Sleeve Bearing Wear

[MechEng2005]

Greetings all,

I have an application where I need to look at a Ampco bronze bushing to determine the life. I have determined the static loading and verified that the material will not yield. However, I am looking to see how much wear can be expected.

First off, I have an equation for the pressure of:

P = F/DL

where P is the nominal pressure, F is applied force, D is diameter, and L is the contact length of the bearing/shaft. However, do I need to calculate the pressure of the shaft on the interior of the bearing and add the pressure for the housing on the bearing to get the total pressure? I would think so, but the examples in my reference only calculate the pressure based on the contact between shaft and bearing interior. My bearing wall is about 75% of the shaft diameter.

Secondly, does anybody know where I can find a wear factor to use for wear? I have looked at the lubrication, with general grease, and found that it is boundry lubrication. The speeds are very slow (< 1 ft/min). My reference lists wear wear factors for a number of materials, but not for Ampco (not surprisingly). The best I can do at this point is make a graph of the amount of wear in a given time/cycles versus the wear factor for the range of factors I do have.

Oh, and I also found that I had a VERY low value for what my reference calls stable lubrication, which requires:

uN/P >= 1.7x10^(-6)

u: dynamic viscosity
N: speed, in Revolutions per minute
P: Pressure

When I use this equation, I end up with units of revolutions, though the reference seems to think it is unitless. I don't see how revolutions would cancel, and think I am correct. I think my value is very low since my speed is low and pressure is high. If anybody is familiar with this equation, could you verify that the result of uN/P really does have units of revolutions?

Anybody have any suggestions for a different way to look at or calculate wear? Or anyplace I can find more information?

Thanks in advance,
-- MechEng2005

 

[electricpete]

do I need to calculate the pressure of the shaft on the interior of the bearing and add the pressure for the housing on the bearing to get the total pressure?

Shaft on bearing - yes. Housing on bearing - I have no idea what you're talkiong about. Why would some pressure between housing and bearing affect the wear between bearing and shaft.

uN/P is the Stribeck number. High numbers move you toward hydrodynamic lubrication. Low numbers move you toward boundary lubrication. You have already said you are in boundary lubrication.

Revolutions is typically viewed as a unitless quantity.

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[MechEng2005]

I appologize, I wasn't very clear in my OP.

My question concerning the pressure between the housing and the bearing was for a static analysis, not related to wear. If I have a shaft inserted into a sleeve that has a downward force on the sleeve of 10,000 pounds, then the nominal pressure on the inside of the sleeve of:

P1 = F*(Dshaft)/L

The sleeve transfers this force to the housing, so I would expect a reaction pressure between the housing and sleeve of:

P2 = F*(Dhousing)/L

Then, when I am determining if the stress in the bushing to see if it exceeds an acceptable amount (i.e. yield), wouldn't the maximum stress, at a location between the shaft and housing in-line with the force be:

P = P1 + P2

since the sleeve would have compressive pressures from both the shaft and the reaction of the housing?

-- MechEng2005

 

[electricpete]

Well, I'm not a mechanical guy, but that doesn't sound right to me.

Let's say Dshaft ~ Dhousing.

P = P1 + P2 = 2 * F * Dhousing / L

How did we double the force? I don't think you count the force and the reaction force. Only one or the other.



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[electricpete]

Now if there were some stresses associated with interference fit between housing and bearing, those would have to be accounted for.

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[electricpete]

I have to add that most of the applications I work with do not have an interference fit between bearing and housing.

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