Got a problem I need your help with. I have a Lee Pro 4-20 bottom pour pot. When it works it works great. I smelt ingots and wheel weights in a Lyman Big Dipper. I do not mix COWW and SOWW. I assume the ingots from others are marked correctly. The process I use is a two step process = First the Lyman to melt the wheel weights then the Lee bottom pour to make bullets. Ingots are assumed to already have had the melting and fluxing process completed. In the Lyman I flux them with pine sawdust. I've run across about 20 pounds of ingots poured by someone else marked PB into Lyman 1# ingot molds that have left a coating on my Lee Pro 4-20. It also stopped up the bottom pour valve. It seems to have a brown, rusty interior that, when hot, is almost sticky, but, scrapes off quite easily as a black residue on the molten metal surface. I skim that off and toss it out. When it is hot the interior looks like caramelized sugar. I use the Lee for bullet pouring only.
The last ingots from someone else batch was heated in my Lee pot to under 700 degrees (measured by a digital thermometer). The fully heated alloy was silver on top, never had that blue or yellow sheen develop. I fluxed the alloy and had the same results. My Lee pot was stopped up in less than a dozen pours. I noticed that as the temp dropped below 600 degrees the alloy quickly became mushy. Took the Lee apart and cleaned it out. I'm ready to try again with COWW I melted, fluxed and made ingots from, not this stuff.
I don't have much experience with melting pure lead. I assumed the ingots were pure lead (after all they were stamped PB) so I added 3% tin with the same results. My thinking is my sawdust flux material is leaving a resin on the interior of the pot and that is what is stopping up the valve. The material most likely is pure lead (now with 3% tin). What do I have here? SOWW or pure lead or what? What is causing the Lee pot to plug up?