Material suggestions for specific application 2

[lstewart]

Wondering if anyone could help suggest a material for a specific application I have? I'm looking for a material that has a low coefficient of linear expansion that can be bought in sheets of 60" x 110" x 0.036" (thick). The sheet are waterjetted with a pattern and are placed in a press that heats up to 525 degrees F. Currently we use 304 stainless steel but it tends to warp and crease.

 

[EdStainless]

Almost anything will have lower expansion than 304.
I assume that you need some level of corrosion resistance.
Start by looking at 439 stainless. It will be as low as you get in a stainless, very similar to straight carbon steel.
It also has better thermal conductivity than 304 so it will heat more uniformly.
In order to get better than that you will need to go to low expansion alloys, this will get expensive and tricky.

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Plymouth Tube

 

[EdStainless]

Or commercially pure Ti grade 2 (or gr1 or gr3, doesn't matter).
the only catch is that you will want to heat and cool the sheet a few times before you cut it since it may not expand the same in all directions.

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Plymouth Tube

 

[TVP]

lstewart,

Without any other input, I think Ed's suggestions are definitely a good place to start. If you don't really need chemical/corrosion resistance, then there might be some other options to consider. Can you provide some additional details on the application and its expected service conditions?

 

[lstewart]

Thanks for the suggestions! I may have to stick with stainless because I do need the corrosion resistance characteristic. I will definitely check out 439 stainless.
To expand on the application details I'll mention that the sheets are heating in the press at 525 degrees F for long periods of time and are restraind by a set of shims on each side, which doesn't help the matter of creasing, but with our current process its hard to get away from using these shims and that is why I want to reduce the expansion as much as possible.

Are there any low expansion alloys out there that have some level of corrosion resistance?

Thanks again for the info.

 

[EdStainless]

The thermal expansion of Ti is a fair amount lower than for steels. It will be about 1/2 of what you see in 304. And the corrosion resistance is fantastic.

The standard low expansion alloys (9%Ni, 36%Ni) rust rather fast in open air without a coating on them. We have a lot of Invar (36%Ni) pipe and we have to coat it with oil.

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Plymouth Tube

 

[Compositepro]

A better solution would probably be to fixture the sheet to allow for thermal expansion. What is it attached to? Generally you want to match CTE -not have zero CTE. If the temperature fluctuates relative to what it is attached to you need to accommodate this. It can get complex and simply finding a low CTE material may not solve all your problems.

 

[metman]

Kovar has an average of 3X10-6"/"/degree F in the temperature range you are working 77-500F. It is a high temperature Nickel/Cobalt/Iron alloy. Not familiar with its corrosion resistance but it might meet your requirements.

Here are some links:

http://www.hightempmetals.com/techdata/hitempKovardata.php

http://en.wikipedia.org/wiki/Kovar

It is quite ductile 30% Elongation in 2" so if your 304 is buckling maybe Kovar would be ductile enough to stretch and yield with its much lower CTE.

 

[lstewart]

Thanks for all the suggestions. I'm currently looking into using the 439 stainless and I'm getting qoutes on Ti. I'm doing more research on Kovar to try to find info on its corrosion characteristics. I'm also exploring ways in which I can allow these sheets to float instead of being restricted on each end.

My one question with the 439 ss is how magnetic will this sheet be? I'm slidding this sheet onto a steel surface, will the magnetic force act as a constraint or will the thermal expansion be able to overcome the magnetism? (note: the sheet does have an oval pattern cut out of it so probably about 70% of this 60"x110"x.036" sheet is removed)

 

[EdStainless]

439 is fully ferromagnetic, but unless you platen has been magnetized there shouldn't be an issue.
Of course Ti is non-magnetic.

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Plymouth Tube