How do yo let your kiln cool down?

Patrice Lemée

Patrice Lemée

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Aug 13, 2002
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I have 2 blades to do in my brand new Evenheat! :D First time I fire it up. (Well except for the dummy cycle they have you do the first time).

One is 1095 the other CPM154. I wanted to do these the same day but now I read in a post that you should let the kiln cool down with the door closed to prolong the life of the coils. Is this true? I mean with the door closed I imagine that it will take a pretty long time for the kiln to cool down enough to start the next knife. (Since I also read that you should start cold).

Thanks
 
I've always let mine cool down with the door closed, it just seems to make sense that cooling the coils as slowly as possible eases the stress.
Why don't you put both blades in the oven at the same time? Set the temp and soak for the 1095. It should not bother the CPM 154, most heat treat recipes for that steel call for a midpoint soak to ease the stress before taking it up to critical.
The temp inside the oven should not drop very much when you pull out the 1095 for quenching. Then adjust the temp and soak for the cpm154.
 
Joe's suggestion is what I would do.

Place both blades in the cold oven. Program the oven as follows:
1) preheat to 650C and hold for 10 minutes
2) ramp to 815C and hold for 10 minutes. Remove the 1095 blade at the end of this hold and quench it.
3) ramp to 1065C and hold for 30 minutes. Remove the CPM-154 blade and plate quench.
4) ramp to 200C for four hours.

If you are not tempering in the Evenheat, just end the program after the 1065C hold. If you are tempering in the oven, put both the blades back in the oven once it gets down to 200C. After 2 hours,pull them out and cool in water to room temp, dry off ,and put back in the oven for the rest of the time (the other two hours). If you are doing Cryo or sub zero treatment on the CPM-154 blade, you will have plenty of time while the oven drops to 200C to do it.

BTW,Set all ramp rates at full.
 
thats what i would do to tho its not often that i run high carbon low alloy and SS/ high alloy in the same day.
I like to let the kiln cool with the door closed but when i use simple steel i leave the door openn an inch or so to get the blades into temper faster. remember that the kiln will hold heat even after the air inside has cooled the temp probe off. when the temp gets close to the 200c close the door and see how far the temp climbs
 
From testing I've seen done, heating steel below astenitizing temperarature does not cause grain growth, so you can throw both knives in there.

From testing I've done myself, at least on A2, it's OK to throw something in the hot oven, just needs a longer soak.
 
Leave the door open for it to cool down, when it reaches the temp. you want, put the blades in and close the door. Watch the temp reading over-shoot your tempering temp by a couple hundred degrees. You have to let it cool from the outside in. With the door open to cool, the chamber can be at the temp you want while the insulation around it is still much hotter. When you close the door the hot insulation can push you way past your temp.
 
Well that's good to know. I was not aware that it stresses the coils to let the kiln cool with the door open. Damn... better stop doing that.

Rick
 
Cooling with the door closed does extend coil life. I have a concern with doing both blades in one cycle. Presumably, the stainless blade will be in a foil envelope. Opening the door and cooling mid cycle causes the envelope to contract - almost shrink wrap the blade and sometimes this can lead to foil sticking to the blade. With 1095, you have enough to think about in quench without having to worry about getting the door closed up quickly.

My inclination would be to do the 1095 first - then let the oven cool to about 800 - 900F and then put in the stainless blade and envelope and treat as usual. I suggest letting it cool to 800 or so because I'm reluctant to put a well sealed envelope into a very hot kiln. It can blow up envelopes with rapidly expanding air inside the pouch. I haven't had this problem since I started the cool to 800 thing. You won't waste much energy - just a bit of cooling time.

Good advice above on watching for temperature rebound when tempering.

Rob!
 
Some good info, thanks guys. I never thought about the open door just cooling the air inside faster.
Stacy, I'll give that a try, thanks. No cryo for now. By the way, for oven temperature (including kitchen ovens) we did not make the metric switch around here. Maybe they tried but for some things like this and workshop measurements, people are still using the English system.

I'll let you know how it turns out.
 
Oups, I was typing while you posted Rob. I'll do it that way then. It should reach 800 fast enough. And yes, I read your info that came with the kiln and I was worried about the envelope blowing up. I put some paper in there but not sure if I put too much or not enough. (2 pieces of thin brow paper maybe 1"x2"-3")
Thanks
 
Slowly cooling the kiln with the door closed reduces thermal stress caused by uneven cooling that will extend the life of both the elements and the firebrick. For the elements keeping the door closed also helps reduce oxydation of the coils themselves by reducing the amount of oxygen in the kiln.

I only keep the door open for as long as needed, if one looks at the electric coils during a soak they become yellow hot, and there is probably oxydation going on to those coils each time I open the door to grab a knife (wrapped in a stainless foil pouch also to keep oxygen out) to quench and let in more fresh air.

Its a good idea to keep a spare set of coils. Coils in the kiln will burn out when you need them the most, and they are not expensive for the Paragon.
 
Patrice,
OK - 1200F,1475F, 1950F, 400F. I thought you French-Canadians were the first to go metric. I guess there are other folks just as stubborn as the USA.
I would not be concerned about the foil packet collapsing. The packet will not form a vacuum unless it cools much,much more than the few degrees it will when you open and close the door. Rob's way will work, but probably isn't really necessary.
 
backup coil or 2 is a good plan tho i have had my kiln few i think 7 years and have not yet needed to replace any (whatch now i ll burn both in the same day :) )

dont touch the coils and let them cool slowly and they will last a long time i have run mine from anywhere in the 120f range all the way to 2125f. but most the time its 1475f 2030f or 400f temper (now and then 1200f for S anneal )
 
Just to follow up. Since it was my first time using the kin I decided to do both knives separately. Letting the kiln cool down with the door closed. I was surprised by how long it takes to cool down from 1950. :eek:
Everything went fine. Love the kiln! :thumbup:

Thanks again for your help!

PS: Thanks for the straightening during temper tip Rick. I tried it and the blade (1095) is almost straight after the first cycle. Just a little tweaking left for the second cycle. Mush less stressful than doing it with the 3 point jig. :thumbup:
 
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