The Tools For Soldering

The heat sources normally used for soldering are the electric soldering iron and the gas blowlamp. The once popular traditional flame-heated soldering iron is now rarely used.

When deciding which tool to use you should remember that it is a waste of time trying to solder with a tool that is not powerful enough for the job. Equally well, one which is too powerful may heat up the solder too much and weaken the joint. For very delicate work, you will most likely need to use an electric soldering iron. Some gas blowlamps can do this job well too. For bigger electrical jobs and for soldering jewellery and model-making, you can use a blowlamp which takes a fine or extra fine burner a flame which is quite hot but not too big or diffuse is needed or one of the more powerful soldering irons. For plumbing work soldering capillary joints a gas blowlamp or blowtorch is the most sensible choice. For soldering large lumps of metal (or brazing), you need a powerful blowlamp. You should also think about the following points:

o the temperature the solder and joint have to reach ordinary solder melts at about 250°C, and this temperature must be maintained in the joint all the time it is being made

o the thermal size of the joint and its immediate surroundings - a large joint will need a larger source of heat to enable it to reach the required temperature, and when soldering metals, such as copper, which are very good conductors of heat, a steady supply of heat is needed to keep the temperature high

o the position of the joint if the joint is near temperature-sensitive electronic components like transistors, it is wise to insert a heat sink between the joint and the component to mop up the heat used in soldering to prevent it from travelling. A mass of metal is the usual heat sink, and a good heavy pair of pliers will often do the trick On the other hand, if the joint has a large surface area and is exposed to the air, it may radiate the heat away too quickly. This can be overcome by enclosing the joint in a temporary brick hearth, or by burying part of it in a bed of ashes. Never lay the joint on a good conducting surface.

Brazing
Brazing uses alloys of copper and zinc which melt at much higher temperatures than solder (700 to 800°C) and give stronger joints. A special flux or a borax paste is needed. Braze (or bronze) welding uses the same sort of alloy, but instead of running it into the joint a fillet is built up on the surface. If the joint is small, it may be possible to reach the temperature required with a gas blowlamp, by playing the flame directly on the joint. If this is not successful, a more powerful heat source is needed.

A brazing attachment is available for use with an arc welder. This usually takes the form of two carbon rods fixed in a hand-held clamp. An arc is created between the tips of the two rods, and the resulting flame is used to heat the joint.

This source is both powerful and fierce, so it is advisable to practise this method before attempting to use it for repair.

Oxy-acetylene welding equipment is frequently used for brazing the heat is easily controlled by using the appropriate size nozzle and the torch is easy to manipulate. Unfortunately, these advantages tend to be outweighed by the difficulty in getting hold of the gases.

by Tauqeer Ul Hassan