PID for a Sandia forge

J

James Puckett

Active Member
I have ordered a PID controller to get me a temp reading on my Sandia forge. Can I drill a hole into the forge body or just stick the probe straight into the door of the forge?
 
Well, I'm not sure what a Sandia forge is, nor now it's shaped. I did a search and didn't find anything definitive. You could just stick the probe in thru the door, but wouldn't that get in the way? I think most folks just drill in thru the side (or top?) to get the ceramic sheath to the point of concern for reading temps. You do have a ceramic sheath to protect the TC? I trust it's not the stainless steel type probe?

Ken H>
 
To get the truest readings, I'd recommend locating a TC as close as possible to where your "use area" of the forge will be....while trying to keep it out of harm's way. Generally this will be approx midway of the forges length, in the upper 1/3 of the forge's height. In reality, the whole key is choosing a location where you believe you can get the most accurate readings.

Things to think about are...

-a vertical forge is almost always a couple hundred degrees hotter in the upper 1/3 of the chamber
-the COOLEST temp area in a forge is always right at the end of the burner's flame
-This might not be relevant to this particular thread, but you also have to think about moving your heated work piece from the forge...to where ever it is you're going to. I field a lot of questions from individuals who are using their forges for heat treating....and have to carry their workpiece from the forge....to 10+ feet away to a quench tank, or annealing tub......you MUST realize that whatever actions you're trying to accomplish, the specified temp refers to WHEN the actual action is taking place....for example, if you're quenching at 1550F.....that means 1550F when the steel hits the quenchant....that can't happen if you heat to 1550F, then have to walk 10' to the quench tank. Same thing holds true for annealing, and any other heating/cooling operation.
-Finally, resign yourself to the fact that you will be replacing a TC when used in a forge application. I mention that because when I buy TCs, I usually buy 3-4 at a time, just so I have a replacement when the previous one goes out.....and to ensure I'm replacing it with an identical type/model.
 
Since it's goin in a welding forge.....just make sure it's in the upper 1/3, and out of harm's way. If I'm lucky, I can get about 3-4 months out of a SS sheathed TC in my welding forge. I've tried buying the "high dollar" ones, that are rated for 3,000F, but they don't last any longer then the $20 SS sheathed models.
 
Wow! Ed, I had no idea the SS sheathed TC would last 3 months in a welding forge. I used #12 AWG (14?) TC wire spaced and held in place with ceramic, then this slide inside a ceramic tube for protection. The ceramic tube does slow response down compared to bare TC tip being in forge, but sure lasts a LOTS longer. 3 months huh? Do you have a link to one of those SS sheathed TC? The only SS I've seen were rated <1,000 ºF). These were cheap low end SS TC.

Ken H>
 
http://www.omega.com/pptst/JTIN.html

Near the bottom of that page there are drop down boxes to "build your own" TC. Heres what I get....

(1) K
(2) SS
(3) 14
(4) U
(5) 12

That will get you a type K TC, Stainless sheath, 1/4" diameter, Ungrounded/2 wire, 12" long. The hole for the TC on my vertical welding forge is near the top in the rear/left quadrant. I gently put a 90 degree bend in the TC...about 3" from the sensing end, poke it though a strip of kawool (kawool stays between the TC and the exterior of the forge).....place it in the hole, and let it hang there. Only about 1" or less sticks out on the interior of the forge lining.
 
Thanks Ed - that looks about the same as the SS TCs I use in tempering oven. Rated at 500ºF I can see why they only last 3 months or so, but with only an inch inside you get a fast response and not so much of the TC exposed to high heat. I might try that, just sticking in an inch when I'm just using the forge. Last I used the forge much was with a muffer pipe for HT'ing some 440C blades. There I had the ceramic sheath extended inside the forge, then on to inside the muffer pipe to have temperature right at the blade. Since getting an electric HT oven, I've not used forge much as the SS blades I'm now doing are all stock removal.

Ken H>
 
The Omega page that Ed linked to, gives an option for an XL sheath material. It's Omega's proprietary material, rated to 1335 degC/2435 degF.

Whilst I do not know whether it will last several times longer when permanently installed in a heavy-use welding forge, it does seem to hold up much better than 310SS (rated to 1100 degC/ 2012 degF) at the higher temperatures in intermittent use, based on my (admittedly limited) experience.

I tend to use a 24" handled thermocouple, 1/4" diameter to check the temperature distribution in forges. Mostly I use 310SS sheath material and an insulated junction because it's what I can get from my local thermocouple supplier. The Omega XL material allows a grounded junction for much faster response if that is important to you.

I bought a couple of the Omegaclad ones with grounded junctions in type N for heat-treat ovens I built and have been quite impressed.
 
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