Jump to content
I Forge Iron

Recommended Posts

I doubt a huge lenses could be successfully and productively used to forge steel ...

Altho it's a very good way to heat up small crucibles and melt nonferrous metals..for casting jewelry and other trinkets. . or experimenting with stuff. . .

One could build a furnace that receives concentrated light from an arrangement of mirrors. but that would require adjusting the mirrors very often.

Link to post
Share on other sites

I dimly recall seeing at a solar energy conference down in Texas somewhere, Austin, maybe, back in the last century a picture of a humongous solar array focussed on a piece of wide flange, sliced it like a torch going through wax. I think the rig was set up by one of the government energy labs. No practical value that I know of. Didn't some Greek hero in ancient times set the enemy fleet afire with such a weapon?

Link to post
Share on other sites

In a 1970's Mother earth news there was a solar collector made from a bunch of 1' sq mirror tiles that had an auto tracking feature. It was used to run a steam engine IIRC and produced 1600 degF.

I thought about using one for a solar forge but then I was exposed to the high winds that are a regular occurance out here and decided that making such a structure windproof was beyond my interest level.

Link to post
Share on other sites
I dimly recall seeing at a solar energy conference down in Texas somewhere, Austin, maybe, back in the last century a picture of a humongous solar array focussed on a piece of wide flange, sliced it like a torch going through wax. I think the rig was set up by one of the government energy labs. No practical value that I know of. Didn't some Greek hero in ancient times set the enemy fleet afire with such a weapon?

Yes ..It was Archimedes . .more of a well known scientist/inventor/mathematician . . . He made all sorts of contraptions to defend Carthage from the Romans in the Punic wars ...altho he was killed by Roman soldiers that were rampaging around after the city fell.

It is said he was killed because he would not follow the soldiers' orders because he hadn't finished his latest theorem.
Link to post
Share on other sites

This thread reminds me of elementary school science class.......and discovering that you could use a magnifying glass(and sunlight) to catch a piece of paper on fire.

My uncle told of using a magnifying glass to light cigarettes when he was out of matches..

I guess if you could multiply the effect by 100, or 1000 times, you might be on to something.

I suspect there might be some kind of physical limits on how mush heat can actually be generated this way.....but I'm no scientist and occasionally I am wrong( well......more than just occasionally).

If the idea really works, it could supply a lot of the world's energy needs.

Who knows.

Link to post
Share on other sites

about a mile from my house is the aluminum panel manufacturer that prototyped these for Sandia National Laboratory National Renewable Energy Lab

Stirling Energy Systems Inc
Vid > http://www.stirlingenergy.com/video/time_lapse_footage.wmv
Major CSP Projects

have a contract with Southern California Edison to install a 500 megawatt plant thats scheduled to open in 2009

Link to post
Share on other sites

the use of lenses to generate heat is not of practical use to a smith because of the focal point. The size of the lense that would be required to have a focal point large enough, well I am not a math guy but I do know that the focal point is the crucial factor. Sounds like a good one for the myth busters eh?

Link to post
Share on other sites

I made a solar cooker. It could get one hot dog to about 300F. Nice and sizzly. Unfortunately, it took me about as much time to make as my washtub forge. I also had to sounce a special piece of mirror plastic, since aluminum foil wasn't shiny enough. The hot dog would barely get warm. A quick heat transfer calculation showed that the design is marginal because convective cooling around the diffuse focal point is too high. Either the focal point had to be sharpened, or steps had to be taken to cut down the losses. Wrapping the hot dog with foil did not help. Buying special solar foil that was flat black on the outside and shiny on the inside helped a lot.

For those of us who think that kaowool, IFB and fireclay is hard to find., that solar stuff is much worse. For larger applications, where convection is not so much of a problem, it might be OK. For example, solar might work well for a glass annealing kiln. About 900 F for a few hours.

Link to post
Share on other sites

I think the controlling point is the wattage available from 1 sq foot of land put out by the sun.

If you know how many watts your heater must have and figure out the efficiency of your collector you can calculate how much you need.

I envisioned a heavily insulated (kaowool of course) forge "box" with a narrow slit to allow the focused power to track down the slit to make repositioning less frequent. If the watts go in it *will* get hot until the losses equals the input.

Link to post
Share on other sites
  • 1 month later...

I've been looking at solar powering a forge. It looks like a big fresnel lens could do the trick but may be limited on how big an item you can heat, or at least how quickly you can heat it. I've seen a claim that 2500:1 concentration can easily burn through 1/4" steel. The big screen TV lenses are about 4' x 3', approximately a square meter, and will focus to a square centimeter for 10,000:1. You could back out of the focus and heat 4 square centimeters at 2500:1, but that's still only about a 3/4" square and the surface will heat much quicker than the inside. Getting farther from the focus may help. I plan to check local TV shops for a (hopefully) cheap lens. The intensity of the light will require a welding helmet, maybe an auto darkening one would allow you to see what you're doing when you get to the anvil.

A more elaborate setup would be to use mirrors. Most solar furnaces rely on some kind of parabolic mirror(s) to concentrate light. I do have an old satellite dish, but coating it with mirrors would be a lot of work and probably expense. With flat mirrors the concentration will be limited to the number of mirrors, but you can collect a lot more sunlight (area) than the lens. My idea is to use the light from several 4x8' arrays reflected (from below) onto the bottom of an oven (possibly with some concentration), which I hope would heat the iron more evenly and avoid having to look "into the light". Unless they are set up for sun tracking, the arrays will have to be adjusted fairly often, probably every 5 minutes or so for optimum temperature.

Anybody have any ideas what would make a good oven floor? Firebrick was my first thought, but it would reflect a lot of light. I need something that stays dark on the heated (absorbing) side while incandescing on the other - not asking for much, eh? Could a ceramic material have a flat black coating that would stay there at 3000+*?

Thanks and Good Luck!

Link to post
Share on other sites
  • 2 weeks later...

stumbled upon this today, a solar forge demo and plans that might actually be large enough to be useful

Woodware Designs -- The Solar Forge


# Temperature Requirements

The most likely use of a Solar Forge is as heat source for small businesses. The following table shows the temperatures that are needed to work some common recyclable materials into new products:

Steel, work.............800-1000........430-540
Steel, anneal..........1350-1500.......730-820
Steel, melt.............2500-2700.......1350-1460
Aluminum, melt.......1218................660
Brass, melt............1652-1724........900-940
Bronze, melt..........1562-1832.......850-1000
Copper, melt..........1981...............1083
Lead, melt.............621.................327
Zinc, melt..............786.................419
Silver, melt............1762................961
Gold, melt.............1946................1063
Glass, work...........1200-1800.........650-980
Glass, melt............2000-2400........1100-1320

From this table we can see that the Solar Forge is just a toy unless it can raise a bar of steel with a cross-section larger than your thumb to a good hammering cherry red (800 F, 430 C) in 20 minutes. Furthermore, to be of commercial value, it must be able melt a crucible with 2.2 pounds (1 kilogram) of aluminum (1218 F, 659 C) in one hour. These will make good test criteria for Solar Forge prototypes.

No Solar Forge prototype has yet passed these tests.

The design seems to be detailed and viable (tracking, parabola construction, size, contact assistance), if it was primarily employed as a boost heat source to a propane forge I think there would be considerable cost savings. His viability standard for steelwork seems reasonable, and the failure of his prototypes indicative of exactly how large an array one would need to build to make a forge solely powered by sunlight.
Link to post
Share on other sites

Old 5 to 6 ft satellite tv dishes are parabolic lenses with their focal point at the receiver pole. Since they are old technology they are a dime a dozen and have their own tracking devices. It would seem like a little tinfoil and some B/S engineering one could come up with a workable unit.
Telescope builders have earth synchronous timers and gear units to track the sun.

Link to post
Share on other sites

Hmmmmmm. "a good hammering cherry red (800 F, 430 C) in 20 minutes" Even in well-regarded refereed journals, misstatements such as these weaken the credibility of the article. I would not commit a few thousand dollars to build a prototype after seeing these figures in the plans.

I think that when I was beginning, one of my problems was not getting the metal hot enough. But this is ridiculous. First, 800F is not "cherry red". I cannot see 800F reliably, not even at night. And I have a pyrometer. Second, "cherry red" is not "good hammering". "Good hammering" is light orange or yellow (2000F +). Again, these are my preferences, and some smiths may prefer cooler, but not that cold.

Link to post
Share on other sites
  • 1 year later...

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...