[chrispare]

well over the last few days ive built a small furnace and a propane burner.
last night i fired up the burner and turned it down just enough to keep a flame stuck it in the pot to slowly bring up the temp to dry.
when done i stuck in my crubicle with some alumn turned up the burner and 2 hrs later it is still not melted why? obviously its not hot enough but why isnt it?
i built the burner from backyardmetalcasting.com
any ideas

thanks chris

[keebler303]

more heat
less heat LOSS
a thermocouple would tell you quickly what temperature you are reaching. You can buy some thermocouple wire for around $10, measure the voltage with a cheap multimeter and then use the thermocouple response charts to see what temp you are at.

Once you have enough heat...

What type of aluminum are you starting with? If its little bits, the oxide layer on the surface will tend to hold the stuff together and make it look like it's not melted, even though it is inside. If its bigger pieces, you will have trouble getting enough heat transfer from the crucible to the aluminum, as only the corners of the block will be touching. It would be best to have a furnace where the whole atmosphere is at temperature, not just the crucible. That will help greatly with melting.

Matt

[paprjam]

What kind of regulator are you using? You need 5 to 10 pounds pressure. If you are using one from a bar-b-cue, it isn't near enough pressure. If you have a high pressure reg then you might need to check alignment on your gas jet, or the orifice size, or the air into the burner. I guess I'm assuming you built a venturi type burner.
Mine is a 1/8" copper tube stuck into a piece of auto exhaust pipe with a blower attached. The copper tube is attached to an HP reg, at about 10 PSI. The melt starts in about 10 min and ready to pour at 20 or less. Usually the metal is ready before I am and I get it too hot.

[awerby]

I think following Paprjam's advice above and constructing a blower/burner will give you something that will work much better. You want to use a pressure blower, not a squirrel-cage type. Something out of a vacuum cleaner should be fine; equip it with a flap to regulate the air input. Use a pipe about 1.5" or so in diameter attached to the blower and run the gas into it at an angle, somewhat back from where it enters the furnace. Make sure the blower is running before you turn on the gas, and adjust the air/gas mixture to get a low roar; as it warms up, you can gradually increase the airflow.

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

[drmico60]

Have a look at the Mike Porter style of burner. I have a small furnace and use this type of burner and it easily melts a litre of aluminium in 20 minutes. If you are interested full details can be found here:
Foundry - mikesworkshop
Mike

[chrispare]

SUCCESS,
after taking another look at what I was doing I figured it out.

My furnace was too small for the propane burner i built.
The furnace has an internal dia of 3in and the cruibicle i was using was 2 in
if I used a small blowtorch it would work pretty good, but put the big burner in and all the heat and flame just comes out the top.
So i rigger up a square furnace with some fire bricks I had here and presto the propane burner heats her up in about 30min from cold (I can turn it up but then alot of flame comes out the top so I figure there is alot of wast doing that).

So pretty much I guess Im just going to have to build a bigger furnace, But first I am going to try doing some casting (got any ideas for a first lost foam cast).

thanks for any and all help/suggestions from the fourm, I think Im going to be here alot (Ill post some pics of my stuff when I get it all done)

chris

[Vermiculite]

Congrats
For one of your first projects, what about a flask?

If you are planning to do some sand casting later the cope and drag will be usefull. See here. If you still want to use your smaller furnace you could make a smaller burner. I liked "Gas burners for forges, furnaces, & kilns" By Michael Porter.

Be safe

Verm