Kiln Konundrum

[Natedizzle]

So,

Let's see if anyone here can help, since the experts are still confused by this one...

I recently built a giant annealer for our studio. It has two refrigerator style doors that open into two chambers, this way I can run decals and anneal on he same day. Each chamber is 27"x19"x39" tall, and each side runs on a 50 amp breaker, I believe the actual usage is 30-32... I wired each side with a fuji PXR-3 and 50 amp SSR relay.

Now for the fun part. I fired it up, and slumped an entire load of tubes into a pile while reading dead on 1043. Since that didn't work, I checked all wiring, called a few kiln experts, replaced my thermocouple, tried 3 different fuji's... I have run it on a few occasions now, and I can get 12mm rod to bend into impressive noodles when inserted standing up while the fuji reads 900-950 in about 3 minutes. I can get 4mm rods to bend with the door open. But I put a 3mm sculpture on the floor, and it didn't slump even thru repeated cycles.

I'm at a loss, please help!

Nathan

[NUBBLET]

sounds like maybe heat loss , possibly close to controller? so the controller stays on when not needed .

I had this happen to me and finally realized my connection to the pyrometer was loose , when I redid it it instantly jumped to correct temp which was way too high.


Could it be a sticky switch? holding on never off? or even debris causing thew switch to not shut off?

I would check second option first but u may have already.

[LTD]

I was slumping stuff in a new kiln recently. Thermo couple was not inserted fully in to kiln. It was reading about 400deg low! I have also seen random temp jumps and fluctuations due to wrong wire used to lengthen thermo wires, and loose connections on crimp on terminals used to connect wires to back of digi controller.

[Natedizzle]

Every connection is tight and has been checked 10-20 times now, my thermocouple wire is from Seattle pottery supply. The thermocouple is fully inserted, and has been replaced. The kiln seals completely, maybe a 2mm crack on half of the top of the door.

I have not replaced the relay, but i know it's working since the kiln thinks it's sitting right at 1043 without overshooting...

Thanks for the suggestions, keep em coming!

[LTD]

Ghosts?

[earlbacher]

have you asked the pros if there is a way to recalibrate the controller??? if all the connections are good, that sounds like the one thing to think about

[glassblowingBiker]

do you have any thing other than a fugi can you go old school with it and just use a pyromaiter (not spelled right ) ill hope you can guess what i mean that would but about all i can offer Up

[Natedizzle]

I do have an analog pyrometers, and it has been reading the same as the digi... Which doesn't help my sanity!!!

[NUBBLET]

figure out how much the % of temp set to actual temp( second pyrometer) and set it that new adjusted amount and see if it still goes too high. this should tell u more if the switches and such r all good and free of crap.

have u listened to see if the element ever goes off?

[Greymatter Glass]

is the fuji set to ºC instead of F?

Without being able to poke around in it myself it's almost impossible to diagnose... but here's what I would check:

Thermocouple:
You say your analog pyrometer reads the same as the digital, so have you tried a new thermocouple?
Are you using the correct thermocouple? (K, I would assume)
Is the thermocouple hooked up with proper thermocouple wire? Regular copper wire will not work.
I assume each chamber is on it's own controller with its own thermocouple, right? They're not cross wired?

Go to a pottery store, ask if they can loan you a calibrated TC, they may want a decent deposit.


Bad controller. Is it using those cheap ass 1/16 DIN Fujis? I have seen more of those fail than all other controllers combines. Well, the older Sentry 2.0's in the F-240s overheated pretty bad, but aside from that... Digitry, Bartlett, Skutt, Orton (Sentry), Omega, Watlow... take your pick, but Fuji's suck, and would be dead last on my list.


Bad relay. Do you have a multi meter? Make sure the relay works.

Improper wiring.

Wrong elements?


Anyways...like I said, without being there, it's hard to guess... but i would suspect a bad thermocouple. Even if it's brand new, it could be bad. They're not hard to fix tho... but they're also pretty cheap.

-Doug

[LTD]

I do have an analog pyrometers, and it has been reading the same as the digi... Which doesn't help my sanity!!!

This covers any other ideas I had... I still say ghosts

[Greymatter Glass]

Also, pictures of the TC and inside of the kiln would help...

[petto]

marcel would be the guy to ask for sure, maybe he will chime in.

[Greymatter Glass]

Every connection is tight and has been checked 10-20 times now, my thermocouple wire is from Seattle pottery supply. The thermocouple is fully inserted, and has been replaced. The kiln seals completely, maybe a 2mm crack on half of the top of the door.



Missed this... I still think you're getting bad data from your thermocouple.

Make sure you're using the right type of thermocouple. Unless you have reason to do otherwise, you want a K type thermocouple. Make sure it's K.

get a multimeter or volt meter with a millivolt setting and then look at this chart:
http://www.greymatter.org/glass/tc-table.html


If you don't have a reference junction (a TC frozen in a block of ice, hooked up in parallel to your TC) then your reading will be slightly off, but will be the most accurate if you read it at the TC instead of at the end of any TC wire.

If you have anything but a K type TC the reading will be WAAAAY off, if it's close...you probably have a K type.

Also, if using thermocouple wire, make sure the polarity is correct, otherwise you're going to get bad ...signal...power..whatever.

[Slimy-E]

random guess, but how many places is temp read at i would think it could be a few 100 degree varents bin something tall big

I dont have a clue just took a swing

[menty666]

Where is the thermocouple located in the kiln?

If it's cool enough for safety at the bottom but melting things at the top, that would imply that you're getting a false reading and the thing's on overdrive, kind of like having your home's thermostat where it's hit by the sun. It's warm, the rest of the house is cold.

If thermo was low in the kiln, it would read cold and keep heating, but since your heat's going up inside the box, anything higher in the kiln would get toasted.

In theory.

[Eric S]

are your elements evenly spaced all throughout? maybe if heat is rising, they should be closer together at the bottom of the kiln and further apart at the top?

[LarryC]

Is the controller programmed to read a K type thermocouple? My Omegas can be programmed for a dozen or so different types of sensors/thermos. Should be a configurable item in the setup menu or a physical jumper setting depending on the type of controller.

[Swampy]

So,

Let's see if anyone here can help, since the experts are still confused by this one...

I recently built a giant annealer for our studio. It has two refrigerator style doors that open into two chambers, this way I can run decals and anneal on he same day. Each chamber is 27"x19"x39" tall, and each side runs on a 50 amp breaker, I believe the actual usage is 30-32... I wired each side with a fuji PXR-3 and 50 amp SSR relay.

So you have two chambers, each has it's own controller, TC and SSR?

or you have two chambers, an element in each chamber that runs from one common controller and SSR?

Post a schematic of your wiring.


Apart from what everyone else suggests, all I can suggest (in no particular order) is;

Fire one chamber at a time and see what happens.

Some controllers have a facility for one or more TC's so you can set it to read a mean of two zones.

Read your controller manual and Tune your controller at a set point (to calibrate it to the TC at a set temp).

Put your TC in a kettle and let it boil... should read 100degC.

Is the TC type selected on your controller?


Hope this helps anyway.

[somewhere]

Wow shitty.
You are sure the fuji is set for k and not s? The second pyrometer backing up your reading really baffles me. Boro just doesn't slump at those temps. Call TTI Global for a fuji tech they really are helpful.

Fuji controllers have serviced our shop for many years with zero problems. And we run a lot of them.

Good luck. Let us know what happens.

[gn0me]

One interesting aspect of kiln design is that at extreme temperatures, convection by physical contact with air is not the main method of heat transfer.

Try to envision the elements themselves as light sources. Anything the light shines on gets heated up, with brighter spots being heated more. That means that if you have elements in the side of the kiln, spots facing those sides will get hotter... this is why the most even firing slumping kilns have elements in the top of the kiln, putting everything at a more or less even distance from them.

This, combined with the large heat capacity of firebrick, and the thermocouple being in contact with the firebrick itself leads to very bizarre (and painful) kiln design issues. I found this out recently in some misadventures with an AIM kiln.

I powered the kiln on for the first time a couple days ago. The thermocouple was inserted fully into the kiln. As a control, I stuck the thermocouple from my box controller just inside the door. Something strange occurred - the kiln's thermocouple read 150 degrees Fahrenheit lower than the thermocouple just sticking inside the door, at the bottom of the kiln. Odd, since heat (usually) travels upwards, and since the doors are usually the coldest part of a kiln.

I thought the kiln's thermocouple was damaged and in need of replacement, or the controller had the wrong thermocouple type... however, for the sake of science, I left the kiln on, and the thermocouples where they were. After about an hour, the temperatures matched precisely(ish - within a couple degrees). Ramping the kiln up and down yielded the same temperatures from both, with a slight, but noticeable lag from the controller's thermocouple.

I realized a couple things: the elements, being set into grooves in the firebrick, left the thermocouple in a shadow. Being about 3/4" into the kiln made it appear as though it would be getting an accurate reading, but it was actually 150 degrees shy of the temperature of the middle of the kiln... it didn't get an accurate reading until the firebricks heated thoroughly (and transmitted more/blocked less of the radiation). The thermocouple being in contact with cold firebricks only exacerbated the problem.

All that said, there should be a few things you can do:

Get an independent thermocouple into a few different spots of the kiln, and see if you can measure something similar. Your main thermocouple may be in the shadow of a kiln brick or it may be contacting something cold. Check to see if work slumps after the kiln has been sitting at 1000 degrees for a couple hours. Try to get the tip of the thermocouple away from the walls of the kiln - you can get an excellent quality, quite long thermocouple from Omega (http://www.omega.com/ppt/pptsc.asp?ref=KMTXL_NMTXL)

Run autotune on the Fuji controller in mode 2 to reduce overshoot. Check to make sure the controller is set up to get input from a type K thermocouple, just in case. Here's a manual (http://www.instrumart.com/assets/108/PXR3Manual_409c.pdf) Specifically, P-n2 in the second block should be set to "3." While you're there, be sure PVOF and SVOF settings are at "0"

You may need to redesign the kiln a bit to avoid cold spots. There may be a need for elements in the door. It also sounds like you have a common wall between the two firing chambers. This wall is going to have some thermal leakage when both sides are firing. You may need to reduce the element density on this side of the kiln. Remember that heat is primarily transferred from light, not air, and that negates much of the effect of heat rising, and of air evening out the temperature of the inside of the box.

Be sure to let us know how things progress! Barring any of this, it's going to be down to pictures. Show us your sexy bitch.

[Icarus]

^^^^

Somebody rep this dude. I did it too recently to do it again, but that was some hardcore knowledge that just got dropped right there.

[gn0me]

Now you know... and:

http://img.printfection.com/14/170839/S0TZy.jpg

...the other half is kicking some ass.

[rabidgod]

Heat rises.

Does the elements start at the top, and run down through the kiln? Just thinking the elements could be losing their heat as the current flows through towards the bottom of the kiln, possibly from in efficient voltage. Is it + or - 10% of 230v. What's the running voltage at each relay, and what's the running amperage at the panel on either leg vs the running amperage at the incoming power into the kiln?

Take digi temp readings at the bottom, middle, and top of the kiln, there should not be any wild measurements in temperature, I assume. Heat rises, so I figure each zone might have a 10-20 degree differential, I'm guessing.

Are the set points on the controller set to cut out at 1 degree off, 2 degrees off, 10 degree over? Mabey the elements fire until it reaches over the temp, then you would see residual heat bring the temperature rise as latent heat is released and absorbed.

Placement of thermocouple to read an average temperature.

Sorry, I'm just spit balling

Just looking at it as a hvac tech, and how I would diagnose a call of a heater or a/c running past It's set point and over conditioning the space.

.02 - rg!

Edit - man , I should really read more than 5 posts before I chime in..

[The Bigles]

not knowing anything about kiln design I would have to say that it is probably the fault of nick voorhees.

[Aymie]

That's just too funny. Poor Nicky. Why is everyone always picking on him?

[daveabr]

I saw this thing in it's early stages, when I was at your party for GAS. Sweet little build. Hope it gets figured out.


Does it ramp up and hold at any lower temps? Or is it just firing, all the way up, no stopping?

[Greymatter Glass]

not knowing anything about kiln design I would have to say that it is probably the fault of nick voorhees.

Well, if Nick's been around I would have said that first, obviously.



That's just too funny. Poor Nicky. Why is everyone always picking on him?

http://www.youtube.com/watch?v=JbyYoeirX_w

[Emmett's Glass]

not knowing anything about kiln design I would have to say that it is probably the fault of nick voorhees.

Or Sam welded a gremlin inside it, or maybe the fact that your shop is on an Indian burial ground. Who knows?
E

[Greymatter Glass]

Nick Voorhees welded an indian into it?

[CripSkillz]

Nick slumped your mom!

[spanglerc]

Gnome, never seen a better solution to a problem since the fire extinguisher.

[Swampy]

If you ever figured it out Nate, it would interesting to read your solution.