More about Soldering and Brazing
TYPICAL ALLOY MELTING TEMPERATURES FOR SOLDERING (C)
Belmont* (Sn/Pb/Cd) 149
Sn63 Pb37 (eutectic) 181
* Trade names
When using a multi-stage soldering process for multiple joints in proximity, start with the highest temperature alloy and progress to a lower temperature for subsequent joints.
Unfortunately, many of these solders are no longer generally available and may have to be obtained from specialty electrical or jewelry suppliers.
TYPICAL ALLOY MELTING TEMPERATURES FOR BRAZING (C)
Copper alloy 1093
Nickel alloy 1038
Silver bronze 870
Silver alloy 702
Aluminum alloy 582
Brazing is also called hard soldering and is applied at temperatures above 450 C
A brief summary of the process is usually provided by brazing torch manufacturers such as BernzOmatic, as reproduced below.
Brazing (Hard Soldering)
Hard soldering on such metals as silver, gold, steel and bronze makes a much
stronger – and neater – joint than soft soldering. A propane torch will not
produce sufficient heat to efficiently braze or hard solder. Higher heat
brazing torches such as the BernzOmatic JT539 Swirl Flame Brazing Torch and
the TS5000 Trigger Start Adjustable, High Output Torch, are recommended. Hard
soldering is used extensively in jewelry making and in the plumbing industry
when a particularly strong point is required. Special solders are sued for
hard soldering in which silver is the chief ingredient. As in soft soldering,
the first step is to carefully clean the area where the pieces are to be
joined. Sandpaper, emery cloth, a file or steel wool can be used for this
step. If at all possible, clamp the pieces to be joined so that they will not
move during the operation. Apply the proper flux to the metal – type of flux
depends upon the solder being used and the metal to be joined. There are more
than a dozen different types of brazing rods and fluxes.
When working with brazing rods, use a rod that matches the color of the work
to be joined. If you are joining silver, for example, use a silver solder.
This is an alloy of silver (8 parts), copper (3 parts) and zinc (1 part). If
the job involves soldering gold, use a rod containing gold, silver and copper.
An inexpensive flux for fairly large jobs consists of powdered borax mixed
with water to the consistency of cream. Heat the joint with the torch until
the solder starts to melt when it is applied to the metal. Use the tip of the
inner core of the flame, which will be the hottest part.
Many brazing rods are flux coated or flux cored. These require no additional
flux. The melted flux left behind after the job is finished will leave a dark brown
residue. It can be removed from the soldered joint by immersing the item in a
solution of 1 part sulphuric acid to 2 parts water. Important: Always add acid
to water, never water to acid. Best to wear rubber gloves and goggles when
doing this job. Allow the work to soak in this solution for about 20 minutes.
Flux can also be removed by immersion in boiling water, provided this is done
before the joint has cooled.