Thrust Pads

[ArkSeaJumper]

Another puzzle for you all

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This is a photo of one of a set of thrust pads I have had to change, I am not really concerned about the scoring, as much as the dimpling effect in the white metal on the pads face. This face should be smooth.

See the comparison photo.

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[ArkSeaJumper]

A close up for you

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[JK]

This is an excellent one!
There were 4 of us, the PDM engineer (predictive maintenance), the LO analysis guy, myself and the other marine engineer, clustered around the computer monitor having a look. Consensus, after a lot of debate, is that is a pretty cool pattern LOL.
( what can I say, we just found out we are getting a pay cut so our work GAF is low.)

Is this shaft reversing?
Is this the original thrust pads or have they been re-furbished?
If they have been re-babbitted, was it a pour or centrifugal casting?

[ArkSeaJumper]

To answer your questions first.
No the system is CPP, the shaft only goes one way, the pad in the middle photo is an ahead pad, one of 9, with astern pads, all with the same pattern.
These are the original pads, the gearbox they came out of has 8000 hrs only.
The makers have no interest in referbing these.

We have 13 of these gearboxes, I have inspected 10 so far, the only ones with the pattern are the newer ones the top 4. I will have to change the pads on these 4.

[The Dieselduck]

I would lean to say that it is a defect in manufacturing. The pattern, in a argyle fashion, is just too perfect to be simple wear. Like JK said it seems perhaps the babbit separated due to a bad process. The rest of the wear was probably accelerated by the babbitt falling off. It would not surprise me to hear that a company sweeps this under the rug, shit does happen, but sometimes its nice to hear that you are not going crazy and that a defect does indeed exist, if that is the case here.

[JK]

I was thinking the same thing Martin.
Since it is in the newer gearboxes it could be a manufacturing design issue.
Is the pattern in the steel back, and as the Babbitt wears, the pattern is being exposed?
The cracking in the babbiit is concerning. It is good you caught this before the Babbitt started to disintegrate.
Had the bearing temperatures start to spike, Arksea, did your LO analysis start to show high metal content or was it a routine inspection?

Have you ever noticed that this type of discovery is made when: a/ the ships budget for the year is either gone or just about gone, and b/ everyone around you is shrieking that the ship needs to be in service.

There is an excellent company here in Canada that I send all my stuff to:
http://cbb.ca/en-index.html

Somewhere on my work computer, I have pictures of failed Babbitt bearings from a L&S gearbox . I must see if I can find them. It has a good background story to go with it.

[ArkSeaJumper]

Unfortunate, this was discovered the hard way, the oldest of these vessels had a catastrophic failure of the thrust pads. The pads failed, to the steel, and badly damaged the thrust face, so we had to strip the gearbox completely.
The first alarms were the differential pressure on the HP lub oil filters, followed by the high temp on the pads. Of course the ship was sailing down a river at the time, (Loaded) so had to continue for a little while before going to an anchorage.
The oil analyses does show, with hind sight, an increase in iron, but not across these ships , I would say this is more likely the clutch wearing. The clutch is giving us a lot of problems also.

The manufactures are unofficially helpful, I can talk to the worker bees on the phone and they will point me in the right direction, but I get nothing official, or any admitting of liability, strangely enough.

What I am slowly finding out is the assembly of these boxes was moved to an other country, (cheaper labour), nobody will tell me exactly when, but I have a feeling I know.

It almost looks as if the pads were machined with this pattern before assembly, with one theory being, someone felt there should be dimples or oil pockets, to trap oil on the face of the pad.
This is definitely not the case, the oil will not form a wedge on this type of surface, too many escape routes.

[JK]

These pads must have failed in a very short period of time, I had thought it was a failure over a period of weeks.


In the gearbox that we had bearing problems with, the high tin levels in the LO analysis indicated there were bearing issues and we were monitoring it very closely.
When the temperatures started to climb, we brought the ship in and had a remote inspection by fibre optics done through the inspection ports. As the gearbox rotated by the turning gear, you could see the babbitt moving up and down on the edge of the shells. Then we dismantled the cover which is a fairly labor intensive job. When the bearing caps were lifted off, the babbitt fell out.
There were a couple of problems that we found. The port engine was misaligned, it was at the correct vertical distance for growth, but they had set it above the centerline, instead of below. The gearbox whirl had not been taken into account and all the journal bearings had worn on the top of the bearing.
The second thing was the bearing thermometers pockets had been screwed tight to the bearing caps. Several of the journal bearings had babbitt failure directly below the pockets where they could not expand. There was an adhesion problem with the steel back. Then when the journal bearings went for rebabbitting, they didn't match the drawings so they had to be spray welded and machined true. We also found ahead pad on the reverse side of the collar.
To make sure the engineers had a fighting chance the next time around (hopefully not for a long time or never ) I had RTDs fitted at the bearings and a remote temperature display in front of the engines and in the control room.
These specific gearboxes are rather interesting. They had been designed for roller bearings, but the owner wanted the bearings, so the manufacturer had redesigned it.

[ArkSeaJumper]

Very hard to tell, how fast it failed, after all I only have examples of the astern pads, the ahead pads are completely wiped. Even CSI wouldn’t tell much from them. The white metal was , mmm, elsewhere in the gearbox.

[JK]

The Irish CSI, a new series coming to a TV near you .

So if the Mfr is not taking responsibility, where do you have to ship the pads for refurbishment?

[ArkSeaJumper]

I have decided not to referb.

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[JK]

Wow, that is impressive in a car-accident-sort of way.

[Dieseldame]

This pattern looks very similar to a pattern I saw in an online video course on Mechanical properties of materials out of Michigan U (ITunes U based) as an example of a type of metal fatigue. The course instructor's name is Walt Milligan, his email is [email protected], maybe he will have some insight into what the pattern represents.

DD

[ArkSeaJumper]

Thanks for that, I will hold off for the moment on contacting him, I am almost convinced this pattern was put on the pads before instalation. Anyway I have a meeting with the makes in a few weeks.
I will forward to all the answers then.