Heat treat oven wip

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1 shot

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Mar 4, 2015
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I'm building an oven. I've already got the skin on and bricks in. I haven't cut the grooves for the elements yet mostly because I'm trying to figure out what gauge and how long and how I am going to arange them. The chamber of my oven is 9in wide 6.5in tall and 22 in deep. I've gone through the tutorial about how to make them but I'm still kind lost. Here are my questions

Is 4000w on 240v enough?
I think I should be using 14awg kanthal a1. Right or should I be using 15 or 16?
I'm guessing I will arange the elements in the oven based on the length?
I can post some pics later if that will help
 
4 kW on 240V is plenty. For a 22" oven, I find 3 kW works ok but is fairly slow to reach working temperature.

If you can, I'd certainly recommend you use 14 AWG Kanthal A1. A few of us over on the British Blades forum had element failures with 16AWG that have not recurred since changing to 14AWG.

You'll need more groove length for the larger-wire elements. I have found the best way to cut the grooves is with a router, though it makes a mess. Wear a suitable mask.

If you are intending to temper in it, use a short output cycle time (I use 2 seconds) and a ramp/soak controller to avoid overshoot. Otherwise it can be a problem with powerful elements running at low temperatures.

Pics would be nice: I'm wondering how you got a 9" chamber width? I once built one 9" wide using mostly Insulating Fire Bricks, but used a layer of Ceramic Fiber board backed with a layer of calcium silicate board for the roof: jointing the roof bricks held no appeal at all.
 
Great thanks, now I just have to figure out the length. I'm about to watch that video again.

I plan on using the solo PID, however I could use a suggestion on which model. I want the one with the two pulse out puts right?

The bricks fit tight together for the top. I was considering murdering some of them together but not all so I could still remove them. Then I was going to cover with perlite or vermiculite.
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I went through the math again but it doesn't seem that my calculations are correct. Here is what I got.
At 240v getting 4000w that gives me 14.4ohm. Wire is rated at. 0.2123ohm/foot This means I need 67ft of wire?
If I went with 5000w that gives me 11.52 That means I need 54.26 ft of wire?
Is all that right?
Do I have room for all that wire?
What inter diameter should I have it coiled to?
 
One more question.
Would it be easier to make it two elements instead of one really big element
 
Watts = Volts x Amps

Amps = Watts/Volts = 4000W/240V = 16.67 Amps

Volts = Amps x Ohms

Ohms = Volts/Amps = 240V/16.67A = 14.4 Ohms.

You are OK so far.

14.4 Ohms/ 0.2123 Ohms/ft gives 67.82 ft of wire.

You have your side bricks arranged to give a 4 1/2" wall thickness, so thinning down the wall by the depth of the grooves is not really an issue for you. You can think in terms of the size of groove that you'll find easy to cut. I used my side bricks to give a 3" wall, less the groove depth, so wanted to keep the groove pretty small. I'd been using 16 AWG elements that fitted a 10mm groove, so stuck with that. I got them wound by a company that does that sort of stuff for the pottery industry: they had the Kanthal in stock and supplied the wound elements for less than I could buy the material anywhere else. They also checked my math.

If you go for a 1/2" groove (because it's easy to get cheap router cutters that size), you'll have 2 wires of 1/16th diameter plus the former to get into 1/2". A 3/8" former would make the element quite tight in the groove but 5/16" would give a bit of clearance.

We're getting into rough calculations from here on.

When wound, the neutral axis will be somewhere near the centre of the wire, so each turn will have a 3/8" neutral diameter and will take (Pi x 3/8") of wire: about 1.18 inches. We'll be approximate and call it 1.2 inches for 10 turns/foot.

We therefore need 68 ft x 10 turns/ft = 680 turns.

Each turn is 1/16" along the length of the former before stretching, so we need 680 turns x 1/16" = 42.5" of unstretched coil.

You want to stretch it, and between 2 and 3 times was recommended to me. I used 3 times. I'm pretty sure more would be fine and I would not want to go much less if using staples to retain the element in the groove.

42.5" x 3 = 128"

You have a 22.5" long chamber and should easily be able to cut 20" long grooves. You have 2 side walls, so you need to accommodate half the length on each wall: call it 65".

65" / 20" per run means that you'll want a little over 3 runs of groove per side. You'll need extra groove length to make the turns and we're on rough numbers here, so 3 runs would be fine.

However, 4 is probably easier to wire up, since it keeps all the connections at one end (the back).

You should be able to accommodate the element length quite easily.

I don't think I would go to 5000W in your shoes. At 4000W, you should get a reasonable surface loading and good element life. Going to shorter elements and higher wattage really bumps up the surface loading and shortens the element life. If you get them wound by a pro, they should be able to advise/calculate and will have much more experience than me.
 
I usually use 2 elements, one on each side, connected in series. Each of the elements can be thought of as a 120V element: half the 240V element.

2 are a bit easier to handle than one big one, though there's not much difference in the overall scheme of things.

Initial cost is not much different, but if you damage one and have to replace it, it's obviously cheaper to change the shorter one.
 
Thanks a lot you have been a tremendous help.
I was considering 5000w because that guy on the video said I wanted a Pd of over .8 and 5000 would give me .95w/cm and 4000gave me .76w/cm. And also because it would be less feet but it seems that is not an issue.

I was going to order from Krueger pottery supply. It seems like they do everything I need.
http://kruegerpottery.com/repair-parts/kantal-wire.html
 
1 shot said:
One more question.
Would it be easier to make it two elements instead of one really big element
Click to expand...

If you go this way join the elements outside of the oven. I had many troubles when my oven elements were joined inside.


Pablo
 
I second that: use the doubled, twisted pigtails that Krueger offer.

The outfit I bought mine from were pretty insistent that bolted connections would be more reliable than terminal-strip connectors. As their experience exceeds my own by several orders of magnitude, I went with bolted connections: bent the twisted wire to a U-shape (maybe getting on for a P-shape but definitely not crossing the wires over) and this was clamped between 2 stainless mudguard washers on an M6 (1/4") stainless allthread. The copper wire got a crimped lug with an M6 clearance hole and this was clamped between another pair of washers on the other (cold) end of the allthread, avoiding any need for high-temperature wire/connectors.
 
I am not sure of availability or application, but my newest heat treat oven has the new TAP controller. I really like the fairly large screen and the menu driven system. Entering things is really easy, and setting up a multi-part heat treating program is really simple, and you can have it sound an alarm at each stage (if you choose to, and you choose which stages) so that you have an audible clue of what is going on. I talked with one of the designers from the company that makes the actual TAP controller a couple of weeks ago and the app for smart phones and tablets should be available in January. It is already set up so that it can be connected (Ethernet port) to a network, and there is a USB port as well for loading updates and such. With the app you could enter programs or just monitor what is going on and have a record of the firing temperatures on your device. The controller already maintains a memory with graphs of each firing.

It's a pretty cool controller, with some unique features, and may be worth considering for a build.
 
Sorry, missed the question in post #5 about the Solo controller.

I've mostly been using the AutomationDirect Solo SL4848 VR or the Omega CN7823. As far as I can tell, they are the same controller. Prices vary and I usually go for whichever works out cheapest at the time, factoring in the need for a suitable thermocouple if I don't already have one, and shipping.

Both Omega and AD provide excellent support should you need it, so there is nothing to separate them on that score.

Both controllers have one DC pulse output to drive the SSR and a relay output which can be assigned to an alarm. The DC pulse output is rated at 40 mA and will happily drive 2 SSRs each rated for 20 mA input in parallel (I used a pair of Fotek SSR-25-DA units on a sword oven with no problems at all). I'm not 100% certain, but I don't recall there being an option to run both outputs as control outputs in a heat-only or cool-only application, allowing you to feed the 2 SSRs separately. If you think you need to do this, please check with customer support that it's possible.

The second, relay, output can be used to feed a light or a buzzer if needed.

I have also used the bigger Solo 9696VR-E. It's slightly easier on my fat fingers and ageing eyes and the bigger display makes it easier to read across the shop. It has extra alarm relays so it looks like it would be possible to configure a "high, good, low" red,green,red light arrangement, though I've not actually done it myself. That might be useful for letting you know whether the oven is keeping up with the ramp/soak program because.

The TAP certainly looks like being an excellent controller. It should be much easier for the non-technical end-user to program than something like the Solo which is aimed much more at industrial users. It should also be able to give the user a much better idea on what is going on. Right now though, the TAP price seems high and it seems very new: I'd be inclined to let others, like Evenheat, do the beta-testing and wait until everything is finalized before buying in.
 
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