2 part question on PID

[bruce381]

How do you calibrate the temp? i used ice water and found probe was off 10 deg.

Other question is as pot was warming and I was yelling at TV (Biden) I noticed the temp was going up 1 deg about every 5 seconds.

But when temp got to about 625 is slowed / stopped and changed to going up like 1 deg every 10 seconds or more.

Then after about 3-4 deg it went back to the normal 1 deg per 5 seconds.

Is that some liquidus thing going on or a lousy Lee pot?

 

[RicinYakima]

Ice water is not consistent, but better than nothing. If your crucible is not perfectly clean, the salts from the slag and fluxing will lower the melting point.

Change of rate is called "latent heat of fusion". As the alloy changes from solid to liquid, it takes more BTU's to raise the temperature one degree. Once it is all liquid, the rate will stabilize.

• latent heat of fusion: the energy required to transition one unit of a substance from solid to liquid; equivalently, the energy liberated when one unit of a substance transitions from liquid to solid.

HTH

 

[Rick]

Yep Rick nailed it. An easy way to visualize it is . . . The heating element is producing energy in the form of heat. When the alloy is solid the only thing the energy can do is raise the temp. As the alloy begins to liquify some of that energy is used to change the alloy into a liquid and the temp rise slows.

 

[Brad]

With a PID you don’t really calibrate it. What it will do is help you maintain a consistent temp. It will “learn” how your pot heats and cools and turn on and off the element to keep the temp stable.
If the pot temp is slightly off from true temp does it matter? Will you notice a difference between 710 and 700? I would far rather have a stable 710 than a fluctuating 700.
One of the the neat things about a PID is being able to see what happens to pot temp when you add an ingot or a cold dipper to the pot.

 

[Rick]

A cold dipper? Uh oh be very careful with that. Or anything cold for that matter.

 

[L Ross]

One of the reasons I love this forum is that I get to read the reports of all of you guys that try all of this new stuff out. Not to mention all of the intriguing technical terms. I am such a dolt. I take an old RCBS pot with most of the paint flaking off, turn the dial to 800, dump in enough ingots to fill it up, flux, skim, cover with soft wood saw dust and cast until there's an inch or so of alloy left and start over.

I am blissful due to my ignorance of how many degrees my melt is, how hard my alloy is. My bullets are plain old lead colored and thus confirm my Fudd status. I have adopted both Ben's Red and Ben's Liquid Lube.

If I need super uniform plus or minus .1 grain weight sorted bullets, (for when I over think things for my BPCR or Schuetzen rifles), I ladle cast 25/alloy from a 50 lb. pot over a turkey fryer. I use my 1902 Mercury filled thermometer from print shop I got a bunch of Lino and stuff from, (including the best flux I has ever used in tin cylinders), and turn up the flame until I get 775 degrees. I mentally count each step and use a fan to cool the sprues. Those bullets never get sized and are pan lubed. All of that attention to detail makes me feel all warm and fuzzy and deludes me into thinking I have great ammo as a result.

But you know what still is the single most important aspect of accuracy at the end of the day? Don't yank the damned trigger. The guy that yanks the trigger the fewest times will out shoot every other shooter on the line, at the match, in the field, or in a gun fight. I wish there was a magic easy solution to stop yanking the damn trigger. I buy one of those, and a spare.

 

[JonB]

As Brad says, "If the pot temp is slightly off from true temp does it matter?"
BUT...
If you still feel the need to calibrate, you should find a way to do so near the operating temperature. Measuring devices are typically less accurate when they are out of their useful range, meaning if you calibrate a PID/Kprobe at 33ºF, it could still be off several degrees at 700ºF .

If I were to calibrate my PID/Kprobe (I haven't and don't see the need), I'd get some pure lead...must be pure and not some near pure scrap that you scrounged from a less than reliable source. Factory marked ingots of pure Lead will melt/freeze at 621.5ºF. Cycle your pot a few times above and below the melt/freeze of the metal...if your PID reads 621, then you are golden. If not, then most of these PID's have a parameter to correct the reading...If you have a manual, I hope you are fluent in chinglish

 

[JonB]

SNIP>>>

One of the the neat things about a PID is being able to see what happens to pot temp when you add an ingot or a cold dipper to the pot.

Or if you dump the HOT sprues directly back in the pot at the same rhythm as you are casting.
The PID learns that swing and if it's 15 or 20 degrees, it learns to over shoot your set temp a little higher, so the dip becomes less lower.

 

[Mike W1]

Somebody please correct me if I'm wrong on this!!! If you observe the P, I and D settings AFTER you autotune the setup and into the future as well you're going to find they do not change unless you autotune again. When autotune is finished the PID doesn't "learn" anymore from what I can tell.

 

[Mike W1]

I have a number of TCs and PIDs as well as a VOM that will read temperature. The difference between the various ones is pretty minimal. Suspect that the afore mentioned lead method would be the most accurate to set the offset but I doubt it's worth the bother for our purposes.

 

[358156 hp]

Being ten degrees off is plenty good. I crunched the numbers and came up with 0.0137931034483 percent, calculated at 725* with a 10 degree variation. The pots cycling variation will be higher than that. As far as the variance in temperature rise goes, you are working with an alloy (I assume), cast bullet alloys generally consist of pure lead, antimony, tin, and traces of other elements. all of which melt at different temps. You may simply be seeing this in play. Pure lead has the highest melting point IIRC at 622*, tin at 450*, and antimony at 1166*, according to the online guide I found https://www.engineeringtoolbox.com/melting-temperature-metals-d_860.html. Even though you're dealing with an alloy, the components all affect melting rates. Your 625* point is right at the melting point of lead.

I find the antimony number I posted above kind of interesting, does antimony even melt at cast bullet alloy temps? I often see lead in a cold pot "sweating" around the melting point of tin, little molten beads form on the surface, then gradually get larger at pot temp increases. I've always assumed that alloys were completely homogenous once established, but now I wonder about this position, perhaps they're only homogenous at full temperature.

Questions beget answers, which beget more questions.

 

[RicinYakima]

"I've always assumed that alloys were completely homogenous once established, but now I wonder about this position, perhaps they're only homogenous at full temperature."

They are almost "completely homogenous" in the liquid phase. As the liquid solution cools, different things happens. For example, freezing beer; as it approaches 32* first the carbon dioxide floats off into the atmosphere. Then the water turns to ice, at less than 32*, until you have a concentrated solution of water and alcohol. Next ice crystals form a matrix with alcohol trapped between, finally the alcohol freezes solid.

The metals in the lead solution act the same way.

 

[popper]

Purpose of the PID is to get your alloy to casting temp as quickly as possible without extreme overshoot and hold it there as the pot drains. It will always over/under shoot some. Once tuned, PID numbers stay the same till next tune cycle. Some better controllers will try to tune each time the unit is turned on.
completely homogenous takes time at temp and stirring. I usually wait 15-20 min before casting, stir every once in a while during casting, depending on alloy content

 

[Dimner]

One of the reasons I love this forum is that I get to read the reports of all of you guys that try all of this new stuff out. Not to mention all of the intriguing technical terms. I am such a dolt. I take an old RCBS pot with most of the paint flaking off, turn the dial to 800, dump in enough ingots to fill it up, flux, skim, cover with soft wood saw dust and cast until there's an inch or so of alloy left and start over.
....

There is an absolute joy in simplicity, in other hobbies I am exactly like what you are describing. For this hobby however, for me, it's the journey... not the destination

I get to cast far more than I have time to shoot, so casting and all the tinkering and the do-dads and whats-a-thingers and the experimenting make my day.

To put it another way... I had this marlin 336 in 30-30. I decided to play around with this old 311467 single cavity mold. Had the day off, no one was home. Made up just 12 bullets to get an idea of velocity. Didn't worry about any variables, alloy, sizing, anything. Just a dose of Rx7(in my notes somewhere), bullets tumbled in BLL and I was off to the range to see what was gonna happen.

They shot .5 moa at 50 yards. The weirdest feeling when I saw that. I was crestfallen because this project was over and I didn't get to play around. The journey was far too brief.

 

[L Ross]

There is an absolute joy in simplicity, in other hobbies I am exactly like what you are describing. For this hobby however, for me, it's the journey... not the destination

I get to cast far more than I have time to shoot, so casting and all the tinkering and the do-dads and whats-a-thingers and the experimenting make my day.

To put it another way... I had this marlin 336 in 30-30. I decided to play around with this old 311467 single cavity mold. Had the day off, no one was home. Made up just 12 bullets to get an idea of velocity. Didn't worry about any variables, alloy, sizing, anything. Just a dose of Rx7(in my notes somewhere), bullets tumbled in BLL and I was off to the range to see what was gonna happen.

They shot .5 moa at 50 yards. The weirdest feeling when I saw that. I was crestfallen because this project was over and I didn't get to play around. The journey was far too brief.

A good and valid explanation and indeed if I think about it I find merit in the idea from the other end of the equation. I wanted my own shooting facility for years. I had a primitive range at my Up North property, but since we moved down here and created Thorn Hollow, I now have a set up that rivals many gun clubs.

Now that I have a stable, repeatable recipe for 1 to 2 MOA rifle ammo out as far as I can shoot, I wish I had 100K rounds of ammo ahead and didn't have to cast and reload at all. I find my skills are perishable, doggone it. I find shooting from a rest to be boring until the range becomes enough of a challenge, so I prefer to shoot a lot off hand. My rifle shooting is almost acceptable but my hand gun skills have eroded something fierce. Part of it is my eye sight. I went to the eye Dr. and at 67 I have 20/20 in my Master, (right ), eye and better than that in my left eye but with perhaps the beginning of a cataract. Heck, she told me that two years ago and no change. But why can't I see handgun sights very well any more? Oh, I'm fine at 7 to 12 yards or so, but get out about 25 yards or so and I start to have trouble with 6" targets. I think the term is presbyopia or presbyterianism or something.

I have really started to shoot .22's in a big way. We have held a .22 BPCR rules silhouette match here for, I dunno, 12 years maybe a little more. I'd practice up for that, but after the Match I'd start working on Cast Bullet for Military rifles in June. Well, then we let sporterized mil-surps in with 6X scopes. That led to heavier barreled .308's and so on.

So the science of bullet casting is fascinating and useful, but dang it, I need 40 lbs. of XCB's as soon as I can get 'em. I just realized what a dunce I am. Instead of filling the pot, casting a pile, throwing the sprues back in, topping off the pot and waiting for everything to come back up to temp, why don't I just fill two pots. Run one down quick refill it with the mould on the hot plate and switch to the second pot and keep going? See how helpful you guys are? You're the best!

 

[bruce381]

Ian and Lamar know me from years ago that I work in a oil lab so I'm kinda anal on testing things ASTM routines are 3-5%.
Will bring home a lab thermometer just cause I like to over think everything.

Good info here does Knowing where at the "latent heat of fusion" is add do me any good?

I'm sure not anyway thanks to all.

 

[dannyd]

We all have our anal Issue: 20 years working on helicopters will make you real anal. I really over think things sometimes.

 

[RBHarter]

A very wise man once told me " it doesn't matter so much what the gauge reads/displays so much as it reads the same every time , and the results are what is needed " . I find that while a bit remedial and vague if your truck doesn't heat on the hills , knock , rattle or ping it doesn't matter if it only shows 25 lbs of oil pressure and runs 220° . A new gauge might show 35/190° it doesn't change the the fact that it has enough cooling and sufficient lubrication .

The same is true of our casting , based on my NOE branded thermometer I cast at about 765-785° and at 725° I can't get liquid lead inside a mould . I've meant to stick it in a pan of boiling purified water with a inhg and altitude correction and see it it really reads 212° F corrected . On the other hand if I know I pour good bullets 765 in 35+ cal iron 2 cav and I have to go 775° in aluminum under 40 cal do I need to know that the temperature is 741.7° O/U 5° ?

 

[358156 hp]

"I've always assumed that alloys were completely homogenous once established, but now I wonder about this position, perhaps they're only homogenous at full temperature."

They are almost "completely homogenous" in the liquid phase. As the liquid solution cools, different things happens. For example, freezing beer; as it approaches 32* first the carbon dioxide floats off into the atmosphere. Then the water turns to ice, at less than 32*, until you have a concentrated solution of water and alcohol. Next ice crystals form a matrix with alcohol trapped between, finally the alcohol freezes solid.

The metals in the lead solution act the same way.

And I've seen these things happening, but never thought it out fully until I read your post. Thank you Ric!

 

[JonB]

Somebody please correct me if I'm wrong on this!!! If you observe the P, I and D settings AFTER you autotune the setup and into the future as well you're going to find they do not change unless you autotune again. When autotune is finished the PID doesn't "learn" anymore from what I can tell.

Popper said, " Once tuned, PID numbers stay the same till next tune cycle. Some better controllers will try to tune each time the unit is turned on."
====================

So, I was thinking about what Mike said here...and then did some reading about my PID (model #JLD612). Mike, you are correct...or better said, my PID is not a "better controller" as Popper mentioned. What I seen, that I "thought" was learning, was likely spike events when I had put some culled cold bullets in the pot between pours along with the hot sprues...making for a bigger spike. Because this is not something I did a deep look into, I just noticed one thing, a time or two, and assumed it was learning. Thanks for the correction.