First melt!

May 20th, 2012

Today it finally isn’t raining so I got outside and fired up the furnace. Originally I was just planning on cooking the crucibles but things went so well I couldn’t wait and went ahead and melted some aluminium!

I set everything up outside on top of some dry bricks from under the house. On opening my bag of BBQ fuel I was surprised to find it wasn’t charcoal! I am not sure what it is but I decided if it burns and gets hot I might as well try it.

IMG_2155_1 Set up outside.

This morning I went to Bunnings, almost out of habit than any other reason, so I picked up a metal cold drinks bucket. This I filled with dry sand. Luckily I had a bucket full of sand I previously dried for use with my hand held sand blaster. I packed the BBQ fuel around the crucible. Then how to light it? I tried using a small gas torch but it didn’t really work so in the end I cut up some kindling and used that on top of the BBQ fuel.

IMG_2157_1 IMG_2158_1 Starting the fire.

I moved the blower away to start with then when the flames were established I attached it fully to get a good, roaring fire.I then put the lid on once the wood had burned down enough. Soon things were glowing nicely. I think it took about 20 minutes once the lid went on. I did one silly thing. Since the lid hadn’t been on yet I knew it wasn’t hot so I didn’t wear my gloves. When the lid went on some flame shot out of the hole so a few singed hairs on the back of my hand!

IMG_2164_1 IMG_2167_1 Hot!

The crucible was glowing orange and had a nice layer of scale on it so I took it out using my lifting cradle. That worked extremely well. I am glad of the big loops on the ends when wearing the thick gloves.

IMG_2169_1 Hot crucible.

I put that crucible aside to cool and heated up the second one. That took almost no time once the lid went back on. It was so quick in fact I decided why not see if I can melt something. I took that crucible out and put back in the cold (well still pretty bloody hot) one. I am not sure if you are supposed to heat the crucible and then let it cool before using it or if it just has to be heated to red before adding aluminium for the first time. The heat builds up a layer of scale on the metal helping to protect it from the molten aluminium. Apparently it will erode iron out of the steel and eventually weaken it.

IMG_2170_1 Oxide layer on crucible.

As well as scale there was some fused ash from the BBQ fuel. Next time I will use real charcoal.

I put some of the can my parents have picked up for me on their walks on top of the lid to dry them out. You want no liquid in the cans when you plunge them into the pool of molten aluminium in the crucible to avoid steam explosions. Cans are so thin you can’t melt them directly, they’ll burn. Instead you can dip them into a pool of already molten metal.

IMG_2171_1 Cans drying.

To make a pool I shoved in some short lengths of aluminium extrusion ripped off the original body that my Austin 7 came with. They just poked though the hole and melted down. I also added some offcuts of aluminium sheet I have folded into lumps. That all melted down well. I also tried adding some balled up tin foil I have been collecting as well as aluminium from the necks of champagne bottle. The tin foil wouldn’t go down the hole and instead sat there bobbing about in the updraught like some kind of red hot Bernoulli blower! With the lid off I was able to add the foil and the cans. The crucible was about 3/4 full I guess.  There was a lot of dross I scraped off with my spoon. I then lifted out the crucible with the cradle and using the hook tipped the aluminium into my baking pan. That I had put on top of the sand in the drinks container in case I spilled any molten metal where it shouldn’t go. I was able to pour 5 ingots. The cradle and lifting hook worked really well.

IMG_2172_1 Poured metal!

There was a little smoke from the pan but I stayed away from that.

There was a pile of dross and some left over aluminium in the crucible. I sat all that on top of a metal sheet (the lid of my old washing machine actually).

IMG_2174_1 Lots of dross.

I let everything cool a bit and then emptied the still hot left over fuel from the furnace. Some of it had vitrified onto the sides of the flower pot. The pot has cracked but is holding together. The steel sheet on the bottom of the lid has warped. I used aluminium pop rivets to hold it to the metal sides and of course the aluminium melted! It’s still held in place and seems to work.

IMG_2177_1 IMG_2178_1 Vitrified fuel in the furnace.

I was able to chip away most of the crap when things had cooled. The grating survived really well. In face the inside of it still has paint. The air rushing in must cool it very well. The furnace lid has some fine cracks but is all holding together. It should all be find for more firings using proper charcoal.

The ingots simply fell from the pan when tipped up.

IMG_2179_1 5 ingots and a blob!

When they had cooled (which takes a surprisingly long time) I weighed them and found each is just under 200 grams. In total I made just under 1kg work of metal. I may saw one in half to see how the metal looks inside. With a full crucible I guess I can pour about 1.2kg of aluminium.

IMG_2182_1 Ingots.

Now I have got that far everyone keeps asking well, now what do you do with them. Next I need to get some green sand and make some flasks and try casting something. I might first try some lost foam casting. Everything went really well. I do need to use proper charcoal next time and I also need to get a full face shield. I was using my welders helmet which works fine but I found the view a little restrictive.

Posted in Home Foundry | | Top Of Page

Comments are closed.