A brazing alloy filler metal made up of copper and 5 to 10% phosphorus. Phos-copper begins to melt at 714°C (1317°F) and is completely molten at about 832°C (1530°F). Phos-copper is considered to be a self-fluxing brazing alloy in which the phosphorous prevents oxide formation on the copper surfaces.
However, if gas-tight or liquid-tight joints are required, or brass, bronze or other alloys are being joined, a paste flux is recommended. The paste is mixed with water and applied with a brush.
Phos-copper may be used to join copper and copper alloys, and has limited use for brazing silver, tungsten and molybdenum. These alloys should not be used for ferrous and nickel base alloys or on copper base alloys with more than 10% nickel to avoid formation of brittle, intermetallic phosphide compounds. Brazed phos-copper joints can be used for continuous service up to 150°C (300°F). Lap joints are recommended, but butt joints can be used where strength properties are less stringent. Recommended joint clearances are 0.03 to 0.13 mm (0.001 to 0.005 in.).
Brazing. The procedure for brazing with phoscopper depends on the material to be brazed and the brazing process, but the following are general procedures:
(1) Clean all joint surfaces thoroughly.
(2) If flux is needed, apply a paste flux mixed with water to all joint surfaces.
(3) Heat the joint to between 800 and 830°C (1475 and 1525oF), using a neutral flame if heating with an acetylene or other gas torch.
(4) Apply phos-copper rod or wire to the heated joint, ensuring that it flows into the joint gap.
If phos-copper ribbon is to be used instead of wire or rod, it should be inserted into the joint before heating, then heated to 830°C (1525oF), or until the braze has melted and flowed throughout the joint. Excess amounts of the phos-copper braze alloy in fillet joints, for example, should be avoided.