Copper: Meaning, Types and Uses | Metals | Industries | Metallurgy

In this article we will discuss about:- 1. Meaning of Copper 2. Mechanical Properties of Copper 3. Refining 4. Types 5. Uses.

Meaning of Copper:

Copper is a very important metal in industry as it has great corrosion resistance property. It has got good strength which is maintained at moderate temperatures. It is very ductile and can be worked into complex shapes. It can be very easily welded, soldered and riveted. It has got very high heat conductivity and electrical conductivity.

Mechanical Properties of Copper:

Ductility can be increased at the expense of hardness and strength by annealing. Copper and its alloys can be easily joined by soldering, brazing and welding.

Refining of Copper:

Blister copper, as obtained after roasting and converting the copper ore, contains about 98.5% copper and the rest 1.5% is made up of nickel, iron, selenium, tellurium, lead, arsenic, antimony, bismuth, sulphur, precious metals, etc. Such a copper cannot be used in industry.

So it is further refined by the processes in the sequence given below:

1. Fire Refining, in order to produce purer and homogeneous anodes.

2. Electrolytic Refining, for refining precious metals and removing the impurities.

3. Second Firing, for adjusting the physical properties of electrolytic copper for use in industry.

After electrolytic refining operation, cathodes may be used directly for making alloys, but if copper is to be rolled to fabricated forms, it is melted and cast into wires, bars, cakes or billets. After the second firing operation, the correctly refined castings solidify with an approximately-level surface, the gas evolved during solidification balancing the shrinkage that would otherwise occur. This is known as tough-pitch copper and it has a density of 8.4 to 8.7 g/cc when cast, 8.89 to 8.92 when worked and annealed.

Types of Copper:

Following are the different types of copper used in industry:

(i) High Conductivity (H.C.) Copper:

This type of copper has as high purity as 99.9% copper (silver being counted as copper). It is largely used for electrical purposes. The presence of even traces of certain impurities (particularly phosphorus, arsenic, iron, titanium and silicon) decreases the conductivity of copper considerably.

(ii) Best Select Copper (B.S.):

It is refined copper containing small quantities of various other impurities which prevent its being classified as H.C. copper. It is widely used in industry.

(iii) Arsenical Copper:

It contains up to 0.5% of arsenic. The conductivity of arsenical copper is quite high though lower than H.C. copper. Arsenic gives increased strength to the copper at ordinary and moderate temperatures. Upon annealing arsenic raises the softening temperature by about 100°C. Arsenical copper has greater resistance to oxidation at moderate temperature than H.C. copper.

(iv) De-Oxidised Copper:

De-oxidised copper, arsenical or otherwise, is obtained by removing oxygen from copper by the addition of de-oxidants to the molten copper. Phosphorus is commonly used as a de-oxidant, but decreases the conductivity.

Oxygen free copper of high conductivity and density is now-a-days made by casting without contact with air. This is more ductile tough pitch copper and is immune to embrittlement by hot reducing gases unless it has been allowed to absorb oxygen during fabrication.

The presence of oxygen in copper is considered desirable in making the copper slightly harder. Before the commercial adoption of electrolytic refining process, oxygen was used in neutralising the effect of certain impurities. Oxygen is harmful if the copper is to be welded or otherwise heated in a reducing atmosphere, as it causes embrittlement of copper and renders it useless.

Uses of Copper:

Copper is used in huge quantity for making copper wire. It is used for making alloys such as brass. On account of its high resistance to corrosion, it is used in the form of copper sheets in chemical work, and food and brewing plants.

Copper can be cold rolled extensively upto 870°C and beyond it hot-worked. Cold rolling increases the hardness and strength. Copper wire above 0.10 mm diameter is commonly made by drawing from a hot-rolled rod without annealing but smaller sizes involve intermediate anneals. Copper shapes of electrical switch parts are made by extrusion, brushes and commutator sections by rolling and drawing.

Copper containing small amounts of silver or antimony retains the properties attained by cold working to a higher temperature than pure copper (about 320°C compared with about 205°C). This is useful where comparatively high temperatures are to be withstood, as in soldering or enamelling operations.

Addition of 0.5% arsenic to copper allows it to be used at temperature of upto 300°C without loss of strength. Addition of 0.08% silver prevents it from softening during soldering and addition of 0.5% tellurium produces free-cutting characteristics.

Copper alloys find extensive applications on account of their heat and electrical conductivity, good cold and hot- working properties, machinability, and corrosion resistance. Commercially pure copper is best-suited where high thermal or electrical conductivity is desirable. Where strength combined with high conductivity is the consideration than alloys containing cadmium or other elements are used.

Brass is the cheapest copper alloy. It contains high zinc content and is widely used unless high corrosion resistance under stress or the special mechanical properties of other alloys are required. Brass with 30—35% zinc is best-suited for deep drawing and forming operations.

Leaded brass is used when much machining is to be done, particularly for automatic screw machine work. For high elastic strength, the tin bronzes are used. For corrosion resistance, alloys of copper with aluminium or silicon or nickel are most suited.

IS: 2378—1978 specifies the designation and other characteristics of copper and its alloys. According to it copper is designed by letters Cu followed by letters CATH, ETP, FRHC, or DPH (indicating the important characteristics) ; these being for cathode copper, electrolytic tough pitch copper, fine refined high conductivity copper and phosphorised high residual phosphorus non-arsenical grade copper respectively.

Copper alloys are designated by symbol Cu followed by symbols for next most significant elements and their percentage in the decreasing order. Sometimes a letter for method of casting is placed before the designation and letter for surface finish at the end.