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Extension spring question

Extension spring question

Extension spring question

(OP)
Is it possible for an extension spring to be 20 inches long while unloaded, 32 or so inches long fully extended(12" max displacement), and have an initial load of 30-40 lbs? All other properties are virtually not important. If so, where could I buy them?

RE: Extension spring question

(OP)
Already tried that one. Thanks for the response, though.

RE: Extension spring question

What do you mean by "initial load"?

RE: Extension spring question

(OP)
Initial load is the load required to initiate the spring to extend. The load when the spring is extended by an 1 or less would be cool too.  

RE: Extension spring question

might want to look into "garage door" springs... very large extension springs.

-Dustin
Professional Engineer
Pretty good with SolidWorks

RE: Extension spring question

You have too many options for a closed solution set.

I would expect this to have a minimum core diameter, or perhaps maximum OD with spring wire diameter?  What about material?  If the extension is a foot, what sort of load is required given a preload of 40 lbf?

Regards,
Cockroach

RE: Extension spring question

I think you will have to get that initial tension down to get a 20 inch spring.
Get a copy of Machinery Handbook and look a t their excellent spring design section.

I took a peak and can tell you you re talking about 250 turns of 0.1055 dia wire with an outside dia of  .533 inches ( very low index) with minimal initial tension, 100,000 psi at max extension.


 

RE: Extension spring question

If you can not find an off the shelf spring then you will need to custom design one. The problem I see with such a spring is the number of cycles of the 12" deflection. If it is a spring for a static application then such as spring can be designed. For cyclic application, much work needs to be done to see if such a design can be designed.

http://www.webspawner.com/users/israelkk/

RE: Extension spring question

I've had good luck with Century Springs out of California over the years.  With a 30-40lb initial load, you might consider using multiple springs (2x 15lb, or 3x 10lb springs). If you are considering custom springs, you might want to investigate a custom Drawbar spring in this instance, especially if these are going to be horizontally mounting.
http://www.centuryspring.com/

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RE: Extension spring question

Maybe a 50lb gas shock?


 

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