ID of Babbitt lined Bearing 1

[ahafeez3131]

Dear Fellows

We have a Babbitt lined journal bearing with excessive wear. Now we want to re-Babbitt the bearing. For the re-babbiting we have to give finished ID to be maintained. The shaft dia (journal) is 330 mm, with a speed of 3000 rpm.It is an oil lubricated bearing. What should be the ID of finished bearing. We have an old drawing showing "OIL CLEARANCE 0.416 to 0.516" . Does this means that the ID would be 330.416 to 330.516, but we are not sure about it. At another place on the same old drawing it says 330.832, but it is not a very clear drawing. Can any body guide me in this mater.

Also what surface finish we demand for this material.

Regards

 

[MikeHalloran]

I'm guessing that the oil clearance spec is radial, so the minimum bearing bore diameter would be 330.832, and the maximum would be 331.032.



Mike Halloran
Pembroke Pines, FL, USA

 

[ahafeez3131]

Ok, i am attaching the view of Bearing. Please have a look at it.

Regards

 

[electricpete]

OEM is of course best one to ask for clarification. In absence of OEM input, I vote to treat the 0.466 mm nominal shaft/bearing clearance as diametrical (rather than per-side),
for two reasons:

1 – that is the way I usually see it specified. It is checked using plastigage or calipers.... either one directly computes diametrical. (for clearances checked with feeler gage I often see clearances as per-side... but this clearance is not checked by feeler gage).

2 – You have a 330mm 13.1” shaft.
Clearance is specified as 0.466mm = 18.5 mils.
That is about what I’d expect for diametrical clearance. For electric motors (may not be exactly applicable, but the only reference I know), for 13” shaft, ANSI/EASA standard AR100 specifies a clearance of 14-16 mils. 18.5 is a little on the high side per that spec, but 9.25 would be way low.


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(2B)+(2B)' ?

 

[electricpete]

2 - If you looked at how it's called out on the drawing, it suggests the shaft is laying on the bottom.
The 0.466mm dimension is called out specifically on the top side indicateed by two lines spaced apart. There are no such lines on the bottom. There is a little bit of extra fuzzy circular line on top of shaft which is not present on the bottom...I believe this is mean to suggest presence of clearance on top and not bottom (shaft resting on bottom).


=====================================
(2B)+(2B)' ?

 

[JJPellin]

I agree with the interpretation provided by electricpete. In addition to the bore, you need to be sure that the oil distribution grooves at each side are maintained. The print shows to the overall dimension at these grooves. But, these grooves do not normally extend the full width of the bearing. There need to be dams at the ends to keep the oil from spilling out the ends. Hopefully, your worn bearing is still in good enough shape that you can duplicate the oil distribution grooves with the dams at the ends.

Johnny Pellin

 

[stgrme]

I would not recommend proceeding with any machining of the bearing due to inconsistencies in the dimensions in millimeters and in inches. I would contact the original manufacturer to obtain clarification before proceeding.

Dimensions not converted correctly:
- 330.000 mm actually equals 12.9921 inches
- 330.832 mm actually equals 13.0249 inches
- 330.416 mm actually equals 13.0085 inches

I agree that 0.416 mm to 0.0516 mm is a diametral clearance because it is only shown at the top of the bearing.

Please note that the dimension of 330.832 mm at the horizontal joint may indicate that the bore of the bearing is elliptical. One way to obtain an elliptical bore is to add shims (spacers) at the horizontal joint before boring the bearing. After boring, the shims are removed, producing the elliptical shape.

Please consider these issues before taking action.

Best of luck!

 

[ahafeez3131]

Thank you very much for all the informative advice. Can anybody comment on the surface finish we should consider for the Babbitt ID surface in mm system.

Regards.

 

[Tmoose]

What do you know about the size, form, and finish of the shaft journal diameter?

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http://machinedesign.com/article/proper-film-thickness-key-to-bearing-survival-1214

The professor says this -
"Such shafts commonly run on soft babbitt bearings with an Ra = 64 in......After a few start-ups and running hours, babbitt typically polishes to about Ra = 16 in."

 

[JJPellin]

On closer examination of the drawing, it appears as if stgrme is correct. The bearing is designed to have an elliptical bore. This is what is commonly called a "lemon bore." It would have to be bored with a shim at the split line. So, the question of whether the clearance is specified on the radius or on the diameter takes on a new significance. The clearance of 0.416 mm is diametral in the vertical direction and radial in the horizontal direction.

Johnny Pellin

 

[jkwhalen]

The bearing bore is clearly elliptical.

I'm surprised the journal diamter is exactly 330 mm - did you measure it in several locations?

For a 330 mm journal the vertical bore should be 330.416 +.1/-0 and the horizontal bore should be 330.832 +.1/-0

I wouldnt worry about the conversions to inches. The bores above result in clearances of 1.0013 mm/mm vertical and 1.0025 horizontal - industry standards. (Results in a 0.5 preload)

Babbitt surface finish of 32 rms is sufficient.

We rebabbitt bearings all the time and this is what we would do given the information supplied. However we would probably cut the tolerance in half since 0.1 mm is rather generous. Oh and we would attmept to measure the bearing bore as recieved best we could (depending on condition).