[TheForge] How to melt steel with sunlight:

[Bruce Freeman]

Small (like 11") plastic Fresnel lenses are cheaply available
(http://www.scientificsonline.com/large-surplus-fresnel-lens.html $7
ea) -- 121 sq inches each.
1.5 sq. meters is about 2325 square inches -- about 19 of those
Fresnel lenses.  So, if you made an array of 19 lenses, with their
foci all at the same focus, then you'd have the equivalent lens.
However, since you'll be using other mirrors to direct the light to
the lens, then you can probably do with fewer Fresnel lenses if you
focus the mirrors on one or more of the Fresnel lenses.  Maybe as few
as five Fresnel lenses would do the trick.
With no liquid involved, the whole assembly of mirrors and Fresnel
lenses could be mounted on a swivel to follow the sun.

I have another idea, but it's pushing the boundaries a bit.  View this
page:  http://gr5.org/index_of_refraction/
Now, imagine layers of glass or clear plastic, each a circle slightly
smaller then the next lower one, overall, forming the shape of a lens.
 Between and around these, use a liquid of the same index of
refraction as the glass.  The boundaries between the layers will
disappear.  Now IF the viscosity of the liquid is correct, then the
liquid will bead at the edges of the layers and form a continuous
surface to the lens.  (That's pushing it, I know.)  Voila', an
assembled lens.  Drape a sheet of thin transparent plastic over the
top to preserve the liquid.

Of course, yet another means is to skip the lens entirely and use tiny
mirrors, each with a controller to point them in a direction such that
the focus the sun on the same point.  The trick is to get the
controllers cheap enough!

On Fri, Nov 26, 2010 at 6:23 PM, peter fels & phoebe palmer
<artgawk at thegrid.net> wrote:
> Thanks Bruce;
> That's delightful!
> Brings me back to my old proposed solar forge
> If one were to use an array of cheap mirrors with tracker/step motor
> rigs like Kurt's,
> combined with a big lens...say a pool of water in a plastic sheet hung
> from a frame.....
>  or a big sheet of slumped glass in a frame filled with water or oil....
> Would that get up to forging temps?
> It looked like they were ready to weld there.
>
> On 11/26/2010 2:42 PM, Bruce Freeman wrote:
>> How to melt steel with sunlight:
>>
>> http://blog.makezine.com/archive/2010/11/2_square_meters_of_sunlight_focused.html
>>
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-- 
Bruce
NJ