What happened????
It's hard to explain but I couldn't get the aluminum to melt correctly tonight. I first loaded up a crusible and all the aluminum melted as before with no problems. I skimed off the dross and added additional aluminum to the melt. When I checked back on the melt is appeared that aluminum had "foamed up". That's what it looked like when looking down into the crucible. I scrapped down the sides and tried to stir it all together. I let things heat back up and rechecked the melt again. This time the whole melt was no longer liquid, all foamy looking. The aluminum will not melt to a liquid form again. The aluminum looks just like solder when you get it too hot or try to resolder without using any flux.
Did I get the melt too hot?
Things to mention.
1.) I used a new larger crucible today.
2.) The aluminum was aluminum I broke down/melted in a fire before. I melted the aluminum in the fire to get it into smaller pieces to fit into the crucible.
Can you remelt aluminum over and over or do you need to add flux or some other additive? Sorry here, I'm very new to this.
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Hard to guess what went wrong.....Did you put a large "cold" piece in?
Al can be remelted forever....ishwithout changing.
If you get it hot enough it will oxidise.....I've had it way too hot and always been able to reuse it.....A tip for too hot a pour is to dip a cold ingot in the melt.
Turn up the heat on the puppy as your new crucible may have soaked up the otherwise sufficient heat output....No idea of your setup so only guessing.
Keith
I did put several small "cold" pieces into the melt. Then I really heated things up to try and melt the "foam".
How hot is too hot?
What does the aluminum look like when it oxidizes?
Is it a mistake to stir dross back into the melted aluminum? I thought the dross would just raise back to the top.
I think I might not be getting things as hot as I thought. Just got in from trying to remelt again. Things I found.
1.) I think the curcible is too big for my foundry. Too big around and too tall. I used my smaller curcible I've been using and things did get alot hotter looking. I usually do all my melting outside, but due to rain I melted inside last night and today. Things look alot different....glow much brighter inside. I was able to remelt the "foam" I scouped out before. The bottom part of the larger curcible gets very hot down low where the propane burner is located and gets much colder at the top.
2.) The pipe I used to make the larger curcible is galvanized pipe. I didn't realize it was galvanized on the inside of the pipe also. I think it didn't mix well with the aluminum melt. lol
Things I learned today.
1.) I need to buy a temperature gauge.
2.) I need to buy a real curcible.
3.) I need to build a larger foundry.
4.) I need not be such an idiot.
Hello,
When you are melting the aluminum don't add any large amounts to the melt unless the pot/crucible is almost full, and you will still need to be careful not to add too much. If you add too large of a charge of metal to the melt it will have the effect of freezing up the melt in the pot/crucible, and you may have a hard time getting that much metal to re-melt. The melt will begin to look more like mush than molten metal when it begins to freeze up and you need to increase the heat very quickly to avoid it freezing up. Experiment a little when melting to get a feel for what is the safe amount to add and then don't add more than that at any time. Also be sure to let the melt heat up some between adding charges so the temperature does not go too low. You can actually get a feel for the consistency of the melt by stirring the metal and have a good feel for the heat of the metal by seeing how the metal will either cling to the stirring tool or just leave a thin layer of molten metal on it. It takes some time but try to make observations about your melting process(what works and what doesn't) so that you can use them in future melts.
You can get by with the use of a cast iron pot for melting aluminum(I found some cheap Chinese cooking pots at thrift stores etc. and simply cut the handle section off). There may be some contamination of the metal but it is not visible in the castings and as long as you are just melting parts for your own use this should not be a problem. I have used a cast iron pot for all of the castings for my gingery machines with very good results. I found petrobond molding sand to be an asset to my molding setup also.
I hope something I mentioned here helps you out.
Regards,
Last edited by metalworkz; 05-20-2010 at 10:18 AM. Reason: spelling
Regards,
Wes
Just as an aside (good words Wes) what cost is an A8 size graphite crucible in the US? they can be bought here for £38... $54.50c compared to old steel pipe it's a big difference in cast quality...not much difference from cast iron pots though.
Keith
A8 from Budget Casting Supply is $37.50 US. That's with free shipping.
One other thing you may try with your melt is add some Lite salt to it for flux. I use the 50/50 stuff from Krogers. Put about a Tablespoon in some foil and push it down into the melt and stir. Or you can melt it in a stainless cup and let it cool and it will crack into nice sized cubes, just drop a couple of them in. It works well for dirty Aluminum with paint and oil on it.
I don't think the zinc in the pipe would have had much effect on the Aluminum. There are Zn/Al alloys. It probably just wasn't hot enough.
Be careful with the Zinc fumes.
$37.50 sounds like having no excuse not to have oneOriginally Posted by paprjam
Keith
Paprjam,
I think your right about the zinc. I made another crucible the same size as my orginal that I was having great luck with before. I put a couple of chunks from the foamy/mushy melt I had dug out from the larger crucible disaster. I had the same thing happen and I know I was plenty hot enough. I cleaned out the smaller new crucible and reloaded with new aluminum and melted down a couple batches just fine. I then melted nearly a full melt then dropped one of the foamy/mushy chucks into the melt. It appeared to be nearly all dross. I guess maybe I got the melt/aluminum too hot and oxidizide it?????? Keep in mind here I'm new and don't know what I'm talking about. Wish I knew for sure what had happened.
Have a great day,
Bob
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