 In the previous classes we have seen the principle of the metal casting process. We have seen that in the metal casting process whenever we want to manufacture a particular component with a particular geometry, first we will create a similar cavity of the same geometry and we will pour the molten metal into that cavity. After sometime the molten metal solidifies, then we remove that molding medium and we get the solidified casting. This is the simple principle of the metal casting process. We have seen the different classifications of the metal casting process and also we have seen the different terms used in the metal casting process and today we will see the molding sands and design. These are the different types of the molding sands. One is the green sand, second one is the coarse sand, next one the dry sand, next one the loam sand, next one the facing sand, next one the backing sand and finally the parting sand. Most of the times we hear these words and some people may not be able to distinguish among these different sands. Let us see what is the purpose of each and every sand which is mentioned here. First let us see the green sand. Green sand is also known as tempered or natural sand which is just a mixture of base sand like silica sand, zircon sand with binder and moisture. This is the green sand means when the moisture is present it is known as the green sand. It is commonly employed for the production of ferrous and also for the production of non ferrous castings. So this is the green sand. Next one we will see the coarse sand. In the previous class we have seen that core means yes it is an object which is kept inside the mould cavity. If we want a casting with some hollow space inside or with hollow cavity inside what we have to do? We will be placing a core inside the mould cavity so that the molten metal does not talk in that particular space. This core is made up of the coarse sand. This coarse sand used for making coarse and it is also known as oil sand. This is highly rich silica sand mixed with oil binders such as core oil. The core oil is composed of linseed oil, resin, light mineral oil and other binder materials. So this is the coarse sand. Next we will see the dry sand. Green sand that has been dried or baked in a suitable oven after making the mould and core is known as the dry sand. Sometimes if the just now we have seen we have seen that if the moisture is present then we will call it as the green sand. Sometimes if the because of the presence of the moisture sometimes we get the defects like blow holes and porosity. So to avoid these defects we dry this moisture then this sand is known as the dry sand. It has more strength, rigidity and thermal stability and it is mainly suitable for larger castings. So remember that the difference between the green sand and the dry sand is green sand means almost the same composition but it contains the moisture whereas when we what say dry out the moisture then it becomes the dry sand. Next one the loam sand. It is a mixture of sand and clay with water to a thin plastic paste whereas in the case of the green sand we mix the water but it does not look like a paste. Of course it becomes sticky but it is certainly it is not a paste but here the sand becomes like a paste and it possesses high clay as much as 3250 and moisture up to 18%. This much clay we do not mix with the green sand. So this is another difference with the loam sand and shape is given to the mold by sweeps. In the case of the conventional sand molding process we used to ram the molding sand. We dumped the molding sand inside the molding boxes and with rammers we used to ram or it is done by the machine molding whereas here we do not do the ramming but we do the molding by the sweeps means there will be one sweep pattern will be there and this as we rotate this sweep pattern a mold cavity is created inside this loam sand. This is particularly employed for large grey iron castings. Next let us see the facing sand. It is applied as an initial coating around the pattern so that the mold cavity will have a smooth surface. We have seen that in the previous class we use a model to create the mold cavity inside the mold means if we want to make a particular casting with a particular geometry initially we make a pattern. This pattern will have the similar geometry as that of the final component. Most of the times this model which is technically called as the pattern has a rough texture because most of the times it is made up of the wood. Because of the rough texture of the wood even the mold surface cavity surface will have a rough texture and as a result even the solidified casting will have a rough texture. Now we want to minimize this rough texture. So what we are going to do is we are applying this facing sand over the pattern. This facing sand is a fine sand then just we sprinkle on the just on the pattern before we compact the molding sand. Then what happens? The rough texture of the pattern is minimized and over that we put the molding sand and then we complete the ramming. So it comes in contact with the molten metal. So it must possess high refractoriness means when the molten metal of high temperature is poured into the mold this facing sand layer should not burn. So that is the important characteristic the facing sand must possess and it is made up of fine silica sand and clay without the use of the used sand. It is used only once repeatedly it cannot be used. So this is the facing sand. So facing sand is to improve the surface finish of the cavity and also to get a better surface finish on the solidified casting. Next one let us see the backing sand. Backing sand or floor sand you is used for backup the facing sand and is used to fill the whole volume of the molding flask. Now we see initially we take the molding box and inside that we put the pattern and over the pattern we sprinkle the facing sand to minimize the rough texture of the pattern. Then over that we put the molding sand that is molding sand it contains the what is a valuable ingredients and costly ingredients and we do not want to fill the entire flask with the costly molding sand. So for that purpose for filling up the purpose we use the backing sand. It is used right, it is a used molding sand and it is mainly employed for the backing purpose means filling the purpose right. The backing sand becomes black in color due to addition of cold dust and burning and coming in contact with the molten metal. Say we use the cold dust to improve its strength that is why it becomes black in color and also as we it is repeatedly used and when it comes in contact with the molten metal it becomes it burns and it becomes dark that is why it is also known as black sand next one parting sand. It is applied along the parting line so that the sands in the drag and cope do not stick to each other and say we have seen that in the molding system we generally we use two molding boxes right. The lower molding box is known as the drag the upper molding box is known as the cope and we put the pattern and yes we mold the two boxes and these two mold boxes what right there in between these two molding boxes there is a separation because before pouring we have to separate these two molding boxes after molding is over then we have to withdraw the pattern and we have to withdraw the sprue pin and the razor pin. So because that is why there must be a separation when we are ramming the sand the molding sand which is rammed in the cope box should not be sticking to the sand that is molded in the drag box. So what we do before what say after the compaction of the drag box is over then we place the cope box over the drag box and before placing the molding sand into the cope box we sprinkle little amount of parting sand on the what say compacted sand of the drag box. Then we put the molding sand into the cope box then we start ramming then what happens the sand which is molded inside the cope box does not mix with the or does not stick with the molding sand that is molded inside the drag box. So that is the purpose of the parting sand it creates a separation between the cope box and the drag box base sand like silica sand without any binder and moisture is used as the parting sand. So this parting sand does not contain any binder and moisture it is a dry and clear sand. Now these are the types of the molding process I mean the sand conventional sand molding process. One is the green sand molding process these we have already seen in the classifications of the casting process. The second one is the dry sand molding process the finally the chemical sand molding process under the chemical sand molding process we have the shell molding and carbon dioxide molding and no bake molding. Among these green sand molding is widely developed than any other molding process because of its simplicity and because of its economy and a large castings can be produced using the green sand molding whereas with the what say CO2 molding and the shell molding it is very difficult to produce very large castings. Now we are going to what say learn more about the green sand remember that green sand means the molding sand which contains the moisture. Now why green sand molding that is the fundamental question there is dry sand is also there and chemical sands are also there why because first point is reasonable cost the cost is reasonable when we use the green sand. High productivity economical and also very large castings can be made using the green sand. And this green sand of course when we remove the moisture it becomes the dry sand mold yes again we can manufacture very large castings and easily adaptable to manual semi auto and automatic molding machines. Remember that this molding can be done manually and also on the semi automatic machines and also on the fully automatic molding machines and this green sand can be molded in all these cases manually it can be molded using semi automatic machines it can be molded and using fully automatic machines also it can be used that is why this green sand molding has become popular. Now this is the general composition of the green sand. So these are the ingredients we have the base sand binder this is also known as the clay and we mix the additives and also the water. Base sand is say it is present 85 to 90 percent binder which is also known as the clay it is between 6 to 11 percent. Next one we mix the additives and the proportion is 2 to 8 percent and water is 2 to 5 percent. Now what happens as we what say for the molten metal right part of the binder becomes inactive once the temperature crosses about some 500 degree centigrade or 600 degree centigrade then it loses its binding property though it is physically present it becomes inactive. So then in such a case that portion of the binder which has lost its property but still physically present it is termed as the dead clay. Now what happens first time when we first time prepare the green sand and yes we make the mold this what say dead clay may not be present but this sand is repeatedly used yes we pour the molten metal the molten metal solidifies and we break the sand mold and we take the casting outside the same sand will be remixed and it will be reused to make another mold. And what happens previous time a part of the binder has lost its properties that has become the dead clay. So dead clay becomes a component of the green sand except the first time second time onwards there will be dead clay in the molding sand or the green sand. So now we will see these are the green sand components one is the base sand now let us see the components base sand first one second one the binders binder means the clay next one the additives next one the water this should finally the dead clay. Though dead clay we do not add intentionally the part of the binder or the active clay once it what say comes in contact with the hot metal it turns into dead clay and this is this becomes a component of the green sand. So these are the five components of the green sand now we will be seeing all these components in detail initially let us see the base sand what is this base sand commonly these are the commonly used base sands one is the silica sand second one is the zircon sand third one olive in sand fourth one chromite sand fifth one aluminum silicate sands these are the commonly used base sands. Now let us study these sands in detail first let us see the silica sand what is this silica sand material used for its economic advantages and sufficient thermal resistance. So silica sand has got the sufficient thermal resistance means it can withstand very high temperatures and it is available abundantly on the river beds and also on the sea beds if we go in the summer to the side of the river beds and we can see there what say clear sand on the river beds. So this is the silica sand and we can see these are the silica what say sand beds look like this and again we can see these are the silica sand beds. Now this is the silica sand components again silica sand has got three components one component is silica dioxide and it is present up to 98 percent again it contains aluminum oxide maximum it contains 0.13 percent and also it contains iron oxide up to 0.06 percent and say this is the distribution of the silica sand and it is used for all the general applications. So we have seen the silica sand what is its source and what are what is its chemical composition and what are its properties and applications we have seen for the silica sand. Now let us see for the zircon sand zircon is the oldest mineral available on the earth or known on the earth. It is also very hard mineral and has a very highly high melting point and the melting point is 3000 degree centigrade it has a very high melting point. So again we can see these are all the zircon sand lumps and beds we can see here and this is the typical chemical composition of the zircon sand. The zircon sand contains the following ingredients right. So the components one is the zirconia zrvoto it is up to 65.9 percent it contains. Next one it also contains silicon dioxide up to 32.554 percent. Next one zircon sand also contains alumina aluminum oxide 1.15 percent. Next one it contains titanium dioxide up to 0.27 percent and it contains ferrous oxide Fe2O3 up to 0.04 percent. Next one it contains silica right again silicon dioxide it contains free silica up to 0.1 percent. This is the general form of the zircon sand. So in general it appears as the zirconium silicate zr SiO4. Now what is its application? We have seen that the what is the silica sand that is the silica base sand is used for all the general applications. What is the application of the zircon sand? It is used in such application where high refractoriness is required. See if we are making what say alloys are the metals with moderate or the low what say melting temperatures no need for the zirconium sand. We can use the silica sand as the base sand. But if when we are pouring alloys of high temperature high melting temperature at such times we need a base sand of higher refractoriness and zircon sand contains the higher refractoriness that is why. Where high refractoriness is required we use the zircon sand. Next one so we are learning about the base sand. So we have also already seen the silica sand and the zircon sand now let us see the oleven sand. Oliven sand it is one of the most abundant minerals on the earth. Oliven is named after its oleven green color this sand looks green in color. Oliven sand source and lumps here we can see these are the sources and lumps of the oleven sand and they look green in color that is why it is known as the oleven sand. And here we can see a single grain of the oleven sand you can see this is a single grain of the oleven sand which looks green in color and these are the grains of the oleven sand we can see different size grains are there all look in green in color. This is the typical chemical composition of the oleven sand. It contains magnesium oxide 46 to 50 percent it contains silica dioxide 41 to 43 percent it contains iron oxide 6 to 8 percent and it also contains loss on ignition up to 2 percent maximum 2 percent and this is the general form of the oleven sand it is the general form is the magnesium iron silicate 2 Mg Fe O Si O2. So this is the chemical composition general chemical composition of the oleven sand and we are seeing we are learning about the base sands and we have already seen silica sand zircon sand and the oleven sand. Now let us see the chromite sand chromite sand is a byproduct of the ferrochrome production in the ferrochrome alloy industries so this comes out as a byproduct this is not a natural mineral and what is the chemical composition yes it contains the chromium oxide 46 percent minimum next it contains silica dioxide 1 percent maximum it contains iron oxide 26 percent it contains calcium oxide 0.15 percent and it contains aluminum oxide 15 percent finally it contains magnesium oxide up to 9.8 percent. So these are the different what say elements are the different components present in the chromite sand this is the general form of the chromite sand it appears as the iron chromium oxide Fe O Cr O3 so this is the general form of the chromite sand we have seen silica sand zircon sand oleven sand chromite sand now let us see the aluminum silicate sand. Aluminium silicate its chemical formula is Al2 Si O5 occurs in 3 common forms one is the cainite next one the silimeanite next one the andalucite these 3 minerals have high refractiveness and low thermal expansion they are widely used in the precession investment casting foundries and often in combination with the zircon flow right. So this may not be used in the commonly used in the green sand molding but we have seen that what say under the special casting process there is a process called investment casting process where the pattern is made up of the wax right. So around the wax we give a ceramic slurry coating repeatedly we give the ceramic slurry coating after a shell is created what we do we heat the system and the wax inside the shell will be drained out then we pour the molten metal into the shell right. In that process this sand is used and right this aluminum silicate sand in combination with the zircon sand it is used. Now let us see the what say a thermal behavior of these sands what happens right. So this is the y axis is the percentage expansion and x axis is the what say pouring temperature or the temperature and its behavior corresponding to the temperature we can see on the y axis. Let us see the silica sand this green colored one indicates the what say silica sands behavior thermal behavior. Now it starts expanding water reasonably from 200 degrees centigrade onwards. Now when it comes to 600 degrees centigrade what happens it reaches the maximum expansion and that expansion continues till about 1400 degrees centigrade. So silica sand has the highest thermal expansion. Next one let us see the zircon sand the zircon sand yes again it starts what say expanding from right from 0 degrees and it what say continuously it is expanding up to 600 at about 600 degrees centigrade it what say considerably what say increases expands more and yes and this is its expansion behavior and its expansion is little lower than the expansion of the silica sand. Next one we will see the olive sand this pink colored one indicates the thermal behavior of the olive sand. Now we can see here it is why as the temperature is increasing it starts expanding yes maybe at about 600 it is more expanding and yes it is continuously expanding but certainly its expansion is lower than the expansion of silica and zircon sands. Finally we will see the chromate sand. Now this blue colored one line indicates the thermal behavior of the chromate sand. We can see up to almost up to 400 degrees centigrade there is no thermal expansion it is thermally stable and maybe at about 800 degrees centigrade it what say expands a little and it continues even after 1400 degrees centigrade it continues to be what say it contains little expansion it shows the little expansion. Now when we compare all these sands silica sand zircon sand, olive sand and chromate sand silica sand has the highest thermal expansion and next to that zircon sands expansion is more and below zircon sand, olive sand is the one which occupies below the zircon sand and remember that chromate sand has the minimum thermal expansion it is thermally stable but it is costly. Now here we can also see this is the thermal behavior of the bentonite. Bentonite means it is a what say binder we will see we will study about this bentonite after sometime. Now these are the base sand materials right yes we can see here silica sand, chromate sand, zircon sand and olive sand right and formula of the silica sand is silicon dioxide SiO2 and its specific density is 2.65 right and its bulk density is 1.6 and its sintering point is 1730 degree centigrade and thermal conductivity is low and reaction is high and utilization with almost all the metals it can be used and it is what say it is it has got the price is low and coming to the chromate sand and its chemical formula is FeO CrO3 and this is the specific density and this is the bulk density and sintering point is 2095 degree centigrade and thermal conductivity is high and reaction with the molten metal is low and utilization it is used for the steel and manganese castings and right it has got the higher price. Next one is the zircon sand and its chemical formula is ZR SiO4 and this is the specific density and bulk density and the sintering point is more than 2200 degree centigrade. Thermal conductivity is very high and reaction with the molten metal low and utilization it is used for the steel castings and price is high. Next one this is the olive sand. So, this is the chemical formula 2 Mg FeO SiO2 and this is the specific density and this is the bulk density and sintering point is 1857 degree centigrade, thermal conductivity low and reaction with the molten metal low and utilization it is used for the steel castings and price is medium or the moderate. Now we will see the binders we have already completed the base sands and we have seen the different types of the base sands and their origin and applications and their chemical constants we have seen. Now let us see the binders. First of all the question is why we have to use the binder. Binders are added to give cohesion to the moulding sands. Cohesion means ability of the moulding sand particles to stick to each other that is the cohesion. So, the binders enable cohesion to the moulding sands. Next one binders provide strength to the moulding sand and enable it to retain its shape and mould cavity. It also it gives the cohesion property not only that it enables to gain strength and retain its shape after we compact the sand. So, that is the purpose of the binder. Next one binders should be added in optimum quantity as they reduce the refractoriness and permeability. These binders are the fine powders. So, there is a property called permeability for the moulding sand. Permeability means ability of the moulding sand to allow hot gases to pass through the neighbouring sand grains like this, like this. It has to enable through the neighbouring particles. So, what happens when we add excessive of binder it fills those what say gaps between the neighbouring grains and the ability of the steam or the hot gases to escape through the neighbouring grains comes down drastically. But we need it unless we add the binder we cannot get the cohesion. Unless we add the binder we cannot get the strength that is why we must add the binder, but it must be optimum then and we have to balance the strength the cohesion and also the permeability we have to balance. That is why we have to add the binders in an optimum quantity. These are the common binders used in the green sand. One is the bentonite, another one is the fire clay, next one illite, next one limonite, next one kaolite. So, these are the common binders used for the green sand mixing. Now, let us see all these binders one by one. First let us see the bentonite. What is bentonite? Most of the time this is the main clay or the main binder important binder used in the moulding sand. Many a times people use bent what say in the for what the word clay instead of using the clay or instead of using the binder they use the word bentonite. So, it is so important and it has become very popular among all the binders. First of all what is this bentonite? Bentonite is a type of clay whose main constituent is Montmorillonite belonging to the smectite group. And what is its chemical formula? Bentonite is an absorbent aluminium phylo silicate consisting mostly of Montmorillonite. Here we can see what phylo, phylo means thin sheets means it is available in the form of thin lamellar sheets that is the physical structure of the bentonite. Next one it is a structure bentonite has a sheet like structure just now we have seen. And its division particle size is less than 2 microns. Dispersion possibility to make colloidal suspension with more or less stability in water. Now what is the source of bentonite? Bentonite is a relatively soft stone formed over geological time by the natural alteration of volcanic tufts due to acid or alkaline rain. So bentonite comes from the what is a volcanic tufts. So this volcanic say tufts are laid underground for several years. And over that we can see acid rains or alkaline rains will be there and because of that we get the bentonite. And bentonite will be inside the ground and we can take it outside that is the source of the bentonite. And this is how we can get the bentonite initially this is the mining. So this mining say often we can see this bentonite mines where there is what say previously there was volcanic eruption. So next this is the exploitation with machinery we have to take that material. Next one this is the stocking. Next one it is the activation and after that there will be drying and milling finally it is the packing. So this is the right bentonite from mining to the foundry right. So here we can see first stage the mining exploration exploration. Next one mining exploitation next one ram material stocking we can see here. Next one activation next one drying right next one stocking. And finally we can see milling right finished products to stock and packing and delivery to the foundry industries. Now the question is why it is called as bentonite? The first industrial exploitation at the beginning of the 20th century started at a mine located near Fort Benton in Wyoming province USA. This industrial exploitation of bentonite was done in a place called Fort Benton in USA. That is why it is known as the bentonite. This explains the origin of the term bentonite which was first a trade name. How does bentonite observe moisture? That is the question right. So why we are adding this bentonite this bentonite is a binder or a clay. Why? It was a first of all it improves the cohesiveness of the moulding sand. It induces the strength to the moulding sand right. The aluminum phyllosilicate bentonite layers have a slightly negative charge that is compensated by the exchangeable ions right. Calcium ion or the sodium ion in the intermediate layers. The charge is so weak that the cations calcium ions or the sodium ions can be absorbed with an associated hydratous shell moisture. Here we can see bentonite layer structure and here we can see it is present in the form of the sheet like structure layered structure and we can see this is the sodium ion and here we can see calcium ion. The space between these layers is maximum with the sodium ions. How does bentonite act as a binder? That is the next question and here we can see this is a sand grain. This is a sand grain and this is a sand grain and here we can see this is the bentonite. It what say acts as a bridge between the sand grain and sand grain what say holds both the sand grains together by forming a bridge and same thing we can see here also. So that is how it makes a bridge between the sand grains and holds them together that is how it improves the cohesiveness of the molding sand. These are the types of the bentonite. One is the southern bentonite and another one is the western bentonite. Southern bentonite is also known as calcium bentonite. It is also known as non-swelling bentonite and its temperature of destruction is 700 degrees centigrade. Coming to the western bentonite, it is also known as sodium bentonite and it is also known as swelling bentonite and its temperature of destruction is 1000 degrees centigrade. Sometime back we have seen that the clay loses its properties when it comes in contact with the molten metal. Yes, these are such temperatures. Say southern bentonite loses its property when it is heated up to 700 degrees centigrade whereas western bentonite it loses its property when it comes in what say when its temperature crosses 1000 degrees centigrade. Once they cross these temperatures they become the their term as the dead clays. Which bentonite to choose? That is the first question. We have seen that there are two types of the bentonites southern bentonite and the western bentonite which bentonite to choose. Calcium bentonite is better known for its ability to quickly develop green properties. It offers better flow than sodium bentonite and lower deformation. It offers lower deformation. A molding sand with calcium bentonite has better ability to flow into the deep and tight pockets around the pattern. That is why the both bentonites can be blended at different ratios to achieve roughly average physical properties. So, we have completed the bentonite. Next we will see the fire clay. So, fire clay is the next what say binder or the next clay among the binders. It is used next to the bentonite. What is this fire clay? It is usually found near the coal mines. The hard black clumps of fire clay are taken out and pulverized for use in the foundry. Since the size of the fire clay particles is very large they give poor or moderate bonding strength to the foundry sand. So, it is used or right usually found near the coal mines. So, this is the typical appearance of the fire clay. Next one we will see the illite. Illite is found in natural molding sands that are formed by the decomposition of mycassious materials due to weathering right. So, it is found in the natural molding sands. Illite is a phylo silicate or layered aluminum silicate. Here also we can see the word phylo. Phylo means layers what say layered and leaf like structures. Illite possesses moderate shrinkage and poor bonding strength than the bentonite. So, bentonite is widely used. Next to bentonite this illite is used. So, this is the typical appearance of the illite. Next let us see the limonite. Limonite is an iron ore consisting of mixture of hydrated iron oxide and hydroxides in varying composition right. So, the chemical composition is FeO, OH and NH2O right. This N varies right and this is the limonite ore and limonite deposit from the mine and here we can see this is the limonite deposit. So, this limonite is another binder used for developing the strength and cohesiveness of the molding sand. Finally, we will see the kaolinite. Kaolinite is a clay mineral with the chemical composition aluminum ALO2, SIO2, O5 and in brackets it is OH4. So, this is the chemical composition of the kaolinite. Next one it is also a layered silicate mineral like bentonite. It is also known as chena clay and this is the what is the typical mine of the kaolin and here we can see this is all the kaolin. Friends till now we are learning about the molding sands and we have seen the molding sand ingredients right. The base sand, the binder, the additives, the moisture, the dead clay we have seen and among this we have covered so far the base sands and the binders. We will continue the remaining ingredients in the next lecture. Thank you.