Brazing Copper to Copper with Sil-Fos®

Brazing Copper to Copper with Sil-Fos®


Welcome! As brazing and soldering
specialists, Lucas-Milhaupt offers comprehensive expertise on brazing
procedures. Today, we are going to demonstrate brazing copper tubing-to-
fitting assemblies with Lucas-Milhaupt’s Sil-Fos. Step one is to 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 bushes, 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. When joining copper tubing to copper
fittings with Lucas-Milhaupt Sil-Fos brazing filler metal, no flux is required. The phosphorus in the Sil-Fos brazing
filler metals gives them a self-fluxing ability when used on copper. However, it is required that a flux be used
when brazing other copper alloys such as brass or bronze. Step two is to insert the tube. Make sure
the tubing makes contact with the bottom of the fitting. Support the tube and fitting assembly to
provide a consistent gap around the entire circumference of the joint. 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. Step three is to apply heat and the alloy
to the braze area. 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 upon the size of the joint. Experience will determine the amount of
time needed. Next, move the flame onto the fitting.
Then direct the flame from the fitting back onto the tube a distance equal to
the depth of the fitting. Begin applying the alloy to the joint to be
filled. Do not use the flame to melt the alloy. The alloy should melt due to the
heat of the part. Step four is to allow the alloy to be drawn
by capillary action to the bottom of the joint. The alloy flows from the outside to the
interior via capillary attraction. Heat towards the bottom for a second or two to
pull the alloy through. The alloy will flow to the area with the
highest heat. After brazing, inspect the joint for a
uniform fillet around the braze joint. As we have seen, you can braze copper
tubing-and-fitting joints quickly and easily with Lucas-Milhaupt’s Sil-Fos products. To review, our steps were one, clean the tubing and fitting. Two, insert the tubing making contact with the fitting. Three, uniformly apply heat and the alloy. Then, four, watch as capillary action draws the alloy and a fillet is formed. For more information, please visit our
website, or contact your Lucas-Milhaupt representative. Thank you!

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