Turbine D wrote:
Old Engineer
I liked your analogy as to the spline wear being the "canary in the coal mine".
Here is why:
Spline coupling allows a shaft to be easily dismantled while providing a high-torque capacity for minimum size. In addition, it can allow relative axial and radial motions between the coupled shafts. ...
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... Thus, misalignment makes the vibration of a system more complicated.
This information is from:
Research Article
Meshing Force of Misaligned Spline Coupling and the Influence on Rotor System, [by] Guang Zhao, Zhansheng Liu, and Feng Chen
School of Energy Science and Engineering, Harbin Institute of Technology, Harbin 150001, China
Could this be a viable explanation as to increased loading on the bearings and bearing structures at high thrust levels, e.g. takeoff?
Turbine D
Yes, I believe it could. Thanks for posting that very graphic description of the view of the Chinese authors in this spline matter.
I had some background written up on the reasons involute gear section splines are used (a known and calculable tooth line bearing stress) and why they rotate in mesh (the clearances for free assembly preclude simultaneous contact of all the teeth, particularly when the shafts are misaligned. But the reply page timed out; I recovered only the quote. Maybe just as well, as it shortens the post.
I think that spline binding, loss of oil film therefrom, hence wear, hence loss of involute tooth form, hence loss of uniform motion, hence chipping of teeth from wear and increasing impact in mesh, will eventally lead to significant non-uniform rotational speed of the turbine and compressor disks. If severe enough, the gyroscopic effects may pound dents or grooves into the bearing races. Initially, it may just be loss of oil film in the bearings, roughening the races, leading to wear and heating.
Just some thoughts to pursue. Causes of gear teeth and bearing failure can be very hard to understand as to specific cause.
OE