I am buliding an electric heat treatment oven

[BeaverNZ]

I am making an oven from soft refractory bricks primarily for heat treating aluminum motor cycle parts but will be able to go to a bit over 1000 Deg centigrade so will be able to be used for steel objects as well. I will also have a ridgidised kaowool roof and kaowool around the bricks as well as they are not a good insulator, the kiln sizes are 660 deep 400 wide and 230 high inside. I have used my die grinder set up to be used as a router with a 1/2in round nosed carbide burr to cut the grooves for the elements to go in. The elements are 3x3000 watts at 400 volts so it will be 3 phase. I had the elements made up by a company that makes kiln parts, i am doing this as I cant get an oven the size I want. I have a Shimaden controler for the temp control and will have thermocouple and relays etc for the control of the oven 

The bricks are held together with 8mm through bolts of threaded rod and satinite

[BeaverNZ]

I have got the body of the oven all together, Got more done today than hoped now it will have to be left for a few days to dry a bit. I think I will have a vertically swinging door so its gets out of the way when unloading and maybe kiln sheving if I can source some. I have painted/trowelled on a layer of the satanite in the hope that it hardens after high heat. The elements will be held in place by 1100 stainless tig wire pins pushed into the bricks.

[Buzzkill]

I'm not sure what you meant by "vertically swinging door."   The door on the professional setups stays in the same orientation when opened but moves away from the body of the oven and upwards.  That way the hot inner surface of the door isn't a hazard to you while loading or removing objects.  I'm guessing that's probably what you were thinking, but thought I'd bring it up just in case.

I'm a little jealous.  That thing is a beast.  I wouldn't be able to power it.

[BeaverNZ]

Yes thats what I ment Cheers

Edited April 24, 2023 by Mod30
Remove excessive quote.

[BeaverNZ]

I have almost got the oven completed so I can take it to the sparky to be wired up, I havent taken any pics of the frame of the oven but it has an angle iron frame that the clading is Tec screwed to and under that there is 50mm of Koawool insulation so it should be well insulated. The door will have Koawool insulation that i am going to retain with stainless steell cotter pins for the first 25mm layer then that will be held/joined with sodium silicate and there will aslo be a high temp rope seal around the door. The control box will have venting pannels at the top and bottom to allow lots of ventilation.

[BeaverNZ]

I have got the kiln all finished and have had the electrican come and connect up the sparks and smoke. It seems to run well heating up about 1 deg every two seconds and it doesnt have more than about 5 Deg of overshoot when coming up to temp. the cover is of the control cabinet just to make sure there is no melty bits going on inside. I need to put some handles on the door which I ment to do before I painted it. It seems to be very well insulated so far and not even warm on the outside

[timgunn1962]

What's with the thermocouple wiring? Looks like different colour-coded plug and socket and the cable doesn't look like thermocouple cable?

 

[Rojo Pedro]

Super cool. Looks very well done

[Steve Sells]

looks very professional

[BeaverNZ]

21 hours ago, timgunn1962 said:

What's with the thermocouple wiring

The Thermocouple is from a supplier of refractory and related things for a local alumium smelter and its what they supply them, The cable is just instrument cable supplied by the sparky

[timgunn1962]

That's about what I guessed. It WILL give errors.

Any combination of dissimilar metals in intimate contact will produce a small voltage (the Seebeck effect). The Voltage varies with the combination of metals and the temperature. 

There are a number of metal combinations that are useful for measurement and their alloy combinations and Voltage:temperature relationships have been published as standards. The standards include the colour-coding. Type K is a combination of a specific Nickel-Chromium alloy and a specific Chromium-Aluminium alloy. The wiring components need to be made of the same materials as the thermocouple "legs". If they are not the same materials, each joint will involve dissimilar metals and will produce its own Voltage. At the controller, the instrument measures the Voltage it is receiving, looks it up in its look-up table, and displays the corresponding temperature. Obviously, if the received Voltage is not just that produced by the "hot junction", the measurement will be "wrong".

[LarryFahnoe]

Very helpful explanation, thanks Tim. I have a thermocouple on a small forge that doesn't read right, so this gives me another thing to check into.

--Larry

[Buzzkill]

7 hours ago, timgunn1962 said:

If they are not the same materials, each joint will involve dissimilar metals and will produce its own Voltage.

So, if I understand this correctly, the correct (or at least lowest error) way to wire this would be with a matching yellow plug and wiring that connects directly to the SSR (no splices or other types of connections).

[Frosty]

Thanks for a glimpse into another learning curve Tim. I love being on a learning curve.

Frosty The Lucky.

[timgunn1962]

4 hours ago, Buzzkill said:

So, if I understand this correctly, the correct (or at least lowest error) way to wire this would be with a matching yellow plug and wiring that connects directly to the SSR (no splices or other types of connections).

 

That's it, though with the OP being in New Zealand, it's entirely possible he'd find it easier to source connectors and cables to a different standard, and therefore different colours, and would get the same results with them.  The important thing is that everything between the junction and the controller is the same material as each leg of the thermocouple. Connectors are fine, so long as they are made from the same materials. 

I'd expect no problem with the thermocouple. The yellow colour-coding looks to be the American standard for a Type K. I'd expect it to connect to either another yellow connector, or a green one most places in the world outside North America, then on to the controller using matching Yellow or Green cable. 

https://www.thermocoupleinfo.com/thermocouple-color-codes.htm

The different-colour connector connected to the yellow one on the end of the thermocouple will be for another thermocouple type: see the colours in the link. I'm colourblind and can't tell with any certainty which type from the pic and the link. There will be 2 dissimilar junctions in the loop: one on the positive side and one on the negative side. There will also be 2 more junctions where the "wrong" thermocouple connector joins the (presumably Copper) cable. That's 4 extra junctions and 4 extra sources of error.

It's worth noting that the thermocouple cable cores need to be connected correctly. Using the correct cable but connecting the wrong way round will give 2 extra junctions, each with their polarity opposite to the "hot" junction. The instrument will see a Voltage corresponding to the hot junction temperature minus twice the Voltage corresponding to the temperature of the extra junctions. Because it's fairly easy to connect things incorrectly, I buy "transition junction" Mineral Insulated thermocouple assemblies with a long enough cable to reach the controller. That way almost all the connections are done at the factory and all i can louse up is the final connection. If I do it's dead easy to diagnose because the indicated temperature goes down as the forge, kiln, whatever, gets hot. 

There are, as mentioned above, thermocouple extension cables that have the cores made from the thermocouple alloy. There are also thermocouple compensating cables. These are made from alloys selected to have identical thermoelectric properties to the thermocouple alloys over a narrower temperature range that includes normal cable operating temperatures (the range over which water is liquid and perhaps a few degrees below freezing). For type K, the Nickel-based thermocouple alloys are cheap and compensating cable doesn't save much money. However, when you get to types R, S, and a few of the others, it makes a huge difference to the costs. R and S are Platinum-based and running several miles of Platinum extension wire around, for instance, a brick-making factory would be cost-prohibitive. Using compensating cable is a no-brainer under those circumstances. Again the compensating cable needs to match the thermocouple type.

The best guide to thermocouples I have found is the "Labfacility Temperature Handbook", though Omega and others also have good guides of their own.

http://www.controlsdrivesautomation.com/orgfiles/ZORGF000011/IPE/Enhanced companies/labfacility/Temperature Handbook.pdf

 

 

 

 

[BeaverNZ]

Hi Tim

I was aware how a thermocouple works but was interesting to read what you had written, I will have to find out more about the plugs etc. I thought the dissimmilar metals just had to be at the hot and cold ends, It does seem to read correctly as I have checked it with my laser temp measuring thingus and there was only a deg or two different at 600 deg cent. Im only a dumb old welder but have always listened to people who know more than I so thanks Cheers

[Buzzkill]

9 hours ago, BeaverNZ said:

Im only a dumb old welder

After seeing the pictures of your oven construction I'm not buying that for a second!

[Frosty]

You aren't supposed to Buzz, that is a definitive example of how a master bull shooter uses understatement to brag. To quote Walter Brennan, "It ain't brag if it's a fact." 

Your oven is as brag worthy a project as I've seen Beaver. I feel lucky to have followed along.

Frosty The Lucky.

[Buzzkill]

Fair enough.  It's not just the oven though.  The machines in the background tell a story of their own.

[Frosty]

No, you're right Buzz, I miss or space so much anymore and I don't think I'll ever learn to keep my mouth shut. Seriously, I've been admiring the tools in BeaverNZ's shop since first glimpse and just spaced it running my fingers.

Frosty The Lucky. 

[BeaverNZ]

The mill is a recent thingand is something I have wanted for many years and I can finally stop all the dodgy settups in the lathe, The tooling is costing me just as much as the mill though. He who dies with the most toys wins

[Frosty]

Oh YES, a vertical mill is a rock star even if 95% of what you use it for is as a drill press, nothing beats a vertical mill as a drill press. And NOTHING kills a drill press like using it as a vertical mill.

Cutters are expensive but a person with a mill and an indexing vise CAN make their own cutters. Tungsten carbides are easiest, all you need is a flat to braze the carbides to so you don't need to worry about heat treatment.

Oh okay, that's getting carried away, fantasies from a guy who's wanted a vertical mill since jr. high school metal shop. <sigh>

Frosty The Lucky.

[BeaverNZ]

On 10/12/2023 at 9:24 PM, timgunn1962 said:

That's about what I guessed. It WILL give errors

Hi Tim Yes you are correct, the acutual temp is about 50 Deg cent high at 520 setting. I put a piece of RHS in and heated that up and meassured it and its the amount out so will have to get it setup they way you said with the right wires etc. I will see if I can source the plug with the wires factory attached cheers for the advice Beaver PS I have found with things in the past if shiney or light coloured dont give the correct temp reading when shot with my laser temp probe.

[BeaverNZ]

Oh and I forgot to say it takes 40 mins to go from 11 to 580 deg cent but I allowed a good long soak time before taking my temp measurement

 

[BeaverNZ]

I have sourced the correct plug and wires and tested it today and I had a piece of RHS in the oven to shot with my lazer thermometer and also had another thermocouple that I remembered I had with a multimeter and it stil reads 10% low to the actual temp even after allowing a long soak time. What I think my problem is now is the prob is right at the back top corner and it must be a dead area as far as curculation goes, I did wonder about putting it there but it is the best place to not get damaged but I will relocate it to the more central place at the top of the oven. Both the Lazer and the multimeter read the same temp so they are probably correct.