New silver-plating line at Leoni’s Weissenburg location
Our Weissenburg location saw the installation of a state-of-the-art silver-plating line for copper conductors in autumn 2012.
The machine meets all of today’s technological requirements. It can handle wires featuring diameters between 0.8 and 2.6 mm. Using a 1.8 mm input wire, the coating on the finished product can range from 3g to 150g of silver, which equates to a plating thickness of 1.15µ up to 57,21µ. The control system adjusts both the amperage required and the throughput speed as a function of the wire gauge and the desired plating thickness, in a process that is almost completely automated.
In order to ensure outstanding results on a permanent basis, first-rate quality of the pre-material is considered an absolute must. Any flaw on the surface, however small it may be, will further corrupt the product downstream. Thus, a tiny spot on the silver-plated wire might have stretched out to several meters after the drawing operation. Hence the pre-material is meticulously checked for the consistency of its diameter and surface. Prior to actually being silver-plated, the wire is also degreased for an optimized adhesion of the coating material to the surface. As a consequence, disruptions of the coating material can virtually be ruled out.
Not only is the plating thickness strictly adhered to, but its centricity must be maintained at all times as well. Our new machine has been proven to meet the highest standards in this regard. Complying with the specified plating thickness represents a two-fold challenge: in the event of the coating being too thin the functionality of the conductor might be impaired, while over-plating translates into wastage of material that the customer will eventually have to compensate us for. (cf. our article on the MetaScope 3 measuring device)
The entire manufacturing process around the new silver-plating line has been geared towards producing the finest quality. This includes a whole number of checks implemented to continuously verify both the machine operating flawlessly and all parameters being maintained.
Galvanisation – technology
The technology of galvanisation was named after Luigi Galvani, an Italian physician and scholar, who made some important observations as early as the18th century. He is considered as the discoverer of galvanic electricity.
The galvanisation technology (in this context also known as electroplating) deals with the electrochemical precipitation of objects carrying metallic coatings. Both coating material (e.g. tin, nickel, gold or silver) and base material are treated by way of immersion into an electrolytic bath. An electric circuit (DC) needs to be set up, with the coating material connected to its positive pole (anode, e.g. silver pellets) and the base material connected to its negative pole (cathode e.g. copper wire). At the point of the current beginning to flow metal ions are detached from the coating material. They suffuse the electrolytic bath and settle on the base material.
Galvanisation - purpose
There are basically two areas where galvanic plating is applied:
This term comprises all those applications that aim at optically embellishing an object. While tubular steel furniture or parts of motor vehicles are chrome-plated, jewellery or cutlery are often gold-plated or silver-plated.
Lyonese Wares, i.e. single wire, threads, flat wire, bouillon and pearl are frequently gold-plated or silver-plated. Their fabrication moved to Nuremberg in the 16th century and this is where the origins of the LEONI corporation are to be found. To this day these products are manufactured at our Weissenburg location and they are used for fine pieces of sacral embroidery or in the traditional textile industry, not to forget decorative applications in the fields of crafts, floristics and creatives.
All these applications do require surfaces that are visually perfect. Any kind of shading, blemish or flake has to be avoided. At the same time, we have to try and consume as little coating material as possible in order to remain cost-efficient.
This field revolves around improving the functionality of a product. Tin or nickel coatings prevent oxidation, which would hamper downstream processing of electrical conductors in particular. At the extruding stage, for example, high temperatures constitute a critical process parameter.
Another phenomenon galvanic coating averts apart from oxidation is corrosion.
The use of silver or tin as a plating material enhances the solderability of wires, which is of particular importance when it comes to automated processes. By avoiding galvanic corrosion or the formation of local cells, the durability of crimp connectors will be increased as well.
Use of silver in galvanisation technology
Technical properties of silver
- Precious metal
- Chemical Element
- Chemical symbol „Ag“
- Specific weight 10,49 g/cm³ (at 20°C)
- Melting point at 1234,93 K (961,78 °C)
Fields of application for silver
The highly conductive coat of silver ameliorates the properties of an electrical conductor used in high-frequency technology. With frequency rising, currents are pushed to the surface of a conductor (skin effect). Therefore it is essential to ensure a plating thickness as consistent as possible, without any imperfect spots whatsoever, which could adversely affect resistance due to the cross-section being altered.
Silver is employed in medical technology because of its antibacterial effect, e.g. as a coating material for endoscopic tubes.
In textiles silver threads can prevent bacteria from growing and thus unpleasant odours from arising. In water filters a coat of silver is applied owing to its antibacterial effect.
The highest reflection value of all metals can be found in fresh uncorroded silver surfaces, with over 99.5% of the visible light being reflected. This quality has turned silver into a most popular item for decorative purposes.
The issue of silver tarnishing
Air contains traces of hydrogen sulphide (H2S), an agent silver reacts with in the presence of atmospheric oxygen, which triggers the formation of silver sulphide (Ag2S). This makes the silver gradually go black. The effect described above is temporarily amplified through the sulphur content in the air going up as a consequence of winter being the most intense heating period. This makes the silver tarnish faster. There is generally no lasting remedy to stop silver or silver alloys from tarnishing. From a technical perspective, this does not pose a problem relative to electrical conductors as their conductivity is not compromised.
However, those conductors may sustain optical drawbacks as seen in speaker cables with a transparent insulation. The process of tarnishing is significantly slowed down by means of storing the conductor in a place that fulfils three preconditions: it should be as dry, airtight and sun-protected as possible.
Benefits engendered by new silver-plating line
LEONI has years of experience in galvanic plating under its belt. Its entire know-how in this area is now concentrated around the new state-of-the-art silver-plating line in Weissenburg, which also entails a much higher overall capacity. We are now able to supply our customers with products boasting various types of coating from 3 different locations in the US, the UK and Germany. This translates into greater flexibility and process stability coupled with shorter delivery times to the benefit of our customers.
Whatever you demand - protection or embellishment of the surface, better conductivity, antibacterial quality or enhanced technical properties – the new silver-plating line provides custom-made plating thicknesses of the finest quality.