Torsion spring creep

[Manifolddesigner]

Hello,
I'm an ME and our family business is garage doors. My brother asked me why garage door tornsion springs relax after several days/weeks/months and if there's anything that can be done. It seems to relax about 1/2 wind after a couple of weeks.

I couldn't find much that was useful on creep in any of my textbooks and googling around didn't produce much in the way of practical solutions.
Springs vary in wire gauge and length depending on the weight of the door, but invariably are rated for about 10,000 cycles and have about 7+ winds of preload that reduces to zero and back during cycling.
All at room temperature and low speed. For reference all are 1.75" ID, wire gauge varies from .207"->.272" for standard stuff.

My question to you guys is:

What if you over-wound the spring initially (8 or 9 or 10 winds) and then dropped it immediately back down to 7.
Would this help (or hurt?)
What other single factor could we change that would affect the creep most significantly? Just going to higher cycle springs (larger wire, longer)?
(we're assuming its a creep problem, not an issue where the spring is slipping on the cones)
I'm trying to convince him to take some more data.


Thoughts?
Jason

 

[TVP]

Search for "stress relaxation" or "load loss" instead of creep. There should be lots of info available.

 

[desertfox]

Hi Manifolddesigner

without knowing details of the spring in question but following the advice of the previous poster I found this link
which may help

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA302507

 

[israelkk]

The springs needs to be redesigned for long term relaxation (years). Without exact requirements and space limitations there is no way to give you an intelligent answer. If as you said Garage doors is family business you should get an expert with proven experience for such problems. Who designed those springs or you buy them off the shelf? To check if it is a relaxation/creep problem you can record the spring ends relative position for a new spring and then after suspected relaxation/creep check the ends relative position again and see it there is a permanent rotation between the ends.

https://sites.google.com/site/israelkk/home