Spring steel alternatives for product application

[mononomoto]

Hello Everyone,

If possible I would really appreciate your opinions and insights on the appropriate/optimal material selection for the use I will describe below.

Essentially I am researching candidate materials to for a product which can exhibit similar mechanical properties as the "Slap Bracelets" toys (popular in the late 80's and 90's). While very cost effective, due to expect usage scenario, the spring steel normally used in the production of the toys might have limited suitability for my intended application.

The two alternative materials that come to mind which may or may not actually be suitable are titanium/titanium alloys and a shape memory alloy such as Nitinol. I read that one company uses a proprietary titanium alloy (developed for aerospace) for its coil springs - but am not sure if such a specialized material necessary for my application.

While not complete, here is a tentative list of criteria and considerations which impact the material selection, in no particular order.

1. The optimal material should be able to achieve much more exaggerated "resting states" (i.e. tighter complete coils) compare the toys mentioned above.
2. Dimensional stability through a wide temperature range (0ºF - 1600ºF) in both "orientations"
3. End product should be able to withstand prolonged use while exposed to the elements without significant degradation to its function.
4. Specification of material (primarily gauge) can be determined by other factors such as:
a.lifespan/durability
b.ease of manufacturing/production
c.function (such force necessary to activate the orientation transition)
d.safety (speed and force of the orientation transition)
5. The "flat" dimensions of the end product would require 48 square inches of material.
6. While the cost of material and fabrication is expected to be significantly higher than spring steel, the MOQ cost /pcs should still be under US$10, under $5 if possible.

I thank you all in advance for your time and consideration and for bearing with me - any insights and/or suggestions would be most appreciated.

Man Chiu Yeung

ps. I apologize for any inaccurate terminology or faux pas that I may have unintentionally made. As you can probably tell my understanding of engineering is quite limited to say the least...

 

[EdStainless]

wrt #2, do you expect it to work over this temperature range or simply survive, and then function at room temp?
Nothing will work well at that temp, but there are alloys that would survive.

You do realize that what drives the force and strength of these devices in the modulus of elasticity. Therefor you need high modulus materials, which rules out Ti if want more force (though the temp limit already took care of that.
Strength will determine how deep of a 'cup' you can put into the material and then how tight of a coil it will form.

The only material off hand that I can think of that would meet the criteria is an age hardened Ni based alloy.
A strip of material 3" x 16" x 0.030" thick should meet the $10 limit. Alloys like 718, 725, and X-750 to name a few.

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P.E. Metallurgy, Plymouth Tube

 

[mononomoto]

Thank you EdStainless!

To reply to your question and to clarify with more details:

wrt #2 Sorry, I should have been more clear. I would want it to survive in that range and maintain functionality after returning to lower temperatures. 1600º F would be a extreme/worse case scenario - in normal/recommended usage the upper range is expected to be quite a bit lower, my guess would be around or under 1000º F.

As for the material's strength and the relationship to the "cup" it can attain, thank you for enlightening me. There is some flexibility in design parameters for the "cup", in that for one (narrow) orientation one "coil" plus a slight overlap should be fine, while in the other (long) direction it would be as tight a coil as permitted by the material (tighter and smaller the better if all other factors are the same.)

Does this additional information have any impact on your recommendations?

In addition, is it possible to achieve the opposed cup with just one layer of material or is it necessary to use two layers?

Once again thank you in advance for your time and consideration.