I experienced disintegrating boolits yesterday. I was cycling my automated Master Caster with 45 caliber boolits. When things happen automatically, you gotta figure out a way to inspect your product. This particular mold is challenging as it's a dual cavity design. The weights differ, so ensuring your pour is generous on the smaller cavity is crucial to fill out the base of the larger cavity. I had stopped to inspect the boolits. I didn't see any deformity so I resumed. At some point I recognized lead particles spewing in several directions upon the carrier opening, instead of boolits dropping down into the bucket. I stopped the machine.
Temperature, low 700s. Under 750 for sure. Remember, it's automated so cooling time is fixed. Manually, this has never happened. My hunch is that the core temperature of the mold increased beyond a typical temperature to cool the boolit in that timeframe. 452 size is an interesting size for a Magma in that it's the greatest diameter permitted for a 2 cavity mold. Does that chamber size play a role in possible overheating in a Magma sizes mold? And is there a temperature at which an iron mold becomes difficult to cool from simply the surrounding air?
Remember, the machine's pour, and dropping of boolits, is automated so I couldn't just let it sit in a post-pour, pre-drop position.
My design has a "Big Boolit" feature and Hatch recently advised how to get a little more flexibility out of it. I was able to run this mold with that feature enabled. Basically it enhanced the cooling time--probably 'bout 50% more time. Although the boolits cast were atrocious(previous issue resulted in lead splatter on face of mold), they didn't fly apart when the mold carrier opened. I'm confident in future casting with this mold as long as I extend the cooling time.
However, I'm still baffled about it all. One unique feature of my automated Master Caster, and some others, is that the fan is inoperable. Or, it doesn't serve a purpose, as the mold doesn't remain under the direction of the fan. The mold carrier is either in the lead pour position or it is extended in the open position to release the boolits.
When casting by hand, I'd always allow a mid step to the throw. This intermediary position allowed the fan to blow on the sprue. It was an indicator, for me anyway, when to pull down completely. Once the shine of the sprue was gone and it hardened, I'd pull the handle. At that time, I never really thought about the temperature of the mold, and whether this step allowed the mold to maintain a equilibrium temperature.
i just thought of it as cooling the sprue.
There are members who have automated their Master Casters and have designed them in such a way as to retain this mid point in the cycle. I know this only through videos posted on this board. Though I'm running a Hatch design, and am pleased with it, I wonder why others have chosen a more complex automated cycle. Not clear whether they may have experienced specific issues with the original design or simply wanted to mimic the manual movement. As down-up-down seems more complicated from a control standpoint, I do wonder about their motivation. In general, ya try to make things as simplified as possible. There's gotta be a reason why others have chosen a different method. This role of the fan is intriguing to me. In retrospect, I wish I had a way of knowing the temperature of that 45 mold when the issue occurred. If I could compare it to other successful cycles, it would provide some correlation.
The issue of boolits falling apart as I mentioned above has not occurred with casting of any other sizes. I have cast larger;however, those molds are single cavity and require the respective orifice plate.