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Author: Subject: Metal melting propane furnace construction
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[*] posted on 31-5-2004 at 22:20


Good old sewage pipe...That is whay my melting pots be made of, only I welded on a 5 mm thick plate on the bottom and attached a few legs.

If you are going to be melting Al, (based on your temp range), you may concider moding your vessil a bit. Find a smaller diameter pipe about the same length as the length of your cruciable. Cap the bottom of this pipe. Drill a large diameter hole through the smaller pipe with a matching hole in the larger pipe neer the bottom. Join the two together. This way you can pour out your metal from the bottom and not have to worry about the oxide and crud that is floating on the top (in the case of Al).

Also, attach a ring or a circle at the bottom opposite the side you will be pouring out of. This will allow the use of a hook to tilt the cruciable.

You may also want to consider capping your vent coming out of the top and relocating it to the side opposite the burner input a short distance below the lid. Supposidly that is suppose to help hold in the heat.

How do you plan to make the molds for your casts? (Heard of the "Lost Foam" process? Its slicker than shit!)
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[*] posted on 1-6-2004 at 03:12


Won’t the iron dilatate much more than the cement? Why not ask a plumber to make threads in a piece of steel pipe and screw an end cap to it? Or just ask to solder it shut.
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[*] posted on 1-6-2004 at 05:47


I am now seriously considering building a propane/air combustion furnace (to replace my butane bunsen). Axehandle, you can take this as a compliment, you make the project look very attractive :).

I had an idea last night for a modification to the furnace design (which incidentally kept me up far past my bedtime :P).
If...
A = Picture
And...
B = Word
Then...
A = B x 10<sup>3</sup>

<html><a href="http://www.geocities.com/xxramielxx/CAV_furnace.JPG">linkage</a></html>

//NB
- Lid not shown (just a usual lid, same X-section area as the vents).
- The crucible is to sit flush with sides of the furnace.
- Part marked 'Intake' can be to your pleasure (I love Axehandle's version, personally)

I was just trying to figure out a way to make the hot air do more 'work', as opposed to a large proportion of it just flowing around the crucible and straight out the top - without transferring heat (convection s|_|xx0r :().

Whaddaya think? old idea, wont work, good idea, too hard to cast.

Sincerely
- Ramiel

ps. I drew all that with paint, :cool: ;)
*cracks knuckles*
pps. [edit: spellink]
ppps. [edit2: Thanks, I broke my teeth on winamp skins - doing all of them in Paint was a learning experience (I got 4 1/2 stars for one :cool: )]
pppps. woah, geocities account suspended - link only, sorry folks.

[Edited on 1-6-2004 by Ramiel]




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[*] posted on 1-6-2004 at 05:56
Off Topic, but I really couldn't help it


Quote:
Originally posted by Ramiel
ps. I drew all that with paint, :cool: ;)
*cracks knuckles*
pps. [edit: spellink]

[Edited on 1-6-2004 by Ramiel]

LOL :D:D:D

Thats a very good paint picture btw :o

Edit2: Wow, winamp skins using paint?? :o

[Edited on 1-6-2004 by Saerynide]




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[*] posted on 1-6-2004 at 08:34


Thank you all for your input. I'll soon redesign some concepts.



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[*] posted on 1-6-2004 at 19:21


Axehandle you may be interesting in these links:

http://www.backyardmetalcasting.com

The Shed: Propane Furnace

Propane funace at 1328F

The shittiest Howto on the net about propane - It sucks

I am planning to build a charcoal furnace this summer. I like charcoal because its cheap and my mom thinks that because its used in the grill its safer:D I want to melt and cast Al into ingots and then work on casting in greensand and possibly build a homemade lathe from the castings.

I like this site as an example of what I want to build.

http://mypeoplepc.com/members/waygat/castingfoundrylathe/id1.html

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[*] posted on 1-6-2004 at 20:56


Ah, the homemade lathe: the virual batchelor exam of metal casting.
:):)
:D:D
;);)




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[*] posted on 8-6-2004 at 05:59


I went to Bunnings today and picked up a rather special deal I spied many moons ago. This stuff called <html><a href="http://www.lcainc.com/fondu.html">Ciment Fondue</a></html>. Apparently it can [easily] stand 1270<sup>o</sup>C. It had been ordered in especially for a customer, but after a long time without being collected, put out to stock - I felt kind of cruel walking out with half of his special order. >: D

I plan to test a few mixes with bentonite and pearlite prior to casting my design. Do you have any suggestions with regards to mixing ratios, people?

It says that it is ideally suited to refractory mixes. Sets in a few hours. Highly resistant to mechanical shock. I think I'm in love. :cool:

Oh, and Axehandle, you may be interested to know that it was first designed to be a refractory material resistant to sulphur oxides - of particular interest to your sulphuric acid plant methinks? :)

Hope this is a positive contribution to the thread after that last inane contribution. :\

- Ramiel

[edit - grammar falling apart. tired]

[Edited on 8-6-2004 by Ramiel]




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[*] posted on 9-6-2004 at 09:36


Quote:

I plan to test a few mixes with bentonite and pearlite prior to casting my design. Do you have any suggestions with regards to mixing ratios, people?

Don't use more perlite than 2/6 (by volume), or the refractory will be very fragile. If the cement does not contain sand, add some sand (SILICA!, else: KABOOM (small explosions leading to cracks)). As for bentonite, I don't have an exact measurement. I think my old furnace had about 1/10 (by dry volume) bentonite, but you could add it slowly until you get the right "feeling" (soft cookie dough like). It's not critical, its only job is to keep the mix together after dehydration.

Edit1: I know this thread seems to have died, but secretly I'm developing an ELECTRICAL furnace! Well, it's not so secret now, I suppose. Today I finally got the 0..15A, 220V single phase power dimmer I ordered, as well as 36m of 0.7mm Kanthal D wire (good up to 1300C) and a huge Al coolant thingie (for the thyristor dimmer).

BTW, that cement looks great! If I find a local dealer selling it I'm going for a sack...


[Edited on 2004-6-9 by axehandle]




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[*] posted on 9-6-2004 at 11:46


How much do you pay for electricity in Sweden? Isn't an electric furnace going to be pretty expensive to operate, compared to a gas furnace?



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[*] posted on 9-6-2004 at 12:14


Quote:

How much do you pay for electricity in Sweden? Isn't an electric furnace going to be pretty expensive to operate, compared to a gas furnace?

Currently I pay SEK 0.7863 (== USD 0.104292) per kWh including energy taxes and VAT.

I don't know if it will be more economical than propane, but I won't have to deal with the hassles of refilling, and it's a fun project to boot!

Edit1: Here's the mold for the heating chamber. It's a spaghetti container with a 2m length of 10mm OD PVC hose spiraled around it, with electrodes made of de-zinced M6 threaded rod temporarily glued in place. Once the refractory is semi-cured, everything plastic will be removed, leaving only an empty cylinder with a spiral groove for the heating coil, and ofcourse the electrodes to provide a connection to the outside.

More pictures soon to come.



[Edited on 2004-6-9 by axehandle]




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[*] posted on 9-6-2004 at 13:18


How are you going to remove the plastic? I doubt it willbe easy to remove 2m of tubing through solidified fire cement (or whatever u are using). I take it you plan to thread the heating wire through the spiral?
Then, how about the properties of the wire itself? Resistance is proportional to the length, and resistance goes up with higher temperatures. Have you accounted for it? I am asking because there is a chance that you either overheat the wire (meaning that the resistance is not high enough, thus the wire should be longer), or that that you don't achieve high temps due to too high a resistance. But I guess you looked up the specs of the wire.
Then - how are you going to avoid the fire cement from cracking where the wire is? The heat distribution here is everything but homogenous, and there is again a good chance that the cement cracks directly around the wire...

I thought myself of making a nice 'n big electric furnace - but those were the problems i always thought of. The way I would have gone about it would be to use tiles, with wire that doesnt contact any of the tiles directly. Thats tricky to do, I know. Things have to be insulated pretty well, and holes avoided to prevent hot air from escaping and cooling the whole thing down.

Looking at my electric muffle furnace - it is also made of tiles, with thin wire wound about them. They are all exposed to the actual heat chamber. IIRC, pottery ovens also have their wires exposed, and are made from tiles (my grandma was a pottery maker ;) )

At last - I would also prefer using an electric furnace. I wouldnt worry so much about the money of the electricty, but much rather I'd be concerned about safety - no flammable gases (and particularly a 50 litre gas tank), and no massive CO2/CO evolution.




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[*] posted on 9-6-2004 at 14:55


Quote:

How are you going to remove the plastic? I doubt it willbe easy to remove 2m of tubing through solidified fire cement (or whatever u are using). I take it you plan to thread the heating wire through the spiral?

Nope, I'm going to wait until the refractory is semi-hardened, i.e. tomorrow or perhaps tomorrow night, depends on how long it takes :), then I'm going to crack that plastic container (it's made from a hard plastic that seems very fragile), pull out the pieces and then pull out the spiraled hose. The groove will then get a "U" shape. Unfired refractory of this type doesn't get really hard until it's fired, until then it's slightly less hard than hardened gypsum, so it shouldn't pose any problem, and if it does, I'll burn the little bugger out with a slow charcoal fire....

Quote:

Then, how about the properties of the wire itself? Resistance is proportional to the length, and resistance goes up with higher temperatures. Have you accounted for it? I am asking because there is a chance that you either overheat the wire (meaning that the resistance is not high enough, thus the wire should be longer), or that that you don't achieve high temps due to too high a resistance. But I guess you looked up the specs of the wire.

All calculated and accounted for. The coil will be adapted to a maximum current of 15A, and I'm going to use the power regulator in the inserted picture to regulate the current. I'll have to steal power from the stove to do this, all the other fuses are 10A....

BTW, this wire is made for applications like this. It actually gets a protective coating of Al2O3 after a few firings (it contains Fe, Cr and Al). It's Kanthal type D wire, good upto 1300C, incidentally used in pottery ovens :). According to the specification, it has an almost constant resistance within its normal usage range (room temp.... 1300 C).

Quote:

Then - how are you going to avoid the fire cement from cracking where the wire is? The heat distribution here is everything but homogenous, and there is again a good chance that the cement cracks directly around the wire...

Aah -- that's where the <i>expensive</i> power regulator comes in -- I'm going to start at 1A and go up <i>very</i> slowly to dehydrate the refractory without cracks. I'll know it's done when the steaming stops.

Quote:

I thought myself of making a nice 'n big electric furnace - but those were the problems i always thought of. The way I would have gone about it would be to use tiles, with wire that doesnt contact any of the tiles directly. Thats tricky to do, I know. Things have to be insulated pretty well, and holes avoided to prevent hot air from escaping and cooling the whole thing down.

What about sealing with fireproof cement, the kind used when building indoor hearths? It's good upto 1400 C. About holes: I will have one in the (hinged) lid, about 20mm in diametre, covered with a small plate of borosilicate glass at the top to peep through.

Quote:

Looking at my electric muffle furnace - it is also made of tiles, with thin wire wound about them. They are all exposed to the actual heat chamber. IIRC, pottery ovens also have their wires exposed, and are made from tiles (my grandma was a pottery maker )

Yup, I got my idea from a pottery oven :).

Quote:

At last - I would also prefer using an electric furnace. I wouldnt worry so much about the money of the electricty, but much rather I'd be concerned about safety - no flammable gases (and particularly a 50 litre gas tank), and no massive CO2/CO evolution.

You've read my mind. I was getting very nervous around my 10kg propane bottle, and tired of refilling it. I'll still build a propane furnace though, for larger melts. But after my beard-singing accident, I'm a bit shy to use propane.

I think I got the refractory right this time, but I won't post the exact proportion of ingredients until I know it works, to save anyone from repeating any of my mistakes. I have recorded the exact amounts this time...

<b>Pictures</b>

Power regulator, back (the regulator is a thyristor based module screwed onto a humongous heatsink):


The front, the controller knob is visible in the middle:


Edit1: Oh, and I should mention that my girlfriend Anna helped me mix the refractory.

[Edited on 2004-6-9 by axehandle]




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[*] posted on 11-6-2004 at 08:51
har-dened!


The entire apparatus sans electrical gear:


The apparatus with the hinged lid open:


A view of the chamber, one of the electrodes for the heating coil to be placed in the spiral can be seen at the bottom:


A closeup of the peephole in the lid (the recession will be covered with a pane of borosilicate glass:


Now the refractory just needs a couple of days to fully solidify, then I'll mount the coil and the power regulator!




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[*] posted on 12-6-2004 at 07:19
Refractory formula


I haven't fired the refractory yet, so there is no guarantee that it will work, but I hereby announce my refractory formula in the interest of science. I've come up with the proportions myself through trial and error.

This is for approximately 16 litres of refractory:

4.8 litres of silica sand
7.2 litres of portland cement
7.2 litres of expanded perlite
1.5 kg of bentonite powder
10 litres of water




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[*] posted on 14-6-2004 at 04:55
Arrgghh!!


Why do you always run out of M6 nuts when you need them?!?!?! I only need 2 more to finish the furnace.... sigh.



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[*] posted on 15-6-2004 at 04:00


Happy to see you have gone electrical! Will cost you some more but it’s quite safer.

Just for future reference: My experience with high power triacs is not a happy one, but I’ve built the circuits myself. The worst is that, when they go “kaput”, they release full power! A $0,01 old fashion fuse may save you a headache.

The power regulator you bought seems reliable but, if it proves otherwise, think about on-off regulation. Sort of a Pulse Width Modulation with alternating current and a 0,1 hertz frequency. I did that using a 555 CI and a fat relay. It’s no good as light dimmer, but makes no difference in controlling the heat of a coil.

Nice casting of refractory. Congratulations to Anna!
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[*] posted on 15-6-2004 at 06:55


Quote:

Happy to see you have gone electrical! Will cost you some more but it’s quite safer.

That's the general idea. As I wrote a time ago, I had a fuel-air explosion in my newest propane furnace that cost me half my beard. That's the main reason I'm going electrical.

Quote:

Just for future reference: My experience with high power triacs is not a happy one, but I’ve built the circuits myself. The worst is that, when they go “kaput”, they release full power! A $0,01 old fashion fuse may save you a headache.

Yes, I've been concerned about that. More to protect the regulator than the coil -- the latter is easily replaced. But the only danger to the regulator is overheating, am I right? (I'm thinking about adding a 220V fan I have lying around to that huge heatsink.)

Quote:

The power regulator you bought seems reliable but, if it proves otherwise, think about on-off regulation. Sort of a Pulse Width Modulation with alternating current and a 0,1 hertz frequency. I did that using a 555 CI and a fat relay. It’s no good as light dimmer, but makes no difference in controlling the heat of a coil.

Yeah, I considered that but in my experience, when I build a circuit, it always ends up being more expensive than buying a premade one... But I could easily hack together a solid state relay with a 555 based PWM circuit --- I've done it before, for an ignition coil driver circuit.

Quote:

Nice casting of refractory. Congratulations to Anna!

Thank you. I will relay the praise.




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[*] posted on 15-6-2004 at 08:16


Quote:
Originally posted by axehandle
(snip) But the only danger to the regulator is overheating, am I right? (snip)

I don't know if it's overheating. TRIACs seem to just fail for no apparent reason...
Quote:

(snip)... But I could easily hack together a solid state relay with a 555 based PWM circuit (snip)


Oops! No. "Solid state" means a TRIAC. I meant a good old fashioned relay going "click-clack" in a... say... 10 seconds cycle controled by a 555. "on" varying from 0 to 10 seconds and "off" (therefore)from 10 seconds to zero.

Aaww! Never mind. That power control of yours seems to be a commercial item whose project has probably been tested to exhaustion!
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[*] posted on 15-6-2004 at 08:38


I certainly hope so... it's supposedly good up to 15A, but I'm only going to use 13A tops or so.

I finally got the M6 nuts. Now it's dinner time, then it's hellfire time. I have to dehydrate the furnace very slowly though, it will probably take 10 hours.....

Edit: I didn't know that solid state relays were triac based. Thanks for pointing it out.

Ediit2: You know when you get a huge blister because of coil winding, and then cut off the skin to expediate the healing process? Don't accidentally get 30% HCl in the wound, it hurts. The nuts are de-zinced though..

Edit3: <b>Coil mounted....</b>


[Edited on 2004-6-15 by axehandle]




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[*] posted on 15-6-2004 at 10:45
Swedish Power !!!!


<b>IT WORKS !!!!</b>

Lid open:


Peephole (quick and lousy shot to avoid barbecuing the camera, the heat from the hole is too bad even for my hand):


Edit1: OK, I've been dehydrating the refractory for about 5 hours, and will continue tomorrow (there's a lot of water to drive out). The innermost layer seems dehydrated though -- it continued to glow red for a while after I turned off the power. This is good news since I'm only using 7A or so-so. Using the full 13A the coil is designed for should make the inside glow yellow!


[Edited on 2004-6-15 by axehandle]




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[*] posted on 16-6-2004 at 00:05


Very nice :D



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[*] posted on 16-6-2004 at 02:08


Thumbs up ! :D
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[*] posted on 16-6-2004 at 03:31


Thank you!

Now I'm going to document the entire process and call the document "Electrical Furnace HOWTO". Well, perhaps not now, but later today....

Dehydration is commenced again, this time I'm going to run it until completion, then I'll test melting some Al in a phosphate cement bowl.

The power regulator+heatsink mount (believe me, that heatsink is <b>not</b> overkill, the regulator would fry without it!):


[Edited on 2004-6-16 by axehandle]




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[*] posted on 16-6-2004 at 05:33


Have you tested it with Al? How does it compare? I mean, the time it takes to melt it.

Once I worked in a factory where they had this "aluminum pot". It was just like yours. It just stood there all day with molten al inside. Must have been well insulated. When you needed some, you lift the lid and picked it with a "spoon"(my english fails, the thing you use to serve soup). They were developing a new design for an eletric motor.
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