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.
FUEL GASES
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.
FLAME EFFECTS
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.
9 COMMON SOLDERING MISTAKES
HERE ARE 9 COMMON MISTAKES JEWELERS MAKE WHEN SOLDERING
THINKING LOWER KARAT = LOWER TEMPERATURE
Lower karat does not equate to lower temperature. If a lower temperature solder is needed compare flow points. Know your metals.
NOT STRESS RELIEVING PLATINUM
When soldering gold to platinum, the platinum must be stress relieved first. Stress in the platinum could crack the solder joint when cooling.
USING CADMIUM SOLDER ON PLATINUM
When using gold solder on platinum, make sure it is cadmium free. Cadmium can make platinum brittle.
USING A WORD, NOT A FLOW POINT
Soft, medium, and hard are ambiguous terms and differ greatly from solder to solder and supplier to supplier. So, compare temperatures, not terms.
OVERHEATING THE SOLDER
Excessive heating can cause porosity. Solder will not flow onto a piece until the temperature of the piece reaches its flow point. Use direct heat on the solder joint, not the solder.
USING PASTE SOLDER FOR SIZING
Paste solders are best for soldering small pinpoint joints and seams but will not fill a gap. Size with sheet solder for better results.
USING THE WRONG SOLDER ON DISSIMILAR METALS
When soldering two dissimilar metals together, use the lower temperature metal for soldering. For example, when soldering silver to gold, use silver solder.
USING SOFT OR REPAIR SOLDER WHEN SIZING
Use a hard solder when sizing to prevent porosity and avoid seems.
BUYING ONLY BASED ON PRICE
Quality is like karma. Poor quality will come back to you. When choosing a solder provider, look for one with a wide selection, product knowledge, published temperatures and gold content.
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
