Coppers

Copper

Today, over half of the copper produced is used in electrical and electronic applications and this leads to a convenient classification of the types of copper into:

  • Electrical (high conductivity)
  • Non-electrical (engineering).

High Conductivity Coppers (Electrical)

Wrought high conductivity copper has excellent ductility and, as a result, is available in forms such as wire, tube, extrusions, bar and sheet.

The main grade of copper used for electrical applications such as building wire, motor windings, cables and busbars is electrolytic tough pitch copper CW004A (was C101) which is at least 99.90% pure and has an electrical conductivity of at least 101% IACS minimum. Tough pitch copper contains a small % of oxygen (0.02 to 0.04%) so if the high conductivity copper is to be welded or brazed or used in a reducing atmosphere, then the more expensive oxygen free high conductivity copper CW008A (was C103) may be used.

Wrought high conductivity coppers (CW004A and CW008A) can only be strengthened and hardened by cold working such as occurs on cold drawing or bending (typically tensile strength 250 N/mm2 with 12% elongation). They cannot be strengthened by heat treatment so, if a stronger grade of high conductivity copper is required, then small amounts (less than 1%) of alloying elements such as silver, cadmium, magnesium or tin are used.  These additions give solid solution hardening and contribute to work hardening when the alloys are cold drawn into wires or tubes or rolled into sheet. However, there is a small loss of conductivity. These alloys, with 90 to 100% IACS values are typically used for overhead conducting and catenary wires on railway and tram systems to transmit electric current to the electric motors of trains and trams.

High conductivity copper may also be produced as die and sand castings (CC040A), typically for electrical switchgear and electrode holders.

The electrical conductivity of castings may be slightly lower than in wrought copper, however a minimum value of 93% IACS is guaranteed but values up to 100% are reached.

Higher Strength Alloys
Small additions of silver, cadmium, magnesium or tin are used to give a small increase in the strength of copper conductors but, for significant increases in strength, the heat treatable copper chromium (0.5-1.2% Cr) and copper chrome zirconium (0.1% Zr) alloys have been developed in cast and wrought form. These alloys combine high strength (tensile strength 450 N/mm2 with 10% elongation, up to 400oC) with high electrical conductivity (75 to 78% IACS) and high thermal conductivity. The properties of these alloys are developed by a heat treatment process which involves heating to 950-1000oC (solution treatment), followed by water quenching then reheating to 425-500oC (precipitation hardening). In addition to this heat treatment wrought alloys are strengthened by cold working. Applications for these alloys include resistance welding electrodes, switchgear, heat sinks, current carrying arms and steel casting moulds where copper would be ideal from the electrical and thermal conductivity standpoint but is simply not strong enough.

Free Machining Copper
An addition of approximately 0.5% tellurium or sulphur raises the machinability rating from 20% to 90%, based on a scale where free machining brass is rated at 100%. The particles of copper telluride or copper sulphide act as chip breakers leading to excellent machinability without substantially affecting the electrical conductivity which is rated at 93% IACS. Free machining copper is used where a large amount of repetitive machining at high rates is required. One example is in the production of gas, laser and plasma cutting nozzles which involves the drilling of small holes in rods followed by cold forming to the finished shape. Other applications include screws, fasteners, contacts, connectors, clamps and bolts used in the electrical and semi-conductor industries.

Further information:
Publication 44 – Machining Brass, Copper and its Alloys

Engineering Copper (Non-Electrical)

The usual grade of copper used for engineering applications is CW024A (was C106). Many of the applications of copper depend upon properties other than its high electrical conductivity.

The properties which make copper the standard material for engineering, including architecture and plumbing, are:

  • Thermal conductivity – the thermal conductivity of copper, 394 W/mK, is about twice that of aluminium and thirty times that of stainless steel. This means that copper is used for components where rapid heat transfer is essential. Examples include saucepan bottoms, heat exchangers, car and vehicle radiators and heat sinks in computers, disk drives and TV sets.
  • Corrosion resistance – copper is non-reactive and does not rust or become brittle in sunlight
  • Ease of joining – by brazing or soldering. The latest technology called CuproBraze® is used to fabricate strong and reliable brazed copper/brass heat exchangers for cooling in vehicles which include cars, trucks, locomotives, tractors and JCBs.
  • High ductility – tubes are easily bent even when hard
  • Toughness – does not become brittle at sub zero temperatures
  • Heat resistance – withstands fire well, melting point is 1083oC
  • Antimicrobial – copper is a naturally hygienic metal which slows down the growth of harmful germs such as E.Coli, MRSA and legionella. Copper’s ease of shaping, corrosion resistance and antimicrobial properties make it ideal for brewing vessels.
  • Range of colours and malleability – widely used by designers and architects for exterior and interior applications.
  • Recyclability – copper is 100% recyclable without loss of properties. The price of scrap copper is high.

FAQs

I am at the design stage of an engineering project, part of which may include the use of a copper alloy casting. Since considerable machining is involved I am interested in machining data for cast copper alloys.

Machining data for copper casting alloys are similar to those of their wrought counterparts. The most easily machinable are classified as Group 1 and include CC491K (LG2) with a rating of 90% (this rating is based on a 100% value for free machining brass CZ121,CW609N). The more difficult alloys to machine are classified as Group 3 and include the aluminium bronzes such as CC333G (AB2) with a rating of 20%. For further details see CDA publication 44 Machining Brass, Copper and its Alloys.

I am designing a power lead connector for a large earth moving vehicle. The connector is crimped to copper wires to make electrical contact. I propose to machine this component from brass CW606N (CZ131) bar followed by tin plating. Any advice please?

The brass selected is free machining with good ductility and is an excellent choice for this application. I suggest that the component is annealed in the range 400 to 600oC to give maximum ductility to ensure that the crimping will be successful. There is no need for tin plating; in this environment the brass will darken with time with no loss of properties.

It is important that the lead content (1.6 to 2.5%) of this brass is maintained at the specification level in all of the connectors since higher lead levels may lead to cracking on crimping. With this in mind I suggest that the source of the brass is from the UK or Europe where full certification will be available.

I am in charge of a large renovation project and I have to recommend surface treatments to protect a number of outdoor copper, brass and bronze objects including hand rails, wall plaques, door handles and statues?

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.

I am looking for a copper alloy bearing material to operate between a stainless steel shaft and a stainless steel plate both of hardness about 700HV. I require the bearing to have a hardness of about 400HV.

The only copper alloys to meet the hardness requirement are the CuBe alloys. The alloy CW101C, (CuBe2, UNS C17200) when aged at 315oC will have the required hardness.

I am making an item which will form part of a compressed air system on a train. The drawing calls for copper tube in grade CW004A (C101). My stockist has offered CW024A (C106). Is this suitable?

Yes. CW004A is an electrical grade of copper and in this application electrical conductivity is not an issue. CW024A is the usual grade for engineering applications and is widely used to carry water, gas and air. The mechanical properties of the two grades are the same.

I intend to use copper as a cladding material but I do not want to wait for the natural patina to form. What do you suggest that I might use?

Copper sheet is available in pre-patinated form.  As well as green, other attractive colours such as brown, brass and gold are available.  See www.kme.com and www.aurubis.co.uk.

Is copper an essential element?

Yes, copper is as vital as calcium, iron and zinc. An adult needs 0.9 mg of copper every day to maintian good health. Nuts, seafood, wholegrain cereas and offal are good sources of copper and a balanced diet should provide adequate copper.

We are experiencing difficulty with the performance of copper washers (CW024A, 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 BS EN 1652.  The hardness range given is 65 to 95 HV.  You should carry out periodic hardness tests.

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

You have reached the limit with CW024A (C106) copper.  Cold drawn phosphor bronze wire is capable of much higher strengths up to 600 N/mm2.

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.

What significant antibacterial advantages does copper have over polybutylene plastic and stainless steel in cool potable 'soft' waters?

Copper demonstrated an antibacterial advantage over polybutylene for every temperature range and water hardness condition studied. In all water conditions copper demonstrated either stronger or equivalent antibacterial properties compared to stainless steel.

This section introduces coppers and copper alloys for conductivity applications and provides details of properties and uses.

For equivalents of copper alloys worldwide, their chemical compositions, material designation and national standards