Before pouring into the mold, the metal to be casted has to be in the molten or liquid state. Furnace is used for carrying out not only the basic ore refining process but mainly utilized to melt the metal also. A blast furnace performs basic melting (of iron ore) operation to get pig iron, cupola furnace is used for getting cast iron and an electric arc furnace is used for re-melting steel. Different furnaces are employed for melting and re-melting ferrous and nonferrous materials. The following are the factors which are responsible for the selection of furnace.
(i) Considerations of initial cost and cost of its operation.
(ii) Relative average cost of repair and maintenance.
(iii) Availability and relative cost of various fuels in the particular locality.
(iv) Melting efficiency, in particular speed of melting.
(v) Composition and melting temperature of the metal.
(vi) Degree of quality control required in respect of metal purification of refining,
(vii) Cleanliness and noise level in operation.
(viii) Personnel choice or sales influence.
Heat in a melting furnace is created by combustion of fuel, electric arc, electric resistance, etc. A furnace contains a high temperature zone or region surrounded by a refractory wall structure which withstands high temperatures and being insulating minimizes heat losses to the surroundings. For refining and melting the ferrous and non ferrous materials, various furnaces are used.
Furnaces for Melting Different Materials
1. Grey Cast Iron
(b) Air furnace (or Reverberatory Furnace)
(c) Rotary furnace
(d) Electric arc furnace
(a) Electric furnaces
(b) Open hearth furnace
3. Non-ferrous Metals
(a) Reverberatory furnaces (fuel fired) (Al, Cu)
(b) Rotary furnaces
(i) Fuel fired
(ii) Electrically heated
(c) Induction furnaces (Cu, Al)
(i) Low frequency
(ii) High frequency.
(d) Electric Arc furnaces (Cu)
(e) Crucible furnaces (AI, Cu)
(i) Pit type
(ii) Tilting type
(iii) Non-tilting or bale-out type
(iv) Electric resistance type (Cu)
(f) Pot furnaces (fuel fired) (Mg and AI)