Building tempering Oven

[Natlek]

Last time I used kitchen oven I make mess , huge mess I put in oven to temper three relative long Parang from 15N20 steel . I set temp. on 250 celsius ........BUT I forgot to clean blade from quenching in oil .You can imagine what happened....smoke and smell as on the battlefield If I repeat that I will slip in my shop for rest of my life So I decide to make tempering oven .I will use 4 heater from two toast oven /they are cheap and easy to find for replacement / and all necessary electrical equipment ,the same one is used in HT oven .Dimension of chamber ..... 450cm. long , 12cm. height and 15 cm width . I like to hear from you guys what do you think of this building concept ? I want to build this thing as best as I can .I have available whatever material you think is best to use ? My plan is this .......................
1. 1 - 1,5mm stainlees sheet
2. 5 cm. kaowool
3.ceramic tile ??????????????????????
4. heater ...they a rated to 750celsius , so I think that I can temper even on 400-450 celsius ??
5. glass ceramics as radiation shield ?????????????
6. internal fan for air circulation

 

[Stacy E. Apelt - Bladesmith]

It may be overbuilt, but it should work.

I would use plates of 1 or 2 mm steel instead of the glass plates. They will heat up and radiate the heat evenly.

 

[godogs57]

Went to Walmart, bought a toaster oven and oven thermometer. Working perfectly for 20 years.

 

[Natlek]

You can buy good cake from the bakery but not as good as from Grandma's I like to build things .......that I was doing all my life .
Thanks @stacy , I will use SS steel . It will be much easier to do that way. I try one heater ...they get very slow to glowing temp ? Is it that ok ?

 

[mete]

Ceramic tile ??? of course !
I had needed some tempering and had a simple [ no computers ! ] toaster oven but it had no insulation. I needed to limit the temperature swings. Then I needed some insulation . I had saved some nice Italian 10 mm ceramic tile from my kitchen renovation and now I have a proper tempering oven !!

 

[joedhiggins]

I think it is significantly overbuilt. Agree with Stacy about the steel muffle. I would probably build the exterior out of mild steel in lieu of stainless and save yourself a big chunk of money. I also think I would eliminate the fan. If I was going to use SS, I would probably replace your ceramic walls with SS (or even mild carbon steel, the temps you get to arent going to beat up carbon steel that bad). As long as you are careful with your wiring, you shouldn't have any shorting problems with those elements, and they will be a lot easier to mount to steel than to ceramic. Just have the contact/wiring lead junction happen in the inswool.

You can buy insulated wiring good up well into the operating range of that oven, so no fancy stuff required there. (https://www.amazon.com/dp/B001ALK97C/ref=nav_timeline_asin?_encoding=UTF8&psc=1) are you running the elements in paralell or series?

If you do the inner box out of steel, I thinnk it would make the whole project a lot easier. Weld up a 5 sided box (no front, no top) for the chamber lining and get all your elements positioned. Build a lipped lid for that box that has your steel muffles (3mm is fine) welded to the underside, that way you can remove the lid and have easy access to your elements. Weld up the exterior 10cm larger in width and height. and lay in your inswool and the box. I would probably use IFB for the door, not required but it will make it easier. I would also probably use some of that spun firberglass gasket material that they use for oven seals around your door, as that should handle the temperatures you are looking to use.

I would eliminate the fan as well. Without ducting and cooling, it is likely to last poorly and I dont think with the muffles you are going to have a meaningful heat gradient in the oven. If you are worried about said gradient, thicker muffles are an easier solution.

I think this would still be pretty overbuilt (which ain't bad), save you some money, and be easily repairable as you should be able to pull it appart very easily.

 

[Randy3000]

You can buy good cake from the bakery but not as good as from Grandma's I like to build things .......that I was doing all my life .
Thanks @stacy , I will use SS steel . It will be much easier to do that way. I try one heater ...they get very slow to glowing temp ? Is it that ok ?

With 4 elements, it may be fine. The problem i ran into with usibg 2 toaster oven elements is they take too long to change temp for what my pid was capabale of handling well. When i rebuilt my oven to use 4 elements, it worked perfectly. I use quartz tubes. Exposed elements like yours may be better, but then you have a barrier around your elements so i dont know what that will do.

 

[Natlek]

Ceramic tile ??? of course !
I had needed some tempering and had a simple [ no computers ! ] toaster oven but it had no insulation. I needed to limit the temperature swings. Then I needed some insulation . I had saved some nice Italian 10 mm ceramic tile from my kitchen renovation and now I have a proper tempering oven !!

You are kidding or you think that ceramic tile is good idea , mete ?

 

[Natlek]

I think it is significantly overbuilt. Agree with Stacy about the steel muffle. I would probably build the exterior out of mild steel in lieu of stainless and save yourself a big chunk of money. I also think I would eliminate the fan. If I was going to use SS, I would probably replace your ceramic walls with SS (or even mild carbon steel, the temps you get to arent going to beat up carbon steel that bad). As long as you are careful with your wiring, you shouldn't have any shorting problems with those elements, and they will be a lot easier to mount to steel than to ceramic. Just have the contact/wiring lead junction happen in the inswool.

You can buy insulated wiring good up well into the operating range of that oven, so no fancy stuff required there. (https://www.amazon.com/dp/B001ALK97C/ref=nav_timeline_asin?_encoding=UTF8&psc=1) are you running the elements in paralell or series?

If you do the inner box out of steel, I thinnk it would make the whole project a lot easier. Weld up a 5 sided box (no front, no top) for the chamber lining and get all your elements positioned. Build a lipped lid for that box that has your steel muffles (3mm is fine) welded to the underside, that way you can remove the lid and have easy access to your elements. Weld up the exterior 10cm larger in width and height. and lay in your inswool and the box. I would probably use IFB for the door, not required but it will make it easier. I would also probably use some of that spun firberglass gasket material that they use for oven seals around your door, as that should handle the temperatures you are looking to use.

I would eliminate the fan as well. Without ducting and cooling, it is likely to last poorly and I dont think with the muffles you are going to have a meaningful heat gradient in the oven. If you are worried about said gradient, thicker muffles are an easier solution.

I think this would still be pretty overbuilt (which ain't bad), save you some money, and be easily repairable as you should be able to pull it appart very easily.

Thanks for your opinion , I appreciate it Look , the only expense in this build is purchase of necessary electronic all rest I already have ...Motor for fan will be outside of oven so no heat ? I see that in some high price oven ?
About ceramic tile , yes will be more complicated to build ,but if it is better solution then steel I will use them ? I solved everything how to build this oven /most as you describe / I need opinion on material I intend to use .As I say already , cost is out of question in this oven ... I have everything mentioned here ?

 

[Natlek]

are you running the elements in paralell or series?

That's what I meant to ask here I do not know how this electronics work.I mean on PID temp controller and all other stuff ?

 

[Natlek]

Here's how I will mount fan inside chamber

Except heaters inside everything is ceramic.....?? That s way I was thinking that it is good idea to use ceramic tile and ceramic glass ?

 

[Natlek]

With 4 elements, it may be fine. The problem i ran into with usibg 2 toaster oven elements is they take too long to change temp for what my pid was capabale of handling well. When i rebuilt my oven to use 4 elements, it worked perfectly. I use quartz tubes. Exposed elements like yours may be better, but then you have a barrier around your elements so i dont know what that will do.

With that barrier/shield my intend was to stop direct radiation from elements to blade steel ?? Especially when they start to glow....IF they ever get to that temp ?I have no idea how they will work inside to keep constant temp ??

 

[Stacy E. Apelt - Bladesmith]

I agree that the blower probably isn't needed, but it will assure even temperature everywhere.

The high temp door gasket isn't needed, either no gasket or a stove door gasket will be fine.

I would use one layer of 1" Ins-board for the refractory between the insulation and the heaters. It can even be cemented together with satanite or stove cement.

Use Hi-temp 12 gauge wire with fiberglass insulation for connecting the heating elements.

The control is a simple PID and SSR setup like shown in the stickys. Use a 40 amp SSR, even though the load will be much less. A heat sink is needed for the SSR.
Use a 10 gauge TC (any gauge below 14 gauge will work, but the heavier gauges will last longer). Tyke K is the norm, but you could use a J or RTD if you want). It doesn't need a ceramic sheath, just the ceramic insulator beads, leaving an exposed tip. I would eliminate the top element and place the TC dead center in the top with the tip sticking out at least 1".
You can buy low price PID,SSR ,and heat sink setups on ebay. Some even have a suitable TC.

For the outer shell, 20 gauge sheet metal will be fine - mild steel, stainless, aluminum .. let availability and cost decide.

 

[Randy3000]

As far as parallel or series it depends on the resistance of the elements. Put a multimeter on them. If one element is 12 ohms, let's say, then to run all 4 elements you would need to 2 parallel circuits with 2 elements in series in each circuit. The equivalent resistance of that circuit would be 12 ohms (24 ohms in each parallel branch) and would pull 10 amps off a 120 volt supply. This will make a 1200 watt system. Sure, one element alone will draw the same current and have the same power output, but it may exceed what the element can handle and also uneven temp distribution. Also, if you can get two parallel circuits, that gives you the option to switch one circuit off to reduce current (e.g. after reaching temp) so you can run something else off the same outlet.

Muffles can cause more exaggerated temp swings since it takes time for heat to go from element to thermocouple, and that lag time may be more than the pid is capabale of controlling. That is a real issue i had, and it caused a +/- 20 degree temp swings for what i had. I removed muffles and measured no temp swings. I prefer measuring no temp swing.

 

[Stacy E. Apelt - Bladesmith]

With a fan the swings should be less. The PID should learn the swing time in 15 to 30 minutes warm up. I agree that bare elements should be fine , especially with a fan. If the muffle is used, it should be fairly thin, just enough to diffuse direct radiation. 16 gauge would be fine.

 

[Natlek]

I agree that the blower probably isn't needed, but it will assure even temperature everywhere.

The high temp door gasket isn't needed, either no gasket or a stove door gasket will be fine.

I would use one layer of 1" Ins-board for the refractory between the insulation and the heaters. It can even be cemented together with satanite or stove cement.

Use Hi-temp 12 gauge wire with fiberglass insulation for connecting the heating elements.

The control is a simple PID and SSR setup like shown in the stickys. Use a 40 amp SSR, even though the load will be much less. A heat sink is needed for the SSR.
Use a 10 gauge TC (any gauge below 14 gauge will work, but the heavier gauges will last longer). Tyke K is the norm, but you could use a J or RTD if you want). It doesn't need a ceramic sheath, just the ceramic insulator beads, leaving an exposed tip. I would eliminate the top element and place the TC dead center in the top with the tip sticking out at least 1".
You can buy low price PID,SSR ,and heat sink setups on ebay. Some even have a suitable TC.

For the outer shell, 20 gauge sheet metal will be fine - mild steel, stainless, aluminum .. let availability and cost decide.

Thanks again @ Stacy ! About element .... I plan to be mounted on side walls , two for side like on picture? That way I will get 50cm. length of oven and I hope even heat inside .............

 

[Natlek]

As far as parallel or series it depends on the resistance of the elements. Put a multimeter on them. If one element is 12 ohms, let's say, then to run all 4 elements you would need to 2 parallel circuits with 2 elements in series in each circuit. The equivalent resistance of that circuit would be 12 ohms (24 ohms in each parallel branch) and would pull 10 amps off a 120 volt supply. This will make a 1200 watt system. Sure, one element alone will draw the same current and have the same power output, but it may exceed what the element can handle and also uneven temp distribution. Also, if you can get two parallel circuits, that gives you the option to switch one circuit off to reduce current (e.g. after reaching temp) so you can run something else off the same outlet.

Muffles can cause more exaggerated temp swings since it takes time for heat to go from element to thermocouple, and that lag time may be more than the pid is capabale of controlling. That is a real issue i had, and it caused a +/- 20 degree temp swings for what i had. I removed muffles and measured no temp swings. I prefer measuring no temp swing.

Thanks for this post Oven will run on 220V ....does this changes something in calculation ?

 

[Stacy E. Apelt - Bladesmith]

I would use high temp wire crimps on the 12 gauge (or 10 gauge) hi-temp wire and screw them tight to the elements. The front element can be wired through a small hole in the brick and down a larger hole to the bottom. A simple metal channel under the bottom to route the wires through would be a good idea. You can plug the holes in the brick with satanite or just a plug of ins-wool after everything is done and tested out. Back elements can go straight out the back. Put all the power connections and PID stuff in a metal box mounted on spacers an inch away from the back.

 

[Randy3000]

Thanks for this post Oven will run on 220V ....does this changes something in calculation ?

Not if you run each circuit off a different hot (assuming your 240 is a four wire, has 2 hot wires, a neutral, and a ground).

If you were to power both circuits off both hot wires (or if your 240 is a 3 wire, two out of phase hots and a ground) it would double current and quadruple power output, which i think 240 usually will have at least a 30 amp breaker ( easily check by looking at the breaker, it has to be printed right on it) and so 20 amp isnt too much, assuming the elements are rated for it, but is overkill for the application. You could run all 4 in series and it would draw 5 amp and output 1200 watt which is pretty good.

This is all assuming the elements are 12 ohms each, you really need to measure this!

 

[joedhiggins]

I agree that the blower probably isn't needed, but it will assure even temperature everywhere.

The high temp door gasket isn't needed, either no gasket or a stove door gasket will be fine.

I just meant an oven gasket. I used the term high temp to indicate something made of fiberglass or ceramic fiber, not traditional gasket material.

As to the blower, my worry would be properly insulating the rotating shaft. Doable, but with the combination of the partial vacuum behind the fan and an uninsulated/sealed shaft entrance, you are likely to get a meaningful temperature gradiant from front to back in the oven. I am not sure of a great way to seal the shaft other than more gasket material, but then I am unsure of how well that gasket will last in a high temp/friction environment. There is I am sure a way to do this, but I dont know off the top of my head.

Thanks for this post Oven will run on 220V ....does this changes something in calculation ?

Yup. Current is voltage over resistance (I=V/R) so, figure out the amperage of the circut and the specced wattage of the elements. In series, the resistance will double so if one element is 10 ohms, 2 in series will be 20. In paralell, the resistance is halved, so 2 10 ohm elements in paralell will make a 5 ohm resistor. After you have figured out the resistance of an element, determine your minimum resistance by deviding your voltage (nominally 220, but test with a multi meter) by your max current (whatever the circut is rated to. in the USA, the amperage would be printed on the breaker, not sure of code there). Take that value (in a brittish circut that would be 220V/13A or just under 17 ohms). Based on the above rules, determine what configuration of elements would give you a resistance greater than that minimum. Form there you should be good.

Double check your work by calculating the wattage of each element by dividing the voltage (nominally 220) by the resistance of your specific setup, as you measure it. That will give you your expected current draw (which should be a number smaller than your max circut amperage). Multiply your amperage by your voltage to get wattage and then divide that wattage by the number of elements in your array (assuming a symetrical array) and ensure that number is less than the watage the elements are specced for.

Thanks for your opinion , I appreciate it Look , the only expense in this build is purchase of necessary electronic all rest I already have ...Motor for fan will be outside of oven so no heat ? I see that in some high price oven ?
About ceramic tile , yes will be more complicated to build ,but if it is better solution then steel I will use them ? I solved everything how to build this oven /most as you describe / I need opinion on material I intend to use .As I say already , cost is out of question in this oven ... I have everything mentioned here ?

My suggestion on materials was mostly from an ease of construction/mounting perspective. A SS wall will stand up better than ceramic in this case as the temperatures are not high enough to cause meaningful ablation of of the steel via oxidation. You shouldn't have any concerns of shorting these elements to the stainless as long as you are concientious about your construction. And if you have to pull it all apart to replace an element of otherwise fix something, it will be much easier with a stainless internal box rather than a ceramic one. Finally, based on your design I assume you can weld stainless, so doing things like mounting the steel muffles will be much easier and more resiliant with this construction.

I don't think any of my recomendations would make it a less capable or shorter lasting oven, but maybe I am wrong, so feel free to deviate as you see fit.