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.