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Limestone and Stainless Plate Expansion / Contraction

01/27/2010 12:30 PM

Alright guys/gals,

Here's my next question/project.

I am being commissioned to build two mounting posts, one for a keypad entry and one for a mailbox.

Limestone is in the mix in and around the area. I would like to use it in my design.

The question is this, What is the difference in expansion and contraction between stainless plate and limestone? The stainless might be 1" thick and the limestone might be 2" thick. I am thinking of the stainless as the spine/structure to weld to the bolt/base plate and then 'gluing' the stone on either side. The stone would basically be for aesthetic and not bear any weight. My first thought was epoxy which made me wonder about the difference in movements of the two materials together being that epoxy is very unforgiving to those kind of forces. If they expand and contract at a very similar rate, it might not be a problem. Then I was thinking of using a flexible adhesive to allow for some movement. I would have a fair amount of surface area adhered.

Thoughts? Questions?

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#1

Re: Limestone and Stainless Expansion/Contraction

01/27/2010 1:52 PM

Kaye & Laby give α/(10−6 K−1) ~ 10 for steel and 8 - 12 for marble/limestone, so they're reasonably compatible. Need to do some "worst-case" sums depending on the length of the mating faces.

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#2

Re: Limestone and Stainless Plate Expansion / Contraction

01/27/2010 5:59 PM

WWWOOOOOOWWW!! there's a lot of info on there, makes me wish I had gone to college to learn the math. Thanks JohnDG for the link and the info. I will post when I have further info.

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#3
In reply to #2

Re: Limestone and Stainless Plate Expansion / Contraction

01/27/2010 7:35 PM

Hint for the sums, which aren't too bad:

A figure of, say, 8 means 8 x 10-6m per degree K for a 1m length.

Assume your limestone slab is, say, 1.5m long, and assume a temperature change of -10ºC to +35ºC, i.e. 45ºK.

With a coefficient of 8, the length increase over the temperature range will be

1.5 x 8 x 10-6 x 45 = 0.00054m = 0.54mm

At the other extreme, a coefficient of 12 gives

1.5 x 12 x 10-6 x 45 = 0.00081m = 0.81mm

Say your steel's in the middle of this range, i.e. a coefficient of 10. For the same length and temperature change, it's length would increase by 0.675mm.

With these assumptions, the differential length change between the limestone and the steel would be somewhere between -0.135mm and +0.135mm.

Hope this helps, and I'm not trying to teach my Grandma to suck eggs.

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#4

Re: Limestone and Stainless Plate Expansion / Contraction

01/28/2010 8:43 AM

There is not only the difference in expansion and contraction between stainless plate and limestone to consider.

Also you must consider the thermal conduciveness of the different material, heat travel into the material at different speed, especially a problem when exposed to sudden sunshine. Typically faster in metal compared to stone.

Therefore make considerations in design and choice of material thickness

Wbr

Knud

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#5

Re: Limestone and Stainless Plate Expansion / Contraction

01/28/2010 9:04 AM

Put Stainless studs in epoxy. I can't think of amyreason why a key needs a 1" thick mounting plate. If it does then you are not going to get effective services out of mounting it to t 2" thick piece of limestome. The same is true for the mail box unless you are recieving/sending a ton of something.

Use the studs for mounting so that you can easily use the same mount for other arrangements in the future. If you need heavy duty stuff then leave the limestone alone and driive a used railroad rail 16 ft into the ground and mount your stuff to it.

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#6
In reply to #5

Re: Limestone and Stainless Plate Expansion / Contraction

01/31/2010 6:27 PM

It's more of a design issue over just mounting a plate for entry.

It is a sculpture for some folks that spend money on that kind of thing.

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