Resource Library

What surface treatments can be used to protect outdoor copper, brass and bronze objects?

Brasses will slowly tarnish in the atmosphere; outdoors the process is more rapid due to the effect of moisture, salt (in marine environments) and pollutants such as sulphur dioxide (acid rain) in industrial areas. The tarnishing can be greatly delayed and the range of colours, which give copper alloys their aesthetic appeal, maintained by either lacquering or waxing (or both).

Lacquering: one of the most effective lacquers is Incralac. Lacquers must be applied in dry, factory conditions and are not suitable for protecting components which are handled by the public, such as handrails, since acid levels of moisture in the skin (pH 5.5) damage the lacquer.

Waxes: copper alloys may be more cheaply protected by waxing. It is important to use natural non-reactive waxes such as Carnauba or Beeswax, not synthetic waxes which will eventually granulate and absorb water. Natural waxes are not affected by UV light.

Why are copper and copper alloys used in coinage?

Since ancient times copper has been used in coins; the Romans used copper widely in this application. The reasons for using copper are its excellent corrosion resistance, ease of stamping, good electrical conductivity for vending machines, antimicrobial properties and ease of recycling.

What are the benefits of using cast copper rotors in high efficiency motors?

Induction motor rotors were traditionally made by die casting aluminium around a stack of steel laminations, so forming the rotor bars and end rings. Copper has much better conductivity, which would result in better efficiency, but was not used because it was difficult to die-cast due to its higher melting point.  The casting issues have now been solved by improvements in die materials and process control.

Using copper offers a range of options to the motor designer.  If the rotor size is unchanged, efficiency can be improved. On the other hand, the rotor size can be reduced while maintaining the original efficiency, so reducing the cost.

What are the benefits of flame-free jointing techniques?

Copper flame-free jointing can be done by press fittings and push-fit fittings. The benefits of these types of fittings are:

  • Work can be undertaken with occupants in the building
  • No flux fumes
  • No additional ventilation required
  • No need for hot work permits/certificates
  • Quick to install
What alternatives are there to the leaded free-machining brasses such as CW614N (CZ121)?

Brasses have been developed where the lead is replaced by silicon. These are marketed under names such as Envirobrass and Eco Brass. They are slightly more expensive than the leaded brasses and not quite as machinable, but have excellent mechanical properties.

We manufacture an aluminium component which we clean in a tank which is also used to clean copper and brass. How can we avoid contaminating the aluminium with copper?

The best solution is to use separate tanks since copper ions will always migrate to the aluminium. Failing this, immerse the aluminium component in a 5% solution of nitric acid. This will dissolve any traces of copper.

We have supplied hard drawn copper wire CW024A (C106) to a customer who is making springs. We have achieved a tensile strength of 370N/mm2 but he requires a much higher value. What is your suggestion?

You have reached the limit with C106 copper.  Cold drawn phosphor bronze wire is capable of much higher strengths up to 600N/mm2.

We have supplied copper nickel tubes to the UK from overseas. The wooden boxes containing the tubes became saturated with rain water at the port of exit and on arrival in the UK were heavily tarnished (green). Is there any way of cleaning the tubes?

If the oxide is tenacious grit blasting may be required. This should be followed by pickling in a hot 5-10% sulphuric acid solution containing 0.35g/litre potassium dichromate. The pickled tubes should be rinsed thoroughly in hot fresh water and finally dried in hot air.

We have purchased castings in CC333G (AB2). The standard BS EN 1982:2008 suggests in Annex A, clause A6, a stress relief heat treatment, but gives no details. Do you have a recommendation?

Heat to 450oC for one hour and air cool. This should be agreed between you and the manufacturer when ordering.

We have produced a number of tin bronze castings which show extensive porosity. The result of this is that the castings have failed a pressure test and show fluid leakage. It has been suggested that weld repairs may be a solution. Is this so?

No, the usual solution for treating porosity in castings is by impregnation where the casting is placed in a vacuum and the porosity is filled with either a polyester or epoxy resin. This process is approved for military applications (except Class 1 castings).

We are experiencing difficulty with the performance of copper washers (CW 024A, C106) in service. In some cases they are too soft and they flow whilst others are so hard that they do not form a seal. What do you suggest?

You have the correct grade of copper.  I suggest that you require the half hard condition.  This is expressed now as H065 in EN1652.  The hardness range given is 65 to 95 HV.  You should carry out periodic hardness tests.

Warm roof or cold roof?

Warm roofs do not require ventilation and are suitable for all pitches and are preferred for low pitched and flat roofs. Cold roofs require ventilation and should not be used on low or flat pitched roofs.