Public Service Announcement For PIDs

358156 hp

Well-Known Member
#1
I have been having an issue with inclusions in my castings for the past few days. I've been getting more and more dross on top of my alloy. My trusty PID assured me all is well temp-wise, so I went looking for other issues, contamination for the most part. And I fluxed, and I fluxed, and I fluxed. Three rounds of wood shavings, then a round of beeswax. The beeswax melted quickly, then spontaneously combusted. The PID read about 750*, and the only time I've seen beeswax burst into flame that quickly is at temps over 800*. So I unplugged my built in thermocouple & hooked up the one I use for my powdercoating oven- 825* & climbing. I tossed in my old Lyman mechanical thermometer, and it agreed with the PID, 825+. It occurred to me that the PID seemed to be hunting for temps more lately, and now I know why. I'll use my PC thermocouple until I get a new one from Auber. I need to order a few other things from them anyway.

So, verify your pot temps every once in a while with a different TC, or a mechanical thermometer, or both.
 

RicinYakima

High Steppes of Eastern Washington
#2
Uncle Russ (RIP) built my first one almost 15 years ago. It lasted 12 years which I consider good. If I get 12 years out of my new RCBS built in unit, I will be happy.
 

fiver

Well-Known Member
#3
quite often they need a simple auto tune.
you basically operate it at the highest and lowest setting and do a full re-set on the unit.
this re-teaches the puter it's boundary's and allows it to right itself quicker in making the small changes you want it to have to keep the alloy at a consistent temperature.
 

358156 hp

Well-Known Member
#4
I don't think it needs an auto tune. The original TC registered over 75* lower than the temp registered by a second TC on the same controller and my Lyman mechanical thermometer.
 

358156 hp

Well-Known Member
#6
I do agree with you, and will take care of that when I get my new TCs. With so many guys still on their original TCs, I'm a bit baffled why mine only seem to last 2-3 years. The one on this particular pot is built in, and I have to nearly completely disassemble the pot to replace it.
 
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fiver

Well-Known Member
#7
does it get any sooting or corrosion on the tip?
is the leade coming in contact with any hot spots?
how about the back end of the probe?
the TC should have just the tip being heated up, maybe slide it back some?
 

Mike W1

Active Member
#8
Know I don't cast as much as some of you guys so haven't had any troubles yet. Somewhere on the Auber Q&A's I believe it said something about not submerging the tip more than 3" which is one reason I used their 6" TC for my Lee 10# pots. I have a hunch Auber probes "might" be a bit better than the run of mill ebay ones but that's a guess. What one needs to know is the temperature range of the TC. Mine are placed 1/2" off the bottom and the sides which seemed to be the consensus on what I'd read before building the units.
 

popper

Well-Known Member
#9
The insulation and wire in the TC breaks down with heat and movement - insulation in the probe is high temp but is low temp outside the probe. Just replace. Makes the pot go full bore intermittently. My auber one died after a couple years, replaced with an industrial one but it has slower response.
Edit:wire is iron & Constantin, they won't take much flexing. Internal insulation is asbestos or a ceramic material, then just kynar or another low temp plastic. Both wires should be ungrounded, check for a short to ground of the pot. The sheilding is for mechanical as well as elec. interference protection, The PID controller also has an offset temp that can be used to correct the sensed reading, check that.
 
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358156 hp

Well-Known Member
#10
My TC is an Auber, but it is the washer type, and is attached to a heat sink that goes through the floor of the pot. My TC isn't exposed directly to lead, but rather a 1/2 plug (bolt actually) that goes through the bottom of the pot. It has proven to give identical results to the long probe type TC that seems to be most commonly used. Since I primarily ladle cast with a bottom pour pot, I needed to keep the pot opening as uncluttered as possible. My original TC was originally threaded through the bottom of the pot, and the first one lasted for years, but I got a batch of bad TCs that blew out really quickly, so I scrapped that format entirely and went this way to avoid having to but a replacement pot. I'll post pics when I change my TC in about a week.
 
#11
So why do you think the inclusions might be pid related? And I’m asking because I don’t know and I’m interested in what you believe the relation is.
 

358156 hp

Well-Known Member
#12
My inclusions looked just like the oxides from the top of the pot, which was oxidizing pretty heavily. I retested the next day and found my pot TC would work fine for about a half-hour, then the temps would start cycling again. They did not do this with the replacement TC in place.