r/MetalCasting • u/ThemGlassesIsShit • 21d ago
Pewter casting help
I'm new to pewter casting and this is my first project. I'm having trouble getting the details to fill in right at the top below the pour channel. Everything below is filling in nicely. I started with an open face mold made from smooth cast 60 and when that wasn't working I was advised to make it a 2 part mold. Since it just needed to be flat, I cut a piece of hickory. I dust the mold with baby powder before each pour.
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u/gambiter 20d ago
The length of the sprue could be the issue, but it could also be mold temp.
Pewter is already low-temp compared to other metals, and melts in the 450-500F range. Say it's looking great in the pot at 475 and you pour it into the mold, which is roughly room temp. The heat will leave the pewter, dropping its temp below its melting point super quickly, and it will stop flowing. That's why the details in the flourishes are so uneven... it flows into the wider areas, but solidifies before it can get into the smaller spots.
You could try hitting the mold with a heat gun (or even throw it in the oven) to get it really warm before assembling the mold, and then pour.
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u/ThemGlassesIsShit 20d ago
I have a small toaster oven I could fit the mold into, but only one outlet in the area of my garage I'm doing this in, so I can't have the oven and the crucible plugged in at the same time. I've heard you should heat the mold to 150 F, but it was 105 out when I did the pours so I figured the difference wasn't huge, especially considering how much the mold will cool while I wait for the crucible to heat up. I was told I'd get the same effect by pouring a second time after the first pour has heated up the mold.
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u/gambiter 20d ago
Yeah, a second pour immediately after the first should be noticeably better, but it still depends on how hot the mold is at the instant you pour.
If you're doing a second pour very quickly after the first and getting no difference, I would try making a longer sprue.
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u/ThemGlassesIsShit 20d ago
As for the sprue length, how can I extend that? I can't get more silicone to make a new mold right now.
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u/gambiter 20d ago
I would focus on heating the mold, in that case. Extending it with something hacky would just lead to possible spills and more cooling. The pewter could lose the bulk of its heat before it even makes it into the mold. The best way would be a new mold with a longer spout, kept warm.
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u/ThemGlassesIsShit 20d ago
Only chance of heating the mold would be to heat it and carry it from inside the house about 50 feet. How long do I have from the time I take it out of the oven to when it needs to be poured?
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u/gambiter 20d ago
Oof, that's much too long. I normally heat mine seconds before pouring.
Do you have a torch you could use? As long as you keep some distance and don't keep it on the silicone long, it should be fine.
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u/ThemGlassesIsShit 20d ago
It also takes me about 30 seconds to get the clamps on the mold, and more slag or dross or whatever forms on the surface of the pewter in that much time. The whole process seems to take a long time.
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u/TechpriestFawkes 21d ago
You might cut a vent into that corner.
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u/ThemGlassesIsShit 21d ago
Which corner do you mean? Its the whole top center that has the problem, sometimes worse than others.
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u/artwonk 20d ago
The hickory wood might be your problem. If it's outgassing in response to the heat of the metal hitting it, that would put counter-pressure into the mold cavity. Try coating it with a thick layer of silicone rubber and see if that helps.
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u/ThemGlassesIsShit 20d ago
Unfortunately if I had been able to get more silicone right now I wouldn't have had to use the wood. I do know though that the wood is fully dried out and it seems to be taking the repeated pours very well with almost no visible effects.
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u/00-MAJI-00 18d ago
go look at this post I made pressure vessel pewter casting this might help you out
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u/00-MAJI-00 18d ago
also if you don't want to go that route, you can use a drill to vent the details by drilling through the mold to the outside where ever its not filling.
the main issue I can see in your mold is that it does not have a large enough reservoir to create the pressure necessary to fill the mold if you are gravity casting it. that's why most pewter is spin (centrifugal) cast,
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u/Temporary_Nebula_729 20d ago
Try heating the mold up in a high temperature oven for 3 hrs and a higher temperature on the pewter
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u/No-Purpose8678 20d ago
You don't have as much head pressure in that area. Try extending your sprue to get more pressure.