More about Soldering and Brazing

March 12, 2018

TYPICAL ALLOY MELTING TEMPERATURES FOR SOLDERING (C)

 

Bi/Pb/Sn                        95

Tix*                              135

Sn/Bi                           138

Belmont* (Sn/Pb/Cd)  149

Sn63 Pb37 (eutectic)  181

Sn60/Pb40                  188

Sn50/Pb50                  213

 

* 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.

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