REPAIR & MAINTENANCECardan Shaf sReview of the basics & Why Precision Alignment is a Musthen it comes to mechani- construction, and how they work. The with the pump shaft, but both shafts are BY RICH MERHIGEcal failures and down- basic makeup of a u-joint consists of two still in the same vertical plane. Angular times, the premature yokes and four pivot pins. A hole in the horizontal misalignment is similar, how-Wwear of cardan shaft yoke carries the pivot pins which oscil- ever, both the motor, and pump shafts or joints is a very common culprit. What late as the joint rotates. All of the bearing on the same horizontal plane. In the situ-causes this premature wearing of the actually occurs in the tiny space between ation where a cardan shaft is experienc-joints? Misalignment. The maintenance the pins and the yoke holes they lay with- ing angular misalignment, there will be a of cardan shafts, unfortunately, is often in. Because of the movement these joints signi? cant change in rpm’s of the driven challenging due to their size, function, sustain, ample lubrication is required at shaft. The inconsistency of the rotations and accessibility, making their alignment all times. To prevent these joints from is commonly referred to as cardan error. one of the most commonly overlooked, seizing, lubricant must remain in con- This deviation causes vibration, which, and misunderstood issues a ship’s opera- stant circulation around them, if not, you triggers a ? uctuation in bearing loads, ul-tor can experience. run the risk of disaster striking. For this timately resulting in premature wearing A cardan shaft is a type of coupling reason, cardan shafts are typically in- of components and reduced mechanical that connects two machines that are stalled with a three to six degree angle life of machinery. The greater the differ-offset from one another. One is usu- present at the u-joints. This, however has ence in the yoke angles, the worse the ally a stationary machine, a motor, or been challenged time and time again, misalignment. The greater the misalign-BY TERESA DRUGATZthe driver, the other is the machine that where case studies have shown that the ment, the worse the variance in speed. will be “driven.” Cardan shafts are spe- difference between the angles should be When properly aligned, yoke angles are ci? cally utilized to allow for the parallel less than 0.25 degrees. And, of course, in equal to one another when both ends of misalignment caused by these two ma- a perfect world, with a perfect precision the shaft are on parallel planes, for both The Authorschines being offset. This con? guration alignment having been performed, the the vertical and horizontal axis. makes up a drive train, with the cardan angles would be equal. Besides angularity, phasing is another Rich Merhige has over 31 years shaft transmitting torque, and rotation. Given the way cardan shafts are con- important concept when it comes to the of condition monitoring experi-In vessels, cardan shafts are placed be- structed, and the role they play, do they alignment of cardan shafts. Here, the po-ence. He founded/is President tween the engine and gear box. They are actually require alignment? Despite the sition of the yokes on both ends must be of AME, which is recognized as not able to be directly connected to ei- “? exibility” of cardan shafts, and their set parallel, so they fall in line with one an external specialist for condi-ther piece of equipment because move- ability to allow for offset, they are not another. When the yokes are not set par-tion monitoring by ABS. ment must be allowed, so it is attached able to absorb angular misalignment be- allel, every time the drive revolves, the rich@AMEsolutions.comusing “universal,” or u-joints. A “single” tween the shafts. Offset has been shown driven machine will speed up and slow cardan has two u-joints, one at each end. to have no affect on alignment. Angular- down twice. Teresa Drugatz joined AME in A “double” cardan has three or more of ity on the other hand, can produce mis- Cardan shafts are, by design, con-2010 as Of? ce/Marketing Man-these joints. These allow for necessary alignment that results in excessive vi- structed for tight spaces that are not eas-ager. She holds a bachelor of movement without becoming uncou- bration and speed ? uctuations. Angular ily accessible. Traditional laser align-science in communication from pled. To understand the true function and misalignment can be vertical or, horizon- ment procedures required that the cardan the University of Miami.workings of a cardan shaft, it’s important tal. If the angular misalignment present is shaft be completely removed in order for teresa@AMEsolutions.comto have a good overview of the u-joint’s vertical, the motor shaft is under an angle alignment to be achieved. An “offset” Laser Set-up. Cardan Shaft Alignment.38 Maritime Reporter & Engineering News • NOVEMBER 2014MR #11 (34-41).indd 38 10/28/2014 10:27:31 AM