 In this video I want to talk about a process that we can use in order to inform a selection of rolling element bearings for a particular application. So in this process we're going to make use of two tables from the juvenile textbook and table 14.1 is a table that gives some example bearing specifications for a given set of bearings. Now of course these are just more I would consider them example tables. If we were looking at at you know making an actual selection we'd probably use a supplier catalog for a particular bearing supplier. Table 14.2 gives example rated load capacities for bearings and these are at a life of nine times 10 to the seventh cycles and assuming 90 reliability. So it's kind of important to keep those things in mind as we make use of these example tables that the textbook provides. So the the important thing to consider when it comes to using these tables and making the selection. I mentioned that table 14.2 assumes a desired life of nine times 10 to the seventh or I think as the book lists it 90 times 10 to the sixth. So this table 14.2 assumes a bearing life of 90 times 10 to the sixth cycles which is also nine times 10 to the seventh and you'll probably see me write it that way and it assumes 90 reliability. However that's just one particular life rating that we could potentially use in our design. So we might need to adjust that to to account for what we actually want for our our rated life. So two equations that we're going to make use of to do this are one an equation that looks like that or equivalently I can rearrange this equation and present it a different way as this. Now in these two equations the variable C is the rated load capacity while C required C sub required is the required load capacity. Oops f sub r is the radial load for the application of the bearing and l is the life at the load f sub r and l sub r I've already mentioned is nine times 10 to the seventh specifically when we're talking about using table 14.2. Now of course if we're using a different source of data, a different catalog, different table, that l sub r could be different. So this is something to keep in mind that this is just for this particular table that we're talking about. I also said that this assumption for the two equations and for that table is for 90% reliability and we can make an adjustment to that. We can adjust our reliability by modifying these equations with a reliability factor case of r and I end up with something like that where I've factored in this case of r value which is again a reliability factor. We can read this reliability factor from the textbook so that's one correction we could make. We could also make a correction for shock loading so if we expect there to be a suddenly applied load to the bearing we might need to make a correction for that in which case we can introduce an application factor so this application factor would be multiplied by f sub r for any shock that we might see and that again comes from a table that we can read from the textbook. So these equations are also making assumption about the type of loading that we would that we would be carrying and in them you only see this radial load that we've described. Now the problem is that many times bearings are expected to also carry some thrust load when we when we would submit them to a particular application. So we can make some adjustment to account for thrust loading. I'm going to call the thrust load f sub t and to do that we can introduce what we call an equivalent load and substitute it for f sub r. So the same equations can then be used but now using an equivalent load and the equations vary depending on what type of bearing we're talking about but I'm just going to show the equations for radial ball bearings the textbook provides equations for other types of bearings so if we look at the ratio of the thrust load to the radial load we can make some corrections. So if it's less than if that ratio is less than 0.35 then we don't really need to make any correction we can just say that the equivalent is equal to the radial load it's not enough of an impact for that to matter. From 0.35 to 10 we make a correction by the following equation and finally if f sub t over fr is greater than 10 so we have high thrust loads then we use the equation 1.176 times f sub t for the equivalent load and just to be complete then this of course results in our equations now being of the form kr l sub r c over fe ka 3.33 as well as so these two equations now have been corrected a couple times I've taken into account this reliability factor kr this application factor ka as well as this equivalent load which allows us to account for thrust uh thrust loading so this set of equations would be the key ones uh which kind of account for all of these things we can then use these uh in order to calculate a a expected life under a given loading for a given bearing uh and that's this first equation the second equation allows us to take a uh an expected life and come up with a load requirement that that would accomplish that so kind of two different ways to look at the same problem another useful thing provided by the book is table 14.4 gives some guidance as to uh what the appropriate life specification for a bearing should be under given different given conditions so depending on how precise things need to be um how long we expect it to last how much service uh time it's expected to have how much what that design life should be so anywhere from you know 100 hours of design life up to 200 000 hours of design life as examples which we could then convert to um a number of cycles based on how fast uh how fast the thing is spinning so i'll go ahead and and stop there thanks