Author Topic: 1/2" Steel Stone Heating Data  (Read 1965 times)

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Offline sum1else

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1/2" Steel Stone Heating Data
« on: November 26, 2011, 01:01:27 AM »
Here is some information about my oven setup and stone setup. This may be helpful for many interested in baking on a steel plate. I bought a steel plate because of posts I read on this site. I ordered it from MetalsDepot.com. I took various measurements over a heat cycle using an oven thermometer and an infrared thermometer. Unfortunately the data is not as “controlled” as I would like it to be, however it should still provide useful information.

A photo of my setup is below. I have a simple gas oven in a NYC rental. It is not a quality unit, probably the cheapest digital oven available. Before lighting the oven, I set the oven temperature at neutral calibration--0 degrees adjustment. I have no oven modifications. My ˝” x 12” x 12” A36 steel plate sits on the top rack of my oven, just under the broiler.

Here is some background info to provide a benchmark for others to compare to, because its likely that 1) my cheap laser gun is not perfectly calibrated and 2) you will get different numbers:  

At .95 emissivity (ignore all this if you don’t have an IR thermometer), the back of my hand registered at 95F. An ice pack (black polyester) from my freezer registered at 18.4F. Water at a rolling boil correctly measured between 210 and 212F. At .80 emissivity, the same pot of water registered at 227-230F. I took measurements on the top of the stone, bottom of the stone, and the ambient temperature of the oven. You can see the oven thermometer’s position in the photos. All at .80 emissivity, with the oven light on. It is was very hard to get a stable reading on the steel in the oven for a few reasons. Most important was that there is burnt up flour/oil on my plate that affected the readings. To compensate, I set my thermometer on “average” mode for readings, and moved the laser around the surface for a few seconds on each reading.

My oven was set to 525F. It goes up to 550, but I’ve been using 525 lately because of trouble keeping my broiler lit. I opened the oven each time I had to take readings, letting out heat. At the 40 minute mark, I opened the oven for 2 minutes (way too long, because I was taking various other measurements with the laser). Each time I opened the door to take a reading, the oven thermometer dropped by approx. 25F.

After taking the 70 minute reading, I calibrated my oven by +35 degrees. I then re-set it to bake @ 525 degrees, and took more readings. I lit the broiler 20 minutes later. It would not light, so I let out some air for a minute. I then ran the broiler for 6 minutes, taking measurements in 2-minute intervals. I suspect the temperature dropped so rapidly because I kept opening the door to measure. I measured the broiler’s flame at 975 degrees  8)

Here are the data points, and graphs are attached as images. The most encouraging part of this is that my oven was not maxed out at the 550 setting, and was not recalibrated during the entire preheat. I think I could get another 50 degrees out of the plate if I had it set at 550 +35 calibration the entire time.

I hope this is of use to someone. I would love to hear some comments about your predicted bake times, and how you are running to buy a steel plate!

« Last Edit: November 26, 2011, 01:13:25 AM by sum1else »


scott123

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Re: 1/2" Steel Stone Heating Data
« Reply #1 on: November 26, 2011, 01:49:06 PM »
Really nice job, Tyler.  That tells us a lot about your oven setup and how the steel is reacting.

You'll obviously want the calibration bump to keep the broiler on as long as possible during the bake, but I don't think you'll need it for the pre-heat, as the non calibration numbers (560ish) are right on the money. I would calibrate up, then pre-heat the oven to 500.  That should give you the same 560ish plate while allowing the broiler to stay on longer so you don't have to open the door.  Opening the door, so far, has worked out pretty well for you, but, generally speaking, opening the door usually translates into uneven baking.

Could you do me a favor and check the BTUs on the oven?  I get the feeling it's a bit low in that department. I never thought it would take longer than 70 minutes to pre-heat 1/2" steel, but, looking at your data, and the fact that it's not really leveling out, shows that some ovens might not put out enough heat to fully saturated the steel in shorter times. Opening the oven door to take frequent readings is obviously going to extend the pre-heat time, but I don't think it should extend it that much. Now that you've got an IR thermometer, I'd like to see you take the following readings:

Day 1: 525 for 80 minutes, door closed, then read the temp (bottom of plate, top of plate). 2 more temp readings at 30 minute intervals.

Day 2: Same as above, but 60 minutes to start

Day 3: Same as above, but 40 minutes

Once you get that information, you'll know exactly how long you have to pre-heat the plate for.

One thing to be aware- there's a tendency to think that driving up the surface temp of the steel with a broiler will somehow result in faster bakes. It might, to a very small extent, help, but, overall it's fairly superficial.  The goal is not to get the hottest surface possible, but to fully saturate the stone, inside and out, with heat.  This is why the bake setting is superior for pre-heating.

Offline sum1else

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Re: 1/2" Steel Stone Heating Data
« Reply #2 on: November 26, 2011, 02:02:08 PM »
Scott, I will definitely keep the oven calibrated upward, especially now that I have a thermometer inside. The BTU sticker is attached. I believe you are looking for the Oven reading @16k BTU.

I'll also try the other plate experiments you suggested throughout the week, so I can nail down the preheat time and temperature.

Quote
One thing to be aware- there's a tendency to think that driving up the surface temp of the steel with a broiler will somehow result in faster bakes. It might, to a very small extent, help, but, overall it's fairly superficial.  The goal is not to get the hottest surface possible, but to fully saturate the stone, inside and out, with heat.  This is why the bake setting is superior for pre-heating.

I figured that it would not penetrate much at all on broil. It is good to know that it does have the power to heat the plate surface up significantly, so I know that I can definitely brown my cheese with it.


scott123

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Re: 1/2" Steel Stone Heating Data
« Reply #3 on: November 26, 2011, 05:24:54 PM »
Tyler, 16K feels a bit low.  I have to admit that I haven't researched home oven BTUs all that extensively, but I have seen a trend that newer ovens, both gas and electric tend to be a lot weaker than old ones. A strong oven really should be able to pre-heat a 1/2" steel plate in an hour.  Further experimentation should prove useful in that regard.

When you get a chance, could you get a photo of your oven's temp probe?  Can the probe be easily unclipped (don't actually unclip it, just look and see if it might be easy). I've been mulling over a new gentle oven mod using wadded aluminum foil. I'm basically picturing aluminum foil being gently balled (maximizing air pockets) and then combined with other wads to make a thick blanket, which could then go around the probe or just up against it as a shield between the broiler and the probe. I'm pretty sure something like this would give us another 25-50 degrees- enough to keep the broiler on during the bake. You could pre-heat the oven normally and then slide this wedge/cover into place right before baking.
« Last Edit: November 26, 2011, 05:28:59 PM by scott123 »

Offline sum1else

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Re: 1/2" Steel Stone Heating Data
« Reply #4 on: November 26, 2011, 09:42:34 PM »
The temperature probe is held on by two small hex bolts. I can't get behind the oven to see whats going on back there. I'm interested to hear what you figure out with the foil mod. Like I said, I am in a rental, so messing with the electronics is not a choice. However, something temporary would be fine with me.

Offline sum1else

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Re: 1/2" Steel Stone Heating Data
« Reply #5 on: November 27, 2011, 02:17:04 PM »
500 preheat, 80 minutes, did not open door at all.
Oven thermometer: 535   Steel Plate: Top 607, Bottom 608

Broiler would not start. Let out some air for 30 seconds and it started. Launched pizza. 3 minutes in broiler shut. Let heat out 10 seconds and flipped broiler off/on and it remained on for the duration. (5 min cook total).

After cooking, Oven: 450, Top: 510, Bottom 545 (this seems wrong, but too late to tell)

I then re-set the oven to 500, and after 12 minutes, the oven thermometer was 525, top 600, bottom 605 and  launched a second pie. (In my NY style thread)

scott123

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Re: 1/2" Steel Stone Heating Data
« Reply #6 on: November 28, 2011, 08:18:31 PM »
Tyler, I can't tell, can you slip some sort of sleeve around the probe or is clamped on both ends?

Offline sum1else

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Re: 1/2" Steel Stone Heating Data
« Reply #7 on: November 28, 2011, 08:40:50 PM »
No, I could slip something over it. Its just a post sticking out into the open air. I took the photo from an angle to show the bolts.

scott123

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Re: 1/2" Steel Stone Heating Data
« Reply #8 on: November 28, 2011, 08:50:14 PM »
Alright, then here's what you do.  Take a long piece of regular aluminum foil and gently wad it up in such a way that it forms a thick air bubble infested pocket.  The more air the better.  Slide this onto the probe right after the 500 (calibrated) preheat and before the bake. Between the air pockets and the emissivity of the aluminum, you should have no problem keeping the broiler on during the bake.

It might even work with a 525 preheat, but I'd try 500 just to be sure.

Offline sum1else

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Re: 1/2" Steel Stone Heating Data
« Reply #9 on: November 28, 2011, 08:59:19 PM »
I'm gonna burn my hand off.

Looks like I'll need those welding gloves suggested in another thread


scott123

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Re: 1/2" Steel Stone Heating Data
« Reply #10 on: November 28, 2011, 09:23:12 PM »
...or perhaps a set of extra long BBQ tongs.  Or maybe save yourself some cash and poke the end of the aluminum pocket with a bamboo skewer and use that guide the sleeve into place.

Lastly, maybe you could put the sleeve over the tip of the probe and then when it's time, use something long (a yardstick) to slide it into place.

Edit: or just make the bottom of the sleeve flat and launch it onto the probe with the yardstick, using the yardstick as a thin peel.

Offline sum1else

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Re: 1/2" Steel Stone Heating Data
« Reply #11 on: November 29, 2011, 10:26:57 PM »
I do have an aluminum yardstick.. I will try this on my next pie if I remember--this Friday evening.