Length of time to reach kiln temp

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Maineiac1

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May 3, 2017
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just bought my first kiln. It’s an older model and a paragon KM36D. I just fired it up for the first time and to reach 1950 degrees took about 1 hour and 15 minutes, is this abnormally long? The unit seems to run great and hold a temp okay
 
Make sure all the coils are heating. If one isn't working, it will take a lot longer.

The main issue is your oven is rated at 2000F max. The last little bit is a squeak on many ovens. It takes a good while to fully soak the bricks and get above 900F. I have an oven that has a 2000F rating and it will barely go past 1900F and ... won't reach 2000F at all.
 
Stacy E. Apelt - Bladesmith said:
Make sure all the coils are heating. If one isn't working, it will take a lot longer.

The main issue is your oven is rated at 2000F max. The last little bit is a squeak on many ovens. It takes a good while to fully soak the bricks and get above 900F. I have an oven that has a 2000F rating and it will barely go past 1900F and ... won't reach 2000F at all.
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Okay it looks like all the coils are glowing. Seems like just one coil.. do you think I should go another route if I’m looking to get into stainless? Or will this be suitable but barely? Plus the neck pain of length of time it takes. It seemed to hold 1950 no problem even after I opened the Door and shut it, seemed to recover pretty good
 
Just a thought are you leaving the knives in while warming up?
Or do you have a knife rack in place?
Maineiac1 said:
3600 Watts, it’s a larger 36” deep 5.5” wide and 4.5 in tall chamber..
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So that's just over 0.5 cu ft. At 3600 Watts that's just under 7000 watts per cu ft. Mine is 8000 watts per cu ft so your quite close and still on the high side I believe. Dan Comeau's site DIY Knifemaker has a heat treat oven build page and he lists a bunch of ovens and their wattage per cu ft. 5000 is the average.

I'm no expert but you could try a couple things:

1. Once it reaches temp and is there fore a while are you able to place your hand on the outside of it? If not, it would appear to be bleeding a lot of heat. And infra red thermometer may help to find hot spots.
2. Do you have anything acting as a heat sink inside of it while warming up? IE, a bunch of blades, blade rack or fire brick? I do notice mine takes much longer to heat up with blades in it. Maybe I'll time mine to see exactly how long it takes. I could be underestimating the time to heat up. I have heard of ovens taking this long to heat up.
3. It appears your coils are working, and if your not bleeding heat and don't have a large heat sink, I would guess its the controller setup. I know very little about these but in my research about these, is that with the wrong settings, it'll take forever to reach temperature as it doesn't want to overshoot so it slows down too much near the desired temperature. It could be a setting issue. Does it have an autotune setting?
4. At 3600 Watt I'm assuming its 240 volts. Have you checked the fuses? You may have 2 fuses (one for each hot lead). If one is burnt out, your coils may only be running on 120v.

If it's getting up to Temp and holding steady I wouldn't think twice about using it. Just work on some blanks or tidy up the shop while it's heating up. Or better yet, turn it on and then wrap your blades in foil.
 
Everybody is talking like 1 hr 15 minutes is too long for his oven to reach 1950F - what would the normal time for an oven to reach 1950F? Of course, that depends on watts and size of oven. I've got an EvenHeat KF18 and it will take well over 2 hrs to reach 1950F. I do have a couple of firebrick inside so the blades in rack are located right below TC tip and these firebrick does slow it down some, but not all that much. This is the oven I've got with .68 cu ft and 3120 watts:
https://usaknifemaker.com/evenheat-kf-18-heat-treat-oven.html

Anybody else have that same size oven that could give your times? The 1 hr 15 minutes of OP doesn't sound bad to me.

Ken H>
 
It doesn't seem too crazy to me. 36" is a pretty big oven. My Evenheat 22.5 takes about 45 minuets to get up to 1500. I let it soak for another half hour after that to be sure everything is stabilized, before any steel goes in, so I get it heating way in advance anyway.
I do have 4 hard fire bricks on the floor to protect the soft stuff, that may be acting as a heat sink and increasing the heat up time. Never thought about it.
 
Okay a lot of good information here, thanks!

It is a 240v and fuses are good. I do have a 36” rack inside but no fire bricks or anything. When it was at 1950 I was able to touch the outside but it was pretty darn warm. I was looking at buying a new kh18 evenheat but didn’t realize how long that one takes to heat up. Maybe I’m okay just paranoid as it’s my first. I’ll give it another test run tonight.
 
all sounds normal. The oven I built is about 3500 watts and is .46 cubic feet. It takes about an hour and 20 minutes to reach 1975.
 
Ken H> said:
Everybody is talking like 1 hr 15 minutes is too long for his oven to reach 1950F - what would the normal time for an oven to reach 1950F? Of course, that depends on watts and size of oven. I've got an EvenHeat KF18 and it will take well over 2 hrs to reach 1950F. I do have a couple of firebrick inside so the blades in rack are located right below TC tip and these firebrick does slow it down some, but not all that much. This is the oven I've got with .68 cu ft and 3120 watts:
https://usaknifemaker.com/evenheat-kf-18-heat-treat-oven.html

Anybody else have that same size oven that could give your times? The 1 hr 15 minutes of OP doesn't sound bad to me.


Same oven just about the same times--- for the last 20 years.
Ken.
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That's a big furnace. Getting all those fire bricks to temp is going to take a bit. An 18" can take nearly an hour so I'd say you aren't that far off if not right where it "should be".
 
The thermo math on your kiln suggests that it should heat significantly faster than you observe. I used numbers for K23 bricks. I am guessing that you are getting something well less than 3600 watts. Any chance your coil had been replaced by a higher resistance element? How hot is the exterior of your kiln getting?
 
I was wondering this myself. If you have an ohm meter measure the resistance of the coil from lead to lead. Please make sure the oven is unplugged. If you don't want to open the panel, you could measure the coil inside of the oven and be fairly close. Just make to to measure as close as possible to each end of the element.

At 240 Volts and 3600 watts the oven should be pulling 15 amps. To do this the element should have 16 OHMs resistance. That's assuming my math is correct.

Watts = (Volts)(Amps) 3600 ... (240)(Amps) Amps = 15
Volts = (Amps)(Resistance) ... 240 = (15)(R) = 16 Ohm's

I guess you could check the current draw if you have a clamp tester. Most people have a simple multimeter so they check resistance.

If your coil is 16 OHM's running at 240, my guess would be a PID setting.

Joe had a good point that someone may have replaced the element with the wrong size. A longer element will give more resistance, and less wattage.

Regardless, I think you got a great deal on a good size oven.
 
Maineiac1 said:
just bought my first kiln. It’s an older model and a paragon KM36D. I just fired it up for the first time and to reach 1950 degrees took about 1 hour and 15 minutes, is this abnormally long? The unit seems to run great and hold a temp okay
Click to expand...
Too fast to reach that temperature may result to cracks in the bricks especially when You have some water in it. I do prefer preheating My furnace with 2 hours from 20 to 200°C and run HT another day. I have DIY electric kiln and in version 1 I had reach time over 2 and half hours from 20°C to 1000°C. I made new heating elements for 3PH and now I can reach 1000°C in 40 min. but I don't do that. In HT is no hurry... ;)
 
Not sure what's ever been replaced as this was sold from someone that knew nothing about knife making. The exterior of it while at 1950 for 15 minutes is verrry warm. I can set my hand on it but its very uncomfortable after 10 seconds or so. I ran it up again and all the bricks inside had the same glow color to it so I will start trying some heat treating and see how it works. I did put a piece of O1 in it at 1450 for 20 minutes (after it cooled down from 1950 at 15 minutes)and it still needed another 15 minutes at 1500 before I could quench. The steel started to heat at the tip (away from the door) well before the tang started to get nonmagnetic. If I look inside, the far back of the kiln just looks so much hotter than near the door, obviously because of heat loss from the door but seems a bit much... Anyways ill try it and work from there. Thanks for all the help understanding these things!
 
Probably the best thing to do is to make some coupons and test them at different temperatures. I'd suggest making the coupons big enough that you can break them to see how the grain growth is. This showed me that my DIY oven was way too hot. I don't have a hardness tester so I just file tested everything. I saved the coupons though to have them test at a machine shop. This should really be done with any oven to make sure you're getting the best heat treat possible.

In reality, you just want a good heat treat so this will let you find the recipe that works best for your oven.
 
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