Hi YouTube, my name’s Geoff and I’m the
VegOilGuy. Today I’m going to be sharing a little lost
foam casting with you. I’m going to be casting an aluminium wheel
and I’ve previously prepared the foam using techniques that I’ve already shared with
you. Now traditionally lost foam casting makes
use of dry sand, but I prefer to use green sand. So let’s start with that.
Green sand needs to be prepared and there’s a true art form right there and I don’t
pretend to have mastered it yet, but it begins with sieving the sand to remove all debris
and lumps. My sand is bone dry and it needs to be moist,
so perhaps every third or fourth sieve load, I spray my sand pile until I see the colour
change, and then it’s back to more sieving. Once I’ve finished sieving, it’s time
to mix the sand and evenly distribute the moisture. You can see the different colours
and that’s should show you that despite spraying as I was going, I never applied too
much water – and that’s key. From this point it’s just a matter of mixing
and spraying repeatedly until I’m happy with the overall moisture level of the sand.
But what is the ideal level? Well as I say, I’m no expert, but here’s
the indicators I use… Notice my hand is fairly clean. The sand appears
fairly dry and I can easily run my fingers through it and my hand is still clean.
If sand sticks, it’s too wet. I grab a handful of sand and squeeze it. It
forms and holds semi-solid shape. Now I gently try to break the shape and it should break
cleanly. If it crumbles, the sand it too dry. So that’s about as perfect as I can get
it. Martin our resident casting guru, tells me
that it’s better for the sand to be too dry than too wet, so I’m leaving it there.
Here’s my home made wooden flask. This is technically the drag, the bottom flask, to
give it its proper name, but notice that mine has a solid bottom, which is unusual in green
sand casting. But this isn’t strictly green sand casting – it’s lost foam casting.
So I begin by loading up the bottom flask, packing it well and levelling it nice and
flat. Whilst I’m talking about proper green sand
casting, as well as out resident guru Martin, I’d also recommend taking a look at SWDWEEB’s
YouTube Channel. Just like me, Dweeb doesn’t claim to be a professional, but he’s pulling
out all the stops to develop his casting skills and is doing a great job of it. So he’s
an excellent source of education, inspiration and entertainment. Check him out.
When I think I’ve got everything packed nicely, I sieve some sand on top to try and
give myself a nice fine finish. Then it’s just a matter of packing it down some more
and striking it off until it’s nice and flat.
Now I add the upper flask, then position the foam pattern fairly centrally.
I begin by sifting on some more sand to completely cover the foam. The idea here is to get fine
sand in contact with the foam to provide a nice fine surface.
Then I gently allows more sand through my finger to fall onto the foam.
Using just my fingertips, I gently push the sand around the foam, encouraging it to fill
every nook and cranny whilst being careful not to damage the pattern.
There’s a small hole here, so I’m using the blunt end of a drill bit to press the
sand gently home. I then start to push with my fingertips, again
quite gently. The trick is to squeeze the sand up against the foam without dislodging
it and especially without damaging it. Green sand compresses really well but don’t
be tempted to overdo the pressure. Follow the contours of the pattern – around
the circumference, between the spokes, in the centre, and press the sand, feeling it
give and bind. Here I’m using the handle of a rubber mallet
to ram the sand, but notice that I’m not going mad. You can apply too much pressure
and bind the sand too tightly – something which needs to be avoided – so just tap
at this stage and notice the movement of the sand.
I’m aiming now to draw level with the tips of the gates.
Using a dry brush, I clean away all the sand from the tops of the gates and use my fingers
to create a little room around them. Then it’s time to remove the screws and
because of the way I’ve prepared the foam, I know that I’ve got a central core of air
inside my pattern. My theory is that this benefits the pour,
enables easier metal flow and release of gasses. Now this is a plaster feeder and for the moment
it has a paper cover on the top the prevent sand getting in.
It fits perfectly on to the foam gate with a gentle push.
This is a plaster vent – again with a temporary paper cover at the top. Then I carefully trowel
in more sand to avoid disturbing the feeder and vent, then this gets compressed into place,
firstly with my fingers and then with the mallet handle.
I’m convinced these plaster feeders and vents greatly improve my casting technique.
They help me get the metal where I want it, keep it hotter longer and vent unwanted gasses.
More sand is added and compressed again, all the time looking to support the feeder and
vent. Eventually I strike off the sand and brush
away any loose excess. Now this is a fine metal rod – it’s actually
a bicycle spoke. I carefully judge the depth to make sure I don’t get within an inch
of the foam, but then it’s a matter of poking random holes into the sand.
And why am I doing this? Well it’s a tip from Martin that you saw me using roughly
a year ago and one I think he’s just used himself in his latest video. As I said earlier,
compressing the sand too much is dangerous. As the foam evaporates and even as the metal
consolidates, gasses are released. These typically escape through the sand – but if the sand
is too compressed they can’t pass through and can dangerously build up and literally
explode – something to be avoided when dealing with molten metal. The plaster and feeder
go a long way to prevent this, but these holes provide an extra source of ventilation and
they really work. Wait and see. I’ve had my home made electric foundry running
at 760 degrees and the metal is ready to pour. The paper covers are removed – and then
the red hot crucible is carefully tilted towards the wide-mouthed feeder.
It was at this point I realised I’d seriously underestimated the amount of metal I needed.
Fortunately it was just enough, but I’d have liked a little more in the feeder.
I know this is dragging on a bit, but keep watching the feeder.
Can you see it? The metal is still red hot.
There – it’s actually still bubbling. It’s still red hot metal.
I told you the plaster feeder keeps metal hotter for longer.
Did you notice the smoke from the spoke holes? Surprising isn’t it. Remember these holes
never contacted the foam, but they were close enough for gasses to find and use them.
I left things a good hour then took the flasks apart.
And look at that… beautifully discoloured sand. And that’s a good thing. It shows
evidence of heat, smoke and gasses escaping into the sand – just as it should. That’s
why green sand blackens with time. Looking at the wheel inside the sand, I was
pleased. Sure it had surface discolouration due to the decomposition processes, but this
could be cleaned up. Here it is half an hour later with the sand
removed. It’s nicely formed, good crisp edges and almost ready to go.
Everything is beautifully straight and flat. It may look rough and sure the texture of
the foam is evident, but that’s just discolouration. Once the surface is lightly cleaned, these
will disappear and the proof of the process will be revealed.
If there are any imperfections, they will have been present on the foam pattern before
the casting. And here it is with the sprues removed and
the surfaces cleaned up a little. I think you’ll agree it looks quite nice. I tend
to put a lot of effort into preparing the foam and then very little energy needs to
be put into the metalwork side. I’ve already heard from some of you guys saying you prefer
to do things the other way round, and that’s okay. That’s your personal choice. Personally
I find it easier and much faster to put a little effort into the foam rather than a
lot of effort into grinding, cutting and shaping metal.
But whatever your preference, I hope you can see how useful green sand can be in lost foam
casting. I find it very reliable and get consistent results, and for me that’s the way it should
be. Next time I’ll be experimenting with dry
sand and a thin plaster coating on the foam, so look out for that video.
So I think we can call that a finished video. I hope you enjoyed this one guys and if you
did, please like it. If you’ve got any questions on this subject,
drop me a line. Don’t forget to check out my website and
please subscribe if you haven’t already done so.
Look out for my other videos on my YouTube channel and send in any comments and video
requests. So that’s it for now guys, thanks for watching.