![Flexible Coupling ,[object Object],www.ludeca.com The shafts can only change their relative position at the two points of power transmission. 1 2](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
More Related Content
What's hot
What's hot (20)
Viewers also liked
Viewers also liked (17)
Similar to Shaft Alignment Tolerances
Similar to Shaft Alignment Tolerances (20)
Shaft Alignment Tolerances
- 1. Short Flex and Spacer Shaft Tolerances Is there really a need for both? www.ludeca.com
- 3. Coupling Examples www.ludeca.com How many flex points? (points of power transmission)
- 4. Misalignment Magnified www.ludeca.com What happens to the coupling when we have misalignment? SHEAR?
- 5. Misalignment Magnified www.ludeca.com This creates 2 ANGLES at each power of transmission point. NO, It’s a FLEXIBLE coupling, so it will deform to accommodate the misalignment.
- 6. Misalignment Magnified www.ludeca.com This creates 2 ANGLES at each power of transmission point. What about OFFSET? Where does that come from? For Short Flex Tolerances, the OFFSET is defined at coupling center.
- 12. Example of both Tolerances www.ludeca.com
- 15. Spacer Coupling Effect www.ludeca.com What is happening to the angle?
- 16. Spacer Coupling Effect www.ludeca.com
- 17. Spacer Tolerances Expressed at EACH FLEX PLANE www.ludeca.com
- 18. Short Flex Only www.ludeca.com Short Flex tolerances need to satisfy a given Angularity AND Offset at the coupling center. Short Flex tol’s have us correcting the two alignments in the best condition!
Editor's Notes
- Welcome to part 1 of 3 in a series discussing rotating machinery alignment tolerances. This presentation breaks down and simplifies the definitions of short flex and spacer shaft tolerances. It will also explain why it is absolutely necessary to have both the short flex and spacer shaft tolerance options when performing an alignment.
- Let’s start by defining the flexible coupling. A flexible coupling has 2 flex planes or points of power transmission. This means that power is transferred from the driver to the driven at these specific points through the flexible element. It is also at these two points that the shafts are allowed to articulate or flex relative to one another to accommodate the misalignment. The type of coupling can be one of many but the design principles remain the same.
- Let’s look at a few examples of typical coupling designs. You can see that the length between the flex planes varies but all have the same principles in design. It is at each flex point where the angular misalignment will be present. Shouldn’t the misalignment be measured and expressed at each flex point?? Yes, however when the distance between the flex planes is small it is more convenient to express it otherwise…let me explain.
- Here you can see that even if there is only a parallel misalignment between the shafts , each flex plane creates an angle at the point of power transmission. However, in almost all cases, there will be both an offset and angular misalignment present between the shafts. You can also see that if we minimize the offset at coupling center we also minimize the angle at each flex plane.
- Here you can see that even if there is only a parallel misalignment between the shafts , each flex plane creates an angle at the point of power transmission. However, in almost all cases, there will be both an offset and angular misalignment present between the shafts. You can also see that if we minimize the offset at coupling center we also minimize the angle at each flex plane.
- Here you can see that even if there is only a parallel misalignment between the shafts , each flex plane creates an angle at the point of power transmission. However, in almost all cases, there will be both an offset and angular misalignment present between the shafts. You can also see that if we minimize the offset at coupling center we also minimize the angle at each flex plane.
- Short flex tolerances express the misalignment as an Angle between the shaft centerlines and as the Offset between the shaft centerlines–projected to the coupling center. Short flex tolerances are a derivative of spacer tolerances and are to be used only where flex planes are 4 inches or less apart.
- Spacer tolerances express the misalignment at each flex plane. In other words, it expresses the misalignment between each shaft and the connecting element or the flex element.
- Spacer and Short Flex Tolerances both measure the relative rotational centerline misalignment but express it in different terms. Short flex tolerances were developed many years ago to safely simplify the alignment tolerances of close coupled machines and were only meant for couplings with a short distance between flex planes. Short flex tolerances are a derivative of spacer tolerances.
- Here is an example of a table that utilizes both Short Flex and Spacer shaft tolerances. Some laser alignment tools have the option to use the option best fit for the application. Having only one limits the tools effectiveness and hinders the aligners ability to get the alignment completed in a reasonable amount of time, if at all.
- Now that we have established that we have two flex planes in most flexible couplings, how much misalignment can each flex point tolerate before there is damage to the associated machinery and its parts? We may never get, or need to get, a perfect alignment, however, we would like to get the alignment as close to zero as possible within reason. I say “within reason” because there comes a point where there is really no beneficial return on a tighter alignment. Absolute perfection cannot exist. Therefore, some misalignment is unavoidable and the question should be, “how much is too much?” And, that, by definition, is your tolerance, “within reason”.
- For some, the Short Flex tolerance has been over-generalized to cover all types and lengths of couplings. As the distance between flex planes increases, the possibility of aligning to short flex tolerances severely decreases when it should actually become easier. That quick alignment has now become a lengthy, tedious process! We will examine this further in the next couple of slides.
- For simplicity’s sake, we show four drawings of the same misalignment between the shafts centerlines but with an increasing distance between coupling flex planes. You can clearly see the dramatic decrease in angularity at each flex plane as the distance increases. Does it make sense to use short flex tolerances for all four cases? Obviously not. If we define the tolerances “at each flex plane” based on running speed and the distance between the flex points we will have a more accurate and achievable alignment.
- For simplicity’s sake, we show four drawings of the same misalignment between the shafts centerlines but with an increasing distance between coupling flex planes. You can clearly see the dramatic decrease in angularity at each flex plane as the distance increases. Does it make sense to use short flex tolerances for all four cases? Obviously not. If we define the tolerances “at each flex plane” based on running speed and the distance between the flex points we will have a more accurate and achievable alignment.
- For simplicity’s sake, we show four drawings of the same misalignment between the shafts centerlines but with an increasing distance between coupling flex planes. You can clearly see the dramatic decrease in angularity at each flex plane as the distance increases. Does it make sense to use short flex tolerances for all four cases? Obviously not. If we define the tolerances “at each flex plane” based on running speed and the distance between the flex points we will have a more accurate and achievable alignment.
- Knowing what we learned in the previous slide, let’s look at another example where using only short flex tolerances for all alignments can actually make the alignment more difficult. Let’s say that we have the first alignment to within the short flex tolerances. Remember, short flex tolerances have the offset calculated at the coupling center. Just like the previous example, the angles at each flex plane get smaller as the distance between flex planes increases which means the alignment is actually getting better. But, you can see the third and forth alignments are getting worse if you apply short flex tolerances! So, in this example, only having Short Flex tolerances makes us correct the two alignments that have the smallest angularities at each flex plane! If we have the Spacer tolerance option, we can measure the angles at each flex plane and easily see that the top two have the biggest angles, and are actually the ones that need attention.
- Only use short flex tolerances when the coupling flex planes are 4 inches or less apart. Use spacer tolerances on machines where the flex planes are more than 4 inches apart. Unless more Overtime is the goal, make sure your alignment tool has both short flex and spacer shaft tolerances.
- Only use short flex tolerances when the coupling flex planes are 4 inches or less apart. Use spacer tolerances on machines where the flex planes are more than 4 inches apart. Unless more Overtime is the goal, make sure your alignment tool has both short flex and spacer shaft tolerances.