User:Lost war

And when we define lubricant, we say it is a substance, which is interposed between two substances or two solid surfaces, so that shearing strength of the interphase is reduced friction is reduced subsequently wear is reduced. I want to give more emphasis on the wear decrease or reduction in wear rate compared to reduction in friction. As it was pointed in earlier lecture wear reduction is much more compared to friction reduction friction reduction can be hundred times, but wear reduction can be ten thousand times using proper lubrication mechanism.

It is a really an interesting and we have number of application, where the lubrication is required. You can see this picture this is of the very, very common example. It is a standard lock mechanism, we have key over here there will be bolt connection having a some geometry of course, it is not a true threaded bolt. But we can say it is a bolt, because, it gets engaged in the door slot and locks the door here we can point, if there is a on and off key, there will be, this component or this bolt will be reciprocating. If there is a reciprocatation, reciprocating motion than friction will be there. And if you do not provide proper lubrication or we do not provide lubrication layer on that or proper coating on the surface. Then there will be high friction and jamming action will occur it will not work satisfactorily for a longer time. Similarly, there is another mechanism and we call as a window lifting mechanism. Window pan is generally lifted, if it is a power drive than we use a gear mechanism. And generally, gear mechanism in this case particularly, it is a motor small size motor is engaged with a complete gear. And the sector gear is moved with this spur gear or a mom gear pair, which ever engagement is there. As there is again tribo surface for satisfactory work, we will be requiring lubrication either solid lubricant, liquid lubricant or semi solid lubricant, so that it can function properly without much restriction or jumping mechanisms. So, another common example is a pendulum clock. We know the pendulum clock has a relative motion, as well as surface to surface contact it requires a lubricant to work smoothly. If we do not provide lubricant again it will not work and it will consume more power compare to it is expected.

(Refer Slide Time: 04:26)

The question comes, how lubrication really helps? It was earlier mentioned it reduces the friction it reduces the wear, but, in addition to that there are couple of more advantages of lubrication. We said many times it reduces the failure possibility due to the certain change in load certain, change in lubrication conditions, certain change in misalignment. If there is a some lubricant, which is stacked to the surface it will work satisfactorily for the fraction of second or transient time. In addition to that we can say if there is a proper lubrication. It reduces the stress concentration. If there is a irregular surface will be filled with the lubricant and that will reduce unevenness it will reduce stress concentration. Many times we have a we know that stress concentration factor goes up to 1.7, 1.8 that means is pride in lubrication mechanism, we are going to get benefit of 40 to 50 percent on that. In last lecture we studied about the camp failure mechanism or a camp failure analysis, where the surface failure, surface fatigue was emphasized. If we provide a lubricant that surface fatigue failure will reduce. It was also mentioned that if we provide a lubricant coefficient of friction will reduce sliding will reduce and that will reduce force requires in tangential direction. If the force required in tangential direction is reducer fatigue failure will reduce or we say that life will be a slightly on a higher side or may be greatly on higher side, depend on the lubrication mechanism which we are providing. And this stress concentration factor which is been emphasized is common in number of devises like a transmission parts. If we provide a lubricant, if we do proper lubrication transmission part stress concentration will reduce. Similarly, bearings some micro pitches generated, or is widely irregular surface that can be reduce the stress concentration can be reduced. Similarly, cam follower mechanism, which has a relative motion as well as reciprocating motion, rotational as well as the reciprocating motion. That stress concentration factor will reduce in that. In addition some time we required sealed phases with a solid lubricant to give mechanical contact. But lubricates that is the way the friction and wear is reduced, in that case the solid lubrication is used, to compare lubrication mechanism with a solid lubricant solid mechanics. We can take this example you can there are two surfaces surface one and surface two subjected to tangential forces. If the surface one and surface two are subjected to tangential force and they are interlinked they are linked one way another way. Then there will be some sought of shared deformation the shared deformation is generally given in angular way that 5 or it can be linear term sigma or say delta x. If you want to represent in terms of a stress you can say that tow is equal to g into 5. Here g is a shared modulus, shared modulus is generally given in terms for giga Pascal for most of the matter is a giga Pascal or polymers may turn out to be mega Pascal. But, if the shared modulus is reduced the shared stress is going to reduce for the share same share deformation. So, that is the advantages, if I reduce this constant share modulus to the eta, which is viscosity in this case, am taking example of liquid and assuming the liquid is a non Newtonian liquid in that case non Newtonian liquid case. Tow with a shared stress can be given as a viscosity into share rate. The share rate is expressed in terms of velocity gradient. Now, if I compare g verses eta, g is a modulus of rigidity or share modulus expressed in terms of giga pascal for most of the material. While eta is generally expressed in terms of mille Pascal second, is almost a difference of thousand or more. That means, whatever the share stress generated in liquid will be lesser than 0.1 percent compared to the shared stress generated in solids. And we know if the share stress generation is much lesser or share resistance is much lesser interphases will glide will move smoothly. It will reduce coefficient of friction and subsequently it will reduce the wear, or in other word. Whenever we are providing lubrication adhesive wear is going to come to the almost zero value or adhesive coefficient of friction will come down to the zero. I cannot say for other mechanisms for mechanism. Yes, it will reduce, but come to the zero level of convergent case, it will reduce friction as well as wear will reduce, but, necessary it comes to the zero. However, if we are providing a lubrication and proper lubrication adhesive wear mechanism will come down to zero. On the wear mechanism will work. If there is no complete separation between solids, if there is a complete separation or lubricant is able to provide thick lubrication completely separating two surfaces. Then that case wear will be zero that is required for most of the applications. We discussed here share stress relation for Newtonian liquid, but if we think about the non Newtonian liquid. We can say behavior may be expressed as a b v. This graph is a shared stress verses share rate, this graph shows clearly the domination of the five compared to tow. While this x can, this there are liquid also which will show the behavior like c c, c c curve and there are few liquids or the semi solid. Let me take example of the grease they will show behavior initially they will not deform at all. If the share force is applied and once it is applied, it will show a Newtonian behavior. A typical Bingham liquid what we say use a term is with a Bingham liquid behaves like that there will not be any share deformation initially. And once the share deformation starts then it will work as Newtonian liquid. So, we treat this kind, of the liquid as the semi solid liquid. It is showing a behavior like solid initially and subsequently it is turning out to be liquid. So, we can say we can conclude from this slide .We say that presence of lubricant reduces the stress concentration factor. That is a substantial as a very good factor for us, a method of the replenishing the lubricant beside overall performance. It is not only the providing lubricant at one instant. It is the continuous phenomena and, if lubricant is wiped out is squeeze out, then we need to again and again bring the lubricant at the inter phase. So, that is important and that is why the lubrication mechanism or study of lubrication mechanism is very essential. There is not only the first side you provide a lubricant and you will say that lubricant will remain their forever. We know share stress lubricant reduce the share stress, but, along with the shearing this lubricant also will be wiped out. Once it is wiped out then again the again share stress will increase, or more force will require. So, that is why we required again and again to replenish the lubricant at the inter phases. That is the important that is why the lubrication mechanisms are important. We will take a few examples to understand, what do we expect from a lubricant naturally we are going to spend some money on lubricant and, if you are studying lubrication mechanism and the way lubricant need to be replenished. Then question comes how much cost will be involved will it that be justified compared to without lubricant. So, we can believe that yeah there will be some expectation, if we keep some expectation and lubricant is full filling. This expectation then cost may not matter that much.