Joining is a very important production technique in the field of jewellery production. Therefore it is useful to know what kinds of different joining techniques are possible.
This paper will give you a rough overlook on joining techniques as well as some tips and tricks to do a good joint between platinum and platinum, and between platinum and gold. Which technique to prefer depends on the worker skill and on the available equipment.
Usually the joining techniques for platinum jewellery are similar to the procedures used for gold and other materials. There is no black magic, only some material properties are different. If you know how it works, it is easy to do a good platinum joint. Some characteristics of some precious metals are shown in Table 1.
|Fine Platinum||Fine Gold||Fine Silver|
|Melting Point °C||1769||1064||962|
|Specific Heat J/g°K||0.13||0.13||0.23|
|Thermal conductivity W/m°K||71||309||417|
|Linear Expansion Coefficient µm/m°K||9.0||14.3||19|
|Table 1: Characteristics of some precious metals|
The biggest differences between the precious metals gold and platinum are the thermal conductivity and the expansion coefficient. You will see the results, if you bond platinum and gold together.
Example: if we solder together two 10mm long pieces, 8ct gold with Pt 950, using a gold solder with a work temperature of 750°C, the platinum expands 0.07 mm and the gold expands 0.106 mm. When the soldered material cools down to room temperature, there will be a lot of residual stress inside it.
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