has anyone seen these kind of molds used by home foundries in america? pouring is 9:00 in they look fragile (when lifted off the casting every one i have seen is very very gentle) they look like clay molds with lots of graphite brushed on and then the outside is coated with rough refractory of some kind. would really like to try this with a few patterns but not sure what that material on the inside is
It could also be grey "Ciment Fondu" on the outside, which is a high strength, high temperature cement based on calcium aluminate that modern dense castable refractories are made from. The inside finish would have to be carefully treated to avoid damage to the surface.
there are definitely a few layers of material it looks like, at least 3 (refractory, clay, graphite) I have seen some with orange, grey and dark black clay at the top where the pour spout is and one video where it chipped off almost like sand. the outside looks kind of like some firebricks i made with 80% pearlite and 20% leftover refractory i had when building my furnace. they withstand insane heatshocks and haven't cracked yet.
That's an interesting video, low tech die casting of sorts, more interesting by far would have been one showing the mold being made.
Happen to have any pictures of those bricks Thomas? Another member here was inquiring about Perlite refractory mix for insulating layer in a furnace build. Was wondering whether you needed to wet the Perlite before mixing with the refractory and any tricks to minimize damaging Perlite during mixing. Was the brick strength comparable to IFB? Best, Kelly
i will get some photos tomorrow in the shop. I have some that are almost as dense as the walls of the furnace (50/50 mix i think) and my plinth(i think thats what its called) is about 80% pearlite mixed with scrap leftover 3200 degree refractory that was used on the walls. they are very light, i only tried to get all the pearlite wetted by the refractory then packed them in wooden boxes for molds. it was mixed with a hoe in a concrete tub. the pilth was packed in the bottom of a plastic mixing bucket for epoxy. I didnt think the 80% ones would hold together at all but they seem really solid after years of having them. still looking for the video factory tour of the mold shop.... its gotta be on youtube somewhere. need to translate the videos to see if i can figure out what the molds are called exactly. they all seem to get them out ASAP after pouring, i suspect they would break if the casting cooled on the mold.
the bricks are as strong as normal red bricks. i have dropped them a few times with no damage, they are hard shell (pearlite is encased in the cement and 100% grey) the plinth has taken the force of an oil burner at least 50 times and shows no sign of deterioration.
http://cast-aluminum-pot.com/a/Products/powerfulcylinderfan/114.html http://www.aluminum-pot.com/ getting closer, these companies make them.
Well that is of great interest because the subject of Perlite came up frequently at the AA forum. It did well in lower temperature regions but always ended poorly when exposed to high heat, melting into a green glass and fluxing everything. Perlite melts at about 2300F which is well within reach of most fuel fired furnaces but it starts softening around 1600F and expands a lot (like 10x) on its way to the melt point. If you have a dense refractory hot face between the Perlite brick and furnace interior I could see how the temps may be lower for the brick but I'd think a plinth in a furnace with an good oil burner would get a good thermal work out........above 2300F. Best, Kelly
My first experimental furnace was based on the Backyard Metal Casting refractory of fireclay, silica sand, cement and perlite. I found once I got up to orange heat, just barely enough to melt brass, the refractory turned into a foamy green mass as the perlite melted and fluxed the other material. This would have been about 900 deg C or 1650 deg F as that's about when brass melts. I think the website mentions the same problem once their furnace gets a bit of heavy use.
here are photos of it I used Unicast 65QS refractory (it was supposed to be good to 3200 degrees) all the chunky bits are pearlite. I don't know what the ratio was. I dumped a bag in the leftover refractory and made sure all the pearlite was wetted down then packed it in the molds to make some extra bricks.
