Thread: Heat Treatment Furnace Construction

I will be watching this with keen interest Ray. A fellow forum member very generously gave me a little oven last weekend. It requires a few small repairs and reassembly. Will be nice for plane blades.

BT

Thanks for posting this Ray...I plan to copy both this and your casting operation. (eventually)

Greg

It sure looks big Ray. Just what do you have planned?

Gas or electric?

Stuart

Originally Posted by Stustoys

It sure looks big Ray. Just what do you have planned?

What about a ultra low setting and knocking out a few pizzas?

Looks interesting, that shed is filling fast.
Do you ever sleep Ray, LOL

Dave

Just an update.

The main support frame is tacked up, and so the whole thing now looks like this.



The bricks are arranged to just make sure we got the height measurements correct, Josh has the whole thing drawn up in SolidWorks, so GregQ, I'll be able to post a full set of plans if you want to make one. The 3d simulation in Solid Works allows you to get the door mechanism working just right, without welding and cutting..

Stuart, Electric of course, the internal dimensions are 600 long x300 wide x200 high, the height might be a little more or less, depending on the work support frame. The books I've been reading recommend against just putting the work against the brick surface, you need to allow for even heating all around, and resting the parts on insulating brick means the surface contacting the brick surface doesn't heat up at the same rate as the top, so we have had to design a support arrangement using stainless steel rods.

DaveJ, Since I stopped watching crap reality shows on TV, I find there's plenty of time in the day.... but, I could always use more sleep I guess....

Bob, I have a book I can recommend, "Heat Treatment, Selection, and Application of tool steels" by William E Bryson, his style is very down to earth, and practical, he covers A2, A6, H13,S7,M2,4140,O1,W1,CPM10V with a detailed chapter of do's and don'ts for each.. There are a couple of other books I've got on order from Amazon, but they haven't arrived as yet.
That furnace you showed looks nice, I'd say perfect for plane blades, chisels, taps, reamers and so on, I recently got some O1 drill rod, for that exact purpose.

The outer shell will be stainless steel sheet. I'll get the local sheet metal place to guillotine the pieces to size.

The control system will be a small networked embedded linux computer with a mysql database of the desired temperature profile, and a graphical display of the actual versus setpoint temperatures. More detail in later posts.

Regards
Ray

PS BobL, How about a 3 second Pizza at 1200C ?

Ray,
I thought you would be using electric but when I saw the size I wasnt sure. Even the little kilns I have seen use lots of kW. How many are you planning on? I guess I am talking about pottery kilns which would have more work to do to start with.

I'm told the best pizzas are cooked very very quickly.

Stuart

Hi Stuart,

I saw a guy on tv interviewing the Dalai lama, and tried to tell a joke...
The Dalai Lama goes into a pizza shop, and asks "can you make me one with everything"
The joke crashed and burned badly..., the Dalai Lama, didn't get the joke at all...



The amount of heat required depends on a number of factors, but the simple equation I've been working on is this one..



H is the amount of heat input in watts
k is the thermal conductivity of the material W/mk
A is the area in square meters
dT is the temperature differential across the insulation
x is the thickness of insulation in meters

So, k for LBK-23's is very low, 0.19 W/mk at 350C, a little higher probably at 1200C, but I don't have data.

A is the area, which for 600x300x200 is 0.72 square meters
x is the thickness, which is about 0.15 meters, not all brick however, around the brick is several layers of zircon fibre blanket, which has a lower thermal conductivity than the brick anyway.

When you plug all the numbers in and take 1200C as the temperature differential, you get an equilibrium heat flow of 1094 watts,
however, it might take hours (days even) to actually get to equilbrium, so I'm going with 2400 watts, and allowing space for extra elements if needed.

Regards
Ray

PS... Here's that Dalai Lama video BBC News - Dalai Lama pizza joke backfires on TV host

Originally Posted by RayG

DaveJ, Since I stopped watching crap reality shows on TV, I find there's plenty of time in the day....

I wouldn't watch that stuff if they paid me,

Dave

Originally Posted by Dave J

Looks interesting, that shed is filling fast.
Do you ever sleep Ray, LOL

Dave

.
Does'nt look like it does it Dave

its a big pizza (or crematorium maybe?) oven he's makin....what does he plan to put in it.....

Originally Posted by eskimo

.
Does'nt look like it does it Dave

its a big pizza (or crematorium maybe?) oven he's makin....what does he plan to put in it.....

Dead pizzas?

Originally Posted by Stustoys

Ray,
<snip>Even the little kilns I have seen use lots of kW. How many are you planning on? I guess I am talking about pottery kilns which would have more work to do to start with.

I'm told the best pizzas are cooked very very quickly.

Stuart

Hi Stuart, I did a little research on pottery kilns, and they seem to recommend around 0.6 w/cm2, that would work out to 4.3 kW or roughly twice what I'm planning on starting with, but for other furnaces, glass annealing types they quote 0.3 w/cm2, which is about where I'm at.

So, just guessing, but, with the 2.4 kW heater, and adding the extra element which I've allowed for, taking it to a total of 4.8 kW, it should be able to fire pottery.. Not that I would ever want to anyway!.

Pizza Crematorium, I like it, I can make you one with everything, (vaporized that is..)

Regards
Ray

Time...you forgot time...when do want to use this oven...from when you switch it on...in an hour or or two or day or two?

Then you have product load to also factor in

Originally Posted by eskimo

Time...you forgot time...when do want to use this oven...from when you switch it on...in an hour or or two or day or two?

Then you have product load to also factor in

Hi Eskimo,

No, didn't forget it, I did the volumetric heat capacity calculations, and with these Insulating fire bricks, they have very low heat capacity and low thermal conductivity. They should heat up pretty quickly, (10-20 minutes rather than 10-20 hours.)

I talked to the element supplier today, and If I email him the furnace design he will make up a set of suitable elements for me, also, it will be good to get an experienced opinion on the design as well.

Regards
Ray