The Shop > Composites & Plastics
3d metalcasting test
mattinker:
Yes, I've cast smal sculptures Aluminium Bronze in plaster using crushed brick as grog. It's the time honored investment plaster mix. I used a potters kiln to dry out the mold pouring into the mold hot. My foundry was hard pressed to get the metal up to temperature, despite my dissolving the Cu into the Al. Unfortunately I haven't got any photos, which is a pity. I'd like to do some more!
Regards, Matthew
vtsteam:
I have some fine grog Matt, I might have to give this a try soon. :thumbup:
tom osselton:
I pulled out my supper yesterday and popped in the molds to melt out the rubber yesterday and was impressed as how clean it was inside the mold (you can do this stuff without a better half) :D and there was no odor to speak of either nor any visit from the fire brigade (alarm's wired in).
Today I put them both in the kiln to see what the effect of heat had on the plaster/sand mix and went from 250C to 450C and finally 700 degrees C over a period of 6 hours then letting it cool down at the same rate as the kiln both the molds are doing fine and there seems to be no sign of cracking although I haven’t handled them yet.
My concern now is if they are to be preheated I have to be able to handle them, so far for casting I have been using welding gloves and on a couple occasions have had to do that hand shaking thing.
Anyways here is the start of some tongs for handling the molds. Strange design I know but you will always have inward pressure lifting by the bottom part of the handle it’s weight should help hold it and they are not that heavy, after all it worked fine for the iceman. I’m thinking the bottom will be curved in the center with a flat section on either side for round or flat molds or I could weld on something so the grippers are interchangeable then flat or round would make no difference which is probably the way to go.
vtsteam:
If preheating is wanted could you just make a circular metal plate to fit the bottom of the kiln, with a rigid bail for lifting both molds out at the same time? You could even tack some short pipe "cup holders" onto the plate to keep them from shifting. A hook inserted into the bail could lift the whole deal out, or replace it if necessary
tom osselton:
vtsteam yes I could do that and set some eyelets directly into the casting I`ll use that as a last resort for now I have done this, so far it seems to be not too bad and seems to have a decent grip but would never use it on a crucible.
well the kiln had cooled off and I pulled them out to take a better look and to use a rasp to open up the entrance better for the pour. The molds looked good no cracks and clean inside.
I`m not sure what the powder is possibly talkum anyways it is slippery and I dropped one and could not catch it, my right arm has nerve damage when they put me back together (arm broke in 5 places) along with the other bones lol. anyways here is what it looked like inside after being fired at 700 degrees c.
As you can see the sand is evenly distributed and did not settle prior to the setting of the plaster and what is left of the mold has good surfaces. I was curious about any residue left in the remaining mold and blew it out with compressed air the pressure was too high and exposed some of the underlying sand so if you try this turn the pressure down lower. Now I have one mold and figure what the H and load up the crucible with scrap and fire the furnace well it starts to smoke and I figure it is the zinc being burnt off and take a look there are some white flames in the crucible and start to think magnesium well the metal is molten and you are a bit in panic mode so I pulled the crucible and made the pour without even thinking about skimming! Now the mold is round and the pattern is square and it ruptures on the side so this is what I got one side totally wasted the other is not that bad and if I skimed it could be useful although the bottom half does dip in the middle it would be machinable but next time I will try it with some thin wall tubing or brass wire to keep it`s structure intact. I`m heading off on holidays tomorow and will take my puter with me so I will try again in two weeks with the addition of a pla plastic mold to compare with. So test one was a cluster F..k test two has to be better I just have to remember `you can`t put a square peg in a round hole! :D
Oh and the casting looked more silver than brass if that means anything to you.
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