Cardan shafts problem - Mechanical Acoustics/Vibration ...

Thank you electripete for the PDF.
Unfortunately i tried to attach photos directly on the message but lot of error appear ...

@greglocock
This is exactly my idea for lot of reasons.
If nothing is cahged for years and only in this period is changed i'm afarid that vendor could be changed manufacturer and new cardan shaft quality is changed.

@Tmoose
thank you for the very detailed information, i'll go to check them and lot of them seems to be related to manufacturing quality and /or assembly error.. this is strictly related about info of Greglocock

Other than mechanical evident failures, what left me puzzled is the fact that it is happening in all the cardans at the same time while all the other surrounding conditions have not changed ..... I think, but I can be wrong, that the obvious cause of the damage is only the effect of a more structured problem

i'm going to verify alignment of some of the cardan shafts, i'm going to verify if nothing is changed on the motor control finding some tips can reveal the righ way to follow

You can find more information on our web, so please take a look.

There are a few down sides, or at least compromises that need to be understood to that misalignment.
1 - The driveshaft rotation is not constant (assuming an absolutely constant input rpm), but varies slightly up and down twice per rev. If the second U-joint yoke angle is ~equal to the first, and is phased correctly ( like this
How big are the roll shaft and motor diameters? Small, compared to the driveshaft? They also have to pass on or oppose the driveshaft's output shaft torque/speed variations. I'd think about NDT-ing them up to the next diameter increase.
2 - A "secondary couple" is created at 2X, trying to bend the driveshaft and tweak the supports perpendicular to the plane of the joint angle, proportional to (but a tiny fraction of, maybe 2-3%)) the transmitted torque. If any coupling style is going to create 2X vibration when misaligned, this is it. Ask any off-roader what happens if she makes suspension lift mods to her truck that also take the driveshaft u-joint angles to extremes (vibration, especially under load).

Dan T

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There is a reason u-joint manufacturer's, and OEMs that use U-joints, specify installation misalignment in the range of 1 - 3 degrees (but equal at each end, so input and output shafts are parallel). I believe it is in an (somewhat desperate) effort to try to briefly impart some rotation to the "needles" (rollers) in the U-joints and maybe thus create a little EHD (elastohydrodynamic ) lubrication between the rollers and journals. Like gears and ball and roller bearings, rolling motion is required to create an oil film powerful enough to separate the surfaces in contact and provide decent life.There are a few down sides, or at least compromises that need to be understood to that misalignment.1 - The driveshaft rotation is not constant (assuming an absolutely constant input rpm), but varies slightly up and down twice per rev. If the second U-joint yoke angle is ~equal to the first, and is phased correctly ( like this http://imghost.indiamart.com/d...61/Exten_250x250.jpg ) the output rpm will again be "constant," without the 2X speed variation. In cars and many industrial applications the driveshaft inertia is relatively small compared to the drive and driven equipment, so the 2X rotational acceleration/deceleration is both innocuous and inoffensive at small joint angles (a few degrees). If the inertia of your driveshaft is freakishly large, then the acceleration required to create the 2X speed variation >>may<< be important. It will be interesting to see if the strain gauges report big 2X torque variations super-imposed on the nominal drive torque.How big are the roll shaft and motor diameters? Small, compared to the driveshaft? They also have to pass on or oppose the driveshaft's output shaft torque/speed variations. I'd think about NDT-ing them up to the next diameter increase.2 - A "secondary couple" is created at 2X, trying to bend the driveshaft and tweak the supports perpendicular to the plane of the joint angle, proportional to (but a tiny fraction of, maybe 2-3%)) the transmitted torque. If any coupling style is going to create 2X vibration when misaligned, this is it. Ask any off-roader what happens if she makes suspension lift mods to her truck that also take the driveshaft u-joint angles to extremes (vibration, especially under load).Dan T

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