Thread: New oven

Nice! For the big blades remember to shield blade from direct radiation heat by elements. They can cause significant overtiming or overheating of parts of the blade... i suspect more so if close to the side than the centre of furnace...

I was able to get away with putting a piece of fire brick in the end of the oven. That is where I thought I was having problems as the point of a long knife seems to be the trouble area in that regard. .

Originally Posted by AndreGrobler

Nice! For the big blades remember to shield blade from direct radiation heat by elements. They can cause significant overtiming or overheating of parts of the blade... i suspect more so if close to the side than the centre of furnace...

I have seen people sawing the firebrick in thin sections and building a little tunnel around the pieces too...

I'm going to have to make a thermo mapping of this oven. With the whole lot of oomph of the heating coils, and the location of the thermocouple, 200 censius on the display does not equal 200 Celsius in the middle of the oven. Or I would not be looking at half a dozen blue razors

Luckily I can re-HT.

For simplicity's sake, I'm going to run the tempering cycle again tomorrow, starting from a cold oven, with polished bits of tool steel at various places. That should give me a good idea of temperature distribution.

I really have no idea about what you are explaining, way over my head, but if you are happy, then I am happy too,,,

Bruno, that is one heck of a big heat treating oven! I can see the issues with heat stratification for tempering.... easy to wind up with hot and or cold spots in that size of a kiln.

Mapping the temps? I hope it works out for you, and yes, just bits of polished steel will do the trick. Hopefully, a rack at a given height (maybe sitting on some kiln bricks will be even enough. The last time I used a kiln that big, it was for initial heat treatment only, and the annealing oven was a forced air unit to keep the temps even throughout the drawer it had.

Good luck and maybe take in some pottery firing to make some money on the side! I mean, you can always spend it on more tools at the end of next year, no?

Regards

Kaptain " Tempering is a pain, re-hardening and tempering again, is a Royal Pain, but nothing is as painful as dealing with the Tax Man!" Zero

Just a suggestion, Make a steel box muffle evener tube on legs to go within the kiln. It would even out the temperature gradients. That way if it was given a slide out drawer, you may be able to do more than one blade at a time.
I have seen quite few variations of this theme.
~Richard

t might also be a good idea to bring the oven to temp first, and then slide in a box with razors when the temp is stable. This way I avoid overshoot durig the heating phase when the coils are going full blast to heat the oven.

Originally Posted by Bruno

t might also be a good idea to bring the oven to temp first, and then slide in a box with razors when the temp is stable. This way I avoid overshoot durig the heating phase when the coils are going full blast to heat the oven.

Good idea! As long as that box is not resting upon any surface of the kiln. It should be on legs to place it in the center of the radiated heat.
An external pyrometer with a lead into the box would definitely help your accuracy.
~Richard

Interesting. If I have a ceramic stacking plate halfway up the oven, why wouldn't I put it directly on the plate, assuming everything is rpe-heated?

In any case, today I finally used it for heat treating a couple of large things I had waiting for heatreatment for quite a while now. I preheated the oven to 820 degrees Celsius, which took about 3 hours. When I opened it, the entire inside and the stacking plates were glowing a mesmerizing orange. Awesome sight to behold

I put the machete in for 6 minutes or so, and when I opened the door, it was nearly invisible, glowing exactly the same like all the rest. When I took it out and quenched it, I wore long sleeves, welding gloves, and a full face mask. The mask was because when the door opens, a large blast of heat comes out. My daughter loved the colors of the inside. Quenching the kitchen knife went about the same. When the oven had cooled to 650 Celsius, I called her over, opened the door, and from 2 meters we basked in the radiant heat

The kitchen knife had a slight kink in the shoulder which was easily fixeable. Long laminated blades can get like that. I have to say though, that with this oven to bring everything to the exact same temperature, the rest remained perfectly straight. I fixed the kink by tempering with the blade under reverse tension. For the machete I tempered it like normal, and then took it out of the oven and kicked the hardness of the spine down another rcouple of points with a small torch.