High Temperature Metal Casting
- 1 Overview
- 2 Required Tooling
- 3 Mediums
- 4 Moulds
- 5 Resources
- 6 Working Notes, Please Log in and Edit
- 7 Raw Notes
A great introductory on the subject is myfordboy's videos.
Fuel burning furnace
- Paul Pengs version of Lionel Olivers "The flowerpot crucible furnace"
Crucible & Trivet
A crucible is a container where the metal is melt. The crucible is stood upon a trivet, which elevates and enables thermal energy to penetrate from the nether, so to speak. N.B, aluminium is apparently highly acidic in its molten state. Most metals don't like acidic environments at all = steel/iron crucibles will degrade further from this. Needless to say a dropped cracked crucible with molten metal is something one do not want. Sure, one can clogg small cracks with molding sand. Research for manufacturing proper (extruded) crucible which trap less hydrogen in the casted material = better quality and easier machining.
Misc useful resources
A Kush Head Pressure Tool could be very nifty tool to have around as you get a reusable feeder and save some time as it works every time.
Pewter is considered a low-temperature metal: See Casting/Pewter.
In the casting process a pattern is made in the shape of the desired part. This pattern is made out of wax, wood, plastic or metal. Simple designs can be made in a single piece or solid pattern. More complex designs are made in two parts, called split patterns. A split pattern has a top or upper section, called a cope, and a bottom or lower section called a drag. Both solid and split patterns can have cores inserted to complete the final part shape. Where the cope and drag separates is called the parting line. When making a pattern it is best to taper the edges so that the pattern can be removed without breaking the mold. This is called draft. The opposite of draft is an undercut where there is part of the pattern under the sand making it impossible to remove the pattern without damaging the mould. The molds are constructed by several different processes dependent upon the type of foundry, metal to be poured, quantity of parts to be produced, size of the casting and complexity of the casting. These mold processes include:
- Sand casting — Green or resin bonded sand mold.
- Lost-foam casting — Polystyrene pattern with a mixture of ceramic and sand mold.
- Investment casting — Wax or similar sacrificial pattern with a ceramic mold.
- Ceramic mold casting — Plaster mold.
- V-process casting — Vacuum is used in conjunction with thermoformed plastic to form sand molds. No moisture, clay or resin is needed for sand to retain shape.
- Die casting — Metal mold.
- Billet (ingot) casting — Simple mold for producing ingots of metal normally for use in other foundries. --Wikipedia
- Sand (100-150FGN; think Fine blastersand)
- Bentonite clay (groundup kitty-litter, Yum/favorite pass-time)
I do not know if the mixture can be air-cured, or if is only safe and functional after being heat-cured. The heat-curing probably helps evaporate the mechanical water.
- 3dtopo.com '50% playground sand and 50% Plaster of Paris.'
Is used where one want space for a cylinder in a engine or say filament & vitamins in a extruder.
Ingredients (from myfordboy below):
- Very fine sand.
- Sodium silicate (Used in loads of applications; homebrewing & passive fireproofing etc, cheap and readily available. UK & US.)
- Boiled linseed oil.
- Flour (plain).
- Wallpaper paste, minimum amounts of water.
- Easiest & cheapest method of generating Carbon dioxide.
- Talcum powder to give a better surface finish.
Ceramic Shell Method
Direct Printing Moulds
You can print a casting mould with a reprap directly using a motor driven paste-dispenser instead of the FFF-head. Perhaps using Ceramic Extrusion. Pastes made from dust or milled particles tend to stick in thin dispenser needles, as the sharp-edged microparticles sometimes nests and clogg the flow. Better fluidity is achieved by using spherical particles instead of milled material and dust. Some tests were performed with glass-spheres from sanding, comercial cenospheres (hollow aliminium-silicate-spheres with some microns diameter), hollow glass-spheres and rock-spheres - all mixed with Sodium Silicate (waterglass) and water. This pastes dries at air and can be heat-cured for faster drying or sintering to a more solid ceramic material. Hollow glass-spheres are good heat isolators but only stable until 600 centigrades.
A great introductory on the subject is myfordboy's videos on youtube.
The OSE network
David J Gingery
There's a classic series of books that describes how to build machine tools from scraps and handtools, written by David J Gingery. This series of books stems from a time when earth's whole biosphere lived under the threat of nuclear war. As such the planets dominating species cultures had to face the very real possibility of rebuilding not only ones own life, but further down that surely narrow and horrid road civilisation and mankind it self.
As part and the first of these series are Charcoal Foundry, which describes how to build a foundry from scraps/free materials, since these things will luckily/sadly enough always be around and very much needed in such a scenario.
Working Notes, Please Log in and Edit
On December 2, 2009 06:23:05 pm Vik Olliver wrote: > Sebastien Bailard wrote: > > Vik, > > > > Do you want to type up some notes on the wiki under > > casting/metal? > > Yeah - when I get a chance to come up for air! Spent the last day > resurrecting my work laptop. Still not quite done. > How long has it been since I backed up my machine? ...
> > Also, you may want to buy some jeweler's investment if you want to go to silver or bronze. > > Less chance of steam explosions and all that. Or look up some investment recipes that use plaster. > > S'okay, I bake my moulds out at 250C. I used to do a lot of low-temp > casting. Mind you, the new furnace just about melts aluminium :) Just > needs a blowtorch to keep it at a pourable temperature. > Are you using pure plaster? Or plaster and a refractory aggregate?
This is a bit of a ramble, sorry:
Baking out your investments at 250C is going to dry out all the water that didn't find dry plaster to turn back into gypsum crystal. ('Mechanical Water')
But if you pour in bronze or aluminum, you're looking at having the remaining H20 ('Chemical Water') in the gypsum crystal disassociating from the gypsum and escaping. Possibly. Possibly violently?
Bronze and aluminum are different animals from pewter, and deserving of healthy respect.
"Plaster of Paris is a type of building material based on calcium sulphate hemihydrate, nominally CaSO4·1/2H2O. It is created by heating gypsum to about 150 °C.
2 CaSO4·2H2O → 2 CaSO4·0.5H2O + 3 H2O (released as steam).
'You get it _hot_, water comes out.'
http://users.lmi.net/drewid/plaster_faq.html#Anchor-the-24925 says you need refractory aggregate.
My copy of From Clay to Bronze says the same. He just uses plaster and sand. And that for bronze, solid investment, the burn out is 540C for 2 days.
This looks good and straightforward, via: http://www.chicagoartistsresource.org/node/9297 "Though there are many variations of the ratio between the sand and the plaster, the formula that I have successfully used combines one part plaster with one part sand by weight. Since plaster and sand are commonly packaged in 100 pound bags, it is easiest to premix one bag of each in a large tin washtub and then add this mixture to your water."
This is nice and technical: http://www.artmetal.com/brambush/forum/bramyak1/messages/109.html
"If there is ANY chemical water left or if there is any wax residue left in the plaster there is likely to be pitting, boiling, gas released from the mold and even a violent BURP or explosion like a geyser that will blow the metal right back out the top at worst or just bubble away at less worse.
Both are real bad.
Both make for casts less desirable (being real kind here... personally I call them poorly shaped remelt ingots)."
As I (partially) understand it from "From Clay to Bronze", we bake out the mechanical water, and then the chemical water, and trust to the wiremesh wrap to keep the investment together mechanically, because the gypsum crystals are toast, so it's just a big weak matrix of calcium sulphate hemihydrate and sand, as opposed to good strong plaster (gypsum).