Compression Spring formulas

[molds]

I am looking for a formula for calculating the spring rate per inch, when stacking three compression springs. (Danly #9-1006-11) I believe the spring has a rate/inch of 120 lbs. I want to stack three of these with guides between them which slide on a core rod. The stack will be compressed .90 of an inch, or .30 per spring. I am hoping that this will solve a failure problem that we are having and the springs will last for 1 million cycles at 7.5 seconds intervals. I apologize for my lack of spring knowledge, and truly appreciate all the help I have been given from this site already. Thanks!

 

[desertfox]

Hi molds

For springs mounted in parallel you just add the stiffnesses together.For Series you add them using the reciprical theorem like you would do for resistors in parallel.
more details of your spring are needed for further help like wire dia , spring o.d. number turns etc

regards desertfox

 

[molds]

Thanks desertfox for your reply.