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> Thermal Expansion Materials
Chantry
Posted: February 17, 2011 09:37 pm
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Hi

To start off, im a product designer by trade so im sorry if this question is reminiscent of GCSE physics. My project needs to rotate a large but reletavly free moving shaft (about 2in diameter) with temperature. I would like to achieve around 15degrees of rotation with a heat range of around 200 degrees (60-260C). This is for a third world environment so I cant use exotic materials.

My idea is to wind a strip of material around the shaft and fit it to a stationary block. The heat will cause the material to expand, and will cause the shaft to rotate. The more windings I have around the shaft, the more rotation I can expect to achieve.

Does all of this sound plausible?
Is a material like copper the best for this purpose, or something like aluminium?
How do I work out the expansion of a metal with heat?

Thank you!

James
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MacFromOK
Posted: February 17, 2011 11:10 pm
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Are you aware that applications of this type (thermometers, thermostats, etc.) are generally made from bi-metal strips (two metals with different expansion rates) in order to achieve the desired rotational movement?

Not sure how well (or if) a single metal will work for this, as the coil may just expand in diameter.

Perhaps some of the other members will comment. beer.gif


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ChipUser
Posted: February 17, 2011 11:15 pm
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Take a look at the properties of Nitinol wire. It may sound exotic but you won't need much to do what you want. It is also known as Flexinol (I think that's a trade name).
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Chantry
Posted: February 18, 2011 12:51 am
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Both bi-metals and Nitinol are both very helpful leads, thank you.
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tekwiz
Posted: February 18, 2011 07:30 pm
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A bimetal strip can be made by simply riveting two strips of different metals together. A little research will show you which of the common metals would be the most suitable.

BTW: A single metal strip won't work, as any motion will be microscopic.


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