Hydrodynamic Journal Bearing on Stamping Press Machine

[nickjk]

Hi All,
I am currently trying to determine if the main and connection journal bearings used on a stamping press could be designed to use hydrodynamic lubrication.
The press is rated at 150tons so for approximation I am using 75 tons of load force at each of the 2 main bearings.
The bearing I am currently studying has the following features:
14" I.D.
4 1/2" width
Supporting Load (75tons) 150,000 lbs
Bearing Pressure 2,380 psi
Length/Diameter Ratio .32
Journal Speed 180 RPM or 3 rev. per second
Viscosity 20 Centipoises at 40c
I used the McKee chart to find my k value which I used to solve my friction value.
k was estimated at .008 and friction coefficient was calculated at .0081

When I calculate the S value to be used with Raimondi and Boyd charts I get a very small number like .0037 which seems like a problem.
Also when I calculated the change in heat the value was extremely high - change of 803 F degrees.

I do not know if the normal hydrodynamic calculations apply because the very high load of the stamping press is only present during 1/8 of its rotation and is not constant. Do you know of any information available on a similar application.

Any suggestions or advice on how to continue with these calculations would greatly be appreciated.
This is my first go at trying to solve this type of a problem.

Thanks in Advance

Nick JK

 

[romke]

is there a particular reason to use a oil with the rather low viscosity mentioned? i would think a somewhat higher viscosity in the range of ISO VG 68 - 150 would be more appropriate given the type of load involved.

whether hydrodynamic lubrication can be more or less achieved will depend on load, speed and oil viscosity, assuming that sufficient fluid enters the bearing. given the dimensions of the bearing, the speed and the (varying) load, viscosity is the only element you can play with to get the result needed.

 

[nickjk]

Hi romke,

I will look at how using a different viscosity will effect the calculations.

The answer to your statement "whether hydrodynamic lubrication can be more or less achieved will depend on load, speed and oil viscosity" is what I am looking for. How do I know based on load, speed and oil viscosity if this application can be hydrodynamic lubricated?
I am sure there is a point based on these features that the crank will not be able to be supported by the oil wedge leaving a boundary type lubrication.

 

[nickjk]

I have been doing some research on Hydrodynamic lubrication for bearings.

Using Raimond and Boyd Charts I studied the numbers while increasing viscosity like stated in romke post above.
At a ISO VG 150 using calculated loads and velocities I was finding minimum film thickness ranging between .0004" to .0008".
I also found during my research that values derived from the charts are based on steady load. That bearings subjected to rapidly fluctuating loads can carry much greater instantaneous peak loads than steady state analysis would indicate because there is not enough time for the oil film to be squeezed out before load is removed. Because of this squeeze film phenomenon calculated values may be 1/3 the actual values.

I have not found any actual calculations or data for fluctuating loads film thickness

Can you please let me know your thoughts?

Thank you,

 

[romke]

in dynamically changing loads like the press you describe and in fact any type of combustion engine the hydrodynamic pressure in the bearing will vary rapidly and at times can temporarily be much higher then anticipated. since the oil more or less is trapped within the bearing and cannot possibly be squeezed out in sync with rapidly changing loads at those very moments temporarily the viscosity of the oil will increase. in practical terms that means that the actual film thickness may be substantially higher then derived from static calculations.

what you may achieve is temporarily elastohydrodynamic lubrication. usually that term is linked to the lubrication of roller bearings and gears, but in journal bearings with a load that constantly changes in magnitude and direction it will also occur - and in fact it is the reason we are capable of building combustion engines at all.

there are various computer programs that let you design and model dynamically loaded bearings and make the calculations required. see for example

http://www.simpack.com/industrial_sectors_engine.html