Arkansas HVACR NewsMagazine May 2022

HVACR NewsMagazine May 2022

Tech News

anyone can use to reduce the likelihood of leaky joints.

There’s a difference between brazing and soldering, even though the practices are similar. Soldering refers to the bonding of metals at a temperature below 840°F; we braze at temperatures above that threshold. Metals with low melting points, like aluminum, should have soldered connections and patches instead of brazed ones. Copper has a relatively high melting point, so we typically braze it. Before you even think about picking up your torch kit, you must ensure that your copper is prepared for brazing. That means that you’ll have to clean it, deburr it, and make sure the fitment is tight. To avoid getting burrs and shavings into the copper, be sure to sand the copper down before you cut it. If you sand the copper AFTER it’s been cut, you may get tiny shavings into the tubing, which may result in restrictions. When you cut your copper, you will want to get an even, clean cut with a proper tubing cutter. A jagged cut will make for a lower- quality connection, so you’ll want to make sure the cut is straight and make many slow rotations with your cutter. You will also have to deburr or ream your copper. When you do that, be sure to have the copper angled downward so that the burr falls out of the tubing, not back into it. Once you have prepared your copper tubing, try fitting it into the place where you will braze the joint. If you have too much of a gap between the two, you may have to use Preparing your copper for brazing

bushings or reducers to make the copper fit together.

Choosing the proper alloy, flux, and brazing rod

The alloy you choose will depend on the base metals; copper-to-aluminum brazing or soldering requires a different alloy than copper-to-copper brazing. However, in any case, all alloys should have good flow, be as ductile as possible, and have a melting point well below the lowest melting point of the base metal(s) you’re joining. The more ductile an alloy is, the more flexible it will be under stress. high-silver alloys tend to be more ductile, which is why 15% silver alloys are generally more desirable than 5%. (You can even find alloys with up to 56% silver.) Brazing rods are made of alloys and may or may not contain flux. Flux may be channeled inside the rods, coated on the rods, or come in an external form that you apply at the joint, and it prevents oxides from forming on the base metal during heating. When you have an external flux that needs to be applied straight to the base metal, lightly coat ONLY the male end of the tubing. Some fluxes are also corrosive, so you’ll want to wipe the flux away with a wet towel after you’ve finished brazing.