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Dear All,

As you know, excessive distortion on a gearbox will be casuing the failure of gearing and bearing. I have a case that insufficient bearing contact caused by gear casing distortion resulted in high bearing temperature after several months running always. The varnish removal system is being used to maintain this compressor running at an elevated bearing temperature now. The soft feet of gearbox and piping stress on the casing already have been checked , no problem. but the leveling offset at both ends of gearbox already got obvious out of allowable tolerance.  it looks like this distortion is actually caused by the heavy compressor volute hanging on lower casing of the gearbox or due to some thermal bowing happening on this gearbox casing.

Does anyone know if any standand is calling for any requirement -e.g. this welding casing should have enough stiffness to reduce any deformation caused by those over-hung volutes and a good thermal stability during the running , as well as how to make this realized during the gearbox casing design.

Thanks for your help in advance.


Tags: gearbox, distortion, compressor

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This company deals with large industrial air compressors, they maybe of assistance

Do you have additional knowledge of this issue? New or old, major failures, just showed up after repairs/overhaul, piping also grows putting stain on stage casing. Any photos to support your analysis? Had one scenario with large gearbox that OEM machined incorrectly during rebuild/reconditioning process, one bearing always hot, wear pattern on babbit bearing showing misaligned high speed shaft (10,500 rpm). Did you use a dial indicator on each gearbox mounting bolt during soft foot checks? Are the two mating surfaces of the gearbox flat? The outside of the bearing holds a wealth of information on how well it is seated.




Thanks for your response and information.

This is a new machine which was just commisioned in last year. after high bearing temperature appeared, site did the checking on those bearings, the wear pattern on the beairng showed obviously uneven contact but however the contact between bearing shell and bearing housing is good. Also the soft foot (by feeler gauge + dial gauge) and piping stress were checked  , no problbem. The only abnormal thing we found is the destortion of gear box, out of the tolerance. low elevation at both sides of gearbox where two volutes being hung on the lower part of gearbox. so,we are suspecting this existing distortion is caused by inadequate stiffness of gearbox casing. 

Currently we are waiting for shutdown windown for futher check and confirmation on the gearbox.

Best Regards,


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