Make sure all joints are clean prior to cutting tubing. Clean tubing and joints with refrigeration sand cloth and wire brush.
Dirt and oil will prevent the proper application of flux and also deter flowing and bonding of the silver brazing alloy.
The use of flux is essential. Assemble the parts to be brazed, then apply a liberal amount of flux to the circumference of the joint.
CAUTION: Do not apply flux to any joint before assembling.
The flux will assist the alloy flow by wetting the tubing surface. It also prevents oxidation of the metal during heating and helps clean by absorbing and dissolving surface residue.
4. Heating and Flowing the Alloy
Apply heat from your torch to the point being brazed until the flux turns clear and waterlike. Apply alloy and continue heating joint until alloy flows around circumference, forming a uniform fillet. Very little alloy is required for a good joint. A rule of thumb is that a length of alloy equal to the diameter of the tubing to be joined is adequate to provide a proper joint.
Proper heat will ensure capillary action and penetration of the alloy. However, be careful not to apply too much heat. This will cause the inside of the tubing to scale, and this scale might later restrict the refrigerant flow in some part of the system.
On a copper-to-steel joint it is very important not to concentrate the heat from the torch on the steel tubing. Apply heat evenly on both tubings and remove heat as soon as alloy flows. Steel tubing scales at a lower temperature than copper tubing.
5. Final Cleaning
When brazing is completed, scrub each joint with hot water until all flux is removed. The residue could temporarily cover a leak. Regardless of the appearance of a good fillet, be sure to leak-test all joints with an electronic leak detector, a Halide torch, or a bubble solution.
SILVER SOLDER AND FLUX
Silver solder is specified for brazing refrigerant tubing. It has a high tensile strength, does not corrode, and will withstand extreme temperature conditions.
There are many types of silver alloys on the market but for different applications. Recommended alloys for refrigeration service include Silver Alloy 1551 or Handy and Harmon p60. These are cadmium-free and wil1 produce a good braze between either copper to copper or copper to steel. In choosing an all-around brazing material, therefore, either the Silver Alloy 1551 or the Handy and Harmon 560 is the best bet because many of the refrigerator tubes are of steel.
Phosbraze 15 or Sil-Fos brazing materials will only work on copper-to-copper joints and are not compatible with steel. They will do a good job on poorly fitting copper-to-copper joints such as might be encountered on the large central airconditioner tubing.
The Silver Alloy Flux and the Handy and Harmon Flux are recommended for silver soldering. They begin to melt and dissolve oxides at about 600° F. and become molten and fully active at 1100° F. to 1600° F.
After the brazing operation is completed, the flux residue must be cleaned off with a cloth and hot water. If it is not cleaned, corrosion may result. Do not allow the flux to dry hard in its container. A thin layer of water should be present after standing, but the flux should be freshly stirred before use.
Chapter 4 Page 10
Stay-Silv Brazing Flux
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