Tempering in oil?

jaxxas

Well-Known Member
Hello,

Haven't been on in a while, had some health issues and ended up retiring a bit early. Also some plumbing issues which required re-plumbing the whole house which I'm only about 60% finished.

But we recently acquired a new toy linked below which while made for cooking gave me an idea on tempering. If you check the link this device {expensive) is capable of very precise heat control and I was wondering if it could be used for tempering. My thought is to use it to temper blades in oil. Thinking avocado oil as it has a smoke point of around 530 F. Possibly using a sand/oil slurry?

Any thoughts, opinion or real life experiences I appreciate your comments.


 

Chris Railey

KNIFE MAKER
Its intetesting but @Kevin R. Cashen or one of the other metallurgists would need to tell me tempering in oil would have the same effect as an oven temper. On the surface my thought is 400 degrees for two hours is 400 degrees for two hours be it in oil or air but I am no metallurgist.
 

EdCaffreyMS

"The Montana Bladesmith"
Chris is correct..... 400 degrees, is 400 degrees, whether that be from a liquid, or air (liquid being conduction, air being convection) The key is..... will the device offer the accuracy required to heat and HOLD the oil temp for the duration needed? I have no doubt what you're wanting to do is possible, but you're going to have to do a lot of experimenting, sizing the oil tank to make it work well. It's not totally about the accuracy of the heating device...... you also have to take into account the "thermal mass".....which includes the amount of oil, and the container holding it....... and the amount of "swing" that takes place when the device turns on/off trying to maintain the set temp. When it comes to tempering.....anything more then a 25F degree swing is unacceptable to me.

My experience with this comes from high and low temp salt tanks...... very often people use high temp salt tanks for austinzing because of their ability to be extremely accurate..... but there is a catch. The amount of salt equals thermal mass. Or in your case, the oil would be the thermal mass..... the least amount of thermal mass you can use to accomplish the job, the better. Why? The more thermal mass, the more "swing" you will usually have... that means the more thermal mass, the more you will undershoot, or overshoot the set temperature. The way I learned this was trying to help another individual with building a salt tank setup...... My tank is 2 1/2" ID X 18" long..... just big enough to do the largest knives I generally produce. When helping the individual I mentioned, he insisted on using a 6" ID X 24" long tank..... he stated he'd likely never need that big a tank...but he wanted it. I did my best to try to explain that he was gona have issues with accuracy..... and he did. His salt tank setup would hold to only within about 200F of the set point..... what happens is that the thermal mass was always trying to play catch up..... the salts would get to temp, the burner shut off, and the temp continue to climb for about 100F.....then it would start to fall until it reached the point where the burner was set to kick on.....and the salts would continue to fall for about 100F before it started rising again........THERMAL MASS.

Same holds true for the "low temp" tempering salts..... folks usually use a product called nitre blue from Brownells for this purpose. These "salts" melt at 400F.....and have a working range up to 900F. The "high temp salts" I mentioned above, melt at 900F, and have a work range up to 2,000F.

I believe the reason we don't see more "liquid" tempering, is because the same results are much more easily and safely achieved with air.....in either a heat treat oven, or even an accurate kitchen oven.
 
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jaxxas

Well-Known Member
Thanks much to both of you, I appreciate your response. I too thought that heat was just heat and it's nice to hear it's likely so from the brain trust here at KnifeDogs!


Ed you raise many concerns which I will heed. Know that this is just an offshoot thought brought about by this kitchen gadget. I have pondered buying a dedicated tempering oven but haven't actually pulled the trigger at this point. Currently I only 'play' at making knives. Certainly I have invested a lot of money to date and I hope to proceed in the future. Were I the only person making those decision it would have already been done!

This 'hotplate' for want of a better description has so far been amazing. So far it seems to hold a preset temp to 2 (1.8 per specs) degrees F temp. It also has a crude 3 step temperature ramp feature. Per the reviews I've read it will hold any temp it's capable of for up to 72 hours. Contrasting that with 2 different ovens and 2 different toaster ovens that I have never been able to hold a temperature swing of 25 degrees F. though I can nearly hold 25 degrees F if I use a pan of preheated sand in my current oven!

Concerning the thermal mass I think I can just play with the size of pot that I attempt to temper in!?

Just a quick example we fried chicken tonight at 330 degrees F, and after adding 3 pieces of chicken the temperature swing was only about 6 degrees and had recovered in less than 7 minutes after dropping to 324 F degrees.

Again thank you so much for your replies! I appreciate your knowledge and patience!
 

Chris Railey

KNIFE MAKER
Thanks much to both of you, I appreciate your response. I too thought that heat was just heat and it's nice to hear it's likely so from the brain trust here at KnifeDogs!


Ed you raise many concerns which I will heed. Know that this is just an offshoot thought brought about by this kitchen gadget. I have pondered buying a dedicated tempering oven but haven't actually pulled the trigger at this point. Currently I only 'play' at making knives. Certainly I have invested a lot of money to date and I hope to proceed in the future. Were I the only person making those decision it would have already been done!

This 'hotplate' for want of a better description has so far been amazing. So far it seems to hold a preset temp to 2 (1.8 per specs) degrees F temp. It also has a crude 3 step temperature ramp feature. Per the reviews I've read it will hold any temp it's capable of for up to 72 hours. Contrasting that with 2 different ovens and 2 different toaster ovens that I have never been able to hold a temperature swing of 25 degrees F. though I can nearly hold 25 degrees F if I use a pan of preheated sand in my current oven!

Concerning the thermal mass I think I can just play with the size of pot that I attempt to temper in!?

Just a quick example we fried chicken tonight at 330 degrees F, and after adding 3 pieces of chicken the temperature swing was only about 6 degrees and had recovered in less than 7 minutes after dropping to 324 F degrees.

Again thank you so much for your replies! I appreciate your knowledge and patience!
That is impressive recovery of temp. Is it an induction plate? If so, it may be cool to experiment with putting the knife directly on the induction plate. No oil needed.
 
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