Over the years I have had the occasional casting investment failure,
almost always on pieces with flat surfaces more than half an inch wide and
more than an inch long. What typically happens is a flake of investment
spalls off the surface and the metal encapsulates the flake. It hardly
happens at all on curved surfaces, smaller or perforated designs.
Let me be clear, this is not something that happens often. I do enough
casting that I run through 1,000 lbs of Satincast-20 in a year.
So earlier this week I had a job to make a 14K bracelet, .75 inches wide,
cast in two pieces 3.5 inches long. I will spare you the play-by-play, but
in all 5 out of 6 attempts to cast the piece failed as described above
using Satincast-20. I solved the problem by using R&R Plasticast for the
final, successful casting.
Something that usually happens about 1% of the time, or less, suddenly has
happened 83% in one week! I switched to a new package of investment after
the first failure.
My guess Steven (and that’s all it is) is old investment. It could also be that the water or investment is too cold, a really sneaky problem I used to have at the beginning of every winter.
I switched to R&R many years ago and really like the results. Not to say anything bad about Kerr, but I have more consistency with R&R. I use both Ultra Vest and Ultra Vest Max. The Max works great with white gold alloys especially and is much more tolerant of timing errors in the mixing and vacuuming. I use a 14 hour burnout schedule with a 2.3 degrees per minute max climb rate (1.5 on the trip from 700 to 1300) and set the max temp on burnout for two hours at 1300 for both investment types and that also seems to help with consistency. I also started using centrifugal exclusively about ten years back. For some reason unknown to me, the combination pretty much stopped spalling.
Now that I’ve said that, watch what happens on my next casting.
Isn’t that the way of it though? It’s kind of like white gold watches. I’ll go six months and not see one, then in three days we’ll take in four. Go figure…
You could also try biting on your tongue on the other side of your mouth, putting a green rubber band on your left wrist and unbuttoning the third button from the top on your shirt.
'This is easy to fix, as I am sure you have found out, casting problems can often be a combination if smaller issues that collect together to create a failure
Simply reduce the powder water ratio to 38/100 for R&R ultravest and Let it bench sit for 4 hrs before starting the burnout and mix for 4-5 minutes, these steps should solve the problem
Other things to check
make sure the temperature of the slurry is 72F
Use deonized water if possible
Make sure the burnout is not too fast
Use RR investment
best of luck
Geofffey Pyle
Arttech Casting CO
800-418-9970