 In the previous lecture, we have seen the moulding sands and their design. We have seen that the different types of the moulding sands. We see in the green sand and we also see the coarse sand and the next the dry sand, loam sand, facing sand, backing sand and finally the parting sand. We have seen the importance of these different sands we have seen in the previous class, right. Next we have also seen that green sand is the most important sand in the sand moulding. What is this green sand? Green sand means the sand which contains the moisture, when the moisture is present we call it as the green sand. So we have also seen that this is the general composition of the green sand. The green sand contains a base sand, the base sand could be silica sand, zircon sand, chromate sand or the oleven sand and it is present up to say 85 to 90 percent and what is a next ingredient of the green sand is the binder. It is also known as the clay. It presents from 6 to 11 percent. Next one the green sand also contains the additives and these additives are present from 2 to 8 percent. Finally the water is present from 2 to 5 percent. Now these are the ingredients which we mix from our side but after we make the mould after we pour the molten metal what happens? The molten metal comes in contact with the sand. Now the clay with that we are adding or the binder part of this binder becomes inactive when its temperature is raised above 500 degree centigrade or 600 degree centigrade. Then though it is physically present it loses all its properties, binding properties it loses. In such a case we call it as the dead clay. So that is how the dead clay also becomes a component of the green sand. Again this sand we will be reusing. So part of the clay has become dead so we again before we make the further moulds we have to add the new clay and again in that new clay part of that will become dead clay. And like this this dead clay keeps on increasing as we keep on using it again and again. So that is how we have seen that so these are the green sand components. The green sand components are the base sand. Next one next component is the binder or the clay. Next one next component is the additives. Next component water and the final component is the dead clay. This dead clay we are not mixing from our sand but it is forming because of the what is a molten metal that we pour into the mould and part of the clay loses its property that is why it becomes the dead clay. And in the previous class we have seen the base sand. We have seen different types of the base sands. These are the silica sand, zircon sand, oleven sand, chromite sand and aluminum silicate sands. So these are the base sands and we have also seen in the previous class different binders. What are these binders? These are the bentonite, fire clay, illite, limonite, kaolinite. Among these bentonite is the most popular binder or the most popular clay. So because of its popularity instead of using binder or clay people call it as the bentonite. Or in the place of binder they even use the word bentonite. So bentonite has become that much popular. And the next component of the green sand is the additives. Now let us see these additives in this class. These additives water and dead clay we will be learning in this lecture. Now the first question is base sand is present, the silica sand, zircon sand, oleven sand or the chromite sand and we are adding to improve the cohesion we are mixing the what is a binder or the clay and of course to temper the sand we mix the water. Then why this dead clay, sorry why this additive? Why we are mixing additive to prevent the burn on defects? Yes when we pour the molten metal into the mould the molten metal is at an elevated temperature may be for the non ferrous alloys it is about 700 to 800 degree centigrade the pouring temperature whereas for the ferrous alloys the pouring temperature is between say 1600 to 1800 degree centigrade. At such high temperature the molten metal may burn the surface of the mould cavity. In such a case what happens the sand burns, once the sand burns even the surface of the solidified casting burns that is how we get the burn on defects. So this problem has to be tackled, so to minimize this burn on defects we mix the additives. Next one to develop a smooth surface on the casting for that purpose also we add the additives. Now remember that the in the sand moulding the sand mould is made up of sand the whatever this what say surface of the cavity it is composed of the sand grains and these sand grains will have some irregularities and into these irregularities if we pour the molten metal what will happen molten metal solidifies accordingly and even on the solidified casting these irregularities will be there and finally we get a rough casting. So to minimize this roughness on the solidified casting we mix the additives right, so to develop a smooth surface on the casting. Next one to prevent metal penetration defects what is this? Now again the mould is made up of the what say sand grains, sometimes the sand grains will be a little larger, the neighboring sand grains let us consider that are present on the surface of the cavity. Now what happens on the neighboring grains there will be a small clearance will be there. Now into this small clearance the molten metal flows and forms the penetration defects and finally it will be what say forming some kind of fins and unwanted projections on the casting which we do not want, so this is known as the penetration defects. So to minimize the penetration defects we mix the additives. Next one what is the next purpose to prevent the oxidation of the metal from the mould atmosphere. Now we pour the molten metal into the mould the molten metal is at a very high temperature and the oxygen is present in the mould right, oxygen is around the mould, this oxygen will really and quickly come and react with the molten metal and forms the and develop result into the oxidation. Once this oxidation takes place the casting loses all its properties and strength. So at any cost we have to reduce the oxidation that is why we mix the additives. There are some more objectives why we are mixing the additives to create a space between the sand grains to expand without deforming. Now what happens in the moulding sand the base ingredient is the base sand the main ingredient is the base sand. These base sands are the commonly the silica sand, zircon sand, chromate sand or the olivine sand. So these are the sand grains and when we tightly compact the sand around the pattern and we withdraw the pattern. Now what happens the sand grains are close to each other and into this mould when we pour the molten metal what happens each sand grains will be expanding. Now when each sand grain is expanding they will be what say expanding and there is no because they are close to each other there is no provision for the free expansion. Then what will happen the mould deformation takes place. When the mould deformation takes place or the mould enlargement takes place that happens casting cannot what say absorb that kind of development that kind of what say expansion the casting cannot absorb. The casting has already solidified in such a case a crack will form on the casting. So that is the adverse effect of the what say expansion of the sand grains why this is happening because there is no space between the adjacent sand grains. So we mix the eddy tubes. Now what happens between the neighboring grains this eddy tube will come and create a space between the neighboring sand grains. So when these neighboring sand grains are expanding this eddy tube is a soft one. So as they expand the eddy tubes enable them to expand and see that no mould deformation takes place that is why we add the eddy tube. Next one to improve the collapsibility of the mould. Now we add what are the ingredients of the moulding sand. We add the base sand like the silica sand like zircon sand or the chromate sand then we add the clay, moisture and eddy tubes of course right. Now what happens after the solidification we break the sand and we want to take the casting outside again this sand will be taken and it will be tempered with water and again another mould will be made with the same moulding sand. Now the problem comes after the solidification when we want to break the sand sometimes it becomes very hard. This breaking of the sand is known as the knockout. Now if it is too hard to break the sand then it requires what say hard efforts laborious efforts and that increases the cost of the labor that increases the cost of production that increases the what say more time. So at any cost we have to see that the mould is not too hard after the casting has solidified. It should be easily collapsible. It should be easily breakable what to do that is why we add the eddy tubes. There is another purpose why we mix the eddy tubes to stabilize green sand properties like green strength, dry strength, dry compression strength and so on. So when we add these eddy tubes these kind of properties will be enhanced right. So how to achieve this by the addition of eddy tubes like cold dust, wood floor etc. In the moulding sand when we mix the eddy tubes like cold dust, wood floor and starch and so on whatever problems we have discussed earlier will be minimized. So that is the purpose of the mixing eddy tubes. Now let us see the common eddy tubes used in the green sand. One is the cold dust, next one is the dextrin, next one is the pitch and finally the wood floor. Let us see all these eddy tubes one by one. First let us see the cold dust. Cold dust is a fine powder which is created by the crushing, grinding or pulverizing of coal. So this is the cold dust which is obtained by pulverizing the coal. You can see yes after the coal is pulverized so it looks like this. So this is the cold dust. So this cold dust is added to the what is a moulding sand along with the base sand and the what is a clay. What does cold dust do? What happens when we mix the cold dust with the moulding sand? Cold dust acts as a lustrous carbon film on the surface of the mould cavity. As a result a good surface finish is obtained on the casting. Next now we have seen that one of the problems is we use the sand grains and the neighboring sand grains will be projected upwards because of that there will be rough texture on the surface of the cavity. Now when we mix the cold dust with the moulding sand, this cold dust acts like a lustrous carbon film. Now you can see this is the moulding sand, this is the moulding sand. So these are all the sand grains, sand grains. Of course through this way we pour the molten metal. Now what and now this is the mould what is a cavity what is a surface internal surface. Now because we have mixed the cold dust see it has made a lustrous carbon film here you see. Now into this cavity on which there is the lustrous carbon film when we pour the molten metal what happens the irregular surface texture of the sand grains will be no more dominating because there is a lustrous carbon film. Because of that the molten metal what say comes in contact with this lustrous carbon film and surface within that film and we get a smooth casting. So that is the best benefit when we add the cold dust to the moulding sand. We get the very good surface finish. There are more things which this cold dust can do for us. Cold dust increases the strength of the mould by making a coating around the sand grains. Now you see these are all the sand grains. Now this cold dust is forming a thin layer around all the sand grains. Because of that the strength of the sand grains is increasing that is another advantage which we can get by mixing the cold dust to the moulding sand. Now this is another advantage. So what happens cold dust produces carbon monoxide and develops a gas cushion. This prevents metal penetration into the sand grains. Now just now we have seen that these are the sand grains in the mould compacted mould and say this side we have poured the molten metal and the molten metal is coming in this direction means from right side to left side it is trying to come inside. Now see now you can notice there is a clearance between the neighboring sand grains. Here you can see some clearance is there and here you can see some clearance is there and here you can see some clearance is there between the neighboring sand grains and this molten metal is ready to penetrate into these clearance. In such a case we get the penetration defects unnecessary pins on the solidified casting which we do not want and if we have to remove them it takes lot of time and that results in the what say increased production right so which we do not want. Now how to minimize this penetration when we mix this cold dust this cold dust contains carbon and this carbon yes immediately it reacts with oxygen and forms the carbon monoxide and this one side the molten metal is coming from right side to left side it wants to penetrate into the sand grains but here you can see this is the carbon monoxide. This carbon monoxide is pushing the molten metal from left side to right side. Ultimately the molten metal cannot penetrate into the clearance between the sand grains that is how the metal penetration will be minimized. So this is the another benefit which we obtain by mixing the cold dust with the moulding sand. There is another benefit which we can get by mixing the cold dust with the moulding sand. Cold dust produces carbon monoxide and prevents oxidation of the metal. Just now we have seen that carbon monoxide is produced and this carbon monoxide pushes the molten metal which is trying to penetrate into the sand grains that is not the only thing which this carbon monoxide does it prevents the oxidation of the metal. Now this is the liquid metal and this is the mould what say mould and this is the mould cavity surface. Now this molten metal can come and it may react with the oxygen which is present in the surroundings but now carbon monoxide is there. This carbon monoxide causes the reduction it is a reducing agent it would not allow oxidation to take place. So no oxidation takes place because of the development of carbon monoxide. So this is the another benefit which we can get by mixing the cold dust with the moulding sand the oxidation of the molten metal will be minimized. So we have seen the among the editors we have studied about the cold dust and it is what say important what say benefits we have seen. Next let us see the dextrin. What is dextrin? It is an organic additive obtained by the hydrolysis of starch. Dextrin improves the moulding sand properties such as dry compression strength and erosion resistance of mould surface. The sand generally it contains the compression strength in the green state means when the moisture is present it contains the required compression strength but the moment we pour the molten metal all this moisture will be evaporating and it goes out then the moulding sand becomes dry in such a state some sands may not contain or may not develop the compression strength. And when we add the dextrin even after the moisture is completely dried out the sand will continue to possess the dry compression strength. Next one by adding the dextrin we also make the sand to develop what say erosion resistance of the mould surface. Because of the presence of the dextrin it has a resistance against the erosion. As the molten metal is flowing into the cavity it is possible that the mould cavity may erode some sand particles because of the addition of the dextrin this erosion of the sand particles will come down. So that is the that these are the benefits that we can obtain by mixing dextrin which is another additive along with the moulding sand. So this is the typical appearance of the dextrin so this is obtained by the starch. Next one let us see the pitch which is another additive. It is a distilled form of the soft coal it can be added from 0.02 percent to 2 percent in the mould and also in the core sands. It enhances hot strength surface finish and mould surfaces again this is the hot strength just now we have seen that by the addition of the starch what happens by the addition of the dextrin the dry compression strength is improved. Now after some time what happens the sand becomes not only dry but it becomes hot because the molten metal is in touch with the mould what say surface for a long time. So no doubt in the beginning itself it has become dry now it has become hot means its temperature has gone up in such a case it is possible that the moulding sand may not possess the strength in a hot state. But by adding the an additive like pitch we can see that the moulding sand possess the hot strength even at the hot state even at the irritated temperature and also it enables to get a good surface finish on the mould surfaces. So that is the importance and benefit that we can obtain by mixing pitch along with the moulding sand. Next one let us see the last additive among the last additive that is the wood floor this is the wood floor. Wood floor is finely pulverized wood just like we have seen that to cold dust right cold dust is pulverized coal similarly wood floor is the finely pulverized wood right its particle range from a fine powder to roughly to the size of a rice grain. So it looks like this so again say there will be fine powders will be there coarse powders will be there but they look like this. So this is obtained by pulverizing the wood it is relatively what is right it is relatively long thin fibers prevent the sand grains from making contact with one another thus they reduce the mould wall movement just now we have seen that the mould contains the sand grains may be the silica sand grains or the zircon sand grains if they are close to each other they cannot expand because all the grains are expanding finally if they there is no space between the adjacent neighbor say neighboring sand grains there will be deformation of the mould. Now when we mix this wood floor this wood floor its particles will be fine powders sometimes there will be long fibers as long as a rice grain. So they will be placed between the neighboring sand grains and these are soft grains. So when the neighboring sand grains want to expand these soft grains allow the neighboring grains to expand without causing any mould deformation that is how there will not be any mould wall movement when there is no mould wall movement no damage to the casting no crack on the casting. So that is the important benefit that we can obtain by adding the wood floor to the moulding sand. Next one it can be added from 0.05 percent to 2 percent in the mould and also in the core sands. It increases the collapsibility of the mould and the core sands. Just sometime back we have seen in some cases it is very difficult to break this sand after the casting is solidified we have to break this sand this is known as knockout. Sometimes it becomes more efforts it requires more labour. Now what happens when we add this wood floor because of the because this wood floor is very soft it enables easy breaking of the mould after the solidification is over. So it increases the collapsibility of the mould and also the cores and also it improves the flowability. Flowability means its ability to flow around the pattern during the compaction process. So these are the different benefits that we can obtain by adding wood floor in the moulding sand. So far we have seen these are the sand what is the green sand components we have studied the base sand we have studied the binders we have just now we have completed the additives. Next one let us see the water which is the fourth component of the green sand. So this is water right one of the most to right influence element right. So sometimes it contains the cations and sometimes it contains the anions. If there is cation there is development of mould sand properties whereas anions it contains the impurities that affect the bentonite properties or the that affects the binder properties. Now what happens is what kind of water to add in the moulding sand we have seen that water can be mixed from 2 to 5 percent but can it be any water or only a particular water we have to mix. There is a reason we have to add the normal water not the salty water because salt deactivates the bentonite's electrostatic bond properties right. You can see this is the case when normal water is added without means no salt is present in that. Now say this bentonite in the bentonite there is sodium what say ions are there. Now the sodium ions they will be improving the electrostatic bond property of the bentonite. Now let us see the next case this is the polluted water. Let us assume there is some salt is present say for example some sodium chloride. Now what happens we can see sodium ion is there and sodium sorry here is the chlorine ion which comes because of the impurity. Now this chlorine and sodium have got the highest affinity and because of that they come close to each other they make a bond ultimately the electrostatic bond property of the bentonite comes down. That is why a salty water or a polluted water what say what say decreases the electrostatic bond property of the moulding sand or the clay. So we have learnt about the water also we have seen what kind of water to add and we have seen that we should not use the polluted water and we should not use the salty water. Next one the dead clay. So this dead clay is not added what say deliberately from our side. We never add dead clay we add only the right clay or the live clay we add but what happens during the process of pouring so part of the active clay becomes the dead clay because it loses its properties but still it is physically present. So this is known as the dead clay. So this becomes the last component or the fifth component of the green sand. What is this dead clay? The part of the bentonite or the clay heated above 500 degree centigrade loses its structural water and settles itself on the sand grains it loses all its properties. This bentonite loses permanently its properties and becomes a dead clay. Once it loses permanently all its properties but it is physically present then it is known as the dead clay. Whereas the clay which is which has not lost its properties is known as the active clay. That active clay only we add as the binder. Next one at each sand circulation a part of the sand grains is coated by this dead clay. This is known as utilization process. Dead clay reduces the expansion of the green sand and permits to fix a part of the free water in the mound. So this is the dead clay and here we can see high utilization and low utilization. So this is the green sand formula. So we can see here we can see silica sand or we can say this is the base sand plus dead clay will be there. Next one active clay will be there then there will be additives will be there plus water. Now how can we say 100 percent the total green sand is the this one this is the what is a silica dioxide or the what is a silica sand are the any base sand plus DC. DC means dead clay and next component is the active clay and there is another component that is the LOI loss on ignition. Some sand or some clay is burnt and it is lost. So this is the loss on ignition. So that is also countable finally here is the moisture. Proportions of green sand for cast iron. So how to make the green sand for cast irons? So base sand is present from 75 to 85 percent. Active binder or the binder which we add freshly are the active clay is from 6 to 10 percent. Next one dead clay this we are not adding that comes by automatically that is generated during the process of what is a pouring and re what is a molding it is generated it is between 5 to 8 percent. Next one loss on ignition this is also not from our side it is generated or developed this is from 3 to 5 percent finally the moisture is 2 to 4 percent. So this is the proportion of green sand for the cast iron castings. Next one proportion of green sand for steel castings. The base sand is from 75 to 85 percent. Active binder or the binder or the clay the fresh clay is 8 to 12 percent. Dead clay is from 6 to 9 percent. Loss on ignition LOI it is from 2 to 3 percent finally the moisture is 2 to 4 percent sorry the loss on ignition is 2 to 3 percent. Next one metal to sand ratio. Next one just until now we have seen how to prepare the green sand. What are the ingredients of the molding sand we have seen? What are the components of the green sand we have seen? What are the different clays we have seen? What are the different binders? What are the different additives? What are the benefits that we can obtain by mixing the additives to the molding sand we have seen and we have seen the importance of the moisture and the concept of the dead clay we have seen. Now the next question is metal to sand ratio. The molding sand or the green sand is ready may be you are going to make a casting of 10 cages. For 10 cages how much sand is to be used? See again the quantity or the consumption of the green sand must be optimized. It cannot be too much if you use too much more than required it is a loss to the industry. So let us see the optimum metal to sand ratio. For this is the typical say metal to sand ratios for ferrous castings metal to sand ratio is 1 is to 9 means if we are making a casting of weight 1 kg we have to use 9 kgs of green sand. Similarly for nonferrous castings the metal to sand ratio is 1 is to 5 means if we are making a casting of weight 1 kg we have to use 5 kgs of molding sand. Now this is the mixing of the green sand. So how to prepare this green sand? So we have seen that the ingredients of the molding sand are the base sand, the binder, additives and the moisture how to prepare them. So we have to put all these ingredients in the right proportion into a sand muller. So this is known as the sand muller. See you can see here there are 2 rollers are there. Here is one roller and here is one roller and there will be 2 blades will be there. Here is one blade and here is one blade. So all these ingredients will be dumped inside and this will be rotating may be for about 15 minutes and after that say all these ingredients are nurtured thoroughly and we get a very good mixture of this green sand. So this is achieved by putting the ingredients through a sand muller which rolls and stirs the sand. Now after this process is known as mulling. After the mulling is over each sand grain is coated with clay. Each sand grain is coated with additives and moisture. So they are that much what is a nourished and mixed. Next one it can be continuous and batch type muller. Sometimes in some industries this what is a sand mixing is continuous. They keep loading and at the same time at the bottom they used to keep unload and this process goes on or sometimes it can be done in a batch wise. Production may be whenever there is a requirement these ingredients can be kept inside the muller and they can be mixed and that sand can be taken and of sometime again it can be operated. So this can be operated in a batch type and also continuously. And you can see this is what is a bigger muller you can see inside. So this is here the door is opened and here we can see there are so many blades are there. So this is a larger muller sand muller and this is the grain sand preparation system for a large scale right industry. They look like this. Now once this sand is what is a prepared right if it is a small what is a industry it is carried manually. But in a large scale industries this will be carried automatically by the conveyors. There will be pneumatic sand conveyors will be there. So this is a pneumatic sand conveyor through this conveyor the sand will be taken from the molding shop to the or the sand shop to the molding shop and these are all the storage systems. So this is the circulation of the system in a sand casting process and here we can see this is the preparation of the molding sand right. So we are mixing the what is a base sand base sand and the binder additives and the water are mixed here and here we are mixing. Now this what is a mixed grain sand is going to the mold shop and here of course parallely we also make the core. Remember core means an object which is kept inside the mold to create some hollow cavities inside the casting. So here a core is made. So this core is also made and the molding is done and inside the mold the core is kept. Now it is the pouring. Now we do the pouring and after sometime the poured metal solidifies and we will be this breaking the sand. So this is known as shake out or knock out right. Now what happens there will be some sand lost will be there and gas emission will be there here we can see and burning out of the clay and what is a sequel means that is the additive burning of the binder and additive will be there. Then sand losses will be there then we what is a take the casting outside. Now this sand will be again going to the sand preparation shop where it will be again tempered with the water again it will be remixed. The problem is it contains it may contain some unwanted metallic objects inside the sand. May be the penetrated metals or sometimes we use the chills. These chills are some other components metallic components or hard sand lumps may be present inside. So they have to pass through the screening here right and there will be a magnetic separate will be there. So when the sand is what say this what say sand which we obtain from the shake out when it is passing again going to the sand shop it has to pass through the magnetic separator. If there are any unwanted metallic objects are there in the sand they will be absorbed they will be caught by the magnetic separator. Next there will be a screening to screen the very hard what say sand lumps finally it will be cooled down again it will go to the what say sand preparation shop and this is the there is another system parallely and the dust extraction system will be there. So when you what say break the sand when we do the shake out or the knock out lot of dust will be arising. So there has to be a system to tap what say collect the dust. So this is the dust extraction system again the sand continues to what say circulate in the same cycle in between yes people add the what say clay or the binder because part of the clay becomes the dead clay. So remember the typical this is the typical sand balance diagram for the green sand. So remember always there is a sand loss for example let us consider a small case right. So this is the moulding shop and this is the core shop and say for example here 900 tons of moulding sand is prepared on a particular session and here for making the course 100 tons of what say core sand is prepared right. Now it is the mould is made after the mould is made right there will be knock out knock out means after the casting is verified we break the sand we break the sand and take the casting outside this process is known as knock out. Now again this what say it is going to the mill room and you can see we are not getting the 100 percent sand by the time you see it comes to the again moulding shop it is only 95 percent of sand we are getting there will be sand loss will be there right. So best is 5 percent best is 5 percent and again we have to add the new sand generally about 5 percent of new sand is added and along with that a proportionate amount of the what say binder or the clay is also added. Again when you are making the what say or when we are re-tempering the moulding sand. So remember always there is a sand loss in the what say circulation system. Friends with this we are what say concluding this we have learnt about the moulding sand design and we have seen that the moulding sand contains the certain ingredients the moulding sand mainly contains the base sand this base sand can be what say silica sand or chromite sand or zircon sand or the olivine sand. So these are the popular base sands so this is the this base sand is the main ingredient of the grain sand. Next one we add the binder this binder we add to develop the cohesion between the sand grains. So among the binders bentonite is the popular binder and the third ingredient is the additive. Additive is mixed for obtaining several benefits to reduce the metal penetration or to reduce the oxidation or to reduce the mould one moment to improve the collapsibility of the what say sand after the solidification is over or to get a fine surface finish or a less stress finish on the mould coating we add the additives. Next we add the moisture and we have seen that the moisture should not be a contaminated moisture it should be free from the salts. If there are salts are present what happens these salts react with the sodium which is present in the bentonite and they reduce the binding action of the bentonite. And we have also seen that every time when we add the clay part of the clay becomes dead clay after it comes in contact with the molten metal this is known as the dead clay. So every time we have to compensate this so we have to add little more clay every time when we reuse this. So this is all about the grain sand design. Thank you.