Home made cast Aluminium

[norman valentineParticipant @normanvalentine78682]

ChrisB, trying to melt a whole cylinder head would take a long time. It is best to reduce it down to small pieces. An angle grinder is slow and will not cut big pieces. I have tried cutting large parts, wheels, with an angle grinder and used a large hammer on partly cut pieces. It is hard work.

Due to changing domestic circumstances I have had to use different approaches. When I first started casting I used to build a large wood bonfire and stack the wheels on top, as it reached melting temperature the aluminium would run out of the bottom of the fire and if you got to it before it cooled too much you could break it into small pieces with a hammer. This produced dirty material which I had to remelt in my furnace to cast clean ingots. This cost me nothing as I was using peat as fuel which I had obtained free.

When I had to start paying for fuel I used a different approach, I collected as much scrap wood as I could and built a fire in an oil drum that had a hole in the bottom and was perched on bricks. As the aluminium melted I placed a loaf tin under the hole  to catch the molten metal and produced 3 kilo ingots. Too big but they were clean,

Nowadays I live in a home closely surrounded by neighbours, I collect small pieces of aluminium that will fit into my crucible. I find it very restrictive.

As for casting blocks for machining I use bean cans, old tobacco tins or anything that is near to the size that I need. I do open topped castings, I am not looking for precision. Yes, it takes longer to machine it to size but hobby time is free.

Edited By norman valentine on 25/08/2020 19:19:02

[Nick WheelerParticipant @nickwheeler]

Posted by norman valentine on 25/08/2020 19:17:17:

As for casting blocks for machining I use bean cans, old tobacco tins or anything that is near to the size that I need. I do open topped castings, I am not looking for precision. Yes, it takes longer to machine it to size but hobby time is free.

That's only really true if your hobby is making swarf. If you actually want parts, whatever they might be for, producing them is just a time consuming step.

The rest of the band didn't care how I made the lower bolt

to reattach this

into the bell. I would much rather the job had taken less than the 2.5 hours it did.

[norman valentineParticipant @normanvalentine78682]

Nicholas, what you are talking about is very different from what I was saying, If I want parts for a particular job of course I will make patterns that will produce a part that needs minimal machining. If I need a part such as the raising block for my toolpost on my lathe, I will cast it in a tobacco tin and save myself quite a lot of money. No my hobby is not producing swarf and your sarcasm is not appreciated.

[ChrisBParticipant @chrisb35596]

Hi Norman, no wouldn't attempt to melt a whole head (would need one hell of a furnace!) I'd bandsaw pieces off and melt say a kilo, should be managable. Would like to know if an electric oven (not a household one) would be up to the job, in theory it should as it can reach the alu melting temp and beyond. My idea would be to melt the alloy in a steel form and leave it to cool slowly in the oven…might be a couple of years from now to see the result given the slow pace of my projects!

[JasonBModerator @jasonb]

There is a guy on Traction talk who has also written in ME who uses a couple of electric ovens for aluminium and bronze casting so should be upto the job. Although it mostly shows the patterns this album of some of his work does show a couple of the castings too

Edited By JasonB on 26/08/2020 07:31:37

[JasonBModerator @jasonb]

Last two posts about CoC moved to here to keep this one about casting.

[I.M. OUTAHEREParticipant @i-m-outahere]

After a few conversations with Rob i found out the pearlite is just the stuff you put in pot plants and is mixed into a sand cement mix to line the furnace . I reckon if you scavenged around for an old lpg bottle you could make a furnace for $20-30 bucks at most. You would get a decent amount of aluminium from just one car rim and if you can scavenge one for free well you're in the box seat then !

[ChrisBParticipant @chrisb35596]

Hi, yes I heard about perlite – I was going that route initially, perlite mixed with liquid glass (sodium silicate) but gave up on the gas type furnace, mainly fearing a mishap with gas in my workshop which happens to be the basement of my house!

I then changed my mind to build an electric oven, I have all I need but it's still in the bottom of the to do list. For insulation I got aeriated concrete blocks, which should work well and are relatively cheap compared to insulation blocks. In theory temps of 1100'C could be attained, and as Jason mentioned there's a chap who's been doing this in an electric oven, there's hope it could work. Not that I'm trying it out any time soon.

[not done it yetParticipant @notdoneityet]

Portland cement may not be the most long-lived material for a furnace. Cement gives up the ghost at temperatures well below 1000 Celsius. Concrete analysis often relies on heating at 900 degrees to break down the item under analysis.

[John RutzenParticipant @johnrutzen76569]

Home made furnace linings are not a good idea, they break down very quickly. it's much better to use ceramic fibre blanket which is available from pottery suppliers or Artisan Foundry. You can get a coating which you apply to the surface. This is a whole lot better insulator.

[ChrisBParticipant @chrisb35596]

Agreed, portland cement will not be up to the job as you say, what I intend to use tho is slightly different. It's not homemade material, I bought these bricks from a construction material supplier. Apparently it's good for 1200'C, the brand which makes them is Ytong. For added surface heat resistance I'm coating the internal surfaces with a mix of aluminium oxide and liquid glass. That's the plan at least. I tested a small piece of brick in a direct flame till it glowed yellow, the material did not degrade but I noted some shrinkage.

[JasonBModerator @jasonb]

Those Ytong blocks are really no different to Thermalite/Celcon type aerated blocks and won't give much in the way of insulation in a furnace, all so as they are made by a reaction between the gypsum in portland cement and aluminium powder which causes the bubbles you are back to the issues mentioned above about ordinary cement.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by ChrisB on 26/08/2020 18:13:22:

[…]

I bought these bricks from a construction material supplier. Apparently it's good for 1200'C, the brand which makes them is Ytong. […]

.

I had never heard of YTONG, Chris … but that was clearly my loss

Impressive range of products: **LINK**

http://www.ytong.gr/index.php?option=com_content&view=article&id=47&Itemid=27&lang=en

MichaelG.

.

Edit: Contradicted by Jason before I had even posted 

… the man must be psychic !!

Edited By Michael Gilligan on 26/08/2020 18:30:31

[ChrisBParticipant @chrisb35596]

Researching these bricks before I bought them I'm sure I had seen somewhere videos of it being tested, one side heat being applied with an oxyacetylene torch and the a hand on the other side of the brick. And there was another gentleman who used it in a furnace with temperature of up to 1300'C. I hope they are right!!

I'm not saying it's better than insulation brick, but it could be a cheaper alternative, especially for me as the only way of getting insulating brick is to import it, and believe me, it's expensive!

[Andy_GParticipant @andy_g]

Posted by not done it yet on 26/08/2020 16:10:01:

Portland cement may not be the most long-lived material for a furnace. Cement gives up the ghost at temperatures well below 1000 Celsius.

High alumina cement is better at high temperatures. Last time I needed any it was available at my local builders' merchant at about double the cost of Portland cement. Mixes well with Perlite…

[I.M. OUTAHEREParticipant @i-m-outahere]

I think the unit Rob made had a steel liner which eventually burnt away and yes the pearlite cement mix is degrading but he only uses it every so often – probably when he runs out of aluminium bar so he fires it up to build up his stock . If i were going to do a lot of casting i would use the proper stuff but i’m really only likely to use this system once or twice a year at most and i do like the idea that i can make a simple furnace out of junk and cheap materials that i can get from my local hardware store !

[not done it yetParticipant @notdoneityet]

Biggest 'don't' is don't spill the hot metal – it spits like hell on earth or cement – work on a sandbed is best.

Biggest thing is safety.

I would not be casting metal inside my home – do it outside. Not only a danger of fire, but fumes and escape limitations.

Wear appropriate safety clothing – (thick) leather apron, heavy duty foundry boots (no openings at the toe end).

Keep water away from the area where metal is molten – it can cause an explosion if the two come together, as water takes up a huge volume when vapourised suddenly to those temperatures. Especially so, if molten metal is dropped into water. I believe (several?) were killed in a Welsh foundry accident when molten metal spilled onto a wet area, some years ago while the crucible was being transported from the furnace to the pouring area.

A lad at work was hospitalised while melting white metal (only 400 degrees?) from a large bearing when the liquid metal hit water.

We used to pour molten metal from a large crucible into water to granulate it – perhaps as much as 50kg at a time. The melted metal was often around 1800 degrees Celsius. A dangerous operation at the time as the crucible tipping device was operated by hand – with no brake – and not controlled remotely! The metal was poured (slowly) into rapidly swirling water from about a metre and a half and the tank was about 1000-1500l, as I recall.

Induction furnaces were used and temperatures of molten metal often exceeded 2000 degrees Celsius by a significant amount.

Edited By not done it yet on 27/08/2020 08:21:15

[ChrisBParticipant @chrisb35596]

Would 7075 and 2024 series scrap aluminium be good candidates for melting? I have access to good amounts of scrap pieces of these materials, I know they are unweldable but would they make useable roundstock if melted?

[I.M. OUTAHEREParticipant @i-m-outahere]

I had a rummage around on the interwebby thing and one thing that was fairly constant was the mention of how casting will lower the tensile strength of these alloys and 2024 is regarded as being moderately machinable so I don’t know what casting will do to that with either alloy .

You could make a test piece up by melting a small amount and cast a small billet – the suck it see approach !

[JasonBModerator @jasonb]

Those alloys will tend to have a T number after then which is the temper, melting will in effect anneal then so you loose the hardness and other properties. If you can get it for free try a small pour and see how it goes

[ChrisBParticipant @chrisb35596]

Yes sure will try it out and come back when I have the means to do it (will be a while!) Tried an online search for information on melting these alloys but didn't find much. As you say trying it out is the way to go.

[BazyleParticipant @bazyle]

7075 is high zinc low copper and 2025 the other way round. So they both have an alloying element to provide hardening. From a baic casting you get the -0 properties instead of eg -T6 heat treated. So it will have large grain size and the alloying element distributedinto in larger areas both of which make it soft.

From the phase diagram, not testing, you could harden it by holding at 400c for a while to put the zinc and copper into solid soultion and then quench to make them recrystalise throughout giveing a finer grain with inclusions at the grain boundaries which gives strength. It's 40 years since I did my metallurgy degree so can't remember the details.

[John PParticipant @johnp77052]

Hi Chris

Melting these metals you will loose much of the strength of the original
alloy ,as you have found out there seems to be little information out there
on the heat treatment of aluminium.I found these two books from
Camden were most useful ,the book on the left has 35 pages
devoted to the treatment of aluminium and its alloys ,but just like the
casting will require a lot of time to make up some of the equipment
needed for this .The temperatures needed to do this vary according to
the copper content of the alloy and need careful control for the best results.
These books are still on their listing,the one on the left is the one that
you need.

It obviously can be done the 2 cast turbocharger rotors on the right are in
as cast condition and still have the test marks on the riser .For critical
components like this they are best made from a known alloy, the
milled compressor wheel on the left and the unmachined blank are
2014 t6 aluminium.
My own furnace seen here is a modified Gingery furnace use MPK
bricks built around 1990 , will hold an A8 crucible.

John

[ChrisBParticipant @chrisb35596]

Are those compressor wheels your work John? Impressive!

I'm not after having the material properties in as purchased from the suppliers, I know that would be next to impossible to replicate. But if the alloy could be melted into useable bar stock at a considerable cost saving, then why not. For sure I would not use it for something like you're building!

EDIT:

Btw, what do you think of this Jason: https://www.metallab.net/ytongfurnace.php   He is using Ytong blocks for his ovens with good results if used lower temperatures. 

Edited By ChrisB on 29/08/2020 12:10:36

[JasonBModerator @jasonb]

While better than say a dense concrete block they will not perform as well as a vermiculite block or the "wool" mentioned earlier, I think we covered this on an old thread of yours.

However they are cheap, easily available and better than nothing so could be used to make up a simple furnace as in your link, if you are only doing a few heats a year then the extra bit of gas used would still be less than the cost of better blocks. If you find you start to do more billet casting or even get into casting parts then you can get better blocks for the MkII furnace. It could be a false economy to spend out a lot on making an efficient furnace that won't get much use as the money spent on it could go towards buying barstock.

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