[Burningleon]

Hi, I am brand new to metal casting. I've only even being doing metal working of any kind for the last year or so.

I build the "two bucks" furnace and the "upwind" propane burner that are featured on backyardmetalcasting.com to create the set up in the link below.

"2 bucket" crucible furnace

The only differences between my set up and his is that my propane burner has no regulator to control psi, my crucible is made of the refractory material, (measures 4 in outside diameter and 3 in inside diameter) and that the hole I put in the bottom of the bucket is the same size as the top bucket. (approximately the diameter of a soda can)

On my first attempt to metal aluminum my burner was creating a loud roaring sound and I could only open the nozzle on the propane tank so far or it would blow itself out. One of the times it blew itself out something happened and it would only release a small amount of propane. I fixed this by completely drilling out the previous mechanism in the tubing. (It was one of those push pin pieces where it has to be pressed in to release the gas similar to a tire valve)

On my second attempt the burner was not roaring by any means. I was a calm steady flame. I could have the nozzle to the propane tank fully open with out much difference. After 40 minutes of this all I achieved was an orange refractory, crucible, and aluminum. No where near the pink to purple color shown in the images on backyard metal casting. At best the aluminum was malleable.

On my third attempt I decided to try melting aluminum with charcoal so I put what charcoal I could fit into my refractory along with my crucible. It wasn't a whole lot but I had flame coming out the top which I did not really achieve with the propane burner. After several minutes the crucible and refractory were not even orange. So I tried hooking up my propane burner while it had the charcoal burning and putting a fan underneath it to blow air into the charcoal. This still failed to achieve the desired melt. Or even make the aluminum malleable. Admittedly I did not have a direct air source such as a hair dryer or a leaf blower and I did not use the propane burner for very long before I gave up on it.

I am trying to cast a 2 gear racks and a gear wheel for a project of mine among other less complicated things. I made the molding sand by mixing silica sand with fire clay. I am having the issue of the sand getting stuck in the teeth of my gear and coming up in the teeth after I try to ram it. I'm also kinda worried that when I pour the aluminum it will knock down the sand and ruin the gear pieces.

Also I suppose it should be noted that my major sources of aluminum is crushed soda cans. I don't really have any good solid pieces to use.

Thank you for all of your help. I appreciate any ideas or advice you can give me. Just let me know if there is anything else you need to know.

[TOTALLYRC]

Your big problem would seem to be the crucible being made from refractory which is an INSULATOR!!!!!!!

Refractory is used to keep the heat inside the furnace and will keep the heat out of the inside of the crucible that you made because the heat is applied from the outside.

Mike

[Burningleon]

I know it's supposed to be an insulator. I'd read on one of the other forums that a guy made his crucibles out of refractory so I just figured It'd be an easy solution since i was sure to have left over refractory after I made my Furnace.

Any ideas where I can get/make a cheap crucible?

[DMF_TomB]

1) for foundry supplies in small quantities
BCS - Budget Casting Supply
.
2) I would absolutely positively have a pressure regulator on propane. in my experience a orifice of 0.035 to 0.040" will work best at 2 - 30 psi and use about 1 - 4 lbs per hour.
.
3) new furnace always takes longer as water vapor evaporates.
.
4) castable refractory comes in many types. an insulating refractory is softer and lighter and usually can take only lower temperatures but if you get one rated for 2300F or 2600F it will insulate better and need less fuel than the heavy denser castable refractories.
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5) i suggest read a book on sand casting. making gears is not normally done with sand casting unless they are large and for slow speeds

[Burningleon]

1) what kind of crucible would you recommend?

2) It is a #57 hole. I'll need to contact a propane specialty place to see if I can get a cheaper regulator. I just bought the only tubing they had at Lowe's without thinking about it needing a regulator. Wasted 20 dollars plus the adapters cost I suppose.

3) I've had this furnace made for a while now. Over a month. I just got around to firing it up for the first time maybe two weeks ago. I wouldn't think there would be any water left to evaporate. I don't see any steam coming off of it.

4) So what does that mean for the refractory that I am using.

5) The gears are for very slow speed. Just part of a prop. The aren't tiny but there aren't huge either. The gear wheel is about 1 inch diameter from tooth to tooth. If i remember right I think the teeth were 1/4 to 3/16 of an inch tall.

[Burningleon]

Here are some pictures of my set up.

ImageShack(TM) slideshow

[jimmy111]

Your big problem would seem to be the crucible being made from refractory which is an INSULATOR!!!!!!!

Refractory is used to keep the heat inside the furnace and will keep the heat out of the inside of the crucible that you made because the heat is applied from the outside.

Mike

No.
It should work just fine. But you need to calcine both the furnace and crucible first. This can take quite some time depending on the mass of refractory you have and the burner size.

If you are using propane a regulator is not absolutly necessary but is very helpful for control. Keeps you from freezing your tank too.

You will have to play around with your fuel/air mixture. You need to have enough propane so that there is a small amount of orange flame coming out the vent in the top of the furnace. If it is blue you have too much air and an oxidizing condition inside the furnace. Just a small amount of orange is a slightly reducing condition. You may not see the orange. You may need to ignite the flame with another propane torch. It is Carbon Monoxide too so be careful.
This is important especially when you are sintering the lining. It will take you a lot of propane to sinter. You should have at least 3 bottles around and drive it up to a red heat. The first time takes a long time because of the sintering but after that it will take much less heat.

The refractory crucible is fine too. A piece of steel water pipe works good too.

[Burningleon]

Alright. So I don't need to buy/make a new crucible?

Can you please explain "calcine" and "sinter"?

[jimmy111]

Any refractory is a type of ceramic. What you are doing is making ceramic pots.

Calcining is heating the material untill whatever organics are in it burn off. Mainly the water in the clay. But there can be other things such as glutrin, wood products, sugar, fluxes and the like,

Sintering is melting the particles together.

The clay will melt first depending on what type of clay it is it will melt at a different temperature. It is the binder. This is what you want to happen. Sometimes the sand will melt too. When the sand melts you get glass and it will fracture as it heats and cools down. You dont want this to happen. Depending on the binder mixture the clay will form dendrites that will help to lock the refractory together. These will continue to form each time you use your furnace and require more heat but will lessen as time goes by.

[Burningleon]

Alright. So should I just keep using the refractory till sinters and everything naturally to do I need to specifically heat with the goal of sintering it?

[jimmy111]

You have to cook it first. It might take all day to get it to a red heat. After a few heats it will probably take about 40 minutes or so to get it hot.

[Burningleon]

Alright. So whats your advice on getting it red hot? I don't really wanna burn through a whole tank of propane. Would that be cheaper than keeping a charcoal fire lit for hours on end?

[jimmy111]

You will probably need more like 3 tanks the first time.
You can use charcoal if you want. You will just need to rig up some sort of way to blow air in thru the tuyere with a shop vac or air compressor. Any small blower will work for that one.

[Burningleon]

Alright. Got it. The Lowe's here is having a sale on Charcoal. So I'll go pick some up.

BTW, I got my new regulator. It took hours to find a store that would have them. The guy didn't like the tubing I already had so he just built me a brand new one. The regulator he put on there isn't adjustable but he said it was made for 20 psi. I don't really have any way of knowing if he's right since it doesn't say 20 psi on it but I can probably punch in the serial code or something and find out. He seemed a little confused and said he wasn't sure the tubing was going to work which is kinda worrisome but because he wasn't sure about it he gave it to me for free which is a nice plus. I just wish I still had the bags to the reducers I got from Lowe's so that I could return them and get some money back.

[Burningleon]

Alright. Gonna hopefully be free to sinter it on Friday. Can you give me a quick step by step as for what I should be looking for. You said red hot but how long do I leave it red hot? Stuff like that. Do I let it cool of naturally or should I try to cool it down quicker. Figure water is probably a bad idea. Will the ash from the charcoal cause me any problems? Should I sinter the crucible too?

[jimmy111]

No water. Dont even think of it.

Put a couple of inches of charcoal on the bottom. turn on the air.
Light it and get it red hot.
Add a couple of more inches and let it get hot.
fill it up with charcoal and put the top on.
The charcoal will drop and as it drops add more until the liner (refractory) glows red hot. You will know when this happens. It might take all day.
When it gets red hot, put a cover over the vent hole and let it cool down overnight.

[Burningleon]

Lol, I didn't think water was a good idea

Alright. Thank you. I'll let u know how it goes.

[Burningleon]

By the way my refractory is 1.5 parts Portland cement, 1.5 parts perlite, 2 parts sand, and 2 parts fire clay. I don't know if that means anything special to you about sintering it or not.

[Burningleon]

Alright. So I think I sintered it. I don't really know what I'm looking for. I just tried to follow the instructions.

I basically had the whole thing full of charcoal. Took me about 3.5 hours and 20 lbs of charcoal to get it to where it was red hot. I never actually saw the bottom bucket red hot. Originally I had the refractory half full of charcoal and burning. I saw the bottom bucket get orange. Then I put my crucible in there upside down (hoping some of the slag left over in it would come out) so that it could sinter too. I then put on the top bucket and filled it completely with charcoal till I could see the very top of it had turned red. Here's hoping a did it correctly.

Here are some pictures. ImageShack(TM) slideshow

I think the Galvanized steel of my buckets may be oxidizing in the first picture. The 4th one is looking into the pipe I had the air blowing into. As you can see I don't see any kind of glow. It's got to be solid ash. The last picture is looking up into the drainage hole. Also no glow.

[Burningleon]

Alright. I've let it cool. There are a few spots that look good. White or light brown like fired clay would be. But then there are some black spots that have me worried. Here's a link to the pictures.
ImageShack(TM) slideshow

What do you think? I was worried 3.5 hours wasn't long enough since you said it could take all day but it looks like I may have accidentally formed a little glass. Or maybe that's just perlite or something. I don't really know what I'm doing. Please advice.

Btw. My crucible cracked during the sintering process so I'm gonna need to make a new one. Should I pour myself another refractory one and if so should I alter my recipe. Maybe no perlite for less insulation? Or should I just go and by myself some steel pipe? I really want to avoid actually buying anything as I've put so much money into this without a single successful cast yet.