Aluminized Steel Plate

[shuboyje]

If you want to drastically oversimplify things like that, then yes as a matter of fact with my current setup I have preheated my 1/2" steel to over 700F in 10 minutes.  But it doesn't work like that.  For one most people are using 1/2" steel with nearly twice the thermal mass of your plate, meaning it will have nearly twice the preheat time.  Second, every oven is different.  I know you have tried multiple ovens with good results, but if the standard gas ovens you have used it with are out performing your commercial quality convection oven I am going to guess they just so happened to be pretty powerful ovens and lead to a fast preheat.  I would guarantee some of  the anemic ovens many users here have would not give the same results.

Understand I'd love to be wrong here, I'd love for there to be an even better material out there.  There is just no theoretical reason for this material to be better then standard steel, and there I have not personally seen anything posted in this thread that changes that.  That all said I am curious to see and hear about anything you can do to change my mind because I truly would love to be wrong about this one. 

Just one question.  Does anybody else preheat only to the cut off in the oven and obtain same temperaure?

Ron

[Meatballs]

Like I said...

the plate lost 20 degrees cooking a 12 inch.  Recovery time is minutes, I can show that exactly on a future bake.

It will only take, say, 3 minutes or less to reheat.  I'll get exact times next time I bake in the oven.  Suffice it to say, it recoups heat quickly and continually.

I have an e-mail in to Cacdo Technical Services asking some specific questions posed here, if and when I get a reply I'll post the info here.

Ron

[TXCraig1]

Understand I'd love to be wrong here,

You might get your wish. Look at table 4 here: http://www.aksteel.com/pdf/markets_products/carbon/AlumT1.pdf

It shows the thermal conductivity of aluminized low-carbon steel to be 89 W/m°C at 20 °C

Thermal conductivity of plain low carbon steel is about 64 W/m°C at 20 °C.  That's an increase of almost 40% for the aluminized steel! (http://www.efunda.com/materials/alloys/carbon_steels/show_carbon.cfm?ID=AISI_1010&show_prop=tc&Page_Title=Carbon%20Steel%20AISI%201010)

The effect on specific heat capacity is negligible as you would expect (+7%). http://www.efunda.com/materials/alloys/carbon_steels/show_carbon.cfm?ID=AISI_1010&show_prop=sh&Page_Title=Carbon%20Steel%20AISI%201010

I don't know if this is mitigated to any extent because aluminized steel reflects 80% of radiant heat. This AK Steel product is also relativly thin compared to a pizza steel, and I don't know if that causes a meaningful difference. I would think that the thicker the Al is relative to the steel, the greater the impact on thermal conductivity, but I don't know.

I think this does suggest it's worth taking a closer look. There may be something to this.

CL

[scott123]

It shows the thermal conductivity of aluminized low-carbon steel to be 89 W/m°C at 20 °C

Prior to hearing this, I would have bet just about any amount of money that aluminized steel had the same thermal conductivity as regular steel.  I'm glad I didn't  In that sense, I do stand corrected.

Looking at the bigger picture, though, while 89 is almost 40% larger than 64, compared to cordierite (3ish) and aluminum (205), the difference is not that drastic. There's also the question of the aluminum to steel ratio and it's impact on conductivity that you brought up. At .015" (the smallest thickness they offer), if that's what they're using to calculate the 89 W/m°C number, then I have no doubt that as the thickness increases and the ratio of aluminum to steel decreases, the conductivity will decrease as well. Even if they're testing the conductivity using their greatest thickness, .14", it's not the .2" of the cadco.

Regardless of what the final conductivity figure clocks in at, bake times are a component of thermal conductivity and mass.  .2" of aluminized steel isn't going to outperform 1/2" of steel, even with increased conductivity.

I'm still skeptical, but, I'll concede that the difference in conductivity is sufficient to warrant further investigation.

Ron, if you really want to test this, get your hands on some steel.  I'm not sure if 1/5" steel can be easily found. If you can't get 1/5", get 1/4". If you really want to go crazy, buy an 8 x 16 steel plate, cut your cadco plate down to that size as well, combine the two side by side in the oven and bake a pizza, on both, at the same time. Or... if you don't want to carve up the cadco, just bake a pizza using the cadco, then, bake another pizza, at another time, using the steel, repeating every step carefully.

[shuboyje]

That is very interesting Craig, but Scott does bring up an interesting point.  A thin aluminum coating would have an impact on the thermal properties of 24 gauge steel, but would have much less of an impact on 1/2" steel where it would make up a much smaller component of the thermal mass.  Aluminized steel is commonly used in thin sheets for mufflers, ovens, and other high temperature parts.  Considering the thermal conductivity number will not be static due to this, I would bet that number is indicative of it's common usage in the form of thin sheet, and not plate.

I guess we'll have to keep digging to get to the bottom of this and see if there is any other info about the thermal conductivity that specifies thickness.

[Meatballs]

Craig, THANK YOU!

My area of expertise lies outside the fields of thermodynamics and metallurgy.  But, I knew somebody here would have the smarts.  I can give measurements, I can photograph pizzas, most of all though, I know when a pizza is good.  I've been getting some really good pizzas off of this plate for some time but it wasn't until I tried it in a regular, moderate quality, electric oven that I realized something was going on.  I mean, I launched a pizza off a cardboard peel cut from a pizza box at a beach house and produced something better than you can get for 50 miles around in a cheap oven (I did use my skills, broiler after preheat, etc.)

I can tell that there is something going on with the metallurgy and design of the plate but I can't tell you exactly what.  My home gas oven is powerful, its marked to 500 but the knob keeps turning to an guestimated 600.  I've taken it to 520 - 550 but hesitate to go further because the plate has a nonstick coating.  The nonstick is, by the way, flat black.  I feel it may have some impact in infrared absorption but, again, outside my field of expertise.  I read the information you posted, but, its mostly Greek to me, I really would appreciate your take on the information in simpler terms without the Lambas and T1's and all.

Scott, as to cutting the plate, well...no.  But, I am considering buying a full size plate and cutting it down to fit my gas oven so I can launch 14 to 16 inch pies.  A scrap off of that would be useful for comparisons.  Amazon shows a CAP-F (full size plate) at an external website for $45.00 with shipping that fits my retired budget.  As to the steel plate... there us a steel fabrication industry here that probable could probably supply such, what type of steel and how much does it cost, because it will probably end up down on my shooting range as a target.  How big a piece would I need to get the numbers if I lined it up with a piece of scrap from the full size plate?  I suppose I could bake a small pizza over both pieces of material.

Ron

[TXCraig1]

Prior to hearing this, I would have bet just about any amount of money that aluminized steel had the same thermal conductivity as regular steel.  

So would I, and after further thought, I don't think I believe the thermal conductivity number in the AK Steel product data sheet.

Here is why I say that - we can think of the problem in terms of conductive heat transfer:

Fourier's Law of Heat Conduction:  q = k A (ΔT/s)       [1]

q =heat transfer (W)
k = thermal conductivity of the material (W/m°K)
A = heat transfer area (m²)
ΔT = temperature difference across the material (K)
s = material thickness (m)

This formula can be extended to calculate heat transfer across multiple materials in series:

q = (ΔT) / ((s₁/(k₁A)) + (s₂/(k₂A)) + ... + (s_n/(k_nA)))     [2]

We can use these thermal conductivity values:

Low carbon steel = 64 W/m°K
Aluminum = 205 W/m°K

And these thicknesses provided by AK Steel (the extremes that should give the highest k):

Low carbon steel = 0.15in (0.000381m) – the thinnest they offer
Aluminum = 1.2mil (0.00003048m) – the thickest they offer

We’re calculating a constant k for the clad metal, so it doesn’t matter what you use for A or ΔT and long as you use the same values throughout the steps (see [4] below).

Insert the values into [2] and solve for q (remember there are two layers of Al – same thing in [3] when you figure s for the Al-steel-Al clad).

Rearrange [1] to solve for k = (qs)/(AΔT)       [3]

Insert q from [1] and the other values into [3] and solve for k = 70.7 W/m°K which is a lot lower than 89 W/m°K. I just don’t see how you can get to 89 with any reasonable set of assumptions. It almost looks like they did a weighted average k which would not be correct.

Inserting [2] into [3] and simplifying yields

k_clad = (s₁ + s₂ + … + s_n) / ((s₁/k₁) + (s₂/k₂) + … + (s_n/k_n))     [4]

which can be used to calculate the thermal conductivity for any n-layered clad material.

Back to the question at hand, if you use a steel thickness of 0.2in, and aluminum thickness of 1.2mil, the increase in thermal conductivity over plain steel is about 0.5 W/m°K which is completely insignificant. The thicker the steel, the less the increase.

I guess this brings back to where we started. Sorry Ron.

CL

[tinroofrusted]

Thanks to Meatballs and everyone else for their comments on the aluminized steel plate.  I have held off on buying a carbon steel plate just because they are so heavy and I didn't want to deal with all that weight.  I went ahead and ordered the Cadco CAP-H, 20" x 13 1/2" Non-Stick Aluminized Steel Pizza Heat Plate. The cost was $34.00 with free delivery.  It's a perfect size for my oven, (an Electrolux with convection). I think I will try it out sitting on top of a couple of really well heated pizza stones and see how that goes.  I will report in to let you know how it goes.