Recently got interested in the idea of doing a spot of casting. Always wondered how they managed to cast such complicated things as engine blocks in
sand without the sand falling down etc. Found a couple of websites with locost metal casting info but nothing really comprehensive. Some enticing
stuff about building your own propane smelter and casting your own lathe..
so anyway, anyone done this kind of stuff and know any good websites or books? I might trug down the library and see if they have anything.
would be kind of nifty to have a home-cast aluminium badge on one's locost, would it not? or how about home-cast knobs, handles, gearknob, etc..
Search under model engineering...there are one or two books for the amateur foundryman...I have one somewhere....
Basically, there some rules of thumb, some physics and chemistry....but more common sense than rocket science.......
The model engineering gang have a similar "surely, I can make that?" mentality that Locosters have...
Don't you agree Mr Jenkins?....
Not really applicable to home casting but things like cylinder heads and blocks have sand molds that are "glued" together with a two part
urethane based binder. Basically you mix up a slurry of sand and the urethane binder, blow it all into a giant metal clamshell called a
"corebox" with air pressure and set the urethane by pumping in a gaseous catalyst or "tea gas". The hardened core sections are
assembled, molten metal poured into the voids, and the sand bashed loose with great stonking pneumatic hammers. Et voila...
Home casting is easier using the "lost wax" process. Basically, you carve the item you want to cast out of a piece of wax (rigid foam
insulation is a good substitute), embed the wax in a pot of plaster of paris (or similar) and pour the molten metal into the plaster mold. Some
processes molt the wax away with the hot metal, some bake it out before the metal is poured, if you use the foam it can be melted out quite cleanly
with gasoline (definitely want to let it dry thoroughly before you start waving molten metal near it). Things to consider are: (a) metal needs a path
in AND a path out so your mold can be fully filled, think funnel in and funnel out, both pointing up so gravity pushes all the wax & air out (b)
some metals "flow" better than others, lead and bronze cast well, ali and steel can be tricky, old pistons are supposed to be a good
starting point as they are made of special alloys which flow well.
Have fun, Ted
Lost foam is also a neat and simple method of casting. It has been at leat 15 years since I did this so I can't remember if the foam is anything
special , but it is carveable and you can glue and tape it together. Then you pack it into a container using wet sand, making sure that any high spots
under the sand have a "tubeule" (new word?) of foam that vents to the surface.
When you pour molten metal, in my case aluminum, into the sand packed bucket, the metal vaporizes the foam. Let it cool for a long time, remove from
sand, wash down and Viola! rough cast part.
The hardest part if I recall is preventing air bubbles from remaining in the casting. Also, as you pour the molten metal into the mould, it cools
rapidly and small details at the lower portion sometimes don't get any metal.
Doing this was a LOT of fun and now I think I'd like to try it again on some bits for the car. Nothing quite like a "one-off"!
Graber
quote:
Originally posted by Alan B
Search under model engineering...there are one or two books for the amateur foundryman...I have one somewhere....
The model engineering gang have a similar "surely, I can make that?" mentality that Locosters have...
Don't you agree Mr Jenkins?....
about 20 years ago I installed some equipement at volkswagens huge plant at hannover. they stamped all their own panels, made their own exhausts and
did their own castings.
As has been said, they use these solid glued together sand structures. I remeber seeing some for exhaust manifolds. Look quire weird, but definatly
made out of a solid sand like substance.
atb
steve
Chaps,
As of 1/3/04, I'll be starting my new job at my fathers art foundry. No more 2 hours on the train
Anyway, lost wax is the way we do it.
Wax orig into mould (plaster of paris/grog mix).
Web site not good, but
http://www.l-a-f.demon.co.uk/photos/photo09.htm
Is a pic of a bird in a mould showing the feed and air sprues for pouring and breathing of mould. Note all high points have an "air".
Mould is baked in the kiln for a couple of days (depending on size), until the wax has all gone. This is checked by sticking a flame under the pouring
hole (moulds are upside down in kiln!). If there is smoke or a flame (burning wax gas) coming out, it ain't baked. Also, you need to ensure that
all water has been removed from mould, as pouring liquid metal at 1500 deg C will instantly vapourise any moisture, will potentially dangerous
consequences.
When mould baked, it's removed from kiln, turned over, covered in plastered scrim to reinforce and metal poured in.
Mould opened after a couple of hours, feeds cut off, and bronze (like I said - art foundry) put into diluted sulphuric acid bath - to break down
plaster core. Then item washed out, welded, chased, coloured, waxed and polished.
Anyway, more info on site (as yet unfinished after about 4 years), so bit crap.
Also pics of casting!
ATB
Simon
[Edited on 30/1/04 by Simon]
Funny how your mind works...I couldn't remember what I had for breakfast yet I recalled instantly the guy who wrote the books I was thinking of
which I haven't read for 20 years (at least).....it was Terry Aspin..
http://www.amazon.com/exec/obidos/ASIN/1854861468/qid=1075469230/sr=2-1/ref=sr_2_1/002-6913643-3335256
Oh yeah...didn't have any breakfast...explains why I'm starving....
quote:
Originally posted by Alan B
....it was Terry Aspin..
quote:
Originally posted by Alan B
Funny how your mind works...I couldn't remember what I had for breakfast yet I recalled instantly the guy who wrote the books I was thinking of which I haven't read for 20 years (at least).....it was Terry Aspin..
http://www.amazon.com/exec/obidos/ASIN/1854861468/qid=1075469230/sr=2-1/ref=sr_2_1/002-6913643-3335256
Oh yeah...didn't have any breakfast...explains why I'm starving....
try
http://www.visi.com/~darus/foundry/
or
http://www.backyardmetalcasting.com/index.html
for online fun in casting
very good fun using the hair dryer as an air pump to get a hotter furnace
[Edited on 30/1/04 by timf]
I should say f**k off...but I'm beyond such juvenile responses....
Or am I?.....
quote:
Originally posted by Alan B
I should say f**k off...but I'm beyond such juvenile responses....
Or am I?.....
This brought back a few memories.
I decided that brass casting was suitable for making some classic car parts I needed but couldn't buy.
Enter one huge gas ring and a crucible.
Large amount of brass cut into small bits, and put into crucible one by one.
Cue much amazement from the assembled throng at"how much brass you have to put in before you can see it in the bottom"
Then we noticed the crack in the crucible.
£40 quids worth of brass - gone, on the plus side we were the only house on the street with a "brass inlaid" drive!
Cheers
Chris