Soldering Copper Tube
Soldering is a process that joins base metals using a filler metal (solder) which melts at a lower temperature than the base metals.
Most soldering is done with solders that melt at temperatures ranging from approximately 175oC (350oF) to 290oC (550oF).
In order to consistently make satisfactory joints, the sequence of operations presented in ASTM Standard Practice B 828, Making Capillary Joints by Soldering of Copper and Copper Alloy Tube & Fittings, should be followed. It should also be noted that Canadian codes prohibit the use of solders containing more than 0.2% lead in potable water systems. There is a wide variety of solders available which can be used in place of the once standard 50% tin-50% lead solder, commonly called 50-50. They melt at slightly higher temperatures and may exhibit different flow characteristics.
Soldering Copper Tube
A suitable flux must be used when making a solder joint. Flux acts as a cleaning and wetting agent, and when properly applied, permits uniform spreading of the molten solder over the surfaces to be joined. Flux is a chemically active substance, and only enough should be applied to remove and exclude oxides from the joint area during heating and to ensure that the melted solder will wet the surfaces to be joined. Do not overflux!
ASTM Standard B 813, Liquid and Paste Fluxes for Soldering Applications of Copper and Copper Alloy Tube, covers the requirements and test methods for liquid and paste fluxes
for soldering copper-base materials.
Measuring
Accurately measure the length of each piece of tube needed. (Figure 3) If the tube is too short, it will not reach all the way into the cup of the fitting and a good, strong joint cannot be made. If the tube is too long, strain may be introduced into the system.
Cutting
Cut the tube to the measured length. It can be cut with a disctype tube cutter (Figure 4), a hacksaw, an abrasive wheel, or with a stationary or portable bandsaw. Care must be taken that the tube is not deformed while being cut. Regardless of the method used, the cut must be square in order that the tube will seat properly in the fitting cup.
Reaming
All cut tube-ends must be reamed to the full inside diameter of the tube, to remove the small burr created during cutting. If this rough inside edge is not removed by reaming, erosion corrosion may occur due to localized turbulence and high flow velocity near the joint. A properly reamed tube-end provides a smooth surface for optimum flow.
Also remove any burrs on the outside of the tube-ends, to ensure proper insertion of the tube into the cup of the fitting.
Tools which may be used to ream tube-ends include the reaming blade on a tube cutter, half-round or round files, a pocket knife, or a special deburring tool. (Figure 5)
With soft temper tube, care must be taken not to deform the tube-end by applying too much pressure. If soft temper tube is deformed, it can be brought back to roundness with a sizing tool, which consists of a plug and sizing ring.
Cleaning
Removal of all oxides and surface soil from the tube-ends and fitting cups is essential for the proper flow of solder into the joint. Failure to remove such oxides can interfere with capillary action and may reduce the strength of the joint and cause failure.
Lightly abrade (clean) tube-ends using sand cloth (Figure 6) or nylon abrasive pads for a distance slightly more than the depth of the fitting cups. Clean fitting cups by using abrasive cloth, abrasive pads, or a properly sized fitting brush.
The capillary space between the tube and fitting is most effective from 0.002 to 0.005 in. (0.05 to 0.13 mm), but may be up to 0.010 in. (0.25 mm). Solder fills this gap by capillary action.
This spacing is critical for the solder to flow into the gap and form a strong joint. A certain amount of looseness of fit can be tolerated, but too loose a fit can cause difficulties, particularly with large size fittings. It may also allow too much solder to be fed into the joint, resulting in a blob forming inside the fitting.
Chemical cleaning may be used if the tube-ends and fittings are thoroughly rinsed after cleaning according to the procedure furnished by the cleaner manufacturer.
Do not touch the cleaned surface with bare hands or oily gloves. Skin oils, lubricating oils and grease impair the soldering operation.
Applying Flux
Use a flux that will dissolve and remove traces of oxide from the cleaned surfaces, protect the cleaned surfaces from reoxidation during heating, and promote wetting of the surfaces by the solder, as recommended in the general requirements of ASTM B 813. Using a brush, apply a thin, even coating of flux to both the tube and fittings as soon as possible after cleaning. (Figures 7 and 8)
WARNING: Do not apply flux with fingers. Chemicals in the flux can be harmful if carried to the eyes, mouth, or open cuts.
Use care in applying flux. Careless workmanship can cause problems long after the system has been installed. If excessive amounts of flux are used, the flux residue may cause corrosion. In extreme cases, such flux corrosion can perforate the tube and/or fitting.
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