Tempering Oven Build -WIP

Stuart Ablett

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Tokyo Japan
OK, I'm on to building the Tempering Oven

donor_hot_plate.JPG
I found a donor hot plate thing, it draws 1200 watts max, so should do nicely, it was $12 delivered to my door, I promptly cut it up in to pieces :D :thumb:

I took two bricks, and stagger jointed the edges together, then I carved out a depression for the hot plate to sit in, with two holes going right through the bricks for the wiring.

mock_up.jpg
I then built up a mock up of an oven around this hotplate thing, hooked it up and let it rip! :D

It took about 8 minutes to get to 600C...........

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I slid one top brick aside to take a look see, yep, it's hot! :rolleyes:

The one problem I'm seeing is the temp control on this unit is not very good, I ran it through a good dozen cycles and the low point where the heater kicks back on and the high point where it kicks off is about 80C different........ not so good.

I need to hit a temp between 540-570C for 62 minutes, according to the steel maker.

I guess I'l try to find some kind of controller that is more sensitive? :dunno:

Any ideas guys? :huh:
 
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I don't really think it is a "Thermostat" as it is the knob you see on the control panel thing with the red light on it. There are a set of contact point there, by adjusting the knob, the distance between the points vary, and the temp that it kicks on or off does too.

I know to keep it right on a certain temp, I need something that is in the oven, I guess that is what I'm looking for, something I'd wire into the circuit somehow, that would have a relay in it.......?

:huh:
 
Just had an idea. A rheostat, if you can find one. Or some other way to control the current to the element. Temperature is then related to the amount of current. Not the time it is on and off. Should be more stable. Assuming you can find a control of some type.
 
Stu,

You can get a ceramic probe that will work, from a clay supply store. They should have those down around the art area near Ochanomizu, or thereabouts. I mostly remember stationary and other art though, but there must be a city for clay supplies somewhere...:doh:

You can order one from Clay Planet in Santa Clara.
 
Thanks Alan, but I'd need more than just the probe, I'd need something to turn on and off the heat, right?

This is where I got to this morning........

tempering_oven_built.jpg
That is the basic shape, all stagger jointed together, lots of work, and lots of white dust everywhere!

inside_view.jpg
I put the heating element on the top, I figured it would not matter much, and it would take a lot less abuse up there, I very much doubt it will make much of a difference on the heating up part.....:dunno:

Here it is with the top removed......
top_removed.jpg
...... I wired the heating element into the two blocks, I'll have to get some high temp joint cement or something to fill in those holes, a bit of heat could come out of them!

Now I got to build a frame for it, then I'll crank it up and see how it goes.

Cheers!
 
Thanks Alan, but I'd need more than just the probe, I'd need something to turn on and off the heat, right?
You mean you want not only the ability to monitor the temp, but to control it for you also? I think that would be an elaborate setup. For the most part, you can keep propane at a constant rate, so if you get the forge to a specific temp, it should hold pretty good, at least mine did when I measured and heated it for forging brass (around 1300F deg.).

What your problem most likely will be is keeping the temp. low enough so that you can stay in the range you've listed, which seemed to be similar to the brass figure I put in above. I don't have a conversion table so not sure how much 540C-570C is, but I think it's about 2x the figure, so you should be around 1100 degrees.

You will most likely have a difficult time getting your burner down that low.

Did you put a flare on it? If so, you may need to adjust it so that you can turn the flame down low enough, there's a fine area that you must adjust that will allow low vs. high flames. Ideally you want to be able to use an idle loop as I installed on my forge, but in order for it to work correctly, the flare needs to be adjusted, otherwise the flame will go out when it's low.
 
Stu,

I see that this is not your forge, it's another brick box...:doh:

Get a hot plate with a temp gauge on it!:D
 
The hot plate does have a temp thing on it, but the sensor, or rely on it has an 80C range, so it if turns on at 530C it goes to 620C before it turns off.

I'm hoping that this will not matter much, as once the steel is up to temperature, it will not effect things much, the time from power on to power off is less than a minute....:dunno:

This is what I got done today........

framed.jpg
The frame on this one is much like the frame on the other forge.

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I'm doing a test run here, letting it run full chat, to see how hot it does get....

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It was still climbing, but the high heat wires were starting to smoke where the come out of the oven, so I shut it down.

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I opened the door to take a cook see, yep, I could make toast in there no problem :D

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Ready to give the 62 minute temper routine tonight, I ran out of time today.

Wish me luck! :wave:
 
Stu

What are you giving for fire brick over there. I finally found some locally butt they are $5.00 each or a little over with tax. I had bought some before but they weren't really fire brick.. Just brick for a fireplace.

Garry
 
Garry, look at a Pottery place, these are the same bricks they using in pottery kilns.

I paid 580 yen, plus 5% tax, so 609 yen or $5.08 US

There are different kinds, rated by temp the ones I'm using are the 2600F (1430C) bricks, they also have 2800F (1540C), but they are $2 a brick more, and I'll not need that extra bit, as my forges don't get that hot.

The brand name is Isolite.

Cheers! :wave:

I found this place.......

http://www.sheffield-pottery.com/NC26-G-26-SOFTBRICK-STRAIGHTS-p/nc26.htm

$3.86 per brick, but with a $0.50 per brick packing fee, so I think for $5 a brick you did OK.
 
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Well, I fired up the tempering oven tonight, got it up to temp, and waited 62 minutes :D

A funny thing happened, before, with the oven empty, but the door closed, I would get a swing in temp of about 80C from when the heating element turned off, to when it turned on again, but with the three pieces of steel in there, the swing was reduced a lot, just under 40C from off to on :thumb:

I guess the steel would hold the heat in there longer or something?

Anyway, those three are done!

tempered1.jpg tempered2.jpg
They were nice and shiny when they went in, but now they are a dull gray color.

Thanks for reading along!

Next time around, I'll be using straight carbon steel, MUCH easier to work with! :D

Cheers!

I guess it worked? :dunno:
 
Yeah, $5 is not bad for the refractory bricks, for just plain old fire bricks, like the yellow ones you see under the oven and the forge, those are used for like backyard BBQ pits. I get them for about $1.50 each.

Anyway, I cleaned up the steel, and sharpened the business ends.......

sharpened.jpg

Hard to get a good pic of them, but they seem a LOT harder than before, and seemed to sharpen up nicely, I can shave my arm hair with the skew! :thumb:
(the two scrapers are upsidedown, so you can see the sharpened faces)

Next up will be some handles!

Cheers!
 
Great looking chisels you have there Stu. If you ever need to know you can always do a test of which holds holds an edge longer the chisles you made or the HSS ones you purchased. Maybe you can use some keyaki as the medium. :thumb:
 
Looks great, Stu. Lemme know if you're interested in selling an Ablett skew or scraper. (Still waiting for Doug Thompson to make his skews and scrapers available.)
 
Well, I did get the Lacer-esque Skew done, and I got started on hardening your steel Alex......

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Here are the three pieces getting a hot bath, this time around I learned to put a piece of steel on top of the blanks, as the flame blasting on them is not good, it makes them difficult to sand smooth later, this way they have a lot more uniform heat. (not that you can see it in this pic.... :rolleyes:)

I got the forge up to 1200C (2200F) a lot quicker this time round, the new burner is a LOT better! :thumb:

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It was a bit stubborn to get over the 1200C mark then it rolled right on by and I had to cut the pressure to the burner a lot, I guess once all three blanks were up to temp things just kept on getting hotter!
Alex_1235.JPG

Wonder how hot it would get :rolleyes:


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This time round, I also found that opening the back door a lot more made thing climb faster and stay hotter, I guess it is the amount of air getting to the flame.... :dunno:

I only got one heat soak done, I'm just about out of propane, you can see the tank icing up.....

Alex_ice_tank.JPG

Won't be long Alex and I can send you these blanks, hardened on one end, and still annealed on the other.

Cheers!
 
this time around I learned to put a piece of steel on top of the blanks, as the flame blasting on them is not good, it makes them difficult to sand smooth later, this way they have a lot more uniform heat. (not that you can see it in this pic.... :rolleyes:)
Stu, soak them in vinegar overnight, and then brush with amonia to stabalize the vinegar, that should get them all cleaned up with little effort. I used some of Junko's rice vinegar (Japanese women seem to always keep this stuff around;)) once and it worked fine. Recentely one of her friends moved back to Japan and left a gallon of white vinegar, which my wife doesn't use and gave to me...:thumb:
 
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