18k Yellow gold casting with cracks but rest of piece is solidify

Jewelry Discussion
1

Hello everyone. I am still having cracking problems with 18k Yellow gold casting.

Problems: multiple cracked lines but rest of piece is solidify and flexible.

Tree would consist of 90pc of jewelry , thick items on top and thin on bottom . Sprue shouldn’t be a problem because 18k white would come out with success. I don’t believe its contaminated alloy problem because 70% items are cracking and 30% good with gold flexibility all mixed on different areas of the tree.

18k white, 14k white& yellow, silver casting successful.

My casting spec 18k Yellow:

-using a closed vacuum & pressure casting machine with Argon gas.

-mold wax injection

-3 x 7 inch tree , mixed with men ring (top) , earrings, pendants

-1200F Flask

-cast with pure 99.99kt and 18k yellow alloy

  • purchased alloy and homemade alloy with same outcome.

-Vacuum - 30hg 4min

-Pressure -2.5kg 15 seconds

-Have tried quenched after 10min / No quenching with same results

-air cooled 1hr with same cracked results

-our thermocouple type K keeps burning out so we just eyeball our gold melting temperature and press pour

Inspecting the tree after cool down with our microscope and it looks like the cracked lines are SHINY , so I’m assuming it cracked after cool down.

Not sure if my temperature , vacuum , or pressure is off . Please help me.

Thank you.

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2

You’ve got a good mystery here! I can’t help but think there’s something wrong with your alloy, but that’s just intuition. But you did say that you think your alloy is good, so that’s probably not it?

I think your flask temp is too high. Try dropping it down to 900F. Also, you said you tried this, but for sure while you’re sorting this out, let your flask completely cool before digging out your castings. 18 kt is prone to thermal cracking by quenching too hot.

Your thermocouple is down, so you’re winging it with metal pouring temp. It could be that your metal is way too hot.

I’m a big believer in trial and error experiments. Rather than casting a tree of multiple waxes, cast one object at a time and try different things.

Let’s see what others say. Like I said, you’ve got a good mystery here!

Jeff