For many years, I would melt the lead/tin, flux it, and cast a while. When the surface would get black (oxidize), I would flux again. When casting hot (which is most of the time since I cast a lot of hollow-base bullets), this could be as little as 10 minutes and certainly less than 15 minutes between fluxing. Then the mould and pin would have to get heated up again after fluxing, which lost several bullets before I got keepers again. While doing that, the surface would start getting black again. There was entirely too many rejects this way.
A few years ago, I decided to try boric acid on the surface. It works in protecting the surface from oxidizing. I could cast until the pot needed to be filled again, usually 5 or so pounds (half bullets and half sprue). I would scoop up what boric acid "glass" I could, put in the sprue and new lead/tin, melt it all down, flux it, and pour some more boric acid on. The problem with this is that the boric acid "glass" always got on the walls and built up, insulating them, until I had to take some coarse files to break it off. This was ugly work.
I decided to see what happened if I did not flux, did not use boric acid, and emptied the pot. What I would like to know from the people here is what is happening at each stage and what it means to the mix.
Here is what happens with my bottom pour pot. After fluxing, the surface starts to turn black as usual (from what I read, that is probably tin oxidizing on the surface). If ignored, the black will get darker and heavier. Eventually, it starts getting thicker (but still black). It starts getting a rough surface. Continuing on, it starts to get even thicker and starts lightening the color. It becomes a yellow-brown color and looks like a bunch of very small popped popcorn packed together. When in this state, it bridges the pot from wall to wall and stops moving. The lead/tin continues to get sucked down and there is a gap between the melt and the yellow-brown stuff. I can completely drain the pot. The yellow-brown stuff doesn't move once it bridges. When I break it up, it is about 3/16" to 1/4" thick and comes apart as a powder. It feels much, much lighter than lead or tin. It is easy to break up, clean off the walls, and thow away. What is it made from?
I have no doubt that there is tin in there, but I question how much since it feels so light. I don't seem to have problems with casting towards the end (this is with 2% to 3% tin mixtures in pure lead) like I would expect if I lost a lot of the tin. I have plenty of tin on hand. If replenishing it is all I have to do, this is a much easier way to cast than the first two ways I mentioned above. Can anyone here lead me through what is happening and how to quantify how much tin is being lost?
A few years ago, I decided to try boric acid on the surface. It works in protecting the surface from oxidizing. I could cast until the pot needed to be filled again, usually 5 or so pounds (half bullets and half sprue). I would scoop up what boric acid "glass" I could, put in the sprue and new lead/tin, melt it all down, flux it, and pour some more boric acid on. The problem with this is that the boric acid "glass" always got on the walls and built up, insulating them, until I had to take some coarse files to break it off. This was ugly work.
I decided to see what happened if I did not flux, did not use boric acid, and emptied the pot. What I would like to know from the people here is what is happening at each stage and what it means to the mix.
Here is what happens with my bottom pour pot. After fluxing, the surface starts to turn black as usual (from what I read, that is probably tin oxidizing on the surface). If ignored, the black will get darker and heavier. Eventually, it starts getting thicker (but still black). It starts getting a rough surface. Continuing on, it starts to get even thicker and starts lightening the color. It becomes a yellow-brown color and looks like a bunch of very small popped popcorn packed together. When in this state, it bridges the pot from wall to wall and stops moving. The lead/tin continues to get sucked down and there is a gap between the melt and the yellow-brown stuff. I can completely drain the pot. The yellow-brown stuff doesn't move once it bridges. When I break it up, it is about 3/16" to 1/4" thick and comes apart as a powder. It feels much, much lighter than lead or tin. It is easy to break up, clean off the walls, and thow away. What is it made from?
I have no doubt that there is tin in there, but I question how much since it feels so light. I don't seem to have problems with casting towards the end (this is with 2% to 3% tin mixtures in pure lead) like I would expect if I lost a lot of the tin. I have plenty of tin on hand. If replenishing it is all I have to do, this is a much easier way to cast than the first two ways I mentioned above. Can anyone here lead me through what is happening and how to quantify how much tin is being lost?