Rocket forge

Just curious if any metal pounders have tried a rocket style forge.
My only frame of reference is in the DVD's and it seems that the depth to the heat might pose a problem for me since I couldn't easily see the heat of the metal/color. It definitely appears that it gets hot enough but for small or intricate peices is it problematic without the clear visibility offered by a conventional forge?
Most of my work is done in a ferriers forge though I do occasionaly use the gas forge or a larger brick one if larger/longer pieces are being worked.

depends on your goals. i have had smaller L shape rocket stoves ive made out of aluminum self destruct by melting. that particular day i had the small rocket stove running in the driveway with the feed/air port facing a 10-15 MPH wind... couldn't have asked for better unless i piped a blower directly to the thing..lol

i would think you could bring most metals to cherry red provided you used hard woods and had a forceful air flow into the rocket.

I've never built a rocket stove or done any smithing so I really have no idea if it's possible, but I think it would be pretty easy to build a TLUD gasifier to make charcoal cleanly and efficiently (and you can cook on it so you get more uses out of it) and then use the charcoal that you get out of that in a rocket stove set up to get a really hot fire going. I know that's an extra step, but I think getting a hot enough fire to use as a forge by just using wood would be kinda hard.

I couldn't find anything exactly like what you're looking for, but here are some videos that might help you come up with something.
http://www.youtube.com/watch?v=txSD9i0R1Hs (making charcoal indoors using a rocket stove)
http://www.youtube.com/watch?v=YYDlaBFk2L8 (Charcoal making using a TLUD)
http://www.youtube.com/watch?v=4xA9nBqxPmY&list=FLA2xPFL8p_9wO8Iuwvv_pbA&index=1 (a small, portable forge). I think if you used one of the two methods in the other videos to make charcoal and then used that along with this, you could have something good. If you adapted this into "rocket forge" you could probably get away with not having to use/make very much charcoal at all).

Best of luck, this sounds really cool!

I don't know this for sure, but I have heard that the gasses from the wood weaken to the metal. That is why you use charcoal or coal to blacksmith. In charcoal the gasses have all been cooked out already.

So I was watching the Wood Burning Stoves 2.0 and i heard that the core temp of the rocket mass heaters being used at the labritory was getting up to 2500F. and the melting point of many metals are below this

Metal Melting Point (oC) (oF)
Admiralty Brass 900 - 940 1650 - 1720
Aluminum 660 1220
Aluminum Alloy 463 - 671 865 - 1240
Aluminum Bronze 600 - 655 1190 - 1215
Antimony 630 1170
Babbitt 249 480
Beryllium 1285 2345
Beryllium Copper 865 - 955 1587 - 1750
Bismuth 271.4 520.5
Brass, Red 1000 1832
Brass, Yellow 930 1710
Cadmium 321 610
Chromium 1860 3380
Cobalt 1495 2723
Copper 1084 1983
Cupronickel 1170 - 1240 2140 - 2260
Gold, 24K Pure 1063 1945
Hastelloy C 1320 - 1350 2410 - 2460
Inconel 1390 - 1425 2540 - 2600
Incoloy 1390 - 1425 2540 - 2600
Iridium 2450 4440
Iron, Wrought 1482 - 1593 2700 - 2900
Iron, Gray Cast 1127 - 1204 2060 - 2200
Iron, Ductile 1149 2100
Lead 327.5 621
Magnesium 650 1200
Magnesium Alloy 349 - 649 660 - 1200
Manganese 1244 2271
Manganese bronze 865 - 890 1590 - 1630
Mercury -38.86 -37.95
Molybdenum 2620 4750
Monel 1300 - 1350 2370 - 2460
Nickel 1453 2647
Niobium (Columbium) 2470 4473
Osmium 3025 5477
Palladium 1555 2831
Phosphorus 44 111
Platinum 1770 3220
Plutonium 640 1180
Potassium 63.3 146
Red Brass 990 - 1025 1810 - 1880
Rhenium 3186 5767
Rhodium 1965 3569
Ruthenium 2482 4500
Selenium 217 423
Silicon 1411 2572
Silver, Coin 879 1615
Silver, Pure 961 1761
Silver, Sterling 893 1640
Sodium 97.83 208
Steel, Carbon 1425 - 1540 2600 - 2800
Steel, Stainless 1510 2750
Tantalum 2980 5400
Thorium 1750 3180
Tin 232 449.4
Titanium 1670 3040
Tungsten 3400 6150
Uranium 1132 2070
Vanadium 1900 3450
Yellow Brass 905 - 932 1660 - 1710
Zinc 419.5 787
Zirconium 1854 3369

source: http://www.engineeringtoolbox.com/melting-temperature-metals-d_860.html

and so it seems that it would be possible to create a rocket mass forge.

Is this the right place to post this? or is this thread dead? IDK forum ettiquet.

Nicholas Mason wrote:I don't know this for sure, but I have heard that the gasses from the wood weaken to the metal. That is why you use charcoal or coal to blacksmith. In charcoal the gasses have all been cooked out already.

This is true. Forging on a wood fire is almost never done because:
1. It's hard to get it hot enough, even with plenty air forced air, and
2. The wood gas makes your steel act funny.


But.
They say a well-tuned rocket is smokeless because everything is completely consumed. All the molecules of lignin, etc, everything that the wood is made of, all broken back down to CO2 and H2O.

If that's the case, you certainly might be able to do some forging on your rocket by, perhaps making a hood at the top of your riser so the hot hases collect their momentarily and have to turn sideways. That would give you a spot hot enough to forge.
Or you you could have a hole through the side of the riser and out again. You could pass long stock into the hot zone and out the other side.

It could work, kind of. The problem, though, is control. A forge works by getting hot when you push air across the fuel. A rocket, though, works when the insulated riser gets so hot it causes all the combustibles to combust. And the thing about that is you can't just just turn it up and down or on and off. It ramps up and down depending its fuel load and riser temperature.

That's definitely not an ideal situation for forging. Anything that reduces your control over what's happening is pretty undesirable. Think about this. Your workpiece is so hot you can't hold it. Need an intermediate linkage (tongs). Your hammer needs to move faster than your arm can swing it without an intermediate linkage (handle). You can even tell how soft your material is without an intermediate linkage (color). It's pretty amazing we can EVER make steel do what we want. So when you consider that, how hard it is to control even the basic parts of the process, it would probably not be ideal to seriously reduce the controllability of one of your system's parts. I picture it leading to aggravation at best. Can't see it leading to happier working or better work.

But don't take my word for it. Try it!

Wood gas does not affect steel. I have built and used a gasifier forge, forging spikes into more useful (or at least artistic) stuff. I used Virginia pine (sappy, knotty) and can't see a better use for it.

https://permies.com/t/29960/biogas/Homescale-Bio-Gas-Syn-Gas

Temperature of gasses and insulation inside the riser may not translate into heating chunks of metal to those temps with any speed.

hi there,
i am a professional black- and blade smith and have built two rocket stoves by now. you can reach forging temperature in a rocket stove without any doubt, but:

- depending on what your goal is, the fumes DO affect your steel. if you are just doing artistic stuff and heat your stock only once or a few times this may not matter. if you are forging blade steel or load bearing parts it definately does! the biggest problem is the sulpuhr content of wood, what makes pine woods especially bad suited. (this should be solved by burning charcoal instead of wood)

-the conduction of heat from hot, flowing gas to solid metal is very inefficient.(i see no solution for this problem; which does not mean there is none, of course)

-as far as i can tell by now, welding temperatures are not usually reached in a rocket stove (you need to have significant higher temperatures than melting point), which is a big drawback. at least i would not consider forging on such a device as i need to weld quite regularly and don`t like machine welded joints in my work for several reasons. other people probably have other standards though. (maybe you can get a hotter burn by using charcoal, but i doubt it would suffice)

i have thought about highly insulated boxes on top of the usual barrel, containing another small fire and similar complicated devices. as it is relatively simple to build fairly efficient forges that can be run with charcoal and hand- or footpumped air i have temporarily given up on this project. (sometimes i have to think about it though and google if someone has had any good ideas about it. )

if any of you has found a working model, please let us know!

take care,
afghani

Funny thing, coal has 10X the sulphur content of wood.

well, i was just requoting this info i learned in school, from otherwise really competent staff ("you should not make a forge fire from wood, as it does not burn hot enough and the sulphur content makes your stock brittle"). but your remark really made me thinking. what must be also considered is that coal has twice the energy content per mass of wood and that you normally don`t use regular coal for smithing, but specially sulphur reduced coal (not all that much reduced as it seems: ca. 0,4% compared to around 1% in regular coal and to around 0,05% in wood). and i just found out on my research of wood contents that seemingly the biggest part of the sulphur is usually left behind in the ashes and does not even gasify (but i guess this is for regular stoves and not for the extreme temperatures of rockets)

probably the sulphur thing is not a problem at all! and probably i should just find out if it does affect the steel before posting crude theories based on badly researched facts...

also i have not yet found a way to short-term regulate my rockets; whereas a forge can be nearly shut down when you work your stock and then comes back to welding temp in a few moments (this really saves fuel). on the other hand i don`t need to save fuel so bad if its only sticks and punky stuff i get for free instead of expensive coal...

ok now,...
i don`t know where i had my head yesterday. was thinking about deleting the last post for its poor information. it`s been a while since i went to school and the routine did get hold of me since then, but fortunately most of it came back to me last night.(,i believe )

"red brittleness" or "hot brittleness" (direct translation from german; don`t know and can`t find english term) is caused by sulphur and carbon in hot (red glowing) steel and makes it brake apart. so sulphur is less a problem in low carbon "construction material" steel (soft steel). it is a problem in high carbon steel (hard steel).
if you use a (anthracite) coal fire you pile the new coal around the fire and pour water on it from time to time. this helps drive out the sulphur from the coal before it gets in contact with the steel (you can even see it as a thick yellowish smoke rising from fresh coals).
if you are forging (high carbon) blade steel, it is generally recommended to use char coal (which contains no sulphur) or at least a mix with charcoal. especially if you want to weld it, because the higher the temperature the more sulphur could diffuse into the steel.

a coal fire is generally a pit containing burning coal with a possibility to blow in air surrounded by a heap of non-burning coal. this creates different zones in the fire that can be used for different purposes (i.e.:burn of coatings, lowering the carbon content of the steel,...). for forging you generally want your stock in the zone that is the hottest but has no more oxygen left and also no contact to the surrounding air. that is, it is covered by burning coal on all sides that keep oxygen out (and of course heat your stock faster). this is called the reducing part of the fire.
in a rocket stove the equivalent would be directly in the heat riser and it would only exist if there were no excess oxygen. i believe both my rockets and most other well functioning rockets i have seen have at least a little excess oxygen (mine i think have plenty, which of course is not ideal in any case). for a rocket forge you would need to be able to control the airflow very accurately to the point, where it juust stops smoking. but i am sure people have made such devices already.

and then of course all my objections only make sense if you want a forge for serious work. to just make steel glowing hot, play around a little, forge some nails or hooks or spikes almost any decent rocket without barrel will do...

i hope this paints a more complete picture.

take care,
afghani

but man i can`t stop thinking about this rocket forge. i really have been sick of buying coal for a long time. there has to be a way...

I know about the various stages of coal/coke in a forge fire but it's impossible to fully control where the sulphur goes in the fire.

This is more like a gas forge than a coal forge, but I built and ran this for almost nothing (mostly salvaged parts). I'm sure it could be refined, and would need to be for professional use. With a single iron there was some waiting but two would keep you busy.


Won't reach welding temp as is (camera makes it look hotter), but the upside is it won't burn steel. Considering how hard it is to get carbon to migrate into steel (see case hardening techniques) I'm not worried about sulphur at this temp. How far could it penetrate? How much do you take off finishing a piece?

The fuel scoop was one of the first things I made from a spike.

there has to be a way...

and this here looks pretty promising and awesome. thanks for posting! (should have looked at you link right away)
the look makes me instantly think of a bloomery (which is basically a rocket stove with extra air blown into it, that is fuel-fed from the top)

is there already a way to regulate the fire? would you say it needs more fuel than a regular rocket? would you mind maybe posting a crosssection sometime?

great inspiration anyway...
it is the final straw for me. i am just gonna build a prototype myself as soon as possible. (and then i can find out how much of a problem the sulphur will be for my purposes, if it has enough power and so on...)
maybe to build it like a bloomery isn`t the worst idea. the forced secondary air could provide a means of regulation, too.

i don`t know how easily the sulphur stuff compares to carburizing, because sulphur is already fatal in traces whereas you need significant amounts of carbon to make temperable steel; also for most works including tool steel you have to reheat more often and often use only thin sheets that than get welded together, but do expose a lot of surface before. and as i said before, for ornamental stuff and non-load bearing funktional stuff like your scoop made from regular construction steel this is probably never a problem. maybe it isn`t for any purpose. it`s just that i mend a lot of tools and during the beginnings of my apprenticeship i wrecked a pickax (my own pickax i wanted to fix after work) and was told it was because i had used fresh coal. then, when i started making knives a few years ago i experienced "red brittleness" on my first try with welding high carbon sheet steel on an anthracite fire. i changed to charcoal or charcoalmix for these purposes and never had any problems since, but the burnt child dreads the fire...(or the sulphur)

and you wouldn`t need to take material of, because the problem only occurs with "red" heat. i guess you already know about the structure of steel; "red brittleness" is caused by the lower melting point of the sulphur-carbon-compound on the grain-boundaries.

Afghani Nurmat wrote:there has to be a way...

and this here looks pretty promising and awesome. thanks for posting! (should have looked at you link right away)
the look makes me instantly think of a bloomery (which is basically a rocket stove with extra air blown into it, that is fuel-fed from the top)

is there already a way to regulate the fire? would you say it needs more fuel than a regular rocket? would you mind maybe posting a crosssection sometime?

great inspiration anyway...
it is the final straw for me. i am just gonna build a prototype myself as soon as possible. (and then i can find out how much of a problem the sulphur will be for my purposes, if it has enough power and so on...)
maybe to build it like a bloomery isn`t the worst idea. the forced secondary air could provide a means of regulation, too.

i don`t know how easily the sulphur stuff compares to carburizing, because sulphur is already fatal in traces whereas you need significant amounts of carbon to make temperable steel; also for most works including tool steel you have to reheat more often and often use only thin sheets that than get welded together, but do expose a lot of surface before. and as i said before, for ornamental stuff and non-load bearing funktional stuff like your scoop made from regular construction steel this is probably never a problem. maybe it isn`t for any purpose. it`s just that i mend a lot of tools and during the beginnings of my apprenticeship i wrecked a pickax (my own pickax i wanted to fix after work) and was told it was because i had used fresh coal. then, when i started making knives a few years ago i experienced "red brittleness" on my first try with welding high carbon sheet steel on an anthracite fire. i changed to charcoal or charcoalmix for these purposes and never had any problems since, but the burnt child dreads the fire...(or the sulphur)

and you wouldn`t need to take material of, because the problem only occurs with "red" heat. i guess you already know about the structure of steel; "red brittleness" is caused by the lower melting point of the sulphur-carbon-compound on the grain-boundaries.

I had the gasifier regulated with a shutter over the blower opening, set so there was 1/8" crescent (out of a 2 3/4" hole) opening. Basically using very little of the blower's capacity. As I recall, more opening didn't help. After the blower box I had a divider box to get most of the air to the secondary 'jets' (holes). If I were to set it up again I'd do something like this:

but with as little metal as possible. Regulating voltage plus the butterflies should give great control (the upper fan needs a larger duct too). I used a 3" throat, a bit larger would probably be a good thing. A more insulative oven might help too. I used mud/perlite/straw with a couple brick pieces to reinforce the sides of the opening. There was also a 'mousehole' in the back I could cover with a brick. It took a while (1/2 hr) to get up to good temp and glowed for a while after shutdown.

I can't compare it to a rocket as I haven't tried such a thing for forging (and I think the excess air would be a big hindrance). But gasifiers burn fuel completely, there was never much ash to clean out even after a long day. I never noticed any ash other than from paper being blown out but I can't imagine where else it went.

I have seen sulphur condense on iron from the fumes of green coal, I know what you're talking about. Fire management... but in most cases that means having some coal 'coking' around the edges of the fire and no guarantee the sulphur is not drawn into the fire - especially when you stop feeding air from the bottom. Making enough coke beforehand avoids that. Now you have me wondering. I made some tools from files and haven't had any trouble with them. Then again I've never smelled anything like green coal fumes coming from my gasifier.

I've made a couple primitive knives with the forge finish right up to the edge, but I was thinking most knives and other "good" work are finish ground/filed. From your experience the problem goes much deeper anyway, so moot point.

thanks for your answer, bob.
this gasifier approach definitely could be an option too...

and you`re right, most knifes are finished. but this is to remove the oxide layer because of look, sensibility to rust and for cutting properties. i just meant you would not have to do that because of sulphur. the sulphur liquefies your grain boundaries (where most of your carbon is anyway) at forging temp and thus the steel crumbles apart when you hit it.
this may be a bit off topic, but these are top-of-the-notch knives with oxide layer still mostly on: http://en.wikipedia.org/wiki/Nakiri_b%C5%8Dch%C5%8D

by the way; if you used files, the steel still can have very different carbon contents. wood files or rasps have only about 0,4% carbon whereas precision metal files can have up to 1,4%. also, considering the facts and your experiences i do believe less and less the sulphur content of wood gas is a problem... hope to find out soon anyway and will be posting my efforts and results here

I can't imagine a 0.4 carbon file being useful for long, even in wood. Files aren't specified for use other than coarseness AFAIK (you wouldn't want to use a rasp on metal in most cases but double and single cut work fine on wood). One that I recall reusing for a hot cut was a 1" wide Nicholson single cut mill file. Most wood tools are high carbon steel, with 0.4 carbon content you really don't get much hardening. I don't expect spike knives to hold an edge very well, and I don't bother with tempering.

Here are some spectro analysis of files, about the middle of the page:

http://www.iforgeiron.com/page/index.html/_/blueprints/original-series/bp0002-junk-yard-rail-road-steel

"Rail anchors" make decent tools for some purposes.

Crystals VS grains in the structure of steel gets confusing to me sometimes. It took a bit of searching but I like this reference I found some time ago:

http://www.iforgeiron.com/page/index.html/_/blueprints/original-series/bp0078-the-metallurgy-of-heat-treating-for-blac-r306

I'm not sure what you mean by most of the carbon being at grain boundaries or how they would be 'liquified'. At forging temps the grains are consolidating and growing, but hammering breaks them down. The carbon migrates around until the metal cools, and can get trapped within the iron crystals if cooled fast (quenched).

Looking around the 'net I can't find much pertinent, but it seems iron has a much greater 'affinity' for sulphur than carbon and it forms iron sulphide, which is a better explanation IMO. In this piece:

http://www.anvilfire.com/21centbs/chapt-13.htm

the 5th paragraph echoes what I was saying about the fire and 6th paragraph talks about the condensing smoke. I have seen that advocated as a finish. However when he talks about steel absorbing carbon from the fire I wonder. I think that lies somewhere between "unproven" and "wives tale" which smithing has more than it's share of. That's why I had wondered about absorbing sulphur.

I use a Japanese style charcoal forge for blade making. I have used both pine charcoal and hardwood charcoal in this forge, both seem to work just fine for working awagane steel.

In this style forge you can heat 29 inches of length with total control by working it with a sliding motion.

The folks at Wheaton Labs have finally done it! The innovators at the annual Permaculture Technology Jamboree have come up with a working forge! Check out the action!