SOLDERING WHITE METAL [The Art of Soldering]


This is probably the most difficult area of any soldering application. One reason is the definition of white metal.

Quite simply, it is a term describing castable materials with melting points from approximately 60°C to around 250°C.

As can be seen, this immediately presents a problem as to which solder to use. At the extremes the difference in the white metals can be seen by the material's coloration. A blackish appearance will represent a lower melting point, whereas a silvery appearance indicates a higher melting point. Unfortunately, the manufacturers of these kits do not see fit to inform you of the melting point of the material you are supplied with in their instruction leaflets. It is therefore recommended that you contact the manufacturer and get him to supply this very important information before you start to solder, as a different technique will be required for the higher melting point metals to that of the lower ones. It is my experience that the better the quality of the kit then the higher the melting point of the white metal will be.

As most people reading this will be novices at soldering, I would advise that no white metal is soldered using a full temperature soldering iron. This means that you will need a soldering iron controller of some type. Remember the warning earlier in this guide regarding the power of 12 volt soldering irons and their requirement for a power supply usually much greater than that available from a normal model railway controller. The most practical solution is a mains controller which enables you to reduce the temperature of the soldering iron. The only other solution is a solder station but these are very expensive.

The type of solder you use will depend on the quality of white metal you are working with. For melting points above 140°C I would recommend a tin/lead/cadmium combination solder with a melting point around 140°C. The cadmium acts as a catalyst and helps the solder to attach itself to the white metal. This type of white metal will be the easiest to solder.

For melting points below 140°C, beware. These will be much more difficult to solder and, unless you are prepared to experiment with a cheap model first, it is most likely that many accidents will occur when soldering. Even with a good quality soldering iron controller, it will be very difficult to keep most irons to a temperature low enough to be safe when soldering this grade of white metal.

Beware also of the "solders" that melt at very low temperatures. Some of these are in fact white metal itself and will in effect be recasting the joint rather than properly soldering it. This will mean actually melting the white metal along the joint to effect the recasting.

Once you have decided which type of white metal you are using, and are prepared to commence soldering, it is advisable to experiment with soldering the odd pieces you find in the kit. If you ruin these then it will not matter. Adjust the temperature of the soldering iron until you can continually solder satisfactorily and get good joints. When you are happy, you can commence with soldering the white metal.

The technique is the same as with all the soldering applications already described and all the areas covered still apply.

The correct size of soldering iron and bit are still very important, although the heat will not dissipate through this metal so readily as with brass, copper or nickel silver. This will mean that the heat will tend to be concentrated in a very small area around the soldering iron bit, and will not travel. Therefore, more care must be taken when soldering, especially larger parts, to prevent dry joints.

I still recommend inert fluxes for this material, even though it would be very much easier to solder using an active flux.

The problem of continued corrosion of the joint still applies, and unless you can remove the flux completely it will eventually damage your model, as well as the paint you will be applying afterwards.

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