Tom, Ironman, thank you.
Ironman, to answer your question:
1.) I made a new pattern, reversing the draft, so I could place a riser on the non-channeled side. I could not put a riser on the old pattern because it would mess up the channel. Previously the riser was beside the pattern -- the only place it could be with the pattern draft the way it was oriented.
By altering the draft orientation and placing the riser on top of the pattern, any buoyant slag could go up the riser rather than get trapped in the channel section of the casting. Also the channel section now faced downwards, so it would naturally be protected.
While these changes would help deal with any slag in the mold, I have been on a concerted effort to eliminate slag coming into it in the first place. So:
2.) I altered my melt method to add iron later in the furnace cycle -- after the crucible and furnace walls had reached a red heat. My furnace has more mass than a blanket insulation furnace, so it has a longer warm up period. There is no reason to put iron in during this period and allow it to oxidize. I started with an empty crucible.
And to save fuel, there is no reason to run the warm-up at full throttle. 1/4 throttle works fine to bring the furnace walls and crucible to red heat. Time is more important than burner temperature for this. Once it is at red heat, metal can be added, and the furnace run at full throttle. At this point the furnace will melt at an average rate of 1 pound per 5 minutes. Gradually accelerating to 1 pound per 3 minutes.
3.) I gave it a longer post melt heating period to try to get the pouring temperature as high as I had patience for. That was about 15 minutes after all the iron was melted. I wanted any slag to come to the top and amalgamate, and for the casting to be fluid enough to give any slag time to come up the riser.
4.) I altered the mix ratio of the flame -- I had been running slightly richer on previous melts -- I went almost neutral -- ie. a couple almost imperceptible whisps of black smoke from the lid edges (not the glory hole). I believe this created hotter furnace temps.
5.) I increased the pressure of the burner to 60 PSI. This burner is an atomizing burner. There are two air sources, the blower (a vacuum cleaner) and the atomizing air nozzle fed by a compressor. That last one is what was increased to 60 PSI. This fed more fuel at a smaller droplet size. The flame was naturally bigger.
6.) The new better quality larger capacity crucible did not add slag to the melt, and its larger size (with more metal) retained heat better when bringing to the pour.
In other words, a lot of variables were adjusted. Apparently for the positive.
