 Good morning friends, in the previous classes we have been learning about the different steps involved in making a green sand casting. We have learnt how to prepare the green sand and we have seen how to design a gating system and in the previous two lectures we have seen the different casting defects that could evolve during the what is a manufacture of a green sand casting. Now in this lecture let us see the melting furnaces and practice. Now before learning about different furnaces used in preparing the molten metal, let us see the melting temperatures and pouring temperatures. For any metal or for any alloy there will be two temperatures, one is the melting temperature at which the solid metal actually melts means that the phase change takes place. Now there is another temperature that is the pouring temperature means this pouring temperature is always greater than the melting temperature because if we just pour at the melting temperature then the molten metal cannot flow into the entire cavity. In order to ensure that the molten metal flows into each and every corner of the mould cavity the pouring temperature of the metal or the alloy should be little greater than the melting temperature. Now for grey cast iron the common melting temperature is 1370 degree centigrade and its pouring temperature varies between 1510 to 1590 degree centigrade and for cast steel the melting temperature is 1480 degree centigrade and the pouring temperature ranges between 1600 to 1720 degree centigrade. And for copper the melting temperature is 1083 degree centigrade and the pouring temperature varies between 1130 to 1200 degree centigrade and for nickel the melting temperature is 1453 degree centigrade and the pouring temperature varies between 1500 to 1590 degree centigrade and for aluminium the melting temperature is 660 degree centigrade and the pouring temperature varies between 700 to 760 degree centigrade and for zinc the melting temperature is 420 degree centigrade and the pouring temperature ranges between 450 to 480 degree centigrade and for lead the melting temperature is 327 degree centigrade whereas its pouring temperature ranges between 350 to 380 degree centigrade and for tin the melting temperature is very low we can see it is 232 degree centigrade whereas it is pouring temperature ranges between 280 to 290 degree centigrade. Now let us see the copper and 4% nickel alloy the melting temperature is 1175 degree centigrade whereas the pouring temperature ranges between 1220 to 1280 degree centigrade and for gun metal where the copper percentage is 85% tin is 5% zinc is 5% and lead is 5% and it is melting temperature is 1040 degree centigrade whereas the pouring temperature varies between 1100 to 1180 degree centigrade. So these are the melting temperatures and pouring temperatures of important alloys cast alloys. Now these are the important furnaces used in the melting one is the crucible furnace next one cupola furnace next one electric arc furnace next one induction furnace next one resistance furnace rotary furnace and reverberatory furnace we will see all this one by one first let us see the crucible furnace. Now crucible furnace is the most simple furnace there is a crucible we can see here inside this is the crucible it is made up of graphite plus silicon carbide plus clay plus resin and some more binders will be there it is a simple furnace. Now the fuel used in the crucible furnace is it can most commonly it is the coke or oil and sometimes even gas is used. Now here we can see crucible is kept here gas and mixture of gas and air will be passing here inside it will be burning and the charge will be kept inside the crucible after sometime the charge will be melting and the molten metal is ready for tapping. Now again there are 3 types of crucible furnaces one is the lift out crucible second one is the stationary pot means molten metal is to be ladled next one tilting pot furnace. Now here we can see this is the lift out crucible means say here there is a structure is there inside what say ceramic structure we place the crucible and we place the charge inside the crucible and we burn the fuel and the air mixture and after sometime the charge means the metal to be melted or the alloy to be melted that is the charge the charge which is inside the crucible will be melting then we have to remove this cover and we have to lift up the crucible. So that is all about the lift out crucible next one is the stationary pot means here we can see this is the what say ceramic structure and this is the crucible and this cannot be lifted one thing is we need to tap the molten metal from the stationary pot. Next one we can see tilting pot furnace here we can see yes inside there is a crucible is there and the system is such that this can be rotated by rotating this wheel this can be tilted one side or even to the other side. Now we put the fuel or we put the charge inside the crucible let the fuel burn after sometime the charge inside the crucible will be melting and it is ready for tapping. Now unlike in the case of the lift out crucible what we have done after what say melting is over we have lifted up the crucible and we were able to take it to a what say the convenient place of pouring but here we cannot lift the crucible means we have to bring another crucible and we have to tap the molten metal by tilting. So that is the tilting crucible furnace so this is the tilting pot furnace. So these are the what say three types of the crucible furnaces now these are the advantages of crucible furnaces one is the low installation cost there is nothing just a crucible and a structure to support it there is no high tech machinery and low melting losses. Now here we are coming across a new term called melting loss what is this is what is this melting loss means generally in every melting there will be loss of material suppose if we melt say 100 kgs of cast iron we would not get 100 kgs of molten metal maybe we may get 95 percent of molten metal means 5 kgs of melting loss is there so this is the melting loss but in the case of the crucible furnace the melting loss will be very minimum. Next one uniform heating of the charge this is not a very big furnace this is a small furnace that is why the uniform what say heating will be uniform. Now what is the application of the crucible furnace useful for melting nonferrous metals and alloys. Next one let us see the cupola furnace cupola furnace is the oldest and simple furnace cupola is derived from Latin word kupa which means cask or barrel it is like a long barrel it is very much like a blast furnace it is used to melt cast iron and steel. Now this is this is the construction details of a cupola furnace just now we have seen that the cupola means a cask or a barrel now here we can see there is a barrel kind of structure a cylindrical structure or a barrel. Now there is a steel ceramic shell will be there and this is the charging door charging means an entrance through which we place the what say charge the charge means the molten metal or the solid metal to be what say melted that is the charge we place the charge along with that we put the what say fuel and also the flux right so this is the charging door and this is the charging floor and here we can see the wind boxes. Next one tires this is the slag spout means through which we collect the slag. Now here we can see there are bottom doors and they can be dropped down so that the entire after the melting is over if any ash is present any unwanted what say material is present everything can be dropped down so that is the purpose of the drop drop doors or the bottom doors and here we can see this is a spark cluster means when we are burning the coke and we release what say air at a high pressure and because of that the hot burning coke may fly it is that time the spark cluster will prevent the burning coke to run away or to fly away from the cupola. Next one this is the preheating zone and the melting zone and here we can see again there is a what say tapping spout is there here sometime back we have seen this is the slag spout means through which we collect the slag and here it is the tapping spout means it is the spout or it is the what say entrance through which we collect the molten metal. Now it has a steel shell 6 to 10 meters high the steel shell is given refractory lining inside and the usual diameter of the steel shell is 0.5 to 2.5 meters it rests on a cast iron base plate and has generally 4 legs the cupolas are generally they have dropped down doors yes here we can see this is the shell and these are the dropped down doors at the bottom there is a tap hole to remove the molten metal we have already seen and there is a slag hole to remove the slag there will be tire tires to introduce air into the furnace the furnace has an opening of a that is the charging door the top of the slag stage is covered with a spark cluster that also we have seen. Now these are the steps in operation of a cupola one is the preparation repair of refractory lining the furnace might have been used previously and what is this furnace it is a very simple furnace it is a steel cylindrical shell and inside there is a refractory lining is there now it might have been used previously and the refractory lining might have been damaged now we need to repair it. Next one what about the what say at the things at the bottom there might be unwanted ash might be there or unbent coke might be there or sand unwanted sand might be there at the doors so those must be removed they must be cleared so that is the preparation and repair of refractory lining. Next one lightning and burning in the coke bed after we prepare the what say close the bottom doors yes we place the coke and we have to lighten it and we need to burn the coke bed while the coke is being burned charging is done charging means introducing metal coke and flux one by one into the furnace that is the charging so that we do after lightening the coke we do the charging then when we do the charging it will be melting yes melting will be going on starting of the then when the melting is going on starting the air blast we need to introduce the air and again we also need to do the charging charging means what say sending metal coke flux inside the furnace dropping and after sometime this will be the whole what say mixture or discharge will be melting after the molten metal is ready then we need to tap before that we need to tap this slag unwanted slag will be floating above the molten metal first that should be removed after the tapping of the slagging is over then we need to tap the molten metal into a ladle next after the burning is over then we need to drop the bottom means there will be what say unwanted coke will be there unburnt coke will be there unwanted sand will be there and ash will be there so all these should be released from the furnace then that is the dropping the bottom these are the merits of cupola furnace simple construction what is cupola furnace it is a gas or a barrel just a cylindrical shell low initial cost it is not very costly and it is simple to operate relatively very low operating cost it is a cost of operation is not high we need fuel may be coke or an oil and offers very high melting rate you see 1 to 35 tons per hour can be melted that much charge can be melted per hour it can be operated continually means what say it can be operated intermittently means today we have say 2 tons of what say charge is there we bring what say load that to 2 tons of charge into the furnace after it is melted after the molten metal is tapped you stop the furnace on the other hand you can keep on loading what say charging you can keep on charging and you can keep on melting and you can keep on tapping the molten metal that is the what say operation of the cupola furnace continually now most important thing is it does not require electric power no electricity is required that is the what say one of the advantages of the cupola furnace now these are the demerits of cupola furnace close temperature control is not possible suppose we are melting the cast iron and we require say some 1600 degree centigrade and you aim 1600 degree centigrade and you heat it and try to melt it accordingly finally you will melt or you will land up 20 degrees or 25 degrees more or 25 degrees less exactly it may not be possible to get 1600 degree centigrade that is the close temperature control is not possible next one carbon and sulphur pickup takes place during melting yes this cast iron contains carbon and sulphur let us see the composition of the cast iron so this is the typical composition of cast iron carbon is present say 1.8 to 4 percent silicon 0.5 to 0.3 percent manganese 0.15 to 1 percent sulphur 0.03 to 0.25 percent phosphorus 0.05 to 1 percent and the balance is iron so this is the typical composition of cast iron now here we can see sulphur is present and carbon is present and when we are operating the cupola furnace we generally we burn coke what does this coke contain the coke contains carbon coke contains sulphur and because we are burning coke inside the cupola furnace carbon from the coke will be entering into the molten metal sulphur from the coke will be entering into the molten metal but this is the limit for the carbon 1.8 to 4 percent and for sulphur this is the limit 0.03 to 0.25 but because we are burning coke the limits will be increasing more sulphur will be there and more carbon will be there then finally what will happen the properties of the cast component will be changing sometimes what is a cast component becomes brittle and it will leads to cracking so that is one of the demerits of cupola furnace next one loss of iron silicon manganese takes place during melting due to oxidation yes iron is present in the cast iron silicon is present manganese present these are useful alloying elements in the cast iron now this iron will be reacting with oxygen and forms iron oxide and it goes along the slag same is the case with the silicon silicon reacts with oxygen and forms silicon dioxide and goes along with the slag same thing can happen with manganese manganese reacts with oxygen and goes along with the slag finally the component or the properties of the cast structure or the cast component will be different then what are what have been gained so that is what can happen that is the loss of iron silicon and manganese during the cupola operation next one precise control of composition is difficult yes why because we may aim certain composition but because say sulphur pickup is there carbon pickup is there and loss of silicon loss of manganese because of these things this will go without the knowledge of the operator or without the intention of the operator finally we aim some composition but finally we will arrive at some other composition so precise control of composition is difficult next one environmental pollution takes place cupola releases lot of smoke and because of that environmental pollution takes place so this is the sectional view of a cupola now let us see the electric arc furnace now this is the electric arc furnace and here we can see these are the electrodes and an arc will be created and because of the high temperature of the arc the charge will be melting so that is the simple principle of electric arc furnace now these are the what say different components that are inside the electric arc furnace and here we can see this is a steel vessel the whole furnace is a steel vessel with refractory lining inside this is a steel vessel with refractory lining inside and this has got a removable roof is there this is the removable roof and this is the charging door means this can be open and can be closed and charge will be dropped through this door to inside the furnace what is the charge charge means the molten what is a solid metal to be melted along with the flux next one here is the slag door these are the construction details through which we can separate the slag from the furnace and finally here is the tapping spot through which we can what say extract the or we can get the molten metal we can tap the molten metal from the furnace and at the center we can see these are the graphite electrodes are there and there is power supply is there to the graphite electrodes so these are the construction details of the electric arc furnace and here we can see the charge is what say kept here and because of the arc created the charge will be melting now let us see yes when these are what say electrodes come in contact with the charge what will happen arc will be created there will be initiation of arc now here we can see average electrode consumption is 1 to 4 kgs per ton of metal so this much of what say electrode will be consumed so here these are the consumables electrodes now arc is intensified here we can see arc is intensified so this is the furnace now the molten metal is ready for tapping now tapping of the molten metal is like this yes it is here we place a ladle and into this ladle the molten metal is tapped now these are the types of arc furnaces one is the single phase arc furnace and this is generally used for melting non ferrous alloys next one this is the three phase arc furnace and it is generally used for melting steels now let us see the advantages of arc furnace precise control of composition is possible in the previous case in the case of the cupola the greatest demerit of cupola furnace is that precise control of composition is not possible because there will be sulphur pickup there will be carbon pickup and there will be manganese loss there will be silicon loss because of that there won't be precise control of composition but in the case of arc furnace there will be precise control of arc what say composition next one close temperature control is possible again this is what say another demerit we have seen in the case of the cupola precise control of temperature was not possible due to several reasons but here close temperature control is possible next one high thermal efficiency quality of molten metal is high what is this in the case of the melting with the cupola furnace the what say quality of the molten metal may not be very high by there will be impurities will be there we are burning coke and coke contains what say ash and slag will be collected at the top and all these can mix with molten metal so that is how the molten metal coming from a cupola furnace is not very clean its quality is not very high whereas in the case of arc furnace the quality of molten metal is high molten metal can be melted in short duration next one these are the limitations of arc furnace high power consumption high melting costs very high power is consumed that is how it results in high melting costs next one high installation costs chances for oxidation of liquid metal next one chances for carburization of liquid metal why because we are using graphite electrodes because of that the carbon in this graphite electrodes will be entering into the molten metal that is how our carburization of liquid metal takes place carburization means addition of carbon into the molten metal next one let us see the induction furnace now what is the principle of the induction furnace it is the electromagnetic induction high frequency current is passed through water cooled copper coils this is known as the primary coil there will be what say primary coil will be there copper coil and high frequency current is passed through this coil then what happens secondary currents are induced in the metal charge by electromagnetic induction now this secondary current will be passing through the charge charge means the solid metallic blocks to be or solid metallic pieces to be melted now this secondary current will be passing through the these what say charge blocks or the metallic pieces then what happens the metal charge offers resistance to the process of secondary current and develops heat when what say current secondary current is passing from one piece to another it encounters resistance and because of this resistance heat will be developed and this heat will be utilized for melting the charge now this is the typical construction of an induction furnace and here we can see these are the copper induction coils and this is a refractory material and around the refractory material there is a copper induction coil is there now inside yes this is a structure and this can be closed there is a cover and inside we have kept the molten metal now when we pass the electricity high frequency current through this what say copper induction coils what will happen because of electromagnetic induction there will be secondary current will be passing through the charge charge is this one the red colored one is the charge now this will be passing from one piece to another and that is how heat will be generated because of the resistance that the current encounters while passing from one piece to another now here we can see there is a electromagnetic mixing is also there here yes manual steering may not be required and because of the electromagnetic induction there will be magnetic mixing will be there so mixing will be uniform and here we can see this is the actual photograph of an induction furnace and this is the what say copper coil and through which high current is passed and inside there is a what say refractory crucible is there and inside the crucible where there is a charge now because of the secondary current yes heat is generated and that heat will be melting the charge that is kept inside the crucible yes after melting is over yes we are tapping this is that is how it can be tilted by rotating a wheel it can be tilted and the molten metal is being tapped now these are the advantages of induction furnace narrow melting vessel low diameter to height ratio and less oxidation now here the what say diameter will be less height will be more for the crucible in which we place the charge because of that what will happen lesser diameter means lesser area is exposed to the atmosphere then in such a case there will be less oxidation will be there so that is the first advantage of induction furnace next one low crucible wall thickness and less expensive next one relatively small area of molten metal is in contact with the slag now one of the what say problems that can encounter in melting is segregation of the slag from the molten metal most of the times we leave some what say slag inside the molten metal or while collecting the slag we also remove the molten metal now what happens here the what say area of contact between slag and the molten metal is very low why because the diameter itself is low in such a case what will happen the chances of removing the molten metal along with the what say slag will be less no corporizing during melting down that is what we have seen in the case of the cupola furnace there was carbon pickup and even in the case of the arc furnace there was carbon pickup means extra addition of carbon into the molten metal which is not required that is the carburization or carbon pickup that would not arise in the case of the induction furnace next one magnetic stirring of the melt produces excellent uniformity of the melt composition the charge will be stirred magnetically that is how there will be excellent uniformity of the melt composition next one melting takes considerably less time within few minutes we can get the molten metal these are the limitations of induction furnace initial cost of the furnace and its auxiliary equipments is very high and it is not suitable for melting large quantities of metal may be it may be suitable for small quantities or the moderate quantities not very large quantities but we get molten metal of high quality now these are the induction furnaces types types of induction furnaces one is the low frequency induction furnace and it is used to melt nonferrous alloys and the second one is the high frequency induction furnace and it is used to melt steel and alloy steels next one let us see the resistance furnace now the what is the principle of operation resistance element is heated by passing high electric current that is the simple principle of resistance furnace there will be a resistive element will be kept inside the furnace and when we pass the electric current that will be heated up and that heat will be utilized to melt the charge these are the advantages of resistance furnace accurate temperature control is possible because we keep the thermostat control to hold the liquid metal sometimes we used to add say certain additives or what say some modifications we used to do to the molten metal we add certain things like grain grain refiners or alloy additions or inoculants we used to add that time we need to hold the furnace at a certain temperature most of the times this may not be possible to hold the temperature at a particular temperature but this resistance furnace has a thermostat control we can set the temperature at that temperature is the temperature will continue as long as we on the furnace and at that particular temperature we can hold the liquid metal after making the what say additions or after adding the modifications next one application it is used to melt steel and nonferrous alloys next one let us see the rotary furnace what is your rotary furnace it is a horizontal cylindrical shell you can see here this is a horizontal cylindrical shell the steel shell is lined with refractory material inside so we can see here there is a steel shell inside we can see there is a refractory material is there or the refractory lining is there inside now the shell is mounted on rollers and here we can see these are the rollers here is one roller and here there will be another roller this side there will be one more roller third roller one more roller will be there generally there will be four rollers will be there now these rollers will be rotating as these rollers are rotating this what say furnace also will be rotating at a very small speed low speed may be at one revolution per minute slowly it rotates now what is the fuel used in the rotary furnace pulverized coal or oil metal to fuel ratio is 5 is to 1 when we are using the coal or 6 is to 1 when we are using the oil what does it mean means for 5 kgs of charge 1 kg of coal is to be used or for 6 kgs of charge 1 kg of oil is to be used now here we can see certainly this is a cylindrical shell horizontal now here we can see there is a burner is there inside which the what say fuel and air will be burning and there is a what say inlet fuel plus air inlet is here so through this inlet the mixture of air and fuel will be going inside it may be oil plus air or the pulverized coal or air will be going inside and it will be burning here now here there is an outlet is there so this is the exhaust outlet through which the hot gases and smoke will be going out of the furnace now yes the furnace is in operation we can see when it is being in on condition yes it is being fired and it will be slowly it will be rotating slowly it will be rotating yes we can see here we can this is the exhaust from a rotary furnace yes now this is the tapping of the molten metal now these are the advantages of rotary furnace molten metal does not come in contact with the fuel hence no carbon or sulphur pickup certainly we are using the coal which contains carbon and sulphur when we are using a fuel which contains carbon and sulphur certainly there must be carbon pickup and sulphur pickup but fortunately in the case of the rotary furnace no carbon pickup takes place no sulphur pickup takes place why because the molten metal does not come in contact with the fuel only we are burning the mixture of fuel and air on one side the hot gases will be just passing above the molten metal and they will be leaving but that they are not penetrating into the molten metal that is how no carbon from the coal comes into the molten metal no sulphur from the coal comes inside the molten metal hence there is no carbon pickup and there is no sulphur pickup whereas in the case of the cupola furnace we have seen there was carbon pickup why the carbon are the coke we are burning that is going the carbon from the coke is going inside the molten metal the sulphur from the coke is going inside the molten metal such thing won't happen in the case of the rotary furnace next one liquid metal from cupola can be super heated in a rotary furnace. Now one of the drawbacks of the cupola furnace is that the pouring temperature cannot be raised maybe we can just to heat the molten metal by the time we tap it becomes the viscosity becomes very thick high and it is very difficult to fill the cavity with the molten metal because the pouring temperature is not very high. So super heating this is known as the super heating means more what is a heating the molten metal above its melting point is known as the super heating. So sometimes super heating becomes difficult with the cupola furnace whereas large quantities of charge can be melted very easily melted in a cupola furnace problem comes with the super heating. Now this rotary furnace can be used for super heating now we can tap the liquid metal from the cupola furnace and that can be what is loaded inside the rotary furnace. Now you on the rotary furnace and you burn the mixture of air and the pulverized coal now because of that the temperature of the molten metal which is already inside the rotary furnace will be raising up we can what is a cause the super heating to the molten metal which we are bringing from the cupola furnace using the rotary furnace. Allowing of certain elements like molybdenum nickel chromium can be successfully done every time when we maintain alloy we add some additives these are known as for the purpose of the alloying. So these are known as the alloying elements so to get the required compositions we add maybe molybdenum is required we add molybdenum little molybdenum maybe little nickel is required we add nickel or little chromium is required we add little chromium so this is known as the addition of the alloying elements. Now what happens if we try to do it with cupola furnace yes we you add nickel or chromium these they will be reacting with oxygen and they become oxides and they will be removed along with the slag. So addition of the alloying elements in the cupola is difficult. Now fortunately we have the rotary furnace now you tap the molten metal from the cupola furnace and bring it and pour inside the rotary furnace. Now you add the alloying elements like nickel or chromium and you heat it during this time as it is rotating the alloying elements also will be melting and they will be mixed thoroughly with the melt and finally we get a very uniform composition along with the alloying elements. So alloying of certain elements can be successfully done using the rotary furnace. Now what is the application used to melt and superheat cast iron and nonferrous alloys. Next one the reverberatory furnace what is this it is a long rectangular structure with removable arched roof it is a all the most of the furnace are cylindrical in the what is in the shape but reverberatory furnace is rectangular is a rectangular structure with a removable arched roof. We can see what is the fuel used oil or pulverized coal. Now the flame and hot gases heat of the furnace roof and walls. Heat is reflected and radiated from the roof this heat melts and superheats the metal. Here we can see something interesting in the case of the what is a cupola furnace the fuel is going inside the melt and contaminating whereas in the case of the rotary furnace the fuel is not going inside the melt but just passing above the melt. But here in the reverberatory furnace it is the fuel is not even going above the what is a charge but first it is going and touching the roof and it heats the roof and from the roof radiation comes and because of the radiation there will be superheating of the metal or melting of the metal. So that is the most what is a interesting and special feature along with the reverberatory furnace and here we can see yes this is the what is a reverberatory furnace and here we can see this is the burner and fuel and this is the roof. This is the roof and here the hot gases will go and touch the roof and the radiation comes and strikes the charge and here we can see this is the stack through which the hot gases can escape and this inside chamber is known as the hearth and you can see here this is the molten metal and remember that in the reverberatory furnace the fuel does not come in contact with the molten metal. It even does not go above the molten metal as in the case of the rotary furnace it first strike the roof and the radiation comes and heats the charge that is the what is a interesting what is a phenomenon that can takes place inside a reverberatory furnace. Now these are the advantages of reverberatory furnace it is easy to operate no direct contact with the fuel yes that is what we have discussed just now. Hence carbon pickup and sulfur pickup are eliminated as the fuel does not come in contact with the molten metal no carbon pickup no sulfur pickup. The possibility of oxidation and melt loss is minimum it is used to adjust the composition of the metal from cupola. Yes again this can be used in conjunction with the cupola furnace just like a rotary furnace can be used in conjunction with the cupola furnace. What are the drawbacks of the cupola furnace the most advantage of the cupola furnace is its simplicity and large quantities of melt can be melted using a cupola furnace but accurate composition control is not possible in a cupola furnace but that can be achieved in a reverberatory furnace yes we can tap the molten metal from the cupola furnace and we can what is a pour it inside the reverberatory furnace and here we can adjust the composition of the molten metal what is required if some other element is required we can add here that is how we can adjust the composition of the molten metal from the cupola using this reverberatory furnace. And here lower noise emissions lot of noise is not generated as in the case of the cupola furnace or in the case of the arc furnace these are the applications of reverberatory furnace melting of cast iron melting of nonferrous alloys for duplexing operation with cupola what is this duplexing operation means say inside a cupola furnace say accurate what is a composition is control is not possible. So, have the molten metal from cupola and put it inside the reverberatory furnace then you add the required alloying elements that is the what is a accurate what is a composition of the what is a composition accurate control of the composition or temperature control inside a cupola furnace accurate temperature control may not be possible then obtain the molten metal from the cupola and pour it inside the reverberatory furnace. Now, you heat inside the reverberatory furnace the temperature of the molten metal can be increased to a required level or to a satisfactory level. So, that is the duplexing operation with the cupola. Now, let us see the selection of melting furnaces. So, how to select a melting furnace what are the factors that will be coming into picture the first factor is the initial cost of the furnace. So, what is the cost of the furnace what is your project accordingly this factor has to be considered. If the what is a cost budget is very less one has to go for the cupola furnace and fuel and operating costs. So, this is another factor what fuel is available and what are the operating costs. Next one kind of metal or alloy to be melted what is your metal or what is your alloy is it the ferrous or non ferrous accordingly one has to choose the furnace. Next one melting and pouring temperatures of the metal to be cast what are the pouring temperatures to be obtained. So, this is another interesting what is a important factor to be considered. Next one quantity of metal to be melted whereas, we know that cupola furnace can be used for what is a melting large quantities whereas, an induction furnace can be used for melting small and moderate quantities of charge. So, what is the quantity of metal to be melted accordingly one has to choose the furnace. Next one maintenance costs this is another important factor next one melting cost per unit weight of the metal how much what say melting cost per unit weight of the metal. So, this is another important factor next one quality of the molten metal what is the quality required do require high quality molten metal then certainly cupola furnace is not the right choice may be induction furnace is the right choice. Next one let us see the overall comparison of melting furnaces. Now, you can see here this is the crucible furnace and mode of melting is solid fuel oil or gas and application is most of the alloys except steel. Now, this is the second one is the cupola furnace and mode of melting using coke and oil and application it is used for melting cast iron and steel electric arc furnace again there are two types one is the single phase and another one is the three phase single phase in both the cases arc is utilized for melting the charge single phase is used for non ferrous alloys whereas, three phase arc what say furnace is used for melting steels. Next one is the induction furnace again in the induction furnace there are two types one is the low frequency and another one is the high frequency low frequency induction furnace in both the cases electromagnetic induction is the mode of melting whereas, in the case of the low frequency induction furnace it is used for non ferrous alloys high frequency induction furnace is used for melting steel and alloy steels. Next one resistance furnace is there now its mode of melting is resistance caused to the current flow of current and what are the applications it can be used to melt steel and non ferrous alloys. And next one is the rotary furnace what is the mode of melting by burning polymerized solid fuel gas or oil and this can be used to melt non ferrous alloys and cast iron. Next one reverberatory furnace what is the mode of melting solid fuel gas or oil and this can be used to melt non ferrous alloys and cast iron and remember that rotary furnace and reverberatory furnace can be used for the purpose of duplexing in conjunction with the cupola furnace means for adjusting the composition and for raising the what say super heating means raising the pouring temperature for these purposes rotary furnace and reverberatory furnaces can be used for duplexing. Accordingly seeing considering all these factors one has to choose the furnace. Nowadays the sophisticated methods have come the vacuum melting has come it is quite expensive, but one can get accurate temperature control very high quality composition without any impurities even these what say vacuum furnaces are, but however these vacuum furnaces are costly. So today in this lecture we have seen different furnaces and their construction details and their mode of melting and the their applications. And in the next class let us see the next topic that is the solidification. Thank you.