Ultimate Guide to Making a Cheap but Effective Aluminium Forge.

Step 4: Melting Aluminium

This is pretty much the most dangerous part so have water near by and wear thick leather or welding gloves as well as safety glasses and make sure the area is well ventilated.

You're going to want to fire it up and put in your crucible.

I'd wait until the bottom of the crucible is red hot. (just a personal preference.)

Start out with small pieces of aluminum. (I had "pipes" from an old wind chime.) You could use cans but they tend to have a lot of slag. I'd wait until you have a nice quantity of aluminum before using cans.

You'll probably have a rough start so go slow. After you get a good quantity of aluminum it will be able to maintain a melting temperature and you can melt down large pieces in seconds. I have found an old knock off of a razor scooter in th back of my garage that has worn out it's usefulness. I found a new use for it's aluminum.

I have found covering the crucible with the top half of the empty propane tank helps keep the heat in and keeps things moving along nicely.

I had a troublesome piece of scooter that didn't want to release it's steel screw so I dunked it in the pool of molten madness and that half didn't come back. A mallet made short work of the obstructing piece of metal and allowed us to make a deposit in our crucible.

After you either fill up your crucible or run out of aluminum, you need to scrape off the slag. The slag will be floating on the top and will look a little different than the metal underneath.

We used a scrap piece of metal to scrape off the slag. We used the same scrap to make a hook to pick up the crucible and another piece to fit in the holes on the bottom of the crucible so you can easily pour it. You could use a small screw driver for this.

Make sure you have something to pour the aluminum into. I am just going to save them for later so I'm pouring them into one of those "mini muffin" tins just because they're small and fit in the crucible. You could just use an impression in wet sand or something. Muffin tins are faster. But don't expect to use them for muffins again.

Pour gently into the mold of your choice. IT IS HOT! WEAR PROTECTIVE EQUIPMENT!

Because I'm impatient, I wait until the aluminum in the tins are solid then throw them into a can of water. The water may boil violently after a short delay. It is a sight to behold but dangerous.

You now have aluminum ingots.

Comments

[cacci]

Could you melt salt (NaCl) like this?

[ElFantastic0]

yes, you can; however, depending on your objective, you may achieve poor results. Melting salt in a steel crucible will contaminate the salt to some degree (and it tends to eat up the crucible). Also, like the prior response suggested, avoid melting wet salt. The issue isn't so much that the salt will explode. It might bubble a bit as it melts, but the majority of the water will be lost before the salt is even able to melt. The problem is if you're trying to melt a mixture of salts in correct proportions by mass (e.g. to make fluxes). Seemingly dry salt stored in permeable containers will contain a remarkably large amount of water. This will offset any attempts to weigh out the salt charges. The only way to fix this is to dry the salt by heating it. Last method i used was to alternately roast and grind the salt, though a prolonged roasting would work too.

I know these are old comments, but i reply for the sake of anyone who ever hits this via google (like i did)

[lasermaster3531]

sure. you could melt salt in this thing, but make sure that there's no i repeat NO water in the salt. if there is, it might explode. maybe use something else other than the steel crucible or use one only for salt, because it might do something weird if you try to melt something else like aluminum in it, because aluminum's melting point is higher than salt's boiling point. also, don't heat it red hot. use an IR thermometer and get it to 900 deg Fahrenheit, but not lower than 800 and not higher than 1000.

[curvy77]

when i melted my aluminum cans (all i had and quite a bit =) ) there was lots of slag at the bottom and it fused with my crucible. pushed it down with stick adn squeezed out enough aluminum for 1' by 4' of aluminum ingot. slag at bottom normal?

[coocooachoo568]

Truthfully, i dont like this ible. sorry. i thought it was REALLY cool, but it turned out to be not. i made this thing EXACTLY like this ible said, but in the end, it failed epically. i even had the same crucible as him.  nothing melts! I tryed aluminum cans to a small aluminum pipe. all that happens is the aluminum cans and pipe turn a goldish brown and never melt. is there any possible way to fix this? i have a top and everything. i dont see how this works. HELP!

[Twitcheth]

How hot is your torch burning and what material (steel) is your crucible? Heat passes differently through different metals. Also a good way to tell if your torch is hot enough is simply if you see lots of flames theres not enough oxygen and not enough oxygen means it isnt burning as hot as it could be.

[curvy77]

i dont know about using gas to melt it but wood and charcoal work great for melting it. mostly wood. i used the last of my embers from a steel knife craft and i melted 3 aluminum cans in a soup can before the flame went out. (i had a blow dryer to help fan the flames)

[dcarr1]

what gas you using?

[coocooachoo568]

propane

[Firestorm_101]

I am just now getting into this sort of stuff but what may help is, in order to do larger pieces of metal like pipe, you must first already have a pool started. Cans are good but they must be denser otherwise they will oxidize and never burn. Cut off the ends, smash the tube flat, and fold it up into little square strips we'll call feedstock. It will be thick enough to melt effectively but not too big as to radiate all of its heat away. Good luck, hope this helped.

[cheeserdane]

i Iook your lid idea and with the other half split the top banana style to start a lid that can still let precious air in, but reflect more heat back to the metal.

[didgitalpunk]

you say have water nearby. i would rather use a CO2 fire extinguisher or a powder one because if water gets in some of your metal, it vaporises instantly and creates an eplosion of molten metal. insted , the co2 stops and pulls heat out of everithing to expand the powder in somme extinguisher is sodium bicarbonate. when heated high enough the bicarbonate transforms in co2 stoping irival of oxigen and so.

[pinkhairkid]

question does it have to be quickrete? could you use just concrete mix?

[Steve66oh]

The best material to replace the quickrete would be "Insulating Castable", search for it online. I don't like the rocks in quickrete or concrete, or the lime - a castable refractory mortar would do this job the way the pros do it....

[sharlston]

it has to be quick crete concrete has bubbles and bubbles explode

[jdc123]

what kind of torch is advised for something like this?

[punkhead58]

He used propane, however, oxy-acetylene would go a lot faster.

[matroska]

Hey Mr Shark500, I'm planning on actually builing this model of foundry, but I'd need some help as many of my questions are unresolved :( I thought maybe with your foundry experience you could help me out?

I was thinking either through IM or the instructables PM page.
Thanks! Your project is really motivating me, and I find it so well done!

[superhubbardman]

Delicious, delicious alumuffins
:D
good ible, 5 * and faved

[justin55]

im not sure exactly what the cause was but last weekend i had a propane torch and i decided to heat a penny with it and discovered that it melts, then i did it on my wet carport and it exploded all over my face and it looks like i scraped up my face really bad, i could have been blinded easily and i recommend being very careful with water!!!!!!!!!

[leebryuk]

It's the same reason that you don't place water onto a grease fire. The water rapidly (very, very rapidly) turns into a vapor. When it turns to a vapor it expands and moves outwards. In the case of a very hot liquid, the water turns into water gas and pushes everything outwards. There is no need for a chemical reaction. Rather, the physical transition between phases is what causes the explosion.

[snowdruid]

actually if the grease or oil is hot enough the water decomposes into hydrogen an oxygen instantly ignites and creates a huge fireball might look cool but is very dangerous

[leebryuk]

Water decomposes into hydrogen and oxygen around 3,000C. Then plasma incineration. Cooking oil (such as canola) top out around 500F. So it is simply a phase transition. As a solid or liquid transitions to a gas they expand and occupy much more room. When this transition and expansion happens very quickly it is termed as an explosions. A bomb undergoes a chemical reaction that gives off heat and gas at the same time which makes it occupy more room very quickly. Gundpowder is a great example. Just a tiny bit can hurl a tank shell for miles. Water thrown into a 500F fire immediately and rapidly expands into a gas. This transition throws oodles of burning oil into the air. Not a lot of fun to be around. But no chemical reaction is necessary.

[Jonny Appleseed]

some pennies melt because at some point they started making them out of zinc (someone correct me if I'm wrong) that explosion was probably the concrete exploding underneath the molten metal when it was heated, because there is still small amounts of water in the cured concrete...when you heat it, that water turns to steam, creating lots of pressure, eventually it explodes due to built up pressure , thats why you use so little water in the cement when you make this furnace, you also have to ram it in to eliminate any air pockets.

[jasontimmer]

In 1982 they switched from basically pure copper pennies to copper coated zinc. In fact, pre-1982 pennies are worth more as scrap copper than they are as pennies.

[morgantheblack]

1944-1982, US pennies were 95% copper. 82 and newer are a zinc blank, with a copper wash.

Wikipedia on Pennies

[Shark500]

well put

[Shark500]

ya probably shouldn't have done that. ; ) chicks dig guys with scars. be safe, be well, and thanks

[idon]

hahah true that, Hockey player here. split my chin open 4 times now. 9 stiches each time. funny thing is, i didnt realize i cut it till the EMT came up to me and was like, your going to need stiches. i looked in his mirror and i had blood all the way down my neck. happens evrey time.. i still get some hot *** biznatchesss

[prideofgumbo]

I made one of these and I can't get it to melt anything. Can't figure out where I am going wrong. Bigger torch maybe?

[ClemensY290]

the best way of not getting injured by these reactions is not to do it

[koga wolf]

i didn't know that

[Tinkers4fun]

A very nice way to condense aluminum into more manageable sizes for recycle or future use (added to favorites)

[ArtificialPulse]

haha, metal muffins. :-) you rock.

[NV1]

Awesome!!! Do you think this could melt copper scrap?

[maxa]

dose it go throw a lot of gas can you make a instructable on making stuff with the slag

[Wyle_E]

The slag is mostly aluminum oxide, which could be used in a refractory mixture for lining your next furnace. The problem is that you'll have to melt a *lot* of aluminum to get enough slag to build a furnace. Thousands of words have been published on the Web about homebrew refractories.

[ichiwazaryu]

Slag could be all sorts of stuff, not just aluminum oxide.

[futex]

u do know if u have one drop of water touch your alloy it will cause a explosion so devastating u and your family will die?? keep glass and wet cans AWAY. I work for Australians biggest alloy smelter caprol alloy. i would love to have this in my shed great idea... but dangerouse

[ichiwazaryu]

That isn't quite true. But certainly not a recomended procedure.

[kenny94]

you mean somthing like sodium

[A good name]

One drop? An explosion to kill him and his whole family? No. Just... no.

[Shark500]

i want to say this right now, just so every one can see.. out of spite i dropped some molten aluminum in the can of water.... Guess what happened.. absolutely nothing. it solidified. After 15 or so tests (in full protective gear mind you) NOTHING HAPPENED. I'm not saying that large quantities of aluminum won't react somehow but.. seriously. if you don't believe me then try it.. for lack of a better statement, MYTH BUSTED!

[nanoassembler]

Here is a SAFE analogy to bust your myth busting: Put a few TINY drops of water in a frying pan; fill the pan with just enough cooking oil to cover the drops; heat the pan on high on your stove; it won't take long to get snap-crackle-pop spurts of oil flying out of the pan. The cooking oil is analogous to the molten metal, because it has a muchmuch higher boiling point than the water. The water drops boil into steam and coming rushing out with a splash of oil (or metal).

[ichiwazaryu]

YOu have to remeber that droping a little aluminum INTO a big bucket of water wont do much because the aluminum is a light metal and can't hold that many therms. Droping WATER into a hot crucuble can be another matter. 1 cubic inch of water converts to 16 cubic inches of super heated steam ( which is very dangerous). This "expolsion" can cause the molten metal to splash on you. Always wear good safty equipment.

[Behb]

If water get trapped in the molten aluminium it can explode to.

[ComandoDIY]

so basically I would be able to pure my melted aluminum into sand and if the sand is dry it will just cast the aluminum like a mold would???

[Wyle_E]

You can make a mold from sand, mixed with a little bentonite clay, and cast metal in it. See www.backyardmetalcasting.com for details and a good page of links. There is also the "lost foam" method, where you carve a model of the part you want out of plastic foam (the closed-cell type used for insulation, not florist's foam), add a tall foam funnel, and bury it in sand with the top of the funnel (the "sprue") showing. When you pour the aluminum into that, the foam burns out as the metal flows in. Sounds crazy, but it actually works. Some of the sites linked from backyardmetalcasting.com discuss this process in detail.

[A good name]

Well you could, but it would likely absorb some of and sand and make the ingot of lower quality.

[Snail Boy!]

I have two questions. Does the metal object put into the crucible have to be pure aluminum? Also, is the slag useful for anything?

[Shark500]

1. it would help but no. as long as it's not some type of high melting point alloy. 2. the slag is not useful for anything.

[A good name]

Slag can be used for paving roads. (correct me if I'm wrong)

[depayton]

This is great. But what do you plan to do with the finished ingots?

[justin55]

oh, and by the way thanks for the great instructable

[random squigles]

Good one. But I strongly recommend you not use sand wetted with water as a mold. The steam explosion can send semi molten globs of aluminum in random directions at high speed. Murphy’s Law would dictate at least one red hot glob will land on something flammable out of eye sight or down your shirt. Use dry sand mixed with motor oil instead.

[solidification]

Its not so much a "steam explosion", rather a hydrogen explosion. Aluminum without its oxide layer (which can be produced in a convection of aluminum) is an extremely reactive metal. (more reactive than Sodium or Potassium that you might have seen placed in water etc). The Al rips the Oxygen off the H2O to form Al2O3 releasing a bit of heat and H2 gas. The H2 gas is bad for the casting in general because of the pockets left behind in the solidifying metal AND H2 gas, (HOT H2 gas) reacts with the oxygen in our air to form H2O again. The expanding gasses fling molten metal everywhere. And just to note, Al has a great thermal conductivity. So when it lands on clothing or skin, it will dump its heat very quickly.

[random squigles]

Thank you for that explanation. It never occurred that the explosion from using sand wetted with water was the Aluminum reducing the water and the resulting hot H2 being immediately oxidized again.I always thought it was just a good ol mechanical steam explosion.

[Biotele]

Molten aluminum is a great source of Hydrogen when mixed with water (steam). You can also remove the protective oxide layer of aluminum at room temperature and have it react with with cold water, by using a gallium alloy.

I explain this in my instructable

http://www.instructables.com/id/SODA-CAN-HYDROGEN-GENERATOR/

[salec]

So, basically, if I would submerge piece of aluminum in plain water and scrub it with sandstone or wire-brush, I would instantly get little hydrogen bubbles rising from its surface? Would there also be any heat release?

[solidification]

there is also oxygen gas dissolved in water at room temp. If you managed to penetrate the oxide layer it would grab something to get back to the most stable state. If O2, CO2 is available this would be the first choice since it takes less energy to grab those. (covalent bonding vs hydrogen bonding). For such a small reaction site, the heat that would be most measurable, would be the heat created from friction (scrubbing). When the convecting aluminum reacts with water, it has the potential to react with ALL of the water. In the sink scenario, it only has the exposed metal to react with. (that small surface area reacts quickly and seals the surface again. This is why its called a self protecting oxide layer) If you did the same speculation trial with ideal, pure water in a clean adiabatic environment where there was only Aluminum, and H2O and the temperature and pressure was reasonable for the reaction to take place, The Al would then grab the O off the H2O. The H2 would probably dissolve back into the solution, any heat would be absorbed into the water and all would move toward equilibrium in the system. So, no. not noticeably.

[Biotele]

you need to scrub the aluminum atom layer by atom layer, because a protective oxide layer is immedialy formed. But if you submerge the alluminum in a solution of draino, draino will melt that layer and the reaction proceed. Yes, a lot of heat is produced. Google "draino bomb" and watch the movies. They are self explanatory. The idea behind using gallium is that reaction is faster and there is no toxic material used.

[solidification]

this is way off topic, but Ga and an alkali hydroxide have very different mechanisms to disrupt the Al2O3. Neither of the two "melt" the aluminum oxide layer. In fact, the fat Gallium atoms are pretty impervious to the layer with some assistance. That cant be said for a strong base or strong acid however. (HF working the best).

[sehrgut]

Dry sand mixed with motor oil?!?!? First, that'd be a flammability hazard, not to mention the fumes. Secondly, it's easy enough to do it the right way -- especially as some kind soul above has already provided this.

[irongus]

that is true, there is also a cancer risk in using motor oil in a greensand mix like this...the smoke coming off is the culprit. i recommend the gingery series on making your own shop tools out of cast aluminum. lots of people do it this way, and it is as safe as can be for casting molten metals.

http://www.lindsaybks.com/dgjp/djgbk/series/index.html

gus

[Biotele]

Gingery is a wizard. He is amazing. I love all the lindsey publications.

[John Smith]

There isn't as much water as you'd expect. If you make your sand right, you should be safe.

[Shark500]

well, it's sand and clay. but i see your point. I just don't think motor oil has the surface tension to bind the sand well enough. Thanks for the comment

[solidification]

Clay rich sands can handle water with lower melting point (and less reactive) metals (like Sn). Best stick to oil-cationic binder sand or slip.. or investment plaster. The biggest problems with water/clay binder is the cracking in the mold but the cast parts have poor as-cast finish and the superheated metal will absorb hydrogen very easily as it is poured into this mold. for a reusable sand, Petro-Bond is pretty nice and cheap. (but Slip and Plaster have much better finishes and are not really that expensive in the long run)

[scotth61]

You'll want to search for a SAFE way to make your green sand.... I wouldn't add water to it at all, as when the molten aluminum hits it, it could vaporize and explode in your face. Not a good thing, unless you're into extreme pain. I have done a bit of sand casting, and the sand that we used did in fact have oil mixed into it. It's not as flammable as you'd think.

[flamesedge]

You do know that aluminum actually weakens when cooled with water like that? Most other metals strengthen with the same process but not aluminum.

[Shark500]

Good to know. I'm just going to re melt the aluminum anyway so, in this instance, it really doesn't matter. Thanks for the comment.