Charcoal instead of gas?

[tool_man]

When looking at the price of LP gas and natural gas versus charcoal,one notices that charcoal is dirt cheap.About $3.50/10 pounds at the local Wal-Mart.I know it is a pain to melt with,distributing it around the crucible,pulling out the charcoal with tongs and then packing it around the crucible again for the next melt.In the book "Casting Aluminum" by C.W.Ammen,he states that 3.7 pounds of charcoal is needed to melt and superheat 100 pounds of aluminum.Now that definately makes it an attractive alternative.I wonder if it is possible to build a furnace with the charcoal under the crucible with an upward forced draft.Or.....maybe a stainless steel bar cage around the crucible to retain the charcoal?Any thoughts about this?Think about it and post your ideas.

[nikolatesla20]

Hi, one benifit to using charcoal is because the charcoal touches the crucible, and transfers heat more effectively. So you wouldn't really want to hold the charcoal off of the crucible with bars. Not to mention that if you get the charcoal hot enough those bars aren't gonna take it for long (the bars would need to be made of a refractory material).

I have a small charcoal furnace and really it is easy to use in my opinion, and usually even after I take out the crucible the charcoal pretty much stays in the shape it was while it was burning (it does not cave in right away) unless I bump it around a lot anyway.

I personally like charcoal, even though it's dirtier to handle, because it's simple, and less hassle to set up, and it gets very very hot.

You may be able to get away with having the crucible above the charcoal, but you would need a very insulated furnace to help contain the heat better, since charcoal itself is "self-insulating" you usually don't need insulation, you just need refractory lining. If you moved the crucible up you would now need insulation. Not to mention that for charcoal you need good airflow so a lot of the hot air is going up out the lid cover vent - it still seems to work best to have the crucible buried in the charcoal (look at cupolas which melt iron - the iron is actually sitting ON the charcoal or coke - no crucible at all!) but you could try it if you want to see if it would work out.

-niko

[Bent]

"he states that 3.7 pounds of charcoal is needed to melt and superheat 100 pounds of aluminum"

That sounds of a lot of aluminum for just 3.7 pounds of charcoal ??

Bent

[tool_man]

Thank you for your reply nikolatesla20.Good to get input from someone who has experience in this area.I recently found a gas fired crucible furnace for an unbeleivably low price so,I will be going that route for now.I have a natural gas hook up here .....only use it for heat in the winter but,I get charged a minimum each month whether or not I use it.Might as well get my moneys worth....right?Bye the way....I like the handle.Nikola Tesla was a remarkable person.Not many people are familliar with the many contributions he made.

[tool_man]

Hello Bent.That is what is stated in the book.Maybe we can get some information on that from nikolatesla20.He seems to have quite a bit of experience using charcoal for melting.

[nikolatesla20]

Well to be honest I would not know for sure, but I would not doubt it, depending on the type of charcoal used. Aluminum is really a low melting point metal, and 4 lbs of charcoal is an entire bag. When I melt using briquettes, they are still very intact when I'm done, but I'm only melting about 1 lb of AL or so. The one thing you find however is that once the AL is starting to melt, any new AL you add melts very quickly once you dip it into the already molten AL (just dont add it too fast). Of course you should also take into account the BTU of charcoal - http://basquescharcoal.privatedns.com/metalurgy.htm states about 13,440 BTU/lb, so 4 lbs (close to 3.7 lbs) would be 53760 BTU's.

Now really it depends on the efficiency of your furnace.

However some web sites I've found say the very efficient ones can melt AL at around 1100 BTU/lb, so really that would only allow melting 48 lbs then. However once the AL is molten it takes less to keep it there, so maybe you could get higher amount then. But most homemade furnaces are only like 10-12% efficient I hear, so once again really depends on the furnace design.



another nice page:
http://www.energysolutionscenter.org..._equipment.htm

-niko

[tool_man]

Glad we cleared that up.LOL.
I think you just hit on the point.There are so many variables.Quality of the charcoal,insulating properties of the refractory,how it is operated,ect.I think Mr.Ammen was giving a general,if not optimistic assesment from the point of a person with a great deal of experience in foundry work.Your results may vary widely.

[CharCad]

[QUOTE=nikolatesla20]Well to be honest I would not know for sure, but I would not doubt it, depending on the type of charcoal used. Aluminum is really a low melting point metal, and 4 lbs of charcoal is an entire bag. When I melt using briquettes, Of course you should also take into account the BTU of charcoal - http://basquescharcoal.privatedns.com/metalurgy.htm states about 13,440 BTU/lb, so 4 lbs (close to 3.7 lbs) would be 53760 BTU's.

I'd like to add something from practical experience. This is both melting aluminum in micro-foundries and currently building and operating prototype micro-charcoal retorts to make true foundry grade charcoal from wooden cargo pallet scrap.

There are major differences between "charcoal briquettes" and "real charcoal".

1. Charcoal Briquettes.

Briquettes are a compressed manufactured product made using charred wood mill waste, a starch binder, a percentage of anthracite coal in the case of Kingsford briquettes and powdered limestone. They don't come anywhere close to 13,440 BTU/lb for two reasons. The first is the amount of inert binder and limestone material, probably 25%. Second, the limestone gets calcined during combustion. This is what causes briquettes to leave so much ash behind compared to a wood fire of similar size. Chemically calcining lime is an endothermic (heat absorbing) reaction that reduces the total amount of heat energy (btus) released into the foundry.

2. Real Charcoal.

Any species of wood and anything else containing bio-cellulose can be used to make char or "charcoal". The available btu/lb of char is a function of two variables. The first is the species of wood used and the second is the temperatures reached during 'charring'. Charring begins at 450 degrees Fahrenheit. To get the highest possible energy yield from any char it's necessary to obtain a very high carbon percentage. These higher carbon percentages come from higher charcoal retort temperatures. Equal or greater than 900 F. The hotter the better. Any unconverted cellulose and lignin left in the char will also cause endothermic reactions in the char when you combust it later.

Mark

Attached are couple of pics of one of my prototype retorts during testing. It's made from a junked electric water heater tank.

[tool_man]

Thank you for the insight CharCad.I thought all charcoal was created equally.I may build a charcoal furnace one day but,for now I will stick with natural gas.I bought a Johnson gas Model 900 crucible furnace off E-Bay for $250.You gotta love that.LOL.

[CPS]

I don't want to poo-poo the guys that still use charcoal, but I will tell you this: now that I've switched to gas (been casting for 3 years and did charcoal for 2 months) I will NEVER use charcoal again. It does work, isn't dangerous when not in use, and doesn't require building a burner. Absolutely great for beginners to see if you like casting. However the pluses for propane make a charcoal furnace look like a toy, at least in my eyes. I've been wondering of hooking up to a natural gas source would make me feel the same about my LP setup. No running to Wal-Mart for fill ups!

Either I was doing something wrong or that statement about 100 pounds of aluminum for almost 4 pounds of charcoal is nuts.

My furnace is made from 2 buckets (the 2 bucks furnace on www.backyardmetalcasting.com) and I built my burner from his description too. I did spring for very expensive refractory cement from a local fireplace dealer. It holds up so much better than what I mixed up from directions in books and the net for my first furnace build. I use 20lb tanks from Wal-Mart and they quite a bit of aluminum from each fill. Having a spare is the best way to go in case you're halfway through a melt and start running low. I recently bought a Harbor Freight 4.5" bandsaw, and not hand-cutting scrap and sprues is awesome.

Good luck in your switchover, I think you'll like it.

Craig

[CharCad]

Originally Posted by tool_man Thank you for the insight CharCad.I thought all charcoal was created equally.

Far from it. Even real chars differ wildly in energy content. It's an interesting field with a lot of underlying science. And it's doable well locally at very little cost and seemingly simple methods.

I may build a charcoal furnace one day but,for now I will stick with natural gas.I bought a Johnson gas Model 900 crucible furnace off E-Bay for $250.You gotta love that.LOL.

Gas is 'easy', I agree. A lot depends on how much money you are willing to spend and also how much you metal you want to cast.

For $250 you could also have bought a MiG welder, then used free junk hot water heater tanks to make both char retorts and a large char furnace. Then charcoal scrap wood pallets and never pay another gas bill. And still own the MiG welder to use for other tasks. I love that.

For $250 you got a gas furnace, but then had to pay about $50 for a full 17.5 lb propane tank, right? And $50 more for a back up tank. So I make that $350, plus $20 for each tank exchange. And if you don't find a great 'deal' on eBay, the furnace costs how much? Mifco wants thousands even for small crucible furnaces.

You can do things with real char for next to no money, and which are very expensive with NG, LPG or propane. A real char furnace isn't limited to a 4" pipe crucible. Real char has enough energy to heat 5" and 6" diameter pipe crucibles for large aluminum castings, too. The rising price of all gasses these days makes doing that very expensive otherwise.

And for anyone who EVER wants to pour iron, real char in a cupola is the only practical low cost system. Just try getting ahold of real coal coke these days. Expensive and only available in 'small' quantities from a few dealers. Meaning a long trip or shipping charges equal to the price of the coke.

Regards,

Mark

[CPS]

Mark,

My brain is always stuck in "aluminum" mode. I think you are absolutely correct on the iron deal.

I think my setup cost me around $300 or $350 to build due to the expensive castable refractory cement. However since then I haven't had to repair the furnace, and it's made me a lot of money which I used to buy equipment. The $200 bandsaw and all kinds of blades, batteries, propane, Petrobond sand, etc have all been paid for with money made from casting. The initial investment has therefore paid for itself, and he could do the same thing with his Ebay purchase. However, if he's just in it for fun, I think you're right - do it cheap and have a blast.

For what it's worth, I also plan on making my own charcoal maker too. Everybody should have one for iron or larger home built furnaces, and what if the world comes to an end? That's a great way to have good char in nice quantity no matter what you use it for. I get tons of pallet wood at work for free - and free is ALWAYS cool. Propane just happens to do it easier for now due to my smaller pours.

Craig