Compression spring design

[spiru]

My question has to do with the prestressing of spring. A spring is prestressed to increase the working life of the spring by inducing wanted stresses within the material. This is done by setting plastically deforming the material when the spring is compressed for the first time due to the plastic deformation the springs' free lenght is reduced. my question is if there is a standard to what is the setting length of the spring. Is it the solid length (L block) or is it the minimum working length (L2) of the spring length.

 

[desertfox]

Hi spiru

According to the book "Spring Design" by W.R. Berry the spring should be pre-stressed after all heat treatment and
compressed to its solid length at least several times,some
references recommend 12 times others 5 times but always to its solid length.

hope this helps

desertfox

 

[spiru]

hi desertfox,

thanks for the help.
Is it possible that the prestressing occurs at a lenght smaller than the minimum working length always given that the stress is greater than the elastic limit of the material.

 

[desertfox]

Hi spiru

Yes any compression spring can over stress at any time during compression of the spring, but this would be down to the design.
Compression springs are based on torsional stress of the wire and typical values if you don't want to over stress them is to limit that stress to a value of 40 to 50% of its
tensile strength.
Just recently I re-designed a spring for valve which was giving inconsistant air flow, the reason the valve was performing badly was due to the spring during operation becoming over stressed. After the spring over stressed and took a permanent set on length it also lost some of its pre-load and therefore opened the valve to early.

regards

desertfox