34 replies to this topic

[BeaverDamForge]

Well, I got a freebie 38x28 lens (along with the front surface mirror ;) ) from a local TV shop, and some 6x6 slate tiles for $0.96 at Lowes. Now to find the time and weather to experiment... :rolleyes:

Good Luck!

[Ice Czar]

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

Woodware Designs -- The Solar Forge

however..

Quote

# 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:

Material..................F...................C
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.

[habu68]

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.

[evfreek]

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.

[grimcat27]

RainsFire said:

hah, no kidding.. I'de like to try it to, but here in Oregon it rains from September to June..

where are you in Oregon I'm moving there this summer

[Phil Krankowski]

Robert Palumbo was one of my professors in school. He is participating in a solar furnace project with the purpose of developing a process to make ZnO into metallic Zn through disassociation, a process similar to reduction. It turns out that you can make an "air battery" using Zn=>ZnO reaction, enough to power some small cars.

There is an experimental solar furnace built in Switzerland that achieves 2000F. It looks like a glass walled office building built into a hillside to get enough collection area.

palumbo solar furnace - Google Search

A lot of articles to wade through, most requiring membership. Sorry, I don't have membership either. You might need to brush up on your calculus to understand some of this though. I know there is a formula for calculating the area of collector needed to bring a chamber to a given temperature for a given solar incidence in these articles. Your solar incidence is either measured or reported as a seasonal average for your area, but will vary from day to day.

Since I haven't used this level of math in years, I would need to brush up to understand it too.

Phil

[ThomasPowers]

If they can't get it to pass at the false temp data it sure isn't going to pass with the correct temp data!

And 20 minutes is a long heat!

[Sweany]

YouTube - Stirling Engines - Solve Energy Needs?

[Dave Budd]

my forge is solar powered :)

well, the electric blower runs on batteries that are charged by photovoltaic panels :D

does that count?

[pauldude000]

jayco said:

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.

Truthfully speaking, a frsnel lense is no joking matter. A good large one (4' x 4' or 3' x 5') can reach temperatures up to an in excess of 5000 degrees F.

These lenses do not just provide a tiny pinprick of light either. You are talking a quarter inch to quarter size spot of that temp. You can quite easily smelt brass with one.

Theyt are just expensive as all get out, and you have to keep them clean and relatively unscratched. (They are not made of glass, but if I remember correctly are a polycarbonate plastic.)

For forge work though... I doubt it. Not enough watts to provide enough heat over a big enough area.

A bladesmith could use a fresnel lense on a frame to smelt his bolsters etc.. though.

[jason0012]

There was an anvils ring article years and years ago that mentioned a solar forge someone brought to the Dupres Wisconson conference(1984 or 86? I wasn't there) The article mentioned that it could reach welding heat, but only on a sunny day. It was built by someone from sunny climates out west.

[ThomasPowers]

And just a belated reminder "smelting" is reducing ore into metal; melting is melting! As brass is an alloy you don't "smelt" it!

[ianinsa]

Speak to Grant, buy an induction heater, use 20+ jack russels to run "hamster wheel" type generators/alternators. Use the sunlight to bask in glory!
Sadly Forge tempratures are achiveable but not currently economicly viable. Better off the grid solutions are available! Without your neighbours bitching about your "solar array"

[Conrad Hodson]

jason0012, on 04 April 2010 - 10:54 AM, said:

There was an anvils ring article years and years ago that mentioned a solar forge someone brought to the Dupres Wisconson conference(1984 or 86? I wasn't there) The article mentioned that it could reach welding heat, but only on a sunny day. It was built by someone from sunny climates out west.

This talk of lenses vs. parabolic mirrors is neglecting designs already proven from the 19th century. The favored design for solar steam engines back then turned out to be a trackable mirror in the form of a cone with the tip missing. It had a linear (not point) focus which they used to heat a tubular boiler. Their boilers would get to red heat _viewed in bright sunshine_ and would melt down if the water feed failed, so they're surely hot enough for a forge.

This design has several advantages for a forge. The work goes in through a small hole in the peak of the cone, along its axis. Which means the smithy is always in the shade, a major advantage in the kind of sunny climate you need to make one of these things useful. The heat is even, from all sides of the workpiece.

One small and one large drawback: the small one is that your iron will oxidize like crazy, unless you come up with some kind of gas shield for it. (Usually, our forges have an automatic gas shield of carbon monoxide, methane or propane due to a slight excess of fuel over air in the working zone.) Putting some charcoal in a holder alongside the work, with holes or nozzles to direct the CO vapor, should help, but I haven't actually worked this one out in practice.

The bigger problem is wind. Most of the 19th Century examples worked very well, until they were wrecked by high winds. Most of the areas (in this country at least) that have lots of sunshine have at least occasional violent winds, though the occasional sheltered valley or basin might be found. Some of the subtropical desert areas of the world are not so windy, and might be a good place to try this.

As always with alternative energy, location is everything. The installation that works to perfection on one site can be a heartbreaking waste of time and money the next state, or sometimes the next mile, over!

Conrad Hodson

[Nakedanvil - Grant Sarver]

fat pete, on 06 January 2008 - 08:40 PM, said:

it might be cool to use it to run your tools and lights.....not a whole lotta kw being used in 1 guy shop....

Hey! I got those, solar powered lights! Called windows!