I don't recommend you try any of this unless you know what you are doing and have done your research and have appropriate safety measures in place, should anything go wrong. Please don't try to hold me responsible for YOUR mistakes and misjudgements. I'm only presenting this information here because someone is interested in small scale hobby metal casting and may not know what they're getting into ... as someone has already mentioned, casting of very small parts is difficult, as the thinner and smaller your sprues and feed lines get, and the smaller the parts are, it's difficult to get the metal all the way into the casting before it begins to solidify.
To create home made Sodium Silicate (water glass)
200 grams of caustic lye (sodium hydroxide ... NaOH, or the main bad thing in BLEACH, only in it's PURE POWDER FORM - THIS STUFF IS VERY DANGEROUS)
300 grams of silica gel (the little dessicant pack bead thingies - you can substitute kitty litter crystals ... the clear ones)
400 ml distilled water (I used tap water, didn't really notice anything off or bad about it ... but my water here is OK to drink.)
DO THIS OUTSIDE OR IN A VERY VERY VERY WELL VENTILATED AREA
Pour all the water into a stainless steel or other suitable container ... using glass (pyrex) may work, but don't blame me if your wife kills you. SLOWLY stir the water while adding the caustic lye (sodium hydroxide - I get mine from Home Depot ... DEPP brand drain opener). This will be a very exothermic reaction and smell extremely strongly of bleach, which it basically is. It will get hot, it may even BOIL ... do NOT get it on you or on your clothing. This can cause bad chemical burns!
After all the caustic lye has been dissolved, slowly add the silica gel beads perhaps 40 - 60 grams at a time, stirring them and letting them dissolve to create sodium silicate and heat ...
You may need to actually add MORE heat to help speed the reaction towards the end, and dissolve almost all of the silica gel into solution, as well as to cook out almost all of the water. There will be a little silica gel at the end still left over that wont dissolve because you ran out of caustic lye in solution, which is a good thing .... that stuff is nasty.
Once you have it, you can use sodium silicate and compressed carbon dioxide gas to help solidify your moldings, giving them a bit more durability during the pour ... mix the sodium silicate into your disposable greensand, keeping the majority not in use in a sealed container. It will "cure" in the presence of carbon dioxide, if it's dry enough.
Small castings can be made through several different types of methods ... centrifugal casting is one such method, where the heavy liquid metals are pulled into the bottom of a molding by the use of centripetal force. Another method is via lost wax casting, where a wax positive is created and the molding is created around that, which is then hardened or cured. The wax is then melted and poured from the mold immediately before the metal is poured into it ... the key to this method is to KEEP THE MOLD HOT so that the metal stays liquid until it has filled every detail within the molding.
Final method that I'm aware of would be pressure casting or injection molding, where the metal is injected into the mold at pressure to ensure that it fills the entire cavity completely. The use of sprues and risers all around the molded part help ensure that air has sufficient time to escape. This method is NOT easy to do or practical to attempt for the home foundry enterprise.
I don't recommend you try any of this unless you know what you are doing and have done your research and have appropriate safety measures in place, should anything go wrong. Please don't try to hold me responsible for YOUR mistakes and misjudgements. I'm only presenting this information here because someone is interested in small scale hobby metal casting and may not know what they're getting into ... as someone has already mentioned, casting of very small parts is difficult, as the thinner and smaller your sprues and feed lines get, and the smaller the parts are, it's difficult to get the metal all the way into the casting before it begins to solidify.
If you are having SOME difficulty with a mold that has some thinner sections .... keeping the entire mold hot or at least uncomfortably warm MAY help. If you are using greensand this is a bad thing, as driving off all the water will cause it to lose it's integrity. Use of sodium sililcate for the molding rather than greensand will be more effective with a hot mold, but then you'll want to discard the used sand rather than reconditioning it and reusing it like with greensand.
Lost wax process requires wax and a good plaster of paris mix with refractory sand and pearlite to assist in keeping the mold's form. The wax itself is NOT lost in this process, as the melted wax can merely be poured back into a container and saved. The mold, however, is destroyed when the item is removed at the end. A process can be carried out where you simply create a "master mold" that you use for casting the wax positives, and then you can make a bunch at a time.
I don't recommend you try any of this unless you know what you are doing and have done your research and have appropriate safety measures in place, should anything go wrong. Please don't try to hold me responsible for YOUR mistakes and misjudgements. I'm only presenting this information here because someone is interested in small scale hobby metal casting and may not know what they're getting into ... as someone has already mentioned, casting of very small parts is difficult, as the thinner and smaller your sprues and feed lines get, and the smaller the parts are, it's difficult to get the metal all the way into the casting before it begins to solidify.
Yes, I repeated that paragraph 3 times, but it bears repeating. People DIE every year, experimenting in their back yards with things they don't fully understand ... chemical spills and exposure, fires, molten metal accidents, ect ... I'ld rather NOT log on to IAP and find your (anybody's) obituary. If you don't REALLY KNOW what you're doing, leave it to the professionals ... or at least an amateur who does know what they are doing.