 Let us learn about two casting processes. One is the evaporative pattern casting and the other one is the plaster molding. So, first let us learn about evaporative pattern casting and then we will see the plaster molding process. First, let us see the evaporative pattern casting. What is this evaporative pattern casting? This is also known as expendable pattern casting and this is also known as last foam casting. And let us see before going to the what is a principle involved in this process, let us see the history. So, the first patent for an evaporative pattern casting process was filed in April 1956 by Harold F. Schroyer. So, in his patent a patent was a pattern was machine from a block of expendable pattern polished in pattern and it was supported by traditional green sand during process during pouring process. Here, we can see the pattern was supported by traditional green sand and this process is now known as full molding process. But later some modifications were done and we will see them later. And in 1964 MC Fleming's used unbounded sand for this process. You see here the first person the Harold Schroyer used what say traditional green sand for supporting the pattern whereas, in 1964 MC Fleming's used unbounded clean and dry sand for supporting the pattern. So, that way the second step was different from the earlier process. Robinson foundry at Alexander city, Alabama was the first North American foundry to use evaporative pattern casting process. General Motors used this process to produce the 4.3 liters V6 diesel cylinder head during 1981. A study found in 1997 that this process accounted for approximately 1,40,000 tons of aluminum castings in the United States. Now, let us see the principle of this evaporative pattern casting process. So, here the pattern is made up of poly strain or styrofoam. So, this is the poly strain pattern or the styrofoam pattern and here we can see the pouring cup is there and this is the sprue and the whole thing is the pattern whose shape is similar to the casting which we want. Now, we have to make a ceramic slurry or a refractory slurry such that when we apply a coating around this pattern there will be what say micro, what say pores will be there so that permeability will be better during pouring, hot gases can escape. So, it is coated with gas permeable refractory slurry and then it is dried. Then what happens, hard shell, thin hard shell around the pattern is created. Now, you see here we have to take a moulding box, only one moulding box not two boxes. Inside the moulding box we have to place the pattern, remember this pattern is already coated with a refractory slurry means a thin coating is created. Now, that pattern we have to place inside the moulding box, then sand is packed around the pattern, dry sand is packed around the pattern, it should be what say packed then what happens sand support is created around the pattern. Then what will happen, molten metal is poured into the portion of the pattern that forms the pouring cup and sprue and here we can see this whole thing is the pattern and this is the pouring cup. So, this process is somewhat different from the other process in one sense that in all the previous process, so before pouring the molten metal we remove the withdraw the pattern from the mould. But here the most specialized special feature is that we would not remove the pattern from the mould, without removing or withdrawing the pattern from the mould we start pouring the molten metal. So, that is the most interesting feature of this process. Now molten metal is poured into the portion of the pattern that forms the pouring cup and sprue, so here we start pouring the molten metal. Then what will happen, as the molten metal enters the mould the poly strain foam is vaporized ahead of the advancing liquid. One side molten metal is coming and it is falling on the what say poly strain pattern or the evaporative pattern then what will happen, within fraction of seconds this pattern will be evaporating. So, it will be going in another way, one way it is coming and another way the vapor is going out. Thus, so as we keep pouring more and more metal, more and more pattern will be evaporated and it will be escaping. How long this will continue till the entire pattern is evaporated we have to keep pouring the molten metal and till the entire cavity is filled with the molten metal. Now, the resulting mould cavity is filled with the molten metal, yes the pouring looks like this. Now, after that the metal is cooled and solidified, the shell is broken and the part comes out means after that even we remove the moulding box then we what say this sand it is not what say sand mixed with the clay, so no need to break it as we do it in this case of the green sand. The automatically once we remove the moulding box even the sand just falls down because it is clean and dry sand. Then this shell is to be broken, this shell is to be the thin shell which is which we created around the pattern should be broken then what happens the part comes out the casting comes out. Now, these are the advantages of evaporative pattern casting used for precision castings of ferrous and non ferrous metals both ferrous and non ferrous metals can be cast using this evaporative pattern casting and not only that very precision castings can be made precision means with extreme what say dimensional accuracy and very good surface finish and complex ships can be obtained. Next one high dimensional accuracy can be achieved, thin sections can be cast, so this is a special feature which we have seen in the case of the investment casting process, but investment casting process is a time taking process and this process takes less time and here also we can obtain the thin sections. Next one complex ships can be cast, so this is also a special feature which we can see in the case of the investment casting process, so here also we can make the complex shaped components, but with less time. Now another advantage is one piece plus less expensive and easier in the case of the green sand molding generally we use two boxes sometimes even three boxes one is the lower molding box that is known as the drag, the upper molding box is known as the cope, so these two boxes must be assembled carefully, otherwise there will be some mismatch will be there, but here there is no such problem, there is no mismatch between the cope and drag, first of all there are no two molding boxes, there is only one molding box is there, so there is no question of mismatch and also the assembly time that will be eliminated. Next one few air steps are involved compared to the sand casting process, in the case of the sand casting process we have to prepare the molding sand, we have to mix the additives, we have to mix the clay, we have to mix the water and that should be mold for a predetermined time, then we have to carry it to the molding shop, then we have to make the mold and it should be compacted, then it should be pattern must be withdrawn very carefully, again the two molding block boxes should be assembled, so much of time is involved in the case of the greens sand molding process, here few very few steps are involved, just make the what is a polystyrene pattern, then make a what is a coating around that and pack it inside the molding box, start pouring that very simple, no need to mix binders or additives, so in the case of the greens sand molding process, we mix the binders and additives, what happens when we mix binders and additives, so these cause pollution inside the plant, whereas in the case of the evaporative pattern casting, we do not mix binders or additives, so as a result there will be clean environment within the plant. Next one multiple castings can be combined in one mold to increase pouring efficiency, suppose if we are want to small castings, so suppose we want say 4 or 5 small castings, so no need to make 5 what is a molds, so all these can be joined together, assembled together, for all these what is a 4 patterns, the all can be what is a kept inside a single molding box and it can be compacted with the sand, then simultaneously molten metal can be poured, means simultaneously we can get castings of 4 or 5 castings, so no need for skilled labour, once there are skilled labour, they will be demanding higher remuneration. Next one fettling and machining is minimized, so this is another drawback in the case of the greens sand molding, fettling means after the solidification is over, we have to break the sand, so that is the shake out, then metal will be solidified inside the riser, metal will be solidified in the sprue and in the geating system, so this must be cut off, so that is the fettling process, so sometimes what is a labour have to be used for that purpose or what is a heavy machines have to be used under that consumes time, so that is minimized or eliminated in the case of the evaporative pattern casting. Now high levels of sand reuse are possible, in the case of the greens sand molding, so the sand cannot be used for infinite times, only it can be used for certain number of what say molds after that it has to be discarded, various here thus we are using dry sand, so high levels of sand reuse are possible. Next one no need to remove the pattern, in the case of the greens sand molding, we withdraw the pattern for that a skilled labour is required very carefully used to withdraw the pattern, so that requires skill not only that that takes time, sometimes this is done by machines, so these machines are expensive, so here there is no need to remove the pattern, while the pattern is still inside the mold, we keep pouring the molten metal, as we keep pouring the molten metal, the pattern evaporates and escapes from the other side, so no need to remove the pattern. Now lower capital investment, we do not require heavy equipments for this process, so these are the advantages of the evaporative pattern casting process. Now let us see there are drawbacks also, what are the drawbacks of evaporative pattern casting, the pattern is expensive, next one every casting requires a separate pattern and the process becomes costly, in the case of the sand casting process most of the times we use wooden pattern or a metallic pattern, so those patterns can be used for making thousands of what say castings, but here one pattern can be used to make only one casting, so that is a drawback. The pattern evaporates and it is not reusable, in the case of the green sand molding the same pattern can be used for making several molds or for getting several castings and here it is not possible, even in the case of the investment casting, for each what say casting we make a wax pattern, but that wax can be recovered, the same wax can be melted and it can be used for making another wax pattern, so that way in the investment casting process the wax is reusable, whereas in the case of the evaporative pattern casting the pattern is not reusable, why because it is evaporating, as the sand is unbounded sand may fall down during pouring, so here in the case of the what say the first person the shroyer he has used the green sand, but later people started using the unbounded sand, so this unbounded sand sometimes it may fall down during pouring, that be the case a defective casting will arise. In addition to this what are the other drawbacks, so during pouring of the molten metal the pattern evaporates and it escapes through the pouring component, what is that these fumes will cause what say environmental pollution, so this is another drawback of this evaporative pattern casting process. Now these are the applications of evaporative pattern casting, used to manufacture crankshafts for engines, aluminum engine blocks, manifolds and so on, in fact nowadays evaporative pattern casting is used for more and more applications. Now here we see a what is a real application for making engine block, so this is the engine block, so here we can see metal is poured into mould for a last form casting of a 60 HP three cylinder marine engine, here we can see only one mould box is there, only one moulding box and this is the pouring cup and the molten metal is being poured and as it is being poured the vapor escapes and finally it fills, after solidification we have to what is a remove this box and we have to remove the sand, then we have to break the what is a shell, a thin shell which we have created with the ceramic slurry, refractory slurry then finally we get a casting like this. So this is a real practical application of the evaporative pattern casting. Now these are the types of evaporative pattern casting, so in this evaporative pattern casting process EPS polystyrene foam or the thermocole is used as the pattern material. Now broadly this can be classified into three types, one is the last form process means this is the one which is widely used nowadays, the second one is the full mould process which was used in the beginning but now also it is used and finally the ceramic shell process. Now we will see all these one by one very briefly. Now what is this last form process, the pattern is packed with the dry sand, sometime just now I told you this process widely used nowadays. So in this process no doubt the pattern is made up of the evaporative pattern. So but after making the ceramic shell around the pattern, the pattern is packed with the dry sand, in the case of the full mould process the pattern is packed with the greens and moulding process. So that way this is a combination with greens and moulding and let us see what is the ceramic shell. So this is a combination with investment casting process means what is that here in the case of the investment casting process we make a what is a ceramic shell, thick ceramic shell around the wax pattern that too this ceramic shell is made say 5 to 7 times, a coating is given, a refined refractory slurry is made and the wax pattern will be dipped into that and it will be taken out and a stucco is rained on that, again it will be dried then again it will be dipped into the slurry taken out, stucco is sprinkled on that and it will be dried like that this process will be continued for 5 to 7 times means 5 to 7 times this will be dipped in the ceramic slurry and it will be dried. In the same way here also a thick shell is created around the poly strain pattern evaporative pattern then what is a we keep pouring the molten metal. So it is a combination with the investment casting process. So these are the three types of the what is a evaporative pattern casting process. Now the steps in processing of the poly strain pattern. So these are the steps for processing the poly strain pattern. One is the first step is the pre expansion, second step is maturing, third step is final molding, fourth step is poly strain pattern assembly. Now let us see what are these in the case of the pre expansion tiny spherical poly strain beads are expanded to about 40 times their original size using a small quantity of pentane and its proportion is 5 percent by weight as a blowing agent. Now the second step is the maturing what is this as the material cools the pentane liquefies and a partial vacuum is formed inside the bead. Next one the third step is the final molding. In this final stage the pre expanded stabilized beads are reheated with steam in a mold and the next step is the poly strain pattern assembly. In this process the pattern is assembled by gluing poly strain foam runners and risers. This means even if the size of the casting is small several patterns are joined together and assembled. So that comes under the poly strain pattern assembly. Now these are the steps involved in the evaporative pattern casting process. First step is make the die, second step pattern expands pre expanded what is a pattern pre expand pattern beads. First step is making the die, second step is pre expand pattern beads. Next one fill and expand patterns. Third step assemble patterns. Fourth step dip and dry cluster we have to make the ceramic slurry. So in that ceramic slurry the assembly or the pattern will be dipped and it will be clustered. That means what if there are several patterns they will be assembled together. If it is a single pattern as what is a razor and a sprue or to be glued so that also comes under this clustering. Next one invest cluster so we have to make the ceramic what is a shell around that. Next one pouring while pouring the what is a pattern evaporates and comes out and molten metal fills that mould and it solidifies. Next step is cut off. If there are more castings multiple castings so this should be cut off and even if it is a single casting the razor and the sprue must be cut off. Next step is the inspect castings finally shipment of the castings. Now let us see a comparison between last wax process and the evaporative pattern casting process. Last wax process means it is the investment casting process and here this is our present topic the evaporative pattern casting process. In what way these can be compared and which one is better let us see. Now composition of pattern first what is a comparison. In the case of the last wax process or the investment casting process the pattern is made up of wax blends, wax generally this a single wax is not used. The wax are mixed together and a blend is made so pattern is made up of wax blends whereas in the case of the evaporative pattern casting the pattern is made up of expanded polystyrene foam. Next one the next comparison is the density of material used for pattern. In the case of the what is the investment casting process density of wax patterns is 700 cases per cubic meter. What happens if that be the case the patterns will be very heavy handling of the patterns would be difficult. Whereas in the case of the evaporative pattern casting density of expanded polystyrene patterns is 42 cases per cubic meter the weight of the pattern or the density of the pattern is drastically reduced in the case of the evaporative pattern casting process. Sufficient for strong because the weight is less because the density is less does not mean that the pattern is too delicate they are strong enough study, dimensionally accurate and light patterns. Now next comparison is maximum weight of the cast part it is well below 500 cases even 500 cases nowadays is the extreme case but in the case of the evaporative pattern casting process no limitation of weight of the cast part. Next one preheating of the ceremixial in the case of the last wax it is required sometimes what will happen during preheating the ceremixial can crack. Whereas in the case of the evaporative pattern casting process pouring is possible at room temperature no need for preheating the shell. Next one rejection of shell during the process. In the case of the last wax process or the investment casting process so the ceremixial has a tendency to crack due to the expansion of the wax. Whereas in the case of the evaporative pattern casting process do you think that the expansion of the shell takes place or the expansion of the polyester takes place no. Because without what say any preheating we straight away pour the molten metal as the molten metal is entering into the what say mould the pattern evaporates and escapes. So there is no question of the expansion of the shell. So no question of the cracking of the shell. So no question of rejection of the shell during the process. Next one method in the case of the last wax process it is difficult and has limitations in addition to the problem of razor backfilling. In the case of the evaporative pattern casting flexible razors are simply glued on the pattern to shoot the method. The feeding ability of razor is improved with the use of exothermic sleeves. Next one in the case of the last wax process the ceremixial thickness is 10 to 15 mm means to make this 10 to 15 mm thickness shell we have to mix what say dip the wax pattern into the ceramic slurry 5 to 7 times. Again generally people make say two types of the slurries one is the extremely fine slurry and another one is the coarser slurry. Initially one has to dip the pattern into the fine slurry then into the coarser slurry every time one has to be taken out and the what say stucco has to be sprinkled it has to be dried out again it has to be dipped into the slurry. So, it is a time taking process this process takes lot of time several hours of time whereas, here the shell thickness is only 5 to 10 mm depending on the size of the component and in the case of the investment casting process to achieve this 10 to 15 mm thickness several hours are required that much time is not required in the case of the evaporative pattern casting process. So far we have seen several comparisons in all these comparisons we have seen that evaporative pattern casting is superior to the investment casting process or the lost wax process. Now what are the process parameters of the evaporative pattern casting process? So these are the there are five types of the parameters first type is the moulding sand based variables, second one is the vibration based variables, third one is the vacuum based variables, fourth one is the pouring material based variables, fifth one pattern based variables, sixth one coating based variables and in the first one that is the moulding sand based variables type of moulding sand shape size and size distribution. What is the shape is it angular sub angular or round? So that is the shape of the what is a moulding sand and the size what is the mesh size and size distribution. So these come under the moulding sand based variables next one vibration based variables frequency amplitude of vibration and time of vibration. So after the sand is compacted inside the sand what is a moulding box so it is vibrated so that sand settles down inside the moulding box because it is not a green sand it is dry sand so that is why it is given vibrations. Now the frequency of that vibration amplitude of the vibration and time of the vibration these come under the vibration based variables. Next one vacuum based variables degree of vacuum imposed so that is the one variable among under the vacuum based variables. Next one pouring material what is a best variables pouring time and temperature. Next one pattern based variables density and size of the poly strain beads. Finally coating based variables material slurry and the thickness and the dry what is a drying time. So these are all the process what is a parameters of the evaporative pattern casting process. So with this we are completing the evaporative pattern casting process. Now let us see the plaster moulding. Now before learning the plaster moulding let us see the history plaster moulding right plaster has been used throughout the ancient history in the Egyptian, Greek and Roman civilizations. Primitive plastering was carried out using clay and mud to keep out the cold and wet. Plaster mouldings have been used for classical architectural design from the ancient Greeks. Now following the fire of London Bridge in the year 1912 King John ordered that all shops brewers and bakers should have their walls plastered inside and outside to make them safe from fire. So from this we can see this plaster has been used for centuries for several purposes. During 17th century decorative plaster mouldings were created or items these were created. After 18000 AD gypsum or plaster of Paris became more common. So in the beginning what was the material used? So it the people have used clay and mud as the plastering material. But later you can see in the 1800 AD gypsum or plaster of Paris became more common. Gypsum is a mineral calcium sulphate which is a common form of sedimentary rock used to make plaster by heating it to 150 degrees Celsius and then grinding it into a powder. Plaster of Paris is called plaster of Paris because around Paris there were large deposits of gypsum used to make this plaster that is why it is known as the plaster of Paris. Now in the case of the plaster moulding what is the moulding material? The moulding material is just like in the case of the green sand moulding what is the mould material? It is the green sand similarly in the case of the plaster moulding the moulding material is plaster of Paris or it is the gypsum commercially and chemically it is the calcium sulphate. Now what is the material of the pattern? Aluminium alloys, brass or zinc alloys. Sometimes plastic is used and rarely would also used. Now there are three types of what is a process under plaster moulding. One is the conventional plaster mould process. Second one is the formed plaster process, third one the Antioch process. We will see all these one by one first let us see the conventional plaster mould process. Now in this process suppose this is the component to be made. So this what is a pattern should be like this a metallic pattern or a wooden pattern should be like this. So this is the pattern. Now prepare the slurry by mixing plaster of Paris with water. So that is the first step in the conventional plaster moulding process. Now plaster of Paris and water proportions are 5 to 8 means plaster of Paris should be 5 parts and water should be 8 parts. So prepare that slurry by mixing these two ingredients. First step sprinkle talcum powder over the pattern. So this is the pattern over the pattern sprinkle talcum powder so that the slurry may not be sticking to the pattern. Next one apply parting agent, tincture or mould soap over the pattern. So this also will enable us to prevent the sticking of the slurry with the pattern. Now place the pattern inside the moulding box. So this is the moulding box. Inside this moulding box place the pattern. Now pour the plaster slurry over the pattern in the drag. So inside there is already pattern. Now around the pattern we have placed the moulding box. Now pour the plaster slurry over the pattern in the drag moulding box. Now this plaster will be setting in few minutes. After that on the four sets there are four what is a boxes are there. So these must be separated. Next one pour the slurry in the cope in the similar way we have to make the cope also. Now again four boxes will be kept. Now pour the slurry in the cope separate the boxes after the setting. Now you see this is the mould. Now scrap off any plaster that might have run down. If any plaster is unnecessarily occupying anywhere that must be scrapped off or that must be broken and eliminated. Separate these two halves of the plaster moulds. So these must be separated. Now pattern is still inside you can see. Now which does the pattern from the plaster moulds? This pattern is withdrawn using a screwdriver or some what is a appropriate tool. Bake the moulds in an oven at 120 degree centigrade for about 20 hours. So this must be baked so that the moisture will be evaporating and also the plaster moulds will be hardened. Assemble the moulds and clamp them. After that these two moulds must be assembled and they must be clamped together. Pour the molten metal into the cavity. After pouring after right after solidification remove the solidified casting using high pressure water jet. Now these are the advantages of the conventional plaster moulding process. First one is complex shapes can be cast successfully cast. So this feature we can see only in what is the investment casting or die casting. So here complex shapes can be easily cast and offers excellent surface finish. Next one minimum machining is required. Fine details can be obtained. Next one thin sections can be cast as small as 0.6 millimeters and this process offers good dimensional tolerance. Setting of mould takes less time less than 15 minutes time. Now what are the limitations of conventional moulding process? Not suitable for ferrous castings. The sulphur in gypsum reacts with the iron and results in defects. So this gypsum contains sulphur. So because of that there will be some defects will be there. So not suitable for making ferrous castings. More expensive than sand castings. In the case of the sand castings the same sand can be used for making several castings whereas in the case of the plaster moulding we have to use the plaster of Paris and once we use it that is all we have to break it and that cannot be used again. So it is more expensive than the sand castings. Not suitable for large castings 38 grams to 7 kgs whereas in the case of the sand castings even 10 terms castings are nowadays made using sand castings. Plaster is not reusable so that increases the cost of the production. Next one baking cost is extra. Conductivity of the plaster is poor so slower solidification. So the properties may be affected. Next one low permeability gas defects arise. What is this moulding medium? It is the plaster of Paris. So it is less permeable during pouring or during solidification if any hot gases are arising so they cannot escape through the moulding medium. So it is it has got the low permeability so hence there will be gas defects. Now let us see the second process the formed plaster process. The formed plaster process is a modification of the conventional moulding process conventional plaster moulding process. In the case of the conventional plaster moulding process the first one what was the drawback it has got the very less permeability it does not allow hot gases to escape through the plaster mould. So to overcome this what is a drawback this limitation some modification has been done finally people arrived at the formed plaster process. So it is similar to the earlier one but some modification is there. What is that? We will see. Prepare the slurry by mixing plaster of Paris with water and the plaster of Paris and water proportion is 5 to 8 means what is a proportion of the ingredients is exactly same as that of the earlier one. Now here the modification comes into picture blow air into the slurry half of its volume should be with air bubbles. So once the slurry is made we will be blowing air into the slurry so that there will be so many bubbles half of the slurry is filled with the bubbles. Now while the bubbles are still present in the slurry pour the slurry with the bubbles over the pattern in the drag. Now the process is similar same way only here the what say variation is there blowing air into the slurry. Now pour the slurry with the bubbles over the pattern in the drag. Now slurry sets in the drag box. Next one repeat the process for the co-pulsor co-pulsor can be made in the same way. Now bake these two moulds in an oven at a 120 degree centigrade for about 2 hours sorry so about 20 hours then what will happen these moulds plaster moulds will be hardened then any moisture is present that will be evaporated. Now inside there were bubbles were there now because of that the bubbles the air bubbles the permeability will be enhanced permeability of the moulding medium will be enhanced. Next assemble the moulds and pour the molten metal the process same like the first one one difference is here we blow the air into the slurry. Now what are the advantages of the formed plaster process good permeability no gas defects because we have what say filled off of the slurry with the air bubbles because of that the permeability is enhanced significantly. Next one premature setting of the slurry does not arise these are the disadvantages of the formed plaster process strength of the mould is reduced why in the case of the first one the entire mould is filled with the plaster but here half of the mould is filled with the air bubbles so naturally the strength will be less. Next one the setting time is more maximum weight of the casting is about 5 kgs whereas in the case of the first one up to 7 kgs can be made because here the moulds strength is less so only 5 kgs can be made finally the third one the Antioch process. Now again why this Antioch process plaster plaster what say plaster moulding is very good it offers us very good dimensional accuracy very good surface finish but the one a drop back is the mould or the moulding medium does not have sufficient permeability means it does not allow hot gases to escape through that that is why people made the first what say alteration they mix the what say air into the slurry with the slurry so they could enhance the what say permeability but what happened the strength came down. So instead of 7 kgs people were able to make only 5 kgs casting so strength came down. So now again this became a challenge strength so we people wanted to increase the permeability and also they wanted to increase the strength so that is how they landed in the Antioch process what is this process in this process strength is enhanced and also the permeability is also enhanced. Now preparation of the slurry first step now what are the ingredients of the slurry fine silica sand 50 percent here we use fine silica sand whereas in the first two what say categories we do not use the fine silica sand. Now gypsum 40 percent and talc 8 percent and Portland cement sodium silicate will be 2 percent in addition to that 50 now water will be 50 percent of the above ingredients you see even the proportion of the ingredients is different here there is a major difference fine silica sand will be 50 percent gypsum 40 percent and talc 8 percent and this is the 2 percent in addition to that there will be water 50 percent of these overall ingredients then all these will be mixed together. Now preparation of the mold for the slurry after we prepare the slurry pour the slurry over the pattern in the drag in about 7 minutes plaster develops and gains good strength for the slurry over the pattern in the co-pulse also in the same way in about 7 minutes plaster develops and gets good strength next one with the patterns from the plaster molds as usual now dry the molds for 6 hours and bake in oven for 15 hours assemble the molds and pour the molten metal. Now what are the advantages of Antioch process improved strength of the mold larger castings can be made why we are mixing 50 percent of the fine silica sand. So because of this presence of the silica sand the strength of the mold will be more that is how larger castings can be made. Now incorporation of the chills is easy conductivity of the mold is very high in the case of the first one the conventional molding process we have seen the conductivity of the mold is very poor why plaster of Paris offers very what is a poor conduction of the heat. So here because we are mixing fine silica sand conductivity of the mold will become high hence faster solidification once there is faster solidification mechanical properties of the casting would be improved. Now better permeability less chances for gas defects because we are mixing silica sand what happens because of the silica presence of the silica sand it leaves some pores somewhere everywhere. So because of this pores hot gases that may erase during pouring or solidification will be escaping through the mold improved mechanical properties. But what are the limitations of this Antioch process poor sand recovery. So that is the drawback of this process and process is expensive again we have to mix the fine silica sand it is not in the case of the sand casting process the entire sand can be recovered only little sand is what is a burnt. So there is a sand loss but most of the times most of the sand is reused it is recovered but here the sand recovery is very poor and the process is expensive we are mixing the plaster and that plaster cannot be used the process is expensive. Now these are the applications of the plaster molding process means overall overall. So these are all the applications of plaster molding used to cast brass, bronze, aluminum, magnesium, manganese and their alloys and remember this cannot be used for making ferrous castings. Now aircraft parts can be made using plaster molding cams can be made molds for plastering and rubber industries can be made and quick prototype parts can be made using plaster molding process and also not only that art castings can be made using plaster molding process. And here we can see use of plaster molding in making statues for making art castings. So initially one has to make the plaster mold into that plaster mold one has to pour the molten metal then we get the statues like this. Friends in this lecture we have learnt about two special casting process one is the types of what say evaporative pattern casting process. So again this evaporative in this evaporative pattern casting process we use the expanded poly strain of or the foam or it is the thermocol is used as the pattern material. Now this is broadly classified into three types one is the last form process next one full mold process and the ceramic shell. In the case of the last form process the pattern is packed with the dry sand and this is widely used nowadays whereas in the case of full mold process it is what say the pattern is supported with the green sand and in the case of the ceramic shell it is a combination of the investment casting process. A thick ceramic shell is created around the poly strain pattern similar to the investment casting process. So that is how we have seen the evaporative pattern casting is superior than the last wax process or the investment casting process. Then we have seen the plaster molding the plaster molding is what say classified into three types one is the conventional plaster mold process the second one is the formed plaster process and the third one is the anti oak process. In the case of the conventional plaster molding process only plaster of paris is used plaster of paris and water plaster of paris and water the proportion is 5 to 8 5 parts of plaster and 8 parts of water is used to make the slurry and that slurry is used to what say flow around the pattern finally we make the molds and we pour the molten metal but the drawbacks of this process is that it has got the less strength and less permeability. In the case of the formed what say plaster process the plaster is made similar to the first one but here air bubbles are blown into the slurry 50 percent is filled with the slurry then we this slurry along with the air bubbles is poured over the pattern. So, permeability is enhanced but strength will be reduced in this case. So, in the third process again the efforts have been made to enhance the strength also 50 percent of the ingredients will be fine silica sand and the rest of the 50 percent will be plaster and what say other ingredients. In addition to these 50 percent additionally will be added what is that 50 percent water then the slurry will be made. So, in the case of the Antioch process because we are using fine silica sand the strength is significantly enhanced. So, it can be used for making very big castings and also the permeability is improved mechanical properties are also improved as the solidification will be improved. So, as the solidification is faster in the case of the Antioch process but the drawback of this plastering plaster molding process is that the plaster is expensive and the plaster cannot be reused. So, that way the cost of the production goes up. So, with this we are completing the plaster molding process also. So, we will meet in the next class. Thank you.