Procedures for Brazing Pipe and Tubing
CUT PIPE SQUARE
Cut to the exact length required using a tube cutter or hacksaw. If a hacksaw is used, a sawing fixture should also be used to ensure square cuts. Remove all inside and outside burrs with a reamer, file, or other sharp edge scraping tool. If tube is out of round, it should be brought to true dimension and roundness with a sizing tool.
CLEAN TUBE END AND INSIDE SURFACE OF FITTING
The joint surface areas should be clean and free from oil, grease, or oxide contamination. Surfaces may be properly cleaned for brazing by brushing with a stainless steel wire brush or by a stiff rubbing with emery cloth or Scotch Brite®. If oil or grease is present, clean with a commercial solvent. Remember to remove small foreign particles such as emery dust, by wiping with a clean dry cloth. The joint surface MUST be clean.
SELECT BRAZING ALLOY
Refer to the Harris Filler Metal Selection Guide for recommended brazing Filler Metal selection. When brazing copper to copper, alloys such as Dynaflow®, Stay-Silv® 5, or Stay-Silv® 15 are recommended. These alloys contain phosphorus and are self- fluxing on copper. When brazing brass or bronze fittings, Stay-Silv® white flux is required with these alloys. When brazing iron, steel or other ferrous metals, select one of the Stay-Silv® brazing alloys such as Safety-Silv® 45 or Safety-Silv® 56 with Safety-Silv® white brazing flux. Do not use phosphorus bearing alloys as the joint may be brittle. To estimate the amount of brazing alloys needed, refer to the Harris Estimating Brazing Alloys chart.
PROPER FLUXING is important because the flux absorbs oxides formed during heating and promotes the flow of filler metal. When using Stay-Silv® white flux, apply it only with a brush. To prevent excess flux residue inside refrigeration lines, apply a thin layer of flux to only the male tubing. Insert the tube into the fitting and, if possible, revolve the fitting once or twice on the tube to ensure uniform coverage. Stay-Silv® white brazing flux is available in 7 oz, 1/4 lb, 1/2 lb, 1 lb, 5 lb jars, 25 lb and 60 lb pails.
ASSEMBLE THE TUBE AND FITTINGS
Insert the fluxed tube end into the fitting. Maintain support to ensure the proper alignment until the brazing alloy solidifies. After brazing maintain support for a few seconds (or more) depending upon the size of the joint area.
The assembly is now ready to braze, using brazing alloy in rod, wire, or in coil form manually fed into the joint.
ADJUST TORCH FLAME
Oxygen/Acetylene. For most brazing jobs using oxygen-acetylene gases, a carburizing or neutral flame should be used. The neutral flame has a well-defined inner cone See diagram. Avoid an oxidizing flame. Excess acetylene removes surface oxides from the copper. The copper will appear bright rather than having a dull or blackened surface due to an improper oxidizing flame.
Air/acetylene using swirl combustion tips.
Brazing with air/ acetylene torches is a popular alternative to oxygen mixed fuel gas. The fuel gas flow aspirates air into a mixer that contains an internal vane that spins the gas to improve combustion and increase flame temperature.
If the tank has a delivery pressure gauge set the delivery pressure at 14-15 psi. If the tank has only a contents gauge delivery pressure is preset at the factory so open the regulator adjusting screw all the way by turning it clockwise until it "bottoms."
Open the torch value. Opening about 3/4 of a turn will provide sufficient fuel gas delivery. Do not try to meter pressure, (reducing the flame), by using the torch handle valve. If a higher or lower flame is required change to a different tip size.
HEATING THE JOINT AREA
Always keep the torch in short motion. Then...
1. Start heating the tube, first applying flame at a point just adjacent to the fitting. Work the flame alternately around the tube and fitting until both reach brazing temperature before applying the brazing filler metal.
2. When a flux is used, it will be a good temperature guide. Continue heating the tube until the flux passes the "bubbling" temperature range and becomes quiet, completely fluid and transparent and has the appearance of clear water.
3. Direct the flame from the tube to the flange-base of the fitting and heat until the flux that remains in the fitting is also completely fluid.
4. Sweep the flame back and forth along the axis of the assembled joint, tube, and fitting to get and then maintain uniform heat in both parts.
APPLY THE BRAZING ALLOY
Feed the alloy into the joint between the tube and the fitting. Only after the base metals have been heated to brazing temperatures should the filler metal be added. At that time, the flame may be detected momentarily to the tip of the filler metal to begin the melting process. Always keep both the fitting and the tube heated by playing the flame over the tube and the fitting as the brazing alloy is drawn into the joint. The brazing alloy will diffuse into and completely fill all joint areas. Do not continue feeding brazing alloy after the joint area is filled. Excess fillets do not improve the quality or the dependability of the braze and are a waste of material.
WHEN MAKING VERTICAL ALLOY-UP JOINTS heat the tube first, then apply heat to the fitting. It is important to bring both pieces up to temperature evenly. Keep the flame directed toward the fitting. If the tube is overheated, the brazing alloy may run down the tube rather than into the joint.
WHEN MAKING HORIZONTAL JOINTS heat the circumference of the tube first, and then apply heat to the fitting. Deciding where to start feeding the alloy will depend on the size of the pipe and operator preference. On large diameter pipe, however, sometimes the best approach is to start at the bottom of the pipe. As the alloy solidifies, it will create a "dam" and help prevent the brazing alloy from running out of the joint as the remainder of the connection is filled. When adding alloy, make sure both the pipe and fitting are up to temperature.
CLEAN AFTER BRAZING
All fluxes residues must be removed for inspection and pressure testing. Immediately after the brazing alloy has set, quench or apply a wet brush or swab to crack and remove the flux residues. Use emery cloth or a wire brush if necessary.