Process for gold electroforming of watch cases and jewellery
Introduction
An Indian enterprise offers Swiss technology for gold electroforming of watch cases and jewellery from 14 to 22 carat alloys. The different stages for producing watch cases and jewellery by electroforming are
- Model manufacturing for electroforming
- Electroforming: gold depositing
- Emptying the electroformed item
- Finishing of the items.
Model manufacturing
Models, the exact reproduction of the piece to be electroformed are basic items for elecroformed. Models must adhere to two conditions.
First, these must be electrically conductive. It is better to use hard metal core. Second, the metal must be easy to dissolve after electroforming without any alteration of gold deposit. These two conditions afford the choice of two types of metallic alloy - fusible alloy and zinc alloy. fusible alloy is made up of lead or tin with bismuth or antimony. Its melting point is about 100 to 150 degree C and is used like a wax as it can be cast in rubber or silicon moulds. Zinc alloy has a higher melting point of 400 degree C and can be case in rubber or silicon moulds, as for the traditional solid cast process. The moulding process with rubber or silicon moulds allows to obtain any kind of shapes or forms in very good conditions. Other moulding techniques can be used as casting in steel moulds for the production of watch cases in long runs. Models can also be realised by mechanical process (as stamping, pressing etc.) which is easier and more economical. It should be noted that electrolytic deposit is not a Masstic even if it gives a nice look by its brightness and its power of surface levelling. Elecroforming reproduces exactly the original surface i.e. model's surface with or without flaws. These realised models will be secured on the rack for the following operations
Electroforming
Ternary alloy Au/Cu/Cd are chosen because of their suitability on account of minimum internal strains and crystalline structure allowing to realise adequate thickness. Whatever is the fineness of gold 10, 14, 18 kts the process is the same. Colour of coating depends upon the quantity of the three alloys it contains - 14, 18 kts alloy as a yellow colour named champagne, 10 14 kts with more copper will get a pink colour. Thickness of the coasting will be according to the time of the depositing. Depositing speed is 1 micron per 2.5 minutes i.e. about 4 hours and 20 minutes for 100 microns (0.1 mm). Maximum thickness is according to the type of pieces, between 60 and 500 microns. For jewellery and watch making average thickness of coating varies from 80 to 300 microns. In the electroforming process the main operation is electrolytic depositing which can be entirely automatic. Electroforming is followed by emptying the metal core from the electroformed item and finishing of the electroformed items.
Areas of application
Jewellery
Advantages
- Gain of weight for large and voluminous items.
- Possibility to realise any complex form and design which could not be obtained by stamping, pressing and other traditional technique.
- A very good quality for polishing and finishing with very smooth and bright metal surface.
- The allowance for manufacturing small series without any expensive tools. Only a machine or hand made model is needed.
- Deposit of gold fineness from 9 to 18 karats possible.
Economic data
Available on request.
Transfer forms
Negotiable
For further information please contact
Technology Bureau for Small Enterprises,
APCTT Building, Near Technology Bhawan,
PO Box 4575, Off New Mehrauli Road,
New Delhi-110 016
