"Set" height calculation 3

[neophite]

I am very new to spring design and need some help with what I hope is a simple calculation. I have a spring that takes a shorter height “set” after application (I believe it is being bottomed to solid height and cannot prevent this from happening in the application) and need to be able to calculate this shorter height at the design stage (before I have samples). Can anyone help?



Thanks in advance.

 

[israelkk]

You can find some formulation in the book Spring Design A Practical Treatment, W. R. Berry 1961. However, to my best knowledge and 30 years of personal experience the calculations of the spring length are not accurate because the parameters may change with every wire batch.

I real life the spring maker makes test samples longer than the desired spring and bottoms them to find the free length needed before bottoming that will give the desired spring properties after bottoming.

Anyway, designing for a spring bottoming during application is a bad idea. With each bottoming the spring enters the plastic zone and the spring will have a very!!! short life cycle. If the spring is designed to stay bottomed for long periods it will become even shorter due to relaxation.

Taking your words that you are new to spring design and my experience I am pretty sure that a spring that will not bottom can be found. However, more information regarding forces, deflections, maximum solid length, maximum outside diameter/minimum inside diameter, type of application (static/cyclic/impact), environment, etc., is needed.

http://israelkk.googlepages.com/home

 

[jackpot]

Also, as some springs are scragged or "set" the diameter may increase - if the dimensions are critical to the application this increase must also have to be considered.

Jack

 

[TVP]

neophite,

It is common for a spring manufacturer to coil/wind the spring longer than the final intent, compress it (cold or hot) to remove the set, and the final result will be the spring that meets the length, force, etc. requirements. Even springs that bottom out during impact loading can be successfully designed to achieve > 100,000 cycles before failure, but it requires high quality raw materials, shot peening, etc.

 

[JAlton]

Have you considered installing a lift stop inside the spring to limit travel and prevent the spring being compressed to solid height?

J. Alton Cox

http://www.delucatest.com