DIY casting respect

[julianf]

http://www.youtube.com/watch?v=Zt8L5OVu7zw

note: they only make an ingot, but, still - looks like zero spent on equipment!  : )

[Julian]

The first aluminium casting I did used a bean can (not recommended) on the front room fire, making a work lamp for the lathe which I'm still using today.

If you've not tried metal casting, dream up something to make, it's great fun.

[julianf]

See, for me, that part is easy - all i want is (good) slabs of aluminium for machining.

I could melt small amounts easily enough - i reckon when the cast iron hotplate of the rayburn starts to glow its probably going to be hot enough in the firebox, but i can only do small quantities then.  Also, as its covered in machine oil it may get a little exciting to be doing indoors?

I guess, volume wise, id be wanting to do something like 4ltr batches.  That'd give me an ingot of, maybe, 25 x 35 x 5 (cm) after wastage? (3500cc)

I like that ive just noticed people using the bases of fire extinguishers.  Ive only seen them using fancy graphite crucibles before, which are money, but we have Brett, so that may be that side taken care of : )

Our oil boiler is not in use at the moment, so i could use the burner from that as the heat source.

[Julian]

The classic home foundry is based on a 20 ltr can and is a piece of cake to make.

Cut the top off about 2" down.  Make holes in the sides at 90° to take 6 or 8mm reinforcing rod forming a cross inside.  Get some "grog" fire clay mixed with fine gravel ... can be bought ready mixed and quite cheap.  Pack the lid flush with the cut edge.  Make a 2" hole, 2" up from the base of the can and a hole to take a 12" length of cast iron down pipe at a 30° angle pointing up, 2" from the top opposite to the hole in the bottom. Pack a 2" layer of grog in the bottom up to the hole. 

Then line the tin with a 2" layer of grog ( you can use another 20 ltr can cut up to act as an internal former spaced with bit of wood) and break out the bottom hole.  Pack it around the down pipe, which should be supported until the grog drys.  Put somewhere warm to dry for as long as possible.  Once air dry, light a gentle wood fire in it to dry it further, the slower the better.  You can make a three legged stand with grating about 4 - 6" tall, but many people don't bother.

Get hold of some coke and start a fire going.  Once its got hold add coke, allowing enough room for the crucible.  Stuff a vacuum cleaner or something similar on blow into the bottom hole and let it run.  Aluminium will melt quite quickly, but other metals may need a top up of coke.

For aluminium you may get away without a blower if you have a suitable length of stainless chimney liner you can run up a tree or brick wall to create a draft.

I've melted cast iron in one of these, but it took a couple of charges of coke and even then the iron chilled too quickly resulting in a very hard surface, but it was still possible to machine with some effort.  Melting iron, it's quite astounding when you open the furnace ... it's incandescent to the point of being uncomfortable to look at and very scary the first time you try and pour it!

[photoman290]

i know how scary molten cast iron is. i worked in a foundry once, when i was young and foolish. the job we hated doing was changing the hydraulic hoses under the 7 ton pot of molten iron. the hoses would blow in the middle of the pour so we had to go underneath and change them with 7 tons of molten iron over our heads. it was hot but not excessivly so. must have very good insulation around the  pot. if we coundnt fix it  in time it took a wekk to chisel out the cold iron. i gave up working in the engineering trade after that.

[photoman290]

damm! just lost an hour looking up the company i i was working for at the time. they still exist but have moved. lots of pics of the place i worked at.

[Dickjotec]

Cast aluminium is not ideal for machining. I used to do a lot of it at school with the kids. You don't know the ally you are using and it can turn out too soft so it rags on the tool or have gas or other inclusions in it. Even when degased with chlorine it is can still have gas pockets. It is ideal if the casting is not going to be machined or if the machining is in an area that is not seen but for CNC work solid stock workers much better.

[julianf]

I did not really realise it was possible (well, feasible) to do other metals.  I guess brass isnt much higher, which might be useful.

Julian - do you have a diagram of what youre describing?  I can follow your description, but if its from a book or something, then i could probably find it.  I know you mentioned a book previously, but, when i looked, it seemed more on casting, whilst all i really want to do is make ingots, to physically machine there after.

So, what i need at this point is a way of melting the metal, and moving it to the ingot mould.

Coke and a blower are possible, but i was thinking along the lines of a central heating burner running on bio.  From your experience, would you say this is a bad idea, and i should stick with coke?

[julianf]

Cast aluminium is not ideal for machining. I used to do a lot of it at school with the kids. You don't know the ally you are using and it can turn out too soft so it rags on the tool or have gas or other inclusions in it. Even when degased with chlorine it is can still have gas pockets. It is ideal if the casting is not going to be machined or if the machining is in an area that is not seen but for CNC work solid stock workers much better.

Dick,

All the stock i have is 6000 series.  I assumed (possibly incorrectly?) that if i used only that material, then i would end up with that material at the end?

Im aware of chemicals you add to make the dross float up, and to degass, but i have no idea yet where to obtain them.

[Julian]

There you go, just a rough section but you should get the idea.  The grey areas are "grog" ...





I used to get  crucibles, casting sand and grog etc from a place called FL Hunt (think it was FL but I could be wrong).  I'm pretty sure I read they went bust, but a quick google reveals these people who seem to sell all the kit along with dental supplies for some obscure reason ... http://www.johnwinter.co.uk/ .  They have a whole page on fluxes and degassers.  I'm sure if you search the model engineering forums you'll find more willing to sell small quantites.  I remember I used to grind up cat litter (unused) as a source of fullers earth ... but I can't remember what I used it for, possibly core making.

There was a general school of thought in the model engineering world that if you used scrap of the correct type, the casting process didn't alter it's properties too much.  For aluminium, I used to smash up gear box casings and bell housings, they seemed to machine OK.  Pure ali. would certianly be a different matter.

[Dickjotec]

Cast aluminium is not ideal for machining. I used to do a lot of it at school with the kids. You don't know the ally you are using and it can turn out too soft so it rags on the tool or have gas or other inclusions in it. Even when degased with chlorine it is can still have gas pockets. It is ideal if the casting is not going to be machined or if the machining is in an area that is not seen but for CNC work solid stock workers much better.

Dick,

All the stock i have is 6000 series.  I assumed (possibly incorrectly?) that if i used only that material, then i would end up with that material at the end?

Im aware of chemicals you add to make the dross float up, and to degass, but i have no idea yet where to obtain them.

It is far better if you use a known stock but it is also heat treated after production (hard half hard etc) the stock I have used was also drawn which again refines the structure.
This is one link to degassing tabs.
http://artisanfoundry.co.uk/store/product_info.php?products_id=67&osCsid=932b7bbb45af1524a27fd64a7709dd8e

Not used those particular ones but I imagine they are mostly the same.

I would also invest in a graphite or fireclay crucible . It is easy to make pickup tongs and a pouring ring. When you pick the crucible out of the furnace make sure the pickup tongs and the pouring ring are red hot. I have had a crucible crack out of the ring and deposit a gallon of liquid aly on the floor. Oh you should pour over a sand try containing dry sand, liquid aly on concrete goes about tike mercury but it is hot!

[Julian]

There you go Dick's found another good supplier and I'd agree with his comments about a crucible, especially if you want to experiment with other metals and the dry sand bed is a very good tip.

I remember visiting a foundry in India many years back.  That had a sand floor on top which all the spills went, but the workers were walking round in shorts and bare feet!

As to running a furnace on bio, I've no idea if it would work.  I hadn't even heard of bio when I was playing at casting.  If it's something you're not doing on a regular basis, I recon coke would be a lot less hassle to set up and you know it will work.

Worth investing in a chrome leather apron and some leather boots if you don't have some already.  In place of a visor I used a welding mask with two, clear glass screen in place of the tinted.

[Dickjotec]

The apron should go over the boots. We used to use leather spats over leather boots as well. You don't want to get a boot full of molten aly.

[julianf]

Just wanted to run this idea past you quickly -

Get a used MAPP cylinder.
Grind the end off it
Weld on some sort of hoop for a 'handle'
Load it with swarf
Put in in the rayburn firebox

If i can melt the swarf down into even impure ingots, i think it will motivate me to go further.

So...

Assuming i have the MAPP cylinder in the firebox full of molten aluminium, then what?

My concerns are -

Stuff getting in there - should i fashion some sort of lid also?
Then what to cast the ingots in - i guess a cupcake tin, but any better ideas?

Is the degassing done at ingot stage, or at final cast?  Ie can i just get on and do this, or should i buy some 'stuff'?

Thank you : )

[Julian]

Go for it if the Aga gets hot enough.  My first experimental ali casting was done on the lounge hearth using a log fire, a tin can and a pair of mole grips (wearing gloves!)

Don't make the MAPP cylinder too deep, you'll need to scrape off the dross the melt.  Recommend you make pair of tongs to grip the circumference of the cylinder you can use them to lift in and out and pour.  A lid is a good idea to stop contamination from the fire.

I've not read this anywhere, but I suspect the amount of dross is related to the surface area of what you're melting, guessing the surface oxides, so swarf may not be the best feed stock.

Make an "L" shaped hook to scrape off the dross, preferably on to dry sand, but with ali you could probably use a steel tray.

I never tried a steel mould for ali but I guess it should work ... there's only one way to find out!  As an alternative you could make an impression in VERY SLIGHTLY damp sand (better to get green sand or similar) or fashion one from a plaster and sand mix, but make sure it's thoroughly dry before pouring.

Any degassing additive should be added to the crucible after removal of the dross and stirred in but I never used it.  Give it a go without, you've little to loose.  If the casting is porous, then get some degasser.