Revealing Kiln Test.

Thanks Rick. Calibration is key. I never understood why people just assumed machines are accurate in their readings. What a good reminder to check and double check.
 
Nice test thanks for sharing. I also let my Evenheat come up to temp and equalize a bit before putting the blades in. I have noticed while tempering in the Evenheat that if the temp falls when it ramps back up it can over shoot by 20 or 30 degrees then come back down.
 
Just for clarity guys...

Normally, I DO allow my kiln to equalize BEFORE I put in my blades. This test was set up to reflect the temperature spikes during ramp up proceedures and to validate the infrared/radiant heat scare that a few of us have been trying to get across to folks.

It is also important to note that the Tempilstiks can melt BEFORE the piece they sit on gets to temperature. I found this out while using the T-stiks to "calibrate my eye" when using an open forge. I was originally pre-marking the steel and gaging the temperature by when it melted.... that was the wrong way. I needed to apply the marker to the steel OUT OF THE HEAT SOURCE to get a true reading of the steel itself, rather than reading the forge.

The experiment in this thread was all about getting to know my own kiln than nailing the temperature for a good heat treat. If you have a kiln, I strongly urge you to do your own testing. Tempilstiks are easy to find online.

As for the Sugar Creek Kiln...

230 Volt
11 Amp
2530 Watt

I should be able to hit the stainless temps but admittedly, I'm somewhat afraid(however unjustified) of buring out an element. Perhaps someone who regularily hits these temps can try an experiment. Besides... my Tempilstiks only go to 1800F.
 
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This is my Sigar Creek Big Knife Kiln.
IMG_0088-2.jpg


When it was all nice and pretty inside. Note the thermocouple location and the way the elements are tucked down inside a J-channel so they are not directly exposed to the chamber. This may or may not have helped. I have no experience with exposed coil kilns.
IMG_0011-10.jpg
 
Rick Marchand said:
The worst mistake a beginner can make is to announce that every blade he did up to that point is crap.:eek:

Ha!... I'm messin'...:p:thumbup:
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Rick, I thought this would be a good place to give you a dose of your own medicine :) Thanks for the testing and saving me even more headache!
Jason
 
jawilder said:
Rick, I thought this would be a good place to give you a dose of your own medicine :) Thanks for the testing and saving me even more headache!
Jason
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Ha! Nice one, bud.

Hey, I hardly attempted anything outside the capabilities of an open forge while I was using one for heat treat... and if I did on the occasion use O1 or 1095, I made no claims to be reaching its full potential.
 
Thanks for doing this and posting the results. I definitely learned something here. But I would like to respectfully disagree with one of your conclusions

Rick Marchand said:
Conclusions:

... 6. If a digitally controlled electric kiln can fluctuate this much, how crazy-off is trying to eyeball it in an open forge? In other words, don't fool yourself into thinking you can nail complex steels in a forge.
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In your first experiment your kiln overshot your temperature by several hundred degrees. I would submit that an experienced bladesmith with a keen eye for color and decalescence would never come close to screwing it up this badly. Instead, your experiment has shown us all the folly of relying too heavily upon a digital program to get it right. I bet there are at least a few bladesmiths reading this right now, thinking "oh crap, have I been overheating all of my blades all this time?" simply because they did not take the time to get to know their kiln as you have.

There are lots of bladesmiths out there heat treating all kinds of complex steels with forges and achieving superb, consistent, and reliable results. Some have built special heat treat furnaces that allow them to heat their blades evenly and control temperature and atmosphere with a great deal of precision. Meanwhile, I'm sure there are plenty of guys out there who have bought kilns just like yours thinking that all they need to do is punch in a couple of numbers and the computer will do the rest, never bothering to check actual temperature or test their blades.

Who would you rather buy a knife from?
 
bladsmth said:
Yes, Rick, I should have said "Blade can reach 1800". I have edited it.

As to why the temperature display doesn't show this over heating, there are two reasons:

1) The TC is often encased in a white ceramic sheath, which reflects infrared radiation, and reads the ambient chamber air. Air is not as easily heated by infrared radiation as a metal blade is. The TC is also placed in a position quite a bit away from the blade.

2) The PID which controls the program "learns" as it cycles. The on/off control gets closer and closer as it figures out exactly how long to fire the coils each cycle. Once it gets it figured out, the oven will maintain a very even heat. In the early parts of the learning curve, the PID is like most new drivers. It only knows two positions - "Accelerator Flat on the Floor" and "Hard Brake". During these learning steps, any small mass metallic object that can absorb the heat energy ( like your blade) may overshoot the chamber temp. The readout only shows the air temp. not the blade temp. Page Steinhardt has had to do studies in his metallurgical occupation where they drilled holes in a metal object and placed a dozen thermocouples directly in the object to see how much variation there actually was. It made the company change its HT regimen to allow for fully soaking the oven chamber BEFORE placing the metal object in for HT.
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EXACTLY THIS. Emmissivity of the item being heated changes its reaction to IR radiation. Additionally, thermal mass effects response times of the TC.

On ovens, kilns, etc we take a minimum 5 point (position) temp verification within the chamber. More is better.

In industry CALIBRATION is only one step or piece of the equation. We perform Installation Qualifications, Opetarational Qualifications, and Performance Qualifications.

Lastly, to when needed, we use the PID to control triacs for proportional phase angle power INSTEAD of a SSR on/off circuit. You gain much finer control of the power and therefore the temperature.

Sorry for kurt response, using phone. Back can't sit at computer.
 
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True, Wulf. I agree... this test really has no bearing on the performance of open forge heat treating... and I'll ammend my statement. I am one of those simple forge guys who went to great lengths to familiarize myself with judging temps and using tips like muffle pipes and Tempilstiks to fine tune and get closer to the mark. Still.... as I stated in my last post, I think it is unrealistic to think you are nailing complex steels that require pre-heating and extended soaks, in a coal or LP forge. There are few who can judge(if any at all) even a 100F difference in temperature by eye. Once you get into pyrometers and PID controlled furnaces, we are no longer talking "simple forge".
 
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Good stuff.

Got me wondering some things. What effect would heat tret foil, being pretty reflective, and anti scale compound like PBC being preet dark, have on uv heating? I wonder if the foil would keep the steel from spiking like that.

I have a small sugar creek kiln. When I do stainless I foil wrap the blade and put it in a cold oven for the full ramp up. The kiln takes a long time to get up to 1950. Could the uv be causing the blade to go hotter than 1950?

This may motivate me to get a pyrometer to check the temp of the steel during the cycle, somehow attach the probe to the steel...
 
Rick Marchand said:
Once you get into pyrometers and PID controlled furnaces, we are no longer talking "simple forge".
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True, true ... and a good pyrometer is maybe just a little bit more accurate than an eyeball. After all when judging by color alone your assessment can vary quite a bit based on ambient light and other variables.

I guess the important point, for me at least, is that when heat treating it's critical to verify as best you can that you're getting your temps right, regardless of the method you're using - coal forge, kiln, salt pots, etc. And finally, test every knife! Even if the temps appeared perfect, you don't know for sure that it worked until you know for sure that it worked!

Good thread
 
Well said, Wulf. Some say a caveat of using a kiln/furnace is not being able to see the decalescence point of the transformation.
 
Rick Marchand said:
Use it in appropriate applications under controlled conditions and compare several different heat treat processes.
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So where can the benchmarks be found to make comparisons? What you are describing might find the best in the bunch of blades you have on hand but to determine if it is at "full potential" you need to know what that actually consists of.

If someone claims they are getting the "Full potential" out of a steel then that should be measurable and not just a belief. It would be a great reference to the knifemaking community for those who claim they are getting the "full potential" from various steels to document it and provide the data so we have a benchmark to compare to.
 
If you choose not to "believe" the suggested heat treat schedules of the steel suppliers, that is fine. If you want to heat treat in a forge, with a torch, in a kiln... or quench in Parks, Goop, Houghton or Canola.... I have no problem with that and do it myself regularily. Anything is fair game as long as you are honest about it with your customers and yourself. If you are heat teating by simple means(LP forge, by eye) and claiming all the superior properties of O1 (that are based upon the suggested heat treat schedule in the spec sheets) I have to say that you are not being intellectually honest. You may believe that you are hitting the mark everytime but are only fooling yourself. On the other hand, if I follow a HT regime that coincides with the industry specs, it is fair to say I can expect to get darn close to those listed properties.... even if I can never measure them, myself.

To suggest that the optimal properties are immeasurable leads me to ask why someone would choose a steel based on those same properties. You can buy a Ferrari(O1), but if you only have the means to put 4 spark plugs in it , you are probably better off with a good running Honda Civic(1084).
 
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The temp sticks are accurate to +/- 100 I believe. The way we test our ovens at work is with several small scrap or drop pieces of stock placed in differant areas of the oven. Then Rockwell test them after quench. In my opinion this is the only way to know exactly how it's performing. If everything is good, all pieces should hit the right number on the Rc. scale for the given material. We do this monthly, besides the normal everyday heat treating. I also do it at home with my Paragon. I agree 100% on your findings while ramping, ramp as slow as possible. There is some debate on cold oven vs. hot.
 
I am asking a legitimate question.

If you are claiming to be reaching full potential that should be measurable. There are many variables as you know and just following a cook book approach does not guarantee "Full Potential" if anyone is going to make a claim of reaching full potential then it has to actually meet the bench mark of "full potential" not just believe it does. It is very important to be honest when making claims for all knifemakers and claiming "full potential" when it is really an assumption probably is not the best description.

Some data should be easy to gather from those reaching "full potential".
 
Properly functioning equipment, known composition steel, industry proven HT protocol, industry tests and standards - rockwell, charpy, % martensite, grain size, etc. Sample proven in application. Then you have your benchmark.
 
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