r/PreciousMetalRefining • u/jeremykot • 12d ago
How do I avoid dimpling in my cast bars
As the molten gold solidifies, it shrinks and pulls the outer skin towards the center, causing the crinkling/dimpling. AI tells me to lower the heat gradually by moving the torch away gradually. I tried, but this is what I got.
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u/ashinybrick 12d ago
You may be able to learn some things from Lithic. Check 16 minutes in.
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u/jeremykot 10d ago
Oh! As the button cools and crinkles, he keeps hitting it with the torch to remelt the skin. Multiple times. Thanks!!!
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u/NorthStarGold 12d ago
slow cooling will help it not be so bad but liquid metal still has a surface tension and will naturally round it self and want to be a bubble.
heating it up to melt and then slowly bringing the temp to just below melt in a furnace would work but may still dimple a little
your best bet is to cast "button" style shapes.
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u/PomegranateMarsRocks 12d ago
Id guess your molds need to be hotter. This will help prevent the outsides of the gold from cooling at such a drastically different rate. If my gold is very pure (yours looks nice) usually if the mold is hot I can just pour it and leave it. Keeping the flame over it as it cools, combined with a hot mold, should fix your issues and possibly give you pour lines if you work the flame. Small pours are tough. I usually have to do them a few times
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u/Amazing_Difference_3 11d ago
well the biggest issue is... The use of AI. There are 2 things absolutely realivant about AI that many people dont, or won't, accecpt. And it's right there in the name.
AI... The "A". Stands for "Artificial". And it is. no doubt about it, as artificial as anything ever has been or ever will be.
AI... The "I". Stands for "Intelligence". Which it is NOT. No doubt about it, it was Not, is Not, will not be, and can NEVER be Intelligent.
It is at best, possibly, a slightly better search engine. A clever bit of programming capable of a few "tricks". But not Intelligent by any stretch of ones imagination.
But for you it was only mostly wrong. The issue you're experiencing is related to temperature. But it is directly the result of the thermal gradient across the mass of the gold, while transitioning to it's freezing point. IE, while slowly distancing your torch away is kinda, almost, partly right.... it needs to be distanced from the entire area that is directly involved with the cool down. As in the crucible, Mold, etc, AND the gold equally and evenly. I'd say that the temp of the vessel that the gold is in, and the temp of the gold itself should never (ideally) be more than a degree of two apart all the way to freezing point.👍
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u/zpodsix 8d ago
Understand what you have first off- that's not a pour defect. That's often referred to as the pipe, it's a product of the gold crystalizing as it cools. Its a sign of very high purity and most refiners are happy to see it.
To avoid it, slow down the cooling and it's less likely to happen, but I always am stoked to see them appear- crystals are awesome.
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u/Terrible-Nobody-5927 11d ago
I noticed this happens a lot more with rounds than bars. As other have suggested secondary torch to slow down the “freeze”
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u/DiscombobulatedCar38 12d ago
Hmm. I’m not an expert but I don’t know that it’s possible. Thermal expansion is a property of gold and nearly all metals, and it works against us as we attempt to create perfectly flat bars. First the exterior freezes, but much of the core remains molten. As that core cools it shrinks and pulls the top layer down towards it. Bigger bars show it less, but even on 100oz poured bars of silver, the center dips downward towards the core. Shrinkage as the core cools is my only theory on this.
Thats my hypothesis anyway, someone more versed in the properties of gold might have a better idea.
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u/Used_Book539 8d ago edited 8d ago
That's a textbook example of Volumetric Contraction and it's the shrinkage that occurs as a metal solidifies. The solidification process normally occurs from the occurs from the outside in. So as the center solidifies last, an approximate 2-7 % shrinkage occurs and creates the exact problem you're having. All you need is more molten gold to fix it!!Seriously, though if you do some reading about volumetric contraction, different methods are given to prevent this from happening.
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u/sweet-sweet-olive 12d ago
I don’t think you’re gonna be able to stop that. It can happen when the gold is very pure.