setting of springs

[hermatician]

hey, i am working on VHCF behavior of springs,and i wanna know that why exactly the spring has to be given a set?

my springs were set by the manufacturer and thus it should not have change in length after compressing but it had a change after compression ???

i cannot think as the spring is given elastic strain why it is taking a permanent displacement/strain???

 

[MikeHalloran]

Virginia Health Care Foundation?
Voluntary Human Care Foundation?
...


... If you meant Very High Cycle Fatigue, ask your librarian to fetch this:

http://iopscience.iop.org/1742-6596/240/1/012040

Mike Halloran
Pembroke Pines, FL, USA

 

[TVP]

Your assumption that it should not have taken additional set when compressed completely to solid is erroneous. Springs that have been compressed to solid one time by the manufacturer will still take some small additional set when compressed completely to solid during use. Usually the first three cycles (free to solid) cause plastic deformation and stress redistribution, after which any additional amount of set is caused by stress relaxation. Do you know the exact procedure used by your supplier for set removal?

 

[hermatician]

Thanks for your reply, i got some idea about what i needed from your reply, i guess.

provider of spring has done solid compression( not exactly but has compressed to 12mm ( to get a free length of 37mm apprx) well should not give these details here.

he compressed it thrice i guess, but what i know is that for different springs of diff spring rate, should be compressed at diff lengths while setting.

problem is in the test, when we r giving displacement, the actual displacement is changing because of loss in length and my team discussed and still thinking on it but i want to know that why this happens. i mean u r giving elastic deformation so it sud get recovered but why?

 

[israelkk]

How much length it lost compared to the maximum deflection? Usually if preset was designed and done correctly it will not reset more than 2% of maximum deflection. According to the literature 12 presses to solid are needed to stabilize the spring. A better approach is to compress the spring to solid and hold the spring compressed for at least 24 hours. If the spring is designed to work at a high temperature, the preset process should be performed at that temperature. The preset must be the last operation in the spring manufacturing process.

Preset operation as a mean to adjust the free length is a wrong approach and is not a real preset process. Preset process is used to induce favorable compression stresses in the spring wire so higher loads can be achieved from a thinner wire diameter.

If your spring length is changed after load then the stresses are probably too high for the spring wire and the spring needs to be re-designed.

With proper design the spring free length is not important. The proper definition is to define load/s at compressed length/es.

Please provide more info regarding the type of loads, cyclic, static, load for short time or for long periods.

 

[hermatician]

thanks for the best answer I wanted. and thanks all. specially Israelkk.

 

[mkmarizani]

Scragged/preset spring should show permanent set on subsequent loading. Try long duration preseting, the spring shld be compressed three times, holding it at the solid height for 2 minutes in the first two strokes and for 48 hours at the last stroke. Permanent set shall not exceed 3 mm of free height of spring, which is measured before scragging.