Dry Journal Bearing Design & Projected Area

[thehusker]

I'm trying to design a dry journal bearing. It will be used in a 0-90 degree operating butterfly valve. All of the formulas I find deal with film thickness for the lubricant (generally oil). I'm going to use a 17-4 stainless shaft in a dry Nickel-Boron coated 316 sleeve. I need to calculate a projected area so that I can figure out my unit loading and size the bearing, but I don't know what portion of my projected area I should use. In theory I have line contact, but realistically, there will be some contact area. Any help would be greatly appreciated!

 

[tlee123]

Hertzian stress analysis will give contact area once you know the radii, modulus of elasticity, and contact force. See Roark.

Is this what you're looking for?

 

[thehusker]

I'm pretty sure that's what I'm looking for. What I was HOPING for was a generally used rule of thumb which, as you pointed out, would use the radii, material properties and force.

I really appreciate your response.

 

[israelkk]

Very simple.
1. Assume only 120 degrees of the diameter is in contact.

2. Assume the reaction forces are at the far ends of the busing

3. Calculate the reaction force at each end of the bushing.
4. Using the bushing/shaft ultimate compressive stress calculate the area of contact that will hold the reaction forces (area X ultimate compressive stress = reaction force).

If the contact area width is small compared to the bushing length then you are done. Otherwise, repeat the calculations using the distance between the middle of the areas of contact to recalculate the reaction forces.