First Fire

[Bovine]

My first blow with @6lbs of charcol could only maintain 1200*F for a couple of minutes. I don't see a way to melt aluminum with that temp using about a two pound crucible.

 

[terrywerm]

Correct me if I am wrong here, but are you using a shop vac for your air supply, then only pointing it at your furnace so that you don't get too much air in there?

 

[jixxerbill]

If its heat you want, you already have the hole in the side just build one of these and your set...
http://metalcast.boorman.us/reil_1.html

Here is mine..

 

[Bovine]

Terrywerm,
My shopvac is my only air source I could muster. Another reason for only pointing the shop vac is because of the plastic tube.
I did place my crucible in the furnace and packed charcoal around it an was able to manage 1200 degrees.
I will keep you posted on how it turns out.

 

[Bovine]

Jixxerbill,
I have seen the burners for propane but for now I think I will stay with this basic method.

 

[metalmad]

Hi Bovine
I feel your doing yourself a disservice by discounting gas so readily,
I often do aluminum and occasionally brass with my gas burner, When I started I was using about 20 PSI but now run the furnace at about 2 and a half PSI and have long since given up counting how many pours per refill, its that many, as I don't use a air blower all I need do is crack open the valve and light the furnace.
It Is far cheaper than running the Barby as only one burner is used at 2.5 PSI ;D
Pete

 

[jasonh]

I use a hair dryer for air and charcoal for fuel. I have no problem bringing a 6lbs of Al to pouring temperature. My suggestion- Make some sort of adapter and get the air piped to the bottom of the fire.

 

[geoff p]

Beans tins! They make great, zero-cost adapters - I have the 6V fan from a hair-drier wedged into one tube, which in turn sort-of-slides into a bins tin, which is cut and splayed and self-tapping-screwed to the furnace.

I pack the furnace 1/2 full of charcoal before lighting and keep packing small charcoal around the pot as it melts. My furnace doesn't have a lid - it's really a cooking-pot stove - so I know there is plenty of room for improvement, but it works for me.

 

[Banjoe]

Good idea for the air blower, but you may be cooling off out outside of the crucible with the excess air flowing around the unit.

The jixxerbill approach will give you a concentrated air and fuel supply to put you over the top when it comes to temperature control.

 

[jixxerbill]

As metalmad has stated I also run mine at 2 to 3 psi of propane and can bring my AL to 100 deg above melt in about 10 to 15 minutes. But I have to confess I get my propane at an extremly good price (my brother-in-law is manager for propane company) Good luck whichever way you decide to go..Bill

 

[terrywerm]

Bovine,

I think I would try making an adapter with a bypass valve in it if you plan to stick with charcoal. This way you could plumb the shop vac to the adapter, which would fit into the tuyere of your furnace. The bypass valve would open to atmosphere and would give you the ability to dump excess air. You might have to put a damper in the part of the adapter that fits into the tuyere also, then find a happy balance for the two valves. I'm just thinking that a shop vac might be too much air, I know mine would be way too much. The motor part of my shop vac comes off and can be used as a leaf blower, and that son of a gun could blow the charcoal right out of the furnace if it was used full bore.

To make a long story short, I think you've got a shortage of air in your furnace. Not much of a shortage, but a shortage none the less. Once you plumb it straight in you will have too much though.

 

[100model]

Bovine When I started melting aluminium I used coke but I had no lid also the vac pipe was connected to the furnace. There were no problems melting aluminium.

 

[solarenergyadventures]

Hi Bovine,
Looking at your rig, I can see one problem. Your exhaust vent holes are probably too small. Don't forget that when you heat up air to 2500 F or so, it expands quite a bit, so you must allow enough vent area to get this "bigger" air out of the furnace or you will choke down the airflow and get low temps. According to CW Ammens Book "The Metal Casters Bible", you need about 1 square inch of vent area per 20000 to 25000 btu liberated from your fuel per hour. I find that on a furnace made from a 5 gallon bucket that a 3" to 4 " diameter exhaust port works well. This gives about 7 square inches of area for the 3" hole or 12 square inches for the 4" hole, and allows you to fire from 140000 to 240000 btu per hour. For your air requirement you divide your btu per hour by 100. Therefore at 140000btu/100=1400 cubic ft of air per HOUR or, more conveniently, 1400/60=23 cubic ft per minute. Notice that this is not really a lot of air. I used to run my 5 gallon bucket charcoal furnace with a little 60 cfm squirrel cage fan with the inlet almost completly covered with a piece of cardboard to control the airflow. The squirrel cage fan was great because it was way quieter than a hair dryer or shop vac.

Some other improvements that I found really helped:
1. put a grate in the bottom of the furnace that holds the fuel stack above your air inlet. This alows the air to penetrate the fuel stack evenly and reduces back pressure because the inlet port (tuyere) is not partially blocked with the charcoal. This trick also makes the fuel burn more evenly. I used expanded metal propped up on little pieces of fire brick, and I was surprised at how long it lasted.
2. Don't pack in more than about 4 to 5 inches of fuel. A thicker fuel bed than that is almost impossible to blow enough air through to give complete combustion. I found I got faster melts by putting the crucible on a 4 inch fuel bed, and NOT packing fuel around the crucible. This gave some combustion volume for the CO from the fuel bed to burn completly to CO2 around the crucible.
3. If using charcoal brickets, break each one into smaller pieces. This gives much more burning surface area which creates hotter temperatures. I liked splitting each one into quarters with a masonry chisel.
4. There really is such a thing as too much air.
When your furnace is dialed in, you will have no problem melting aluminum, brass or bronze. Just messing around one time I was able to melt glass with mine!

I hope this helps!
Cheers, Chris