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Melting furnaces
- 1. Melting furnaces Types of meltingfurnaces by, KOUSHIK KOSANAM
- 2. Introduction • A meltingfurnace is an appliance capable of heating materials to such a high temperature that they melt, which from a chemical perspective basically means that they reach the critical threshold temperature at which they convert from a solid to a liquid. • Not all materials will melt, and those that do often have different melting points. • Various furnaces are used for different jobs.
- 3. Types of furnaces: Thereare different types of furnaces, 1. Electric arc furnace 2. Basic oxygen furnace 3. Blast furnace 4. Induction furnace
- 4. 1. Electric arcfurnace • An Electric Arc Furnace (EAF) is a furnace that heats charged material by means of an electric arc. • Industrial arc furnaces range in size from small units of approximately one ton capacity up to about 400 ton units • Industrial electric arc furnace temperatures can be up to 1,800 °C (3,272 °F), while laboratory units can exceed 3,000 °C (5,432 °F).
- 5. Construction It consists ofthree main parts, • the shell, which consists of the sidewalls and lower steel "bowl"; • the hearth, which consists of the refractory that lines the lower bowl; • the roof, which may be refractory-lined or water-cooled, and can be shaped as a section of a sphere.
- 6. Operation • Scrap metalis delivered to a scrap bay, located next to the melt shop. • The scrap is loaded into large buckets called baskets, and the furnace is charged with scrap from the basket. • After charging, the roof is swung back over the furnace and meltdown commences. • The electrodes are lowered onto the scrap, an arc is struck and the electrodes are then set to bore into the layer of shred at the top of the furnace. • Oxygen is blown into the scrap, combusting or cutting the steel, and extra chemical heat is provided by wall-mounted oxygen-fuel burners. Both processes accelerate scrap meltdown
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- 8. 2.Basic Oxygen furnance •Basic Oxygen Steelmaking (BOS, BOP, BOF, and OSM), also known as Linz–Donawitz-steelmaking or the oxygen converter process. • It is a method of primary steelmaking in which carbon-rich molten pig iron is made into steel. • Blowing oxygen through molten pig iron lowers the carbon content of the alloy and changes it into low carbon steel. • The process is known as basic because fluxes of burnt lime or dolomite, which are chemical bases, are added to promote the removal of impurities and protect the lining of the converter.
- 9. Process • Molten pigiron from a blast furnace is poured into a large refractory-lined container called a ladle. • Pretreatment stage • Filling the furnace with the ingredients(cold metal) is called charging. • copper tipped lance with 3-7 nozzles is lowered down into it and high purity oxygen is delivered at supersonic speeds.
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- 12. INTRODUCTION •The purpose ofa blast furnace is to reduce and convert iron oxides into liquid iron called "hot metal”. • The blast furnace is a huge, steel stack lined with refractory brick. • Iron ore, coke and limestone are put into the top, and preheated air is blown into the bottom.
- 13. The Method Three substancesare needed to enable to extraction of iron from its ore. The combined mixture is called the Charge: • Iron ore, haematite - often contains sand with iron oxide, Fe2 O3 . • Limestone (calcium carbonate). • Coke - mainly carbon • The charge is placed a giant chimney called a blast furnace. The blast furnace is around 30 metres high and lined with fireproof bricks. Hot air is blasted through the bottom.
- 14. Reactions •Oxygen in theair reacts with coke to give carbon dioxide: C(s) + O 2(g)CO2(g) •The limestone breaks down to form carbon dioxide: CaCO3(s) CO2 (g) + CaO(s) •Carbon dioxide produced in 1 + 2 react with more coke to produce carbon monoxide: CO2(g) + C(s) 2CO(g)
- 15. • The carbonmonoxide reduces the iron in the ore to give molten iron: 3CO(g) + Fe2O3(s) 2Fe(l) + 3CO2(g) • The limestone from 2, reacts with the sand to form slag (calcium silicate): CaO(s) + SiO(s) CaSiO3(l)
- 16. •Both the slagand iron are drained from the bottom of the furnace. •The slag is mainly used to build roads. •The iron whilst molten is poured into moulds and left to solidify - this is called cast iron and is used to make railings and storage tanks. •The rest of the iron is used to make steel.
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- 19. Introduction • An InductionFurnace is an electrical furnace in which the heat is applied by induction heating of metal. Induction furnace capacities range from less than one kilogram to one hundred tonnes, and are used to melt iron, steel, copper, aluminium, and precious metals. • The advantage of the induction furnace is a clean, energy-efficient and well-controllable melting process compared to most other means of metal melting. • Most modern foundries use this type of furnace, and now also more iron foundries are replacing cupolas with induction furnaces to melt cast iron, as the former emit lots of dust and other pollutants.
- 20. Operation • An inductionfurnace consists of a nonconductive crucible holding the charge of metal to be melted, surrounded by a coil of copper wire. • A powerful alternating current flows through the wire. The coil creates a rapidly reversing magnetic field that penetrates the metal. • The magnetic field induces eddy currents, circular electric currents, inside the metal, by electromagnetic induction.
- 21. • The eddycurrents, flowing through the Electrical resistance of the bulk metal, heat it byJoule heating. Once melted, the eddy currents cause vigorous stirring of the melt, assuring good mixing. • An operating induction furnace usually emits a hum or whine (due to fluctuating magnetic forces), the pitch of which can be used by operators to identify whether the furnace is operating correctly or no. • An advantage of induction heating is that the heat is generated within the furnace's charge itself rather than applied by a burning fuel or other external heat source, which can be important in applications where contamination is an issue.
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