Soldering Brazing Copper Tubing (1973)

[Music] Copper tubing may be joined by a number of methods depending on the purpose for which the tubing is to be used. With capillary fittings, by far the most common system, joints may be made by soldering or brazing. Soldered joints are used where the line temperature does not exceed 250° F. Brazed joints are used where greater strength is required or where temperatures are as high as 350° F. Although soldering and brazing operations are basically simple, the difference between poor and good techniques may be the difference between a poor and a good joint. The tube should be cut to the exact length with a square cut. Tube cutters are generally used and are available in sizes up to 8 in. An alternate method is to cut with a hacksaw, making sure the cut is square. A tube cutter will leave a small burr on the end of the tube which may be removed by a reamer. Care should be taken not to expand or flare the tube. The burr may also be removed by use of a half round file. Remove any metal particles from inside the tube. The end of the tube should be cleaned for a distance only slightly more than it is to enter the socket of the fitting. A fine grade of emery cloth or special wire brushes may be used. Rub hard enough to remove the surface film, but care should be taken not to remove any excess metal. The socket of the fitting should also be cleaned and the same precautions should be observed. Even if the socket looks clean, clean it anyway. Because the chemicals in the flux have a tendency to settle from long standing, it is recommended that the paste be thoroughly stirred before using. As quickly as possible after cleaning, the surfaces to be joined should be covered with a thin film of flux. The flux can be applied with a brush or a clean rag. The use of fingers to apply the flux should be avoided as the chemical in the flux can be very harmful if carried to the eyes. Assemble the joint by placing the fitting on the tube, making sure that the tube is hard up against the stop in the socket. A small twist will help spread the flux over the two surfaces. Remove the excess flux with a rag. The joint is now ready for soldering. The heat may be applied by a propane gas torch, an air acetylene torch, or by induction heating. The flame should be played on the fitting and in a continuous motion so as to heat as large an area as possible. Avoid overheating which may burn the flux and destroy its effectiveness. Overheating of a cast fitting may also cause the fitting to crack. When the metal is hot enough, the solder should melt on contact. If it does not melt, remove the solder and add more heat. When the joint is at the correct temperature, the solder should melt on contact and be drawn into the joint by the natural forces of capillary attraction. If the joint has been properly made, a ring of solder will be observed all the way around the fitting. The solder joints can be wiped with a clean cloth while they're still hot to make them smoother and more attractive. Molten solder will be drawn into the joint by capillary attraction regardless of whether the solder is being fed upward, downward, or sideways. Allow the joint to cool naturally for some time before applying water, particularly if cast fittings are used. Too rapid cooling may cause cast fittings to crack. When joining copper tube to solder cup valves, follow the manufacturer's instructions that are attached to each valve. Particular attention should be paid to the instructions that the valve should be in the full open position before applying heat and that the heat should be applied to the tube transferring as much heat as possible through the tube into the valve. Avoid any prolonged heating of the valve body. If too much solder is used, it may flow past the tube stop and clog the seating area. Strong leaktight brazed connections for copper tubing may be made with brazing filler metals melting at temperatures in the range of 1100 to,500° F. Brazing materials are sometimes referred to as hard solders or silver solders. In preparing to make a joint, the preliminary steps of measuring, cutting, burr removal, and cleaning are identical as the same steps in the soldering process. Fluxing should be done in accordance with the recommendations of the manufacturer of the filler metal being used. If the outside of the fitting and the heat affected area of the tube is covered with flux, it will prevent oxidation and greatly improve the appearance of the joint. Avoid getting flux inside the tube itself. Assemble the joint by placing the fitting on the tube, making sure the tube is against the stop in the socket, and turn where possible. The assembly should be firmly supported so that it will remain in alignment during the brazing operation. Brazing is started by applying heat to the parts to be joined. The preferred method is by the oxy acetylin flame. Heat the tube first beginning about 1 in from the edge of the fitting. Sweep the flame around the tube in short strokes at right angles to the run of the tube. It is very important that the flame be in continuous motion and should not be allowed to remain on any one point long enough to burn through the tube. Now switch the flame to the fitting at the base of the cup. Heat uniformly sweeping the flame from the fitting to the tube. The flux may be used as a guide as to how long to heat the joint. Continue heating until the flux becomes transparent like clear water. Apply the brazing wire at the point where the tube enters the socket of the fitting. Keep both the fitting and the tube heated by moving the flame back and forth from one to the other as the filler metal is drawn into the joint. When the proper temperature is reached, the filler metal will flow readily into the space between the tube and the socket of the fitting. After the joint is filled, a continuous fillet of filler metal will be visible completely around the joint. When making horizontal joints, it is preferable to first apply filler metal at the bottom, then the two sides, and finally the top. Making sure the operations overlap. On vertical joints, it is immaterial where the start is made. If the opening of the socket is pointed down, care should be taken to avoid overheating the tube as this may cause the alloy to run down the tube. If this condition is encountered, take the heat away and allow the alloy to set. Then reheat the cup of the fitting to draw up the alloy. After the brazing alloy has set, clean off the remaining flux with a wet swab or brush. Ror copper fittings may be chilled quickly. However, it is advisable to allow cast fittings to cool naturally to some extent before applying a swab. All flux should be removed before inspection and pressure testing. If the filler metal fails to flow or has a tendency to ball up, it indicates oxidation on the metal surfaces or insufficient heat on the parts to be joined. If the filler metal refuses to enter the joint and tends to flow over the outside of either member of the joint, it indicates this member is overheated or the other is underheated. For larger size tubing, it may be difficult to bring the whole joint up to the desired heat at one time. When heating a larger tube, a double tip torch may be found desirable to maintain the proper temperature over the entire area. A mild preheating of the whole fitting is recommended. The heating can then proceed following the same procedure used on smaller tubing. If the parts to be joined are properly cleaned, properly fluxed, properly heated, and the correct filler metal is used. The finished joint should be a good one. It is worth some study and practice to be able to make good joints. These can be produced using copper tubing and fittings, the proper filler metal and good technique. [Music]