Need Help Building a Viscosity Calculator

[Jwrightnoria]

I am in the process of making a viscosity calculator. The Calculator is going to use the following inputs:

bearing dimensions
rpm
operating temperature
VI

The calculator will return a suggested ISO viscosity grade.

I know of 2 calculators like this that exist. One was written by SKF and resides at

http://www.skf.com/portal/skf/home/products?maincatalogue=1&newlink=first&lang=en

,under calculations > viscosity. The other was written by Exxon Mobil. Both companies refuse to release the formulas used in the calculators. I have been working on this for several days, and I can not find a way to link all the variables in a single equation.

This process is easily done using several independent charts and equations.

The following is my current practice:

1. Survey the bearing. Find rpm, dimensions, and operating temp.

2. Calculate dm. dm = .5(d+D)

3. Use dm and rpm in conjunction with the following chart to find minimum operating viscosity.

4.Use the newly obtained minimum required viscosity and the operating temperature with the following chart to obtain the ISO viscosity grade.

I have been trying to find a "missing link" as to how these two companies are getting these calculators to work. I know that the first chart is a graphical representation of ASTM D341. The second is a simple viscosity conversion from a viscosity at a certain operating temp to a viscosity at 40C (ISO grade).

Anyone have any ideas? I need some fresh eyes to look at this.

Thanks in advance.

 

[electricpete]

Sounds like a curve fitting excercize.

On the first graph, if you ignore the data below 5 on vertical axis, the lines have the same slope on log log scale.

log(v1) = a((rpm)) - b * log (dm)

Solve for the value of b and the function a((rpm)) (maybe a polynomial) that minimize the sum of square of residual errors.

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[electricpete]

In fact you can read b right off the graph and just solve the function a((r))

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[jmw]

Visit this link (

http://www.viscoanalyser.com/page8.html

and go to downloads spreadsheets) to download a spreadsheet for the temperature Vs Viscosity calculations. You just need to enter the viscosity at 40 and 100 for each lube you are interested in.
If you want to adapt this spreadsheet, send an email request to the website for the password.



JMW

http://www.ViscoAnalyser.com

 

[Jwrightnoria]

I don't think your spreadsheet is of any help here. I am trying to find out what viscosity of fluid to use based on size, rpm, and temp. To use your spreadsheet I have to know this, thus defeating the purpose of the original post.

 

[jmw]

Ah, OK.
I thought that what you would be doing was trying to project the operating temperature and required viscosity at that temperature for a piece of equipment.

The ASTM D341 spreadsheet lets you do that two ways, feed in a temperature to find the viscosity at that temp for each oil and enter a viscosity and find the temperature for each oil at which that viscosity will be obtained..... with the spreadsheet populated with the available lubricants, this should then help discover the optimum lubricant with just a few extra IF statements.

JMW

http://www.ViscoAnalyser.com

 

[Jwrightnoria]

Don't get me wrong, this spreadsheet is the next step in my process. First however, I must find a way to calculate the min operating viscosity at operating temperature. Once this is obtained, I will be able to use ASTM D341 to convert this number to an ISO Viscosity grade (@40C).