Brief Description of Gold Plating and Electrolacquering process used for Temple application.
- Process Flow Sheet
- Dent removal wherever necessary
- Cleaning of all the surfaces with kerosene followed by Trichloroethylene to remove all dirt
- Buffing and polishing of the surface
- Electroless nickel plating of surface
- Mask area that do not require gold plating
- Buffing and polishing
- Gold plating of component to required thickness
- Rinsing and cleaning
- Drying,Baking of electrolacquering
- Spray of ceramic mixed lacquer
- Brief description of gold plating process
As explained earlier materials are nickel coated before they are taken to the gold plating.
Gold plating is done in a bath with metal anodes (+ve terminals) and the job as a cathode (-ve terminals)
Depending on the surface area to be plated a suitable ampere setting is fixed and depending on the content of gold to be deposited on the component, the duration of coating is finalized. A detailed note on the calculation has been enclosed.
As explained, Gold plating is continued on a fixed ampere with the required time and then the component is water washed and rinsed.
Based on the quantity of gold deposited, the electrolytic bath is given suitable replenishment, so that the bath concentration will always be maintained above certain limits.
- Electrolacquering process
The gold plated components are dipped into the Electrolacquer bath and a polyurethane film is coated on the metal.
The coating process is continued till the component is covered with a pore free coating and this is indicated by the ampere reading becoming "0"
Hence if there is a small corner of the component not coated, the current will continue to flow and seal that small area.
As soon as the lacquering is complete, the lacquer coating is dried in a hot air dryer for a few minutes. There after the component is taken inside an oven and the lacquer is baked for a few minutes.
At the end of baking, we will have a very uniform coating of polyurethene all around the gold coating and this will seal the plated area from being attacked by the atmosphere.
- Ceramic spray process
Once the electrolacquered component is cooled, it can be taken up for the ceramic lacquer spray and this is done in a spray booth. A uniform spray coat of nano ceramic lacquer is given on the component and this is then baked again in an oven.
- Life of coating
As such with the thickness of around 3 microns, we can expect a wear out life of around 15-20 years for the coating subject to normal handling. With 1.5 microns thickness we can expect a life of 10-12 years.
- Salient Features of Electro Deposition Process for Gold Coating of Temple Articles
The electro deposition process not only gives a covering of gold on the surface of the base material, but also offers a total protection to the base material from the atmospheric corrosion and erosion. This is achieved by the following multi layers of coating.
- Nickel phosphorous coating is given on both inside and outside of the articles.
- The gold is coated on top of nickel.
- The entire plated surface is electro lacquered and baked at 140 deg. C, which gives a fuse bonded, polyurethane lacquer cover on the material.
- The entire gold surface is further coated with lacquer containing finally dispersed alumna particles and again baked in an oven. This gives tremendous wear resistance to the surface.
Thus the gold plated surface is protected from outside against the atmospheric erosion and corrosion. The inside of the base material is protected by the nickel coating.
The functioning of the nickel layer:
- Usually in the olden process the gold is straight away pasted on to the bronze/brass surface Copper alloys like bronze/brass have a tendency to absorb the gold through pores. Due to this, the gold coated on the bronze/brass surfaces gets diffused into the parent material and very soon it comes back to the bronze/brass look. To prevent this problem, in the olden time, they have put multiple layers of gold rake by a process which uses mercury to convert gold and copper into amalgams. The consequences of which have been explained later. But presently we are using a layer of nickel phosphorous, which completely takes care of the diffusion problem and hence the gold remains without affected by the parent material. Due to this our gold coating thickness is less.
Due to the excellent quality of the gold coating through Electro Deposition Process, the life of the coating is more than 4-5 times with the same thickness of gold applied through mercury gold rake process.
- Pollution Control
In Gold Rake process an amalgam of gold is applied to metallic surface, mercury being subsequently volatilized, leaving a film of gold or an amalgam containing from 13 to 16% of mercury. Inhalation of fumes generated by the process can result in serious health problems such as neurological damage and endocrine disorders. The plating process handled in our factory is having proper effluent treatment system approved by the Pollution Control Board.
Benefits of using Electro Deposition Process
Electro Deposition Process as against the gold rake - mercury process:
- Life of the coating is more than 4-5 times.
- Uses latest Technology.
- Better adhesion properties, so peel off possibilities less.
- Higher purity of the gold, since there is no amalgam of copper.
- Faster process time.
- Guaranteed quality, since this is a factory controlled process.
- Environment friendly process as there is no release of mercury.