Silver Brazing

I had to silver braze the brass mounting hardware to the bottom leaf of each spring assembly. The photo above shows six leaves.

The photo above shows the silver brazed joint between the brass and the steel.

Soldering is a process in which two or more metal items are joined together by melting and putting a filler metal (solder) into the joint, the filler metal having a lower melting point than the adjoining metal.

Brazing is a type of soldering that uses a filler metal that melts at a temperature greater than 450 degrees C (842 degrees F).

Unfortunately, not everyone uses the term “brazing.” The model press (primarily British) and books dealing with jewelry making refer to brazing as “Hard Soldering” or “Silver Soldering.” “Soft Soldering” uses a filler metal that melts below 450 degrees Celsius. Soft soldering is used for plumbing and electronics.

The term “Silver Soldering” has become confusing in recent years because plumbers have stopped using lead and many soft solders contain a very small percentage of silver – often less than 1%; but these soft solders are advertised as “Silver Solder!”

I know a live steamer who repaired a steam pipe on his engine using one of these soft silver solders. The package said “Silver Solder” and it was a really low price – what could go wrong? Well, as soon as he applied live steam to the repair it all fell apart! Now he had a bigger problem. If you do not remove ALL of the soft solder and you try to braze the part, the heat required to melt the brazing alloy will boil the soft solder and it will eat holes in the base metal like acid. He really should have known better.

The photo above illustrates two brands of 45% silver brazing alloy. I buy the cadmium free alloy – it is less poisonous. I use 45% silver for most brazing applications. Alloys are available with different percentages of silver. The higher the silver content, the higher the temperature required to melt it.

Phos-copper is a popular brazing alloy. The photo above shows 15% silver.

This photo illustrates “SOFT” silver solder. Do not use it for live steam or where you need mechanical strength in a joint that could be subjected to outside forces.

There are two different techniques used to braze metals together. Which one you are familiar with depends on whether you were taught by a welder or a silversmith/jeweler.

If you were taught by a welder, you mechanically clean the joint (scraper, file, abrasive, etc.), apply flux to the joint, heat the joint with a torch and push a rod or wire of alloy into the joint similar to using a welding rod. This process is fairly quick, but it wastes brazing alloy and leaves more melted alloy on the parts than is needed to join the pieces together. This is usually not a problem for industrial parts.

If you are a silversmith or a jeweler, you will be concerned about excess brazing alloy because it is a different color than the base metal. High cost is another consideration (Yes, they make gold and platinum brazing alloys!).

The photo above is a sterling silver box and a brass and silver belt buckle I made many years ago. The box shows at least five joints, but they are not easily visible because there is no excess alloy outside the joint. The belt buckle however, illustrates excess alloy. It is the gray material between the brass and the silver. It is hard to see when highly polished but as soon as it starts to oxidize, the color difference is very apparent.

Jewelers clean and flux the metal, and heat the parts until the flux melts and gets “sticky.” Very small pieces of brazing alloy are then applied to the joint with tweezers. The entire piece is heated until the alloy flows into the joint. A sharpened steel skewer can be used to push the molten alloy along the joint. Excess alloy can be filed or sanded off if the part is decorative.

I made a steel fixture to hold the parts in position while I brazed one end at a time. You can keep brazing alloy away from an area by making that area “dirty.” Grated rouge and alcohol can be used to make the metal dirty.