Journal Bearing Design - Does anyone use Raimondi & Boyd?

[wdornfeld]

I've been teaching ME students the use of Raimondi & Boyd's Sommerfeld number -> dimensionless variable charts for years. The method is in every machine design text, but I am curious as to if anyone actually uses it in practice. It doesn't appear to have changed much since 1958. I would appreciate hearing from folks who use it, and also from current alternative methods of journal design - even if it is commercial or proprietary software.

 

[EdDanzer]

Even though I do not have a degree in engineering, I have a PHD in the school of hard knocks. For 25 years I have repaired, designed and built, and marketed products containing plain bearings. I have hired a few experienced engineers as well as being the first job for several young engineers. I’ve never heard of the method you describe. We spent some time and money using an early version of CosmosWorks gap element FEA to try to model pin joints in products using hydraulic cylinders as actuators. The results tended to be over kill compared to what is used in practice. One simple method is to divide the load by the film strength (6000 psi works well) to get the projected area of the bushing. Then you need to choose a pin diameter and housing shape that does not create point loading between the pin and bushing. I use the Machinery’s Handbook for clearance recommendation. One other thing to consider is the PV value of the materials being used, but published data is only a fair reference. I probably have spent $50,000.00 on warranty and redesign by using recommended PV values. The best examples I have are boom joints in excavators. Several manufactures use hard steel bushings against hard steel pins. This works ok until there is an over load or lack of lubrication, then the steel galls and the assembly self destructs. Exceeding the film strength of the lubricant will create a dry condition between pin and bushing. We have replaced hard bushings with aluminum bronze with great success. This material can deform to the pin shape without galling or permanently deforming.

 

[wdornfeld]

Thanks for your input. Raimondi & Boyd charts are for continuously rotating shafts riding on hydrodynamic films, so they are for a quite different application than the almost static bearing joints that you work with. A very nice summary of the use of these charts is at:

http://www.utm.edu/departments/engin/lemaster/Machine Design/Lecture 26.pdf

I'm just trying to find out if anyone actually uses these!

 

[EngJW]

Mr. Dornfeld,

I just checked out that link and it is a good summary. It has the same information as in Shigley, but the equation for temperature rise is different. They both give different answers. I don't know which is right, but the one in the link contains density and specific heat which do not appear to be included in Shigley's equation. Do you have any thoughts on this?

PS- I learned this method from an old timer that used to work at GM so it must have been used for engines. Of course today everything is programmed and nobody knows how to do anything. Are you familiar with journal orbit analysis? I will look up the name of the paper if you want it.

Thanks,
John Woodward

 

[TZSiR]

I've heard of them and have read them, but in practice I never use them. I avoid using too many equations when the best way to design something (IMO) is to look at the problem and visualize the solution. I use a computer simply to get the Idea on the internet so I can E-mail it to a client when it's finished. From there it' all in their court until they have reliabilty problems with something I designed. I've only had one occurance of this so far. I specified the wrong material that need to be used in the application, and do to this the swiveling joint had some heat and expansion issue's which caused it to seize.

 

[wdornfeld]

Mr. Woodward -
I looked at Shigley (5th Ed) on page 504, and it looks like equations a. and c. when combined will give the same deltaT equation in the link's Step 13. Shigley uses C sub H for specific heat, while the UTM equation uses C sub p. And Shigley uses gamma for weight per unit volume, while the UTM equation uses rho. Finally, Shigley explicitly shows J as the mechanical equivalent of heat (9336 lb.in. per BTU) in his equation, while the UTM method just "quietly" includes the factor - but says that they use it.
It looked to me that both methods were really the same and should give the same answer. Let me know what you think.

To TZSiR -
It sounds like you may be practicing "intuitive" design. I have seen students use this method on exams, but without the success that you seem to have had! ;-)