My double weekend project - furnce+crucible

[NeoTech]

So i started this a while back, obtaining the cement, bricks, casing..

The casing for the furnace is an old hyrophone, 25l.. Casing is 2mm thick so its quite suitable for this.. I just plasma cut it apart at the seam where its pressed together and saved the rim.
I then welded a piece of tubing into the side of it and slapped cement onto the inside.. So here afterwards i have figured cement is quite corrosive and eats up your skin... good to know.. now.. ;)

I bought fireplace cement its rated for 1100 celsius, so i dumped 5kgs of it in the bottom, lay down two bricks they also rated for 1100-1250C.. Its the hard kind that is a m**f**er to break up.. But after i while i manager to form them.. somewhat.. then i mixed the cement really wet, more like clay then cement so i could form it to the inside with my hands.. And last i put down more bricks on the inside and draped them with cement.. This is now a 40kg piece standing on three legs that got welded onto the casing..

So.. I needed to make a hole in the lid after i cemented it and got the pipe out of it. Just for future reference.. .Cement + Plasmacutter == explosion.. The cement actually starts to boil, form airpockets and "pops" throwing rocks in your face..

And well.. onward, i need a crucible and as my other thread asking about.. well crucibles i went ahead and made one.. The crucible is made of a 100mm pipe, with 10mm wall.. its about 80mm high, not that big of a crucible i guess.. It got turned and a bottom was pressed into the tube with my shop press.. then i cut a small groove and welded the bottom plate into it.. The bottom was cut out of 7mm HRC330 steel, and the pipe is some mystery steel that tends to throw sparks when you turn it.. I turn the bottom plate round by pressing it against aginst chuck and using the tailstock to fix it and then.. shaaallow grooves.. =)


Here is some pictures... Now i need to make a burner... hmm,, will 32mm stainless tubing do? its 2mm wall..

*sorry about the sizes, its linked from my blogg, and i guess you dont want the mini version (150x150)

[andyf]

For small quantities of aluminium, a friend of mine uses a cheap stainless steel sugar bowl as a crucible. It has a slight flare round the top. Seen in use here
http://mikesworkshop.weebly.com/lost-foam-casting.html

Andy

[vtsteam]

Good to see you're forging ahead, so to speak!

If the cement you are using is the same as refractory cement here in the US (really a mortar for laying firebrick in fireplaces) then it is made with sodium silicate (water glass) and absolutely, it will burn your hands if you are using them as a trowel! Very alkaline (in fact made with sodium hydroxide -- lye). Get some rubber gloves to protect those hands for your nice machine work!

Also, cutting torches aren't good to aim at cement or concrete in general.

Probably best to plan all of your torch cutting in advance. But anyway, progress!

Sounds like you are going to go with a burner rather than a simple charcoal melter. I think charcoal is best for learning, and avoids some potential hazards, but I tend to go my own way, too, NeoTech, so I sympathize.

You won't need anything but the smallest of burners for this little furnace to melt aluminum, and maybe propane would be better than oil. That would be easier to control at first, and simpler.

Make sure your lining is thoroughly dried/cured, since it is so thick and applied so wet. then I would use a wood fire or even charcoal briquets to dry it out for 4 to 6 hours before even trying a burner in it. Take it very easy baking your lining or you will have lots of cracks and pops, and maybe splatters of lining out and about. No fun.

If your lining isn't similar to the fireplace mortar/cement I was talking about, but is in fact a true castable refractory, then things will probably go more smoothly -- since it is meant for the purpose and cures rather than dries. In that case follow all mfr's instructions. It's just hard to tell what you mean by cement.

I'm a big fan of the traditional fire clay and sand type linings, and hard firebrick, as you can probably tell.

Anyway, exciting to be on your way! 

[NeoTech]

Yeah, your right is the fireplace stuff.. It has dried for a week.. It will prob. take me a another week or two before i will try to burn anything in this.. My  vaction comes up the 12 of august so i think i will give it a go then.. The furnace sits in my shop next to the dehumidifer that runs 24/7 to keep my shop dried out (its in a stone/concrete basement). But i think i will do as you say and run a bit of birch wood or something in there before i try the burner..

For burner i plan to do a propane burner. I have alot of mig and tig welding supplies i can sacrifice. And propane is maybe not the cheapest fuel in Sweden but its more manageable then lets say motoroil thats my second choice.. And for oil i have 15kW house heating unit.. (the burner part out of a oil stove)... When i get that far i will prob. just run diesel..

Have a long way to go before that.. need to learn the basics.. Crawl before walking, and not start running anytime soon. =)

[vtsteam]

Neo, you could probably even do your first melt with charcoal briquets from the market -- if you have those -- the kind used for grilling outdoors.

Your burner entry isn't ideal for that -- generally it would be just a blower entry (for charcoal), and at the bottom of the furnace. But I wouldn't be surprised if it actually worked well even as high as it is.

Basically you would start a fire with wood kindling, add a layer of charcoal, get that lit (without the blower) , add more layers as they start to burn, then add your crucible and surround it with more charcoal. Once it was all lit, cover with the lid and start the blast. Not too much air because you don't want to blow charcoal embers out of the furnace -- be careful of embers around you starting a fire in leaves -- best to do it in sand -- and have a hose ready.

The charcoal and crucible will gradually drop -- pull it out when needed and add more charcoal. You should have melted aluminum in 20 minutes from first lighting.


EDIT: Also use a wire to poke vent holes in your refractory lining to let steam escape during the initial baking. It will also help your refractory dry more quickly.

[NeoTech]

Hmm think i will try that.. i have couple of bags with fire briquettes.. And 60kg of the stonecoal stuff (coke?). In case of a fire.. But im afraid that can melt the steel crucible even. ;)

But before that.. i need to make a molding bench, get hold of a 3-4 bags of silica sand and bentonite..  There is stuff still missing in the equation of me melting aluminium, but im getting there.

[MetalCaster]

Nice furnace and crucible.
There is a steep learning curve to the casting hobby.

I am always surprised at how many in the online videos handle sodium silicate with their bare hands.  I guess some guys have very tough skin on their hands.

I took a very long time to dry out my furnace using a low propane flame, gradually increasing to a medium propane flame, perhaps 8 or 12 hours.
Very slow process but very necessary to prevent things from exploding.

And also, I have found that in the casting world, the word "wet" is anything that has not been heated by a torch or held in the furnace exhaust stream for a minute or two, such as ingot molds, charging tongs, fresh metal for chanrging the crucible, etc.
I seal my non-steel crucibles in plastic bags when not in use, and heat them slowly at first to drive off any moisture.

The furnace itself will absorb moisture between pours, but that will be driven off when it is fired.

[vtsteam]

Hmm think i will try that.. i have couple of bags with fire briquettes.. And 60kg of the stonecoal stuff (coke?). In case of a fire.. But im afraid that can melt the steel crucible even. ;)

A nice slow charcoal fire to start, with no blast, will do a gentle job of drying out and baking your lining -- you might do this for four hours, renewing charcoal when it drops down, (no crucible). Do this to initially to fire your lining.

Make sure all steaming from the lining has stopped before applying blast. Then give it a gentle blast for say another 20 minutes, then add more charcoal and your crucible, and start a melting blast. You will then have molten aluminum as well as having fired your lining. This would be a nice day long project.

You don't need greensand if you don't want to cast somethng in particular. You can pour the molten aluminum into a muffin tin and make ingots. I bet almost everybody does this at first! Don't use a plastic or teflon coated tin -- use a plain steel one. Slightly rusty is okay -- the rust serves as a release agent -- or you can use talcum powder (the talc kind, not the cornstarch kind) as a release. Just a very light powder coat. Turn it upside down or wipe it out gently with something dry - to leave a very thin coat of release. Make sure there is no moisture in these tins ever. No rain drops! Or perspiration...


ps. No don't use coal or coke, use barbecue charcoal for this.

[NeoTech]

I think its even possible to get hold of a tinpan without plastic or teflon coating these days.  Thats why i thought i would make greensand, so i could cast square blocks and cylinders for machining.. making billets..  =)