Kiln Conversion

P

PointFiveO

Joined
Sep 5, 2012
Messages
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Hi everyone, I've been lurking around here for a bit and I'm trying to get my first few knives completed. I was going to send these first few off and have someone else heat treat them, but I've decided to try it myself. I've done some reading and searching around and figured out basically what process I am going to use. I've got an old Paragon A66B kiln to use as an oven. I've done research on google as well as on these forums as to the feasibility of this. As I understand it precision is required when it comes to temperature, having read that most people taking this route install a digital controller on the unit. Eventually I would like to make my own oven for the horizontal door, but I'm sure everyone can understand that for now I have to deal with what I have.

The issue is that I am no electrician. Now, I am not doing this without guidance. My grandfather is an engineer and worked with complicated electronics on a regular basis in his day. The problem is that he's pretty old these days and he overlooks things, so I'd like to get as much understanding about the process before we do it as possible to avoid any mistakes. We have 220 in the garage that I'm using this in.

So if anyone has any suggestions for me, this is the kind of thing I'm looking to do:

I have: http://www.paragonweb.com/A-66B.cfm

These are the products I've been considering:
http://www.amazon.com/K-Type-SNR-PI...rr&keywords=pid+temperature+controller+k+type
http://www.amazon.com/K-Type-Thermo...8573&sr=8-1&keywords=k+type+thermocouple+1000

As I understand it I also need an SSR.

So the problem is I don't understand the compatibility of the parts. Will those parts linked work with the kiln, and with each other? What kind of SSR do I need? Do I need a certain gauge of wire running to the wall?

If anyone has any ideas, or warnings, or tips I am all ears. Thanks for reading.
 
The thermocouple you showed won't work. And the PID you linked to isn't programable like you would eventually want.

I hope I'm not deal spotting but couldn't find a link to a total package like this. You want a setup like this

There are several posts on here of people converting a pottery kiln to a knife kiln. I have done it myself and took a few pictures of the process. I'm sure you can find it with a bit of google-fu.
 
The first thing I'd advise is that you use a controller that has good support from the supplier, who speaks your language, can talk to you on the phone at a reasonable call charge and is in a timezone that you can live with.

I'd suggest either an Omega ramp/soak controller, or an AutomationDirect Solo, based on personal experience (I'm in England and have dealt with both suppliers). Auber Instruments seem to be highly rated over your side of the pond, but I have no personal experience of them. I understand Auber sell a kiln control kit that would suit your application.

Good ramp/soak controllers are not cheap, but I've never heard anyone express regret at having bought one.

Never buy any controller without seeing and reading the manual for it online first (and bookmarking it in your browser).

If you have a problem, you can ask for help on this or another forum. If you can provide a link to the manual, there's a good chance someone can help, even if they are not familiar with your specific controller. Without a manual, you are very much on your own.

There are different types of output on controllers. You are best off with a DC pulse output to drive an SSR.

An SSR is a Solid-State Relay. It allows a much shorter switching cycle than an electromechanical contactor (a contactor is basically just a big relay).

The output from the controller feeds the SSR, which feeds the AC power to the elements. If the controller calls for half power, the elements are switched on for half of each cycle and off for the rest of the cycle. Up to a point, short cycles allow better temperature control. My testing has shown that a 2-second cycle is about optimum for my home-built ovens/furnaces.

Your SSR will need to be DC input and rated to switch at least the rated current and voltage for your elements. It will also need a heatsink rated, as an absolute minimum, for the current. Some will suggest going for a higher-rated SSR for reliability. I'd not necessarily argue with this, but I'd certainly spend on an oversized heatsink before an oversized SSR.

I'd not choose the thermocouple you linked to. It looks much too fine to last at high temperature or fix in position effectively.

I use Mineral Insulated, grounded-junction thermocouples myself, largely because I install them horizontally with a lot of insertion depth, but it's probably best to use an exposed-junction thermocouple with 2-hole ceramic insulators, fixed vertically through the kiln roof, such that the thermocouple junction can see the elements. Most folk seem to use type K thermocouples, of around 14-16 ga wire, successfully.
 
I believe Omega makes the 7500 series of ramp/soak controllers that are about $100. You can have maybe 6 different reciepes, each with at least 6 segments. They're PID with auto tuning, amd can be had with a DC pulsed output to drive an SSR, and a second relay output you can use with the upper limit alarm function to physically remove the driving voltage from the SSR input. Or, you can get it with a current output and use that to proportionately drive a triac or thyristor: this gives far greater control and at least doubles your element life.
Best,
Steve
 
Thanks a ton for the the advice. After some serious googling of the terms you are using I'll attempt to come up with a new setup. I plan to have it worked out and ready to order on Monday. When I get time to look at it again tomorrow I'll post what I come up with.
 
I'm pretty sure the Omega 7200, 7500 and 7800 are the same units as the Automation Direct Solo controllers. In addition to the programs, these will autotune to 4 different user-set temperatures, then automatically pick the set of PID terms that most closely matches the setpoint.

I build the control panel as a separate unit, with plug-in connections for the AC power and the thermocouple (I also have a door switch which plugs in too). The multiple sets of PID terms means I can build a tempering oven and run it off the same control panel without having to wait for the austenitizing oven/furnace to cool down, or reprogram the controller.

http://www.automationdirect.com/adc...ers/1-z-16_DIN_Size_(SL4848_Series)/SL4848-VR

Tim

stevomiller said:
I believe Omega makes the 7500 series of ramp/soak controllers that are about $100. You can have maybe 6 different reciepes, each with at least 6 segments. They're PID with auto tuning, amd can be had with a DC pulsed output to drive an SSR, and a second relay output you can use with the upper limit alarm function to physically remove the driving voltage from the SSR input. Or, you can get it with a current output and use that to proportionately drive a triac or thyristor: this gives far greater control and at least doubles your element life.
Best,
Steve
Click to expand...
 
Look at this link for a good diagram
http://www.bladeforums.com/forums/s...eat-Treat-Oven-Wiring-Schematic-Future-Sticky
I have got all my parts from http://www.auberins.com/
I run this PID http://www.auberins.com/index.php?main_page=product_info&cPath=1&products_id=4
this thermocouple http://www.auberins.com/index.php?main_page=product_info&cPath=20_3&products_id=39
and these SSRs http://www.auberins.com/index.php?main_page=product_info&cPath=2_30&products_id=30
If you want you can set everything up in a separate box and instead of running the SSRs to the elements run them to a 220 female plug then just plug the kiln into that and set the kiln controls to as high as they go and let the PID "box" run it

The Omega Pids sounds great also. You can run multible programs with the 32 steps available on the PID I use also.
 
There is good info in the above posts, as well as in the sticky on PID controlled forges and ovens.

Three things I will toss out for your thoughts:
1) That is a pottery kiln. It is not really made for knives, and will have a lot of shortfalls. Will it work - yes. Will it work well - no.
2) If you aren't very comfortable with electricity and wiring, and Grandpa isn't reliable....get someone who knows what they are doing to hook up the PID control. What you want is to make a controller box that controls a socket to match the oven cord. Set the oven on HIGH and plug the cord into the controller. The PID will switch it on and off as needed to maintain the temp. The TC will have to be in the oven, of course.
3) With that oven, I highly recommend that you use two SSRs and also add a switch to the lid. This will prevent accidental electrocution. Look at the stickies and some of the recent threads on wiring a HT oven for 220VAC. They have detailed diagrams on using two SSRs and adding a switch in the SSR control voltage line that is door operated.
 
Okay so if I make a box using the exact same parts as Mr. Viall linked, I should be good to go? I had seen the box option before, but I didn't know whether or not it was the right option. But if that's what you all recommend, that makes things quite a bit easier. The only additional materials would be wire, plug/socket, and box materials correct? Any suggestion on what I should be looking for in the way of wire?

Also since it is a ceramics kiln, what should I expect in the way of difference? I realize I'm going to have to be careful of the tasty blast of warm air in my face when I open it, but beyond that what should I be aware of?
 
You don't open it.

Make a 3-4" hole in the top and hang the blades on 1/8" stainless steel wires. Make a firebrick cover for the hole.

Opening an oven like that at 1500F would be a really bad idea.
 
Ah. I had seen the hole in other posts, but I was under the assumption it was an option and people just opened them up delicately. Thanks for the tip.
 
If you want to keep your face and don't like flaming hands, DO NOT OPEN A HOT TOP LOADER.
 
Heh well I didn't expect to just open it and look in. I expected I'd need to do it somewhere without a ceiling close by, with welding gloves or something to give myself range from the machine, and it would be off. But I did foresee the temperature change being an issue, and standing back with a wire seemed somewhat crude (although it was near the top of my list). I'll do the hole instead.

Just out of curiosity, what's stopping me from putting it on its side. Provided I mounted it so it wouldn't roll, and maybe put a fire brick inside as a platform (As to keep it away from the heating element that would be directly below it), and put better hinges on it... Is there an issue? So far I've gotten "it wasn't built for that" a few times, but that's never a good answer.
 
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It wasn't built for that :)

The brick lining is stacked and assembled to be upright, and may collapse if sideways. The coils are attached to be vertical, too. It may work sideways, but you still have a pottery kiln not a knife kiln. It would be a huge, wide, and fairly shallow chamber instead of a small, deep, and narrow one. Such a cavernous chamber is perfect for 12" round pots...not so much for 1/8" by 1.5" by 12" blades. There is also the big door issue.

The hole in the top works well on an 18" or 24" deep kiln. It will take about an hour to heat up and fully soak the refractory before you can hang in the blades. Four soft firebricks will make a good hole cover. Set them as a stack and run two 1/4" pieces of all-thread through them. Put on wide fender washers and nuts. Turn this on its side and you have an 8"X8" cover that is 4" thick. Make the hanger wires from 1/8" stainless wire/rod. Bend a hook, and measure so they hang about 2" down in the kiln. Bend them at 90° so they will hang at that depth, and leave the rest going all the way across the top and sticking out about 6". Make a wooden handle and stick it on the rod with JB Weld. This gives you a very easy to insert and remove blade hook. You just hold it by the handle, lift the blade out of the kiln, and lower it into the quench tank.

BTW, welding/HT gloves are made to be able to touch hot metal briefly, and shield your hands when using long oven tongs. They are not make to put your hands into or very close to 1500F kilns. If you do that they will burn almost instantly. If you don't believe me, stuff some newspaper in one and stick it on a long wooden rod and shove it in a 1500F oven. Not only will the glove burn, but the paper in it will ignite. Now think what that would have done if it was on your hand?

As a souvenir of days gone by, I have a big pair of asbestos foundry gauntlets on the shop wall ( in a sealed plastic bag) that I used when doing casting long ago. These are what folks used to wear when they reached into the oven. There were also asbestos hoods, aprons, boots, and whole suits.
 
Excellent information again, thanks! I knew there must be a good reason people don't go around tipping them on their sides, but until I understand why there's always that itch to do it.

As for the welding gloves, yeah I've watched them burn up a number of times. In fact I've burnt up my share of them heh. Again I didn't really plan to stick my hands in the kiln, but now that I'm not doing it at all my previous plans don't matter.

The hanger you described will be awesome. I was pondering the whole opening of the lid thing due to the time element anyhow. This will reduce the time it takes me to get it to quench significantly. And now I don't have to go buy tongs.

http://shop.clay-planet.com/k-23-soft-insulating-fire-brick-ifb.aspx - Are these along the lines of the bricks you are referring to?
 
Yes.

If you wanted to get fancy, you could attach a hinge to the all-thread on one side and attach the other side of the hinge to a strip of metal which you screw to the top frame. That will allow you to simply flip up the top when adding or removing blades. Probably not worth the trouble, as simply moving the cover will work just as well.
 
Aye, I think I'll stick to moving the cover. If I do take a liking to heat treating I plan to build my own oven this winter or spring. This is really just so I can test the water and get myself familiar with the ovens, the process, and the safety concerns involved.
 
PFO, when wiring the Thermocouple to your control box, make sure and use TC extension wire. Using copper wire for this portion will, in essence, create a second TC and throw off your reading.
 
If a knife oven build is in your future, you are definitely best off building the control box separately. I'd go for plug-in connections for both the thermocouple and the power to the elements. That way, when you build your new one, you have the pottery kiln as a tempering oven.

It means you can just swap the plugs and don't need to wait for the Austenitizing oven to cool below tempering temperature.

If you use a Solo or one of the Omega controllers with multiple PID sets, it's just plug and set the temperature. If you go for a controller with only one set of PID terms, It should take no more than a minute or two to change the settings each time.
 
Excellent news, Tim. I was going to ask if this was a route that would be convenient for my future plans.
 
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