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Is this a possible reason for flashings during casting?

Hello Orchid members!

So I have recently changed my casting set up and of course problems have arisen.
I now have a larger kiln where I am able to put over 14 flasks in, whereas before I was only able to burnout 7 flasks at a time.

I am now getting flashing on pieces which I have previously casted many times with my old setup. Not all flasks are showing this, but there are always a few flasks out of the 14 which have this problem.
I am using the same investment (Optima Prestige) and the same burnout programme and same casting temps. Everything is the same apart from the number of flasks fitting in my kiln.

Can this be the problem? Does the initial dry out need to be longer with this many flasks in the kiln? I can image there being much more moisture in the a small chamber for it to all dry up in the same amount of time over 1hour. Can’t find any info regarding this.
Should I have it ramp to 150c over 2,3 or 4hours?
Btw I let my flasks sit for 2-3hours before putting them in the kiln and I mix my investment all within the guidelines.

All the info out there regarding this saying “your flask temp is too high” or “your metal temp is too high”.I have tried lowering both, but I just don’t see it making a difference. As I mentioned 4 out of 14 flasks show a problem. I believe the cracks arise in the flasks prior to casting.

I am casting again next week, so any advice would be great…
Has anyone had similar problems?

Thanks

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Do the pieces that you cast have flat areas that have sharp edges? Like say a flat toped signet ring? If so those pieces should be slightly tipped. Castings love to flash along vertical and horizontal edges.

Thanks for the info, but no flat edges. Irregular shapes. They casted many times before without any flashing issues.

It sounds like it is something related to the new kiln. The first thing that comes to mind is loading. We’re you loading in a circular pattern and now you are more square? Idealy the flasks are all the same size and the same distance from an element. As you mix up the flask sizes loading becomes more of an art.

If you have not solved your problem…
Some Common causes of flashing…

  1. A rise in flask temperature that causes creation of steam, weakening of investment and subsequent cracks
  2. Wax/plastic pattern material that expands too fast.
  3. Water ratio
  4. Bad investment lot

I have found that many jewelers who cast would benefit from understanding the techniques used by dental labs. :sunglasses:

If you have not already reviewed the extensive knowledge base this is the Santa Fe Symposium papers … search here
https://www.santafesymposium.org/papers

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Thank you of your input. I believe it to be the new kiln, it’s burnout or the fact that there are more flasks now in it. There was no sign of the flasks with the flashing being related to where they were placed in the oven. I usually always place the larger flasks at the back of the oven so they soak at the casting temp longer by the time I get to them.
Found this on SRS’s website. Even though I use Optima Prestige I am still going to try prolonging the first stage of the burnout.

SRS troubleshooting instructions:
Incorrect burnout cycle

  • Ensure furnace ramp does NOT exceed 250ºC/Hr
  • Ensure 1st stage burnout does NOT exceed 220ºC and is held for 4.5 hours minimum.
  • If problem still occurs increase hold time.

Thanks.
I will try a longer burnout and see what happens. The investment was new. I have been going through a bag every 2-3 weeks. I have been using 39:100 but will now try 38:100. We’ll see what happens.