I would like to get some opinions on journal bearing installations and procedures that everyone used when they replace one. Do you just take the old one out and slap the new one in and hit the start button or do you do additional tasks? I have by own opinions and policies, but I would like to see what others do. Please be as descriptive as you can. Thanks.
For any journal bearing, I would never just "slap them in" as you call it. Why did it fail in the first place? It's a good bet there is some sort of damage on the journal so at the very least I would check the journal for wear, rubs, pitting, scouring etc. before fitting new shells/liners. I would also check both shaft and shell diameters to make sure they are going to give me the correct clearance.
On larger bearings, probably 2" diameter and above (really depends on application/speed etc.), after cleaning up the journal as required (and this could entail anything from just a clean to complete re-machining work) I would want to "fit" the shells properly myself. I would NOT rely on what the supplier has given me.
This "fitting" would entail "blueing" the journal, fitting the shell/s and turning the rotor a couple of revolutions by hand to transfer the blue to the contact area on the shell/s. With the weight of the rotor on the bottom of the shell as it will be, you will obviously be looking for a nice even blue pattern along the bottom of the shell. Looking at this blue pattern you can see everything about that bearing assembly including alignment. Any "high" spots (climbing up the shell sides for example) will also be very obvious and these shold then be "scraped" to remove. This procedure should be repeated until you do have a nice even contact along the bottom. If you have never done it (scraping)before, you do need to be very careful as you can obviously damage the white metal quite easily with the hardened steel scraper. You might want to practise on an old shell first!
You can check your final clearances by applying "plasti-guage" or similar along the top of the journal before fitting and tightening the top shell.
That should do for now. I'm sure you'll get loads of other good advice.
Tilting pads? Regular sleeve bearing?
Clean, clean & clean. Set bearing and measure to make sure you have the right fit. Measure clearance and document hard copy to file.
I have Elliott compressors. When setting and aligning I do an electrcal by-pass to start the aux oil pump and have flow before turning the shafts.
I was called to do a start-up documentation. Setup the vibration equipment and did a start. (everything had been rebuilt by a contractor and installed). Upon startup I noticed a rub at 0.03 IPS and told them they would crater in 15 minutes from drag-up of seize of the bearing - they shut-down immediately and babbit had drug-up to remove all clearance. So, a save before it went too far. They had made a pour using diametrical clearance for total clearance.
Thank you for your responsed gentlemen. To answere a few questions. The reason for the change was due to high temperature. I will include a picture of the original bearing and the new. The shaft was cleaned and measured as was the new bearing, prior to installing the new bearing. There was no obvious wiping with the old bearing.
Our instructions for installing and looking for a contact pattern were to blue, install lower bearings half, set shaft on bearing and then remove, without turning the shaft. The shaft is 4.5" dia. The bearing is a shell insert style, not spin casting.
21_FWP_Lower_Inbrd_Brng_-_notice_contact_pattern_becomes_heavier_toward_step_up_gear_3-1-07.JPG (939 Kb, 195 downloads)
picture of new bearing.
new_brg_with_blue_check_no_rotate.JPG (1,246 Kb, 162 downloads)
A feedpump I picture as a horizontal machine. But in my limited experience, the horizontal machines I have seen have axial distribution grooves spaced 180 degrees apart, vertical machines sometimes closer like yours. Is it horizontal or vertical machine?
The old bearing shows a pattern of heavy wear down the center that I associate with heavy load. With light load you should more get uniform wear. With heavy load, the bearing flexes but least flex occurs at the stiffest area where the rib supports the bearing from behind in the center and this is where the wear occurs during heavy load. It's tough to tell whether that wear pattern continues around the whole bearing, but if it does that suggests a heavy rotating load. Otherwise if in one area then heavy static load.
Just to think through all the possibilities: High temperature can come from high load or misalignment or clearance too tight or perhaps oil system malfunction. Plastigage should give you an idea about the clearance (I'm guessing it should be at least 6 mils although OEM should be consulted if possible). Alignment of bearing to shaft is checked somewhat by blue check. You can also do a feeler gage check at the corners of the bearing. Also check oil supply temperature and drain flow from the bearing. Anything unusual on vibration? From the removed bearing, it didn't look like misalignment to me (that should show up as an assymetric pattern), but did seem to look like a possible loading problem. But that is just a rough guess... definitely best to keep an open mind to all the possibilites.
Back to the original question: our standard practice would include blue check and a plastigage check of shaft/bearing and a plastigage check of bearing/housing.This message has been edited. Last edited by: electricpete,
Here is some more info on the pump in regards o some question. Horizontal machine, 5100 rpm, non-lubricated coupling with 10" spool. All clearances at .006 (.005-.007 manufacture rec.) Aligned to manufactures offset at cold condition. We don't have the equipment to perform continuous monitoring for alignment changes nor can we get isolation quick enough to perform a hot alignment check. No vibration indications of any problems.
What oil are you using? At this surface speed, approx 6000ft/min, you should probably be using a fairly "light" turbine type oil, with a viscosity of around 220 cSt @ 40˚C.
I had a largeish (12 ton rotor) steam turbine driving a blower for the FCCU that initially exhibited high bearing temperatures. We couldn't shut it down for operational reasons so we "changed out" the oil, on the run, to a slightly thinner oil, and the temperatures came down immediately.
As far as I know it's still running!
Like the Caveman: IMHO he's spot on with the oil recommendation. I've had large machines run super long w/no brg failure 12+ yrs.
Oil is a synthetic 46 weight. Manufacture calls for a mineral 32. I don't know why we switched to the synthetic. We have four identical pumps using the same oil and bearing temps are 160-190. The 190 is our concern. As our cooling water starts warming up in July our projected temperature will be over 205 degrees. The manufactures rec. limit is 200.
Just to followup some more on my comment about wear down the middle.
The only time I ever saw it before like that is on a 2500hp sleeve bearing motor after a rotor problem caused 0.6 ips housing vibration for several minutes (shaft movement not measured).
There was fatigue damage on the bearing but also a heavy wear cirfumferntial wear pattern right down the axial center of the bearing (on both bottom and top halves, slightly heavier on bottom half).
If you look where the wear pattern is, it is exactly where the bearing is supported on the outside by a housing rib. On your bearing I think the rib is on the bearing but the result is the same. That is the basis of my theory: When the rotor pushes against the bearing, the outsides can flex but the center is stiff due to support from the rib. I don't think normal loading will cause that type of flexing (unless it is a very flexible bearing?) and I haven't seen it anywhere else.
Out of curiosity - has anyone else seen this type pattern? Would you agree it indicates heavy loading or are there other explanations?
Bearingfwbpsmall.ppt (262 Kb, 162 downloads)
In a previous post you mentioned a blue check of the shaft and bearing. Can you expand on this some more? (Where is the blue placed, do you rotate the shaft, what do you do after viewing tne blue printing)?
One way to do a blue check:
Bearing is installed at the opposite end.
Shaft is set on blocks this end.
Bearing is removed. Coat bottom half of bearing completely in blue.
Carefully roll the bottom half bearing back under being careful not to scuff.
Remove the blocking.
Roll a few turns.
Put shaft back on blocks to carefully remove (without scuffing) to check the bearing.
You expect to see a fairly uniform strip of contact accross the bottom of the bearing with 80% contact accross that patch.
Another way to do the same thing is a dry roll scuff check. Scotch brite the bearing nice and shiny. Then roll and the lack of lubrication will cause a scuffing of the shiny bearing surface which gives similar pattern as the blue check.
I think the dry roll scuff check is a little easier to do because you don't have to worry about disturbing the blue pattern while installing/removing the bearing (easy to do). But you may not see the pattern t quite as distinctly.
If I said anything that doesn't sound right, I hope someone will correct me.
Generally the blueing is to check the bearing and fit properly out of the machine for bearing fit purposed and correction.
An in situ check would be lift check and plasti gage.
So I don't think you want to put blueing on a shaft in situ and turn it with weight of rotor on the bearing with no lubricant.
What do you do if you don't see the 80%? Say you only see 25%?
Sam - we do it in-place. Have always done it that way, and I think many others do as well. I don't know any problems caused by it. Note that the machine weight goes onto the dry bearings whether you roll or not. The roll does scuff the surface but I have always ASSUMED it was not destructive. The one possible problem I can imagine is if you got carried away with many many rotationgs you could put a wear pattern on the bearing that might tend to create a smaller radius (shaft radius) pocket in the bearing and disturb the delicate balance of shaft radius slightly below bearing radius which creates the proper preload. But from one or two turns? I'd be interested to hear more comments from Sam or others if this is good or bad or common practice.
If you don't get a good blue check, then the cause is either misalignment of the shaft within bearing as it sits when rolled... or bearing needs to be worked on a little. Investigate misalignment by checking level and do the feeler gage at 4 corners. As far as the bearing, you can try a light scotchbright, but most likely to correct a poor contact pattern you need to give it to someone knowledgeable in bearing repair, especially if you are going to do some scraping.
Having 25% contact area reduces the load carrying capacity of the bearing by 75% and will cause it to run hot. I agree with Pete that you need to have an experienced technician scrape the bearing in. You need to end up with at least 80% contact. On a high speed machine, you also need to make sure that the contact area doesn't get too wide because that can also cause heating. If you don't have anyone on site with bearing scraping experience you should check with your local large motor repair shops.I worked in the motor repair business for 30 years before moving to Trane. We always verifed the bearing to shaft fit using prussian blue.
You can have your standard and blue and check pattern scraping in true.
You can set the rotor into the bearing using plasti-gage (which I perfer). This will give you all cleanances in mils and tell you where to scrape. Blue for pattern; plasti-gage for clearance. I don't see where blue will give you clearance; only pattern - am I missing something? Some will use solder (rosin core) for checking cleanance on some machines. I could be missing something.
As Joe said, verification. Make the bearing round, parallel (taper free) and within tolerance specification.
Me personally, I would not like to set a large rotor on a bearing having only blue and turn the rotor on a 'dry' bearing. I would rather use a standard, scrape-in, then verify.
Cheeezzz! All this just to come back with what I said back on the 12th!
We've been bluing/scraping LARGE rotor weight bearings, and I'm talking 20 ton+ for decades, in situ. There is no harm at all to the bearing by rotating the rotor slowly, as that is where it starts with a great big bang every time you hit the button.
Scraping is not for the amateur. You need to know what you are doing or you will do more harm than good.
By the way, us old engineers also used to "fit" steam turbine casings by blueing and scraping! It's an art and unfortunately, along with apprentiships and good engineering practices, it's dying.
Who said that blue gives you clearance? No-one that I saw. I said that we do both plastigage and blue check (15 March 2007 08:38 AM) which is logical to me since they are checking different things.
|Powered by Social Strata||Page 1 2 3|