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A Guide to Soldering and Brazing

A guide to soldering and brazing

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The plumber is about to melt solder, which is the material used to connect pieces of metal Soldering is the process in which two or more pieces or tubes of metal are joined together. The bonding is achieved by melting a filler metal – called solder – to a liquid state with a soldering gun or blow torch and depositing it onto the join. The melted solder expands into the pores of the base metals, opened by the higher temperature, and cools to form a solid bond.
Wonkee Donkee says 'Soldering differs from welding as it does not involve melting the metal parts.'
Soldering classification There are two forms of soldering:

  • Soft soldering
  • Hard soldering

The difference between soft and hard soldering lies in the temperature of the heating process to melt the solder and achieve the solvent action.

Soft soldering

This particular solder is lead free Temperatures required to melt soft solder range from 90 to 450 degrees C. Solder must also have a lower melting point than the base metals (the metals being bonded. In the case of soft solder, this would be lower than 450 degrees C.
Soft soldering is ideal for those wiring circuit boards, for example. Soft soldering is used for joining small, intricate parts which may damage when soldering has to be carried out at higher temperatures than 450 degrees C. For example, fixing electronic components or wiring to circuit boards…
Using solder to join copper plumbing pipe and the repair of any joints which are not affected by high operating or service temperatures like a central heating system, for instance. …or joining copper plumbing pipe and the repair of any joints which are not affected by high operating temperatures of certain applications such as a central heating system.

As the operating temperature approaches the melting point of the solder, the joint would simply weaken or snap.

Hard soldering

Brazing and silver soldering are forms of hard soldering.

Both use higher temperatures for the melting of hard solder and the subsequent bonding which takes place.

450°C is the temperature which determines the difference between soft and hard soldering In other words,  where soft soldering occurs at temperatures less than 450 degrees C, hard soldering occurs at temperatures over 450 degrees C.
Soft solder is usually tin based and requires a soldering gun as its heat source, for example Soft solder is usually a tin-based alloy (a combination of two or more metals) and melting is usually achieved with a solder gun although some soft solders may require a gas torch.
Hard solder is usually brass based and requires a flame or a high temperature soldering gun as its heat source Brazed joints are used to achieve higher joint strength and fatigue resistance.

Hard solder for brazing therefore requires stronger filler metals than tin, such as a brass based alloy.

This means it needs a higher temperature heat source such as a gas torch or furnace to melt the solder.

Bonding is achieved by pulling the melted brazing solder into the space between the parts being joined.


Like soft soldering, brazing connects two pieces of base metal by melting filler metal and distributing it in its liquid state between the pieces, fusing them together.

This time, however, soldering occurs at temperatures over 450 degrees C.

A brazed join offers strength and durability Where the primary benefit of soft solder is the low temperature used to avoid heat damage to electronic components, for example, a brazed joint is known for its tensile strength, particularly when it functions at high operating temperatures.

In this respect, brazing is especially useful for central heating, ventilation and air conditioning appliances.

One example that brazing is used for is repairing cast iron objects. As brazed solders are created primarily for strength, other applications include repairing heavy cast-iron objects or wrought iron furniture.
Jewellers tend to use silver soldering when connecting precious metals

Silver soldering

This is another form of hard soldering as it uses high temperatures (over 600 degrees C) to make bonded components.

Silver soldering is used to assemble silver jewellery and other precious and semi-precious metals.

Silver solder can contain up to 40% silver Silver solder is an alloy of varying proportions of silver, which melts at different temperatures depending on the application and requires a blow torch, for example, as its heat source.

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