PROPERTIES OF COPPER:
COPPER is one of the few coloured metals. COPPER is ductile & relatively soft and it alloys readily with other metals to for example produce brasses & bronzes. COPPER has excellent electrical & thermal conductivity.COPPER oxides quickly in heated air & polished surfaces are easily tarnished by exposure to the various sulphur compounds & acids present in the atmosphere. COPPER may be deposited as a dull or bright coating & is used for both decorative & industrial purposes.
COPPER is particularly useful as a pre-coating for soft soldered work, pewter & zinc alloy die-casting before the disposition of nickel, gold or silver. Before nickel plating on zinc base die castings a COPPER deposit of 8 to 12 microns is applied to protect the zinc from attack by the nickel plating solution. Electroplated zinc base die-casting for automotive use is a major use of copper plating. COPPER is also largely used in the electronics industry, because of its conductivity it is used to produce the millions of square feet of printed circuit board used each year. COPPER is plated on to slowly revolving stainless steel drums & because there is no adhesion it can be peeled of in a continuous layer to be subsequently bonded to epoxy resin or phenolic sheets. When this is cut up, drilled & suitable circuit patterns are defined on the surface COPPER is again used as part of the through hole plating technique. Electrodeposited COPPER has been considered as a possibility of a partial or complete replacement for Nickel plating; this however depends on the service requirements of the plated deposit & the condition of the basis metal. The use of bright leveling types of solution permits a reduction in polishing required & can even eliminate the need of polishing altogether. The use of a heavy COPPER undercoat (10 microns or more) enables the thickness of the subsequent nickel deposit to be reduced without impairing the corrosion resistance. Electroplated coatings of Chromium & Nickel are examples of the reductions in Nickel thickness which are permissible where an initial copper deposit is applied. Where the COPPER is to be polished the thickness requirement is calculated or measured after polishing.
Recent research has shown that when micro-discontinuous chromium is employed an initial deposit of COPPER prior to nickel plating results in a bigger increase in corrosion resistance than when COPPER is used under conventional nickel/chromium deposits.An interesting application of COPPER is selective case hardening of steel. The COPPER deposit is applied or retained on areas which are to remain unhardened & its presence prevents penetration by the carbon during the subsequent carburizing process. Selective case hardening is now applied to a wide range of engineering components which are prone to wear and tear for example: gears, spline shafts, aircraft & motor fittings. By using this technique the actual wearing surfaces are made extremely hard while the remaining surface is soft enough to permit further machining. This technique also restricts the area of the component which is hardened & therefore the loss in the fatigue strength in the material is greatly reduced. For COPPER plating before selective case hardening copper solution may be used. The nature of the deposits are fine grained and thick coatings can be easily applied, for this reason this process is specially suited for this purpose. The thickness of the COPPER necessary is dependent on the thickness of case to be applied and may vary from 12 to 25 microns. The ductility of COPPER makes it a necessary coating to enable plating on plastics to achieve the high quality that is expected of bright decorative plated components. The COPPER layer absorbs the stresses that are developed between the metal & the plastic when the plated parts are subjected to temperature change. Without it the less ductile bright Chromium/Nickel would crack and blister. In the printing industry COPPER is used for the production of electrotypes & providing the printing surface in gravure printing. COPPER is used in electroforming for the production of wave guides & other electronic & electric hardware. COPPER is also useful in the production of electroformed slush moulds for plastic & rubber items & is used as a back-up for the harder Nickel electroforms used in pressure moulds. Other occasional uses for COPPER are in the building up of surfaces where mechanical loading is not too high, & plating of wire to act as a lubricant prior to drawing. Carbon brushes & arc electrodes are sometimes plated COPPER to improve their electrical conductivity. COPPER plating is also used to provide an anti-fret coating on bearings & housings.