Line shaft Bearings - Vessels

Get thee in haste to your bearing supplier and purchase bearings that are oil lubricated for your application and speed RPM as it could be one of four things: the bearings are the wrong ones for the application, the grease is not staying in place because the seals are blown, or they are not getting enough grease, or they are not being greased adequately.

you have not really told us a lot of information.

What Diam is shaft, Where has grease gone, are seals leaking to let grease escape

Hy, the shaft diam is 125mm and the sealings on bearing house are OK.

The gresa comes out of bearing but not comes out the housing, only the grease is not inside the rollers.

I think the centrifugal force remove the grease from the bearing !

Is too much speed for this bearing and this is a SCHOTTEL propulsion project.

Thanks, Guilherme

Do the bearings become hot immediately after replacement? That would be an indication of overspeed.

5 bearings on a single shaft? Alignment would have to be near-perfect, or this set-up would bend & fatigue the shaft. Is this arranggement allowing any kind of resonance that might be damaging your bearings?

My friend, that is a SCHOTTEL Germany project and several ships with similar arrangement have the same problem, arround the World.

The aligment is OK.

A'm wayting for a result of analisys test made by SKF, because my companie don't support the cost of down time, etc.

thanks, guilherme

SOunds like bad design or bad replacement parts, SCHOTTEL is the one to correct this, unless other parts were used instead of the ones SCHOTTEL wanted to sell you to save $$$

Is there a pattern on which bearings fail? Always inside? Outside? Random. Have you checked/calculated the resonant frequency of the shaft? Have you checked the one per rev vibration level at each bearing? It seems logical that it is a vibratory or centrifigul problem causing the grease to migrate out of the contact area to the outer portion of the assembly leaving the contact areas w/o lubrication.

Well, the bearing near the CAT engine is number 1 and the bearing near the Schottel thruster is number 5.

All bearings fault, sometime 1 and 2, sometime 4, sometime 3, etc.

My ship have two lines shafts, port and starboard side, and in both lines the bearings fault, every month.

Tha propeller is type variable pitch and I can't improve more than 60% of pitch - If the pitch is came to 80%, the bearing temperature increase up to 100 degree celsius and the grease dont support this temp.

Look the SKF catalog and see the bearing part number 22228CCK/W33 - This type can support almost 60 tons load and aprox 2 tons minimum load, but the line shaft is very light, about 200 kg and 700 kg !!

I don't have enough load to turning the roller properly, I think !!

best regards, guilherme

As he changes the prop pitch from 60 to 80% the temp goes up fast. Sounds to me that the bearings are being subjected to a radial load they were never designed to handle. You need a thrust bearing in there some where to handle the prop thrust.Then grease every 2 days if the grease is gone in 3 days.

Hello It sounds like you have Cat driving shaft at 1600 rpm I was on similar (tug)driving aqua master i had experience with overheating and that was caused by too much grease. we opened good bearing ie, one that was not overheating and found the bearing rollers with very little grease in, we then scooped all the grease out weighed the grease, found out how much it weighed Then removed grease from overheating bearing and filled it with exact weight of grease from good bearing, sounds strange but it seemed to work

Ok my friend, you is right, excess of grease cause overheating.

But in my case, I realy put the correct amount of grease, like you, by experience.

Please, tell me what is your rpm speed ?

The roller bearing is the same model ?

What type of grease do you use ?

Thanks, guilherme

Hi guilherme,

With such a large number of broken, overheated bearings, has there been any damage to the shaft(s)?

When replacing the bearing(s) do they still fit the shaft properly?

If shaft(s) have wear or distortion from overheated bearings it could have something to do with your problem.

John

Dear John, thanks for your reply.

The roller bearing in mounting in a taper bush (conical) and when the bearing fault, the bush is damaged.

The shafts are OK, without damage.

In my opinion, the cause is high speed, bearing is not the best for this aplication.

This bearing is too heavy, big rollers and when the shaft is running at 1600 rom, the bearing don't support.

Ithink the maximum speed for roller bearing SKF 22228CCK/W33, with grease, is 1700 rpm, but not 24 hours per day !!

1700 is the reference speed, not work speed, i think.

In my oppinion, is a project error.

thanks, guilherme

SKF indicates as rpm limits 1700 for grease and 2200 for oil.So that a solution could be to change the lubrication but working with oil there is a need for a continous check and the countinous supply is cumbersome. There can be an other reason as well this shaft is on a structure which can -may be- deform under external loads. Even small deformations can generate due to the stiffnesses high loads and combined with a low grease presence it can destroy surfaces in contact.

It could be possible that the grease has not the right oil viscosity. It would be helpfull if you could make a short description of bearingsfailure or even bring a couple of photos.

For instance if rollers do not "roll" then there are flats and when a contact occurs shocks and edge effects destroy the lubricant film. Usually even if loads are reduced rollers will roll due to the shear in the gap. I think we need more input.

The LUBRICATION & COOLING of these bearings could be improved by replacing the grease lube with a recirculating oil system. The oil flow would carry away heat, & constantly replenish lubricant supply.

I'd use a medium-heavy (~ SAE90) hypoid gear oil, because i like the E.P. additive package. (Lighter viscosity for still higher speeds). Filter well, & maybe add some form of cooling (most likely not necessary)

See if you can get the original designer to co-op a solution with you.

You have contacted them????

Hi to all: I am reading my SKF manual (an old one) and there says that suffix "w33" means a circunferenial groove and three drills. I understand that these characteristics correspond to an oil bearing. Am I wrong? I think that for these drill the grease is going out.

Thanks for your comments,

The designer is SCHOTTEL Germany, and they sayd: The project is correct and you must check the foundation.

Schottel never will assume any kind of responsabilities, this is my fight for ten years or more !

Thanks, guilherme

Let us assume they are right. have you checked the frame (or as they say the foundation)? Is it possible that when used there are deformations more important than expected? One of the comments mentioned vibrations and harmonics. Have you done a measurement to quantify for instance the accelerations in the bearing plane in 2 directions? If the elasticity is higher than acceptable the bearing could be overstressed.

Today accelerometers are very affordable and with simple and low cost conditioners coupled with laptops one could make a very correct analysis (fft and other) for a reduced budget.

Nobody has mentioned the role of the harmonics in the system, which react at specific speeds. I chase gremilins in lineshaft bearings for pumps, too often. Key causes: Size of bearing & type for application. Specific speeds. Lubrication. Radial loads.

I would check your bearing spacing versus shaft diameter at specific speeds. Lubrication type rarely is a cause, allthough it can get you past the core issue in some cases.

Good luck.

The one thing I forgot was to ask if the bearings were split and if they(the bearing halfs) are locked together as well. this whole mess sounds as if the bearings should be oiled anyway as a matter of course due to the speed and loading.

It was mentionned before that the bearing is fixed on the shaft with a conus. A split bearing will not be assemblied this way.

The SKF 22228CCK/W33 is a one peace roller bearing.

Yes, lub by oil circulating will be a good solution, but expensive - Will be necessary to change all bearing houses, an oil pump, sealing, a tank, cooling and xx days off hire for this changes, aligment, mounting pipes, tanks (for portside and starboardside), pumps, electric parts, etc.

I'll go ahead, we need a solution as soon as possible.

Guilherme

I had a look at the Schotel home page. Which system do you use ?

The bearings are internal or external with respect to the systems they show?

Could you make a simple sketch since I think it is more complex and it will be necessary to know more about the actual system. Why 5 bearings? I presume the shaft is at least of 2 parts. What kind of couplings between those parts?

Do not be surprised that I ask -for you- silly questions my position is that it is better to ask a stupid question and have a good answer than to avoid the question and take a wrong path.

I'm not an expert on these matters but I'm curious as to the nature of the failure with these bearings. I've seen a few failed bearings over the years and the cause of failure is often indicated by the remains of the original bearing.

Hello

Just a thought what is your shaft coupling to drive, is it a universal corden shaft or similar,? if so, The greasing of these is often overlooked and can cause vibration through out the shaft, Normaly it is better to over grease these so as grease is thrown out of coupling making a mess on deck plate but at least you know they are greased.Shaft has linier movement as well as radial. Just a thought.

I'm in the business of marine shaft alignment and have encountered many different chronic situations that don't always result from an alignment problem. Having read the post, I'd like to offer a bit of input; some of it may be repetitive of other responses.

Bearings: Bearings in a line shaft arrangement are usually of a split design to facilitate shaft removal and or bearing replacement. Your arrangement (non-split) presents a difficult task in removal especially at the rate that you're replacing them. Vessels have a separate or internal gear thrust bearing to absorb thrust due to thermal expansion and vessel flex. It is extremely important that the bearing housing allows for outer race axial movement and that when installed, all 5 bearings are placed in the center of that longitudinal cavity; if not, the bearings will be subject to thrust beyond their design factors and generate excess heat that isn't being removed. The cavity in which the outer race 'slides', has specific clearances to the outer race. Too tight and the bearing will absorb thrust; too loose and the outer race might rotate or oscillate. Over heating of the bearing can cause the bearing to become seized by the housing and again absorb thrust.

Shafting: Sounds like the shafting size is adequate for the application as you haven't indicated a failure. How many couplings are there and what type are they? Was the additional mass and location of those couplings considered in the bearing spacing calculations. Is your bearing spacing too great, too short and or equidistant? Maximum bearing spacing (and I mean maximum) is formulated by:

L=(√((3.21xD)/N) x K L=ft., D=Ø in inches, N=max. shaft rpm, K=modulus constant

K is dependent on the shaft material and should be available from the shaft supplier. Too close a bearing spacing can also present problems in not allowing for shaft flex with the overall movement of the vessel underway. Has the shafting been shop checked for trueness? Have the couplings been checked for run-out while affixed to the shafts. What type of flex couplings are being used?

In closing I will make one other point to consider. You state that the alignment is good, i.e., it has been checked. I am willing to bet that the alignment was checked while the vessel was unladen. Whatever method of alignment check you are using should be repeated in both the laden and unladen states to determine if there is a significant difference. You might also be able to devise a method of monitoring the alignment deviations while underway.

Guest, thanks for your comments.

When I check the aligment, I remove the cardans and put "Pointers" : one on elastic absorber, one on the aft end of the small shaft, one on the other end of the small shaft, one on the aft end of big shaft, one of the other end the big shaft.

Is there any chance that you can provide a (1) dimensional drawing of the arrangement and (2) another dwg. that denotes the reference points and procedure for alignment you are using.

Elastic absorber? Is this a disc that is installed between two flanges?

Cardans, though specified by Schottel, may possibly be adding to the problem. Have a look at http://www.aquadrive.com/ . They make CV joints which might be better applicable to this arrangement. They seem to market towards the yacht market but I have seen commercial applications.

I just recently found this site and quite enjoy it. Guess I'll have to sign up!

I mean "Elastic absorber", but is rely a elastic Coupling Centa, between the engine flyweel and the first shaft flange.

Schottel is the most famous azimuth thruster maker of the world, but this kind of project is not good, in several ships they have bearings fault, but only wuhen the bearings is 22228 CCK W33 model.

This bearing is ntoo big, to much mass on roller, and the speed above 1200 rpm is critical, they dont support !!!

But.....skf said: No, the bearings are good, they are Explorer type, up to 2000 rpm !!!!

On the real world>>>>>>the bearings dont support 1600 rpm !!!

I am the guest and now member who replied the last two times.

Are the other vessels having this problem the same class ship and or application?

At the expense your company is going to with down time and labor and the cost of new bearings, I think you should seriously consider changing the bearing type you are using. For ease of alignment, installation and replacement I recommend the split type. You are on the borderline for rpm but get in touch with Cooper Bearing http://www.cooperbearings.com/ or Craft Bearing http://www.craftbearing.com/ or a like manufacturer and explain your situation. What may prove to be more effective in these types of bearings is that they are roller bearings and rely on the spherical housing to correct for misalignment and eccentricities. You can actually put your finger between the pedestal and cartridge and feel any oscillations which will help you trouble shoot a problem. Of course, proper alignment is critical and the amount of grease applied is even more critical.

The replacement will be expensive but a wise investment considering your down time and even if the problem persists, the change-out for a split bearing of this size is about 1/2 hour. If the bosses are skeptical, suggest changing out one side.

First, this same problems we have in different kind of Hull and applications.

There are a Tug Boat company in Rio, small boats about 28 meters, two line shafts whit 7 bearings each and when the engine rise to 1800 rpm, the bearings temperature drop to 100ºC and more...and....

Another boat is an Offshore supply vessel, 78 meters long, two lines shafts, 5 bearings each line, and the shaft speed is only 1600 rpm 24 hours a day, but the propeller is controlable pitch. When the pitch rise above 60%, the bearinsgs warm !

Yes, you are right, but the shaft diameter is 123mm on bearing position and I dont know if the cooper have a Ball Bearing for this.

I realy know that a split type is better for us.

i'll take a view on Cooper site.

Thanks,

Now I'm really interested in your problem.

1. With the pitch at 60% the bearings run hot and wear out prematurely.

2. With an increase in pitch (torque) at the same 1600 rpm, the bearings quickly heat up and burn out.

Like you, I am a marine engineer and rely on my experience and instincts to figure things out; the engineers at Schottel and the naval architects have already run the numbers on this arrangement so we have to assume they are correct. My instinct tells me that it is one, some or all of the following.

1. Shafts that are untrue or not straight and or the couplings fitted to the shafts are not running true with the shaft.

2. Fatigued or worn Centa element(s) in the couplings and or worn cardans.

3. Alignment of the shaft line: a. bearings relative to each other, b. shaft to propulsion unit, c. shaft to the gear output flange.

4. Vibration and or oscillations that are the result of the above.

It's the change in load rather than speed that leads me to these points. As the load changes the torsion on the shaft changes, thus the deformation of the shaft (if it is untrue) is more exaggerated. The bearings are the spherical roller type so they are designed to 'flex' with shaft bending, but not shaft eccentricity. The eccentricity the shaft transfers to the bearing at that speed is going to create a lot more heat; now increase that eccentricity with an increase in load and what do you have. The same results occur with worn or poorly fitted couplings.

All too often, installers rely on the 'flexible' components of a drive train to absorb all of the 'misalignment'. They can usually get away with a lot but it ultimately results in premature failure of the components flex elements.

Primarily, I perform optical alignment. This is one of the most accurate methods that's been around for many years. I can't quite under stand the procedure you are using to check the alignment, but if the shaft is in place and you are rolling and dialing it, you won't see an indication of misalignment and possibly not even shaft run-out.

Optical alignment is performed with the shaft removed (while it's at the machine shop being checked with the couplings of course) and ideally in split bearings whence the lower pedestal is aligned and secured. The shaft is then lowered and bearings assembled.

By the way, where are you operating out of?

Hy Mareng, thanks for your comments, you know this.

I tell you now, Schottel knows that this bearings dont support this rpm and realy the rollars are spheric type, but NOT support misaligment - The maximum misaligment on bearing is 0,3 degres.

Do you have an e-mail that i can send to you a line shaft drawing ?

This instalation dont have a gearbox.

My method for check the aligment is in the Schottel manual - Remove the cardans and instal points.

The flanges coupling are thight by hydraulic force by skf pump. Is not possible that the flanges are loose.

The lines shafts have today 13.000 operating hours and the Centa flex coupling is original ond OK.

I'm wayting for an vibration analisis made by SKF Brasil.

Thanks, guilherme

You can email me through the forum membership.

Check your mailbox/messages as well.

Dear Mr.guiltherm,

Were you involved in the SELECTION of BEARINGS.? There are definite Principles in selecting the Bearings. What is the centre distance between bearings.? 1600 RPM speed is NOT HIGH SPEED. But bearing failure is abnormal, centres around Selection Criteria.

Pl.post additional details.

DHAYANANDHAN.S