 Good morning friends. In the previous classes, we have seen the introduction to the casting process and we have also seen the classification of the casting process and the principle of the metal casting process is very simple. Whenever we want to manufacture a component, a similar cavity has to be created in a sand mold or a medium compacted medium and we melt the metal and we pour into that cavity. After solidification, we break that sand medium then we get the solidified component. This is the simple principle of the metal casting and we have seen that the metal casting process has been broadly classified into conventional molding process, chemical sand molding process, permanent molding process and finally the special casting process. And in the previous class, we have seen the conventional molding process and the subclassifications in it. They are the green sand molding, dry sand molding and the flaskless molding. Coming to the chemical sand molding process, we have seen the shell molding, sodium silicate molding and no bake molding and we have seen that there is a permanent molding process where the mold is made up of a special steel. So, it will be permanent whereas in the case of the sand casting process, once we make the mold, once we pour the molten metal into the mold, after solidification, we break that mold and the mold is no more permanent. Here, the mold is made up of a special steel and into that mold, we create that required cavity. So, these are also known as the dyes. So, under that we have seen there are two types, gravity dye casting and the pressure dye casting and in the gravity dye casting, the molten metal flows into the permanent metallic molds by means of the gravity. Whereas in the case of the pressure dye casting, the molten metal is injected into the cavity which is between these two metallic dyes by means of an external pressure. Now, let us see the special casting process. Under the special casting process, we have the investment casting, continuous casting, vacuum sealed molding, these are also known as V process. Next, squeeze casting process, centrifugal casting process, plaster molding, evaporative pattern casting, ceramic shell molding, slush casting and finally the steel casting. First, let us see the investment casting. Now, this is the what is a simple principle of the investment casting. Investment casting process means the pattern is made up of wax. In the olden days, the ancient man, when he wanted to manufacture these spearheads or the rudimentary tools, he initially made a wax pattern. Around the wax pattern, he has compacted the sticking sand. Later, he has heated that system and the wax has drained out inside. There was a cavity. Into that cavity, the molten metal was poured. So, this concept was used by the ancient man. Though new methods have been developed, still this process is not outdated. Still, we are using wax as the pattern material. So, in the investment casting, wax is the pattern material. Of course, the ancient man used the sticking sand around to make the mold whereas we use the modern ceramic slurry to create the mold. What are there are different steps in the investment casting process? First one is the pattern production. For that, there will be a wax injector will be there. There will be wax bath will be there. The molten wax will be inside that bath and from that bath, the wax will be injected into the wax dyes. So, these are the two dyes. So, when we close inside, there is a cavity. Into this cavity, the molten wax will be injected and after sometime, the wax solidifies and the wax pattern will be taken out. Now, to gain more production or to increase the rate of production, what we do is we assemble a similar patterns like this. Maybe some 10 patterns or 8 patterns together and they are joined by a central tree or this also acts as the central tree. So, this is the pattern assembly. The next step is we prepare a ceramic slurry. A thick ceramic slurry we prepare and we give the ceramic slurry coating means this assembly will be dipped into the ceramic slurry. We take it outside and we sprinkle the stucco around that and we dry it. Again, we will dip the pattern inside the ceramic slurry, take it out and what say apply the stucco and you dry it. Likewise, the application of the ceramic slurry coating and the stucco and the drying will be done in a cycle maybe 7-8 times. After applying the ceramic slurry and stucco for 7-8 times, there will be a thick shell around the wax patterns. Then it will be baked. Then what happens? It will become hard and before that it will be there will be a process called de-waxing process. Means all the wax which is inside this ceramic shell will be melted and it will be drained out like this. Here we see the de-waxing and in the next stage this is the casting. Casting means pouring of the molten metal into the cavity. So, we melt the metal separately and we are pouring here. The molten metal goes inside the cavity. Initially it goes into this central tree that is the sprue. Then it goes horizontally and fills all the cavities and after some time the molten metal solidifies. After solidification we break this shell the ceramic shell. This operation is known as knockout. Now initially we have assembled we have taken some 8-10 patterns and we have assembled them. Now we need to separate them. So, here we are cutting the individual casting from the central tree. Here we are cutting. So, this is known as the cut-off. Next actually the components produced by the investment casting have a very smooth surface finish. But still a final finish is required. Here we do the final finishing and also if painting is required we do the painting. So, this is the final stage of the investment casting process. So, these are the advantages of the investment casting process. We get the very excellent surface finish. Whereas in the case of the green sand molding or the mold is made up of the sand. What say the cavity surface is made by the sand. Because of the sand grains there will be some irregularities will be there. Because of that the cavity will have a irregular surface. Even the casting will develop an irregular surface. But here we get a very excellent surface finish. This is the advantage, great advantage of the investment casting process. Next one very complex details can be made. So, this method is also used in the jewelry castings. So, we can see the jewelry castings there will be very complex design will be there. It is very difficult to manufacture this kind of complex design by any other casting methods. But using investment casting this is very easier. Next one very thin sections can be obtained. As thin as 0.75 mm we can make. Next one close dimensional accuracy. You can see the dimensional accuracy it will be 0.08 mm to 0.1 mm. This is the dimensional tolerance we can obtain by the investment casting process. Next one complex shapes can be made. Next one no or negligent finishing operation. Sometimes no finishing is required. Maybe few times a little finishing is required. Now what is the problem in the sand casting process. We make the casting and yes we break the mold and when we take the casting outside there will be rough surface on the casting. So, to get a very good surface finish we have to machine and we have to spend several hours on the machines to obtain the very good surface finish. But whereas here in the investment casting process no machining is required. Sometimes and sometimes a little machining is required. Next one castings are free from the usual defects. In the case of the sand castings if the moisture is more there will be some gas defects will be there. Sometimes this sand will be sticking to the castings. So, these kind of defects will not arise in the case of the investment casting and these are the limitations of the investment casting process. Production of wax patterns make the process costly. Wax is costly. There are again different wax are there. Some cheaper wax are there. Some costlier wax are there. Most of the times we make blends of these waxes to obtain better properties. So, that way these pattern waxes are costly and the processes becomes costlier. Next one large castings cannot be made. Whereas in the case of the sand casting process a very small casting can be made, a medium size casting can be made and even a very large casting can be made. As large as about 5 tons casting can be made by sand casting process. But here very large castings cannot be made and the process is relatively slow. Why it is slow? Because we are making the wax patterns. Then we have to assemble them. Then what we will do? We will make the ceramic slurry. This ceramic slurry a preparation itself takes several hours of time. Then we have to dip the assembly into the ceramic slurry. Take it outside. Apply this stucco coating. Then you dry it. Again dip it inside the ceramic slurry. Apply this stucco. Dry it like this. This cycle has to be done some 7-8 times. Each time we have to spend at least 1 hour for dipping into the slurry and applying the stucco and drying. Likewise this ceramic shell preparation takes 7-8 hours and incorporating the course is difficult. So these are the limitations of the investment casting process. These are the typical applications. Jewelery castings can be made by investment casting. Art castings can be made. Difficult to machine alloys can be made by investment casting process. Milling cutters and other tools, impellers and other components and finally it is used in the dentistry and surgical implants. The artificial teeth are manufactured by the investment casting. So we can see here these are the jewelry items. So these are manufactured by investment casting. And here we can see these are all the jewelry components. Sometime back we have talked about a central tree. So this is the central tree or the sprue and through this they are pouring the molten metal and so these are all the individual castings. Of course finally they will separate all these individual castings. So these jewelry items are manufactured by investment casting. And here we can see this is a steam turbine blade which is used in a thermal power plant. You can see this is the turbine blade. It is a very huge turbine blade and you can see these are all the blades. These are all the blades and all these blades are manufactured by investment casting because these blades will have a very complex geometry and if you manufacture it by any other method they require the machining and it is very difficult to machine such a complex geometry. That's why these are manufactured by investment casting process. And here you can see this is a milling cutter. This milling cutter is made up of a difficult to machine alloy. Most of the times it contains a large amount of tungsten and it is very difficult to machine this kind of steel. Now this milling cutter is manufactured by investment casting. So here we can see this is an art casting. Now you see its complex features. If you make this by any other casting process it will have a rough surface. Once there is a rough surface we need to machine it. Now it is not possible to machine this under a machine. But when you make this using the investment casting process that we already we get a very smooth surface. So there is no need to machine it. So investment casting is also used in the art castings. Next one let us see the continuous casting process. So this is the typical setup of the continuous casting. And here you can see this is the molten steel. And this in between there is intermediate to reservoir is there. This is known as the tundish. Tundish and here we can see there is a dye. And the molten metal from the ladle it flows into the tundish. And from the tundish it is flowing through the dye. Then what happens and here initially there is a slab is there solid slab. And this solid slab of the stopper will be here at the beginning. And the molten metal flows and it flows through the dye. And immediately there will be cooling system will be there. And because of the cooling system and it solidifies and it falls on the stopper and the stopper slowly comes down and it slowly comes down and it goes like this. And even the solidified billet it comes like this. And after it comes to a particular distance it will be cut. At an equal distances or at intermediate to distances it will be cut. So this is the simple principle of the continuous casting. And here we can see the horizontal continuous casting. Here we can see this is the holding furnace. And this is meant to means the molten metal. And this is the mould. And the molten metal is going out. And here we can see the cooling system is there. And because of the cooling system and it solidifies. And here we can see these are the rollers. And these rollers they take the solidified casting away from the furnace. And the solidified casting goes in this direction. And here the mould is made by a what is a graphite mould. It is commonly used to manufacture nonferrous components. Nonferrous castings. These are the advantages of the continuous casting process. We get the 100% casting yield. First of all what is meant by casting yield? Suppose if we make a casting by green sand moulding. Suppose if the weight of the casting is 100 kgs. We pour more than 100 kgs of the molten metal. Because the molten metal occupies into the sprue and also into the razor. So if we want to make a casting of 100 kgs about 125 kgs of molten metal we pour into the cavity. So that way in such a case the yield will be 70 to 80%. And here the yield is 100%. That is the benefit. Next one cheaper to produce ingots. So we most of the times we produce the ingots by continuous casting. And we get a better surface finish. And grain structure can be regulated. As soon as it enters into the mould there will be a cooling system. Because of this rapid cooling the grain structure will be improved. The process is automatic. It is a mechanized system. That is why it requires less labour. And here we can see these are all the aluminium ingots manufactured by continuous casting. And here we can see these are these are the gear blanks. This is a gear blank. This was manufactured by continuous casting. Means inside there is a mould. Even the cross section of the mould was similar to the gear blank profile. And this is a as cast material. Afterwards it was machined. And after machining we got the gear like this. So gears are also manufactured by continuous casting. Next one the vacuum sealed moulding process. This is also known as V process. And this was recently developed in Japan. What is the principle of the vacuum sealed moulding? Here we use vacuum to bind the or to hold the moulding sand. Whereas in the case of the green sand moulding we use to mix some binders and place moisture so that some binding action will be developed between the moulding sand. And such a sand we what is the place inside the moulding box. And when we compact yes we get a moulding cavity. And here we won't use the clay or any binder. Even the moisture we won't use. We use a fine and dry sand. And here we use a vacuum to hold the sand. So here we can see here is a platen. Here is a platen. And this is the pattern. This is the pattern. And here you can see a green coloured one. So that is a polymer film. So what we do is so on the board we place the pattern. And here we put the polymer film. And here we seal it. And here also we seal it. Now we apply vacuum here. When we apply vacuum what happens? The vacuum sucks the polymer film. So because of that the polymer film will be strictly adhering to the pattern surface. Now what about this? Yes now we place a moulding box on this board. In the moulding box we place the now we place the moulding sand here. Here we can see here we place the moulding sand. After placing the moulding sand the excess sand will be removed. Now again we can see here. Let us come here. Here again we can see a green coloured one. So we place again a polymer sheet here. And you seal it here. You seal it here. And here there is another vacuum pump is there. And here we apply the vacuum. Then what happens? The vacuum sucks the polymer film. Because of that it goes what say closer to the pattern. And the sand here will be tightly sticking to the pattern. It will not be shaking. Now what we do afterwards? The remember that we have used the two vacuum sources. One to what say this one in the initial stage to make the polymer film and here to the pattern surface. And another polymer we have kept on the sand. And again here we have applied the vacuum. The first vacuum we release. When we release the first vacuum what happens? The pattern will be coming out of the mould. Now we can see here this is the mould. And here it is closed by the polymer film. And here it is also closed by the polymer film. And the vacuum is tightly holding the moulding sand. So that is how we made the one what say half of the moulding boxes or one moulding box or the drag box. Again in the same way we make the coke box also. Then we assemble these two together. And of course when we make the coke box there will be a provision for pouring the molten metal. Then we pour the molten metal. The molten metal goes inside the cavity and it solidifies. After it solidifies then in the case of the sand casting we have to break it and we have to apply external pressure for the knockout purpose. But here just we have to release the vacuum. When we release the vacuum automatically the sand will be falling down and we get the solidified casting. So here we can see this is a vacuum moulding machine used in the deep process. And here we can see vacuum is used and yes we can see the polymer film. So these are the advantages of the vacuum sealed moulding process. One is the simplified sand control. In the case of the green sand moulding we have to add the binder. We have to add the editors. We have to mix the moisture. Then we have to mix it thoroughly this takes time. And very carefully these ingredients have to be controlled. If the moisture is more there will be a problem. If there is a binder is more there is a problem. If the mixing time is not proper is not sufficient again there will be a problem. But here there is no question of mixing editors to the sand. We take the fine and dry clear sand. There is no question of preparation of the sand. That way there is a simplified sand control. Next one no sand reclamation. Reclamation means when it is about to be spoiled we take it and we see that it is again used. So such a case arises in the case of the sand moulding. So part of the sand will become useless or when it is the whole thing is becoming useless we put efforts and see that most of the sand will be reused. So that operation or that process is known as the reclamation. So here the question of reclamation does not arise. The moment you release the vacuum automatically the whole sand falls down and we get the casting. The sand as it is we can use it again for the making the next casting. So the third is the no sand mixing is required. Next one the inexpensive patterns. Patterns are not expensive. No draft or other pattern allowances. In the case of the sand moulding process that what is a pattern will have a taper so that it will be withdrawn from the mould. Here or later that taper has to be machined. Here no such a taper or draft need to be given. Means afterwards we do not have to put efforts to remove that taper on the machines. Next one reduce noise level. In the case of the sand moulding process to prepare while we are making the preparing the sand there will be a noise and here there is no question of such noise and when we are compacting the sand in the case of the sand moulding there will be a noise. Here there is no such noise. So here there is a reduced noise level. Next one better general environment. In the case of the sand casting process we mix the clay and when you after certification when we break the sand the dust will be raising. Here such such problem does not arise. Next one reduced cleaning costs. In the case of the sand casting process because we are mixing the clay water and other editors the sand casting will have a depth what is a film around that this has to be cleaned. In the case of the v process such a question does not arise the casting will be very clean. Next one reduce smoke and fumes. Whereas in the case of the sand casting process when we pour the molten metal into the cavity yes there is moisture in the mould because of the moisture immediately the moisture will turn into vapor and the vapor will be coming out. So that causes some kind of what say inconvenience to the operators. So here such question does not arise. Next one no knockout process. What is this knockout? In the case of the sand casting process after we pour the molten metal after certification is over we have to break it we have to put the physical efforts or we use the machines to break the sand. So this is known as the knockout. Here we that question does not arise. Next one better finish on the castings. Next one better dimensional accuracy we obtain in the v process. Next one finally the less energy consumption. So these are the advantages of the vacuum sealed moulding process. Next let us see the limitations of the vacuum sealed moulding. In this process the skilled workers are required because the vacuum has to be applied in the right time and also it should be applied for the right duration. So this requires skill. Next one the polymer film is expensive and for each casting we have to use new polymer film. Once we use polymer film for one casting so that is that cannot be used for the next casting. So that way the process becomes expensive. Next let us see the squeeze casting process. So this is the simple principle of the squeeze casting process. In the squeeze casting process we get the mechanical properties better mechanical properties and here we can see this is a mould. This is the mould and here the molten metal is coming it is ready and yes the molten metal is poured into the die. So this is the die or the permanent metallic mould and this is the you can see this is the ram and this is the ram will be coming down. You can see here so the ram is pushing downwards and the molten metal is trapped between. In fact here we have shown a very simple what say geometry. Sometimes the casting will have a complex geometry and very thin fins or say complex fins will be there and in the ordinary casting process the metal may not flow into these complex details but because when the metal is still in the liquid state we are applying external pressure by means of this ram. So all these thin fins complex films will be filled by the molten metal. After solidification what we do? Yes this ram comes up and the solidified casting will be ejected like this. So this is the simple principle of the squeeze casting process. It is a well known fact that we get better mechanical properties with the forging. Why? Because we apply the mechanical pressure the grain structure will be improved the same thing happens here. So this is a kind of mixture of casting and the forging process. So these are the advantages of the squeeze casting process. Parts of fine details can be produced as I already told because we are applying the external pressure. The molten metal fills the fine details and the complex details without any difficulty. Next one, shrinkage defects are very less. Shrinkage means internal hollow cavities inside or externally. When we are applying the mechanical pressure externally so this what is a possibility of creation of these internal or external cavities will be minimized. Next one very high production rates close to die casting. Next one no gating and razor and hence higher casting gear. Here we do not see any sprue or any razor or runner that is why we get the higher casting gear. It produces the high quality surfaces. The surface will have a very what is a smooth surface. There will be a smooth surface. Rapid solidification results in a fine grain size which improves mechanical properties. Because we are pouring the molten metal into a metallic dye and there will be a cooling system because of that there will be rapid solidification. Because of the rapid solidification the mechanical properties will be improved. The amount of pressure applied is significantly less compared to forging. Yes by forging we get the better mechanical properties but the amount of force that we apply is considerably very high. But here we have to apply very moderate pressure and we get the better mechanical properties. These are the limitations of the space casting process not suitable for the large castings because the molds are made up of the special dyes metallic dyes. So very large castings cannot be made not suitable for the ferrous castings because the metallic dyes are made up of ferrocelloids. So it can be used only for the non ferrous castings and here we can see the typical what say components produced by the space casting process and this is the squeeze cast knuckle of an automotive. So this is manufactured by squeeze casting process and here we can see there is another component squeeze cast rack and pinion housing for truck application. So this is manufactured by squeeze casting process. Next let us see the centrifugal casting process. There are three types of process in the centrifugal casting. One is the true centrifugal casting semi centrifugal casting and the third one is the centrifuging. So this is the centrifugal true centrifugal casting. What is its principle? There will be a graphite cylindrical mold will be there. So this is the cylindrical graphite mold the one which is looking in the gray color. So this will be what say supported on the wheels bottom rollers here you can see these are the rollers. In fact the rollers will be there on the top also and as the motor here we can see a motor as the motor is rotating the rollers will be rotating this roller and this roller and because of that this cylindrical graphite mold will be rotating. When this cylindrical graphite mold is rotating and here the molten metal slowly is poured into the graphite mold and gradually the speed of the mold will be increased and the molten metal keeps on coming inside then what will happen? Because of the centrifugal force the molten metal will be sticking on to the walls of the graphite mold and the rotation continues till it solidifies till the molten metal is solidified. Once the molten metal is solidified the rotation of the cylindrical graphite mold will be stopped then this can be separated into two halves then we can get the casting outside. Because we are applying the centrifugal force on the molten metal so this is known as the centrifugal casting process and there is another prototype semi centrifugal casting process. In the semi centrifugal casting process the system rotates on a vertical axis whereas in the case of the true centrifugal casting process the mold was rotating on a horizontal axis and here the mold rotates around a vertical axis. So this is the mold cavity the mold cavity is here and this is the mold and you can see this is the cope and this is the drag yes and the molten metal is poured like this and the molten metal flows like this and it flows like this and then the what say mold will be rotating the mold will be rotating. Now what is the benefit? Because in the case of the conventional sand casting process suppose if the cavity has a small fine feature the molten metal may not flow into that but here of course such a small fine feature is not shown here but then what happens because it is rotating because of the centrifugal force the molten metal will be forced to occupy such small details that is the benefit of this semi centrifugal casting process and the third type is the centrifuging and if they are centrifuging in the centrifuging also the system rotates about a vertical axis. So here we can see this is the axis of the system and this whole system rotates now what is this so these are all the individual castings so these need not be cylindrical this can be any casting one thing is they have a fine features they have fine features or small complex features by conventional casting process it may be difficult for us to fill the molten metal into those fine features but now what is happening is this is the central tree or the central sprue and all these castings or all these molds are connected to the central sprue and the system rotates as it is rotating once we pour the molten metal because of the centrifugal force even if there is a small feature a fine feature molten metal will be flowing into those fine and small features so that is the benefit of the centrifuging so there is a difference between the centrifuging and what say semi centrifugal casting right here we make one casting whereas we make so many castings here this that is the centrifuging these are the advantages of the centrifugal casting formation of hollow cavities in the cylinders without course if we have to make what say internal cavities in a casting we have to use course again these course so what are these course we will be studying in the next lecture non-metallic and slag inclusions and gas bubbles are forced to the inner surface so even if these watch a non-metallic slags and impurities if they are there in the molten metal they will be forced to the inner surface of the casting because the centrifugal force falling on them will be lesser so they will be collected at the center of the casting or on the inner surface of the casting we can remove them very easily next one here also no gating system that's why the casting yield is very high next one settling costs are reduced next one casting is free of shrinkage cavities and porosity shrinkage means hollow cavities inside the casting are on the surface of the casting so these will be minimized porosity means gas bubbles inside the casting are on the surface of the casting so this problem also comes down fine outside details can be successfully cast fine outside details it may be difficult for us if it is the conventional sand casting process but here because we are applying the centrifugal force the molten metal because of the centrifugal force flows into the fine details next one it is easy to inspect the castings so these are the demilits of the centrifugal casting process more segregation of alloy component during pouring under the force of the rotation suppose sometimes we pour the alloys the alloys contains the different metals and suppose if one metals density is more and if one metals density is very less the centrifugal force falling on these two metals will be different because of that the individual metallic components of this alloy may be segregated which is not required which is detrimental to the quality of the casting next one suitable only for axial symmetrical components so this is applicable for the what say true centrifugal casting and the semi centrifugal casting next one skilled workers are required for the operation say the mould has to be rotated in the right time and it should be rotated at the optimum speed and it should be stopped at the right time so this needs skill so that's why skilled workers are required for this operation and next one we get the inaccurate internal diameter if the two halves of the mould are not what say coupled properly at such times we get the inaccurate internal diameter so these are the typical components produced by the true centrifugal casting process we can see so these are all the components produced by the true centrifugal casting process next one let us see the plaster moulding process in the plaster moulding process we use the plaster of paris so initially we have to prepare the plaster of paris so this is also known as the gypsum commercially so this will be mixed with water and we prepare a what say slurry plaster of paris or the gypsum slurry we prepare in a container and we yes we place the pattern here so this is the pattern and we pour the what say plaster of slurry here around about the pattern and after sometime the plaster of paris slurry will be solidified after it is solidified we remove the pattern in the same way we prepare the other half of the pattern also at such time we also make a provision for the what say sprue or the pouring cup so that the molten metal can be poured and when we prepare both the halves of the patterns we assemble them yes we are assembling here so this is the drag so this is this part this deep blue colored one is made by the plaster of paris and you can see here this is also made by plaster of paris and these two will be assembled now the molten metal will be poured into this assembly and after solidification we break this plaster and we get the solidified casting these are the advantages of the plaster moulding process complex shapes can be cast offers excellent surface finish what is the mould made up of it is not the greens and mould it is made up of plaster of paris the plaster of paris will have a very smooth surface and because of that even the component cast component will have a very good surface finish and that's why minimum machining is required fine details can be obtained because of this process next one thin sections can also be obtained and we get good dimensional tolerance setting of mould takes less time less than 50 minutes time so these are the advantages of the plaster moulding process these are the demerits of the plaster moulding process not suitable for paris castings the sulphur the gypsum contains sulphur this sulphur reacts with iron and results in defects that's why this process cannot be used for making ferrous castings this is more expensive than sand castings in the case of the sand casting process we use the moulding sand we take the fine sand mix with the binder and the additives and the moisture you mix it and the same sand can be used for making several castings whereas here once we make a what say plaster mould that can be used only for making one casting afterwards we have to break it and that the plaster cannot be used again that way it is more expensive than the sand casting process not suitable for large castings this can be used for making small castings and also to some extent medium size castings say maybe 30 grams to 7 kg beyond that it is not possible to make the castings with the plaster moulding casting process next one the plaster is not reusable like the sand in the sand casting process no it is not reusable next one it has to be baked after the plaster is set around the pattern it has to be baked so for that we have to use an electrical furnace and also that consumes time means production time is increasing thermal conductivity of the plaster is poor whereas the thermal conductivity of the sand medium is very high here the sand moulding medium is the plaster of Paris its thermal conductivity is poor that is how the solidification takes lot of time as this solidification is taking lot of time the mechanical properties that are likely to be obtained will be poor next one low permeability what is this permeability ability of the what say what say mould to allow the hot gases to pass through that whereas it is if it is the sand casting process there will be what say between the neighboring sand grains there will be some gaps will be there through these gaps the hot gases pass through the sand mould whereas in the case of the plaster mould so the such what say pores will be very less that's why there will be low permeability what happens if there is a low permeability the hot gases that are developed inside will be accumulated inside the mould cavity so that results in the casting depends friends today we have seen a few special casting process we have seen the what say investment casting process continuous casting process vacuum sealed moulding squeeze casting process centrifugal casting and the plaster moulding process and in the next lecture we will see the evaporative pattern casting thermi-mixtile moulding slush casting steel casting and also the economics and the overview of the and overall comparison of all this process we will see in the next class thank you