Troubleshooting...'gas' or 'temperature'
Sometimes we chase our tails trying to fix a problem that hasn't been properly identified. "Ask me about hard ingots!" . . . :bigsmyl2:
These 4 on the left have 'gas' problems...from oil or something in the mould that didn't get cleaned out. Those indentations don't have hard edges around the imperfections. They look like the mould is raised in that area because the Pb is seamless all around the divot, (gassing bubble) and in some cases, if it is a long smear of oil (or whatever) it will run up or across in an irregular shape...but the edges look seamless. It will keep showing up in the same area of the same mould cavity from cast to cast. The first, third and fourth from the left I believe came from the same cavity.
Attachment 194628
The casts on the right show 'temperature' problems and hard edges from where the Pb hit that area of the mould and froze and as the cavity filled the Pb came to the edges of the frozen metal and joined up tight showing the hard edges.
I think sometimes when the mould is running 'borderline' hot enough, if we don't get the Pb in the center of the sprue hole it will ricochet off the sprue and loose heat there and when it hits the side of the cavity it freezes. That's why I try hard to hit the center of that sprue with the bottom pour pot and run that stream as fast as the pot will deliver.
I wish I had better examples to show but those end up in the pot again.