problem with thrust bearing on turbine

[mottt]

This bearing is a thrust bearing on a horizontal hydro unit, francis turbine the firm is Voith hydro, this bearing is composed by an axial bearing that support the force of the turbine on their way of aspiration, an other axial bearing that suport the rejection of load effect and a radial bearing that support the radial forces of the turbine and a flywheel that is mounted between generator and bearing. This bearing fail last year with all the antifriction of the axial bearing that support the force of the shaft in the aspiration way, the bearing is totally destroyed, after that we take the spare ones and change with no checkings cause a lot of money was losing, but in august on last year, 4 months after this we dismount the bearing and find a fault on the spare one... i´ll attach the pics from the reports, cause i have no pics other than on the reports. sorry it´s on spanish the text

 

[mottt]

my question is, when we cheecked the runner on the shaft we saw we got 0,07 mm of movement of the axial side seeing it with a dial, What do you think about it? what is on your opinion the maximun run out aceptable on this aplication...you must think this is a two parts bearing doing the axial support...machine is 1000 rpm, ah! radial runnout is 0,02 mm...the total clearance axial way is 0,5 mm.
I have some questions like, what kind of antifriction mixture it´s usual to use on similar applications? what´s is the usual temperature of welding the babbit and the support metal? is this

 

[mottt]

other question: do you know where i could see tables about the plastic point of the babbit that must be used on on application like this.... as you could see on page 3 of report this is the bearing dismounted on august...of last year... after this we mount a new one, on november and today on february, i see the babbit and it´s damage on the same point... what do you think about it?

 

[rmw]

I scanned the report and it seems to be saying that your problem is shaft alignment and maybe a soft foot. That is to say a problem with the fixation of the bearing pedestal. Do you agree with that and if you do, have those two things repaired yet? If those are the problems you can pick the best bearing material in the world and it is not going to give good life.

Are you sure this bearing is getting adequate lubrication. Do you have lube oil temperatures in and out of the bearing?

rmw

 

[rmw]

Another suggestion;

Can you take that report and retype it in a program that has a language translator? Afterwards you'll have to clean up the English because of all the technical terms, but I think you will get more help on this forum if that document can be translated since this is bassically an english speaking forum.

rmw

 

[mottt]

ok, i´ll translate the reports... thanks a lot for your interest.... no I haven´t repair the shaft, cause the customer and their supervisor are talking about an axial movement of the bearing pedestal, but i put a precission level (plumb) on the pedestal and when i run the turbine the plumb is not moving.. and if i put a dial gauge (i see the indicator to move to 0,8 mm, the pedestal is 1000... what is the usual movement of the bearing on load in this application...i have check 0,2 on bearings mounted on the generator.

in anyway, thanks a lot for your attention.

 

[plasgears]

Do you have an oppurtunity to balance the axial load with a counter load by use of a seal placed where you can take advantage of other pressures? This is common in aviation jet engine work.

 

[cbrn]

Hi,
it seems to me there is a combination of two factors in causing the bearing failure:
- unadequate oil circulation inside the bearing, and specifically in the axial thrust part. In fact, this bearing is normally not designed to carry load on the antifriction material directly, at least not in "regime" conditions (only in the very first phases of startup and in the very last phases of coastdown); the oilfilm between antifriction and steel ring thrust surface should carry the load. If there is unproper circulation, the oilfilm can tear and break, causing the metal parts to contact. Other cause can be strong axial vibrations which will cause oilfilm instability and tearing, but sincerely I find it difficult if the turbine is operated properly
- turbine not operated properly, i.e. outside of the guaranteed range, causing out-of-design axial thrust, and/or abnormal vibrations due to flow instability / cavitation. Also included in this "cause", is the possibility that the air injection device (if there is one), used to stabilize flow at partial loads, is out of order. Even more likely, the "upper" cover labyrinth seals may be unacceptably wornout, causing a strong increase of the axial thrust which will cause an out-of-design operation of the bearing; or, the balance piping system may have some element out-of-order, causing the pressure on the back of the runner's crown to increase (and thus the axial thrust to increase).

I'd check, first of all, the records of the bearings temperatures (as it seems you already have some ideas about the vibrational behaviour of the bearing), then check the status of the runner's labyrinths and of the balance piping system. This may not be possible without the co-operation of a turbine specialist, though.

Regards

 

[cbrn]

I forgot: have you already spoken with Renk's specialists? They are generally very kind and provide effective support.