new build in werribee

[david s]

Re: new build in werribee

Looks like I may have to repeat my test.
http://www.fornobravo.com/forum/8/my...tml#post158522

[oasiscdm]

Re: new build in werribee

Yep seems to confirm my son and my tests. Due to the various surfaces during emmisivity of him might prove difficult. I also have thermocouple and a 500c max thermometer. All gave me accurate readings.

Comparable to the it gun held 90deg to the surface.

Lesson learned heat break works. And I do not have to oxy out the SS

Be interested David in your re-test results.

[david s]

Re: new build in werribee

Yes, I shal retest at some point. But the stainless was still way hotter than the arch on which it was resting because I could still hold my hand against the arch, but no way could I have held my hand on the stainless. I think I could have fried an egg on it. So the principle still stands that the more conductive material attracts heat to itself and can be hotter than the material that surrounds it.

[Toomulla]

Re: new build in werribee

I struggle with the idea that different materials in contact with each other can have different temperatures over a sustained period possibly the SS "feels" hotter due to it's better conductivity. The higher conductivity of the SS means that it cannot be a heat break as it will just transfer heat across in an effort to equalise . For a heat break you need high non conduction i.e insulation

[oasiscdm]

Re: new build in werribee

Not seeing it in my results now I know the trap. oven side of hearth was hotter than the stainless which was hotter than the granite. SS is stuffed with calsil, 3mm gap to granite all working as it should. Unless I of course ang that was consistent in over 30 instances of reasons at various times as the oven moved to clearing temps.

Angle the IR gun then that all changes. DRAMATICALLY

Any how I'm a happy chappy.

[Toomulla]

Re: new build in werribee

Yep I can adjust the emisivity on my gun. But to what?

You set the gun to match I.e if you want to read SS set it to 0.1 and if granite 0.9

You also have to match the spot size to the width of the material i.e if the material is 12 mm wide the gun needs tone about 12 times that max away from the material assuming a 12 :1 angle for your gun

[oasiscdm]

Re: new build in werribee

Hmmmm my IR gun is 50:1. Might pose a small problem.

[david s]

Re: new build in werribee

I struggle with the idea that different materials in contact with each other can have different temperatures over a sustained period possibly the SS "feels" hotter due to it's better conductivity. The higher conductivity of the SS means that it cannot be a heat break as it will just transfer heat across in an effort to equalise . For a heat break you need high non conduction i.e insulation

The first oven I built had a small rock with"PEACE" etched into it. It was set into the front of the outside of the oven above the outer arch. Being both black and far denser than the surrounding cement/ sand/ lime shell that contained it, it would become much hotter than the outer shell. We used to use it as a test to see if the oven was hot enough for pizza. If you couldn't hold your hand against it, then the oven was ready. Meanwhile the shell that surrounded it was hot, but you could still hold your hand against it. A second example of this is with my mobile oven which is built over a 3" Hebel base. This base sits in a steel cradle which has 40 x 4 mm galv steel bars supporting it underneath. When the oven heats up and the temp climbs the Hebel is just warm, while the steel is noticeably hotter to the touch.

I totally agree that a heat break should be made of an insulating material, but if stainless must be used for purposes of durability then it should be as thin as practicable, preferably only on the exposed surface.

[oasiscdm]

Re: new build in werribee

Hi guys

I will keep measuring, but the results won't differ. On one test I rested the thermometer on each surface and got the same results, inside hotter than SS hotter than granite. Margins huge. Can't explain it but that is how it was.

[david s]

Re: new build in werribee

Hi guys

I will keep measuring, but the results won't differ. On one test I rested the thermometer on each surface and got the same results, inside hotter than SS hotter than granite. Margins huge. Can't explain it but that is how it was.

Here is your answer. It's the calsil that sits beside the stainless tube that is probably your primary insulation isolating the tube.Your tube is therefore really only being heated on one side only. But it doesn't really matter now because the thing works anyway. Cook away.

http://www.fornobravo.com/forum/51/n...tml#post157630

[oasiscdm]

Re: new build in werribee

Thanks David and others. For a while there I was quite annoyed with myself. But it all works. Next job more cooking curing tempering and door.

Still not getting floor past 400c

David the metal holding the hebel panel in place does get warmer than the hebel.

Around 70c didn't expect that.

Thinking of now making a sliding draw for tools etc just under the hebel panel. Maybe about 8" high and depth of alcove

[cobblerdave]

Re: new build in werribee

Gudday
There's another factor at play here that should be mention is that most of the heat in the entranceway is heat radiating from the fire through the air rather than through the brick.
My oven has no heartbreak. In summer particularly, by the time you have burnt a fire in the dome for a couple of hours the entranceway is roasting hot. It makes it a bit uncomfortable to operate the oven. I have taken to placing just my insulated door in front of the chimney. Not as a blast door as the air is free to flow past the sides unregulated but as a heat shield for the entrance. Never taken any reading of the difference but the entrance I'd definitly cooler. Heat radiates faster though the air than through brick. I recon most of the heat bypasses the heat break through the air.
Heat radiating through the air does some funny things too. I'm ex navy and constantly got to play at the fire ground with some pretty realistic fires. Inside a steel compartment with even a small fire going it gets pretty hot very fast. The heat radiates from the walls making things pretty hot just like inside a WFO .You wear flameproof overalls, boots, elbow length flameproof gloves and a flameproof hood. Everything is covered bar a slit for eyes. It can get so hot the heat will burn your eyelashes off from behind the mask of your breathing equipment. If your silly enought to wear jewelry next to you skin it will attract the radiant heat through you clothes and burn the skin. The girls are in there too, so no underwire bra or metal clips. Underwear and sock elastic doesn't fare to well also, and losses its spring.
The human body, the flameproof overalls and gloves all have an insulating value metal has none. Once those metal atoms start to vibrate it then starts to radiate the heat back by itself. A plastic pen in the pen slot in the from of your overalls will not be at melting point before the metal end has heated up and boiled the ink in it .
Same things happening with the s/steel on the heartbreak its absorbing the radiant heat and once it gets to saturation point it throws the heat back rather than absorbing more like the brick on either side.
Sorry this is not highly scientific but its my practical experience with heat.
Regards dave

[oasiscdm]

Re: new build in werribee

Agree.... the radiant heat made it very difficult working the oven. The best figures re heat break were had with no active fire.

The stainless was always [heat wise] in the middle of temp range but closer to hearth with an active fire.

It's interesting I guess I will learn more as I use it more.

Must get to the temp door though. Like you Dave hebel and some scrap wood

[cobblerdave]

Re: new build in werribee

Gudday Colin
http://www.fornobravo.com/forum/f51/...html#post99622

The Hebel door is not my idea, I got it from this bloke, he warned me as well that even if you call it a temporary door it works and you never get around to building better.

Regards Dave

[oasiscdm]

Re: new build in werribee

Some one else recently did a door from hebel and wood. Cannot remember who any ideas.