Hello I am new here and new to lost wax casting. I wondered if anyone could give me advice on how to sprue a Bracelet. I have tried with no success. Any help would be greatly appreciate.
I think there are 2 issues. One is you aren't giving the air a place to go. So the metal goes down the main sprue and up the sides but then also spills over from the top and that pocket of air has no place to go. If you change the spruing so the 2 parts at the top do not connect to the main sprue but instead connect higher up to the top of the pouring cone I think you'll have much better luck. The other issue, depending on how you are pouring this thing, is that you might not have enough head pressure to force the metal up the sides. This could be fixed with a taller main sprue which provides more pressure that will force the metal up the bands. What setup are you using to pour this? Gravity only? Sponge/steam pressure? Vacuum assist? Centrifugal casting? Also those bubbles on the back can be fixed by vibrating the investment as you pour it in slowly.
Hi thank for the reply. I’m using a vacuum table. I thought about the trapped air but for some reason because I was using vacuum I didn’t think I needed Any kind of air chase. Do you think 4mm sprues would work for the trapped air? I did have the model only about 1/2” from the top. I used the same size sprue for all 3 connections. I didn’t really have a main sprue all 3 went to the cone. I was making it for a present big fat fail.. lol thanks again
I'm less familiar with vacuum assist and how much you can get away with when using it. But the same idea should hold for vacuum assist and regular casting. If for whatever reason the air didn't get out the way it would build up in that location and cause a defect like we are seeing. I'd eliminate that possibility before trying other things. A 4 mm vent would be fine. It just needs to be a small passage to let the air out. Looking at the thickness of the bracelet it might be a good idea to make the main central sprue bigger. If your piece fills up too slowly because of a bottle neck in the main sprue then the metal will cool and not be liquid enough to travel up the sides. This leaves rounded off ends like what you see in your piece. So this may be another beneficial change to make on try number 2.
Hi Silver.just did investment, it’s going in the kiln tonight. I put them just past the edge of the Cone so they should not get filled when I pour. My cast temp was 875 last time. I was thinking 950 this time, you think 1100 is better For silver? Thanks
That looks good. I expect it should work well. Got a photo of your vac setup? With that perforated flask, please tell me you can suck on the whole thing and not just setting it on some vac table...
Spruing is much better now. I agree it should cast correctly this time. Jason is right about the suction part. You need to be sure it has a good suction going on it. I suspect it probably does since you got good detail on the face of the first casting but it couldn't suck out all that trapped air before it cooled too much. If you're using SRS silk investment then the temp of flask should be 750-840f for silver.
Zap we have cheapy vac tables so we only run solid flasks. That's a good chart. I thought he was running gold, my laptop makes his second photo at the top look yellow. Zap have you seen the cheapy method David does with the perf flasks? Maybe he can post a photo of his pipe with a flask sitting in it. It's a good system and he did it on the cheap. I bet others here would like to see it too.
Ofc I want to see it lol David... oh David.... I still like my centrifugal casting. Nothing like shitting bricks as 1900f molten metal spins around in a high speed circle.
I’ll know If it work around 10am and yes the flask drop in to a chamber. I get -25 I think. built it Awhile back ,I will post some pics tomorrow . I used silk last time, this time I’m using r&r ultravest with bandust. .
Hmm. We eliminated the trapped air issue and the head pressure issue but still not casting. I think there are 2 options you can do from here. One is to have the exact same sprue pattern you had except add a small sprue from the main sprue to the tip of each band. That way when the bottom fills up the main sprue will feed the tip of the band and hopefully the metal will merge together in the area where the defect is. I think what is happening here is the metal is cooling by the time it makes it all the way to the narrow tiny section of the band and solidifying before it makes it all the way to the tip. There isn't enough heat in it to finish the casting. Also if you look at how the flask is positioned inside the vacuum chamber the central portion where the tip of the bands are is the farthest from the vacuum. So the vacuum has to suck air and metal out through 2 inches of material at the part of the casting that is the most thin and difficult to pour. I think the second option that would solve a lot of this is to lay the bracelet in its side instead of upright. Have the main sprue still feed it at the back but then split off another 2 main sprues, one to each of the tips. That way you'll have an equal distance to all parts of the band and the vacuum, and you'll be feeding the thinnest part of the band first with hot fluid metal before it solidifies. You'll also have higher head pressure due to the difference in height which will help force metal further and you'll eliminate having to do air risers. Also, after you upload a picture there's an option at the bottom just under the thumbnail that says full image. If you click that it embeds the picture in the post and we don't have to click on thumbnails and close them and reopen next image.
How does thing not have two titties off that cup where you had the vents? I think you are pouring too slowly. Vacuum on, mold hot, metal hot, DUMP fast. You have to move real quick. It's not much metal and cools real quick. Can you video your next attempt? Give someone your cell phone and tell them to hold it in landscape and video it.
Thanks for the advise guys. I will think on it. So close, one side filled all the way. The other 3/8” short. If I made the main sprue even longer would that create even more head pressure? I’m thinking about option 2. I think I’m pouring it pretty fast,just kinda dumping it in one motion. I can try going even faster I guess.
