High Temp Flat Plate

You might consider looking for something with a low coefficient of thermal expansion.

All the heat on one side will warp something for sure. Should be fairly simple to model if you can figure the temperature differential.

MatWeb can help. (nae)

I think kramarat is right on this. Large pieces of steel-any kind of steel-will warp more than cast iron; however, if you're bound to use steel, soak it at 500 °F or so for a few days, then roll it flat. If you can get most of the stresses out, that'll go a long way. Talk to your local heat treater to get the right temperature; I'm just guestimating.

I'm not sure what kind of steel it is, but I just had an image of a short order cook flipping burgers on a big griddle.

Maybe a restaurant supply house would have something made to order.

Cast Iron looks best choice as suggested before, But beside the material selection if you can provide cross holes across its length and width, this can help you to get temp equilibrium in quick time and will provide extra stiffness to plate.

Rakesh, you wrote,

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'...cross holes its along length and width...... will provide extra stiffness to plate...'

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Could you please elaborate?

Yes, Think it the way.

Hollow pipes and tubes are less prone to bending than of solid rods.

Holes will not increase it's stiffness, they may increase it's strength to weight ratio, which does not seem to be an issue here.

Pipe or anything that is hollow is always tough to rap/bend in compression of solids. On that ground which one is more stiff? Providing holes are similar to that of making ribs on rare side of plate and then hiding those ribs by another plate,

In either case, the pipe or hidden-rib plate example, in most cases there will not be a significant difference in stiffness as compared to a solid peice of the same material and same outside dimensions..

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...that is until the point when the pipe wall or plate wall of the hollow structure buckles.

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A shape with holes is not inherently more stiff than the same shape without holes.

on that ground, the solid is more stiff

That sounds about right for 3.5 dozen eggs over medium.

Does it have to be metal?

I guess I think about food a lot. I just thought of the pizza stones that are used to bake pizza in very hot pizza ovens.

How about a cast iron waffle plate in reverse?

I will advice that you use 310H austenitic stainless steel. This material has a high chromiun and nickel content and has the ability to withstand high temperatures.

it can stand oxidation and deformation and is used in furnaces etc. It is available in plates strips and bars.

see ASTM A240 for chemical and physical properties. I wish you the best.

Chike Nwachukwu

Most all of my experience with this issue is limited to fully vitrified materials that have been ground and polished to an accuracy of 1/30 of a wave of light or better, in the visible spectrum.

When the substrate is not at the same temperature as the surrounding environment it's utility as an optical instrument is seriously compromised, until it reaches thermal equilibrium. When that is achieved, the accuracy returns.

This suggests that perhaps you might consider Blanchard grinding the plate, while it is heated to the temperature it will see when used. It also suggests that a material with a low coefficient of thermal expansion be chosen.

There are substrates that have a zero coefficient of thermal expansion (Zerodur being just one) but the costs are prohibitive.

You have not stated what degree of flatness is needed. If repeatability is an issue, then it suggests that some serious annealing be entertained so as to insure that as the the plate is cycled through its temperature range, that it will always return to the flat state achieved when Blanchard ground.

Clear Skies!

Laughing Jaguar

I'm guessing there is about to be another great invention created right here on CR4 folks, a combination deep space telescope/short order grill setup. The reflective coating (applied to a surface with less than 1/30 wavelength flatness) also makes an incredible non-stick surface. Party all day, explore all night. Call me crazy, but I also see a wok model coming out.

Within a .03" is acceptable. I just do not want to end up with a banana when it heats up.

All this talk about food is making me hungry!

Are you opening a restaurant?

I have an 8'x10' set of oil heated top and bottom platens, in my lab, which can be heated to 500*F. These are perfect for producing the perfectly balanced, crispy crust, melted cheese pizza. I can set the gapping of the platens to just the right distance to produce the ideal result without the charring effect of infrared. Come on over and we'll bake one he!! of a pizza! BYOB, of course!

Z

Boiler plate should do

Dear poster

we are a curious lot

what kind of boiler plate and why

You have not clearly stated the application so this makes analysis more difficult. I understand there is a heat source below this plate, the plate itself is supported but not secured. Is the chamber in which this plate is suspended larger than the plate (in which case the heat can move around the plate to the top side as well) or the same size (in which case the heat has to be conducted through the plate to the other side)? Why are you using a plate of this size and thickness? Will the plate be seeing any other loading besides the thermal loading? What purpose does the plate serve, other than separating the heat source from the topside of the plate? Are there any other chemical limitations that would restrict the plates material of construction?

In general you should be fine using conventional carbon steel plate (ASTM A36 or ASTM A516-70) as carbon steel has acceptable coefficients of thermal expansion in this temperature range. Some expansion is to be expected, but if the plate is only suspended and not secured on the edges, there should be mostly linear expansion and very little warpage. If, on the other hand, the plate is secured along the edges, or movement is limited by sidewalls, then the expansion will result in some warpage of the plate. However, 30" x 36" x 1/2" thick plate will take a lot of heat before warping. I would not use any form of stainless steel as its coefficient of thermal expansion is much higher than that of carbon steel.

The plate is the same size as the support below it and the sides are not restricted. The plate is protecting the components that are creating the heat. I could go thinner than 1/2 inch, but I wanted something with some weight so it would stay in one spot.

Thermal expansion of carbon steel is 0.0226" per foot at 350 deg F and 0.0140" per foot at 250 deg F. Therefore, expansion of your 30" x 36" plate would be about 1/16" all around at 350 deg F (0.0565" in short direction and 0.0678" in longer direction). Not significant as long as sides are not restricted. Sag due to temperature should be inconsequential as well.

H grade tool steel may be adequate for your application. Our company uses it daily for hot molding of plastics and thermosets. There are several types, so without knowing what your application is, it is not possible to make a recommendation.

Z

I'm with the folks the suggest you buy your plate/cooktop from a known supplier of this type equipment, it'll be cheaper than reinventing, reinventing never pays. And I don't think it's going to come as a flat sheet either. Most likely it will be a stress relieved fabrication of cast iron and steel. But if your hell bent on doing it yourself, a piece of pickled hot roll wouldn't be very expensive and it'd already be stress relieved. If you heated it slowly up to temp, it shouldn't move much, but it'll be more than .03 out to start. O'yeah, get the plate flame cut not sheared to minimize the out of flatness.

Good luck!

Just buy the wood stove.

The plate is not likely to distort, the way you have described. As a precaution you may rest the plate on two round bars placed from edges at @ .027 x Length distance.