 Myself, Sachin Rathod working as an assistant professor in mechanical engineering department from Vulture and Stop Technology, Sualapur, today we are dealing with the chapter selection of the belt under the course of machine design one. The learning outcome at the end of this session, the learner will able to understand the types of belt. So, before to manufacturing of the belt, we have to know some parameter that we are going to use in the belt and the types of the belt introduction. The belt are used to transmit the power from one shaft to another by means of pulley which rotate at the same speed or at different speed. If the two shafts are rotated with the same speed at that time, we are going to prefer the diameter of the pulley will be the same. If we required the reduction in the speed at that time, we can choose the different diameter of the two pulleys. So, you can think about this. What are the applications of the belt? You can pause this video and think about this. The amount of power transmitted depending upon the following factors means how much powers we are going to transmit that will be the depending upon the following factor. First one velocity of the belt, the tension under which the belt is placed on the pulley, the arc of contact between belt and smaller pulley that the arc of contact is nothing but the portion of the belt is going to contact with the smaller pulley that is that the angle made by that portion is nothing but the arc of contact. And the condition under which the belt is going to use, the advantages. The belt drive gives the transmit the power over considerable distance between the axis of driving and driven shaft. The operation of the belt drive is smooth and silent. As we if you consider the gear drive at that time, the noise will be there. So, unnecessary vibration is going to create it. But in the belt drive, the action will be the smooth and silent. They can transmit only a definite load, which if exceed will cause the belt to slip over the pulley thus the protecting the part of the belt drive against the overload. So, we can protect the parts of the machine as it is overloaded because there the slippage will occur. So, the part will not get damaged other parts of the machine. They have ability to absorb the shocks and damp vibration as we are going to use the belt drive, it will absorb the shocks. They are simple in design. They have low initial cost. Some disadvantages are there. The belt drives have large dimension and occupies more space. The velocity ratio is not constant due to the slippage. They impose heavy loads on the shaft and bearing. There is considerable loss of power resulting in low efficiency. Belt drive have comparatively shorter service life. So, types of the belt. First one, flat belt. So, this is a diagram indicating the flat belt with the pulley. This is a crown shaped pulley and this is a belt, flat belt. The pulley is slightly crowned to prevent slip of the belt to one side. So, if you observe this pulley, it is in the crown shapes to avoid the slippage of this flat belt on the either side of the pulley. It utilizes the friction between the flat surface of the belt and pulley. Example, belt conveyor. If you observe the material handling equipments at that time, the flat belt drive they are going to use. They are relatively cheap and easy to maintain when worn out they are easily to replace. A flat belt drive can be used as clutch by making simple provision of shifting of the belt from tight to loose side of the pulley and vice versa. The belt velocity ratio can be obtained by using a stepped pulley where the belt is shifted from one step to another having different diameter. They can be used in dusty and abrasive atmosphere and required no closed casing. As we required in the gear drive, the casing is required because the particles are mounting on the lubricant. The design of the flat belt is simple and inexpensive. They can be used for long center distance up to 15 m per second. The efficiency of the flat belt drive is more than the V belt drive. This is a figure of the V belt drive in which pulley and the belts are there. It utilizes the force of friction between the inclined sides of the belt and pulley. They are preferred when the distance is comparatively shorter. Several V belts can also be used together if the power transmission is more. We can use the several belts for the power transmission if the power transmission requirement is more. Example the electric motor. The force of friction between a surface of belt and the V groove pulley is high due to the wedge action of the belt. The friction will occurs more in between V belt and the pulley. The V belt have the shorter distance, center distance which results in compacting construction. They permit high speed reduction. Flat belt are hinged while the V belt are endless which results in smooth and quiet operation when at the higher operating speed. So your the V belt are endless, they are going to manufacture as an endless but the flat belt joint or the flat belt drive are hinged means they are going to join the V belt is positive because the slip is negligible due to wedge action. V belt drive can operate at any position even when the belt is vertical. Third type is circular belt or the rope pulley. This figure indicating the pulley and the rope. The rope is in the circular. Several ropes can be used together to transmit the more power. They are suitable for the 90 degree of the twist. The round belts are limited to tight duties. The round belts are limited to light duties machine. If suppose the light duty machines are there at that time only round belt are going to use. If the load is heavy we cannot recommend the round belt. So example is sewing machine. So if you visited the tailor shop at that time they are using the circular belt pulley. So the belt drives are of the following types. First one is the open belt drive, second one is the cross belt drive. In the open belt drive if you observe this figure the upper side is the slack side and the lower side is the tight side. And the two shafts are there on which the driving and the driven pulleys are mounted. As it is an open belt drive the pulleys are rotating in the same sense means if the driving pulley is rotated in the clockwise direction the driven pulleys also going to rotate in the clockwise direction. It is desirable to keep the tight side of the belt on the lower side and the slack sides at the top to increase the angle of contact of the pulley. So this is the angle of contact of the pulley, this angle means how much portion of the belts are going to contact with the pulley, that is the angle of contact of the pulley. So the construction of the open belt drive, this is a simple diagram of the open belt drive in which two pulleys are there. One is a larger pulley another is a smaller pulley. On these two pulleys the belts are mounted that is the open belt drive. This is a complete belt in this, this is a smaller pulley and the larger pulley. The smaller pulley is having the diameter small d, capital D for the larger pulley. Alpha s is a wrap angle for the smaller pulley. Wrap angle is nothing but the portion of the belt are going to contact with the pulley. So for the smaller pulley alpha s is a letter, this is alpha s and this is a alpha b that is a wrap angle for the bigger pulley. Capital D is the diameter of bigger pulley, d is the diameter of smaller pulley, c stands for the center distance. If you observe the triangle O, G, O1, this O, G, O1 we can easily calculate the value of sin beta as the simple geometrical considerations you will get the value of the sin beta is equal to capital D minus small d divided by twice c. These are the steps meanwhile. Also alpha s that the wrap angle is equal to total 180, this is a 180 minus 2 times beta as this angle is beta, this angle is beta. So the wrap angle for the smaller pulley is 180 minus 2 times beta. Similarly, the wrap angle for the larger pulley, this is a wrap angle alpha beta is 180 plus 2 times beta and the length of the belt is given by l is equal to arc FAB plus length BC plus BCE plus length EF. You have to calculate arc FAB is equal to this radius into the angle. So as the radius is small d divided by 2 into alpha s plus BC, BC is nothing but OG, this BC is nothing but OG as well as FE is equal to OG and arc CDE is equal to this radius capital D by 2 into the angle alpha B. So by putting that value you will get the length l is equal to just you have to simplify this. So you will get the answer l is equal to pi in bracket capital D plus small d by 2 plus beta in bracket capital D minus small d plus twice c cos beta. For the smaller value of the beta, beta is equal to sin beta and as sin beta we had calculated capital D minus small d by twice c you will get the value of cos beta as cos theta is equal to 1 minus 2 times sin square theta by 2 by using that relations you will get the value of cos beta is equal to 1 minus capital D minus small d bracket square divided by 8 c square. Just here we have to put the value of beta as beta is equal to capital D minus small d divided by twice c. Just put the value you will get the length of the belt and simplified this. So after the simplifications you will get l is equal to this equation. So this equation is for the open belt drive. Similarly you can calculate the length of the belt for the cross belt drive. This is the equation for the cross belt drive. So I have taken the reference as a VB Vandhari book. Thank you.