Heat Treat Oven - WIP

[JTknives]

The time has finally come for me to build a heat treat oven. I have been getting by with my pid controlled forge for many moons and it has served me well but it's time for an upgrade. I have pulled design elaments from lots of deffrent sources and combined them into one super Franken-oven. The bricks have been ordered and the steel is being cut to shape as we speak and will be picked up tomarow. If when you read this thread you see something funky and off let me know as I don't have time for stupid mistakes.

Features:
1: Fast heating is a must, being that I do one blade at a time I don't want to weight an hr to come up to temp.
2: Paragon style door. I love the non latching counter weighted door that can be opened and closed quick.
3: Smart controller, the controller must be able to save programs and be able to recall them at the touch of a button.
4: Smart argon injection, the oven will have a shealding gas setup that will monitor the O2 level in the oven and inject argon to counter this as well as keep the O2 level low through the entire heating cycle. Can be turned on or off with the smart controller that controlles the ovens heating.
5: Long elament life, the guidelines followed in the kanthal book to a T

So as you can see I got my work cut out for me. But there has been a lot of planning and prepping for this build so everything should go smooth. Let's start off with the ovens size. The heating chamber is 5.5"x5.5"x27", one big driving factor to the size is the 25" long D2 planer blades I get that need annealing. I would rather anneal them in full length so I can use them as needed. Below is the solid model of the oven drawn up to this point. Today or tomarow I will sketch out controller box location and a few other things. But is allowed me to fit and fine tune all the metal parts as I'm having them cut for me.

At fitst I was planing on doing grooves in the side for the coiled like everyone else does but then in my research I came across another way that actually gives better life and allows slightly higher surface loading.
This is coil over rod and then hung from the ceiling. The coil is wrapped around a rod that is hung from the roof of the kiln. In researching this even further I discovered a variant to this which is coil in tube. The coil is wound and inserted into a fuzed Quartz tube. This tube is then hung from the roof. I'm going back and forth on weather or not I'm going to do coil over rod or coil in tube. I like the coil in tube idea because the coil is complety shielded from outside contact. Going this route will eliminate the grooves in the side walls which I'm hoping will help keep the oven shell cooler. The cover page of kanthal pdf has a picture of coil over rod.

In my drawings you can see I have it drawn for coil in tube. The tubes or rods would be cut to span the 5.5" width and set in pockets.

Running the coil on the roof in a zig-zag faction allows me to use much more wire which allows me to up the wire gauge and amps and still keeping the surface load between the recomended 3-4watt range. Still playing with the coil design currently and have not decided yet on a gauge yet but I'm guessing I will use 12-13gauge and 20-25 amp load.

The controller I'm going to use is the TAP controller. Right now it's only found on new kilns. This controller is not made by even heat but the manufacture is not selling to the public currently so I had to find a way to get my mitts on one. So after much research I decided to just get the upgrade kit from Tracy at USAknifemakers. the TAP might look expensive but if you buy any other good quality PID that can store programs and has USB input you will be starting at around $800 was the cheapest I could find. At first I was worried as it says only for ramp master upgrade and that it was just adding features to the current control. But after studying the schematics it's apparent that the TAP controller is a complete pid set up wether it's an upgrade or as us, thy are all the same. The upgrade just has the adaptor harness to allow a plug-n'-play set up.

After tracking down the PDF on how to do the upgrade I can easily see how it's wired up and it's nothing special.

Here is a nice shot of the TAP controller. Just standard plugs so the upgrade is just a wire harnes to plug into the old control harnes.

Then to make sure there was nothing special hiding in that big red even heat box I tracked down a wiring diagram for a oven with and with out a TAP controller and thy are the same.

Also thy where kind enough to list the pin outs for the TAP, so now I'm ready to rock and roll.

The great thing is thy have all the part numbers for everyone on the drawing so I looked up the relay and the transformer and thy are just standard items which will be very easy to aquire.

So that's it for right now but I will have some build pictures very soon as I pick up the metal tomorrow.
But my buddy and I are currently working on the O2 sensor and control board which he has and is programming. In a nut shell the O2 controller will get a signal from the TAP controller. You might be wondering how this can be done. Well I'm going to tap into the alarm output on the TAP controller.

When programming the TAP it will ask if you want to set an alarm at a set point. I will just consider the alarm on or off as O2 control on or off. so I can have the oven warm up and once it hits X temp or X time it will turn on the O2 control circuit which will then start injecting argon and monitoring the O2 level in the oven and hold it to a set %.

So thanks for giving this a read and if you see any major flaw let me know. Thanks guys.

 

[Salem Straub]

Very cool Jarod, looks like your oven will be better in ways than one off the shelf. You are certainly doing your homework- nothing to add except keep the pics coming!

 

[timgunn1962]

A few thoughts/questions.

Have you looked at the AutomationDirect Solo controllers or the similar Omega 7200,7600,7800-series? They appear to be the same controllers rebadged either Omega or AD. Multi-program, multi-segment capability and I've used the RS485 connection with a $5 USB/RS485 converter for logging, though I've not programmed a controller from a PC.

Not as pretty as the TAP, or as end-user-friendly (they are industrial controllers and therefore require a certain amount of familiarity with industrial process control. Accessing the menu for ramp/soak program control effectively gives God privileges, allowing the basic settings to be changed. It's not an issue if the builder is the user, but it's not as foolproof as most dedicated kiln controllers). Recall at the touch of *a* button becomes recall at the touch of several buttons in the correct order, but the cost saving is significant.

What sort of sensor you intending to use to monitor the O2 and control the Argon? Are you looking to modulate the flowrate with an analog valve, use time-proportioning output or just use On/Off control?

Have you considered a simple timer circuit? Continuous trickle flow whilst powered, plus a high-flow bypass on a timer off the door-switch to give a good blast when the door is closed and purge out the O2 before the steel can get hot enough to Oxidize? Assuming that you'll be putting cold workpieces into a hot oven, of course.

The element arrangement seems like overcomplication to me, particularly the transverse tube thing. There's almost always a tradeoff between Mean Time Before Failure and Time-To-Repair. It looks like you are trading a lot of TTR for what is probably a fairly small reduction in MTBF. At .072", 13AWG, you are using the wire diameter I'd like to be using (I went from 16 AWG to 14 AWG after a couple of early element failures, but needed to ensure the new elements would fit in the old grooves) and TBH, I'd expect the thicker wire alone to account for most of the increase in MTBF, even if used in grooves in the walls.

Industrially, a relatively small reduction in downtime can easily pay for itself if a failure would shut down a production line and I suspect this is the driver behind the industrial use of wire-in-tube elements. Could you maybe build 2 ovens with side-wall elements for the cost of one with tubed elements and gain reliability through redundancy instead? That way you get a free tempering oven.

Why do you want a lower surface temperature? I know it may seem self-evident, but is it primarily because you want improved insulation, or primarily for safety?

Additional insulation can be provided quite cheaply and easily by adding a layer of Calcium Silicate board on the outside of the IFB.

The best way I've found of getting safe-to-touch shell temperatures is a second skin, spaced off the outside with some natural ventilation. It's too much hassle for me to do, but the lab. furnaces I've seen all do it this way.

On my first oven, I was unsure what the skin temperature would be and decided to measure the temperature on the surface of the IFBs (I use an angle-iron frame) to see whether I should use plastic-coated steel, Zinc-plated steel or stainless steel for the outer skin. In the event, I found the skin temperature was about 135 degC, 275 degF, but that the heat transfer from the IFB to human skin was so poor as to be safe to touch for any reasonable period of time: I could press my hand on the IFB for 30 seconds without pain or damage. I never did metal-skin any of them. If you are using Argon, bare IFB will not be a realistic option due to the need to seal things reasonably well. An extra insulating layer outside the metal skin might work though.

I've always built the control box as a separate unit with the thermocouple, door switch and power output to the elements on plugs. It means the expensive control box can be used for pretty much any heat control application I might come up with: a second, tempering-only, oven for example. The Solo & 7800 controllers even have 4 sets of PID parameters and can automatically use the parameters from whichever of the 4 autotune temperatures is nearest the setpoint. This means no need to input PID values when switching between Austenitizing and tempering ovens.

 

[Stacy E. Apelt - Bladesmith]

".......
I've always built the control box as a separate unit with the thermocouple, door switch and power output to the elements on plugs. It means the expensive control box can be used for pretty much any heat control application I might come up with: a second, tempering-only, oven for example. The Solo & 7800 controllers even have 4 sets of PID parameters and can automatically use the parameters from whichever of the 4 autotune temperatures is nearest the setpoint. This means no need to input PID values when switching between Austenitizing and tempering ovens. ...."


This is a very good idea for several reasons.
First - it gets the controller off the hot kiln body.
Second - it allows the controller to control whatever you plug into it.

JT,
I have known you for a good long time now ( through the internet), and want to caution you against your own worst enemy. - You tend to overcomplicate simple things.
The wheel is round because it works well that way. HT ovens are simple heating devices with coils on the sides because they work well that way.
Making the oven more efficient by adding a insulating layer of ins-board over the firebrick is a good thing. Using heavier gauge Kanthal is a good thing. Redesigning the coils in a complex arrangement is not.

I seriously doubt that controlling the argon with a sensor would be worth the extra cost over just having it run at a steady trickle.

If you are only doing one blade at a time, many of the things you propose are more suited to industrial quantity production. The argon could be eliminated completely by wrapping the blade in foil. This excludes O2 contact until the blade is cooled to room temp. again .... simple is best.

 

[KnuckleDownKnives]

Great thread, I'll definitely be watching this one...

 

[JTknives]

As to the controller I looked at the solo 9696 whe. Trying to find a good controller and that seamed like a great controller. I loved that the "programs" could be done on a pc with there program. But I could not find anything about the solo actually holding more then one of these programs in its memory.

As to the elaments in tubes, it's not adding that much cost. The Quartz tubes from a kiln parts supplier is like $10-$12 bucks for a 32" long section. And I have had a great conversation with them and thy seams to think coil in tube is a great way to handle elaments especially when thy are large in diameter. Thy also said thy will cut the tubes to any length I want. The big thing I like about the tubes is I can use a coil that would be much larger then normal which allows me to use the much larger gauge resistance wire. Which in turn allows me to bump up the amps and still keep the surface loading in tolerance to have optimal life.

As to the O2 sensor thing, it is just a pipe dream to have it sence the O2 level. The plan was to use a zirconia dioxide sensor and catch the output signal which ranges from 0v to 1v with 1v being zero O2 present. As to the argon flow control I will be using a simaler setup to my propane forge controller. Multi needle valves with a solonoide to control it. I had not thought about a high and low mode for injection, that a good idea. Most likely the sensor won't work out and it will be a controller that just trickles the argon to keep the lv up.

About the shell temp, I don't really care how hot it gets but thought by removing the grooves it might drop the temp a tad bit. But I'm using the fire brick that's 9x4.5x3 so the walls are 3" thick which I believe is the same thickness as the paragon ovens.

Thanks guys for the comments. I got to run to pick up the metal for this but will be back.

 

[Thadbow]

JT, so where did you end up ordering your fire brick from?

 

[JTknives]

Just got if from a dealer on eBay. Cost me a total of $227 for 40 bricks. Got the steel ready do go and I'm going to start assembling it tonight once I get back home.

 

[JTknives]

Bricks arrived today, crazy fast. But apron inspecting them I found a whoops. I ordered K-23 bricks and thy sent me TC-23 bricks. This company had both bricks listed for sale so thy just boxed up the wrong ones I thought. But looking at the invoice it says TC-23. I double checked eBay and it says I bought the K-23 bricks as thy where a bit more then the TC-23. Also the TC-23 bricks really look kinda shoddy. Which I guess are the rejects when making K-23 bricks. So we will see what happens with this.

 

[timgunn1962]

Comparative values for the TC-23 and K-23 IFB are at

http://www.lloyd-ris.co.uk/pdfs/datasheets/Low Density HTI.pdf

The K23 is a significantly better insulator.

 

[JTknives]

Well I realised today that I mad a slight error. I was planing up building a 27" long chamber but some how I drew a 31.5" long chamber. It's not a big deal as I can cut down the sheets of side metal and angle iron. But the question is this. If I have enough bricks and everything to build the longer oven should I just do it. It's only one more row of bricks and I have plenty as I bought 40. Or am I crazy for going as long as 27". What do you think guys?

 

[timgunn1962]

I have built a 22.5" with 3 kW of elements and tested it to 1205 degC, 2200 degF. Time to reach that temperature was around 33 min and it would certainly have gone higher had I tried. I am reasonably confident that a 27" version would reach 2200 degF, albeit a bit slower, on 3 kW.

My chamber was 7" wide and 6" high.

Given the smaller chamber section and increased power you are proposing, I would not not foresee any problem at all with 31.5" on 4 kW.

 

[Teppojutsu]

I'm subscribed JT :thumbup:

 

[JTknives]

Update time.
It's been a busy few days and the duty cycle of my welder does not help. All the steel is cut to the size I need so it's basically just plug and play construction.

Then tack it together

Next the end cap

Everything tacked and cleaned up.

Now the other side is aligned and tacked in place.

Looked good

Next up is working on the lid. The lid has angle iron around it to create the sides of the lid. The ends of the angle iron need 45° angles cut. My abrasive saw lacks in the accuracy need for this so I set up the belt grinder to do the job.

Next I ground the angles onto the ends of the angle iron and started fitting up the joints.

All welded up

Now insert sheet metal top into the frame and weld in place.

Like a glove

Now with the top done I could weld the legs on.

Now flip it over and work on the under belly.

Start tacking up the angle iron side runners.

All the bottom angle iron tacked in place

I know you where thinking that those legs look a little scrawny so time to beef them up a tad.

Leg reinforcements tacked in place.

Now time to finish weld every thing

Thought I would show this little doohickey. The opening was wanting to close up and I needed to hold it at 11.5" so this rod will be welded in place. Adds a bunch more support to the front section.

here it is all ready and cleaned up with the top on.

Today I'm going to be working on the door and getting that fabed up.

That's it for now, I hope it has inspired you guys to go out and start on one. Oh and this is all made from 1/8" thick sheet and angle iron so it's maybe just a tad bit over built lol

 

[JTknives]

Alright I was back at it again tonight after running around all day in town. The plan was to tackle the door tonight so I can lay brick tomarow.

The door sides center punched for 1/2" holes.

All drilled

Next the 45° angles for the bottom of the door sides.

Any excuse to bring out the plasma cutter

Both sides done.

Now I wanted to be able to adjust the door if I needed to or if I needed to replace the handle. I hate makinging something permanent if it's a moving part. So I can up with this little dandy idea. Found these wonderful split bushings and welded one on each door side. I only welded half of the split bushing so the other half could be free to move so it can clamp down onto the 1/2" bar stock.

Door all mocked up and tacked. Tacking is a must when doing this because this was my second go around with this door. First time I wended the sides on backwards so the pivot was at the back of the door.

All wended up now.

The bricks fit perfect with no slop. Don't mind these cracky bricks, these are the tc-bricks that where shipped to me by mistake. I was shipped the correct K23 bricks but I was using these tc23 to mock everything up.

Thanks guys, be back tomorrow with more pictures.

 

[JTknives]

So things went slower then I anticipated today but the results where well worth it. Being that I'm basing my door design off the paragon ovens I have been trying to improve the design as well. Not that there is anything wrong with there design at all I just see some areas to improve it. Paragon welds there door to the pivot rod where me personally thought that was not what I wanted. So that's why I welded in the split bushings, so I could remove the door if I needed to or adjust the handles position. So I figured I would also improve there hinge brackets on the side. These are also welded into place which means you are stuck with any door gap you have or get in the future. My thought was to make this place moveable so you can adjust it so it closes perfectly at the top and bottom. Next was to improve the pivot it's self. Paragon just pivots the rod in a drilled hole in the side plate. I wanted something so I sleeved the hole for the pivot rod

Locations marked and center punched.

Step drilled up to a finish diameter of .375

Setting up the drill for the bushing hole.

All the holes drilled

Now time to connect the dots with the plasma cutter.

All cut.

A tad bit for carbide bur grinding to smooth out the slots.

Slots all done and ready to go.

Now to just the 45° angles

Hoooo lookin good

Hinge plates all done and bushing pressed in.

Laying out and drilling the pilot holes.

Holes tapped for the bolts.

Plate bolted in place.

And do the same to the other side.

It's getting really close being ready for paint.

Next project is to fab up the handle and bend the rod and test fit the door. But now it's time to go back to work till Wenday when I start on this again. Thanks guys

 

[Teppojutsu]

Looks great so far:thumbup:

 

[JTknives]

Ok pictures should be up. It kept saying I was blocked when I tried to post my pictures. Something with how I worded something triggered a warning. Weird

 

[Phixt]

Pretty impressive :thumbup:

 

[JTknives]

Ok had a few min to work on it today while waiting to go to town for air compressor parts.

Start of the door hinge rod.

That looks about right

Looks like a good handle to me.

Welded and ground

After getting it all together and the bricks in the door I relized I wanted just a tad more counter weight. It had enough to keep the door closed but you open it about a 1/2" and it overcomes the handle weight and so the door felt a bit heavy to let open. So after digging around the shop for something to fix this I found this little beauty. Added just the right amount of weight to the handle and well it kinda looks like it has a purpose lol.

Opens perfect.

Even gives a nice resting place for your thumb lol

That's it for now, next will be laying the brick.