Do you remelt sprues with your PID?

[Elkins45]

I built and have been using a PID with my Lee 20 pound pot. It does a great job of holding a pot full of metal at the same temp...until I start tossing the sprues back in. Then in never makes it back up to the set temp again unless I walk away for a few minutes. It seems to me I have three possible options:

1 Set it too high to compensate (which sorta defeats the purpose of a PID)
2 Dont recycle warm sprues (which seems wasteful of energy and time)
3 Try to train it while tossing the sprues back in after I have the mold up to temp and it is casting well (haven't tried this yet but it sounds like a good idea)

How do you use your PID?

[country gent]

I drop sprues into a metal pan and add back when I flux or have to add more metal. This way the sprues are added back in and not building up yet when fluxing or adding metal its easy as the pots going to drop a little normally.

[dilly]

I don't have a PID, but I do have a theory.

Don't let your sprues pile up into one cold pile of lead to be added all at once. What happens if you add each sprue cutting in as you cast.

That way
A) They are much warmer
B) The rate of addition of somewhat cooled lead is more constant, allowing the heating elements to adjust a little better.

[lavenatti]

Retrain the PID.

[dragon813gt]

I pretty much empty the pot and then add the sprues. Repeat this process until all the lead is gone. Mold temp is held in place by a hot plate w/ mold oven. You will constantly chase temp it you add them after every cast. The downtime while the pot is heating back up is used to cull defects and add them back to the pot.

[LabGuy]

Catch hot sprue in leather gloved hand while using same gloved hand to cut the sprue, drop back into pot.

[runfiverun]

how I do it too^^^.

[bangerjim]

I do not use a controller. I just dump the HOT sprues back into the pot ever few minutes. Does not mess up the melt temp at all.


They usually end up in my lap on the THICK leather casting apron I wear!

banger

[dragon813gt]

I do not use a controller. I just dump the HOT sprues back into the pot ever few minutes. Does not mess up the melt temp at all.


Now try it w/ a PID, or even a digital thermometer, and see how it DOES effect the pot temperature. An analog thermometer will most likely not read the change. What I can't understand is why you have to comment in a thread like this. You don't use a PID so why bother posting?

[Mike W1]

I use 2 Lee 10 lb. pots - both PID controlled BTW. Top feeds bottom and is either fed warm ingots or sprues. By the time I need to refill the lower pot I'm feeding it up to temperature alloy. Takes right at 2 minutes to refill and that gives me a little time for a smoke break!

[trapper9260]

What i found if you keep enough melt in your pot and ever so often you put the spurs back in you will not have much problems, but I do not use a PID.It always work for me.

[Walter Laich]

I do use a PID but not sure that this is a requirement for posting on this thread ;)

I heat my ingots on the lid of the pot. After 10-12 pours I add a hot ingot to the pot and put a cold one on top.

I never really 'catch up' with the lead level but by the time it's really low I'm tired and need to stop before I do something stupid

[Geezer in NH]

What's a PID?

[mozeppa]

i have a 90 pound capacity pot with a pid 1/4" off the bottom.

i put sprues in when i add a 10 pound ingot of lead.

dang thing heats great !

it will melt a totally full (90 pounds!) cold pot of lead to casting temp in under 20 mins

[retread]

I drop sprues into a metal pan and add back when I flux or have to add more metal. This way the sprues are added back in and not building up yet when fluxing or adding metal its easy as the pots going to drop a little normally.

My method also. Allows me to keep a good rhythm by not messing with sprues till the next pot refill.

[bhn22]

Catch hot sprue in leather gloved hand while using same gloved hand to cut the sprue, drop back into pot.


I do this too. It seems silly not to, since I already have the sprue in my hand.

[mongoose33]

I throw them in each time as I'm waiting for the sprue puddle to solidify. The PID has learned that I'm tossing sprue cuts back in the pot, and it compensates for it.

Doing this allows me much better throughput because I don't have to remelt a bunch of cold sprue cuts or or worse, cold ingots.

As long as you're reasonably consistent in tossing them back in the pot--and i do it sooner, not later--the PID will compensate.

[bangerjim]

Now try it w/ a PID, or even a digital thermometer, and see how it DOES effect the pot temperature. An analog thermometer will most likely not read the change. What I can't understand is why you have to comment in a thread like this. You don't use a PID so why bother posting?


well, excuuuuuuuuuuuuuuuuse me for voicing my opinion. I thought that was what this place was for, sharing different ideas on many things. :D


I have probably forgotten more about controllers and proportional/integral/derivative control than most on here know. Been doing it since 1972. I used to teach process engineering courses in PID control. I design and sell sophisticated process control equipment and use them all the time. Just NOT on my simple little lead pot.

Some people these days are so concerned about a 7 degree dip in their pot temp. People have been casting darned good boolits for many generations with no more than common sense.

banger

[jmorris]

I have a divider in my drop basket from my caster (bullets fall on one side, spruce on the other) I regularly drop the sprue's back into the pot, blocking the spruce side and dump the bullets and return the sprue's to the pot.

The pot I built will hold over 60 lbs so the periodic addition of small amounts of lead, does not make any difference.

Divided basket can be seen here.

https://www.youtube.com/watch?v=z2U1ujg_nzo

Just cover the other side when dumping "the good stuff" and return the rest to the pot.

[Elkins45]

Catch hot sprue in leather gloved hand while using same gloved hand to cut the sprue, drop back into pot.


I've been doing every other one and the pot isn't catching up.

[John Boy]

* No PID
* Lee 20 lb pots with Bi-Metal Thermometers
* Dump sprues in tin can while casting
* Holt melt temperature constant
* When melt level nears bi-metal band on thermometer ... dump sprues in pot to increase level of melt
Same procedure for years. Dumping sprues in pot while casting will decrease temperature. Up and down temperatures while casting generates multi grain bullet variance ... I cast to bell curve variance less 1gr, normally within a 1/2 grain

[dilly]

Note before anybody goes assuming everything is all the same for everyone, let's keep in mind a few BIG variables. Specifically, the size of sprue cuttings, the type of pot being used, and the rate of casting.

Not being a PID user, some may think me disqualified to even comment. However we have reports of some people saying something works and others saying it doesn't.

I just think we should keep in mind that for some people, sprue cuttings are huge chunks of generously poured six cavity mini ingots. For others, they are minimalistic little nubs smaller than the bullets they cover.

Additionally, some people probably throw them back into a 220v magma caster while others will probably use a Lee ten pound pot. There is no reason to believe they will melt at the same rate.

Lastly, some people use two molds, a faster cadence, etc. and produce sprues much more often than others.

I hold my original theory that adding sprues in immediately causes the least amount of strain on your pot's consistency, unless you are willing to drain almost all the way and wait the painfully long time it takes to bring a whole new batch up to temp. Add them as soon as you cut them and they will be just barely warm enough to be solid. They won't take that much energy. Obviously the smaller you pour the sprue, the less effect they will have on the temperature when it goes back in. Following the generally accepted casting practice of using repeatable rhythms will result in a steady, predictable addition of barely solid lead that should be something that a lead pot should be able to handle.

[GrayTech]

Effect depends on the amount of lead/size of pot. Large pot of lead- adding sprue back as cut won't have much impact. Small pot- bigger impact on melt temp.
If using a pid adding lead and messing with things defeats the purpose of pid. Just collect sprues and add back in when done casting. Would seem kind of obvious I would say.

[GrayTech]

I've been doing every other one and the pot isn't catching up.
Could it be you don't have enough watts heating your pot? How big is the pot, and how long does it take to heat how many pounds of lead to casting temp?

[blikseme300]

Effect depends on the amount of lead/size of pot. Large pot of lead- adding sprue back as cut won't have much impact. Small pot- bigger impact on melt temp.
If using a pid adding lead and messing with things defeats the purpose of pid. Just collect sprues and add back in when done casting. Would seem kind of obvious I would say.

I agree with GrayTech on this one. A PID cannot overcome the lack of heating capability to recover the temperature of the pot. Pots with higher Wattage per Pound recover quicker with less fluctuation in temperature. Personally I add sprues and additional alloy after a large number of casting pours so as to not vary the casting rhythm and to stay focused.

I do have the advantage that my main pot is a 70# unit so typically only add sprues and alloy at the end of the session. This pot is PID controlled and the temperature stays pegged at the set temperature so my casting is more consistent. This really shows when weight sorting rifle boolits as the weight spread is much smaller than when I was using a non-PID controlled pot.

I guess that for some folks bullet weight consistency is not so important but my rifle accuracy at 100-200 yards did improve once I tightened up the boolit weight spread.

[lightman]

I don't have a PID (But I want one), so I can't advise much about your problem. It sounds like the heating element in your pot may be weak. Are you a long way from your power source and running on an extension cord?

Dilly makes a few good points, something worth thinking about. My normal casting routine, not using a PID, is to cast until the pot is about half empty, refill it and take a break until it comes back up to temp.

[robg]

if my boolits look ok I shoot them.i like things kept simple like me;-)

[mattw]

It is amazing how little added material affects the temp. I have an RCBS pot and I take it down to about half and refill it and just walk away and wait. I do love having a pid on the pot, much more accurate and verifies with my in pot thermometer.

[Mal Paso]

I cast sitting. All the sprues go into a pan next to the boolit drop area. Sprues go in the pot when ingots do and I take a break while it heats. It's too far a reach and too disruptive to the casting temperature (Lee 4-20) to bother with the little bit of electricity wasted. My energy is much more valuable (Old Fart).

I don't wear gloves except when loading the pot which I do standing, safety glasses and heavy cotton clothing always.

It really depends on your setup. A buddy of mine runs his Lee 4-20 wide open and uses his sprues like Ice Cubes to control the temperature. Don' need no estinking PID!

Here's mine.

[JonB_in_Glencoe]

My procedure varies, depending on the Mold I'm casting with, I'm using a PID controlled Lee 4-20, but mostly I don't add the sprues to the pot while casting rifle boolits ...and maybe I will while casting pistol boolits, but will generally take a break for the pot to 'catchup'.

Temperature fluctuation [while casting] "WILL" give weight variation...sometimes weight variation doesn't matter...sometimes it does. My goal is as little weight variation as possible.
good Luck.

[gwpercle]

No PID here, cast with Lee Magnum Melter, open top, Lyman ladle and two cavity moulds.
I cut the sprue over the pot so the hot sprue drops back into the pot. In 1967 I started casting like this, never knew it was wrong...nobody told me, so this dog isn't learning any new tricks and it works just fine for me. I tried cutting them over a box and adding them back later but old habits die hard and I keep dropping them into the pot....so I stopped fighting it.
Gary

[montana_charlie]

Now try it w/ a PID, or even a digital thermometer, and see how it DOES effect the pot temperature. An analog thermometer will most likely not read the change. What I can't understand is why you have to comment in a thread like this. You don't use a PID so why bother posting?
What purpose does the PID serve?
It allows you to specify an exact temperature, and keeps that temperature more consistent.

What purpose does a consistent temperature serve?
It works (in conjunction with a consistent cadence) to keep the mould at a consistent temperature.

What does a consistent mould temperature serve?
It produces bullets that are consistent in weight.


If you use a PID to tightly control the pot temperature, do you also weigh your bullets to see if the final goal is realized?


I don't use a PID.
I cut sprue with a gloved hand, and drop the sprue back into the pot immediately.
My sprues weigh more than some people's bullets.
If cutting the sprue reveals a bad base, I will drop that bullet right back into the pot.
I cast bullets that weigh a nominal 550 grains. I get a total spread (from lightest to heaviest) of less than two grains and my 'keepers' spread less than one grain.

Does your PID produce those results?

CM

[dragon813gt]

What purpose does the PID serve?
It allows you to specify an exact temperature, and keeps that temperature more consistent.

What purpose does a consistent temperature serve?
It works (in conjunction with a consistent cadence) to keep the mould at a consistent temperature.

What does a consistent mould temperature serve?
It produces bullets that are consistent in weight.


If you use a PID to tightly control the pot temperature, do you also weigh your bullets to see if the final goal is realized?


I don't use a PID.
I cut sprue with a gloved hand, and drop the sprue back into the pot immediately.
My sprues weigh more than some people's bullets.
If cutting the sprue reveals a bad base, I will drop that bullet right back into the pot.
I cast bullets that weigh a nominal 550 grains. I get a total spread (from lightest to heaviest) of less than two grains and my 'keepers' spread less than one grain.

Does your PID produce those results?

CM

LOL, thanks for telling me what I already know. I hope you feel better thinking you were going to "school" me.

[bhn22]

My original casting procedures kept my bullet weights within perhaps 1/10 to 1/4 of one percent of the as cast bullet weight. I still hold that range today, but I'm now doing this with hollowpoint moulds, and some really weird projects. My PID really only gives me an indicator of when I'm at my most consistent temps, which allow for more consistent fills. I was perfectly happy with my results before the PID, even though my original pot thermostat wasn't terribly consistent. Before, I only cast when my pots indicator light was off, I stopped when it was heating. Oh yeah. I ladle cast too, that's been a major contributor to bullet weight consistency since I gave up on bottom pour.

[montana_charlie]

LOL, thanks for telling me what I already know. I hope you feel better thinking you were going to "school" me.
Just pointing out the obvious in order to establish a background for the two questions I asked ... which you had no answers for.

[Elkins45]

Could it be you don't have enough watts heating your pot? How big is the pot, and how long does it take to heat how many pounds of lead to casting temp?

It's the Lee 20 pounder, however many watts that is.

I can tell you that dipping the corner of a mold into the melt will make the temperature drop faster than a prom dress. I have seen the temp go from 800° to 650° in just 15-20 seconds when a big cold chunk of metal is introduced.

I have one of the older 10 pound pots. I like the idea of using it to feed the big pot. That might take a lot of the variation out of the system.

[Echo]

I always pour, wait, swat the sprue, pop the sprue off, dump the boolits, re-pour, then put sprue back in pot, and try to keep the pot as full as possible. The addition of the slightly cooled off sprue has negligible effect on alloy temp.

[williamwaco]

I do not use a controller. I just dump the HOT sprues back into the pot ever few minutes. Does not mess up the melt temp at all.

They usually end up in my lap on the THICK leather casting apron I wear!

banger

me too.

[country gent]

Pot capacity and volumne is going to make a big diffrence in how X amount of added material affects temp swings. A 5lb pot and large sprues may be alot, a 20 pound pot and small sprues not nearly as much. My pot at 100+ pounds hardly drops by the thermometer when a 5 pound ingot is added. Temp drop is more a result of masses not the heat element or type of control. A small pot just dosnt have the mass to offset the additions of cooler metals the same way a big pot does. I smelted in a pot that held 500 lbs when full for a bunch of range lead. ANd it took several shovels full of scrap to make a big diffrence when it was close to full. There are many things affecting this, Size of pot, amount of alloy in it, temp operating at, ambient conditions, and others I havent really thought of. A pot running at full capacity at upper end of its heating elements range will take longer to recover than one full and operating at mid range of elements range. Add a few sprues into 5 lbs of lead may be 2-3% adding the same amount to 100lbs is well less than 1%

[rsrocket1]

My usual casting PID setpoint is 700F and I mostly use 6 cavity molds so the sprue is one big bar. The sprue goes back into the pot as soon as it's cut so it's still really hot when it goes in. I notice no ill effects even when I am way down low in the pot. I wait for the lead to freeze, count to 5, cut the sprue and turn the mold upside down over the pot.

[Ed_Shot]

My method also. Allows me to keep a good rhythm by not messing with sprues till the next pot refill.
+1 When I empty the pot I enjoy the break waiting for the pot to heat back up.

[HATCH]

On my Master Caster, I put a 5lb ingot in as soon as it can fit.
My PID is set for 750.
With my alloy, when it gets to below 700 I risk the chance of spout freeze.
One 5lb ingot will drop the temp from 750 to around 710 or so depending on ambient temp.

If I end up waiting too long then I just wait.
When I get down to about 1/3 a pot left, I take a break and sort my sprues from my boolits.
Unlike Jim, I just mix them both in the pan.

[mongoose33]

Effect depends on the amount of lead/size of pot. Large pot of lead- adding sprue back as cut won't have much impact. Small pot- bigger impact on melt temp.
If using a pid adding lead and messing with things defeats the purpose of pid. Just collect sprues and add back in when done casting. Would seem kind of obvious I would say.

I'm sorry, but I disagree. The PID accounts for the fact that I'm adding slightly cooled sprues continually and manages that in how it controls the pot.

I've watched the temp as i do this and I generally don't move 5 degrees on a full pot, and not much different from that on a half-empty one. It's essentially no different than if I had a heat sink on the pot; the PID would account for it.

[Case Stuffer]

I feel that post 22 and 30 are fairly accurate. I added a PID to my RCBS Pro Melt which is a 20 pound 800 watt bottom pour that is now 40 years old and prior to having a constant accurate fast acting temperature display I never realized how much cooling effect adding sprues back to the furnace had. The chunks from a Lee 6 cavity 120 gr. thru 200 gr. can
be added back one or two at a time to a mostly full pot without problems with 9 mm. and 45 pistol Boolits , adding sprues from a RCBS 22-55-SP two cavity when casting these little rifle Boolits can cause all kind of issue .


FYI the 22-55-SP sprues amount to 70% of the alloy used

[tiger762]

A few comments:

1. Stir the lead using the thermocouple. Lead has a thermal conductivity of 35 W/m*K. It's not a really good conductor, as far as metals go. Aluminum is 237. Copper is 401. Silver is 429! Your thermocouple is not going to give an average temperature of all the molten lead. It will measure the lead it's closest to. Move the thermocouple around some time. The measured temperature will fluctuate.

2. The three letters of "PID" refer to the three different ways that we can apply closed-loop feedback to a system. You set a reference value (in this case, the temperature programmed into the PID controller). The controller looks at the current value (from the thermocouple) and sees how far away it is from the reference. The Proportional function takes the delta, multiples it by a coefficient, then drives the plant/system (whatever that is, in this case an electric heating element) by that magnitude. Integral control allows the PID to reduce the steady-state error to zero. It takes the difference between reference and current value, and integrates that over time. It will actually induce some overshoot, to balance the generally deficient state that our PID controllers stay in, when heating up lead. Think about it. You set the temperature to 700, then 15 minutes later (900 seconds) it's at temp. That is a LOT of error. Because of this, we don't want a lot of Integral control for this application. If you did adjust the Integral coefficient high, then the PID controller would insist on running the pot temperature OVER the reference temperature, until the "area under the curves" balance. As an aside, there is a function called "integrator anti-windup" which tells the Integral control function to keep its shirt on and not go ape-####. Lastly, Derivative control looks at the rate of change of the error (ref - current), multiplies that by a coefficient, and adjust the plant/system accordingly. Because it's looking at how fast are we getting to the reference point, it can be more aggressive in its management of the plant/system. One thing to keep in mind is that we don't have infinitesimal control over the current flowing through the heating element. It adjusts the duty cycle (fraction on versus off). Given the l-o-n-g duration system dynamics of melting a pot of lead, the 650 Watt heating element is adjusted by adjusting the fraction of time it's on versus off. Mine has a 0.5 second period. Note that the PID is non-linear in that while we can actively apply heat, we have to rely on convection/radiation to apply cooling. When the PID realizes it has overshot the reference temperature, all it can do is turn the element off.

3. I dump sprues right off of the sprue plate into the pot, so they haven't the chance to cool off much. The cooler sprues stay near the top. The pouring (and the thermocouple) is at the bottom. Life is good...


I built and have been using a PID with my Lee 20 pound pot. It does a great job of holding a pot full of metal at the same temp...until I start tossing the sprues back in. Then in never makes it back up to the set temp again unless I walk away for a few minutes. It seems to me I have three possible options:

1 Set it too high to compensate (which sorta defeats the purpose of a PID)
2 Dont recycle warm sprues (which seems wasteful of energy and time)
3 Try to train it while tossing the sprues back in after I have the mold up to temp and it is casting well (haven't tried this yet but it sounds like a good idea)

How do you use your PID?

[blikseme300]

A few comments:

1. Stir the lead using the thermocouple. Lead has a thermal conductivity of 35 W/m*K. It's not a really good conductor, as far as metals go. Aluminum is 237. Copper is 401. Silver is 429! Your thermocouple is not going to give an average temperature of all the molten lead. It will measure the lead it's closest to. Move the thermocouple around some time. The measured temperature will fluctuate.

<snip>


This is why I mount the thermocouple so that the tip is in the alloy and close to the valve of my bottom pour without touching the pot as I am interested in the casting temperature of the alloy. I once did a test with 5 thermocouples in one pot each in a different location and the temperature spread in the alloy was interesting.

Consistency but not true casting temperature can be achieved regardless of where the tip of the thermocouple is located but mounting it to the case of the pot creates larger swings in temperature as this is thermally connected to the heater element(s).

[tiger762]

That's a good point. When the SSR energizes the heating element, it most certainly will be hotter than the lead it's trying to heat up. The thermocouple will be somewhere in between the mass of lead and the element. The exercise is left for the student to do a FEA using Excel, and holding down the F9 key, watching the matrix of temperatures stabilize, LOL...



Consistency but not true casting temperature can be achieved regardless of where the tip of the thermocouple is located but mounting it to the case of the pot creates larger swings in temperature as this is thermally connected to the heater element(s).

[bdbruce]

I ran my Lee 4-20 Pro for at least a year before I added a PID controller, and I made lots of good consistant boolits using the Lee "Dial settings". When I get a "handfull" of sprues and obvious bad boolits in my metal pan, I dump back into the pot. My temp thermocouple is in the middle of the pot about a inch off the bottom. Yes, it does drop in temp but within about 30 seconds the pot recovers enough to continue casting, over time I have figured out my Minimum and Maximum casting temps (about a 10 degree range) and will start pouring when the minimum is reached. The PID controller I got for free is calibrated in degrees Centagrade, so I keep a C vs.F chart nearby. I keep my molds on a PID controlled Hot Plate, so a little recovery wait is no big deal.

[popper]

I use a PID on the Lee 4-20. I collect sprue in a SS pan. Dump back in when pot gets low. Then re-flux to get the junk out - it does collect all that oxided alloy. My shoulder needs a rest after 1/2 pot anyway.