| Before soldering there are three factors which | | | | may be required to ensure full retention of the |
| must be considered. The design must lend itself to | | | | flux paste over the whole joint area. The torch |
| soldering, parts to be soldered must fit closely and | | | | should initially be held some distance from the |
| accurately and the correct solder and flux must | | | | workpiece so that the flame heats the work |
| be used. | | | | generally. If components of different size are |
| Solders are typically classified according to their | | | | being joined the torch should predominantly heat |
| melting points - easy, medium and hard. This | | | | the heavier item. |
| therefore refers to the ease of melting the | | | | There are two general techniques used to apply |
| solder. Hence an easy grade solder melts before | | | | solid solder. Preplacement is where small pieces of |
| a hard grade one. This can be used where a | | | | solder are placed at the joint seam prior to |
| sequence of joints are to be made. Usually a | | | | heating. Heat is then applied until the solder flows |
| solder must conform to the same hallmarking | | | | into the joint. Feeding is where the fluxed joint is |
| rules as the metal being joined - for example, a | | | | heated to temperature and tip of the solder wire |
| 9ct solder must contain at least 37.5% gold. | | | | is fed into the joint and should melt on contact. |
| However, there are some concessions such as | | | | Using both these techniques the joint should be |
| Platinum Solders and some white gold alloys. | | | | heated more strongly than the remainder. The |
| Gas and compressed air mixtures are generally | | | | time and temperature required to complete a |
| the most satisfactory for torch soldering. Fine | | | | joint must be kept to a minimum. |
| adjustment of flame size and temperature are | | | | Gold and silver flux residues may normally be |
| possible. The flame should be kept constantly on | | | | removed by soaking in hot water. Any further |
| the move over the whole joint area, or over as | | | | residues that persist may then be removed by |
| wide an area as can be conveniently joined, in a | | | | brushing. In difficult cases the workpiece should be |
| single application of solder. | | | | impressed in 5 - 10% sulphuric acid solution for 2 - |
| The joint areas must be free from dirt and | | | | 5 minutes, rinsed in hot water and brushed again. |
| grease, and ideally cleaned with a file or emery | | | | For large scale soldering a small furnace may be |
| paper to ensure the solder will wet the parent | | | | used to provide sufficient uniform heat to the |
| metal. Flux should be applied to the joint area and | | | | workpiece. For mass production batch or |
| solder prior to heating. Fluxes promote wetting of | | | | conveyer type furnaces may be used. However, |
| the workpiece by the molten solder. This is done | | | | the quantities of components to be soldered must |
| by removing any oxide films present on both the | | | | be large enough to justify the relatively high |
| parent metal and solder and prevent further | | | | capital expenditure and development of a method |
| formation of oxides during heating. The flux must | | | | for each particular soldering operation. |
| be completely fluid and active before solder | | | | All workpieces can be successfully finished by the |
| liquidation and should remain so until after the | | | | standard practices and processes currently |
| solder solidification. | | | | available. It must be noted that powdered borax |
| If the size of the joint is large further flux | | | | does not always meet the requirements for all |
| additions may be made during the process. It | | | | applications, where the extensive range of other |
| must be noted that warming of the workpiece | | | | solders now available may be used. |