Mini electric kiln project

[grepper]

That's amazing Mr. Jan.  Look at that perfectly even glow over the entire chamber!  It will be interesting to hear about what temps you get.

You will never have to worry about a morning in the shop with a cold cup of coffee ever again!

[Jan]

The glow of the chamber wakes up the feelings of a cave man in me.

I am still waiting for the high temperature sensor. What I know about the temperature now is that it is far beyond 1350°F when steel loses its magnetism. For raw temp. estimation the colour of the heated steel can be used.

   

The kiln insulation is so good that very little amount of heat escapes, but if door is slightly opened the coffee cup would be nicely warm.

Jan

[EOU]

We understand Jan. We couldn't sleep last night. Its like June in Alaska here in Arizona with that new glow emanating out of the East. Perhaps you could tinker on the kiln at night when we're all at work here.  

We learned a little lesson about heat and magnetism ourselves. We make the vises used with the ME110 edge tester and press a rare earth (neodymium) magnet into the vise base. The first few runs we had the vise bases powder coated and then pressed the magnets in. We decided to get smart and press the magnets in to the base and then have the whole works, magnet and all, powder coated. Not smart. The 450F degrees generated during the powder coating process will apparently remove about 90% of the "stick" from rare earth magnets. As they say "live and learn".

We can't wait until you're fully up and running with your kiln project Jan. We have a feeling that we're all going to learn a great deal as a result of your projects and experiments with heat treating and tempering.

[Jan]

Mike, thanks for sharing this story. I am not surprised by the loss of the rare earth magnets magnetism.** Rare earth magnets are basically of two types neodymium magnets and samarium magnets. Neodymium magnets completely loss permanent magnetism at temp above some 600°F. Samarium – cobalt magnets completely loss permanent magnetism at temp above some 1300°F.

I think your magnets were made of neodymium.

The temperature at which materials lose their permanent magnetic properties is called Curie temperature (Tc). It is named after Pierre Curie, who was husband of Marie Curie known for her pioneering research on radioactivity. She was the first woman to win a Nobel Prize.

Jan

**P.S.: You can restore the permanent magnetism (correctly remanent magnetization) of a heated magnet by attaching it to a fresh rare earth magnet. Respect the polarity of the magnets.

[Mark Reich]

That is a great color chart, Mr. Jan, and thank you for the tip on the magnets too!

I think you'll find that the Curie temperature is a starting point from which to work from. 

[Jan]

Mr. Mark and Mr. Scott, I would like to ask you about some practical aspects of knife steel heat treatment.

a)      At what temp do you insert the blade in the kiln?
b)      Do you use the heat treating foil?
c)      How many preheat stages do you use and at what temps? How long do you hold the steel at that preheat stages?
d)      Can cooking oil be used for quenching?
e)      Is there some time delay between quenching and tempering?


Jan

[scott.livesey]

Mr. Mark and Mr. Scott, I would like to ask you about some practical aspects of knife steel heat treatment.

a)      At what temp do you insert the blade in the kiln? for low alloy high carbon steel, 1475F/800C
b)      Do you use the heat treating foil? no
c)      How many preheat stages do you use and at what temps? How long do you hold the steel at that preheat stages? none, this is dependent on the steel you use and the source.  I mostly use O1/1.2510 precision ground flat stock that is ready to be hardened without pre-heat
d)      Can cooking oil be used for quenching?  yes, I use canola/rapeseed oil heated to 120F/50C
e)      Is there some time delay between quenching and tempering?  you want to keep the delay as short as possible.  I quench to room temperature then into ice water, scrub then into tempering oven.  


Jan

[Jan]

Mr. Scott, thanks for your answers to my questions and for sharing your heat treating method.

Jan

[wadebevan]

Jan, my process is pretty much identical to Scott's.
I use O1 tool steel heated to 1475-1500F and soak there for about 10 mins.
Also use vegetable oil from wal-mart, just because you can get gallons of it for pretty cheap.
I used a 'turkey deep fryer' pot for the quench oil because it was on the tall and skinny side - also from wal-mart.
Kind of nice because it comes with a propane burner for the preheat of the oil. And a lid, an important detail in the shop!

Another idea I found on the internet was to cut the top off a recycled argon or co2 welding gas cylinder for the quench tank, which I thought was pretty cool for knife work.

Happy heat treating!!

[Mark Reich]

Mr. Mark and Mr. Scott, I would like to ask you about some practical aspects of knife steel heat treatment.

a)      At what temp do you insert the blade in the kiln? for low alloy high carbon steel, 1475F/800C

a) I always preheat the kiln to the desired temp and let it soak for at least 15 minutes before inserting blades.

b)      Do you use the heat treating foil? no

b) Doesn't apply to carbon steel nearly as much as it does to stainless with long, high temp hold times, but I'd much rather use shielding gas in my kiln instead. That would take practically nothing in your kiln, and greatly simplify your process. Foil makes quenching very problematic. There are anti-scale compounds that work better than foil, but I wouldn't use anything except gas if the situation dictates ongoing anti scale procedure.  

c)      How many preheat stages do you use and at what temps? How long do you hold the steel at that preheat stages? none, this is dependent on the steel you use and the source.  I mostly use O1/1.2510 precision ground flat stock that is ready to be hardened without pre-heat

c) Doesn't apply to carbon steel. If your stainless requires soaking at lower temps, it's for specific temps and time. Probably specific ramps too.


d)Can cooking oil be used for quenching?  yes, I use canola/rapeseed oil heated to 120F/50C

d) You've invested so much time and energy into your kiln, and secured excellent steel. Real quench oil of the correct speed is a very logical, wise investment. It will last forever, and it's one less variable to ever consider. 

e) Is there some time delay between quenching and tempering?  you want to keep the delay as short as possible.  I quench to room temperature then into ice water, scrub then into tempering oven.  

e) Park 50 at 100° is a 5 second quench, which is almost as severe as brine. I maintain constant cooling to -290° F with liquid nitrogen, hold, thaw, then temper. Tempering before the most thorough cooling you're capable of defeats the purpose, but it's a common practice for fear of broken blades. If you totally remove stress risers you will never break a blade.