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Copper and Copper Alloys            

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Copper

Copper and gold are the earliest metals known to man and have been in use for about 10,000 years. The attractive properties which made copper so useful then - good corrosion resistance, attractive colour, excellent workability and good mechanical properties - are relevant today and, in addition, copper has the best electrical and thermal conductivity of any commercial metal. 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:

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.

copper busbar

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 250N/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.

For detailed information on properties and applications, see Pub 122.

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Stagecoach supertram Sheffield

 

Castings - Finch Seaman

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 450N/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.

For detailed information on properties and applications see Pub 122 and BS EN 50149:2001 Railway applications - Copper and copper alloy grooved contact wires.

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The high conductivity of copper makes it suitable for this electrode holder which carries enormous currents to a steel making arc furnace

 

 

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.

For more information see Pub 122 and Pub 44.

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Cold formed and finished machined components for the electrical and semi-conductor industries - Dawson-Shanahan Ltd
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, 394W/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.

 

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Modern radiators joined by CuproBraze®
Copper is easy to join by brazing or soldering
The changing shades of copper with time
Copper used for interior cladding
Scrap copper is shredded and compressed into bales for recycling

Publications and Software

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TN 23 Copper for Contacts open pdf
Copper is present in nearly all electrical contact applications, either in the material of the contacts themselves, as a backing material, or in the construction of the contact carrier connections and terminals of the switch contact assembly. This publication looks at the properties required for contact materials, and identifies those applications in which copper or copper alloys have special advantages.

Pub 44 Machining Brass, Copper and its Alloys open pdf
Detailed advice on machining techniques. Guide to choice of speeds and feeds. Comprehensive list of British and European alloys with details of machinability. Advice on the selection of cutting fluids. 1992. 66pp.

Pub 98 Joining of Copper and Copper Alloys open pdf
Suitability of the many methods now available for the jointing of copper and copper alloys with details of filler materials and recommendations for good joining practice. 1994. 64pp.

Pub 106 Corrosion Resistance of Copper and Copper Alloys open pdf
This large table gives information on the suitability of copper and copper alloys with many different chemicals. Data is given for copper, brass, copper nickel, aluminium bronze and gunmetals at three temperatures: 20oC, 60oC and 100oC . The table shows when specific materials can and cannot be used with the chemicals giving an indication of corrosion resistance. 5pp.

Pub 122 High Conductivity Coppers for Electrical Engineering open pdf order printed copy
This booklet describes the way in which coppers of all types have been developed and improved to meet the design requirements of electrical engineers. The materials described are the commercially pure coppers, low alloy coppers and the copper alloys with good elevated temperature properties used for special purposes. Revision of publication 29 with BS EN standards and the old BS equivalents given. 1998 40pp.

TN 27 High Conductivity Coppers for Electrical Engineering web link
These data sheets, prepared by the International Copper Development Council (CIDEC), were originally published in a series during the period 1968 - 1972 and cover all the main coppers and copper alloys. They contain an invaluable summary of data relating to the physical and mechanical properties of the materials at low, ambient and elevated temperatures which is not available elsewhere. Tensile, hardness, impact, creep and fatigue data have been abstracted from the relevant original literature.

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