 Good morning friends. In the previous classes, we have seen how to design the razoring system. Now, today let us see how to design the gating system. So, today our lecture, the title of our lecture is design of gating system. First of all, what is meant by gating system? It refers to all the sections through which the molten metal passes while entering into the mould cavity. This is the gating system, this is the pouring cup. We pour the molten metal through the pouring cup. The molten metal flows into the sprue, the vertical passes, then it falls into the sprue well, then it passes through the runner, the horizontal passes, then it passes through the gate. Of course, here there is a side razor, then this is the casting cavity, mould cavity and this is the top razor. Finally, the molten metal passes through the sprue, it passes through the runner, it fills the cavity and it raises through the razor. All the sections through which the molten metal passes while entering into the mould cavity is known as the gating system. Gating system means it is the group of elements through which the molten metal passes while entering into the mould cavity. Gating system includes the pouring cup, it includes the sprue, it includes the sprue well, it includes the runner, it includes the gate and so on. Here we can see another what is a casting and with another gating system. So this is the, you can see this is the casting, this is the casting and here we can see a core and this is the side razor and this is the pouring basin and this is the sprue and this is the sprue well and this is the runner. So this whole system is the gating system means all the sections through which the molten metal passes while entering into the mould cavity is the gating system. Now what are the functions of the gating system, why gating system, what are the functions of the gating system, these are the functions of the gating system to fill the mould cavity completely before freezing. So that is the first function, before the solidification commences the molten metal has to fill the cavity perfectly without any gap that is the first function of the gating system. Next one to minimize the turbulence, it is possible that while the molten metal is entering into the mould cavity it may cause turbulence because of that it may erode the sand particles and in which case there will be casting defects will be there. So there should not be any turbulence while the molten metal is entering into the mould cavity. So this is the second function, there should not be any turbulence or the turbulence should be minimized that is the function of the gating system. Next one to avoid the erosion, yes while the molten metal is entering into the cavity it should not erode the sand, moulding sand. Next one to remove the inclusions, yes there will be some foreign particles will be coming along with the molten metal, the sources may be different they may be carried through the what is a ladle in the molten metal or they may come in the moulding system. But whatever be the case the inclusion should be eliminated that is the another function of the gating system. Next one to regulate the flow of molten metal, what does it mean the speed should be optimum the speed should not be too much at the same time the speed should not be too slow that is the regulating of the flow of the molten metal. Next one to consume least metal so that there will be less scrap, while designing the gating system the system should be such that it consumes the least liquid metal minimum quantity of the liquid metal so that there will be less scrap. One should remember that when we are designing the gating system the molten metal fills the entire gating system. But what is required for us only the casting afterwards the metal solidified in the riser will be cut and it will be removed the metal solidified in the pouring basin the metal solidified in the sprue the metal solidified in the runner all this will be the scrap we will cut and remove. So since all these what see elements are going to become scrap of solidification they should consume least molten metal or minimum molten metal. Next one to establish the directional solidification, directional solidification means what does it mean the point away from the riser should solidify first slowly the solidification should propagate towards the riser this is the directional solidification. So a good gating system should enable the or should establish the directional solidification. Now these are the elements of the gating system first element is the pouring cup second element sprue third element sprue well fourth element runner fifth element runner extension sixth element ingates these are also known as gates and finally even the riser is also considered as the one of the elements of the gating system. But design of the riser we have already seen in the previous classes. So in this lecture we are going to concentrate on the pouring cup sprue sprue well runner runner extension and ingates. Now let us see this gating system so this one is the casting this rectangular one block is the casting and here we can see this is the sprue the sprue is a what say vertical passes here we can see the diameter of the sprue at the top is more and the diameter of the sprue at the bottom is less it is a tapered one. Now here the smallest diameter of the sprue at the bottom is known as choke. Now this is the runner the horizontal passes is the runner so the molten metal is entering like this then it will be flowing along the runner like this. Then after flowing into the runner this is the ingate it flows through the ingate. Next one another stream is there this another stream flows through this ingate. So these are the this is one ingate and this is another ingate and this is the top riser. Now here we come across another element that is the runner extension here we can see the molten metal enters through the sprue and it passes through the choke then it passes through the runner and it enters into the ingate like this. Then what is the purpose of this element runner extension because the first molten metal carries certain slags and impurities. So straight away they will be flowing into the runner extension. After these runner extensions are filled with the first molten metal which includes the scrap sorry which includes this slag and other impurities they will be trapped in this runner extension. Next one the next coming molten metal flowing through the will be flowing through the ingates. So that is the purpose of the runner extension. Now let us see the design of the pouring cup how to design the pouring cup. Now here we can see this is a molding box and this is the cope and this is the drag this is the what say here we can see a pouring cup is there this is manually cut pouring cup. In most of the cases in small scale industries and also in some medium scale industries these pouring cups are cut manually. So there are no certain what say hard and fast tools how to cut these pouring cups but these are cut manually but what is the limitation sometimes one may cut too large or sometimes one may cut too small and there are some ceramic pouring cups are also available. We can see here in different shapes and in different sizes. We can see so this is one ceramic cup and this is another ceramic pouring cup and this is another one and this is another one. So they are available in different shapes and different cross sections and also in different sizes. Now these what say ceramic pouring cups have got one specific advantages. They have got the anti swirl bars are there inside. Here we can see there is an anti swirl bar is there just a thin projection upwards. Now what happens when we pour the molten metal in this process it is possible that the molten metal can cause a vortex it may swirl inside the pouring cup and with the swirling is still in progress it may go inside the sprue and also into the mould cavity then what happens if the molten metal is continuously swirling it will erode the moulding sand. So we want to minimize this what say erosion and also we want to minimize the swirling of the molten metal for that purpose here there is an anti swirl bar is there. Now because this bar is there this is a thin projection upwards as the molten metal tries to cause a vortex or as it is about to swirl this anti swirl bar what say prevents and resists the swirling of the molten metal thus the turbulence is minimized. So that is the advantage of these ready made ceramic pouring cups. Now these are the typical dimensions of the pouring cups. Here we can see round inlet and round outlet is there here we can see round inlet and round outlet again they are available in different dimensions. So we can see in one case it will be the inlet diameter the inlet diameter will be 51 centimeters this is the inlet diameter and the outlet diameter the bottom one will be 25 mm the inlet diameter will be 51 mm outlet diameter will be 25 mm and the height will be 38 mm and in another case it will be high inlet diameter will be 127 mm outlet diameter will be 64 mm and the height will be 133 mm. And in another case the inlet diameter will be 203 mm, outlet diameter will be 76 mm and the height will be 140 mm. And in another case the inlet diameter will be 254 mm, outlet diameter will be 102 mm and the height will be 203 mm. So depending upon our requirement we can choose any of these pouring cups. So this is all about the what is a round inlet and round outlet pouring cups. There is another type. Here we can see square inlet and round outlet, square inlet and round outlet. And what are the dimensions? The inlet dimensions are 78 into 90 mm, outer diameter will be 33 mm, height will be 117 mm. And in another case the inlet dimension will be 105 into 134 mm, outlet diameter will be 38 mm, height will be 127 mm. And in another case the inlet dimension will be 140 into 159 mm, outlet diameter will be 51 mm, height will be 152 mm. So we have completed the pouring cup. There is not so much to learn about the pouring cups. Either one has to go for the manually cut pouring cups or the ready made ceramic pouring cups. Next one let us learn about the sprue. What is sprue? Sprue is the vertical passes inside the mould through which molten metal from the pouring basin reaches the runner and eventually the mould cavity. So here we can see this is the pouring basin. Here we pour the molten metal then it passes through the sprue and it falls into the sprue well then it passes through the runner and finally it fills the cavity. So sprue is the vertical passes inside the mould through which the molten metal from the pouring basin reaches the runner and eventually the cavity. So this is the sprue. Rules for design of the sprue. How to design the sprue? What are the rules we have to follow while designing the sprue? The size of the sprue should be optimised to limit the flow rate of molten metal. So that is the first rule. The size of the sprue must be optimised. Second rule is vertex formation tendency in the sprue with circular cross section is higher. Just now I told you the vertex formation means the molten metal used to watch a swirl inside the pouring cup and also the sprue. And what happens? Because of that there will be turbulence. So this is the vertex. So in a circular cross section sprue it is higher. Hence rectangular cross section sprues are better than the circular what say once with the same cross sectional area. Compared to the circular cross section sprues rectangular cross section sprues are better or the square cross section sprues are better. But however round sprues are more economical for small castings. If the casting which we are going to produce is a smaller one so whether we use the what say round what say circular sprue or the rectangular sprue it hardly makes any difference. But when we are making a very large casting and that time if we go for a rectangular sprue it would be beneficial. Next one height of the sprue is determined by the casting and top pressure height. Next one the fourth rule sprues should be tapered by approximately 5 percent to avoid aspiration of the air. The sprue is always tapered it is never a perfect cylindrical what say element. The diameter of the sprue at the top will be more and the diameter of the sprue at the bottom will be less. And this taper should be approximately about 5 percent. Next one standard filter should be placed at the outlet of the sprue or the sprue well as the molten metal flows into the runners. So standard filters are available to what say filter the impurities. Now these filters should be what say placed at the outlet of the sprue or the sprue well. Next one the sprue should be located centrally on the runner within equal gates on each side. So it should be centrally located on the runner so that on both sides there will be equal number of gates are the ingates. Now we will be learning about one law that is known as the law of continuity of mass. What is this law of continuity of mass? It states that the rate of flow of mass of the fluid is constant at any cross section. So if m is the what say mass of the fluid that is flowing at any cross section then m is equal to rho a1 b1 or that is equal to rho a2 v2 or that is also equal to rho a3 v3 where m is the rate of flow of mass. And a1 is the area of cross section at point 1 here that is the area of cross section. a2 is the area of cross section at point 2 here this is the area of cross section at point 2 so this is the a2. Next one a3 is the area of cross section at point 3 so this is point 3 so this is the area of cross section at point 3. Next one V 1 is the velocity of liquid metal at of metal at 0.1. So, here what is the velocity of the metal. So, this is the V 1 and this is the 0.2 and here what is the velocity of the metal molten metal. So, that is the V 2. Next one this is the 0.3. Now, what is the velocity at this 0.3? This is the V 3. Now, the law of continuity of mass says that m is equal to rho A 1 V 1 that is equal to rho A 2 V 2 that is also equal to rho A 3 V 3. Now, if we calculate the volume rate of flow then how this expression would become. First of all what is volume mass divided by density. Now, this in this same expression we divide this by density then what will happen this rho will be eliminated then this expression would become q is equal to A 1 V 1 that is equal to A 2 V 2 that is also equal to A 3 V 3 where q is the volume rate of flow. Just now we have seen that q is equal to A 1 V 1 that is equal to A 2 V 2 that is also equal to A 3 V 3 then V 2 is equal to root of 2 G H B and V 3 is equal to root of 2 G H C. What is this H B? H B means this height of 0.2 similarly V 3 is equal to root of 2 G H C. What is H C? Height of 0.3 you see this is 0.3. So, this is H C this is H C. So, this is the pouring cup this is the pouring cup and this is this proof and this is the exit of this proof which is also known as the choke. Now, A 2 by A 3 from these 2 expressions we can get A 2 by A 3 is equal to root of H C divided by root of H B. Now, from this expression what we can learn? A 2 by A 3 is equal to root of H C by H B. H C is a larger quantity you see H C is larger quantity and H B is a smaller quantity both are the heights here we can see. Now, what is A 2? A 2 is the area of cross section of the sprue at its entrance. What is A 3? Area of cross section of the sprue at its exit. Now, A 2 by A 3 is equal to root of H C by H B means what does it mean? A 2 by A 3 is equal to H C by H B means this ratio is greater than 1 because H C is a what is a larger quantity and H B is a smaller quantity. What does it mean? H A 2 by A 3 is equal to greater than 1 means what does it mean? A 2 or the area of the cross section at the sprue should be larger and A 3 that is the area of the cross section at the exit of the sprue must be smaller. So, that is the interpretation of this expression. So, as the liquid flows down the cross section of the fluid decreases. So, the tamper is provided to the sprue. So, that is why a tamper is always provided to the sprue. Next one liquid loses contact if the sprue is straight which could cause aspiration. If that a sprue is totally a straight one then what happens? Even if we keep a straight sprue the liquid will be taking a tamper inside. Now, as you go to the bottom of the sprue there will be a clearance between the flow of the metal and the wall of the mould. So, there is a clearance there is a gap. So, the air will be entering. This phenomenon is known as the aspiration. What is here? We can see this is the aspiration in sprue. Here we can see three cases we can see here. The natural flow of a free falling liquid it will be like this. Here we can see the area of cross section is more and as we are coming down the area of cross section is less. Next one what happened here? We have arranged a sprue a totally straight sprue is there then what happens? Even if we arrange a totally straight sprue cylindrical sprue what will happen? Still at the bottom it will be occupying a lesser cross section means here there is a gap and this is the mould wall. This is the mould wall this is the mould wall and here is a gap at the bottom because there is gap at the bottom air enters. So, that is the what is a air aspiration. Now, what is the remedy for this? The sprue should be tapered as we see in the third case. Here we can see the sprue is there and it is tapered because it is tapered even the molten metal by default it will be taking lesser cross section at the bottom. So, there is no clearance at the bottom between the mould wall and the flow of the molten metal. Hence, there is no chance for the aspiration. Next one let us see the design of the choke. The smallest area that occurs at the bottom of the sprue is known as the choke area. First of all what is meant by choke area? Here we can see this is the pouring cup and this is the sprue and this is the entrance of the sprue and this is the exit of the sprue then it enters into the mould cavity. Now, what is the definition for this choke area? The smallest area that occurs at the bottom of the sprue is known as choke area that occurs at the bottom of the sprue this is the bottom of the sprue. So, the smallest area that occurs at the bottom of the sprue So means this area at the bottom most of the sprue is known as choke area. Now choke area is designed based on Bernoulli's theorem. Now what does this Bernoulli's theorem state? It is based on the principle of conservation of energy and relates pressure, velocity and elevation. And here we can see the same case this is the pouring cup and this is the sprue and this is the choke. The height of the entrance of the what is a sprue is the h v and the height of the exit of the sprue that is the choke is h c. We can see height of choke and this is the height of the entrance, height of the entrance. It states that the total energy of unit weight of fluid is constant throughout a fluid system. Potential energy means sum of potential energy, kinetic energy and pressure energy. And here we can see the same thing here we can see the potential energy and here of course there are frictional loss are there and here we can see the pressure energy and here we can see the what is a velocity is there and finally so these are all what is a covered by the Bernoulli's theorem. Now let us see the Bernoulli's equation it is like this p by dg plus v square by 2g plus z minus delta f is equal to h. p by dg is the flow energy per unit weight, rho is the pressure and d is the density p is the pressure. Next one v square by 2g is the kinetic energy of the fluid per unit weight, z is the potential energy of the fluid per unit weight, delta f is the frictional loss and h is the total energy of the fluid per unit weight which is always constant along the same streamline. So this is the Bernoulli's equation. Now let us derive an expression for the what is a choke area this is the choke. Choke means what is a area of cross section at the bottom most portion of the sprue is the choke area. Now we are going to derive an expression for the choke area. So here we can see this is the pouring cup and this is the sprue and this is the entrance of the sprue and this is the exit of the sprue. So the area of cross section at the entrance of the sprue is ab the area of cross section at the exit of the sprue that is the choke area is indicated by ac. Now the height of the sprue at the entrance is hb the height of the choke is hc. Let ab is equal to cross sectional area of the sprue at its top this is ab. Next one ac the cross sectional area of the sprue at the choke. Next one vb means velocity of the liquid metal at the top of the sprue means here what is the velocity of the liquid metal that is vb. Next one vc is the velocity of the liquid metal at the bottom of the sprue or at the choke that is known as the velocity of the liquid metal at this point ac is the vc. Next one, H B is the height of the pouring basin. You can see here this is the H B. Next one, H C is the height of the total metal head above the choke. So, this is the H C means this is the height of the choke. According to the Bernoulli's theorem, velocity of liquid metal at the top of the sprue is given by V B is equal to square root of 2 into G into H B. This we have already seen earlier. Similarly, velocity at the bottom of the sprue at the choke is given by V C is equal to 2 G H C. Volume of flow rate flow at choke in a given time is equal to AC into V C into T that is well known to us. Volume of flow at choke in a given time is equal to AC into V C multiplied by time. That is also equal to W by rho where W is the weight of the poured metal and rho is the density of the liquid metal. Thus AC is equal to W by C rho T V C. Here we come across another term that is the C that is the coefficient of discharge. Now, V C we have already derived the expression earlier. V C is equal to root of 2 G H C. So, this 2 G H C we will substitute here. Hence, the choke area is given by AC is equal to W divided by C rho T square root of 2 G H C where W is the weight of the poured metal in kgs kilograms. C is the coefficient of discharge because there is a friction we always have to what is a take this friction into account. That is why there is a C coefficient of discharge it will be between 0.7 to 0.9 and for an ideal fluid it will be 1, but such case will not arise. Generally the coefficient of discharge will be 0.7 to 0.9. Rho is the density of the liquid metal that is kg per cubic centimeter. Next one T is equal to that is the pouring time in seconds. G is the acceleration due to gravity that is equal to 981 centimeter per second square. Next one H C is the height of the total metal head above the choke in centimeters. So, this is the H C. Now, this is the expression we have derived for the what is a choke area AC. So far we have seen the elements of the gating system and we have learnt about the pouring cup and the sprue. Now, let us see about the sprue well. So, this is the sprue well and it is used to catch and trap the first metal and to observe erosion of the sand due to kinetic energy of molten metal. Now, we pour the molten metal in the pouring cup and it will be passing through the sprue. Then what happens by the time it reaches the choke, its kinetic energy will be too much. Now, straight away it falls on the runner what will happen? It will error the moulding wall inside the runner. We do not want such thing to happen. That is why we are keeping a sprue well here because this sprue well contains sufficient amount of the liquid metal and the molten metal flows into this sprue well first. That is why there is no erosion of the moulding sand. Then after this sprue well is filled, then the molten metal fills into the sprue well, then it flows into the runner. So, to prevent the what is a erosion of the moulding wall and to catch the what is a first metal and to observe the erosion of the sand due to kinetic energy we keep this sprue well here. So, that is the purpose of the sprue well, rules for design of the sprue well. The sprue well area is 2 to 3 times the area of the sprue at exit that is the choke means what is the choke area we have to calculate and the sprue well area the what is a cross sectional area should be 2 to 3 times the cross sectional area of the choke. Next let us see about the runner and here this is the gating system and here we can see this is the what is a sprue the molten metal passes through the sprue then it enters into the runner then it enters into the runner then it flows through the ingates like this it flows through the ingates runner is the horizontal channel through which the molten metal flows from the sprue to the ingate right it is the horizontal passes. So, this is the runner this much is the runner rules for runner design typical cross section of your runner is a square. The runners cross sectional area is generally 2 to 4 times the cross sectional area of the choke again it depends upon the gating ratio soon we will be learning about a gating ratio. So, based on the gating ratio this what is a cross sectional area of the runner depends abrupt changes in the direction of the runners should be avoided. If the change in direction is more than about 15 degrees then the joint needs to be filleted. If the what is a change in direction is more than 15 degrees then instead of keeping a sharp corner there should be a fillet corner. Next one runners should maintain a minimum distance from the casting 4 to 5 times the thickness of the gate or the ingate there should be some distance from the casting to the runner the runner should not be too close to the casting then how far it should be from the casting 4 to 5 times the thickness of the ingate. Next one let us see the runner extension runner extension is used to catch and trap the slags and impurities in the first metal that are likely to enter into the mould cavity that is the purpose of the runner extension. Here we can see this is the gating system and yes this is the sprue the molten metal of course above the sprue there is a pouring cup which is not shown here the what is a molten metal is poured into the pouring cup and it passes through the sprue and this is the choke the bottom most cross section of the sprue then it falls what is a flows into the runner. You see here now the first metal may contain some slags and impurities. So, now our task is that this first metal which contains slags and impurities must not enter into the mould cavity somehow we have to divert them so that they would not enter into the mould cavity. So, for that purpose what we are doing we are keeping the runner extension you see here from here to here there is no point in keeping this strictly speaking and here you see this is the runner extension and this is also is the runner extension. Now what will happen when we pour the molten metal it pour what say it comes into the sprue and it passes through this choke and it enters into the runner then first it straight away goes straight this side also it straight away goes straight now it is occupied by the first metal which contains the impurities and slags of the molten metal. After the runner extension is filled with the what say first metal which includes the which contains the what say slags and impurities then the fresh metal continues. Now the fresh metal cannot fill this because this portion is already filled with the first metal which contains the slags and impurities now the fresh metal enters through the ingates like this like this. So, that is the purpose of the runner extension next one ingates or they are also known as gates rules for gates design or the design of the ingates multiple ingates often are preferable preferable for large castings a fillet should be used where an ingate meets a casting right because we use the fillet it what say causes less turbulence. The minimum ingate length should be 3 to 5 times the ingates width what should be the length of the ingate that should be 3 to 5 times the ingates width again it depends on the metal being cast curved ingates should be avoided as far as possible. Friends in this lecture we have seen the elements of the gating system right. So, these are the elements of the gating system pouring cup, sprue, sprue well, runner, runner extension ingates and the razor is also considered as the part of the gating system right. Initially we pour the mortar metal into the pouring cup. So, this is the pouring cup next it passes through the sprue next here it what say falls into the sprue well next one it enters through the runner next one yes it fills the side razor next one it passes through the gate or the ingate then it flows through the mould cavity and it fills the mould cavity after filling the mould cavity it raises through the razor. So, these are the different elements of the gating system we have seen and how to design the pouring cup how to design the what say sprue what say cross sectional area at the bottom we called it as the choke the bottom cross sectional area of the sprue is known as the choke we have seen how to design the choke area and we have seen and how to design the runner runner extension and the ingates. We will continue this in the next lecture. Thank you.