Thread: Heat Treatment Furnace Construction

Hi All,

RC, Of course... I have the same license.

Stuart, You must be going blind , I did edit a few spelling and grammar errors, but that part was always there.. I try to put "EDIT:" when I make a major change to a post. But I wish I had thought to add the tempering furnace to the system earlier. But it only became more obvious how useful it would be after the first couple of trial parts we did. You go from the furnace to quench, then you want to go straight to tempering, but the main furnace is still way to hot, I've been using a modified toaster oven, for now, but that doesn't go to 500-600 C.

Eskimo, Thanks for the vote of confidence... I've spent the last 30 years building stuff for others, (still doing it for that matter) so it's nice to be doing my own boards for a bit of a change.. plus having a few left over bits and pieces is always handy as well.

Auskart, I thought about putting a kw hour meter in there, but as a rough guide, to get up to temperature it generally runs full on at 4.8Kw and 20c per kwh that's about $1 per hour, and to maintain temperature the duty cycle decreases and it drops down to around 50c per hour. I promise to plant a tree for the carbon offset every so often...

NCarcher,
Very good point, during the early trials with these SSR's I measured less than 5 degrees above ambient temperature rise on the heatsink , the CPU board is rated 0-60C, so it's something I'm going to have to keep an eye on, if it looks like getting too hot, I'll have to put a fan in, but I'm expecting that since the enclosure itself is fairly large, there is lots surface cooling and convection should be pretty good.


Regards
Ray

I finally got the door finished, over engineered as usual , Stuart thinks I'm suffering from some kind of furnace door affliction... he might be right...

It's a parallelogram type action, with a 50 Kg gas strut doing the balancing.





The safety interlock kills the power to the exposed heater elements when the door is opened,
the cable (inside the alumimium tubing) is high temperature rated teflon insulated.
Although I don't expect the shell temperature to get all that hot anyway.
The switch is mounted on standoff's to allow airflow under the switch.





The inside of the door is going to be 1250 C when the furnace is first opened, so it's designed to swing up and away from the operator (me)..
and it's well out of the way making it easy to get tongs inside.

The original stainless work support frame has now been replaced by some ceramic stands (look for "kiln furniture", if you are googling)

Still waiting on ceramic fibre rope door seal to finish off the door sealing.

Almost there..

Regards
Ray

PS... Maybe BT can identify the part in the furnace....

Looking good Ray,

Dave

Good work Ray and Josh.
Tried pizza yet?

Originally Posted by Dave J

Looking good Ray,

Just wait until you see the video!

Stuart

Hi Stuart,

Since you asked...

[ame=http://www.youtube.com/watch?v=TUkj6Ypd7sM]Heat Treatment Furnace Door Demo - YouTube[/ame]

Regards
Ray

Yes BT can and he's getting excited.

Originally Posted by Anorak Bob

Yes BT can and he's getting excited.

Keep your eye on the mailbox towards the end of next week...

So it might be out with the files again soon. Make a change from splitting tenths.

BT

Well I like the video
Must be the shaper in me lol

Stuart

Nice action there. Will you need some extra shielding so that the seals in the gas strut won't cook? A failure there could ruin a whole lot of parts.

Michael

Originally Posted by Michael G

Nice action there. Will you need some extra shielding so that the seals in the gas strut won't cook? A failure there could ruin a whole lot of parts.

Michael

Hi Michael,

Good point, I don't know, but I'll check the gas strut temperature when I fire it up in the next few days..

Regards
Ray

Hi All,

I'm getting close to wrapping this project up, I'm well into the testing phase.

The final thing was the door seals, for which I used 1/2" square section braided rope, that's rated to 1260 C, and I ran two strips, one on the door and another around the edge of the door opening.

Here's the final control enclosure.


The single board PC is a 1.6G pentium Kontron running ubuntu linux with a wifi connection to the local network, and talks modbus rs485 to the temperature controller.

The monitoring and control is via a web browser, which means I can use anything that can access the network and run a browser to watch what's happening. Here is a screen dump



The green line is the set point, the ocscillations at the start is the PID auto-tune being tested... around 18:49 I opened the door, which caused a blip.
and later the set point was dropped by 25 degrees to 575 to see how quickly is would cool, and re-settle.

The TP parameter is the duty cycle, which is scaled 0-1000, so 217 means the heater on time is about 21.7% of the time to maintain 575 C, and
the heaters supply a maximum of 4.8 KW, so to maintain 575, requires just over 1 KW... or about 20 cents per hour..

The job in the furnace at present is a sheet of bronze 600x300 that I want to anneal.

Here's a picture of the inside of the furnace at about 750 C..



The door had been open for about 5-10 minutes before the picture was taken... I was heat treating some O1... you can see the square section door seal around the edge.

Still a bit of work to do with the profile control software, and then I'll be starting on the tempering furnace... which will replace the current toaster oven...

Regards
Ray

PS Josh wants to try cooking a pizza....

EDIT: Michael, I've been keeping an eye on the gas strut, and so far it's stayed at ambient temperature, the outer shell is around 50 C, and probably will go higher on a longer high temperature run.

Originally Posted by RayG

The single board PC is a 1.6G pentium Kontron running ubuntu linux with a wifi connection to the local network, and talks modbus rs485 to the temperature controller.





PS Josh wants to try cooking a pizza....

Ray...please speak English....


and why not ...a pizza must be the ultimate test

Are they solid state heater relays?

Great job Ray

Originally Posted by eskimo

Ray...please speak English....

Fluent Jargon...

Originally Posted by eskimo

and why not ...a pizza must be the ultimate test.

The hi temperature pizza ovens usually run out to around 500 F, (260C) With the door closed the furnace was still 270 C after 12 hours cooling from 700 C..

Originally Posted by eskimo

Are they solid state heater relays?

Yes, I posted details earlier, but I used these ones.
The SSR's are from $A5.06ea eBay Australia: Buy new & used fashion, electronics & home d
The SSR heatsinks $A5.73ea eBay Australia: Buy new & used fashion, electronics & home d

They are rated at 25A, and seem to run fairly cool at 10A, the heatsinks haven't gone over 50 C or so.. so far

Regards
Ray