Heat Treatment Furnace Construction

[RayG]

Hi All,

I've been planning to build a heat treatment furnace for years, and after a few false starts and problems finding the right materials I finally got a chance to start the construction.

All the dimensions are related to the size of the bricks. The missing ingredient for many years, I ended up finding a local supplier for the ISOLITE LBK-23 these are a light weight refractory brick good for 1300C, and most importantly very low thermal conductivity.

LBK Lightweight Insulating Firebricks - イソライト工æ¥æªå¼�会社 ｜ ISOLITE INSULATING PRODUCTS CO.,LTD. (http://www.isolite.co.jp/en/products/taika/seihin1-4/index.html)

I got them from Refractory & Ceramic - High Temperature Insulating Materials (http://refractoryandceramic.com.au/high-temperature-insulating-materials.html) in Mulgrave, and they carry a very good range of other refractory products, including the ceramic board we are using on the roof of the furnace.

The door is a muffle furnace type swing up door. More details later.

The general layout and construction can be seen in the following pictures.

http://www.backsaw.net/pics/HT/DSCN0503.JPG
http://www.backsaw.net/pics/HT/DSCN0504.JPG
http://www.backsaw.net/pics/HT/DSCN0506.JPG

The brick arrangement above is for the door.

http://www.backsaw.net/pics/HT/DSCN0507.JPG
http://www.backsaw.net/pics/HT/DSCN0508.JPG

The bricks are supported on 30x30 angle iron, and some of the bricks are grooved to reduce the spacing between bricks to 1mm ( recommended allowance for mortar)

The support frame is on castors, so I can wheel it out of the way when not in use. There are two open cooling shelves underneath, I'll fill them in either with mesh or some kind of grid made up from rods.

Regards
Ray

[Anorak Bob]

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.:2tsup:

BT

[Greg Q]

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

Greg

[Stustoys]

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

Gas or electric?

Stuart

[BobL]

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

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

[Dave J]

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

Dave

[RayG]

Just an update.

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

http://www.backsaw.net/pics/HT/DSCN0513.JPG

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.... :rolleyes: 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 ?

[Stustoys]

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

[RayG]

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..

http://www.backsaw.net/pics/HT/HeatEquation.png

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 (http://www.bbc.co.uk/news/world-asia-pacific-13782645)

[Dave J]

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

I wouldn't watch that stuff if they paid me,:no:

Dave

[eskimo]

Looks interesting, that shed is filling fast.:o
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.....

[Greg Q]

.
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?

[RayG]

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!. :no:

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

Regards
Ray

[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

[RayG]

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

[.RC.]

Dead pizzas?


Maybe Ray is in the Pizza Mafia... :D

[RayG]

Maybe Ray is in the Pizza Mafia... :D

We deliver horse heads on demand as well.. :D

[RayG]

Just an update, I'll post plans when it's all finished, things keep changing...

Josh made up the bearing blocks for the door mechanism, there's a total of 8 required, these 4 are to be bolted to the door.

http://www.backsaw.net/pics/HT/DSCN0512.JPG

The outer frame and trolley is finished, and painted.

http://www.backsaw.net/pics/HT/DSCN0527.JPG

The outside is to be clad with 0.9mm 304 stainless sheet. The sheets are sitting on top at the minute, I leant one on the side for the picture.

Here is the door frame, with the bearing blocks mounted, and the arms are party made.

http://www.backsaw.net/pics/HT/DSCN0529.JPG

http://www.backsaw.net/pics/HT/DSCN0528.JPG

Should finish the door mechanism and test it out in the next few days. Then the next stage is to start the final brickwork and some internal frames.

Regards
Ray

[Stustoys]

That door really has me scratching my head. I'm sure it will make sense once it goes together. Did you get your element yet?

Stuart

Stuart "Why did you surface grind the arms?".
Ray "Because I can" hehe

[eskimo]

that looking really professional Ray (thinking you have way-too much time time on your hands:U)
on those heatload calcs...how long do you reckon it will take to get upto temp?

[RayG]

Hi Eskimo,

I've tried to calculate how long it will take to get up to temperature, but there are too many variables, so I'll just have to wait till we arc it up and see, I'm hoping for less than 1-2 hours to get to 1100C. But I can put in extra elements if needed.

Josh has been making the parts for the door mechanism he designed in solid works, and we got to assemble the mechanism for the first time this afternoon, works nice and smoothly and we can now work out how to do the counterbalancing.

The door in it's closed position.
http://www.backsaw.net/pics/HT/DSCN0545.JPG

Propped open with a bit of wood makes the mechanism a bit clearer.
http://www.backsaw.net/pics/HT/DSCN0546.JPG

Close up of the door bearing
http://www.backsaw.net/pics/HT/DSCN0547.JPG

The bearing on other end of the arm, attached to the frame.
http://www.backsaw.net/pics/HT/DSCN0548.JPG

One step closer..

Regards
Ray

[Stustoys]

Looking great Ray(and Josh),
Are you going to need to chamfer the door bricks?

Stuart

[RayG]

Looking great Ray(and Josh),
Are you going to need to chamfer the door bricks?

Stuart

Hi Stuart,

The bricks on the door are stacked like this... looking from the inside of the furnace..

http://www.backsaw.net/pics/HT/DSCN0506.JPG


So the bottom and sides will only have a faint taper for alignment and sealing, but the inner top edge of the bit that goes on the inside will need to be chamfered to follow the arc or the door as it closes, The bricks are easily filed and shaped so it shouldn't be too hard to get right.

Regards
Ray

[Stustoys]

Ray,
I was just thinking that is you chamfered the roof it might seal better(which it might). It then dawned on me that if you camfered both the roof and the the door you would get a tight fit. But that would need the kiln to be made a little lower and maybe I'm worrying to much about nothing.
Stuart

[RayG]

Hi All, Just a progress report..

Got some cooking foil during the week...:)

http://www.backsaw.net/pics/HT/DSCN0561.JPG

Meanwhile.. here is the construction of the furnace base...

The stainless steel sheet is fixed to the bottom of the frame with M4 stainless button head cap screws. And the first layer of support bricks can go in like so.

http://www.backsaw.net/pics/HT/DSCN0553.JPG

The middle gaps between the rows of support bricks is filled in with ceramic fibre blanket. And the mortar for the floor layer is laid down.

http://www.backsaw.net/pics/HT/DSCN0559.JPG

The floor level layer of bricks is laid down. The specs call for mortar gaps of 1mm, so it's not like normal brick laying, it's more like glueing bricks together.
http://www.backsaw.net/pics/HT/DSCN0560.JPG

The sides are next, and I need to cut the grooves for the heating elements, which I'll have later hopefully by next weekend.

So, next installment, installing the elements and building the sides.

Might get a chance to work on the cooling racks and work support frame before then....

Regards
Ray

PS, Forgot to mention the mortar is Vesuvious TUFSET SUPER a sodium silicate based refractory mortar.

[eskimo]

a drawing board..what ever happened to AutoCad and the like:D

[RayG]

a drawing board..what ever happened to AutoCad and the like:D

Autocad, that's old school, it's all solid works nowadays, and the drawing board is the place I seem to always go back to... :) as in back to the...

Regards
Ray

[eskimo]

it's all solid works nowadays,


Ray...your always mentioning your son uses Solidworks....what does he know about the Student edition..ie is it any good? etc etc..maybe I can/should get my son to get it?

[Jekyll and Hyde]

Autocad, that's old school, it's all solid works nowadays, and the drawing board is the place I seem to always go back to... :) as in back to the...

Regards
Ray

Solidworks is fantastic... When I did my (very) brief stint at uni, Solidworks is what they were using. Some time later, I tried to draw something in Autocad, and gave up after about 2 hours with nothing on the screen. The same part (in 3D) in Solidworks takes me maximum of ten minutes :U. Its FAR easier to just pick up and use than Autocad (which spent all its time shouting at me, and telling me I'm doing it wrong). And then you can just tell Solidworks to make a 2D drawing, and section views from wherever you want, straight off your 3D part!

Only problem with it is the sheer cost (as is normal for programs designed for industry use).

[Anorak Bob]

PS, Forgot to mention the mortar is Vesuvious TUFSET SUPER a sodium silicate based refractory mortar.

Hello Ray,

Is there any chance that you could let me know who supplied the mortar?

Bob.

[Bushmiller]

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!. :no:


Ooooh.... I hope Tea Lady doesn't see this thread. I think that would be fightn' talk.:U.

Kiln build is looking extremely good. Keep up the good work and progress reports.

Regards
Paul

[RayG]

PS, Forgot to mention the mortar is Vesuvious TUFSET SUPER a sodium silicate based refractory mortar.

Hello Ray,

Is there any chance that you could let me know who supplied the mortar?

Bob.


Hi BT,

I got the mortar from these guys, Refractory & Ceramic - High Temperature Insulating Materials (http://refractoryandceramic.com.au/high-temperature-insulating-materials.html)

If you call them, I'm sure there will be a place in Perth that sells it. I'm assuming that you are repairing that nice furnace you showed pictures of earlier, I found them very helpful and if you explain what you are doing, they can offer advice on how to go about it.

Hi Eskimo,

As J&H says SolidWorks beats Autocad. (Although I can't say I'm proficient with either) I don't know about the student version, if it's a good price, i'd say give it a try. The one we are using is was bought by a company that Josh does switchboard layouts for. For home hobbyist use I feel it's overpriced.

Hi Paul,
Thanks for the comments, I take it that tea-lady does pottery? Maybe this thread might be the inspiration to build a pottery kiln...:)

Regards
Ray

[Bushmiller]

Hi BT,
Hi Paul,
Thanks for the comments, I take it that tea-lady does pottery? Maybe this thread might be the inspiration to build a pottery kiln...:)



I think she already has a kiln. She might want to try throwing the occasional plane blade in! This might explain:

http://www.woodworkforums.com/f43/forum-mugs-wip-131788/

Regards
Paul

[RayG]

Hi All,

Just an update,

The elements arrived so I got the support grooves cut into the bricks. This is a quick way to ruin a R7 2 flute milling cutter. (but it was an el-cheapo) .
The brick is held at an angle with some mdf slides, and the crappy Ryobi drill press was dragged out of the garden shed for the task..(it was hidden behind the Waldown).

http://www.backsaw.net/pics/HT/DSCN0578.JPG
The bricks are very soft and friable. I could probably have cut them with a saw and scratched out the shape.

http://www.backsaw.net/pics/HT/DSCN0581.JPG
This is a better picture showing the angled grooves. The grooves are angled to hold the elements in place, there will also be some stainless steel pins every so often to make sure they don't fall out.

http://www.backsaw.net/pics/HT/DSCN0579.JPG

I got the work support frame completed as well. It's made from 20mm 304 stainless rod. Bolted together with 6mm cap screws that come up from underneath.
The idea is that you don't want the part being heat treated to be sitting directly on the insulating bricks. That would cause it to heat unevenly.
Running the bar lengthwise means I can make up a set of tongs that will go between the bars and under the part to grab it out for quenching.
I made the work support in two parts, so I can pull half out if I'm only doing small parts.

Another step closer..

Regards
Ray

[Stustoys]

Ray,
Its coming along great but isnt bar going to add a lot of thermal mass?

Been flipping through the book you have(has yours turnen up yet BT?), I assume you have seen the part about case hardening powders not mixing well with furnaces and S/S foil? I'd never seen that before.

Stuart

[Anorak Bob]

No Stu.

Therein lies the big difference between Amazon and Book Depository. Delivery time can be months with the former and days with the latter. I guess I will just forget about it and get a nice surprise when it rolls up.

Bob.

[RayG]

Ray,
Its coming along great but isnt bar going to add a lot of thermal mass?

Been flipping through the book you have(has yours turnen up yet BT?), I assume you have seen the part about case hardening powders not mixing well with furnaces and S/S foil? I'd never seen that before.

Stuart

Hi Stuart,

I admit to being concerned about exactly that (thermal mass that is), and that's the main reason I decided to bolt the thing together, and also make it in two halves, so I can reduce the amount of extra steel that has to be heated. One other area of concern is the cool down time, the thing is so well insulated I might have trouble bringing the temperature down.

Speaking of powder...
I got some Rose Mill "PBC special" non scaling powder from a knife maker supplier, it's a coating that protects from decarburization, it might be handy for some jobs.

Regards
Ray

[Stustoys]

Ray,
Now you say that (all be it a bit of stuffing about) you could remove all the bars you didn't need each time. I had looked around on ebay for trivets(that could be the wrong name?) that potters use in kilns but couldn't find any. Have you thought about using this sort of thing? "Double Pointed Clay Stilts" Kiln Furniture (http://www.euclids.com/kiln-furn.htm)

I tried to buy some of that powder from the states one time. Their checkout said "give us your CC number and we will just add postage onto your bill"!! so that didn't happen.
The rate I am finding other jobs to do it will be 10 years before I need it anyway, although I did get some case hardening powder.

Thanks BT, I think I might cross Amazon off my list of places to shop.

Stuart

[RayG]

Hi Stuart,

Thanks for that link, I like those silicon carbide support stand off's.. As far as the work support frame goes, being all bolted together I can take out as many of the bars as I like, the other alternative was to weld the frames up, but then I would be stuck if ever I needed to remove bars.. why do things the easy way.. :rolleyes:

That hi temperature PBC Special came from these guys, PBC Special Anti-scale powder 1lb Heat treating metal products and accessories (http://www.usaknifemaker.com/pbc-special-antiscale-powder-1lb-p-650.html)

Not sure I understand why, but it seems the knife makers have all the good stuff nowadays?

Regards
Ray

[eskimo]

Hi Stuart,

the thing is so well insulated I might have trouble bringing the temperature down.



open the door...works a treat on the pizza oven


any reason why you used 20mm bar.....and not say 8mm

[RayG]

open the door...works a treat on the pizza oven


any reason why you used 20mm bar.....and not say 8mm

Hi Eskimo,

Just my usual over engineering... I'm unsure of the strength of Stainless at 1200 C,

Regards
Ray

[Bushmiller]

Hi Eskimo,

Just my usual over engineering... I'm unsure of the strength of Stainless at 1200 C,

Regards
Ray

Ray

How often will you be up to 1200C? Out of curiosity I looked up the melting point of SS, which was quoted a little over 1500C. Even annealing I would have expected the temp to be less than 1000C, hardening in the 800C range and tempering 300C to 400C. That is a generalisation so I probably shouldn't have said anything.

I would guess that at 1200C SS would be at it's plastic limit or very close.

The last time I spouted off my limited knowledge of metalurgy I was, unbeknown to me, talking to a foremost metalurgist:doh:. He never said a thing. I dread to think what he was thinking.

A lot will depend on your grade of stainless. At work our boiler tubes in the hottest area are "cooled" by steam at 593C and the boiler trips at 623C. This is to keep everything well within safety limits and includes the longevity factor of the tubes. We also have a little bit of pressure there (234bar or 23.4MPa), which aggravates the situation further! I think the SS grade is 316, but I would have to check that.

Regards
Paul

[eskimo]

Hi Eskimo,

Just my usual over engineering... I'm unsure of the strength of Stainless at 1200 C,

Regards
Ray

dumb dumb...
that really was quite dumb of me:p
of course..its gunna get awfully hot inside there...and you will need to be able to support the product with it sagging
:stupidsign:

[RayG]

Hi All,

The elements are in and the furnace roof installed. The roof is a ceramic board material that as supplied contains an organic binder that has to be burnt out as part of the commissioning process. There is a tendency for the ceramic board to slump after burn out, so the roof needs additional mechanical support in the form of 310 stainless pins.

This picture shows the internal stainless support frame that the roof pins are welded to.

http://www.backsaw.net/pics/HT/DSCN0609.JPG

The elements end are doubled twisted to reduce the resistance and the heat generated outside the furnace, the elements are run through ceramic tubes to the outside of the bricks and then terminate at the back of the furnace

http://www.backsaw.net/pics/HT/DSCN0614.JPG

Some additional stainless 25x5mm flat is used to provide mechanical support for ceramic feed throughs, and then electrical connection is made with 1"x1/4" stainless bolts and crimped connections to high temperature silicone insulated wiring. The insulation is rated to 150C, and I'm planning to replace it with teflon insulated wiring which is rated to 250C. I would have preferred fibreglass insulated wire, but couldn't find any.

Also, in the above picture you can see the additional layers of ceramic fibre insulation.

The outer shell is now installed on the roof and the sides. It's 0.9mm stainless, and fixed with 4mm stainless button head cap screws. We ran out of the ceramic fibre blanket material and there is another layer to go in the sides.

http://www.backsaw.net/pics/HT/DSCN0616.JPG

Looking from the front with a temporary thermocouple installed.

http://www.backsaw.net/pics/HT/DSCN0618.JPG

We blocked up the doorway with bricks put in a thermocouple and wheeled it outside to do the initial burnout, outside, so that any smoke from the organic binders would blow away...:)

With no controller, and just both sets of elements running flat out, we monitored the thermocouple temperature.

546 in 30 minutes
715 in 60 minutes
832 in 90 minutes
924 in 120 minutes
1050 in 150 minutes.

At that point the temperature started dropping inexplicably, and we discovered that a circuit breaker had tripped. So we will try again when the rest of the insulation is installed.

By extrapolating from the heating curve so far, I expect we should get to 1200 C within 4 hours. :2tsup:

The target temperature we are shooting for is 1230C which is required for heat treating M2.

When the furnace was at 1000C the outside shell never got much above ambient. And the electrical temination area got to about 70-80C

So far so good...

Regards
Ray

[Bushmiller]

Ray

That is looking really good. Thanks for the explanation on 1200C and M2 steel.

Also my reference to our boiler tubes being 316 was totally wrong (I think that is used for washers:doh:). I think it might be 346, but I am not sure of that either. I am just going to have to check my facts:rolleyes:.

Regards
Paul

[Stustoys]

Hi Ray,
You mean the element is double twisted from the terminal until it is inside the furnace?
Did you put your hand on the S/S outside or use a noncontact thermometer? I'd been a little worried about the emissivity of the polished S/S.
Do you have a theory on why the breaker would go after 150 minutes, wouldn't the current go down as the furnace got hotter?
Other that my normally silly questions its coming along great. You must have some big plane blades in mind. Keep it up.

Stuart

[jatt]

Looks good. You are certainly gunna need more than a few solar panels to keep the juice up to this baby.

[RayG]

Hi Stuart,

I have a Non contact IR thermometer with adjustable emissivity, but a bit of masking tape on the spot works too. :) I figure that touching anything with on a furnace at 1000C is not a good idea, not without a temperature check.

The ends of the elements are doubled back on themselves and twisted, from where it exits the inside of the furnace. I had a clamp meter watching the amps on each circuit and I didn't see much of a drop in current as the elements heated up, but I'm new to kanthal elements, maybe they don't increase in resistance as much with temperature as nichrome?

Don't know why the circuit breaker tripped, it's a C curve 20A breaker only drawing 10A, the other element was on a seperate circuit. I'll wait to investigate further when we finish the insulation.

Hi Paul,

The roof pins are 310 stainless, but the other stainless parts, the support frames and outer sheeting are 304. I must look up 346, and see what it is.

Regards
Ray

[RayG]

You must have some big plane blades in mind.
Stuart

Here's a short list, of the sort of things that I think the furnace will be useful for.

1. Heat treatment of M2 D2 and other tool steels (obviously the main motivation)
2. Tempering.
3. Annealing
4. Stress relieving
5. Normalizing (I hope I have the right term here), not quite like Stress relieving, more like when you soak cast iron at high temperature to convert to SG.

6. Furnace Brazing (I want to learn more about how to braze those brass,steel laminated mag transfer blocks.)

7. Someone else, wants me to do some enamelling, basically melting glass onto a copper substrate.

So it's not all about plane blades...:)

Regards
Ray

[.RC.]

I hope a licensed person did the electrical work on it.. ;)

[Pete F]

Ray are you going to control it with a PID?

[RayG]

Hi .RC, Of course... wouldn't have it any other way... :rolleyes:

Hi PeteF,

The control system is one of these... Temperature Controller PID Kiln Ramp Soak 64-Setpoints | eBay (http://www.ebay.com.au/itm/Temperature-Controller-PID-Kiln-Ramp-Soak-64-Setpoints-/350273088734?pt=LH_DefaultDomain_0&hash=item518de72cde)

The main reason for choosing that particular one is that it has a modbus interface, so I can interface it to an embedded linux box with mysql database and wifi web access. The profile is loaded onto the controller and it can then just run stand alone if needed, but I'm logging the actual temperatures versus the programmed profile and I can view current status on any device with web browser, laptop, iphone, etc. Sounds complicated but it's pretty simple, and shares a lot of the code that I've written for other web based control applications.

You could use the controller without the additional user interface, but then you'd have to go through programming all of the multiple setpoints and times, with this interface I can just select a pre-programmed profile and download it.

Regards
Ray

[Pete F]

Cripes, that's going to be a sophisticated set up! Nice. Yes that's a bit more sophisticated than the PIDs I've used, yet the price is good, particularly considering it comes with a thermocouple. I am hunting for furnace myself and will convert it to PID control when I get it. I have a spare controller here but if I didn't would probably also use the one you linked to as it looks to be extremely versatile.

Pete

[RayG]

yet the price is good, particularly considering it comes with a thermocouple.

Pete

Not really, that supplied thermocouple is not suited to kiln operation, you need heavier gauge and ceramic spacers. I'm using this one...Type K Thermocouple Ceramic Kiln probe 8G Temperatuture | eBay (http://www.ebay.com.au/itm/Type-K-Thermocouple-Ceramic-Kiln-probe-8G-Temperatuture-/110714883442?pt=LH_DefaultDomain_0&hash=item19c71f0d72)

Regards
Ray

[eskimo]

By extrapolating from the heating curve so far, I expect we should get to 1200 C within 4 hours.


plus the time it takes to get product upto to temp

why did breaker trip....bit on the small side would be my guess

[Bushmiller]

Hi Stuart,

Hi Paul,

The roof pins are 310 stainless, but the other stainless parts, the support frames and outer sheeting are 304. I must look up 346, and see what it is.

Regards
Ray

Ray

Don't worry about the 346. It is 347!

I was close though:doh:.

Regards
Paul

[RayG]

plus the time it takes to get product upto to temp

why did breaker trip....bit on the small side would be my guess

Hi Eskimo,

It might have something to do with the 2.4Kw fan heater that was on the same circuit...:)

We got the rest of the insulation today, so the next test will be in a day or so.

Hi Paul,

Thanks for the PM, I've sent reply, While talking about stainless, did you see the new 410 Stainless plane by Ron Brese Brese Plane (http://www.breseplane.blogspot.com/)


Regards
Ray

[Anorak Bob]

Ray,
Its coming along great but isnt bar going to add a lot of thermal mass?

Been flipping through the book you have(has yours turnen up yet BT?), I assume you have seen the part about case hardening powders not mixing well with furnaces and S/S foil? I'd never seen that before.

Stuart

The book arrived yesterday. I have only read the introduction. I do like the author's style!:U
BT

[Bushmiller]

Hi Paul,

Thanks for the PM, I've sent reply, While talking about stainless, did you see the new 410 Stainless plane by Ron Brese Brese Plane (http://www.breseplane.blogspot.com/)


Regards
Ray

Ray

My mouth went dry. I wondered what was happening. Then I realised I had run out of drool:-.

Regards
Paul

[RayG]

Hi All,

The insulation is finished, but not the front door as yet, and with a temporary controller installed.

The picture tells the story. red is current temp, green is setpoint.

http://www.backsaw.net/pics/HT/DSCN0625.JPG

Looking through a hole in the bricks that blocked up where the door is going to go..

http://www.backsaw.net/pics/HT/DSCN0622.JPG

Got up to 1230C (the critical temperature for M2) in a little over 4 hours.. :)

Regards
Ray

[Stustoys]

Hi Ray,
Looks great and a little scary at the same time lol
Do you think the door will make much difference?
Have you kept it at 1250 long enough to see what sort of cycle time you are getting? If your maths is right it should be something just under 50% right?

BT, you've got further in the book than I have. I had a quick flick and then went back to MTR. The tour isnt helping my reading time lol

Stuart

[RayG]

Hi Stuart,

+1 For Scary, I kept thinking of all the things that might go wrong...

We kept it at 1250 for about 1/2 an hour, then dropped to 1200 for an hour, I didn't measure the duty cycle, it seemed to vary quite a bit as the PID controller did it's thing.

I think having the door seal properly will make a difference, but probably not a huge amount.

There's a tapered reamer milled from O1 that we will heat treat as a test tomorrow.

I forgot to mention earlier, that I got some Aqua Quench 251 polymer quenchant... good stuff, no flames or fumes and non toxic. 20% concentration is same cooling rate as oil.

Regards
Ray

[eskimo]

looks great..fantastic job Ray

what night is pizza night

[RayG]

Hi All,

The first burn-out also burnt out the silicon insulated wires and terminals. The wires crumbled and broke off as soon as they were touched

http://www.backsaw.net/pics/HT/DSCN0630.JPG

Post Mortem..
Two things that we did wrong, first problem is that we stupidly put a layer of ceramic fibre insulation between the wiring and the outer shell. So there was no way for the heat to dissipate from that area, the second problem was I used silicone insulated wire (rated at 150C) instead of a higher temperature rating, (which is what I should have used in the first place.)

My best guess is that area got up to 300-400C probably several hours after the furnace had been powered down, as the temperature came to equilibrium.

Another thing that failed unexpectedly was the crimp teminals, which were tin plated copper rather than a high temperature nickel plated steel type.

I've rebuilt the wiring temporarily using a mil-spec teflon insulated wire and removed the crimp terminals. This was so we could heat treat an O1 tapered reamer that needed to be done.

I'm going to rewire it with better MGT (UL5107) rated wire which is good for 538 C, it uses glass reinforced mica tape with fibreglass jacket.

The ceramic insulation layer between the wiring and the outer shell is removed.

Still undecided about using the terminals but I'll get some nickel plated steel crimp terminals (good for 480C) and decide later whether or not I should use them...



One step forward , two steps back...

Regards
Ray

Hi Eskimo, Pizza night is delayed while equipment upgrades are in progress... :)

[Stustoys]

Hi Ray,
So I'm not the only one that has those :doh: moments then?
I'd thought by the early pictures you were leaving them uncovered(with the insulation that is).
Wouldn't most of the heat be coming back down the element? One thing I've seen used in a similar situation is a heatsink on the bolt to dissipate that heat so it doesn't get to the insulated wiring. Just a piece of 3mm Alum say 25mm sq with a hole in it for the bolt, it goes between the element and the lug. Get what I mean?

That may save you the need of special wire.

Stuart

[RayG]

Hi Stuart,

I think it would have been ok, if we hadn't put that extra layer of insulation between the wiring and the shell... :~

Here is the specs for MGT class wire

http://www.backsaw.net/pics/HT/MGTWire.jpg

I found some on ebay from this seller.. #12 HIGH TEMPERATURE MGT ELECTRIC WIRE HEATERS PER FOOT | eBay (http://www.ebay.com.au/itm/12-HIGH-TEMPERATURE-MGT-ELECTRIC-WIRE-HEATERS-PER-FOOT-/280665134091?pt=LH_DefaultDomain_0&hash=item4158f2140b)

The price from Digikey for a 100ft roll was just shy of $600.... :oo: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=3111265%20TN005-ND

Regards
Ray

[Stustoys]

I think it would have been ok, if we hadn't put that extra layer of insulation between the wiring and the shell... :~


Yes , but those joints may still get pretty hot. If there is much heat coming down that wire it has to go somewhere.


$20 a ft!!!!!! you'd be measuring carefully lol (edit $6 ft isn't so bad)

$2.50 a ft is much more doable.

Stuart

[Pete F]

Ray I'm unsure of where these terminals are precisely located, but are you able to make up some form of cover with the terminals on it, then from there simply run bare solid copper wire to your standoffs?

It's not uncommon to see old electric kitchen ovens dumped somewhere, you should be able to locate a suitable donor for some high temp wire.

Pete

[RayG]

Hi All,

Just an update on wiring. The MGT wire arrived today, so I've rewired the back panel.

The wire construction is interesting, the conductors are nickel plated copper, and the insulation is mica layers wrapped around the core with a braided fibreglass cover. The UL rating is 450 C, and the non-UL rating is 538 C.

Also the high temperature crimp terminals arrived, and are nickel plated steel. :2tsup:
The crimp terminals I used earlier which vaporized were tin plated copper. Well, anyway the tin coating was nowhere to be found...

All being equal we are back to being rated to 1250 C (inside the furnace that is.. :) )

http://www.backsaw.net/pics/HT/DSCN0676.JPG

http://www.backsaw.net/pics/HT/DSCN0677.JPG

The ramp/soak controller arrived and the modbus comms manual supplied was in Chinese, so I've transated it with the help of google translate. (that was fun! :) )

I now have linux drivers working for programming the controller.

With a bit of luck, I hope to have the full version of the ramp/soak controller up and running next week.

Regards
Ray

[eskimo]

[QUOTE=RayG;1348653]

The control system is one of these... Temperature Controller PID Kiln Ramp Soak 64-Setpoints | eBay (http://www.ebay.com.au/itm/Temperature-Controller-PID-Kiln-Ramp-Soak-64-Setpoints-/350273088734?pt=LH_DefaultDomain_0&hash=item518de72cde)

The main reason for choosing that particular one is that it has a modbus interface, so I can interface it to an embedded linux box with mysql database and wifi web access.
/QUOTE]

What!?

does that mean your gunna control it with your mac?:D

[RayG]

The control system is one of these... Temperature Controller PID Kiln Ramp Soak 64-Setpoints | eBay (http://www.ebay.com.au/itm/Temperature-Controller-PID-Kiln-Ramp-Soak-64-Setpoints-/350273088734?pt=LH_DefaultDomain_0&hash=item518de72cde)

The main reason for choosing that particular one is that it has a modbus interface, so I can interface it to an embedded linux box with mysql database and wifi web access.


What!?

does that mean your gunna control it with your mac?:D


Hi Eskimo,

Well, I could use the mac, but I am actually setting it up so I can use the iPhone... while it might seem like overkill, having remote monitoring is a good thing for a furnace, typical cycle times might extend out to quite a few hours, so, this lets me keep an eye on things without having to be there all the time babysitting the kiln. I seem to remember reading something about pottery makers, spending all night sessions babysitting kilns.

Anyway, here is the current update. Some more parts arrived, notably the SSR's and the SSR heatsinks, so I got the control panel layout roughed in, the din rail PSU's are not the right ones, but they are the right size, the 12V one hasn't arrived yet.

So this is how it looks at the moment..
http://www.backsaw.net/pics/HT/DSCN0681.JPG

http://www.backsaw.net/pics/HT/DSCN0682.JPG

http://www.backsaw.net/pics/HT/DSCN0683.JPG

The SSR's (Solid State Relays) are 25A from ebay, the main furnace has 2 x 2.4Kw elements, and the third SSR is for a future tempering furnace, that will go into the same frame. Each element has it's own circuit breaker and independant 10A supply.

The SSR's are from $A5.06ea eBay Australia: Buy new & used fashion, electronics & home d (http://www.ebay.com.au/itm/370511083970?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649)
The SSR heatsinks $A5.73ea eBay Australia: Buy new & used fashion, electronics & home d (http://www.ebay.com.au/itm/110676470627?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649)

The CPU is a Kontron (good German brand) JREX-PM, it's nice little embedded PC that runs off compact flash instead of a hard drive. A left over from a previous life.. :)

Regards
Ray

[Stustoys]

You just need a one legged stool Ray. I'm told thats how you stay awake watching a kiln.
Looks pretty. (my crimper has turned up so I'll be able to pretty up my vsd soon)
Why three relays?

Stuart

p.s. Did you edit your post Ray or am I just going blind? lol nvm on the 3 relay question ;)

[.RC.]

Gee Ray I hope you are licensed like me doing all that electrical work... ;)

[Auskart]

Hey Ray, Glad it's you paying for the Electricty to run it. :B

[eskimo]

of course..an iphone...why didnt I think of that...what would one do without their iPhone..or should I say..what cant one do with an iPhone:D

very impressive board & layout Ray.
you must have a lot of knowledge in this area

[NCArcher]

Just a quick thought Ray.
They are hefty heat sinks so with the prolonged use of the SSRs during a session, will that heat radiating upwards affect the mini PC?

[RayG]

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...:rolleyes:

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

[RayG]

I finally got the door finished, over engineered as usual :rolleyes:, 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.

http://www.backsaw.net/pics/HT/DSCN1716.JPG

http://www.backsaw.net/pics/HT/DSCN1717.JPG

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.

http://www.backsaw.net/pics/HT/DSCN1719.JPG

http://www.backsaw.net/pics/HT/DSCN1720.JPG

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....

[Dave J]

Looking good Ray,:2tsup:

Dave

[Stustoys]

Good work Ray and Josh.
Tried pizza yet? :D

Looking good Ray,:2tsup:
Just wait until you see the video!

Stuart

[RayG]

Hi Stuart,

Since you asked...

Heat Treatment Furnace Door Demo - YouTube

Regards
Ray

[Anorak Bob]

Yes BT can and he's getting excited.:U

[RayG]

Yes BT can and he's getting excited.:U

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

[Anorak Bob]

So it might be out with the files again soon. Make a change from splitting tenths.:2tsup:

BT

[Stustoys]

Well I like the video :2tsup:
Must be the shaper in me lol

Stuart

[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

[RayG]

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

[RayG]

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.
http://www.backsaw.net/pics/HT/DSCN1733.JPG

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

http://www.backsaw.net/pics/HT/FurnaceScreenDump.jpg

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..

http://www.backsaw.net/pics/HT/DSCN1736.JPG

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.

[eskimo]

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:2tsup:

[RayG]

Ray...please speak English....

Fluent Jargon... :)


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..


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 (http://www.ebay.com.au/itm/370511083970?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649)
The SSR heatsinks $A5.73ea eBay Australia: Buy new & used fashion, electronics & home d (http://www.ebay.com.au/itm/110676470627?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649)

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

[Stustoys]

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..

Maybe you really do need a tempering furance then :wink:.

What sort of cycle time are you using on the SSR's?

Stuart

[RayG]

Maybe you really do need a tempering furance then :wink:.

What sort of cycle time are you using on the SSR's?

Stuart

Hi Stuart,

Yes, the tempering furnace is a must. I'm thinking of making a smallish benchtop unit that will run off a single 10A outlet and still be capable of 1250 C performance.

The cycle time is several seconds, that seems to easily hold to better than 1 C, but then I'm not disturbing the equilibrium....

Regards
Ray