Electric oven heat treating question

D

D. Pfanenstiel

Joined
Sep 2, 2004
Messages
59
Is anyone successful in using a long oven, like a Paragon 36km, in heat treating long blades? I've been fighting mine for years, trying different solutions but running into the same issue. I basically cannot get an even heat down the blade. If I pull the blade after a soak, the tip area is much hotter than the tang. Since the tip goes in first, toward the back of the oven, I think that because the heating elements wrap around the back wall, it's just naturally going to be hotter down there than up towards the door area, where the elements do not wrap around. There is a noticeable graduation of heat down the blade that I would guess being a difference of 100 degrees or more, which is not acceptable. I've tried moving the thermocouple down towards the far end, which keeps that end from getting too hot, but then the tang end is too cool. I've heard of others letting their oven run for an hour before heat treating, to equalize temps, might try that too.

Anyway, just wondered if this oven is headed for paper weight heaven.

Dan
 
How long are you pre-heating the oven?
How long do you leave the blade in?
How are you determining the tip is hotter...by eye? That is not very accurate.
Is the HT coming out poorly?


Take a bar of 1084 steel and HT it. Temper at 400F. Accurately test it every 3" for Rockwell hardness. If there is much variation in the readings you have a problem.....if not, all is OK.
 
Just now tried letting oven run at set temperature for an hour, still no love. There's a good difference between the back of the oven and the front. Put a long piece of steel in and soaked for 10 minutes. Blade comes out a reflection of the oven, hot at the tip and cooler towards the tang. So the oven doesn't equalize even with a long soak. Pretty much narrows it down for me.
 
Dan, I don't know a whole lot but to me you are a master at heat treating long blades/swords. Why don't you just heat treat the same way you did that sword that you quenched in water at the hammer in? Seems to me that one turned out great. You made it look so easy too!
 
I would like to know the chamber size, element configuration and wattage of the oven. If it is very deep and the elements cross in the rear or even make a turn from bottom of the side to top of the side on each side I can believe the rear gets hotter than the front. More coil in a given are would produce more heat. Before you paper weight it, you might try installing new elements and having some straight run of element the rear area. I would think you could fine tune it using this method and maybe tightening the coils in some areas and spreading them in others. If not I would consider adding another PID complete with thermocouple and splitting the front and rear elements between the original pid and the second. That would be my last resort though.
 
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Ray, thanks man! Hope I can do something again this year. Gotta talk to Mike. I was hoping to get the oven functional for various treatments, like getting a really tight temp for ramp down normalizing, tempering after the quench, etc..

Steels laver, you might have hit on something that hadn't occurred to me. I did replace the elements last year and, since it's my first oven, and first time replacing elements, I may have gotten the coil density too high back around that turn. It is pretty tight. The frustrating part would be all the contact with the company, with no solution. I'll give that a whirl today.

Gotta give credit to Mike Quesenberry too. He called and suggested a fire brick at the back to block that concentrated heat situation. That could get implemented too.

Thanks to guys for the input.

Dan
 
I was going to suggest a firebrick in the back, and turning the blade so the tang is inward.

Another almost silly sounding choice would be to set the oven on end, and suspend the sword down the center on a stainless wire hook. The temperature gradient should rise to the upper (door) end, thus (maybe) evening out the hot end problem. The good thing is that this should be easy to try. A bar of steel should be pretty simple to fit across the door opening to hang the blade from. The door should close on it well enough to get the oven sealed.

Reconfiguring the oven to have two or three PID controlled zones is an option, but will be a good bit of work and expense. Hopefully, it can be taken care of by some simpler means.
 
That's another good idea, Stacy. When I got the oven years ago, it was configured to stand on end, might have to go back to that as well. Basically a tall skinny top loader.

Dan
 
Woohoo! Went right out, took that thing apart and yanked the element out. Caressed and massaged those coils into a state of calmness that would solve the worlds problems and stuck it all back together. Ramped it up to 1400 deg (takes about 20 minutes) and all is right with the world. Nice even heat down the length of the chamber.

All great suggestions from you guys but it was Steel Slaver there that got me thinking, which I don't do too well on my own, apparently. Owe you a beer there Slaver.

Thanks all again,

Dan
 
Dan you're a perfectionist and I'm glad to have read this thread... things like this bring encouragement to a newbie as myself....

at first I thought you were just overthinking this, but I'm glad to see you resolved your issue !!!
 
Glad it worked out for you. No need for the beer if we ever met up. Maybe a pointer or two on something you have a handle on.

The double PID idea would only be a last resort type of thing.
 
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