
using our Sil-Fos and Handy Flux product. The phosphorus in self-brazing alloy gives
it a self-fluxing ability when used on copper. However, it is required that flux be used
when brazing other copper alloys such as brass or bronze. Remember the functions of flux
in brazing are, it protects the filler and base metals from oxygen during heating, it
dissolves and absorbs any oxides for cleanliness, flux also helps the filler metal to flow by
reducing surface tension and it acts as a temperature indicator during heating. Step
one, is to remove any temperature sensitive parts then clean the tubing and fitting, parts
should be properly cut and reamed to remove burrs. Cleaning should be performed so that
the surface contaminants are removed without unwarranted loss of the base metals. Lightly
roughen the tube ends and the fitting with wire brushes, steel wool, or fine grades of
abrasive papers. Any residual particles in the joint surfaces should be avoided and any
residue remaining after mechanical cleaning must be removed. Step two is to add flux,
here, we apply flux with a small acid brush. Step three is to insert the tubing into the
brass part. Here, we insert the tubing making sure that the tubing seats at the bottom of the
brass fitting. Support the tube and fitting assembly to provide a consistent gap around
the entire circumference of the joint. Step four, is to uniformly heat the braze area.
We are using an oxygen acetylene torch; however air acetylene, with a proper tip, or any fuel
gas that can rapidly heat copper would also be suitable. A reducing flame is recommended,
the flame should be soft enough, and large enough to envelop both the tube and fitting.
Begin heating with the flame perpendicular to the tube. The copper tube conducts the
initial heat into the fitting for even distribution of heat in the joint area. The amount of heating
depends on the size of the joint. Experience will determine the amount of time needed.
Next, move the flame onto the fitting, and then direct the flame from the fitting back
onto the tube a distance equal to the depth of the fitting. Step 5 is to allow the alloy
to be drawn by capillary action into the joint. The alloy flows from the outside to the inside
by way of capillary attraction; heat towards the top for a second or two to pull the alloy
through. The alloy will flow to the area with the highest heat completely penetrating the
joint. Step 6 is to clean any residual flux from the part using hot water. Cleaning will
help you inspect the joint and it limits the possibility of corrosion. After cleaning,
inspect the joint for a small uniform fillete at the braze joint. The presence of the fillete
indicates that the filler metal has completely flowed from one end of the joint to the other.
As we have seen, you can braze copper tubing and brass quickly and easily with Lucas-Milhaupt’s
Sil-fos and Handy Flux. To review, our steps were, one, clean the tubing and fitting. Two,
add flux. Three, insert the tubing ensuring contact with the brass at the bottom. Four,
uniformly apply heat & add alloy. Five, watch as the alloy is drawn around the joint and
six clean the flux and inspect the joint. For more information, please visit our website
or contact your Lucas-Milhaupt representative.


  1. Hi there!! Thanks for the showing us how to use this flux. I've had a hard time trying to find a flux that can be used with oxyacetylene. But well, it seems I have found it!
    Now, could you please let me know what is the shelf life on this flux?
    Thank you for your information.

  2. What is the parameters for such kind of brazing, like oxygen pressure? LPG Pressure? and flame length? required temperature? etc. Plz tell me on my email ID.


  3. Very sloppy. Flux clogs Txv's and power Pistons. Also In correct flame. 7 on the acetylene 20 on the oxygen "psi"

  4. You did not need to brush the flux all around the fitting once the tube was seated in the socket. Apply flux to the tube (and the inside of the female end) and insert. Apply flux where you want the SilFos to flow.

    The over-application of flux is what resulted in this being a very messy/ugly braze.

  5. Sloppy. Never apply flame directly to the flux, it needs heat up, boil, solidify and turn back to a clear looking liquid then you can continue heating till it melts the silver solder. you should not have globs all over when your completed.

  6. Super Sir, pls help me, I want to develop silver with copper terminals for electric contacts,what is type of flex use in brazing method,in meddle of copper bolt And 1.5mm thick silver

  7. flux also drives out the impurities to the surface,,btw is it possible to melt off a silfoss joint with propane air torch? a buddy of mine said he heated the tubing till it was cherry hot and could not melt the stuff ,some refrigeration guy laughed and told him he would never be able to with propane and needed to use acyt,,i think this is puzzling,,im not sure what that stuff was he could not melt off,because all you need is 600-800 deg C and prop is 2000 deg C

  8. I don't know why these how to braze videos always show the person using a wet cloth. Your supposed to use a piece of Emory cloth or sand paper.

  9. Did he braze that with his eyes closed sheesh that was ugly and I never seen anyone flux before brazing only when soldering I could be wrong but I’ve never fluxed anything I’ve brazed

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