Soldering (soldering) is an operation by means of which a more or less strong connection of separate pieces of the same metal or two or more different metals between themselves is made.
Three kinds of soldering:
There are three types of solder: soft, or weak, hard, or strong, and nugget. In the first two cases, the connection of metals is made by means of a more fusible metal called solder. In nugget soldering, the individual parts of one metal are joined together without any intermediary of another extraneous metal. Nugget soldering is the strongest, and is exemplified by the welding of iron.
Soldering with solder is the less strong, the more the melting point of the soldering metal differs from the melting point of the metals being soldered; for example, lead and zinc can be soldered with tin quite strong, while the soldering of silver or copper with tin is very weak.
The surfaces to be soldered must be purely metallic, i.e. completely free of oxides and foreign bodies, and as close together as possible; the thinner the layer of solder placed between the surfaces to be joined and the cleaner these surfaces are, the stronger the solder.
Therefore, before proceeding to soldering, it is necessary to fit the surfaces to each other, clean them and cover them with flux or flame, i.e. a substance that would protect them from contamination (oxidation, deposition of soot, etc.) during heating.
The cleanliness of the surfaces to be soldered is so important that they should not be touched even with fingers after cleaning.
Complete immobility of the parts to be soldered during and after soldering until the solder solidifies is, of course, a necessary condition for the strength of the solder.
