Hi all, please help me to diagnose one case about gearbox system. The system has been described in detail on attachment. The spectrum indicate high vibration at Gear mesh freq. (GMF) with harmonics and sideband of rotating speed.

Base on spectrum data , can i judge the pinion gear has been wear or it is just a incorrect tooth meshing condition ?  

 Your ideas will be appreciated 

 Thanks a lot.  

thanks

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Original Post
Originally Posted by dominich.vo:

Hi all, please help me to diagnose one case about gearbox system. The system has been described in detail on attachment. The spectrum indicate high vibration at Gear mesh freq. (GMF) with harmonics and sideband of rotating speed.

Base on spectrum data , can i judge the pinion gear has been wear or it is just a incorrect tooth meshing condition ?  

 Your ideas will be appreciated 

 Thanks a lot.  

First of all what are all your tooth combinations?

 

In a case like this the bevel set is suspect but to state it is due to wear or an incorrect tooth meshing condition is difficult.  It could in fact be either, or both, or a few other reasons as well.  Have you visually looked in the unit?  Typically these drive have an inspection port, often nothing more than a large pipe plug (which is overlooked as an inspection port).  If your sketch is orientated to indicate the field arrangement, that places the bevel gear/helical pinion shaft in a vertical position (as is common in a cooling tower).  A common mode of failure in these arrangement is failure of the lower bearings.  The bevel gear/helical pinion shaft lower bearing is frequently the lowest in the gearbox and water tends to collect in that area.  When the bearing fails the two shafts start to run off axis and the bevel mesh frequency elevates.

 

What is the history of this machine?  Has it recently been overhauled?  It is very difficult to properly set up bevel gears.  The task borders on more art than science and even the best of mill rights don't know how to do it properly.  In the previous paragraph I mentioned the lower bearing failing.  But if maintenance has been done and either of the bevel pinion bearings or either of the intermediate shaft bearings are not set properly, then again you set up a condition of the shafts running off axis creating the bevel mesh frequency.

I would say there is too much clearance on the input bearings. The cause could be just incorrect settings or possible bearing/housing wear. 

Hi John, 

  we plan to open the cover of gearbox for visual checking. In recent overhaul, we changed pinion bearing of input shaft. It could be a problem of installation and result in high axial vibration. This gearbox is not in cooling tower so water comes inside gearbox could be eliminated.

 The temperature in gearbox also high ( >70oC)(Oil specification is carter SH 150). That means oil's quality also has problem. In my experience, the normal operating temperature is around 40 - 55oC .    

Thanks Becar, 

 I care about the pinion condition because if i can judge this gear's condition, I can plan to purchase the new one. It takes about 6 months to get them from the manufacturer. Just for your reference.

  

For Carter SH 150 70 deg C (158 deg F) should not be an issue.  

 

Based on what you have said, I would suspect that the bevel contact is not optimum.  I would initate a check to verify the bevel settings and the proper setup of the bevel pinion bearings.

I see some peaks that I guess they are natural frequencies, so it could be worn or backlash. I think we need to see time waveform to confirm these.

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