cardan shaft bearing lubrication

[simisteven]

Hi guys I got such a good response from from last thread so I want to put this one to the experts too. We have four large axial flow circulation pumps coupled to 350kW 6600 volt motor/gearbox via a large cardan shaft rotating at 330 rpm.
Bearing failure on the cardan shafts is far too frequent, often resulting in catastrophic failure of the cardan shaft.
In accordance with OEM specs we use a multi purpose lithium calcium grease. Engen super multi purpose grade 2.
Now we have had the cardan shafts repaired and the local repairer uses Chevron Caltex Molytex Ep which has molybdenum disulphide additive.
Yet the OEM specifically recommends against molybdebum additives.
Any ideas/recommendations out there. I personally believe the OEM recommended lubricant has delivered poor results so I am tempted to go with the Caltex Molytex EP ( one sdhaft already in use with this lube)

 

[Tmoose]

How many hours to failure?
(less than a year?)
Are these all OEM built shafts that are failing?
what is the recommended re-lube schedule?
what is the actual re-lube schedule?
What is the failure mode?
Do you see rust dust powder collecting on the guard inline with the joints a while before the failure?
Why does the OEM recommend against moly? How about other EP type additives?
(once upon a time an SKF application engineer stated that moly creates a thin but measureable layer on surfaces)
How much parallel offset misalignment exists between the input and output shafts?
Has anyone done a torsional analysis?

 

[caoimhin1]

Not too familiar with cardan joint apps myself...but is the bearing movement in these components a high frequency oscillation type. i.e. not full rotation? This might be the reason for not recommending the MoS2 EP grease. Needle rollers used in this type yes?

 

[MikeHalloran]

As Tmoose hinted, there must be some/ nonzero parallel offset between the ends in order for Cardan shafts to survive. If the shaft axes coincide, or nearly so, the joints will not flex enough to distribute the lubricant, and will die young regardless of what lubricant that is.



Mike Halloran
Pembroke Pines, FL, USA

 

[simisteven]

How many hours to failure? 3 to 6 months
Are these all OEM built shafts that are failing? Yes
what is the recommended re-lube schedule? 6 months
what is the actual re-lube schedule? 3 months
What is the failure mode? Total destruction of one UJ usually diagnosed as lack of lubcrication
Do you see rust dust powder collecting on the guard inline with the joints a while before the failure? No
Why does the OEM recommend against moly? How about other EP type additives? Not established reason yet
(once upon a time an SKF application engineer stated that moly creates a thin but measureable layer on surfaces)
How much parallel offset misalignment exists between the input and output shafts? This has been covered. There does appear to be sufficient to allow sufficient movement and rotatio n of the needles in the bearings (Hopefully)
Has anyone done a torsional analysis? Not sure what that is? Please elaborate.

Many thanks for the response, please see my replies.

 

[Tmoose]

HP, rpm, and joint size?

http://www2.dana.com/pdf/IJ900-02.pdf

 

[Tmoose]

================================================

"What is the failure mode? Total destruction of one UJ usually diagnosed as lack of lubrication"

This one has lots of internal rust on 2 dried out caps, and the other bearing journals still a little greasy but etched and maybe dented

http://image.corvettefever.com/f/9253834/corp_0704_03_z+corvette_axle_shaft_repair+U_joint.jpg

http://www.novak-adapt.com/images/pics/mangled_u-joint_montage.jpg

The journal surfaces still look pretty good on this one.

http://128.83.80.200/TACO/grenade.jpg

http://www.todaystrucking.com/images/rr_3272-2.pdf

 

[Tmoose]

If the power delivery/use has pulses then there is risk of exciting torsional resonant frequencies. The torsional bouncing could result in much higher than nominal torque loads. 2 bladed Radial flow pumps can have a lot of "blade pass" frequency radial vibration, and probably similarly high torsional vibration. It would seem an axial pump would have less, but something is hurting those U-joints. It would be interesting if a model with the motor WK2, the pump WK2, connected by the driveshaft's stiffness, had any resonance at blade pass or some other integer or rotating speed.

 

[simisteven]

Thanks TMoose I will check that out. If I recall correctly it is a three blade impeller.