Evenheat oven set up problem

Duncan Tipton

Well-Known Member
Hi all,

I resently purchased an Evenheat KF22.5 with a Ramp master control. I have had a couple if bad goes heat treating O1 and 4140. The just didn't get hard. I have done some tests with an infrared temp gage, and discovered the botom of my oven is about 200 degrees lower than the top next to the thermocouple. My infrared tester only goes to 999 degrees, but I do see a pattern in my tests. Have any of you had similar issues and what have you done to compensate? I was thinking about building a fire brick platform to get my blades up near the top of the kiln. Right now I just have the knife fixture Tracy sells on the floor of the kiln.
 
That is the first time I've heard of that happening. Are both sets of coils working and do they look the same, ie same color red when hot?
 
Tracy, thank you for your response. All the coils work and look the same. Here was my test. I ramped the oven to 400 and held for 30 min, the blade was 250 or so after that time. I then ramped to 600 and held for 30 min the blade was 450 or so. I then ramped to 950 and held for 30 min the blade was 800. I decided to hold for another hour and on half to see what would happen. With 40 minutes left on the timer the blade had reached 950. Maybe the lesson is I must soak much longer to make sure the blade has reached oven temp.

The whole reason I did the test was a batch of 3/16 thick 01 that didn't harden. For that run I ramped it to 1200 and held for 30 min then ramped to 1475 and held for 1 hour then quenched in oil. They ended up less that 40 rc. I then used a torch, heated them to red and quenched in the same oil and they got hard so I figured there was a problem in the oven. Thanks again for your time and ideas. Duncan
 
Give Evenheat a call and explain whats going on. You should have already done this. I work 01 exclusively. I ramp to 1250 for a 45/60 minute soak. For me, this has reduced warping, then to 1485 for a 20 minute soak. There is no need to soak longer, but no harm if you do. I quench in Parks AAA oil warmed to 130°. I get perfect results. Evenheat is going to have much better answers than you get from any forum. Are you using any form of decarb protection?
 
Whether folks realize it or not, this is a common issue with heat treat ovens that have the thermocouple mounted topside. It's not a flaw, it's physics....heat rises, and the upper area of a heated chamber will always be hotter than the lower portion. How much hotter depends on a number of factors.

I've owned both evenheat and Paragons, and both have exhibited this characteristic. When I first started using heat treat ovens, I tried using the "recipes" recommended for given steels, and wasn't getting full hardening....I realized that a recommended soak of 20 mins, meant that ONCE THE STEEL REACHES THE SPECIFIED TEMP....not from when I put it in the oven. My solution to the oven being cooler on bottom was the use a "stand" (either the type the oven companies offer, or build your own from firebrick).

There is a lot more to using a heat treat oven than getting it to temp and placing a blade inside......there are several variables that have to be taken into account and compensated for. The fact that heat rises is simply one of those variables.
That might be a "DUH!" answer to some folks, but I've found that many do not realize those things.

After thinking about it, I have to ask the question.....Why are you folks soaking O1 for such a long duration? Just curious.
 
Last edited:
Thanks for your input guys. I did call Evenheat. They told me how to check the thermocouple and suggested I do a temp test using pyrometric cones. I think my thermocouple is fine and the oven is working properly. The long soak is to make sure it got to temp (but it didn't).

LRB, how long does it take the steel to get to 1485 from 1250? Are you blades at the top or bottom of the oven? I haven't been using decarb with 01.

Ed, in your experience, how long does it take blades to get to temp when placed on the stand?

Do either of you have a way to varify the temp of your blades? I've been looking at that but it's expensive.
 
Interesting Duncan.
I've always used some kiln shelf in the bottom of my oven and that raised it up some. I've also checked my oven with a thermal couple, top and bottom and never found much of a difference. The owner of Evenheat is following along (via my emails) and I will keep him posted.
Unless I'm wrong, you are good for now?
 
Tracy, I suppose I have more testing to do. I will try to raise my blades up to the top of the kiln. Thank you for talking to Evenheat, I'd like to hear if they have any tips or suggestions ( as well as anyone else). I'll let you know how my next tests go.
 
My blades sit edge up in slots I cut into fire bricks. They are near the top. At least midway. I coat my blades with a water based anti scale/anti decarb solution I get from Brownells. I have never timed the heat rate from 1250° to 1485°, but i will guess maybe 10/15 minutes. Not a very long time anyway. Ed, 01 requires a good soak for a good austenite solution. I have read from as low as 15 minutes at quench heat, to 30 minutes. I chose 20 minutes, but 01 could stay at 1475° to near 1500° for a much longer time with no ill effects from grain growth, as long as it is decarb protected. I don't think anything over 20 minutes is necessary, but will do no harm to the grain. The long presoak has reduced warp for me. I still get a little warp in many, but can usually hand straighten while the blade is still warm out of the quench.
 
Duncan, as I mentioned I used fire bricks. Cut slots lengthways in it with a masonry blade in a Skill saw. I believe the slots are between 3/8" and 1/2" deep. I only HT 3 blades at any one time so I can keep them close to center in the oven.
 
I notice some makers heat the oven prior to putting in the blade, I put the blade in at start up. and do a 20 minute soak at 1200, then ramp on up to 1500 and soak for 20 minutes. I figure the blade is at temp as soon as the oven reaches temp doing it this way. I also use a stand to get the blade towards the top of the oven. Is there a reason to put the blade in after the oven reaches 1200 instead of at start up?
Dale
 
The reason to put the blade in after the oven is at temp is to make sure the oven is heat soaked. It makes the temperature more uniform and stable within the oven.

Ed, I can see then point about heat rising, but in a small confined space like an oven interior, time should be your equalizer. Hot AIR rises, but heat diffuses. Given enough time and enough energy in a small confined space, I'd think that the energy should diffuse fairly equally throughout the oven except for right next to the coils.

My guess is that the coils aren't achieving full temp or at least aren't cycling on frequently/long enough. This is causing a situation where there isn't enough energy to fully heat the oven interior. Therfore you get the hot air at the top of the oven effect magnified beyond what it would normally be.

--nathan
 
Tracy, thank you for your response. All the coils work and look the same. Here was my test. I ramped the oven to 400 and held for 30 min, the blade was 250 or so after that time. I then ramped to 600 and held for 30 min the blade was 450 or so. I then ramped to 950 and held for 30 min the blade was 800. I decided to hold for another hour and on half to see what would happen. With 40 minutes left on the timer the blade had reached 950. Maybe the lesson is I must soak much longer to make sure the blade has reached oven temp.

Review your program and verify that your ramp rate is set for "9999". By the above quote, it sounds like the oven will eventually get to desired temp just very slowly. It may be as simple as a programming error.
 
I thought you just popped in the blade and presto it was ready to go. Lol I guess I need to do even more tests when I get my oven in this week. Now I am nervous. I got the same oven as the OP.
 
I also have the same oven. Put the blade in, program, and monitor it occasionaly. Most alloyed steel needs a stress relieveing soak before the oven ramps up to your chosen austenitizing temp. The simple steels probably don't need a preheat, but it would do no harm. DUNCAN, that does not sound right. Is your oven 220/240 V, or 110V?
 
Review your program and verify that your ramp rate is set for "9999". By the above quote, it sounds like the oven will eventually get to desired temp just very slowly. It may be as simple as a programming error.

Good thought Brad, but I measured the blade temp with an infrared thermometer after it had been at the plateau temp for 30 minutes. I used a 4 segment program for my test. I did use the fastest ramp setting (9999). Between each plateau temp I held for 30 min then ramped to the next.
 
The reason to put the blade in after the oven is at temp is to make sure the oven is heat soaked. It makes the temperature more uniform and stable within the oven.

--nathan

This is a very good point I will start doing this. The more I think about this the harder it is for me imagine the oven itself being 400 degrees when the thermocouple has only been 400 for 30 minutes. What do you think?
 
I also have the same oven. Put the blade in, program, and monitor it occasionaly. Most alloyed steel needs a stress relieveing soak before the oven ramps up to your chosen austenitizing temp. The simple steels probably don't need a preheat, but it would do no harm. DUNCAN, that does not sound right. Is your oven 220/240 V, or 110V?[/QUOTE

The oven is 240, and that is what is at the outlet when tested with a multi meter.
 
Back
Top