 Hello friends, Myself, Mr. Sanju Vinayak working as Assistant Professor in Mechanical Engineering Department, Walton Institute of Technology, Swalapur. In this video, I am explaining about worm gas. At the end of the session, students will be able to classify worm gas and they will be able to understand the various applications of worm gas drives. Worm gas essentially consists of a worm, which is a screw and whereas the worm wheel is similar to helical gear and there is a combination of worm and worm wheel to transmit the power. So worm is in the form of helical screw meshing with a special helical gear called as worm wheel. So it is a peculiar construction of the gear drive which is different than all other gear drives such that here is a screw is transmitting power, its linear motion to a rotary motion of the worm wheel. In all other gear drives, we find that the power of one gear is transmitted to another gear, just rotary motion of one gear is transmitted as a rotary motion of another gear. So here it is a difference than all other gear types, the worm gear works and that is why it is a peculiar construction. Because of this peculiarity of this gear, it has got large applications and the most popular applications it is having because large speed reduction is possible. So for high speed reduction, these are the best gears and most compact gears. So it provides an advantage because it is a screw and gear combination, it provides the number of advantages. The first advantage is that it has got very high speed reduction, so 100 is to 1 can be a reduction possible in worm gear drives and that is why they are most compact as compared to other gear drives. We know that for all other gear drives, the velocity ratio is obtained by diameter of one gear or bigger gear divided by diameter of pinion, smaller gear. So diameter to diameter is the ratio for obtaining the velocity ratio and that is why the space required is quite large but here it is something different than that, the diameter of the worm and diameter of the wormwheel, they do not contribute directly as a ratio of getting velocity ratio but number of teeth on wormwheel and number of start of the thread on the worm that contributes for velocity reduction. That is why these are most compact as compared to other gear drives. These work with the helical path that is the threads or helical threads on the screw as well as the teeth on the worm or helical teeth and that is why they resemble the helical gear and we know that the advantage of helical gear is a smooth and noiseless operation. So these are quiet in operation and very smooth in operation. So worm gear drives provide this advantage of smooth and noiseless operation. Another good advantage is that it can provide self-locking condition which is not possible for other gear drives. This is a peculiar drive in which we can obtain self-locking condition because it is a screw we know that power screws if the efficiency of the drive is less than 50 percent we can obtain the self-locking condition that means a reverse power transmission cannot happen. So in case of sometimes overloading condition intended direction power transmission if it stops suddenly it is possible that the power may transmitted in reverse direction which may harm the system. So to safeguard the system from such overloading condition some of the cases self-locking condition is required which is a unique advantage we can obtain in worm gear drive. So these are the important advantages that we can obtain from these drives. As we know that coin has got two sides similarly these gears have got disadvantages also. The major disadvantage is sliding friction. In other gear drives predominantly pinion and gear combination gives rolling friction between their machine teeth whereas it is a screw and gear combination during power transmission predominant is a sliding friction and sliding friction is more severe than rolling friction that is why the frictional losses are quite heavy and that is why efficiency is also less. So as compared to other gear drives the efficiency is less and sliding friction is predominant. So frictional work done is converted into heat we know that and that is why considerable amount of heat is generated. So overheating may be a problem in these gears and that is why a proper and adequate lubrication is very important in worm gear drives and that adds to the cost. And that is why lubrication is must for worm gear drives. So keen attention for lubrication is required. The gears as far as concern with materials the materials are quite high cost that is here the material used for the worm and worm wheel is heterogeneous and the material for the worm is steel whereas the material for worm wheel is phosphor bronze and phosphor bronze is very costly and that is why the cost of materials for worm and worm wheel is also costly. So these are the drawbacks or disadvantage of worm gear drive. So now pause the video and just recall the advantages of other gear drives. So here you can compare all other gear drives with the worm gear drives so that we can have an idea how to select a particular gear drive depending upon the application requirements. Now the types of the worms if you take as far as the construction is concerned the two major types are single enveloping worm as shown in this figure and double enveloping worm. Further these are classified as single threaded worm and multi threaded worm. So the number of start may be single start or number of start may be multi start so depending upon that further they can be classified. See if I take a single enveloping worm gear drive as shown over here it is a worm having cylindrical or straight cylindrical worm. So blank is a straight cylindrical blank on which the thread is cut, heli-soidal thread is cut which is meshing with the teeth of the worm wheel and that is why it establish a line contact between meshing portion and that line contact is transmitting heavy load and that is why contact pressure is considerably large. However, it is a simple in construction and operation and low cost it is more widely used whereas in case of double enveloping worm gear drive the thread is cut on conical cylindrical blank. So conical shape is there on which the thread is cut and that provides a more area of contact between the worm wheel teeth and worm thread. And being the large area is in contact it gives the advantage of contact pressure between the threads of the worm and the teeth of the worm wheel is low. So contact pressure is decreased and because of the decreasing of contact pressure between meshing threads this reduces the wear and also they occupy less space for a given capacity. So the cost is more but these are the two advantages the life is more and also they can occupy less space. Now as far as the application is concerned there are four major areas of application for worm gear drives. So manually operated intermittent mechanism these are best useful for intermittent mechanism particularly when large mechanical advantage or large torque is required to be applied. But efficiency is not important as we know that the drawback is that its efficiency is very less. So efficiency is not a primary comment but however the large mechanical torque or advantage required intermittently just as an example of a steering mechanism we know that we are applying very large torque by use of hand wheels intermittently to change the direction of the vehicle and that includes a steering mechanism. So here we can use the worm gas. If still more torque is required then as for the input is concerned small capacity low cost drive can be used. So low cost motor can be used as the input which drives the worm and that is been transmitted to worm wheel. Efficiency is of minor importance. So opening and closing of large gate walls of the dams or canals or hoist in material handling we can use motorized operating intermittent mechanism we can use worm gear drives. Then motorized continuous operation also we can provide just is a replacement for other gear boxes because it is a space limitations are there that is most compact and silent operations. So we can replace other gear boxes by worm gear boxes in such cases. For example machine tools, spindles or machine tools and elevators we can use worm gears. Motorized speed increasing applications particularly super charges or automotive or centrifuge machines we can use motorized application of worm gear drives where efficiency is also important. So multiple start threads can be used. So multi start threads offer the efficiency improvement. So in such cases we can use multi start threads. Now to have a more idea you are requested to see this video of a gearbox, worm gear box in which you can understand better working of this worm gear box. These are my references. These are my machine elements by Vibhav Ndari and this is a YouTube video that I have been taken up. Thank you.