First time aluminium casting

[jhovel]

I'm just a little excited.... :)
I managed to melt all my aluminium scrap that I collected for a while and converted it into new raw material for the workshop.
Nothing fancy, just poured it into steel tins. All up about 8 litres.
We were cleaning up the bark and crap from splitting firewood, so I connected the outlet of my vacuum cleaner to a bit of SS pipe and poked it into the bottom of the 44 gal drum we had the fire in. Took about an hour to melt some air con compressors, off cuts of castings and various bits of other cast aluminium stuff. The second picture shows one cleaned up on the lathe.
361801 361802

[YBAF]

Plenty of lathe bar stock there. :cool:

[GuzziJohn]

I managed to melt all my aluminium scrap that I collected for a while and converted it into new raw material for the workshop.
Nothing fancy, just poured it into steel tins. All up about 8 litres.


It's the ultimate in recycling. Turning scrap into stock.

A while back I wanted a 70mm a side aluminium cube. I melted some scrap and rough cast a piece of bar stock about 150mm long.
It looked pretty good until I started facing it off. The porosity inside just got worse the further I went. I ended up turning half the bar back into chips before I achieved a reasonable surface.

John

[jhovel]

Yes, John, that is one of my concerns too....
This was a spur of the moment decision - becasue management told me we were burning off the bark today.... :)
So I wasn't quite ready with proper lifting tools or indeed degassing chemicals.....
On the upside, she helped me get the rather heavy steel crucible out and pour the aluminium.
There was a fair bit of dross on the surface and I ran out of handy tins. The last of it went into an impromptu hole in the ground - for next time.... :)
But the facing and turning I did showed quite a good consistency.
Next time I will be better prepared :)

[GuzziJohn]

Hi Joe. I've cast a few little items and this piece was by far the worst. I blamed my new LPG burner which I think was running way to rich.
Casting into tins is a great idea. No need to worry about moisture content in the molding sand.
John

[bob ward]

I find that pouring lumps of aluminium is tricky, anything over 50mm or 60mm cube or round has shrinkage tearing inside. The outside of the lump looks good and is defect free 10 to 15mm in, after that its fairly dodgy.

Incorporating a core reduces the tearing. e.g. pouring into a 90mm dia dogfood tin with a 20mm core gives me a defect free piece of aluminium.

[bob ward]

Found this photo from about 3 years ago that illustrates shrinkage tearing. The casting is 120mm dia x 60 thick. When I drilled it I hit a hollow so I cut it open to see what was happening.

http://i237.photobucket.com/albums/ff28/sirrobertthegood/IMG_0041_zps086a85ba.jpg (http://s237.photobucket.com/user/sirrobertthegood/media/IMG_0041_zps086a85ba.jpg.html)

[jhovel]

Interesting Bob.
I've machined one of my 'tin fulls' into a new tool part (write-up coming shortly - not quite finished yet). The part involved cutting into it deeply and hollowing much of it out. No tears or voids of any kind.
All of my melted aluminium was from castings. No extrusions or other materials. I wonder if that is part reason of your shrinkage tears?

[bob ward]

You are doing well, much better than I can. I'm definitely a castings only aluminium melter.

Shrinkage tearing as I understand it is caused because the outside cools and hardens and has no 'give' when the molten interior hardens. Depending on the alloy, liquid AL shrinks 10% as it converts to solid.

I don't worry too much about it now, I just figure out how to work around it.

[Old Croc]

Joe, I do a lot of casting exactly as you have, except I use a coke forge. An old guy passed on some of his knowledge to me and told me to pack the tins in a wood box surrounded by sand up to near the top of each can and it holds the heat to slow the cooling. The only other advice is to run the pour through a metal sieve as you never know what is hidden in ally castings. Old water pumps have steel dowels and sometimes steel anti collapse rings. I found this out the hard way.
Rgds,
Crocy.

[Woodrow Phathom]

Hello Joe,
I've done a little recycling, smelting of Al, ('dived dumpster' out back of auto mechanics to source material, etc), and found it necessary to first smelt cast into biscuit molds, to create little 'paddies'. There is seemingly always stuff that will jeopardize 'quality' when melting down scarp.
Smaller billets allow you to trim off 'infections' which often present on the surface of smaller castings.
When casting some kooky gift, like a modified German WW2 'desert corp' insignia with volkswagon logo for my brother in law, 'top bloke', former state president of VW club, I used a single smelted hand full of cleaned 'paddies'. The very few dodgy gaps and casting flaws added to the item.
If wanting a billet for a machinist mate to transform into a specific vintage motor cycle component:
I'd melt scrape and cast 'paddies', re melt a few times, getting all the impurities to the surface and cut them out of the processing. Hope this helps.
Me, happily still stumbling and bumbling through the life lived adventure.
Woody.