Welding, soft and hard soldering


Soft soldering

Soft soldering is used to solder electronic components onto circuit boards and make general electrical connections. It is also used to solder plumbing joints between copper pipe and copper connectors. The solder is usually melted using a soldering iron heated by electricity or gas. Soft solder is not as strong as the other methods on this page. Solder is an alloy of tin and other metals - lead is usual but some solders are nowadays leadfree. Solder has a low melting point.

Three Rules of Soldering -

All surfaces must be clean (no grease or dirt),

Both parts must be hot so the solder will flow towards the heat,

Flux must be used to clean the surface and encourage the solder to flow.

Hard Soldering

Soldering with brass or silver. This is much harder and stronger than soft soldering and take place at higher temperatures. This need a blowtorch. The metal parts to be joined must be clean and positioned very close together. A borax flux is applied to the surfaces to be joined. The piece of brass (spelter) is placed one the joint. The joint is heated to orange heat at which point the brass will melt anf flow into the narrow gap. When the joint cols down the brass will solidify and form a very strong joint.

Silver soldering is similar using a silver alloy instead of brass. It melts at a lower temperature but costs much more!

Brazing is used for mild steel, copper can also be brazed.

Silver soldering is used on copper brass and gilding metal and also of course on silver.




Gas Welding (Oxy Acetylene Welding)

Gas welding uses a gas torch which burns a mixture of oxygen and oxyacetylene. The flame is so hot it melts the mild steel welding (filler) rod and the metal either side of the joint. When it cools down the steel weld is very strong. Training is needed to use this equipment Oxy acetylene welding

MIG Welding(Metal Inert Gas)

Commonly used in schools. A form of electric arc welding but carbon dioxide gas surrounds the arc and prevents the oxidation of the molten steel. The joint is clean of slag and very strong. The arc is very bright and a protective eye shield must be used. Argon arc welding is similar but uses a different gas enabling other metals to be welded such as aluminium. Can be used in robot welding on production lines.

Spot Welding

Spot welding is a form of resistive welding and is used on sheet steel welding. Electrodes which are copper tipped are brought together on either side of the joint. When the electric current fows a high temperature is produced, melting the metal at the point of contact. A spot weld is produced.

Robots can be seen on assembly lines, under computer control, producing a pattern of spot welds.Seam welding is similar using electrodes in the shape of wheels.