The purpose of this guide is to provide some basic information for successful brazing.

Brazing is a process that uses a metal with a melting point lower than that of the base material as filler, heated above 800F, melting the filler while the workpieces do not melt, joining two or more metal workpieces together. It is important not to confuse hard brazing with soft brazing, which has a melting point below 800F. Sometimes silver brazing is incorrectly referred to as silver soldering.

To be certified as a competent welder, it typically takes forty hours of classroom and on-site training because it is necessary to weld the main components of the refrigeration system into a closed circuit, and since the closed circuit contains refrigerant, each weld joint must ensure no leakage.

The following information mainly targets metal welding with copper as the base material; this procedure also applies to connections between copper-brass, copper-steel, brass-steel, and steel-steel.

Correctly mix oxygen and combustible gas.

A mixture containing too much combustible gas; this type of flame shows traces of excessive combustible gas, with slightly more combustible gas than oxygen in the mixture, producing a reducing flame that heats and cleans the surface of the welded metal workpieces to quickly and effectively complete the brazing work.

A balanced mixture; this type of mixture contains equal amounts of oxygen and combustible gas, producing a flame that can only heat the base material.

A mixture containing too much oxygen; this type of mixture has excessive oxygen, producing a flame that can oxidize the surface of the welded metal workpieces and form black oxides.

Cleanliness.

To achieve satisfactory welding, cleanliness is essential. All surfaces of the metal workpieces to be welded must be completely clean. The surfaces must be cleaned with a wire brush or sandpaper; there should be no oil, paint, or aluminum on the surfaces; otherwise, contaminants will prevent the filler from flowing and adhering to the workpiece surface, hindering joint formation.

Insertion and gap of workpieces.

The gap between the outer pipe wall and inner pipe wall should be 0.003-0.005 inches.

The inner pipe should be inserted at a joint where its diameter length matches.

Proper heating.

Apply sufficient heat to ensure that the entire area around the joint is evenly heated and that the filler can melt.

Do not overheat to the point where the welded metal workpieces melt; use a torch of appropriate size and employ a reducing flame.

Application of filler rod.

Use the filler rod as a temperature indicator. When the filler rod placed on the heated joint area begins to melt, it indicates that the workpiece is sufficiently hot and ready for brazing.

For better results, preheat the filler rod with an outer flame; hot copper pipes (not the entire flame) will melt the filler rod.

Capillary action.

The filler material forms joints through capillary action by atomic diffusion with the surface of the workpiece, melting and combining; this can only occur when the surface of the workpiece is clean, gaps are appropriate, and the joint area reaches sufficient heat to melt the filler material.

Simple guidelines for quality brazing.

The surface of workpieces must not have oil stains, spots, paint, or aluminum.

Check if gaps between metal workpieces and their insertion are appropriate.

Use an appropriate reducing flame.

Heating of metal workpiece surfaces should be appropriate and uniform.