Help req. re: thermal expansion, etc.

I have something I want to do but I need some tech info. Sorry if this is
a dopey newbie question, but I've been unable to glean anything off Google
that I can use.
What I want to do is use a coiled flat "spring" that will work like a
thermometer "spring". (I *think* the "spring" might be called a
thermocouple, but sorry, it's been over thirty years since I took
Physics...) The purpose of the contraption would be, in accordance with
temperature changes, to either get a flap to slide horizontally on a track,
or open/close a hinged flap vertically.

The info I need is, how to find out what metal would best suit this
purpose, and how to determine the amount of rotation (or pull) I'd get, so
I can try to figure out the size and material of flap I might be able to
coax into operating without operator input (i.e. only on the power of the
Thanks in Advance!
Reply to
Kris Krieger
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Perchance do you mean a "Bi-Metallic strip" ? Historically made of Invar and brass AFAIK. Certainly a good google for the terms will help.
Reply to
Steve wrote in news:438b8fbd$0$351$
Er, I'm a rube so I'm not familiar with that. I'm trying to figure out whether a passive roof/attic ventilation system is possible, and the "spring" idea is the closest idea I could arrive at. I'm assuming that what you mean is somehting like, using a stip that expands more layered with a strip the expands less, could act as a driver? But wouldn't I first have to know the rate of expansion for each strip?
This might not be the right forum for my question, sorry if it isn't...
- Kris
Reply to
Kris Krieger
Just to get my head around your idea and Steve's post, I think the idea behind the bi-metallic strip was to use it to open/close a hinged flap vertically. Since the two materials are bonded together, the difference in expansion between them will cause the strip to bend one way or the other. Although this effect can be useful, I'm not quite sure it would provide enough force in your application unless it is a small flap. If you think about the old thermostats which you turn, they use a pretty long coiled strip of the stuff to get a farily small rotation of a small mercury switch. (granted, the temperature range which produces the rotation is quite small, ~40 deg F)
You will have to look into what different kinds of bimetallic stripping are available to determine if there will be enough force to do your job (in the temperature range you are looking at). In terms of your spring idea, off-hand I can't think of a material or coupling of materials which would be able to do this (at least without more information). Give us an idea of the amount of linear displacement is required to open or close this vent.
Reply to
Seth Imhoff
Not sure of the temperature you want your flap to open at, but it may be similar to the temperature an early Volkswagen engine's thermostatic flaps that reduced the airflow in cold weather. A trip to one of your local auto wreckers would probably provide one or two that could be tested or adapted to suit for not much money.
Hope this helps, Peter
Reply to
Bushy Pete
Ah, such beasties exist for greenhouse ventilation, most of the ones I have seen use a wax filled piston or a "Shape Memory Alloy" spring - or even bi-metallics. All of which are probably available on the open market, no need to make one.
Not a "Rube" just a Newb ! We all start somewhere.
Reply to
Seth Imhoff wrote in news:tPNif.10304$ snipped-for-privacy@fe04.lga:
[ snip ]
Yes, that's the idea :) Something like an outdoor thermometer, the kids that uses the metal coil (spring was a bad word on my part) to rotate the pointer and indicate the temperature.
The reenhouse-vent-openers are a good idea but I am still wondering whether something like this could work. Just idle curiosity
Either 6" laterally (a lightweight flap running along a slick track), or a 6"X4" (apx.) flap rotating up and down 90 degrees, i.e., the moving edge would travel 6.25" to 6.3" inches (the other egde would be hinged).
I've been trying to find info on Google re: thermal displacement, but I don't understand the 2 bits of info that I found because the units are not given in simple cm/degree C or in/degree F .
Also, I don't even know how to start searching for how much mass this thermal displacement could move. ((This is just one more time where I curse my lack of math ability and my rather basic/simplistic understanding of physics ;p ))
The coil could be up to 1' to 1.5' in diameter at maximum temperature (I guess about 150 deg F ) because that seems to be a reasonable height for the sort fo "mini-attic" I'd seen on the older flat-roof houses.
Thanks again for your input!
- Kris

Reply to
Kris Krieger
Steve wrote in news:438c9a6e$0$346$
AhHa! Greenhouses, brilliant! I hadn't thought of that at but I did feel sure that some sort of passive mechanism did exist.
(So there go my drawings and 3D models of coil-and-transmission-gear fla- powering thingamajigs )
I do say Rube because I'm not even remotely a metallurgist or metal worker. I'm just always trying to think of things that could be incorporated into residenced that could work free of external power. ((Well, I do have an idea for a sculpture/fountain/whirlygig type of thing I'd like to make, but that's an entirely different story...)) Then too, my "engineering solutions" to various daily problems do also bear more resemblence to rubber-band-and-paperclip Rube Goldberg devices, than to any sort of actual engineering ;) .
I'm actually a former microbiologist-former, former information analyst, 3D modeler trying to design a residence using as mamy passive heating-cooling techniques as possible. ((Not a job, just a compulsion.))
Part of the design is a way to pull cool air in through vents that run under the ground by allowing hot air to escape up, with this process reversing in cooler weather. So part of the overall design is the vented roof system, where (hopefully!) a system of vents would open to allow hot air to escape when necessary, and then in cool weather, reatain a layer of warm air while still permitting (if this is even necessary) some ventilation to the area.
The roof is flat, or alightly domes, in the design concept, because, as with traditional southwest houses, it would act as a way to trap rainwater and channel it into storage cisterns - but being flat, and based upon the sorts of venting I'd seen back while I'd lived in southern CA, I got this "coil-powered vent flap" idea. (I' was thinking of lightweight material, probably some sort of resin, for long life, with a dead-air-space layer, and the vent opening itself having some sort of gasket.) One thing I thought of was to rotate the flap; the other was to have teflon sliders on the bottom of the flap and use the coil with a simple "transmission" sort of thing to get the flap to slide back and forth.
But the Greenhouse openers are, I'm sure, far more elegant and efficient, not to mention pre-made, so thanks for that suggestion.
((OTOH the coil-thing still has been a fun thought experiment, and I'm still curious whether it could be made to work...))
Many Thanks for your input, because this is something I've been trying to figure out for some time :)
- Kris
Reply to
Kris Krieger
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"Metallurgy Theory and Practice" -1969 by Dell K Allen
Hardbound book and shipping
Reply to
alvinj wrote in news:dn2d58$3p3$
Thanks for the reference! There are also some used ones, total with shipping is $6.15 so that's a pretty good deal ;)
I've often toyed with the idea of trying my hand at some metal working, just making some artsy stuff, nothing industrial. So a basic/fundamental, but informative, handbook is (as always!) much appreciated :) And in all topics, increasingly difficult to find, it seems...
Thanks again - and thanks again to everyone for their input re: my question -
- Kris
Reply to
Kris Krieger

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