Thread: Making a Heat Treatment Oven

Can't offer any help re the electrical side of things, but if you don't know there are 2 types of firebrick, you need the insulating variety. There is the standard type which is almost as hard as a house brick but is a poor insulator, and then there is the much softer insulating type.

Thanks Bob,
I gathered that was the case in the US from the vids i have watched, but i was not sure about over here. I wonder if the type 26 that has been recommended in the US is available here?

Ew

Hi Ewan,

Have a look at this thread, you want to get isolite bricks, and kaowool, or cerachem. https://www.woodworkforums.com/f65/he...uction-137007/

For ramp soak control I'd go for something like the JLD 634 JLD634 Ramp/Soak PID Temperature Controller for FURNACE KILN OVEN. 64 set timer control for $85 you get 64 ramp/soak points, plus rs485 comms

I translated the modbus manual for that model and wrote a linux driver for controlling the furnace. Still haven't built the tempering oven...

Regards
Ray

Firebricks: do a google search for "refractory material australia"

An ebay search for "PID temperature controller klin furnace" will produce several low cost controllers. They usually have a "self tuning" feature to adapt the PID parameters to your oven and temperature range. And most accept a bewildering range of different thermosensors. Not sure if these have an interface to control by a PC. I guess if you want a solution with the ability to internally program a whole process (like today at 12:00 ramp up over one hour to 850C, stay there for 12 hours, then ramp down to 700C and wait 4 hours etc etc ) then its going to be much more costly.

Definitely want the insulating bricks. The ones used in wood fired ovens are designed to absorb and hold the heat and reflect it, not necessarily insulate it and wont have the effect you want.

I forget the actual type I got but they are white, quite soft and very light. I bought mine from Veolia Environmental Services as they deal in refractory stuff as well. I'm just careful with the surface so as to not knock it around too much.

I'm running mine on a standard PID and SSR but I don't have ramp capability but then I'm just using mine for colour case hardening rifle actions so i don't need ramping but I might look at a new controller down the track. Like you I just got my elements off ebay, they are dirt cheap. I've blown one and have a few spares. I figure that's just par for the course with dirt cheap elements but I don't know, maybe if I paid $80 an element I might only get the same life. It might also be how I have them set up and use them but I'm happy enough with it.

I need a bigger shed.

Thanks Ray and Chris,
Ray, with all the searching i did i failed to find your thread.....FAIL!

Chris, as you say there are heaps of low cost controllers, i figure i may as well go with a ramp/soak type controller straight away, i can see myself cooking CI castings in the future. The $80+ ones were all i could find with ramp/soak programing.

Ew

Ewan,

Shame you are not closer; I have 200+ of the light insulating firebricks here.

Ken

Hi Ewan,

I tried searching for that thread as well, and didn't come up in my search either, so I had to dig it out manually..

The bricks we used were from Refractory & Ceramic - High Temperature Insulating Materials in Mulgrave, I'm sure they would deliver.. the ones we ended up using we got at a discount, as they were ordered for the Alcoa refinery and ended up being surplus. They are the ISOLITE LBK type, the key parameters you want are high temperature rating and low thermal conductivity. The LBK28's are a good choice, rated at 1500 C and 0.27 thermal conductivity. LBK Lightweight Insulating Firebricks - イソライト工æ¥#æ#ªå¼�会社 ｜ ISOLITE INSULATING PRODUCTS CO.,LTD.

Of course, you could always hook up a trailer and come down for a visit, and call past Ken's place, he's not far from here..

For heating elements, I got them custom made by AAkilns, AAkilns Home Page I got the thermocouple's and thermocouple ceramic covers from them as well. They also sell on ebay. The guy is worth talking to, and will give you a good run down on Kanthal heating elements and what information is needed to get them made. The K type TC's that go in the furnace are made using heavy gauge wire, ( I'd guess 8 gauge, and go inside a ceramic tube) There is also a special ceramic mounting block ( bartlett mounting block?) for the TC terminations, but remember you have to run compensating cable from the termination block to the controller.

One of the limiting factors is power requirements, I'm running 5 KW, ( two 2.5 KW elements ) on two separate 15A single phase circuits, I could run if needed off two 10A circuits, so the heating elements are split into two separate supplies and SSR's, but controlled by the one PID controller.

Here's the inside of the control enclosure. The extra circuit breaker and SSR is for the non-existant tempering furnace...
DSCN1733.JPG

Regards
Ray

PS... when you start looking for ceramic blocks and stuff to go inside the kiln, the word you want to search for is "kiln furniture" ( I think it was Stuart who told me that secret.. )

Thanks Ray, Ken and Hornet.

Depending on the price of the bricks Ken a leisurely drive might be nice one day......

Ray, I read the whole thread last night. Do you know roughly how many bricks you used? Its about the size i was thinking although i may go a little less tall. I'm also thinking of making a second on that is 1200mm long but only 100mm square for swords...if i ever find the time to get back to them!
Yours seems to be far more professionally built than most i have seen, none have been mortared, a few have had steps cut into the bricks. Also no blanket to be seen, do you think the blanket was worth it? I do like the door design too, the hot bricks always facing away. The most important thing i'd like to know though, is did you cook a pizza in the end?

Cheers,
Ew

Ewan,

Had another enquiry today and checked the bricks. They were from 2 different lots and one lot of 100 are fireplace heavies (that solves my pizza/bread oven construction) and the other pile are definately marked Lite Brick. Sort of cuts down our options. I am guessing for a small furnace I will need at least 50 with a pre cast lid.

It would be cheaper to source them locally with the cost of fuel.

Ken

Hi Ken,
The problem is i don't think i can get them locally......It will be a freight in job i think. I'm expecting i will have to spend upwards of $400 so hopefully i won't be too shocked by the prices.

Ray, i missed asking this before but where is your TC located in your oven?

Ew

Originally Posted by Ueee

Thanks Ray, Ken and Hornet.

Depending on the price of the bricks Ken a leisurely drive might be nice one day......

Ray, I read the whole thread last night. Do you know roughly how many bricks you used? Its about the size i was thinking although i may go a little less tall. I'm also thinking of making a second on that is 1200mm long but only 100mm square for swords...if i ever find the time to get back to them!
Yours seems to be far more professionally built than most i have seen, none have been mortared, a few have had steps cut into the bricks. Also no blanket to be seen, do you think the blanket was worth it? I do like the door design too, the hot bricks always facing away. The most important thing i'd like to know though, is did you cook a pizza in the end?

Cheers,
Ew

Hi Ewan,

No Pizza, well not yet anyway. Cooking a Pizza at 1200C is an exercise in fast reflexes...

I will see if I can get a count on the bricks, I think Josh has some Solidworks files that might help... I'll check.

The door was a bit over engineered, but why not... It's too easy to forget that if you have a swing type door, the inside of the door is going to be at furnace temperatures when it opens, not much fun if it's right in the way as you are unloading the furnace.

Regards
Ray

This another style of door that you might want to consider



I got thee ice from this furnace.

Originally Posted by Ueee

Ray, i missed asking this before but where is your TC located in your oven?
Ew

Hi Ewan,

It's in the middle just below the top, not sure if that's the best place? But it shouldn't be too far off.

I think there is about 80 bricks in total, but the roof is not brick it's ceramic fibre board.

The board is rigid as supplied, but after initial burn-out it needs some mechanical support, that's what the stainless roof pins are for.

You need to run the furnace outside for the first time while you burn out the organic binders in the ceramic board, it smokes a bit and eventually the colour changes to a white-ish colour. You should check the MSDS sheets, loose fibres from some of this stuff can be nasty.

Regards
Ray