SOLDERING USING A GAS FLAME [The Art of Soldering]

Home | Articles | Forum | Glossary | Books




The rules regarding soldering with a gas flame are really the same as with any other equipment. The same requirements apply, especially that of heat, flux and solder. This Section will deal with soldering larger items such as plumbing, car radiators, etc., including larger locomotive boilers and frames.

When soldering with a gas flame the secret is to bring the area being soldered up to temperature slowly. This is done by moving the flame around the joint and never directing it to just one point. If you do, that point will overheat and burn both the work and the solder which will render the solder useless.

Water and Other Copper Pipes, etc.

The method of soldering all copper pipes will be the same, although the materials to be used, i.e. the solder and the flux, are strictly controlled by the Building Regulations for pipes being used for water. These pipes must only be soldered with lead-free solder and special flux. If in doubt ask at your plumbers' merchant.

(i) Firstly clean the joint, usually the end of the pipe, thoroughly using wire wool or similar so that the area going into the joint is bright and shiny.

(ii) Apply flux to the two parts.

(iii) Insert the pipe into the joint.

(iv) Repeat the procedure for all ends of the joint.

Remember that when one end of the joint is heated, the other joints will also reach the melting point of solder because the copper is a good conductor of heat.

(v) When you are ready to solder, light the flame and adjust it so that it is not a roaring flame. A slightly yellow flame is generally very much better than a roaring blue flame, as you are less likely to overheat a particular part of the joint.

(vi) Move the flame slowly up and down the pipe with a bias towards the pipe rather than the joint.

Remember that for a successful joint, the whole area of the copper should arrive at the correct temperature together. If one part is overheated then the joint will not be successful.

(vii) Eventually solder should appear around the whole of the joint. When this has happened move the flame to the other pipes of the same joint and repeat the procedure as above.

When the solder has melted on the first joint, the joining piece will probably be up to the temperature required for soldering. If you continue to play the flame into the joint rather than the pipe then the joint will overheat and burn the solder, which will cause a dry joint. It is important there fore that the flame is applied to the pipe only until the solder melts. With this method of soldering, patience is a virtue.

Take your time and do it properly. The faster you do it the more likely you are to have a problem. When all joints are complete leave the work to cool. Do not touch it because it will be very hot. If the joints are disturbed at this point then they will almost certainly fail.

Car Radiator Repairs

Car radiators and similar large items are probably the most complicated but maligned areas of soldering, and are undoubtedly the least understood of all. Many a time I have heard "But it is only a pin hole. Why can't I use a 1.5mm soldering iron bit? Why do I need a flame and not a small soldering iron?" The answer is simply explained, for the problems are similar to those encountered when soldering copper pipes. The whole area around the joint has got to be heated and not just the pin hole. As the brass around the car radiator is fairly thick then a considerable amount of heat will be required to solder it. Because the car radiator will be working at fairly high temperatures (possibly 140°C), you must be careful as to your choice of solder. A solder melting at around 210°C would be suitable, whereas a lower temperature solder might melt in use.

The technique for tackling these large repairs is as follows:

(i) Thoroughly clean the area around the section to be repaired, using an abrasive such as wire wool or emery cloth. It is very important that every trace of dirt or oxidization is removed from all around the joint, even in little scratches, otherwise the solder will not take on these areas.

(ii) When the area has been thoroughly cleaned, inspect the section to be repaired. If indeed it is only a pin hole, probably caused by a fault in the material, then the repair will be simple. If it has been caused by general corrosion then there will be other areas waiting to fail and it might therefore be better to replace the whole unit.

(iii) If you decide that it is only a pin -hole, check to see approximately what size the hole is. Very carefully drill through the hole with a drill that is slightly bigger than the pin-hole. This will remove oxidization and corrosion from inside the hole. Finally countersink the hole with a larger drill being very careful only to round off the edge and not to drill right through.

(iv) Coat the area with flux, especially in the hole and around the countersinking. A pin or piece of thin, stiff wire may be useful.

(v) Gently heat the area around the repair, but at this point do not direct the flame onto the repair.

(vi) As the temperature rises, try to melt the solder on the repair, not in the flame, and continue to test the repair area for temperature. If you are not sure whether the area is hot enough, remove the flame and test the area with solder. If you keep melting the solder in the flame then the result will be a very poor joint.

(vii) Apply the solder first to the hole, gradually allowing the solder to melt around the repair area. Keep playing the flame around the repair, not directly ever it, and apply further solder until a small mound has formed over the hole and the solder has spread to cover approximately a 1-inch or 1 1/2-inch circle.

(viii) Remove the flame completely and allow the whole item to cool. Again do not touch, as an area this large will stay hot for a considerable length of time.

(ix) Finally inspect the joint. The solder should be shiny, smooth and even, and should not have sagged, other than very slightly in the centre.

As can be seen the soldering of these larger areas needs a lot of care and attention and you should think carefully before you undertake them. If, for example, you heat the area around the neck of a car radiator to such an extent that the solder around the neck melts then you will be in real trouble.

Instead of completing the small repair, you now have a much larger item to repair.

The soldering of all larger items should be undertaken in the same way, with the same care being required. It would help, especially if you are constructing something, if you could get the joints to fix together physically before soldering, so that the solder acts as a filler rather than entrusting the whole seam to the strength of the solder.

Top of Page

PREV.   NEXT   Guide Index HOME