Main precautions in the design of copper parts
Copper is one of convenience metals such as steel and aluminium. It is essential in the electrical and electronic sector, such as the sector of renewable energies and is used more marginally in the foundry, boiler, heat exchangers, …
The main properties of copper led to its success are very high electrical and thermal conductivity, as well as properties including mechanical, and corrosion which make it an ideal material for wiring applications and sheet metal working.
Minera Escondida (Chili) First copper mine of the world
Production and ore grades at Escondida
Today, the copper minerals are being depleted. The largest copper mine in the world (minera Escondida in Chile), which produces nearly 9% of global copper saw its copper contents halve in 15 years. The result translates into an increasing difficulty to produce copper and increasing energy costs (you have to extract and crush two times more ore to extract the same amount of copper. In addition, global demand for copper increases with development of countries. The newly industrialized countries (Brazil, China, India, …) are now major consumers of copper. In thirty years, world population has doubled and the demand of copper per person has increased from 1.6 kg/year to 2, 7. Moreover, copper reserves are depleted and the major copper producers such as Chile (23% of world production) will reach the end of their operation by 20 years. copper prices continue to rise and the crisis had no lasting effect on lower costs.
Evolution of copper consumption /inhab/year
Episode of copper prices decline in October 2008
Copper is a strategic material for many applications related to electronics, renewable energy, …
There is therefore a strategic issue to collect / recycle copper and to eco-design consumer products in order to limit the use of this material and to facilitate recycling at end of life.
One of the first rules of eco-design with copper parts will be to preserve the conductivity of copper and a second time in its mechanical properties (ductility). As discussed in 2) many impurities degrade the expected properties. It is therefore necessary to ensure associations with incompatible metals within the same product and that copper is released easily from these incompatible metals during grinding or recycling.
The substitution of copper by aluminium (which has high thermal and conductive properties) is realized in the context of some applications of high voltage cabling / power but is often difficult to control in terms of corrosion and flexibility of conductors.
Rules of association of metals with copper
Copper is a metal that has unique properties of electrical conductivity. It will therefore maintain maximum purity of copper, especially against some impurities that often come from other alloys.
Influence of impurities on the conductivity of copper (source CICLA; www.cuivre.org)
We see on the figure above that the IACS conductivity decreases strongly with the presence of impurities from convenience metals including: Titanium, Cobalt, Iron, Manganese, Chromium, Aluminium, Tin, Magnesium, Zinc.
Phosphorus also decreases the conductivity of copper, but gives some interesting features for processing and weldability of copper. A research of compromise is to find.
Silver in a positive role in reducing the conductivity.
This is so primarily to avoid associations with ferrous metals (including stainless steel, or manganese, silicon) and aluminium alloys and magnesium alloys and copper alloys such as brass (Zn) and bronze (Sn)
Take into account the limitations of current recycling processes and respect of basic design rules
Rule 1: Avoid associations with ferrous metals
As we have shown in previous sheets, copper is often associated with steel (electric motor, transformer, …) or with aluminium (heat exchanger) which tend by their shape or resilience to trap Copper wires or tubes.
The magnetic separation after shredding will let go stainless metals with huigh chromium content, aluminium and magnesium alloys. They will be mixed with various copper alloys and will undergo further sorting based on the eddy-current or the density.
If parts of mixed composition are not designed to easily release the materials at the time of grinding, sorting by density or eddy current will not give satisfactory results because the conductivity of the mixture or even its density will not be different enough and will lead to sorting errors (see diagram density and conductivity of metals below).
| Materials | Electric resistivity (Ω.m) | IACS (%) |
|---|---|---|
| Silver | 16.10-9 | 106,3% |
| Copper | 17.10-9 | 100% |
| Gold | 22.10-9 | 77,3% |
| Aluminium | 27.10-9 | 63% |
| Magnesium | 46.10-9 | 37% |
| Bronze | 50.10-9 | 34% |
| Zinc | 60.10-9 | 28,3% |
| Nickel | 70.10-9 | 24,3% |
| Brass | 70.10-9 | 24,3% |
| Iron | 104.10-9 | 16,3% |
| Tin | 142.10-9 | 12% |
| Lead | 207.10-9 | 8,2% |
| Nichrome | 1000.10-9 | 1,7% |
Electrical conductivity of the main metals.
Rule 2: Ensure that the different materials are released during shredding.
The principle is to not associate very closely incompatible materials in a part or in the same product. We will choose to combine brittle materials and ductile so that at the time of grinding, the links can break and release the different materials for sorting.
Example of Faurecia: Fan Motor – The project CEMIR of Faurecia
Rule 3: Avoid the proliferation of small copper windings and the multiplication of thin cables or design in order to facilitate their removal.
Cables, copper coils from small power motors, and low power transformers are also sources of copper losses because thin copper wires tend to fray and be cut into small pieces that will hang with other materials or get lost in the fraction of shredder residue.
Microscope photo of the mineral fraction of the ultimate shredding products. Fraction that is deposited in landfills. It still contains 3kg of copper per ton of residue.
It is therefore necessary to avoid this type of design or make that parts made of mixed composition are disassembled before crushing or sorted after a first shredding of the product (currently manually) to go into a specific recycling system.
Rule 4: Beware of pollutants that may disrupt the recycling.
The recycling of copper requires in most cases a pyrometallurgical phase. It is further a great catalyst able to convert organic molecules in pollutants.
To avoid risk of pollution or of extra costs of flue gas treatment at the time of recycling processes, it is cautious to avoid the use of brominated or chlorinated plastics, as well as compounds containing heavy metals (beryllium, mercury, cadmium, …) or radioactive.
Rule 5: Avoid heavy parts that could damage the shredders.
Synthesis
- Rule 1: Avoid associations with ferrous metals.
- Rule 2: Ensure that the different materials are released during shredding.
- Rule 3: Avoid the proliferation of small copper windings and the multiplication of thin cables or design in order to facilitate their removal.
- Rule 4: Beware of pollutants that may disrupt the recycling.
- Rule 5: Avoid heavy parts that could damage the shredders.
References
– M.A. Reuter and A. van Schaik (2012). Opportunities and Limits of WEEE Recycling – Recommendations to Product Design from a Recyclers Perspective. In: Proceedings of Electronics Goes Green 2012+, 9-12 September 2012, Berlin, Germany. In press. 8 p.