Short summary of article about: copper mining and processing – stages and use.
Copper Mining and Metalworking
Already after World War II in the largest industrially developed countries more copper was recovered from scrap than was smelted from ores, and today the relative share of secondary copper has increased significantly. For modern metalworking and rolled copper products the most important properties of copper are its high electrical and thermal conductivity, as well as strength, ductility, and good corrosion resistance. The physical properties of copper are closely linked to its crystalline structure. Copper belongs to the group of metals whose structure is characterized by a face-centered cubic lattice. It melts at 1083 °C.
About half of the total annual production of pure metallic copper (with greater or lesser degrees of purity) is used to manufacture wires, cables, busbars and other current-carrying products of the electrical industry. The maximum conductivity achieved for copper today is 60.1 m/Ω·mm2. This means that a copper wire with a cross-section of 1 mm2 and a length of 60.1 m has an electrical resistance of 1 Ω. Wires of the same cross-section made of silver, aluminum and iron have that resistance at lengths of 63, 38 and 10 m, respectively. In terms of electrical conductivity copper is only 5% behind silver, leaving all other metals far behind. Therefore copper is indispensable in electrical engineering, since electric power must be transmitted with the lowest possible losses.
Any impurities in copper, even silver, reduce its electrical conductivity, and the reduction is greater the further (horizontally) the impurity element is from copper in Mendeleev’s periodic table.
The tensile strength of annealed pure copper is 200—240 N/mm2 with an elongation of about 40%. As a result of cold deformation (work hardening) copper is strongly strengthened, and depending on the degree of work hardening its strength increases up to 380 N/mm2, while elongation falls to 8—10%. Unlike electrical conductivity, the strength and corrosion resistance of copper can be significantly improved by alloying. The most important alloying elements in copper alloys are zinc, tin, aluminum and nickel. Copper alloys, like alloys of most other non-ferrous metals, are divided into wrought alloys, which are used to produce semi-finished products (sheets, strips, profiles, wire, etc.), and foundry alloys, used for parts obtained by casting into sand or metal molds (chills), as well as by continuous casting and centrifugal casting.
Not all grades of so-called pure copper are free of oxygen. On a microsection of a sample of oxygen-containing copper (i.e., containing more than 0.4% oxygen) a structure is visible consisting of primary dendrites of Cu2Q enclosed in a eutectic matrix.
Alloys of copper with zinc are generally called “brass.” Special grades of brass also contain other alloying elements. If the tensile strength in tension of forged brass grade L60 (60% copper and 40% zinc) is 350—400 N/mm2, then in special brasses the strength can reach 800 N/mm2, i.e., it is twice as high as that of ordinary carbon steel.