 Welcome friends, in our previous lecture we have learnt about continuous casting process. Now today let us learn about centrifugal casting process. Now the question is what is this centrifugal casting process and when it was started. So this was developed by A.G. Eckhardt in England during 1809. Now what is its principle, it utilizes the centrifugal forces caused by rotation to distribute the molten metal to the mould cavities. As the mould is rotating, molten metal will be distributed into the mould cavities. So because of the centrifugal force, the molten metal will be sticking to the mould that is how we get the required geometry of the casting. So this is the simple principle of the centrifugal casting process. Now these are the types of centrifugal casting process. One is the true centrifugal casting process. In this again we have two classifications, one is the horizontal true casting centrifugal casting and the other one is the vertical true centrifugal casting. And the second category is the semi centrifugal casting process and the third one is the centrifuging process. So first we will see the true centrifugal casting process and also the horizontal true centrifugal casting. Now what is this true centrifugal casting process? What is the principle? The mould is rotated about a horizontal or a vertical axis and the molten metal is held against the walls of the mould by centrifugal force until it solidifies. The mould is rotated about a horizontal or a vertical axis. As it is rotating molten metal is held against the walls of the mould. Now true centrifugal casting is used for the production of cylindrical hollow parts. So this is the main application of the true centrifugal casting process. Now here we can see the principle, yes here the molten metal is being poured and this is a metallic mould, a cylindrical metallic mould we can see here. And it is supported using rollers, here there are the top rollers and here there are bottom rollers. As the top rollers and the bottom rollers are rotating even this metallic mould will be rotating. Now it is that time the molten metal will be poured into the mould and during pouring the what is a mould will be rotating at a predetermined speed. And this rotation continues till the molten metal inside this what is a metallic mould solidifies. After solidification the rotation of the mould stops then we get the solidified cylindrical hollow casting. So this is the motor which drives the metallic mould. And here we can see the mould details of this setup and here we can see this is the ladle and this is the pouring basin. And here we can see this is the metallic what is a metallic mould this is the cylindrical metallic mould. And here we can see these are the bottom rollers on which the metallic mould is supported and these are the top rollers. Now this is the metallic mould and yes we can see as the molten metal is being poured the metallic mould will be rotating. And this rotation continues till the solidification of the molten metal will be over after that yes we can stop this rotation of the metallic mould then what happens we get a finished casting like this this is a hollow what is a cylindrical casting. So this is an example of the centrifugal casting process and here we can see the animation. So this is the metallic mould the cylindrical mould and here the molten metal is entering as it is entering the molten what is a metallic mould will be rotating and the molten metal will be sticking to the walls of the mould and the rotation continues till the molten metal solidifies then what is a metallic mould will be what is a detached and we get the solidified casting. So long parts are produced using horizontal centrifugal casting process and here this is the what is a true photograph of a true centrifugal casting process here we can see this is the metallic mould this is the metallic mould and this is the what is a ladle through which molten metal is coming to the cylindrical metallic mould. And here we can see these are the bottom rollers and here is one roller and here is another roller on the other side also there will be two rollers and at the top also sometimes there will be rollers and as these rollers are rotating the metallic mould will be rotating it is that time the molten metal will be entering into the metallic mould cylindrical metallic mould. So far we have completed horizontal true centrifugal casting now let us see the vertical true centrifugal casting process. Now why we should go for the vertical true centrifugal casting process why not the horizontal true centrifugal casting process this is used for heavy parts whose diameter is more important than the length at such times we use the vertical true centrifugal casting process. The principle is the same there will be a cylindrical mould will be there and it will be rotating but here the diameter is more important than the length and here we can see this is the rotating what is a mould and the molten metal is being pulled as the molten metal is entering into the mould the mould will be rotating and this rotation continues till the molten metal solidifies inside the mould what is a metallic mould. And here we can see the animation yes this is the metallic mould vertical and it is rotating about a vertical axis and the molten metal is coming like this because of the centrifugal force and it will be going to the sides of the mould it will be going towards the walls of the mould and this rotation continues till the molten metal solidifies. Now true centrifugal casting is carried out as follows first step is we have to apply the syrimic slurry to the mould wall because it is possible that the molten metal may stick to the metallic mould. So that should not happen to prevent this we apply a syrimic slurry to the mould wall and it should be dried and also it should be baked. Next step is rotation of the mould at a predetermined speed and it can start from 300 rpm to and it can go up to 3000 rpm then once this what is a mould what is a keeps on rotating at this predetermined speed we have to pour the molten metal into the mould and most surprising thing is here no gating system is required. We have seen the design of the gating system for a sand mould and also what say we have seen the die casting here no gating system is required. The mould is stopped after the casting has solidified till the time the mould has to rotate. Then the next step is extraction of the casting from the mould and finally the next step final step is the finishing means what is that removal of impurities at the centre using machining grinding or sandblasting. Now in the molten metal there will be some impurities will be there. So these impurities will be subjected to lesser what say centrifugal force as the mould is rotating the particles having lesser dense are subjected to lesser centrifugal force so that is how they are collected at the centre. So these are to be removed using machining, grinding or the sandblasting. Now what are the advantages of the true centrifugal casting process? Flexibility in casting composition of course there is an exemption right. So maybe that exemption is for 0.4 to 0.85 carbon due to segregation. The next advantage is the wide range of available product metallurgical characteristics. We can get different types of the hollow what say cast components and also we can get what say different metallurgical features and can form very large parts. The next advantage is central core is not required for making a hole or pipe and we know that in the green sand casting if we want a hollow casting or if we want a hole inside a casting we used to place a core. So this core has to be made and that should be carefully kept inside the mould then we have to pour the molten metal. That is not enough after solidification we have to separate the moulding box, we have to what say break the mould then we have to separately remove the core. So all this headache is not there in the case of the true centrifugal casting process. We get the hollow cast components, we get the holes inside the cast components but no core is required that is the advantage. Next one, employments of gates and risers is not required, no gating system is there we have seen that is why that is how 100 percent casting yield in many cases. Now the question is what is this casting yield? Let us see this is the definition for the casting yield. Casting yield means it is the ratio of weight of the casting divided by weight of the poured metal hole multiplied by 100. Remember that weight of the casting is not equal to the weight of the poured metal. If the weight of the casting is 100 cases we always pour more than 100 cases may be 125 cases or 130 cases. So weight of the poured metal is always greater than the weight of the casting. So this is the casting yield, casting yield means weight of the casting divided by weight of the poured metal multiplied by 100. So this should be maximum if the industry has to get benefit. So in the case of the green sand casting the casting yield will be say between 70 to 80 percent but it is never 100 percent. But here we get close to 100 percent because there is no gating system as the molten metal is consumed for the gating system there will be what is this casting yield will be coming down. Next one relatively very light impurities move towards the center which can be removed easily. Now the question is how to what say remove the impurities if it is the green sand casting the impurities will be inside the casting. But here the impurities are subjected to lesser centrifugal force because of that they will be segregated to the center. Now after solidification yes they can be identified and they can be removed by machining or by brushing or chipping. So impurities removal is easier in the case of the centrifugal casting process. Next one fettling costs are reduced fettling means unwanted what say elements if there are any such elements we need to remove them like cutting up the gating system riser. So these are the fettling what say process. So these are reduced first of all there is no gating system. So fettling costs are reduced and little scrap is generated cost of production is less. Now these are the disadvantages or the drawbacks of the true centrifugal casting process. First one is suitable only for axial symmetrical components only for axial symmetrical and for making hollow components not for all the components. Second disadvantage is more segregation of alloy component during pouring under the forces of rotation. Now this is another drawback of the centrifugal casting process if the what say generally we use the alloys. Now in the alloys there will be different elements will be there. If the density of different alloying elements or what say almost close there is no problem. It is possible that the density of one alloying element will be very high and the density of another alloying element will be very less. At such times what happens the element having highest density will be subjected to larger what say centrifugal force and the element having the lesser what say density will be subjected to lesser centrifugal force. Then what will happen the element having the lesser density it will be moving towards the axis or the center of the casting and the elements having the higher density will be subjected to higher centrifugal force and they will be moving away from the center of the casting. That is how there will be segregation of the alloying elements in the centrifugal casting process. So, this must be handled very carefully. Next one secondary machining is often required for inner diameter yes inside the inner surface of the casting all the impurities will be collected because they are subjected to lesser centrifugal force. So, these are to be removed sometimes the machining is required. Next one centrifugal castings require very high investments that set up is very costly and expensive. Next one skilled labours are to be employed for this process right because the mould is to be rotated at a predetermined speed and it all depends upon what say a temperature for a particular temperature or for particular alloy it has to be what say rotated at different what say speeds. So, this all what say comes by experience. So, to operate this set up experience and skilled workers are required that is how the process will be costly or it becomes what say expensive. Next disadvantage is the inaccurate internal diameter and finally, it the another disadvantage is the long lead time may happen. So, these are the drawbacks are the disadvantages of the true centrifugal casting process. Now, what are the applications of true centrifugal casting process? Manufacture of pipes, bushings, nozzles, bearings, inner liners for IC engines, bimetal, steel, bronze, bearings and so on. Now, what are the materials cast alloy steel, carbon steel, cast iron, stainless steel, aluminum, copper, nickel. Now, let us see the part size diameter varies from 0.25 meters to 3 meters. You can see the diameter can be 3 meters means very large and length up to 15 meters and weight up to 5 tons means small castings can be made and very big castings can be made. Now, these are the components produced by true centrifugal casting process. You can see here these are the hollow what say tubes or the hollow components cast components are produced by true centrifugal casting process. We will see some more yes these are the tubes or the components produced by true centrifugal casting process. First one again these are the components produced by true centrifugal casting process. Again these are also the components produced by true centrifugal casting process. Again we can see here these are also the components produced by true centrifugal casting process. Now, bimetalic pipes using centrifugal casting process. Bimetalic pipes can be produced by centrifugal casting process and some bimetalic combinations are as follows. we can see here. So, these are the outer layer what say alloys and these are the inner layer. For outer layer it you can see 5 percent chromium steel and for inner layer it is stainless steel. For outer layer stainless steel and for inner layer mild steel, for outer layer mild steel and inner layer copper. For outer layer mild steel and for inner layer aluminum, for outer layer it is copper and for inner layer it is GCI and for aluminum outer layer and the inner layer is GCI, outer layer is stainless steel and the inner layer is GCI, outer layer is mild steel and inner layer is nickel hard steel. Now second metal is poured inside the mould after some time and this time lapse after solidification for the first metal and before pouring of the second metal is calculated by D is equal to K root of T, where D is the thickness solidified and K is the solidification constant and T is the time. So far we have seen true centrifugal casting process and the two subclassifications within that. Now, let us see the semi centrifugal casting process. Now what is this semi centrifugal casting process? Semi centrifugal casting manufacture is a variation of the true centrifugal casting process. Yes here also the centrifugal force will be applied on the mould and also on the molten metal, but there is a variation. What is that variation? What is that difference? The main difference is that in semi centrifugal casting process the mould is filled completely with molten metal which is supplied to the casting through a central sprue. In the case of the true centrifugal casting process, yes no doubt the what say there is a cylindrical mould and it is rotated, but finally the cast component will be hollow, there will be a hole inside, but here in the case of the semi centrifugal casting process we would not get the hollow components that is the main difference. You see again let us see in the main difference is that in the case of the semi centrifugal casting the mould is filled completely with the molten metal. The forces generated by the rotation of the mould ensure the distribution of the molten material to all regions of the casting because of the forces generated by the centrifugal force the molten metal will be what say uniformly distributed into the mould. And here we can see yes this is the revolving table will be there and this semi centrifugal casting process in this process the mould will be rotating about a vertical axis always and here there is a revolving table is there and here we can see this is the moulding box. Moulding box means yes there will be drag, drag means lower moulding box and there will be a cope there will be means the upper moulding box and here there is the pouring basin pouring basin and this is the mould cavity and as the mould is rotating about a vertical axis the molten metal is being poured into the mould. Then what happens as the mould is rotating molten metal is entering the molten metal will be subjected to the centrifugal force. So, it will be going away from the centre if there are any minute details tiny details on the sides of the casting yes molten metal will be definitely entering into those tiny features. So, that is the advantage of the semi centrifugal casting process and here we can see so this is the pouring basin and this is the cope and this is the drag and here we can see a component produced by the semi centrifugal casting. So, this is the wheel with spokes and here we can see this is the pouring basin and here internally we can see there are rips are there narrow rips are there. If we cast this component using ordinary what is a sand casting process no doubt the outer part we may get, but the internal rips it may not be possible for us sometimes there will be some discontinuities will be there, but these discontinuities can be overcome using the semi centrifugal casting process because of the centrifugal force that is falling on the molten metal. So, even this what is a place where there are there may be some discontinuities there also molten metal will be successfully flowing and this is the semi centrifugal casting setup. Advantages of semi centrifugal casting process in this number of modes can be stacked together one mode over the other can be fed by a common central sprue in order to produce more than one casting at a time means one mode can be placed over another mode and all these can be connected by a central sprue common sprue and the molten metal can be supplied to all these modes at a time means at a time we can produce more than one casting. Second advantage is similar to true centrifugal casting and hence it ensures purity. Poor structure forms at the center of the casting so this can be machined if there is any what is a impurity again that will be collected at the center and that can be machined off. These are the applications of the semi centrifugal casting process wheels you can see this kind of wheel. So, this is manufactured by semi centrifugal casting process pull is you can see here these are the pull is. So, these pull is are manufactured by semi centrifugal casting process. So far we have seen the true centrifugal casting process and the subclassifications within that then we have seen semi centrifugal casting process. Now, let us see the third classification of the centrifugal casting process that is the centrifuging process. What is the centrifuging process and what is its principle? In centrifuging casting manufacture modes employed to produce the desired castings are arranged around a central sprue. Here several castings at a time are manufactured within a using a single mode. If it is the true centrifugal casting process or the semi centrifugal casting process only one casting in a one mode, but here within a single mode there will be more castings. So, that is the special feature of the centrifuging process. These modes contain all the necessary geometry for the cast parts as well as the gating system. Runners travel from the central sprue to the mode entrances. This provides a means of increasing the filling pressure within each mode and allows for reproduction of intricate details. Centrifugal casting is often used in conjunction with investment casting process. Because investment casting process involves manufacture of what is a tiny what is a castings. Sometimes castings with internal not internal tiny features intricate ships in which it is very difficult for the molten metal to enter or in to penetrate. At such times we use the centrifuging process. Then what happens as the mold is rotating because of the centrifugal force that is falling on the molten metal. The molten metal will be passing through the tiny details. It is used it is also used with molds made up of silicone rubber with sufficiently higher temperature resistance for repeated use in casting without mold deterioration. So, this process is known as the spin casting means same thing, but here the molds are made up of silicone rubber. In such a case we call it as the spin casting and cast materials for spin casting include zinc base alloys, lead base alloys, tin base alloys, aluminum and plastics. Now here we can see the what is a setup. We can see here there is a again this also what is a carried out about a vertical axis similar to the true what is a semi centrifugal casting process, but what is the difference between the semi centrifugal casting process and the centrifuging in the case of the semi centrifugal casting process. There will be a one mold will be there and it will be rotating about a vertical axis, but only one component is manufactured using one mold, but here there is only one mold, but there will be more components will be there. For example, this is one component, this is another component and this is another component, this is another component means all along the circumference there will be several what is a what is a mold cavities will be there each cavity meant for one casting. So, all these are cast at a time all these are joined. So, after the solidification we have to remove we have to cut and we get so many castings at a time and here we can see more details you can see here this is the central sprue and here this is the one casting this is one casting this is one casting this is one casting likewise there are several castings are connected to this central sprue. Now when we pour the molten metal as the molten metal is entering into this central sprue it will be rotating the mold will be rotating and because of that there will be centrifugal force sub applying on the molten metal and because of that because of the centrifugal force falling on the molten metal they will be passing through the tiny what is a cavities. What are the advantages of centrifuging process? Ensures better quality castings when generated on large scale will be economical just now I have told you in the case of the centrifuging process using a single mold several castings can be made with one sprue several castings can be made at a time. So, that become that is economical castings when generated on large scale will be economical. These castings generate high yield because for several castings there is only one central sprue. So, the what is a molten metal consumed for the gating system is very less that is how casting yield will be higher. The castings obtained by this method cannot be satisfactorily obtained by other casting methods. The what is a filling up of the mold by the molten metal is excellent because of the centrifugal force falling on the molten metal. Next one cleaning and fettling cost of the castings can be reduced denser castings having physical properties similar to those of the forged products. Next one rejection of percentage is very low because most of the castings are sound castings no discontinuities. Next finally easy way to achieve directional solidification. This directional solidification we have already learnt so I do not want to repeat again. Now let us see the centrifugal force centrifugal force acting on rotating body is C f is equal to M e square by R where M is equal to mass in kilograms V is the peripheral speed meters per second R is the radius in meters. Now gravitational force G f is equal to M g where g is the acceleration due to gravity meters per second square g factor is equal to C f divided by G f that is equal to M e square divided by R into M g that is equal to V square by R g. Solving further we get N is equal to 42.3 root of g factor divided by T. So this is the what is a formula for the what is a speed that is to be what is a operated. Now expected requirements of a centrifugal casting machine what are the what is a requirements? The machine must be able to accelerate the mould to a predetermined speed, maintain smooth spinning and this decelerate to a stop in a reasonable time frame. There must be a way to heat and coat the mould before pouring the molten metal. Otherwise what happens the molten metal may stick to the mould. So to prevent this we have to give a ceramic slurry coating this must be dried and this must be heated and also it must be baked. So thus that much provision must be there within the machine. There must be a means to pour the molten metal safely into the rotating mould at a controlled rate position and orientation. There must be a means of adding inoculants or fluxes for some special applications. The role of the inoculants and the fluxes we have already seen. So even this centrifugal casting machine should have means of adding these inoculants and fluxes. Once the molten metal is poured a proper solidification and cooling rate must be established in the mould to obtain a desired casting microstructure. Next one there must be a means of extracting the solidified casting quickly from the mould at elevated temperatures without deforming the casting. Common mould materials first the most common mould material is the metallic permanent moulds. So these are widely used. Next one refractory lined metal moulds. Next one sand lined metallic moulds and finally graphite moulds. The metallic permanent moulds are most widely used because of their reusability. Great casting geometry and high productivity. So these are the common mould materials among these metallic what is a moulds are widely used. Now let us see the defects in the centrifugal casting process. So these there are three types of major defects in the centrifugal casting process. One is the segregation banding, second one is the reining, third one is the vibration defects. First let us see the segregation banding. Bands are annular segregated zones of low melting constituents such as eutectic phases, oxide or sulphide inclusions. So these are the segregation banding. It occurs in true centrifugal casting generally where the casting wall thickness exceeds 50 to 75 millimeters. Banding is more prevalent in alloys with a wide solidification range. Minor adjustments to the casting operation variables such as rotational speed, pouring rate and metal mould temperatures will usually reduce or eliminate this defect. Now let us see the second defect that is the reining. Now what is this reining? Reining is a phenomenon that occurs in horizontal centrifugal casting process. If the mould is rotated at too low speed or if the metal is poured into the mould too fast the metal actually rains or falls from the top of the mould to the bottom. Just like rain the molten metal will be falling down. Why this is happening? Too low speed of the mould or too high speed of the pouring of the molten metal. So these are the main reasons for the reining of the molten metal from top to the bottom. So proper process control can eliminate the reining. So that is why sometime back we have seen that to operate this process skilled labours are required. Only those skilled people know at what rotation there will not be any reining. So if the mould rotation is too low there will be reining or if the rate of entry of the molten metal is too high that time also there will be reining. So these can be controlled by experience. That is why experienced and skilled workers are required to operate this machine. Finally let us see the vibration defect. What is this vibration defect? Vibration can cause a laminated casting and it can be reduced to a minimum by proper mounting, careful balancing of the moulds and frequent inspection of rollers, bearings and other equipments. So using what is a these parameters we can minimize the vibration defects. Now recent trends in the centrifugal casting process. Combustion synthesis in centrifugal casting it is used to fabricate inter metallic components metal and the other one is the ceramic layered components. So to make to fabricate inter metallic components this centrifugal casting process is used in which there will be what is a combustion based synthesis will be taking place. And here we can see this process in details using a diagram. So this is the combustion synthesis in the centrifugal casting process. So here we can see this is the reactor and this is the sample container and this is the igniter which what is a initiates the combustion. Now this is the reactant mixture. Now what will happen when this reactant mixture because of this igniter what is a will be reacting and there will be combustion inside the chamber and because of that as we have seen previously we can fabricate inter metallic components means where one layer is made up of metal and the other layer is made up of ceramic layered components. So this is the recent trend means using the combustion synthesis in the centrifugal casting process. And the next one is the using a yes in the previous case we were using the combustion and instead of combustion why not to electrical heating. So that is the next what is a development in this process and here we can see yes this is the green compact and this is the mould part and third one is the alumina container this is the alumina container and the fourth is the heating coil this is the heating coil means this is heated using electricity. Fifth one is the thermocouple and sixth one is the inertial container this is the inertial container seventh one is the outer steel container eighth one is the electric source this is the electric source and the ninth one is the graphite brush this is the graphite brush and the tenth one is the slip ring this is the slip ring. Now the principle is same we want to manufacture what is a bimetallic parts or the case place where there will be components where there will be metal ceramic layered components will be there. Now using the electricity what and there is a coil heating coil this will be heated up and here there is a green compact is there and because of that green compact yes this will be heated up and we get the required component required component means one layer will be metal and the other layer will be ceramic layered component. Now with this we are coming to the end of this lecture we have seen the principle of the centrifugal casting process and we have seen what is a branch classification of the centrifugal casting process. One is the true centrifugal casting process the other one is the second one is the semi centrifugal casting process and the third one is the centrifuging process. In the case of the true centrifugal casting process there will be either horizontal mould or a vertical mold will be there and these will be rotating at a predetermined speed and the molten metal enters into these molds, but in this case we get a hollow component or a cast component with a hole inside. So that is the specific feature of the true centrifugal casting process and we have seen the semi centrifugal casting process. What is this? This is a variation of the true centrifugal casting process and the mold always rotates about a vertical axis, but what is the difference between the true centrifugal casting process and semi centrifugal casting process? In the case of the true centrifugal casting process, we always get a hollow cast component or a cast component with a hole inside whereas in the case of the semi centrifugal casting process we get a, there won't be any hollow what is a cavity will be there. We always get a, the means the molten metal is always completely filled with the what say by the mold and the third one we have seen that is the centrifuging process. In the case of the, in both these two cases semi centrifugal casting process and the centrifuging process the mold will be rotating at a about a vertical axis. Then what is the difference between semi centrifugal casting process and the centrifuging process? In the case of the semi centrifuging casting process, yes there will be a mold will be there and it will be rotating about a vertical axis, but only one cast component can be produced using a single mold, but in the case of the centrifuging process using a single mold several castings can be made and again in the case of the semi centrifugal casting process the what say cast component will have a symmetrical geometry whereas in the case of the centrifuging process the cast components may not have a symmetrical geometry. So that is the difference between the semi centrifugal casting process and the centrifuging process. So with this we are completing this lecture and we will meet in the next lecture. Thank you.