Extension spring question

[CoolDude003]

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?

 

[ShaggyPE]

I didn't do the leg work, but here is a start:

http://www.leespring.com/extension_spec.asp?springType=E&forWhat=Search

-Dustin
Professional Engineer
Pretty good with SolidWorks

 

[CoolDude003]

Already tried that one. Thanks for the response, though.

 

[MintJulep]

What do you mean by "initial load"?

 

[CoolDude003]

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.

 

[ShaggyPE]

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

-Dustin
Professional Engineer
Pretty good with SolidWorks

 

[Cockroach]

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

 

[zekeman]

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.

 

[israelkk]

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/

 

[MadMango]

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/

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of these Forums?

 

[imcjoek]

Maybe a 50lb gas shock?