Poured bars - radial flow lines

CuKevin

I am curious as to why poured bars exhibit radial flow lines? I’ve not seen these bars poured firsthand, but I am assuming the mold is filled rapidly and then allowed to cool slowly. Perhaps this is not the case?

Thanks for any insight!

CaptHenway

Never thought about it. Are you sure that the radial lines are not on the mold from when it was ground out?

CuKevin

@CaptHenway said:
Never thought about it. Are you sure that the radial lines are not on the mold from when it was ground out?

I’m not sure. I assumed the pour lines were on the top of the bar, not the section facing the mold.

idratherbgardening

The pour lines are on the top of the mold and I think they form from the silver being poured out at the right speed to cool into rings. Modern backyard pourers do it on purpose.

Jinx86

@idratherbgardening said:
The pour lines are on the top of the mold and I think they form from the silver being poured out at the right speed to cool into rings. Modern backyard pourers do it on purpose.

That and it helps to tap the mould as its cooling.

ricko

When we melted reclaimed gold into bars (a previous business that did a lot of plating) we never had those lines.... it would cool into a depression in the center, but no lines. So I have also been curious about these on bars shown here... could be movement during cooling... Cheers, RickO

1630Boston

@Jinx86 said:

@idratherbgardening said:
The pour lines are on the top of the mold and I think they form from the silver being poured out at the right speed to cool into rings. Modern backyard pourers do it on purpose.

That and it helps to tap the mould as its cooling.

Pour and tap at 4:30.

https://youtu.be/eBeeqGV0Eg8

CuKevin

Thank you for posting the video.
He does not seem to be taking special care to pour slowly and it still results in many of those radial lines.

1630Boston

Could be a combination of 'tapping' the mold and heating the surface with the torch. Differential temperatures in material can do strange things
@cukevin
You can see that he is heating the center of the mass so that the edges cool more quickly.

MsMorrisine

Could it be from multiple pours into the mould?

I also think it could be from uneven cooling but am unsure how it would happen.

Jinx86

To pour in graphite moulds it is important to preheat them. The graphite otherwise can be saturated with moisture from the air. That small amount of moisture can erupt when the extreme heat is introduced. Just like using a cutting torch over a cement floor. So the torch he is using is for heating the mould and to help slow the cooling of the material. The torch he is using would have no real effect on the the silver staying molten as it is far too cold of a flame for that. The torch also helps prevent the surface of the bar from caving in as it cools, giving it a much more pleasing look.