In a message dated 2008/02/18, charles.r.patton@........ writes:

> Hi Chris,
> I agree with the liquid flow question, but I'm not certain I understand 
> the "...The contact friction is highly variable between lubricated 
> rolling surfaces."  Are you thinking about surface tension of variable 
> areas of contact on a non-immersed contact pair?  Wouldn't that 
> basically disappear if there was total immersion of wetted surfaces and 
> the oil doesn't use fiberous fillers (such as greases) to thicken it?

       Surface tension is likely to be the least of your worries.

       Grease is a mixture of varios types of soap and oil. A few specialist 
greases have powder fillers. Moly grease for instance and chassis grease. They 
prevent metal to metal contact for various reasons.

       If you roll a bearing very slowly, you get full metal to metal contact 
with very high friction. Increase the speed and the surfaces start to 
separate on a thin film of oil and the friction drops dramatically. The viscosity of 
oil is pressure dependant and varies from a thin fluid to the consistency of 
solid pitch. It is also time dependant. The rolling surfaces also deform 
elastically with increasing load and the contact area increases.

> P.S. I agree with you that I don't know how to fashion the bearing I was 
> proposing -- a half baked idea in formation, I guess.  But in a separate 
> post I do visit a variation that I think is possible using as a starting 
> point the idea of controlling the height change of a mass to control the 
>   period. I would definitely build it without oil first, then dunk it to 
> see what happens!

       I doubt that you will be too happy with the result. There will be 
quite large viscous losses as fluid flows from and into the rolling contact area. 
This will be highly rate and temperature dependant and non linear.

       Regards,

       Chris Chapman   
In a me=
ssage dated 2008/02/18, charles.r.patton@........ writes:



Hi Chris,

I agree with the liquid flow question, but I'm not certain I understand 

the "...The contact friction is highly variable between lubricated 

rolling surfaces."  Are you thinking about surface tension of variable=20=


areas of contact on a non-immersed contact pair?  Wouldn't that 

basically disappear if there was total immersion of wetted surfaces and 

the oil doesn't use fiberous fillers (such as greases) to thicken it?=




       Surface tension is likely to be the le=
ast of your worries.



       Grease is a mixture of varios types of=20=
soap and oil. A few specialist greases have powder fillers. Moly grease for=20=
instance and chassis grease. They prevent metal to metal contact for various=
 reasons.



       If you roll a bearing very slowly, you=20=
get full metal to metal contact with very high friction. Increase the speed=20=
and the surfaces start to separate on a thin film of oil and the friction dr=
ops dramatically. The viscosity of oil is pressure dependant and varies from=
 a thin fluid to the consistency of solid pitch. It is also time dependant.=20=
The rolling surfaces also deform elastically with increasing load and the co=
ntact area increases.



P.S. I agree with you that I do=
n't know how to fashion the bearing I was 

proposing -- a half baked idea in formation, I guess.  But in a separat=
e 

post I do visit a variation that I think is possible using as a starting 
point the idea of controlling the height change of a mass to control the 
  period. I would definitely build it without oil first, then dunk it t=
o 

see what happens!




       I doubt that you will be too happy with=
 the result. There will be quite large viscous losses as fluid flows from an=
d into the rolling contact area. This will be highly rate and temperature de=
pendant and non linear.



       Regards,



       Chris Chapman