Kobelco KS38LNB Screw compressor

[RANGER1]

I am interested if anyone has had much experience with Kobelco screws . In this model ,a few failures of female rotor suction bearing (Roller type).
Oil gallery is common to both male/female rotor bearing and only female bearing failure after approx 30000 hrs.
Has remote oil pump and is not a refrigeration comp
Is used as a booster pump 85 kpa suction/800 kpa discharge pressure on methane

[Grizzly]

Ranger I assume if you have been involved long enough?
Then this comp has had a good service history!
I don't have experience of this particular Make of Screw.
But generally most of the screws that I deal with, may or may not start having bearing issues at 25 -30,000 run hrs.
Is it because this is a more unusual application that you question the run hrs / bearing wear?
Cheers Steve.

[RANGER1]

Steve,
I agree with what tou say and time will tell if this is normal for this application. I just feel that its pretty light coditions for a screw. Normally a booster on ammonia would do 50000hrs easy. The conditions are between a booster + second stage so you could assume all being equal it could last a little longer and not necassarily have damage.
The bearing which has damage and has basically same oil fed to it runs slower.
Hopefully a bearing analysis may indicate reason for failure.
Also when you see this machine it should be bullet proof , as its castings are super heavy duty.

[Grizzly]

Steve,
I agree with what tou say and time will tell if this is normal for this application. I just feel that its pretty light coditions for a screw. Normally a booster on ammonia would do 50000hrs easy. The conditions are between a booster + second stage so you could assume all being equal it could last a little longer and not necassarily have damage.
The bearing which has damage and has basically same oil fed to it runs slower.
Hopefully a bearing analysis may indicate reason for failure.
Also when you see this machine it should be bullet proof , as its castings are super heavy duty.

Interesting stuff Ranger!
As an observation and it may be irrelevant,
But several of the "big boys" have started using Vibration analysis to determine load points where you can get abnormal Vibration.
Having determined these points they are then programmed out to avoid the comp running at these load levels!
Following on from your comments I was wondering if you have a similar situation with your booster comp.
Steve.

[RANGER1]

Vibration analysis is being used to monitor/trend for abnormalities, but these machines run 100%loaded 3000 rpm all the time.
Your vibration comments i thought were mainly used on VSD machines to avoid certain frequencies (vibration) and loads to avoid.

[Grizzly]

Vibration analysis is being used to monitor/trend for abnormalities, but these machines run 100%loaded 3000 rpm all the time.
Your vibration comments i thought were mainly used on VSD machines to avoid certain frequencies (vibration) and loads to avoid.

You are correct Ranger, so as you point out my thoughts are irrelevant in this instance.
Keep us informed as to how things progress and you never know someone else my have some valid input?
Good Luck, Steve.

[US Iceman]

Vibration analysis can also be used to detect the frequency ranges where the bearing failure might occur. So, I would not rule this out.

Has anyone checked the oil quality? I'm not familar with these machines, but if one bearing is the culprit the direction of oil flow or lack thereof may be a determining factor also.

[keepitcool]

Who's package is it on? FES? I have worked with Kobelco machines on FES packages a fair amount and have not seen this issue with only that many hours. I have not seen any Kobelco packages in refrigeration just in gas compression.

[RANGER1]

Its in gas compression and not FES package.
We will have to find oil filter micron rating as well as oil pressure and oil quality.Oil galleries did have coating of sludge.

[TXiceman]

Which side do you feed the oil from, the male or female side?

Ken

[RANGER1]

I have not been to site, but from pictures it looks like oil is fed in both suction and discharge end of machine.

[RANGER1]

The oil galleries are quite big and feed nozzle plates on each bearing. The feed into suction/discharge ends is central,branching off to each bearing.
Nozzle plates were checked for blockage,all ok.
Bearing that failed seemed to be picking up on each end of roller bearing and same on inner race not in middle at all.
Apparently oil may not have been changed in 4 yrs ?

[TXiceman]

Since this is a gas compressor and I presume on an open cycle, you need to pull a gas sample and have it analysized. Also get an oil sample under pressure and have it checked.

You need to be looking at free water vapor, CO2 and SO2. All of these can cause problems with the oil.

What oil are you running? I'd suggest you contact CPI Engineering in Michigan and have the gas data handy.


The reason I ask about which side the oil is fed is that if you are feeding from the male side and the oil is internally going to the female side, it may be a lower pressure and getting someof the gas to flash out which would provide less lubrication to that bearing.

Years ago I had a Howden compresor that was killing thrust bearings and when you looked at the main journal bearings, the female side had a different wear pattern than we were used to seeing. After a lot if investigation, we found the thrust beating cups were not cut true tot he bote and were puttinf a slight angular load on the female rotor. It was just enough to cause a bit of premature bearing wear. We had the cups trued and no more problems.

SO you might check the female bearing alignment compared tot he male rotor bore.

ken

[RANGER1]

Thanks Ken,
Unfortunately had to rebuild compressor in a rush.If similar problem again it may be worth checking bore alignment from front to back and thrust bearing face for true etc. Thrusts running true is also a good idea but difficult to adjust,as you would have to have it machined (you would have to be pretty confident before doing this ).Machine seems reasonably free to turn over for something this size,but alignment of rotors (if incorrect) could put excessive load on this bearing that has failed when running.
Machine looks very similar to a frick and has roller bearings for mains and single row ball for thrusts (unlike most older conventional back to back angular contact bearings).
The client is looking at oil viscosities , type etc.
I guess it will take a bit of time to get all info together to make a more accurate assesment.

[hammurabi]

Kobelco use NSK bearings? Anybody has bad impression of NSK bearings?