Joining metals through Soldering and brazing

There are four major ways of joining metal pieces together. They are by soldering, welding, riveting and mechanical fasteners like bolts, nuts and screws. We will treat only the soldering process in this chapter.

Soldering

What is soldering? Soldering is the process of joining metal surface by means of an alloy called which has a lower melting point than the metals being joined.

There are two types of soldering namely: Soft soldering and hard soldering. When the solder melts below red heat, it is called soft soldering, but when it melts at or above, red heat, it is called soldering or brazing. What determines the type of soldering to be applied is the nature of the metal being joined. Lighter and softer metals require soft soldering, while thicker and harder metals require hard soldering or brazing.

Soft Soldering

The type of soldering makes use of low temperature solders. Soft soldering is applied to small parts were strength is not important. Examples are soldering of wire terminals in radio, television sets and other kinds of electrical work. Soft soldering is also applied on articles made of tin-plate materials and some other kinds of metal having low melting points.

1. Soft Soldering Temperature

In all types of soldering, the basic rule is that the melting point of solder being used should be well below the melting point of the metals being soldered.

1. Composition of Soft Solder

Basically, soft solders are alloys of tin and lead in varying proportions. Sometimes, little percentages or a proportion of a metal called antimony is added to provide strength and hardness. It is possible to produce different types of solder by varying the proportions of tin and lead, with each type having different melting points and behaviour making them suitable for different kinds of jobs. The higher the proportion of tin a solder has, the softer it is and the lower its melting point. On the other hand, the higher the proportion of lead in the mixture, the harder the solder and the higher its melting point.

iii. Kinds of Soft Solder

There are three major kinds of soft solder namely:

Tinsmith solder (melting point 188^oc used in radio and T.V. works).

Blow pipe soldier (melting point 230^oc used for general bench work).

Plumber’s soldier (melting point 250⁰c used for soldering plumbing joints).

1. Tools and materials used in Soldering
2. soldering bit; also called copper bit
3. Solder
4. Flux
5. Source of heat e.g. stove, blow lamp, charcoal, furnace, or electricity for electric bits
6. Enemy cloth or file.

Soldering Bit

The soldering bit is used for applying heat and soft solder to the metal. It is a solid square piece of copper pointed at one end and fastened to a steel bar with a wooden handle on the other end. Soldering bits are made in different weights.

Electric soldering bits are also available. They are heated by electricity, by connecting them to any electric light socket. They are mainly used for fine work like soldering wire terminals in radio and television sets.

Tinning the Bit

The faces on the point of the soldering bit must be heated, cleaned and coated with solder before it can be used for soldering. This is called ‘tinning’.