Weird Problem with Melting Pot

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  • Last Post 28 January 2024
John Alexander posted this 24 January 2024

I need help to solve a problem that I have  never run into or heard of.  I went to my shop and plugged in and set the temperature at 840 F as I intended to mess about and see if I could work out the best way to anneal cases by dipping the necks in lead.  While the pot was warming up I worked on other things with my back to the pot (bad procedure). When I finally checked on the pot about two pounds had leaked out and formed a pagoda looking tower from the ingot mold I had placed under the spout to the spout. The PID read 850, The pot still looked full which I couldn't understand since clearly a lot had leaked out.

When I worked the pagoda out from being wedged between the spout and the ingot mold and tried to stick in back in the pot I found out why. The lead in the top of the pot was still solid. I had twisted the male part of the valve to stop the dripping after removing pagoda.  So I sat there wondering what to do next as the pot got hotter and hotter until it got to 870 and I chickened out and turned it off.  I don't know why the PID didn't shut it off when it passed 840.

The pot is a 10 pound Lee and the air temperature was 60F. I know have a pot with the top full of lead but with a large air void of unknown shape in the bottom part of the pot where i suspect the heating elements are.

I have never had this happen but I assume some of you have and I would like to know how you got things going again.  I will call Lee's tech people tomorrow for advice but would just as soon fix it tonight If somebody provides the solution.

John

 

 

 

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TRKakaCatWhisperer posted this 24 January 2024

the SENSOR for the temperature control may be isolated from the pot OR it may be cooled by the air around it.

Knowing that the sensor is in contact with the pot and where it is located is a good starting point.

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Wilderness posted this 24 January 2024

John - one possibility would be to drill a hole through the cap, then run shot (or bullets) down through the hole to get a melt going under the cap, and go from there.

The cap needs to be in contact with molten material to do its own melt. Lead melts from the bottom up, or at least from the heat source up, with the solid melting mostly where it contacts the liquid. Best sit the top ups on top of the cap for a while so they're not going down cold or wet.

I have read about lead exiting the pot the other way - by blowing the cap. I use an open top pot and dipper, but I always pour out into ingots when I finish my casting session, in part to avoid the blown cap drama.

I suspect the key to your issue is that the molten lead had an escape route through the spout, leaving the cap no longer in contact with molten material.

Someone else might suggest melting through the cap with a blow torch.

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Duane Mellenbruch posted this 24 January 2024

Evening John. Looks like you have found a good reason to store the pot only half full. The heating element wraps around the crucible under the outer covering and is about half way up from the bottom.  While heat does rise, the alloy was becoming fluid from the center of the vertical portion of the pot.  May I guess you were using Lino or another high antimony alloy?  The melt will expand but the top has remained solid and that lifted the valve rod and partly  drained the pot.  Once the melted alloy left the crucible, the sensor for the PID was not going to get a good reading so the element kept heating but the solid alloy was not being heated, just the space below. 

Be glad it was not a 20 pound pot.

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RicinYakima posted this 24 January 2024

Empty the pot after use.

You are fighting three issues: Lee pots only have heat coil on the bottom half the pot, two the K sensor is reading 60 on the top half and three Lee pots have the weakest control rod seal. 

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delmarskid posted this 24 January 2024

I dismantled my Lee 10# pot and packed pushed fiberglass into the gap between the element coil and top. It heated faster and held heat better. The coil only covers the bottom half of these pots. I used to keep a propane torch nearby because I’m impatient.

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vmwilson posted this 25 January 2024

Where does the TC hook in or onto the pot?  Could make a difference.

Mike

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Rich/WIS posted this 25 January 2024

Would melting from the top with a propane torch work?

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Duane Mellenbruch posted this 25 January 2024

Stored empty or half full, no problems.  Only when stored full will you get either a drained pot, or an eruption. 

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Bud Hyett posted this 25 January 2024

This happened to me once with a RCBS pot. The neighbor stopped to talk about rebuilding our mutual fence and I was distracted. Returning to the garage, there was a mound of lead on the ingot mold as you describe. I put the ingot mold under the pot since it was leaking unless you gave a firm push to seal when using.

Drilling a hole in the top, I discovered the dome of lead and surmised the problem. I drilled three more holes in close proximity, then used a propane torch to melt the webs between the holes to make a larger hole. Then I used the propane torch to melt across the top causing the lid of lead to eventually fall in. 

Disassembling the pot, I lapped in the cutoff and the spout to obtain a better seal.

To solve the source of the problem, I now drain the pot down to half full when shutting it off.

Farm boy from Illinois, living in the magical Pacific Northwest

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John Alexander posted this 25 January 2024

Thanks for all the suggestions. Since being lazy is the reason for not draining the pot in the first place as several have advised -- and still lazy, I tried two easy to do but unsuccessful approaches first

First was easiest, I simply turned the PID up to 870 and let it use up electricity for two hours hoping that would eventually melt out the 8 pound plug.  i think I may have come close. The top lead surface got to 595 F which is only 25 f below the pure lead's melting point.  I have no idea how much the 870 degree air (where the sensor is) below the plug melded, but not enough,

My next attempt was to support the pot tipped over horizontally, with an ingot mold below the lip of the pot and melt it out with a small torch I used to solder copper pipe replacements after freezing in Maine. The plug provided an amazingly effective heat sink. The torch couldn't melt even a drop of lead.  I'm sure a serious torch would do the job but that would take it out of the easy class. So my contribution so far is find what doesn't work.

Before breaking down and drilling a hole in the plug and pouring in shot as suggested by Wilderness, I have wrapped the pot with fg pipe insulation to cut heat loss and will let er run awhile this pm.

I might change my mind about being too lazy to drain the pot after use if blowing out the top was likely.  I can't think of a mechanism for that to happen.  Who has actually experienced such a blow up and what are the proposed theories that might cause such an unwelcome event?

John

 

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Duane Mellenbruch posted this 25 January 2024

When casting, we pour a large sprue puddle and then watch the dimple form in the sprue puddle because the alloy cools and contracts in the mold.  When we heat the alloy in the pot, it expands.  If the "cap" is stuck to the sides it has to force the molten alloy somewhere.  It will either expand and lift the rod off the seat and then drain, or it will vent the pressure through a weak spot in the cap. 

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John Alexander posted this 26 January 2024

That sounds like a logical mechanism. However, I have started the heater with a full pot of solid lead probably a few hundred times.  Most of the time there is no leakage, there is no visible raising of the top surface of the solid plug and no lead squeezing up and around the cap to relieve the pressure. At some point the lead surface turns to liquid.

I don't think the lead will solder to the pot walls, it doesn't to mold cavity walls but it may fit too perfectly for lead to squeeze up through the gap.  If it can't get out either the top or bottom and the plug doesn't move the expansion of the heating lead would either 1 -- compress the lead which has an elastic modulus 1/15th of steel -- but still pretty stiff, so the volume increase it needs to expand to relieve the stress would be very small or 2 -- expand the steel pot -- or both.

Then when the force imposed on the lead thermal expansion was greater than the resisting force consisting of the shearing resistance of the plug/pot surface, the plug wouldn't have to go far to relieve the stress in the lead. Hard to imagine that the plug would fly out -- but maybe my reasoning has a flaw? 

What do these incidents where the plug is expelled look like? Does the plug just pop up a bit and relieve the pressure, or does the lead come out and ruin your day.  Does this really happen?

John

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Duane Mellenbruch posted this 26 January 2024

The plug will remain in place being held there by the pot linkage.  the plug is only friction tight and the cleanliness of the pot walls would likely have an affect on any resistance to movement.  These issues seem a lot like, "I have done it this way a thousand times, and now I suddenly got a ring in the barrel". 

Lead expands when heated and goes either up or down since the crucible keeps it from expanding too much.  But it will expand a little before the pressure is vented so that might be why one gets a spurt of hot alloy when the cap gets soft enough to vent the pressure.  It may not happen frequently, but many will place a cover on the furnace while it is coming up to melt temp, and that is also why most are cautioned to not just turn it on and walk away.  Stuff happens. 

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OU812 posted this 26 January 2024

Rest your 10 pound Lee in a shallow baking pan in case this happens again. The same thing happened to me once. The lead poured out on wood picnic table, came close to burning down house.

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John Alexander posted this 28 January 2024

I finally got around to trying to melt the plug by just letting it run at 870 and with the pipe insulation wrapped about the pot and some on top. It fairly quickly melted through the plug.  I will baby sit the pot when I next turn it on.  Interesting but a lot of time wasted.

Thanks to all who offered suggestions.  I am a bit dissapointed that I haven't heard any first hand reports about the pressure under the plug causing things to come out the top.

John

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Duane Mellenbruch posted this 28 January 2024

There have been many comments on other forums, but I got tired of trying to search out the threads.  I know it has been reported, so that is good enough for me to take measures to not suffer the same event.   I know better than checking an electric fence with a water stream.  I could be wrong, it has been known to happen. 

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John Alexander posted this 28 January 2024

Duane, Thanks for trying to find a first hand report of such blow ups. I didn't mean to offend with my skepticism. I have been shooting cast bullets a long time and when I was very young I believed everything I  read on the subject and took it as gospel. However, over the years I and others have found most of it pure BS that often sounds superficially logical.

However, If lazy procedure really can blow hot lead out of a pot we should all know about it, and spread the word to encourage the lazy in our midst to shape up.  

I can do my part for safety by letting people know that I have first hand knowledge that sweeping up a long lost primer with the lead scraps and dumping it in a pot of molten lead will reduce the contents by about a third in an undesirable manner.

John

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