Disc spring deflection

[Sco79]

Spring force equation for disc spring. F= spring force at deflection s. I know the spring force F and all the other values, but s is unknown.

How do you write the same equation: s=...?

 

[tr1ntx]

Very carefully.

You have to run that s/t through the second term and get it separated, i.e., the s/t has been factored out to simplify the equation in terms of F, now it needs to be factored back in. Then you're going to have a quadratic expression in terms of s (I think).

Iteration might be the simplest route to go to home in on an s value that you need.

 

[Clyde38]

See disc spring calculator (attached) at:

http://www.circlips.com.au/disc.htm

This is from a link at:

http://www.roymech.co.uk/Useful_Tables/Springs/Springs_disc.html

Hope this helps. .

[link

http://www.linkedin.com/in/clydehancock

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[/url]

 

[unclesyd]

Here is all the information you will need to work with disk springs.
We cheated on most applications of disk springs as we got the manufacture to do the calculations.

http://www.schnorr.com/docs/Handbook.pdf

 

[israelkk]

Notice that for a force value you will get two "s" values.

 

[Sco79]

Thanks for help so far. Iteration is the easiest way and Schnorr handbook really contains a lot of information, but the equation is always used to calculate F.

I still wonder how the same thing is written 's=...' Looks simple, but after two hours of trying, no success.

 

[israelkk]

This is a third order polynomial equation, therefore there are three solutions values for "s" for one value of "F".

 

[chicopee]

Take a look at my attachment. Hopefully the signs are correct. It seems to me that you did not take algebra when you were in high school.

 

[drawoh]

Sco79,

Look in Roark Formulas for Stress and Strain. Definitely, disc spring are covered in the fifth edition. I have set up a spreadsheet for this, and I have even punched in the values from the Schorr catalogue to verify the numbers.

JHG

 

[chicopee]

A correction to the formula presented in my first attachment.

 

[israelkk]

Sco79

Can you clarify what are you trying to do? Why do you need the "s" value for?

 

[Sco79]

Thanks for the formula, chicopee. I've already forgotten everything I learnt in school.

israelkk,
I have a very simple cylinder with a pile of disc springs inside. Number of springs and stacking order are known and always the same. The spring pile has to be pre-loaded to force F meaning that cylinder rod has to start moving when it's pulled with force F (making spring pile shorter).

Since the F is known at th beginning, I thougt I could directly calculate the cylinder length (pre-loaded spring pile length which is needed) in Excel.

In other words, now I have F (pulling force) as a result in one cell in my calc sheet. After getting that F, I have to "manually" change/guess the s value, to get a matching F for the pre-loaded spring pile. Then I can say "if you have this force pulling the cylinder rod, you need this much space for the pre-loaded spring pile"

(Sorry about my poor english)

Easily done with Excel macro or solver function, so not a big problem at all.

 

[israelkk]

The tolerances on "F" vs "s" can easily be +/-15%, add to this the friction between the springs in the stack and it is even worst. You will any way need to manually calibrate the preload in the spring stack for each assembled cylinder.