Without heat, the soldering process just doesn’t happen, right? Let’s take a look at the different gases used in soldering and how to achieve the flame balance needed for soldering success.
Heating jewelry pieces during soldering is done with torches, which mix either oxygen or air with a gas. Hydrogen, natural gas, acetylene, propane, and butane are the fuel gases most commonly used.
IT’S ALL IN THE CHEMISTRY
One of the most important steps to achieving the perfect flame is to control your fuel-to-oxygen ratio. Consider the combustion of natural gas — mostly methane (CH4). When completely burned, it reacts with oxygen.
TOO MUCH OXYGEN
If there is excess oxygen in your oxygen/natural gas mixture, you’ll wind up with an oxidizing flame. The oxygen not captured by the flame can create oxides on the surface of the metal you’re soldering. This is a flame you definitely don’t want. You’ll know if you created an oxidizing flame by its appearance — pointed, with a conical shape forming at the head of the torch making two flame cones (a bluish, inner flame cone and a dark blue outer cone).
TOO LITTLE OXYGEN
At the other end of the spectrum is a flame with oxygen below the level needed for complete combustion. This results in a reducing flame — another type you don’t want. Its appearance consists of a soft-edged, bushy yellow flame. Reducing flames contain carbon monoxide instead of carbon dioxide and water vapor. Without enough oxygen in the mix, the flame will be cooler, causing unburned fuel particles to contaminate the metal.
It takes practice to achieve the correct mix of fuel and oxygen. The perfect flame contains a balance where there is sufficient oxygen to burn all the fuel present and nothing more.
High-karat golds and platinum are not adversely affected by heating with a slightly oxidizing flame. Lower-karatage alloys, however, require a neutral or slightly reducing conditions to prevent oxidation of the base metal.
When using hydrocarbon fuels, it’s best to avoid using a reducing flame on platinum, because it makes the carbon within the metal brittle. Specifically, acetylene torches should be avoided. Acetylene flames are considered to be dirty for leaving flakes of carbon on the soldered pieces.
HERE ARE 9 COMMON MISTAKES JEWELERS MAKE WHEN SOLDERING
As always, if you need help with tools or questions about metals or soldering, contact Stuller’s Tools Tech Team. Give them a call at 1-800-877-7777 ext. 4300