Holding Blades in Heat Treating Oven?

I don't undestand why your so apposed of putting metal in a furnace other then your blades. I also don't understand how you can claim your blades maintain an even heat in a furnace that heats and cools constantly without shielding the blades from the spiking heats from the coils to maintain the set temp. If your oven is set at 1500 the coils are going to radiate higher heats then 1500 to maintain it, sure the pyrometer will register and maintain the atmosphere at close to that 1500 but only after the coils submit higher temps to maintain it. Its like standing in the middle of a room or backing up to a wood stove, something going to get a lot hotter unless its shielded from the direct heat or a long distance away. Maybe you don't have that problem using foil wrapping I don't know, but I don't do stainless or use foil. I have placed long blades in the oven unshielded and after a set soak time seen the colors of the tip areas a brighter color then the tangs, that told me I needed shielding. Whats your throughts on this?
I don't mean to question your advice I'm just trying to understand and come up with better ways.

I would also be interested in hearing how long you let your furnace heat before you consider it evenly heated and ready to use. Fire brick takes a long time to heat up to critical heats, I sliced a 2" high temp brick in half last year to use as a shield to protect the blade tips on longer bowies from the rear coils and it wouldn't get to the same color as the steel at critical heat for well over 2 hours and that was standing up inside the chamber, I would think that anything laying on the furnace floor would really get the heat drawn from it by the firebrick, if you think about it, if firebrick heated very quickly your funace would glow in the dark after a couple hours.

Thank You,

Bill
 
Bill: Putting metals other than blades and SS foil in a furnace is inviting the oxides of these metals to end up in your furnace walls and on your furnace elements. the less metal burning off inside my expensive furnace, the better. For me, it just makes sense to use the soft firebricks.

As to comparing temperatures of different materials in a furnace by looking at colors, I don't think that would be too reliable.

At the temperatures we run our furnaces to HT blades, much of the heat in the furnace is RADIANT heat. Once the furnace reaches about 1400-1500 degrees, having heated up from RT in approximately 1 hour, the inside of the furnace is all going to be the same temperature, assuming the furnace is properly designed.

It takes about 1 hour, 30 minutes for my furnace to reach 1950F, with blades inside.

Your analogy to standing by a wood stove doesn't apply, because in the case of your furnace we are talking about what is going on inside the wood stove. Once your stove is fired up, and the airflow is good, how much temperature variation do you think there is inside the stove?

BTW, the inside of my furnace DOES glow, well after I am done heat treating. The furnace retains heat until the next day, because of that radiant heat I was talking about.

Hope this helps. Try not to overthink it. I have had my blades metallurgically analyzed by Crucible, I've calibrated my furnaces and, I know my process produces ideal results. Try it!
 
Wow rj, I'm glad I wasn't holding my breath for a response after my last post. :D :D :D

I see what your saying about the metal oxidizing, but the steel I'm using is so small a piece, that a 4 inch hunter has a much greater oxide exchange then my holder. I also use to lay the spine of my blades on a piece of brick with the tang in a piece of brick that was slotted and neither the tang area or the spine would show the same color as areas well away from the brick, unless the oven was given ample time to bring the brick up to heat to illiminate it as a heat sink.. Using the 1" long piece of 3/4" angle iron to hold blade, the whole blade will be an even color when its pulled from the oven. I was having trouble getting the tang areas to harden as high as I was wanting them using brick, but with the angle iron I no longer have that problem, that told me the brick was wicking more of the heat away then I could have imagined. I guess it just comes down to different strokes for different folks, we all have our own ways, and if your happy with your results thats all that matters.

Thank you for the reply

Bill
 
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