Hard disks as a source of aluminium for casting?

I've got a few projects that could usefully start from aluminium castings. I also currently have 120 ex-server hard disks. When stripped of all the steel, copper, magnets and electronics the hard disks yield 12oz-1lb of powder coated or cobalt sputtered aluminium. Probably in three different alloys (case, platters and HP/Compaq mounting brackets)
The question is, does the team think that these will be a good source of casting stock once they've been melted down, de-drossed and cast into ingots?
If they are a good source of stock I can get more disks, since it's in my employer's interests to use me to dispose of all the server hard disks so that we don't have to waste man-hours wiping them or destroying them when we scrap servers.
Of course, anyone in their right mind would realize that it would be far more efficient to buy a scrap auto engine or a pallet of ingots. But these disks are free.
I am starting to run out of places to stick high-powered fridge magnets though...
Any thoughts or experience out there?
Mark Rand RTFM

Mark Rand wrote:
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I suspect that they might be made from "white metal" rather than AL. Can't prove it, but trying to TIG weld a couple WD castings together with AL filler gave pretty sloppy results even with meticulous prep.

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Mark,
The alloy will probably have been spec'ed originally for pressure die casting rather than sand casting. I did a similar exercise with the chassis from mainframe printers a few years back - lot of chunky ingots piled up ready for use. Problem was that when I came to use them they were a pain - couldn't get the metal to flow uniformly, and when I ended up with a sound casting it was vile to machine (I was making a replacement front bearing / mounting plate for a Bridgeport pancake motor and was cnc machining it) - still using the motor but that component is not a pretty example of machining !
A good source of decent alloy is pistons - track down an engine rebuilder and be nice to him <G>
AWEM

On Fri, 19 Jun 2009 23:51:33 +0100, "Andrew Mawson"
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The bastiches scrapped out all of the spares from the 12 cylinder diesel engine at work without telling me a few months back. Included were a couple of pistons. The engine is 17 1/4" bore by 21" stroke, so you can imagine the usefulness of the pistons :-(
I have the feeling that some silicon rich master alloy might help when I try this out.
Mark Rand RTFM

Andrew Mawson wrote:
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Even an alloy intended for sand casting can be horrid to machine when used in the as cast condition due to it being soft and gummy. A company a mate used to work for always had their aluminium sand castings heat treated for machinability reasons.
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Solution treatment is the term to Google for - see the third paragraph down this page:
http://www.azom.com/Details.asp?ArticleID%40
AWEM

On Sat, 20 Jun 2009 14:21:27 +0100, "Andrew Mawson"
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We seem to have varying views on the machinability of the alloys involved. One datum is that they obviously machine beautifully the first time around, so I'm hopeful that it'll be better than extruded rubbish.
I'd already boned up on Solution heat treatment and precipitation hardening.
It's be nice it I could convince the lads in the metallurgy lab at work to do a full assay of the composition of a sample ingot. Trouble is, most of their work got sent to China, so they've lost the will to live...
It would be possible to slice an ingot into coupons and then try solution heat treating different coupons at different temperatures until the correct temperature was discovered. If the batch of metal were consistent enough, that would only need to be done once every 50-100lb of metal, which wouldn't be too bad. That's probably what I'll try. Of course that means building a decent, controllable, heat treating oven. Still, that'll come in useful for and aluminium casting work, whatever the source of metal.
It takes 10-15 minutes to strip down a drive whilst watching the television news. The concentration helps to stop me shouting at the news presenters when they get stupid ;-)
Mark Rand RTFM

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Mark,
I have an alloy analyser - draws a carbon arc off the sample, scans it, and reports on composition and prints it out. As the foundry building isn't quite finished yet (but it does have walls, roof and doors!) the analyser is still packed up from the move, but when it comes out blinking to the daylight post me a sample and I'll run it for you.
Andrew

Andrew Mawson wrote:
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There are several hobby casting groups on yahoo , I belong to the "castinghobby" one . Those HDD cases are probably a ZA alloy , zinc and aluminum , mostly zinc IIRC . Andrew is right about pistons , but also consider extrusions (usually 6061) , wheels and cylinder heads are usually A356 , and anything cast of aluminum is a candidate for the foundry .

Google around to find specs for various aluminum alloys meant for casting. You will see a WIDE range of characteristics. If you intend to put your home made castings to any kind of functional use at all, I'd advise against "mystery metal". You didn't even say whether the parts you are scavenging ARE castings or not. Makes a HUGE difference!!!
Take the stuff you have to a scrap dealer and get what you can. Then go buy pistons, if you want control. I know a guy who had been demonstrating lost foam casting of aluminum for years. He uses pop cans. But I don't think I'd cast B52 landing gear from them.
Learned about tensile strength of various aluminum casting alloys the hard way, Pete Stanaitis -----------------
Mark Rand wrote:
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Mark Rand wrote:
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The cases make great casting aluminum that also machines very well.
The platters may be more exotic stuff, but did you know most of the dull silvery-colored ones are plated with pure platinum? There are some web sites that have simple systems for peeling the platinum off.
Jon

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I suggest you melt like component parts separately and ingot them before using. Label the ingots with the source of the feed stock so you know what made nice stuff and more importantly what is crap that needs blending to be more usefull. Gummy machining material (usually wrought alloys) can be helped a bit with a few percent of copper. Add some small cross section copper like 14ga. wire pieces after the aluminum is fully melted. Pig off as ingots, test machine and then remelt for your project.

Mark Rand wrote:
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Try dropping one of those magnets through a length of copper water pipe.
Watch how the induced current in the copper creates an opposing magnetic field slowing down the magnet's decent. Works best with a cylindrical magnet a little smaller than the inside diameter of the pipe, it'll just ooze down through the pipe.
Jeff

On Tue, 23 Jun 2009 15:39:49 -0400, jeff_wisnia
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I use the added weight to direct the reflector on the industrial, chain mounted 4' fluorescent unit over my SB"A"
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I have a 1/4" dia.x 1" magnet inside a length of 3/8" copper tube clinging to the front of the file cabinet ready for the next "uninitiated person". Gerry :-)} London, Canada

On Tue, 23 Jun 2009 15:39:49 -0400, jeff_wisnia
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The enclosures are probably worth messing with and are probably a ZAMAC die-cast alloy of some sort. It has to be really stable stuff, a hard drive warping as it ages would not be a good thing...
But you would want to know what the alloy is before putting any effort into it - might want to beg or borrow one of the scrapyard spectrometer guns mentioned elsewhere in this thread IIRC.
And every time you melt it, the composition and properties of the metal changes as some of the admixture elements boil out of the pot.
It might work okay if you melt and flux the hard drive cases and pour directly into the flask for the project - but adding another melt by turning it into ingots as an intermediary step is just gonna throw the metal that much more out of whack. Likely to be the difference between success and disaster.
Besides, you have to know what's in the metal if you want to sell the end product in a country where the RoHS Weenies have taken over.
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Isn't that supposed to be 1.8*10E12 ? 10 to the 12th power? I am by no means a calculus wonk, but I seem to recall it that way...
--<< Bruce >>--

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FWIW, Zamac is hardly stable. It's strong -- much stronger than most people would imagine -- and it's reasonably stiff, but it has a strong tendency to creep at even fairly low temperatures, like most zinc alloys.
Through a combination of structural design and section thicknesses, they may have completely overcome the problem in the application you're talking about. But Zamac, for the record, is much more prone to creep than aluminum is, for example.
-- Ed Huntress

Bruce L. Bergman wrote:
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Yes it is....My sig has a caret (like a small inverted vee.) in between the 10 and the 12, but I bet some fonts don't reproduce that symbol.
So, I'll be changing it to an "E".
Thanks,
Jeff