 Hello everyone, this is Shila Ratna Banswade from Walshan Institute of Technology, solar. Today, we are going to see the topic freehand sketches and in that the first mechanical component that is police, learning outcomes. Students will be able to describe different types of police. Before we move on further, I suggest you to pause the video at this moment and recall the types of police and the pulley arrangement that you have seen in the previous classes. Now what is a pulley? For any power transmission system, we require either a gear or a belt that is most widely used. For belt drives, pulleys are required to be mounted on the shafts. Belt drives are used when you need to transfer power at a distance and the space over there is not compact. The pulleys are made up of cast iron or raw iron. The pulleys are mounted on the shaft and attached to the shaft with the help of sunk keys so that the pulley and the shaft rotate together and there is not any kind of play between the pulley and the shaft. As far as pulley drive or a belt drive is concerned, we use a flat belt pulley or a V belt pulley for power transmission. So you can say that flat belt and V belt are the types of pulley transmission systems that are used for power transmission. Flat belt has a smooth surface over the pulley and a flat belt is used for power transmission whereas in V belts, there is a groove provided on the surface of the pulley in V shape and the belt used over there has a V shape cross section. Now coming to the first type that is flat belt pulleys. Flat belt pulleys are available of different shapes and size. Depending upon what kind of application it is used for, its design is based. Flat belt pulley uses a flat belt which has a rectangular cross section. The thickness of the belt is quite large as compared to the, sorry, the width of the belt is quite large as compared to the thickness of the belt. Now moving further, the types. The first type of flat belt pulley is the arm pulley as you can see in the screen. This part of the pulley is called as hub or boss. This you can see a keyhole over here and this part, the outer part is called as the rim. The hub or the boss and the rim are connected with the arms as you can see on the screen and this part between two arms is hollow. There is no material between these two parts. So depending upon application and depending upon the size, the arm may be straight or in a circular format. The cross section with some nominal dimensions can be seen over here. So you can see the shaded portion, here material is being cut, here the material is cut that is at this part and over here there is no section lines showed. Moving further, pulley with a web. In the diameter of the pulley is very small. The hub and the rim are connected by a thin plate which is called as web. So as you can see in the side view, the section lines indicates that there is a filled material, there is a filled material which supports the hub and the rim. To reduce the weight of this kind of pulley, holes are provided on this web surface or intermediate surface so that the weight of the pulley is reduced and it can perform better for a particular application. Moving further, a cone pulley. This is a type of cone pulley for flat belts. Similar kind of thing what you see on screen, a cone pulley is mounted on both the shafts that driven as well as the driver shafts. The same belt can function on all the steps. The pulley mounted on driven shaft whereas the pulley mounted on the driving shaft is in opposite directions. So the smaller of one pulley comes in contact with the larger surface of another pulley mounted on another shaft. So this can give you speed variations that first step, second, third and fourth. This application you can see in most of the lathe machines or drilling machines which are belt operated. Moving further, this is a special type of flat belt pulley where two pulleys are used. One is called as the fast pulley and another is called as the loose pulley. The fast pulley is connected with the shaft with the help of a key whereas the loose pulley rotates freely over the shaft. This kind of pulley is used when there is single driving shaft and on that single driving shaft there are n number of machines or suppose 3 to 4 machines operated on the same shaft. Each machine has their own individual belt for rotation and that belt uses the fast and loose pulley. When you want to cut off the working of a single machine without stopping the driven driving shaft, you can shift the belt from the fast pulley to the loose pulley. When you do so, the loose pulley works for idle time and does not rotate along with the shaft. So that particular machine which has shifted its belt from fast pulley to loose pulley does not operate whereas other machines operate. The diameter of the loose pulley is slightly less as compared to the fast pulley. This is provided to maintain a less tension in the belt. As you can see over here there is a crowning effect provided at the rim of the pulley. This is to avoid the axial slip between the pulleys and the belt. Further, types of V-belt pulleys. On the screen you can see a V-belt pulley. In this gap a belt passes. Now here three belts can be mounted on this single pulley shown on the screen. The belt used for V-belt has a V shape cross section or a trapezoidal cross section. Further step cone pulley. The function and working of this step cone pulley is similar to what we have seen in case of flat belts. Only thing is that the belt used over there was a flat belt and the pulley was with a flat surface. Here the pulley has a V shape and uses V-belt rope pulley. As far as till now we have seen the belt pulleys that is flat and V-belt pulleys. Now ropes are also used for power transmission with the help of pulleys. The rope can be made up of cotton or some other materials or even steel where you need to transfer high load and at high speeds. Example for steel ropes are your rope ways in the hilly regions or lifting a heavy weight where safety is a major concern or rather cases we go for a cotton rope. So you can see the construction is similar to a V-belt but a slight difference is made in the grooves. Here you have a circular groove and there we had a V kind of groove. The rope passes through this gap through this gap and the power is being transmitted. As far as efficiency and other things are concerned V-belt pulleys are far better than the flat belt pulleys and the rope pulleys. In flat belt pulleys there is slippage of the belt over the surface of the pulley. As the pulley functions on the tension provided in the belt because of this tension and the rotation of the pulleys causes slip between the belt and the pulley due to flat surface whereas this kind of thing is absent in V-belt pulleys. The belt fits exactly into this gap and there is no slip between the belt and this surface. So better power transmission with efficiency can be obtained in V-belt pulleys as compared to flat belt pulleys. Selection of flat belt pulleys and V-belt pulleys are done depending upon what kind of application you have and the distance between two shafts that is the driving shaft and the driven shaft. Flat belt pulleys are connected the ends of a flat belt are connected by some means of clamping whereas this kind of clamping is absent in V-belt pulleys. Thus most of the applications we prefer V-belt pulleys for better power transmission and where you want to go for low cost and efficiency does not matter much we go for rope pulleys power transmission. So as compared to gears this type of power transmission is of low cost and gives better efficiency where precision and other things are not that of a major concern. These are the references thank you.