A small trick for tempering accurately in Evenheat kilns...

Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by aarongough, Sep 25, 2015.

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  1. aarongough

    aarongough

    Mar 12, 2013
    Hey guys!
    Just wanted to share a little something with you that I discovered the other day!

    I've always had issues with my Evenheat kiln overshooting the target temperature when tempering... If the setpoint was 400ºF and the kiln was already warm sometimes it would go over-temperature by as much as 40-50ºF.

    Well I finally worked out the issue the other day. I've always previously set my ramp speed for the tempering segment to '9999' however this was incorrect. When set to '9999' the controller basically runs the elements wide open until it hits the set-point, then corrects. This works fine for high temperature steps because of heat-loss, but for the low temperature steps it causes overshoots.

    If you change the ramp speed to something like 1000ºF/hr the kiln will only overshoot your set point by just 3-4ºF before settling down. If you want fastest possible heat-up along with no overshoot you could likely chain some segments like this:

    Seg 1:
    Ramp: '2000'
    Temp: 350ºF
    Hold: 0

    Seg 2:
    Ramp: '500'
    Temp: 400ºF
    Hold: 2 hrs

    That should get you to temp quickly with little to no overshoot.

    Let me know how this works out for you guys, it's been working well for me! I'm using one of the smaller Evenheat 18" kilns with the rampmaster control.

    -Aaron
     
    LCKT707, Ken H> and Storm Crow like this.
  2. S.Alexander

    S.Alexander

    Jul 7, 2013
    That's a great tip. Thanks Aaron.
     
  3. BlackRapids

    BlackRapids

    2
    Jan 11, 2015
    Great tip! Thanks.
     
  4. Kosa_PL

    Kosa_PL

    Aug 25, 2013
    I have better Tip.

    Wanna good precise kiln?
    Buy a better - industrial or lab kiln :)
    My PEM-1 muffle kiln 2,5kW is for 1200*C and with TAIE PFU-48 ( 2 programs with 8 steps) after AT for 800*C, this have overshoot +/- 1*C
    Evenheat and Paragon are Hobby level kilns.

    This PID is with a fuzzy logic.

    or if you want to use evenheat or paragon, just don't use their controllers.
     
  5. aarongough

    aarongough

    Mar 12, 2013
    I would very much like to buy an industrial furnace, and am currently looking into furnaces made by 'Lucifer Furnace Co' in the USA... However the price difference is quite substantial. The Removable Muffle Furnace that I would *really* like is $17k... Which is not going to happen unfortunately.

    My little Evenheat has a done a lot of good work for me, temperature control seems very good except in the exact case that I have outlined in this post.
     
    Ken H> likes this.
  6. Kosa_PL

    Kosa_PL

    Aug 25, 2013
    Aaron, ask people in IZO or KEPKA in Poland, they also making kilns for export.
    In size for knifemakers (like 150x 200x 450mm chamber) you will pay max 5.000$
    From IZO you will get even with PLC control and touch screen.
    Put be prepared to pay about 1k for sea-shipping.
     
  7. aarongough

    aarongough

    Mar 12, 2013
    Thanks mate, I will have a look!
     
  8. PEU

    PEU Gaucho Knifemaker Knifemaker / Craftsman / Service Provider

    939
    Aug 6, 2006
    My self made HT oven uses a really nice PID controller (http://www.automationdirect.com/adc...ss_Controllers/1-z-8_DIN_Size_(SL4896_Series))

    The nice thing about it is that you can calibrate it at four temperatures, if I recall correctly I used 250C/500C/800C/1050C
    It's like having four controllers in one since the oven knows how to accuratelly get to these set points and not overshoot, and if you are not using exactly one it uses the closer one.

    Great advise, again if I recall correctly by Timgunn1962.


    Pablo
     
    olymon likes this.
  9. aarongough

    aarongough

    Mar 12, 2013
    Nice! I actually hadn't seen the PIDs made by Automation Direct, they look nice!

    I have a toaster oven setup that I modified with a PID and a solid-state relay for baking Cerakote. Those electronics will soon be getting moved to a much larger oven so I can do batches of knives more easily!

    I've thought about making a kiln, perhaps I should just do it as I'm sure it would be a fun project!

    -A
     
  10. PEU

    PEU Gaucho Knifemaker Knifemaker / Craftsman / Service Provider

    939
    Aug 6, 2006
  11. Don Hanson III

    Don Hanson III KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Oct 3, 2002
    I have a cheap 24" Sugar Creek kiln that only over shoots 3-4 degs when tempering, then settles down to 1 deg.

    But I also have a smaller Paragon that over shoots 40 degs, then settles down to 20 after 15 minutes. This one I just set 20 degs lower than I want. Works fine, but not ideal.
     
  12. Karl B. Andersen

    Karl B. Andersen

    Jul 27, 2003
    You need the entire oven's mass to be at tempering target anyway. So it should sit at temp for a good 1/2 hour before placing the blades inside.
    By that time, the over-shoot will be smoothed out.
    It's not an issue.
     
    Ken H>, butcher_block and 12345678910 like this.
  13. Rick Marchand

    Rick Marchand Donkey on the Edge Moderator

    Jan 6, 2005
    What Karl said. Overshoot shouldn't be an issue if you understand it.
     
  14. BenR.T.

    BenR.T. Tanto grinder & High performance blade peddler Moderator

    Apr 18, 2011
    They speak the truth!

    It's also important to bring the oven to temp before putting blades in for hardening, overheating can be an issue for the same reasons then as well.
     
  15. Redmeadow Knives

    Redmeadow Knives John Conner / lessismore Moderator Knifemaker / Craftsman / Service Provider

    Aug 29, 2010
    Good tip Aaron, crazy timing, I had the same epiphany recently. I had always left the 9999 Ramp as well, and would get that temp jump right off the bat.

    Having only one oven, how quickly should the first temper occur? As quick as possible from what I understand. It takes about 40 minutes+ before my oven cools down enough to stabilizes below my target temp and I can start a cycle. Does this fall within the window of time for the first temper? I haven't found anything definitive on this.
     
  16. aarongough

    aarongough

    Mar 12, 2013
    I do the same thing in terms of having to wait for first temper and it's not caused any problems that I've seen!
     
  17. samclaymore

    samclaymore

    755
    Jun 7, 2014
    Hey Arron, I like your YT vids. Your down to earth approach makes others feel like they can make basic (but nice) knives too.
     
  18. aarongough

    aarongough

    Mar 12, 2013
    Thanks mate! Glad you like the videos!
     
  19. Rick Marchand

    Rick Marchand Donkey on the Edge Moderator

    Jan 6, 2005
    Aaron... This could come off as dicky but please know that it is not my intent.

    Kilns have ramp speeds for a reason. We should be educating ourselves on their use and take advantage of the controller. We should also have a grasp of basic metallurgical and heat transfer principles. The last thing would be to familiarize ourselves with the steel we use, with regard to it's chemical composition.

    Maybe, I am just having a problem with the chosen title of this thread(OCD and all)... "A small trick for tempering accurately in Evenheat kilns...". It sounds as though kilns need a "trick" to work right. To me, it is like starting a trick thread for a drill press... only to tell us you discovered that changing the RPM to suit the bit size improves performance. Something that anyone who uses a drill press should already know.

    IMHO, this thread should be titled... "How to properly use your kiln's controller."
     
    Last edited: Oct 1, 2015
  20. aarongough

    aarongough

    Mar 12, 2013
    Rick,
    The default ramp speed on the Evenheat controller is '9999' and after doing a austenitization segment the kiln chamber is already nice and warm. The issue I was having was that if after waiting for the kiln to cool down you used a 'default' ramp setting on your temper step then it would overshoot and stay high for quite a while because of the latent heat in the chamber. With it set to a slow ramp instead it will immediately ramp to the right temperature and hold there quite nicely. That little difference easily saves me 30 minutes out of my heat-treat schedule.

    I'm a software engineer and quite familiar with electronics, but it was non-obvious to me that the controller changes it's behaviour when the ramp is set to '9999'. It will heat to the set-point and then try to manage the temperature, rather than doing any sort of ramp control.

    Yes this is a small nugget of information, yes others might 'know how to use their controllers' already. But to me this was non-obvious as I said.

    At least two people have chimed in saying they appreciated the tip, so perhaps I was not the only one with the issue?

    I'm just doing what I normally do, trying to spread helpful information as I come across it.

    -Aaron
     
    Ken H> likes this.
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