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Silver Casting Failures


#1

Greetings,

I have recently purchased a Neutec J2R casting machine and have begun doing some test castings to begin the process of dialing in my routine and settings. I used injected wax designs from my vulcanized mold cutting practice which I am learning (I am improving). I used epoxy to attach the brass gate before making the rubber mold (that is why there is a hefty blob where the gate attaches to the ring). I will solder the gates on my ‘good’ models in the future.

Nearly all ring designs cast completely which is the good news. Once I clipped and pickled the rings, I put them on a ring stretcher and stretched them 2+ sizes to expose any weak spots. More than half of them (most even before stretching) had a visible crack/split in the shank at or close to the gate location. See the photos.

Here are my casting stats:

Investment: Satincast 20
Metal: all scrap sterling including some coin silver (maybe as much as 50%)
Burnout schedule: 12 hour (max 1350 f.)
Flask temp at casting: 975 f. (after 2 hour soak)
SIlver casting temp: 1785 f.

I applied the vacuum to the flask for about 4 minutes before casting/pouring
I removed the flask from the casting chamber about 3 minutes after pouring
Quenched 8-10 minutes after casting.

I understand that these failures are an essential part of the learning process and would greatly appreciate the benefit of your experience. 1. What is happening? 2. How can I modify my process to correct it? Thank you for any ideas you may have.

-Steve Mitman
S20180811_012S20180811_011S20180811_010S20180811_008S20180811_014S20180811_009S20180811_013


#2

Hi Steve,

Congratulations on your studio equipment addition. I think that your shank fracturing is from the mass of the epoxy blob itself. It appears to be making a mini button and pulling metal away from the design area. You might want to try a longer sprue attachment to the tree… maybe another 1/4+ - 1/2". The epoxy is good for creating a smooth transition with a meniscus (raised lip) that a straight silver butt joint would not provide. With that you might get turbulence.

The epoxy, though messy isn’t necessarily the culprit. I use JB Weld more regularly than I should admit. It is possible to lightly file or trim gloppy areas. I’m a tooth pick master adding little bits of epoxy at a time. I never dip the end into epoxy. Instead of using the brass nipple rod inserts… I procured a good 5lb supply of thick copper wire that has the same diameter. It was from some monstrous industrial wiring cable that probably came from a power plant. I cut, file and build nifty branch structures for free flowing sprues which i need for my designs. A single sprue won’t do. The 400F visualizing temp makes them way to remove.

Eileen


#3

Hi Eileen, thanks for your response.

Your idea makes perfect sense to me.

So you recommend that I can still use JB Weld but apply/sculpt a nice fillet transition to the shank without the blobby reservoir (yes, I was dipping into the epoxy directly!). Is the additional sprue length to help eliminate any chance of the main tree sprue (tree trunk?!) can pull metal from the piece as it solidifies? Thank you again.

Mit


#4

I have had the same problem for the last several years after casting successfully for 30 years. Checked all temps, investment mixtures, everything I could think of. I often use 2 sprues on heavy pieces but wax blobs at the sprue base made no difference. The only real change was using a new programable kiln and actually moving to a new house (studio). After trying many changes the only thing that made any difference was raising my casting temp to 1000 degrees and not building really big trees. I asked the casters at a Stuller casting workshop and their answer was " we have failures too". So I am also interested in any feedback.


#5

Steve, that’s my thought. You have made a button of sorts which is causing the shrinkage right where you don’t need it.

If you send your email I can send some pictures of what I mean as far as writable series. I’m making up some today for molds of a short custom production run. The jb weld has a respected place in my “toolbox”.

Eileen


#6

From the photos, looks like crystallization induced brittleness. Once cast, the large tree structure acts as a heat conductor which prevents proper quenching, leading to crystal formation and brittleness.

So, you can try annealing after casting and removal from the tree.


#7

Before purchasing the J2R, I assume you have been casting the exact same silver scrap using other methods and have not had problems?

There are a lot of variables here based on your description that could affect the characteristics of the metal.

  1. What does it do when you anneal the ring and then stretch it? (like Mark suggested)
  2. If you cut and file off the blob from the gate then stretch, does it behave the same way?

I wouldn’t think you can stretch as cast ring two sizes up from the inside without it breaking somewhere.


#8

I think the metal is to hot. I pour silver at 1730F It looks like a hot tear.


#9

As Eileen stated earlier, the sprue gates between the pieces and the main sprue appear to be a bit too small. I would recommend increasing the length around 1/4" - 1/2" longer than they are.

Does the inside of the tear appear to have a crystalline surface, or is it similar to the rest of the cast surface?

Scott Bradford
Rio Grande Tech Team


#10

S20180817_002S20180817_004S20180817_003Eileen, Mark, Arkay, linusd and Scott, Thank you all for your feedback!

I have included a few new USB microscope images of the inside a few of the cracks, which do appear to be crystalline or rough at least. For my next (few) casts I will try the following:

  • Increase the length of the gates to the designs by ¼-½” Although it puts me closer to the sides of the flask, maybe I’ll just increase the angle of the tree ‘branches’.
  • Eliminate the epoxy blob on the wax mold. I’ll use a toothpick to carefully apply epoxy and create a fillet at the transition to the model.
  • I’ll anneal the casts after removal from the tree before stretching/testing with the next batch
  • Reduce my silver casting temp to 1730 f.

Thank you again. In a few weeks, I’ll post an update.

-Mit


#11

Good luck, Steve.

Thanks for posting. I’ve learned alot from the other posted responses to your dilemma.

Eileen


#12

Mostly good advice, but the first thing I’d do is use fresh metal. By using scrap sterling and coin silver you are likely introducing contaminants.


#13

Contaminated silver is an enemy!

I have almost 500 grams (1/2kilo) of silver to refine. My caster said if I use any of this stuff I’d have pinholes everywhere!
When I’m preparing demo-rings pinhole and brittle claws are not wanted.

Moral of this posting, refine & clean your metal!
Please go to:

gerrysdiamondsettingessays.blogspot.ca

I’m Gerry, On my iPhone!