Silver soldering, or hard soldering, as it is sometimes called, is the most durable soldering type and has the most number of practical uses. It is a process where two or more metal objects are joined by melting a filler metal over the joint. The filler metal, which in this case is silver, must have a low melting point so that it can melt and flow over the two metals being joined together. The filler metal used in soldering is called the solder.
Work With Clean Metal Pieces
In silver soldering, it is important to work with clean metal pieces. The joints must be free from any rust, oxidation or grease. You can clean the joints by soaking them in an isopropanol bath. If you are working with pipes that are newly cut, remove any remaining burs to make a clean joint. The insides of the pipes can also be cleaned with a steel brush or any brush that can fit inside the pipe.
Once the metal pieces to be joined together are cleaned, handle them carefully to make sure that they do not get in contact with any dirt or grease. Small pieces can be best handled with a clean pair of tweezers. Bigger pieces can be handled with a pair of pliers or metal thongs. It is also important to keep your work area clean so that the pieces you are working on do not get dirty. A clean joint is important in making a clean and durable joint after it has been soldered together.
Once the metal pieces are cleaned, there is one last step that must be done before they are ready to be soldered with silver. The metal parts must be applied with a coating of flux. When working with pipes, the flux must be applied to both the inside and the outside of the pipes.
Flux contains boric acid, which will protect the metal from oxidizing again while it is being heated. Extra caution must be taken when applying the flux because it is a corrosive mixture. Use protective goggles and gloves when working with this mixture. Apply the flux evenly throughout the metal pieces with an old brush.
Cutting the Solder and Soldering the Pieces
The silver solder must be cut depending on the size of the metal pieces you are working on. A small piece of silver solder can go a long way. You will not need a lot of it. To cut the silver solder, use metal snips. Once it has been cut, apply a coating of flux to the silver solder. Stick it to the side of the joint.
Silver soldering does not close gaps, so the two metal pieces to be joined must have as little space between them as possible to make a clean joint. The melted silver solder will flow into the narrow gap through capillary action. Once the pieces are ready to be soldered, the torch can now be turned on. The metal pieces must be heated first to remove the water from the flux. As the flux is being heated, it will turn white and bubble. Heat the metal parts slowly while constantly moving the flame all over them. The hottest part of the flame must be focused on the joint. The silver solder is melted enough when you see it flow inside the joints. Wrap to joined pieces in a wet rag to cool it down or soak it in an acetic bath. An acetic bath is simply made of white vinegar. It will allow the joints to cool, as well as remove any flux or oxidation.