For those who get their kilns up to temp. before putting the blade in.

Tom Lewis

Tom Lewis

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Feb 24, 2000
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There have been some good posts on why, in order to avoid overheating the blades, it is a good idea to get the heat treating kiln up to temperature before putting the blades in.
For those of you who do this, How do you know how long to keep the blade in when you put it in a kiln that is already up to temperature.
Let's say the steel should soak for five minutes before it is quenched. How do you know when the blade gets up to tempurature so you can start counting the five minutes?
 
When you put cool steel into a heated kiln, the temp drops. When it returns to the previous temp, your steel will be heated as well or at least close. I add a few minutes to the regular soak time from there.
 
Tom,

I don't know if there is a magic answer for this, however, I will offer a few suggestions.

When you place a blade in a pre-heated oven, your oven will probably begin to cycle again. (heat always moves to something containing less heat). Once the oven cycling stabilizes, give it 3-5 more minutes before timing your blade soak. The oven may overshoot the temp a bit, but that is normal. It will not overshoot the temp enough to overheat the blade.

Remember, if the recipe calls for a 5 minute soak at XXXX degrees, then, provided you don't exceed that recommended temp, you can soak it much longer without ill effects. It is always better to soak a little longer at temp, than not to soak long enough and not get everything into solution.

Does any of that make sense?

Robert
 
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Robert is right on, IMO. I would love to instal a window in the door of my kiln. The best way to know when your blade reaches conversion temp is to watch it!
 
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I once did a test with a series of blades in my pre-heated oven and a high temp non-contact laser thermometer.
And when I pre-heat my oven, I let it sit at temp for a minimum of 1/2 hour.
I would place a hunter sized blade in the oven and check it every minute by quickly opening the door and "shooting" the blade for temp.
On average, my blades were up to 1500+ degrees in an average of four minutes.
 
For my kiln, I set the temp to 1420F which is just above curie point. I let the oven come up to temp and equalize/soak for a 30+ minutes. Then I placed a carbon steel blade in the oven, closed the door, and waited several minutes. I opened the door and checked the blade with a magnet to see if it was up to temperature. According to multiple tests I did, for carbon steel blades in my oven, I needed 4 minutes (same as Karl) for the steel to reach target temperature.

For stainless steels, I'm usually doing a longer soak anyway, so I just add 6-8 minutes to the desired soak time. As long as you're protecting the steel and have good temperature control, a few extra minutes of soak isn't going to hurt anything.

--nathan
 
great info guys...

I usually treat 6 knives at a time in 2 phases... so for the time it takes me to put 3 knives in the chamber my temps have dropped 200+F, when it comes back up to desired temp I count my soak... so usually I can count on 18mins for a 10min soak...

heat treating is an adrenaline rush, and while I was in the zone I managed to stab the ceiling of my kiln with a 20" large knife I was trying to rush into the chamber so I could quickly close the door.... :( its an open close case :p
 
Battle Creek Knives said:
heat treating is an adrenaline rush,...
Click to expand...
You shouldn't be rushing brother... there is no need. Heat treat is a operation, just like any other. The less than 1-2 second quenches seem to freak folks out but that has more to do with the quenchant than getting your blade from the heat source to the quench tank.

Here is another tip for electric kiln users...

When you are taking out or putting in a few blades at a time, switch your kiln to idle. The temperature drop you are reading is coming from the thermocouple. When the door opens the hot air rushes out and the thermocouple cools. That sends a message to fire up the elements. The fact is, when you shut that door the walls are putting out heat as well. There is a delay effect going on between the thermocouple and the controller. What happens is the elements are trying their hardest to raise the temperature and end up overshooting the mark. Next time, try switching the kiln to idle and just shut the door for a few minutes. You'll see the temperature rise WITHOUT the elements firing. Once it peaks, turn your program back on. This avoids overheating the kiln and overheating your blades with the radiant/infrared heat of the elements. You may have to push a few more buttons but I bet you are just sitting and watching that readout anyway, right?;):thumbup:
 
Rick Marchand said:
You shouldn't be rushing brother... there is no need. Heat treat is a operation, just like any other. The less than 1-2 second quenches seem to freak folks out but that has more to do with the quenchant than getting your blade from the heat source to the quench tank.

Here is another tip for electric kiln users...

When you are taking out or putting in a few blades at a time, switch your kiln to idle. The temperature drop you are reading is coming from the thermocouple. When the door opens the hot air rushes out and the thermocouple cools. That sends a message to fire up the elements. The fact is, when you shut that door the walls are putting out heat as well. There is a delay effect going on between the thermocouple and the controller. What happens is the elements are trying their hardest to raise the temperature and end up overshooting the mark. Next time, try switching the kiln to idle and just shut the door for a few minutes. You'll see the temperature rise WITHOUT the elements firing. Once it peaks, turn your program back on. This avoids overheating the kiln and overheating your blades with the radiant/infrared heat of the elements. You may have to push a few more buttons but I bet you are just sitting and watching that readout anyway, right?;):thumbup:
Click to expand...


This makes good sense & it's one ore reason that I think a door open-cut off switch on the control side of the relay/SSR is a good idea.
 
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