Dripping Lead Pot & Reactivity of Steel At Elevated Temperatures

[CNC Molds N Stuff]

Most of us know If you dump a ton of oxygen, heat, and fuel on steel it can burn.  Burn may be technically arguable but a very violent reaction resulting in loss of material in its original form results.  Some of us may know that there is some steel loss from reactions at a lower temperature when using a steel crucible for things like casting aluminum and even some material loss with steel molds used for casting aluminum many times.

Still molten pourable aluminum is pretty hot.

I test a lot of fishing tackle molds with lead. It's nowhere near the reactive temperatures mentioned above.  I've got an RCBS Pro-Melt 20lb bottom pour lead pot.  I've had it for years and its worked great for many of them.  I don't think I have ever emptied it.  The last few years its begun to drip.  That's only a minor inconvenience really.  Ask around the tackle making groups and you will find plenty of people who will say they all leak eventually.  I stick an ingot mold under the spout to catch the drips when I am not actively pouring.

Not only was my pot starting to drip the flow was getting to be less and less.  Even with full head pressure (full pot) and the plunger set to maximum opening the flow was getting anemic.  I was thinking various bits of debris must have gotten into the gate over time.  Except it all floats to the top.  Yeah, tungsten is heavier than lead, but I can't think of any other substance in my shop (well there are a couple gold trinkets in the safe) that wouldn't float on molten lead.  Nothing that would be on the mold testing benches.
I use pretty pure lead purchased from a reputable source, but I still get a bit of dross on top.  I figure it's mostly lead oxide. 

I think some of it is some form of iron reactive from the melting pot, valve plunger, and valve nozzle.   After draining and partial disassembly, I am convinced that the steel was reacting at the mere 800F(+/-) of the molten lead.  There was some metal growth like scaley rust "looking" corrosion in the pot itself, put the plunger had layers all the way around reaching as far as the wall of the pot on the closest side.  I don't think there was much oxygen at those depths when encapsulated in lead either molten or frozen, but it looks a lot like iron oxides.

I ran a small aircraft drill through the gate and the flow is as it used to be again.   Well, it was when I was still draining the pot.  I have it very nearly perfectly empty and cooling down right now.  I plan to clean and polish the plunger and valve seat so maybe I'll get several years again before it starts to drip.  I think a proper disassembly and cleaning (scraping) every few years is just going to have to be part of its maintenance, and if what I think is happening is actually happening, be aware it has a finite life.

[Blind Squirrel]

Are you planning to add any weighted hook molds?  I don't have much use for jigs, but a lightly weighted hook mold for the Curly Buzz Frog Mini sure would be handy.  For some swimbaits too. 

[CNC Molds N Stuff]

I've actually got some samples of VMC wide gap hooks all the way up to 13/0 for making weighted hooks.  Captain Hook's Warehouse (Shorty's Hooks), helped me get those samples and let me know if anybody buys the molds he can get the hooks for people even though he doesn't currently have them listed on his website.