Old Vigor Burnout Furnace adapted to heat treating

I've got an 18" 4kW top loading ceramic kiln that I use for heat treatment and other things and I similarly fitted a temperature controller to it. It still has the 2 "energy controllers" fitted, one for each bank but they are normally set to max or off if one bank is not needed. I added a thermocouple to the kiln and connector into the box on the side. The temperature controller is housed in a separate box with tails out the back and mains plugs on the end so I can use it for controlling other things if required, it also allows it to be placed away from the heat. The thermocouple lead currently plugs into the front of the controller box. The finned heat sink is about 3"H x 3"W x 1.2"D and gets warm to the touch when running max duty, like when firing to 1200C, but very acceptable.

One of these days I'll add a temperature controller I have to my small Gallenkamp heat treatment furnace as the energy controller on that is a pain, but the thermocouple read-out is accurate from checks I've done.

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The Vigor furnace is rated at 1.6 KW, being 14 amps at 115 volts. However, the heater coils are old, and only draw 11 amps at 113 volts, or 1.24 KW. At full power (with no voltage drop in the controller), after closing up a bunch of heat leaks, it gets to 1000 degrees C.

If I understand, you electronically control only one of the two banks, the other being on or off as needed, so the electronic controller handles 2 KW at 220 volts.

I thought of having a separate box, but all-in-one is more convenient, and the commercial furnaces have the same scheme that I used, thermal isolation using a set of parallel plates and spacers, so I knew it would work.

Operation at 220 volts cuts the current in half. A solid-state relay (SSR) has a constant voltage drop, being 1.2 volts for the SSR I'm using, so half the current is half the power to be dissipated in the heatsink. This (and the distance from the furnace and its heat) explains the difference in needed heatsink size.

For the record, the old thermocouple that came with the Vigor is made of

14 guage chromel-alumel (Type K), appears to be original from 1979, and reads about 5 degrees C low. It's still perfectly useable.

Joe Gwinn

The controller controls all input to the kiln but if I don't need 4kW then I just switch off one of the elements as they are in parallel.

I have a glass melting furnace in the build stages and that will have its own controller permanently attached for convenience, the current controller was built as a seperate unit so I can use it to control other items if required.

Good point, I had failed to mention that I was running on 230V, the UK standard mains voltage. I didn't occur to me that you were running yours on 115V.

O.K. I picked up a small one at a tool flea market at a collector's gathering. The heated area was about 4" wide, by 3" high, by about 6" deep, with a counterbalanced raising door with a mica window for viewing the interior when hot.

But it came with *no* controller.

IIRC, I think that it cost me something like $25.00 a few years ago.

Since I already had one of the Omega controllers and a stainless steel enclosed thermocouple, all I had to do was to make a housing for the controller and the SSR (a 20A 240V one which I also already had). While I was at it, I added a locking miniature toggle switch (the kind where you pull the handle to enable switching) between the output of the controller and the input of the SSR, so I could use the controller to track the cooldown temperature without having to reset it to cool down.

The oven was on legs about as tall as the aluminum box which I selected for the housing, so I put that box on standoffs on the right-hand side legs to minimize conducted heat from them (and not much heat there anyway).

The box was sufficient heat sink for the 20A SSR, since I could expect no more than 15A load from the wall anyway. I did use white heat sink goop when I mounted it to the chassis, of course.

No tall legs on yours, I presume? Overall, it sounds like a Blue-M muffle furnace which I had a work with the same duty-cycle type controller. That one had the controller in a box to the right as part of the overall oven housing. It did have a heavy-duty thermocouple connected to an analog meter for readouts of the temperature.

No doubt this has long since gone to a surplus sale. :-)

Agreed. I was quite amazed at the Omega controller. About two thirds of the way up to set-point it shut off and measured the coast of the heat on up, so when it reached near the set-point it had a total overshoot of 1 degree F.

I got the controller for half price from someone in this newsgroup in advance of need -- just knowing that I would eventually need it. As it turns out, I was right. :-) Same for the SSRs -- I tend to stock a few for future needs.

I've so far taken mine up to 1850F (1010C) and that took about an hour, so I don't expect it to get much hotter. :-)

Enjoy, DoN.

On my Vigor, the heater volume is 13" wide by 6.5" high by 7" deep. The door swings to one side on vertical-axis hinges.

Hmm. 4*3*6= 72 cubic inches, versus 13*6.5*7= 591.5 cubic inches, a volume ratio of 8.2 to one. Did you get a burnout furnace, or a melter?

I have a Robertshaw "infinite" controller for sale cheap...

OK. I didn't do that.

This would *not* work on my furnace - the box is steel (poor heat conductor) and itself gets quite warm at max temperature.

None whatsoever. There is a ventilated skirt which is an extension of the vertical walls of the furnace. I have it setting on a wood bench, which does not get all that warm.

Sounds like the Vigor for sure.

That's a self-tuning PID (Proportional Integral Derivative) controller for you. These used to be expensive, top-drawer industrial controls, and now they are jellybeans. Mine cost $99 new.

I don't think my Vigor will get quite that hot at present, although if I do some more repairs it probably will manage. One fine day the heater element will fail, and they are still available for about $60, long after Vigor went bust. Vigor must have sold a lot of these furnaces.

Joe Gwinn

OK. But this switching off is manual?

What temperature does this require?

Yes, but we Yanks know where you live...

Joe Gwinn

[snip]

Yes, the energy controllers fitted to the kiln have an off position and a full on position on the knob as well as settings in between.

Depends on the glass but I intend to use one that would normally be gathered at about 1100C, maximum intended glass temperature is 1250C and element temperature will be a bit higher. Maximum for the likes of Kanthal A1 is 1350C IIRC so pushing the upper limit but as I am intending to be a glassblowing weekend warrior it's a workable and cheap option compared to the likes of SiC or MoSi2 elements.

OK.

I won't be doing any glassblowing then. I think that my Vigor has nichrome heaters, but I've never seen nichrome and Kanthal A1 side-by-side either.

Joe Gwinn

Wow Joe, that was me you got that thing from. HA. I guess I should have recognized you as an RCM'er, I've seen your posts here plenty of times. In any event, glad that thing worked out for you. That was about what I was planning on doing with it, converting to an Omega control. We use loads of the Omega CN9000 series. Self tuning and very reliable.

I stumbled on a near looks like new Ney-Dental Vulcan box furnace, the box is about 16" cube with a fancy-pants multi-step ramping digital control. Good for 1100C, It was being disposed of because of a minor electrical issue that was easily fixed, so I got it for a price I could not refuse.

Glad that worked out for you joe. Pleasure to meet you!

-Al A.

A lot more space.

I have no idea. There were no labels -- manufacturer or model number -- remaining on this one.

But there were no provisions for runoff of wax, and the orientation is similar to a brick on its flat side, with the smallest area towards the door.

If the original controller were still present I might have a clue from the range it was intended to cover. But all there was was a pair of stiff wires insulated in asbestos coming out the back to connect to my controller. It works nicely for heat treating small workpieces at least.

No thank you. :-)

[ ... ]

An easy thing to add after the fact -- as long as you have some extra front panel space available.

O.K. Make an aluminum box to mount on the side, with standoffs and perhaps an intermediate sheet of aluminum between two sets of standoffs. Use the original controller box for storing accessories which won't be harmed by the heat. :-)

[ ... ]

O.K. How tall is the skirt? Not tall enough to use it as the mounting point for the controller, I presume.

Proably made by the same company -- whether that it Vigor or Blue-M -- just for different markets. The Blue-M came from a lab supply catalog.

Hmm ... I think that they were $200.00 when I got mine, and since I got mine at half price, I got it for the same that you did. :-)

There was someone on this newsgroup who had several left over unused after a project closed down, and who was offering them here. I'm glad that I got one. I wonder whether we even have the same model? It would take me a bit of work to verify the model now. Mine has the plug-in strip along the top which says that it is displaying in degrees C, but I've switched mine over to display in degrees F, since that matches the information in _Machinery's Handbook_ more closely.

I did have to make a bushing to go around the thermocouple probe to minimize airflow through it. The original hole was something like 1" diameter -- way too much for the skinny probe which I had, so I turned up a bushing of lava, and then cooked it in the oven itself (which turns it from whiteish-gray as machined to pink. :-)

It may be time to do another one, with a larger hole for an alternative thermocouple which I found out in /dev/barn/01 a couple of weeks ago with an analog meter. That would give me a totally power-free way to monitor the temperatures.

Good Luck, DoN.

It could be either I suppose. I assume that one needs both kinds of furnace, or the logistics of getting molten metal into glowing-hot mold become intractible. Unless the melting is done with a torch and crucible.

There are no provisions for wax runoff in mine either. I don't think they worry about the wax, and just let it burn off. I have read of burnoff furnaces with a smoke vent, but I suppose that would only be for large furnaces.

Probably a 14 guage Type K (chromel-alumel) thermocouple.

Chromel and alumel are basically a form of stainless steel.

I made space by removing the original moving-coil pyrometer. The 1/32 DIN controller easily fits in the hole left by the pyrometer.

The pyrometer does seem to work, and I'll calibrate it and use it as a backup for the fancy electronics. It may benefit from a new thermocouple.

That would certainly work, but would stick out very far to the right.

I took my mechanical inspiration from pictures of current furnaces with digital controllers.

About 2.5". One could mount the controller in the skirt, but it would make using the controller quite awkward, as it would be so low, and would expose it to damage from dropped hot objects.

I think that this was an industry-standard design, made by everybody and sold by the pound.

Yes. By the way, the self-tuning feature may benefit from some training. Once or twice, instead of simply turning the power off when done, set the setpoint temperature to a little above ambient, say 50 C, and let the controller follow the temperature down, for the experience.

What I got is a Omega CN7523 controller driving a Omega SSR330DC SSR which is mounted on an Omega FHS-7 heatsink.

In my Vigor, the hole fits the ceramic sleeve insulating the thermocouple reasonably tightly.

One can also make bushings from K23 foam firebrick and glue it into place with furnace cement.

The traditional moving-coil pyrometers are self-powered, and are optimized to work with a thermocouple. They are accurate enough for heat treating. Some pyrometers were designed for mounting in a steel panel, and are inaccurate if not in the panel, so if the panel is aluminum it may be necessary to provide a piece of sheet steel as well.

Joe

Well, I'll be damned. Stands to reason, I suppose.

How about CN7500 series?

I looked at those fancy controllers, but it seemed like a lot of trouble to program for one-off jobs.

Isn't that a RCM staple - stuff tossed for lack of a fuse - and the knowledge to replace it.

Thanks. Likewise.

Joe Gwinn

Well ... I intend to use this purely for heat treating. It is too small to handle a crucible of molten metal safely. You press down on a counterweight on a lever to the left and the door lifts from in front of the heat zone.

There is a shelf in front of it -- slate or perhaps asbestos board. Too discolored with age to tell for sure. About 1/4" thick, FWIW.

Hmm ... no vent here, unless the 1" hole in the back was supposed to be one. But it is not fully at the top of the back.

Nope -- it is the wiring to the heating element. *Nothing* which came with it was for measuring the temperature -- other than perhaps the 1" diameter mica window in the door with an optical pyrometer. :-)

O.K. I've got the alloy definitions in my old CRC _Handbook of Chemistry and Physics_ (otherwise known as the "rubber tables". :-)

[ ... ]

I also added a larger LED to watch the cycling of the heating element.

O.K.

O.K. Can you punch a couple of holes in the side and mount a small computer fan in there to circulate air whenever it is running? Perhaps add a thermostat to keep the fan running for as long as there is significant heat coming through the wall?

O.K. I just went with available Bud Minibox chassis (I didn't at that time have a shear large enough to accompany my 24" brake to make my own.)

O.K. A bad idea, then.

[ ... ]

O.K. A good idea.

Mine is too hard to get to at night. Easier when I can open the shop door -- as I intend it to be when I'm using the oven. And a good fire extinguisher handy, too. :-)

[ ... ]

O.K. But I *had* the machinable lava. It machines quite easily in the lathe (very dusty), and when it is fired it turns pink and *very* hard.

[ ... ]

Right -- the steel panel shunts off some of the magnetic field which of course changes the sensitivity somewhat. IIRC, this was originally mounted in a non-magnetic alloy of stainless, so there is no problem there.

Enjoy, DoN.

Can't be slate at that temperature, so asbestos board is more likely.

My Vigor has a 1" diameter vent hole in the top, with a little metal cover that one swings to the side. I wondered what it was for.

Ah.

The Omega.com website has lots of information as well. As does NIST.

The Vigor had a neon pilot connected across the heating element, and so I left it as it was.

I think one can buy pyrometers on eBay and at ham swap meets. There are now lots of Pyrometers on the dole, having been made redundant by digital controllers.

I thought of this, but couldn't find an 115 volt AC fans that were small enough. I probably can run a 24 volt fan off the controller signal to the SSR, but the fan would run only when the element was on. Perhaps that's enough.

Doesn't Bud (or Hammond) still make steel chassis? Just like in the

1950s?

Yes about the fire issue. I don't run this furnace if I'm not present, at least not until I have some experience with it. The first thing I did with it was to measure temperature versus time under power, to see how long it took and how hot it got. This caused some tightening-up exercises, which allowed the peak temperature to climb a bit. I've had it up to 1,000 C or so.

What make and model is this material? It may be useful.

So, you must avoid the steel.

Omega sells the #14 Type K thermocouples for something like $20 each, so I wasn't tempted to scrounge for one.

Joe Gwinn

Especially if I pull something out at full temperature and leave it resting on the shelf.

[ ... ]

In the top makes more sense than in the back where mine is. So I just use mine for poking in the thermocouple.

[ ... ]

And somewhere I have a ton of literature from Omega -- but I haven't seen it for a while. :-)

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O.K. But neon pilots -- especially after they age quite a bit, tend to flicker on their own. Of course, if you *really* need to know, you use the tiny LED in the controller. :-)

[ ... ]

:-)

"On the dole" -- are you in the UK by any chance? Or from there?

[ ... ]

Hmm ... a tiny switching power supply from a hamfest to power it?

I don't know. I have seen only aluminum ones recently.

O.K. It is still daylight now, and I just checked. It is the Omega "CN9000A". (IIRC, there is more fine detail to the number on a label inside the box.

O.K. The highest that I've had mine is 1850 F (1010 C).

[ ... ]

Well ... I just did a Google search for "machinable lava", and the first hit is:

(they insist on JavaScript being enabled) which says (in part):

====================================================================== Machinable Alumina Silicate L911A (Lava) Machinable Alumina Silicate L911A (Lava) Aluminum silicate is machinable in an unfired state and used in applications up to 1000 F After firing, parts are as hard as carbide & usable up to 2100 F Aluminum silicate has low thermal expansion Aluminum silicate is low cost Aluminum silicate is available in wide range of stock up to 12" in diameter.

Some applications include prototype hardware, insulators, bushings, soldering fixtures, nozzles, welding tips or whatever you need. ======================================================================

This site seems to have more details about how it should be fired, and I obviously did not do it quite right. :-)

[ ... ]

Well ... I already had them, so I did not need to purchase any, yet.

Enjoy, DoN.

It's also on their website.

This neon does not flicker, although it seems to be original.

Neither. But I like their turn of phrase.

I suppose, but we'll see if it's needed.

It's twice the size of the CN7500 series, but would nonetheless fit in the Vigor where I mounted the CN7500. Aside from a larger and more convenient front panel, and more control functions, the controllers seem more or less equivalent.

I googled too, and had many hits, but didn't know which one you had.

I'll look into this. I recall that MSC sells the stuff, but it's expensive.

I did purchase what will eventually replace what came with the furnace.

Joe Gwinn

Of course -- but I don't actually *need* that information at present, and I have lots of places to find it when I do.

[ ... ]

Amazing.

[ ... ]

O.K. I can understand that.

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O.K. Perhaps just a 12V fan and a wall wart to power it? :-)

[ ... ]

O.K.

[ ... ]

machinable lava

was my search string.

It helps that I have some of it already. :-)

[ ... ]

O.K. I already had some nice unused stainless steel clad type K thermocouples -- still got a spare for when this one gets cooked to death. :-)

Enjoy, DoN.

I took a closer look. The neon pilot could have been replaced, as the connection is by means of 0.25" tabs. One can still buy exactly these pilot lamps, so it could have been replaced quite recently.

Is Boston close enough?

Seems clunky. Not clear that it needs a fan either.

Same.

Ahh.

It won't be soon I'll wager.

Joe Gwinn

What color is the Neon - is it orange or red ?

Red means there is a trace element to help it keep going... a nuke particle.

Might be over driven - e.g. - more current than normal so the intensity stays on longer.

Martin

Mart> >

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