Stratification by temperature in the melt.

[nitro-express]

I was having all sorts of goofy things happening with my melt, and I believe part of my problem was temperature.

I am using a plumbers pot to melt the metal, app a 9/1 mixture of WW/(50-50 solder). I would get all sorts of pretty colors, gold and purple on the top of my mix. I was using a thermometer and kept the melt at 750 or a bit more.

My question is this: In the melt is the metal at the surface hotter than the metal at the bottom, with the flame on, and the thermometer at 750, would the surface temperature be significantly higher than 750.

I tried another melt, and as soon as it went liquid, I reduced the flame, and no more colors or excess dross.

I think I'll buy myself an IR Thermometer, they are relatively inexpensive.

[62chevy]

The IF thermometer is good for surface temp at best and shiny stuff not at all. The temp variation from bottom to top is going to be minimal if any and the colors you got is normal for pure lead with tin added but you said WW with tin so have to wonder if all the good stuff didn't get removed from the wheel weights.

650 to 700 should be what you want for a Wheel Weight alloy.

[sqlbullet]

IR thermometers don't work terribly well with shiny surfaces. And dross is a good insulator. So they aren't great in my experience for this purpose.

In a small furnace of say 10-20 lbs, there isn't a lot of variability in the lead. It is probably actually coolest at the surface where it meets air that is 600° cooler. That is certainly the case in my big refining pots.

[country gent]

Several tricks to using the plumbers pot for casting. If you Open it up for a "fast" melt of the starting ingots or solid metals as soon as you see molten start lowering the flame to Normal casting setting. Put a mark or indicator on the valve handle that points in a set spot so you know where setting is at. For what its worth on my big casting pot ( 130 Lbs capacity) I can set it to 725* and cast big bullets for 4-5 hours shut the burner off and cast for roughly 20 mins or so before I start having issues. On these pots the mass of metal holds alot of heat a lot longer than the smaller pots. Even cold metal starting out by the time you start seeing molten around edges the center isnt far from melting temperature. Running it to full melted and then lowering heat may actually run the pot to 800*-850* easily. At this temp tin and antimony may be starting to seperate giving the colors you see. A steel disc floating on the pot may give a decent *target" for an IR thermometer. Cut a 2-3" dia steel disc 1/4" thick and dull blue it. After fluxing set this into melt and allow to normalize and take readings from it then. I use a simple Lyman thermometer with a clip mount on my pot only removing it when I flux or starting out ending a session. Works fine and dosnt get in the way of my laddle. I made the mount so the thermometer is 3/4" from bottom of pot and 3" in from edge. This gives a good consistent reading.

[Mitch]

I am no pro but I think you already found your answer.the lower temp did the trick.i hope you have the dross still in a can there is where your tin and antimony may have went.the more you melt and alloy lead you will notice to low of temp the alloy will set on top and at higher temps the alloys will come to the top. I did the same thing at first.i was told by someone here to flux and take off the dirt then if I had anything comeing off the top after I thought it was clean keep the stuuf you think is excess dross.this was good advise.as for the temps I think the temp of 700 is a good average.all I have a a lyman casting thermometer it seems to work well.

[bangerjim]

IR's will NOT do what you want. Unless you plan on using it for something OTHER than casting and melting, save your money. A simple stirring rod will keep your mix even. Just mix it up. I constantly stir my re-melting pot )plumber's furnace) when re-melting COWW's and raw lead and alloys. Lead is a decent conductor of heat and you will not get that much stratification.........not enough to worry about anyway.

You can do the floater thing as C-G mentioned for the IR, but that floater just gets in my way.

[runfiverun]

no.
the bottom is hotter than the top it ain't exposed to the air it's exposed to the heat.
750 is the point where tin really likes to start oxidizing.