Oil flow rate for a babbit guide bearing

Why do not ask the generator supplier? Most probable he did not only computations but also tests before he delivered the device.

There are spread sheets for hydrodynamic bearings computation but it is better to use supplier as source.

If it is a horizontal shaft machine it may well have a revolving oil ring that just sits on the shaft and rolls along as the shaft rotates. The lower end is submerged in an oil sump and it just spills the oil out of the concaved inner surface of the ring on to the shaft.

This oil ring is mounted in a vertical groove in the middle of the horizontal bearing.

These bearings have a large surface area and this is what keeps the loading forces down. P= F/A (remember that one)

So with a low loading very little oil is needed to provide adequate lubrication.

Vertical shafts have journal and thrust bearings these require a more positive flow but not much.

As stated in the post above check with the original equipment manufacturer. They will no doubt be happy to make your acquaintance and tell you anything they want you to know and sell you anything they can for years to come. It is a symbiotic relationship.

Sorry for the delay in responding to your answer. Could you please explain what the P=F/A stands for and what it means? It is a vertical guide bearing (not load bearing), not a thrust bearing. Thanks for your pervious answer and your time and interest regarding this matter.

Years ago I worked as a millwright in the steel industry and we used these type of bearings in quite a few applications . It was a 90 weight oil the was on a drip application that had one drop ten seconds . The rpm and Dia were very similar to yours .

You just don't want to run it dry as scraping a new bearing was not a fun job

cheers

In a nut shell a bearing has to respect two conditions:

1- the specific load = F/A = Load /Contact area MUST be under a threshold

2- the product between this specific load and the tangential velocity of the rotating part (since there can be a bearing with outer ring turning) MUST be under a threshold which depends on several factors as oil type, design of bearing, type of load, environmental temperature, roughness and several others.

As you see the problem is quite complex wuthout being complicated thus may recommendation not to do some thing which could harm the bearing and contact the supplier, the original designer of the concerned bearing.

An error is easy and then the cost can be too high to make it back.

I see that you do not get the right answer so that here is an explanation why

Your question although apparently simple is not so easy to answer. Of course a superficial answer can always be given but the consequences can be disastrous.

The reasons are as follows:

- The goal is to accept a radial force without destruction of the bearing i.e. without metal to metal contact which means that the oil edge will support the load with a minimal distance between shaft and bearing greater than the roughness.

- This capacity depends on the oil viscosity which depends on the oil temperature reached in function

- Now come the problems, first the oil shear generates heat which has to be eliminated and this is done by an oil flow and by the conduction-convection of the bearing itself.

- As far as I understand the bearing is vertical and because of gravity oil will always flow from top to bottom, this flow also being function of viscosity and thus of temperature.

As you see the oil flow cannot be estimated without an in the depth analysis of the bearing way of working.

The steps should be:

-define the maximal load the bearing has to support

-define the type of oil and obtain information about its viscosity-temperature dependency.

-estimate from the bearing design how the heat will be evacuated via conduction-convection

-estimate the heat generated in the bearing when in function

-estimate the gravity supported vertical oil flow

-estimate the oil flow requested to evacuate the rest of heat

- make the sum of the two

Make sure that the bearing has always this amount of oil at its disposal.

Following graphs show for an industrial oil, first the evolution of the radial portant capacity versus eccentricity and at different temperatures and second the evolution of the estimated heat transferred powers and oil flows versus temperature.

This shows how complex has to be the true answer for a simple question when it is possible due to experiences which in fact cannot be extrapolated to generate a high risk!

Each line indicates in Newton ( 1lb=4.448 N) the radial force for a given relative eccentricity of the shaft. The parameter is the oil temperature in °C. The relative eccentricity is the ratio between eccentricity and radial gap (half of diametral gap)

Blue- power generated by friction which decreases when viscosity decreases due to temperature increase.

Red- estimated Power transferred via conduction-convection

Green-Yellow-Flow required to eliminate rest of heat

Violet- Vertical oil flow due to gravity

Light blue- The oil flow to fulfill both requirements.

Above values are valid only for the oil I used as example (1200 cSt at 10°C and 6.5 cSt at 100°C) and are not valid for the oil you have if it has not same viscosity-temperature evolution. The values were computed for the geometry and rpm you indicated.

In this respect may I inform you that the gap is very small with respect to usual values so that I am asking myself if you gave the diametral or radial gap.

Hope it will help at least as an order of magnitude.

Nick Name

I appreciate your time and effort regarding this matter. I will have to digest it. I may be back on here asking you to explain something I don't understand. As of now the bearing in question is in operation at 1GPM as recommended by the vendor. Thanks again!

Could you measure oil temperature before and after bearing?

According to the graph the temperature should be under 60°C. It would be interesting to check how accurate was the estimation.