Sunflower

With this discussion of how metal expands with heat, it made me wonder if there might be some fun way to make use of it in a blacksmith project!
Such as a metal sunflower that would lean towards the warm sun? Or a dragon head that would lean towards a warm fire?
The coefficient of expansion of steel is only around 10 x 10^-6 in/in/F so if the sun can only heat up one side of a sculpture by 10 deg from the other there's not much expansion there to work with (one thousand of an inch in a 10" piece of steel. But maybe a large sculpture (6 ft tall) might be able to create some interesting movement from heat? Using bimetallic strips could help amplify the effect.
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Leverage helps and so does paint. Black absorbs more heat.
The cool side might be finned or like fingers letting off heat.
Think about a flower opening up to the sun.
Turning might be just heating a twisted square rod. It might rotate a little with the change of temperature. Again - a long lever pointer - like on a big clock. A minute rotation shows up on the end as a small swing.
It is obvious you want to pick the right thermal sensitive materials.
I think it would be neat. I have seen mobiles that moved by changing balance.
Martin
Curt Welch wrote:

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On Dec 28 2009, 11:43pm, "Martin H. Eastburn"

The problem, I think, is that whatever you make will wind up turning AWAY from the sun. If the natural state of the sunflower, when evenly heated, is facing straight up, then the side the sun is on will be heated and lengthened, causing the flower to turn away from the heat source. If, however, the resting state of the flower was with it's head drooping towards the sunny side, then it's possible that differential heating could cause it to "perk up" in the direction of the sun. The difference in the heating would have to be huge though, unless you go bimetallic.
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Yeah, I saw the same issue. I figured it might be possible to solve that by some clever linkage configuration that crossed or something like that.

Yeah, that might cool to see as well.

Yeah, that's the biggest problem with the concept that would need to be addressed. A 10 degree heat difference between the cold and warm side is only going to create a few thousands of an inch of expansion - or something very small like that. Amplifying that into some large amount of movement would be a real challenge.
I thought it might be fun just to start experimenting with the concept by making a long stem (a few feet) out of two strips of steel welded at the top and attached to a stand at the bottom and then heating one side with a torch and carefully watching how much the structure bends. Would it even be enough to see it??? Haven't gotten around to trying that however. Haven't been doing much at all in the garage shop since the damn cold weather set in.
If something like that would show noticeable movement, then maybe a design with a strip going up and down multiple times on each side (coil like), where one side would be shielded from the heat, so that a 2 ft (or 6 ft?) structure would get the effective expansion of a 30 ft structure? If you can get 1/8" of expansion total out of something like that it would be a lot to work with in terms of making something like a flower point in a different direction.
And as you said, there's the option of using bimetallic strips or coils to help amplify the motion as well.
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Curt Welch wrote:

one could always use a thermocouple via an (electronic) amplifier to power a <http://en.wikipedia.org/wiki/Shape_memory_alloy muscle wire.
Wouldn't be *completely* mechanical.
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Or a solar cell - some are small but large enough to throw a relay... and so forth... Martin
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Or think of Bellows that are sun driven that in turn act on a lever. Martin
bigegg wrote:

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Of course, if you want to get this far away from blacksmithing, you could always just plant some sunflowers...they'll follow the sun, and I bet you can find some seeds for less than a buck fifty. ;)
Steel sunflower would be beautiful enough, and it wouldn't have to move at all.
Just my useless $.02
Tal
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Yeah, I was going to comment that it could be solved with electronics but since this is a blacksmith group... :)
The muscle wire is a very interesting twist however. I was just thinking electric motor. If you could get enough power in solar cells to drive it then you need no battery or motor or drive system and it would might be slow and cool. But I'm pretty sure all those wires need more power than you could get in a small solar cells.
Hum, but a little research shows a radio shack solar cell about 1" square in full sunlight could drive small Flexinol wire. You could make a flower out of solar cells and wire them to the muscle wire to make it move. The flower should actually track the sun if done correctly. Not exactly sure about the strength of the wire relative to the weight of the solar cells but it looks to me like it might work. Looks like it would be about $50 worth of parts. Not exactly a blacksmith project however.
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snipped-for-privacy@kcwc.com (Curt Welch) wrote:

Why not exactly a blacksmith project? Many of the inventions of the late 19th and early 20th centuries, especially in farm machinery, were conceived, designed, built, and perfected by blacksmiths.
Heck, many machine tools' earliest iterations were designed by lazy blacksmiths who figured there had to be an easier way. :)
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Yeah, it fits in that way. But if it's made without an anvil, it doesn't seem like much of a blacksmith project to me. :)
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On Dec 28 2009, 8:14pm, snipped-for-privacy@kcwc.com (Curt Welch) wrote:

You might get somewhere by installing a big lens in your sunflower. Focus the sun to a spot, and put a couple of little cylinders of water or propane on either side of the straight-ahead position. As the sun tracks round, the hot spot falls on a cylinder, which heats up, generating pressure on one side of a diaphragm, which turns the sunflower and so moves the spot off the cylinder (if you see what I mean).
The effect is that the spot always lies between the two cylinders, and the flower always looks towards the sun.
I have no idea if there's enough energy available to make this actually work, but it might be fun to try.
R.
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So you weld it during a freezing or worse day. Then in summer - 70 to 100 degree change. And you use lever actions - 100:1 or 1000:1 then it would move 70 to 100 inches if I did that right.
The whole idea was to use lever action to amplify a nominal movement. Painting the acting part black so it might absorb more heat would help.
Martin
jarkman wrote:

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