Question about selection of spring.

I am working over a device in which spring is key part. This spring is supposed lift about 70 kg load at 5-10 centimeters above ground.
I am thinking about using shock absorbers used in motorbikes. I think that springs in these shock ups, if stretched, can lift load of about 70 kg for few cm.
Will these springs work?
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neo wrote:

Were you thinking about permanently deforming the spring by stretching to the required length? That's a bad idea, because you'll induce new stresses in the spring. It might then need to be heat-treated, if it can be used at all. Without knowing the metallurgy of the spring, you'd be flying blind. Better might be to take two springs and cut one down so that their total length meets your requirements. Note that it is generally a bad idea to weld springs, so it would be better to find another way to couple them, if required.
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Oddly enough that is precisely what is done when manufacturing them, when necessary. It is called scragging.
Cheers
Greg Locock
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Greg Locock wrote:

I know Scragging is used on compression springs. They are compressed coil to coil and come out of the process shorter than they went in. I didn't know that it also referred to stretching extension springs.
EJ in NJ
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Ernie Willson wrote:

I believe the original poster was talking about stretching a spring to be used in compression. This will cause yield in the opposite places from where it occurs in scragging, which is not a good thing. You can think of it as "anti-scragging". Depending on the metallurgy, the spring might be recoverable with heat treatment, but without knowing the material you can't be sure about that.
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Mark Thorson wrote:

My point exactly, see:
http://www.eng-tips.com/viewthread.cfm?qid 2116&page=1
EJ in NJ
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