We recently have casted a couple trees that keep coming out with the same casting defect and I was hoping to tap into the Ganoksin community to narrow down possible causes.
I’ll put some photos below, but the issue is small streaks/lines appearing after casting. These aren’t visible on the wax injections, so it is somewhere between investing, burnout, casting, and quenching. My guess is something going off during the investment process.
We have been using this process below before and it has come out fine, but these are chunkier rings than we normally cast. Also, it seems in general the surface is rougher than it was coming out before.
Details of our setup:
Using a Neusprue for the trees and riace wax for the injections
Using a vacuum investment mixer
Prestige Sigma investment powder (using sigma recommended powder:water ratio
Bench cure flask for 2 hours
Steam dewax for 1.5 hours
Burnout following Prestige Sigma recommendations (photo below)
Vacuum Cast brass at 1020 C with flask at 650 C (as per alloy recommendations)
Reminds me of flashing, but only the beginning of it. I would try increasing your bench cure time to 3 hours instead of 2, and lowering your flask temperature. You can also try increasing your investment ratio a bit.
I cast my silver at 1010 and my flask is at 530, 120 degrees lower than yours but the metal is only 10 degrees cooler. Basically you want the flask to only be so hot that you don’t get frozen fills. And you want the metal just hot enough that it fills completely then freezes. With thicker designs you can lower temperatures.
Those are water trails. They happen after the investment is poured into the flask but before it sets. I’ve noticed them when there was too much water for the amount of powder, or when they weren’t mixed thoroughly enough. Excess water makes its way up the sides of the models on its way to the top of the mold. Try a thicker mix, and mix it more before pouring.
What Awebry said. I showed this to my husband who is the expert in casting in our studio. He looked at the photos and immediately said “The investment is too thin.”
Definitely water trails. To completely eliminate the investment problems due to incorrect ratios , we use a food processing digital scale that does Grams, Kilo’s and Pounds. DSW-100 Portion Scale with Single LCD Display ($145 Amazon) . The water and investment is weighed in Grams. This scale will handle up to 60 lbs accurately. The Spring scales that are sold to the Jewelry trade are often inacurate as the springs lose their strength.
Be sure to keep things working during your whole 8 mins working time. Mixing vacuuming, pouring. Don’t finish these things early before the investment is close to setting. If The investment sits very long without mixing the water will separate and run down the side.
Hi Kyle, not sure if you ever solved these issues (I’m hoping so since your last post was almost 6 months). I’ll share what I think might be going on and you let me know if it rings true or not.
The streaking is almost certainly water marking. Here are the common reasons behind it and remedies:
Cause
Remedy
Incorrect powder/water ratio (too much water)
Use correct amount of water (less than currently using) especially in vacuum investing machines
Work time of investment not used up
Ensure the work time is used up and the slurry temperature is 20 - 30 degrees C
Investment powder expired (too old)
Do not use investment past expiration. Best practice is to use investment within 3 months of opening
That being said, I notice on a couple of your rings that there are bubbles attached to the surfaces. This indicates that either your slurry is thick enough already, or that you’re not pulling a proper vacuum with your investment machine.
A few recommendations to help troubleshoot:
Bench cure for an additional hour. You can even leave the flasks in the investment machine instead of moving them. That way, you know they haven’t been disturbed during curing.
Skip the steam dewaxing and dewax directly in the kiln. If you have a tray you can place under the flasks to catch the wax, that would be best. This will at least remove the steam dewaxer as a factor for your defects. You can also try and shorten the dewaxing time by 30 minutes.
Extend that ramp time of 150C to 370C by an additional hour. That slower ramp can help with the thermal transition.
Your casting temps seem high for both your metal and flask, but it’s hard to say w/o knowing what alloy your casting.
Regarding the porosity, start with sprue size. Those signets should be sprued right on the top (thickest part) and with a larger diameter sprue, and as short of a sprue as possible.
Important Questions to Answer:
What alloy are you using?
What flask size are you using and is it perforated?
What wax are you using?
How are you measuring/weighing your investment and water?
