What gasket material should I use?

Hi
I've designed a flow cell made up of 2 pieces of plexiglas with fluid flowing in between. The top and bottom pieces are separated by a gasket
and pressed together by fasteners. The thickness of the gasket therefore defines the depth of the flow channel. I would like to vary the thickness from 0.5 mm to 2mm (after compression) by using gaskets of different thickness. When fluid is flowing through the flow cell, depending on the flow velocity, the internal pressure can vary from 0 to 5 atmosphere. Right now, I'm sourcing for a suitable gasket material. Apart from the main criterion that it mustn't leak, it is also imperative that its thickness be relatively constant after a certain compressive stress. This requirement is necessary as the fasteners are hand tightened and so compression forces can vary by quite alot. Finally, the material should resists acids and alkalies. What would you recommend?
Thanks.
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Philip wrote:

If you put Belleville washers on the screws, you can have nearly constant clamping force over 20%-80% deflection. Alternatively, you can allow the flat surfaces to contact each other after some specific deflection.
Cheers,
Phil Hobbs
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I would go with the use of an edge design that clamped hard onto a stiff spacer and use a low modulus gasket for sealing.
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Philip wrote:

That rules out elastomers -- all elastomers undergo cold flow.

Lead sheet. It's soft enough to be used as a gasket. Easy to cut. Chemically resistant. For less than $300, you can by a brand-new rolling mill (made in India) and make your own sheet stock.
(As others have said, redesigning the joint is the right way to solve the problem -- don't ask one material to do two things: be a gasket and establish a reliable, constant face-to-face distance.)
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Philip wrote:

A related question. Because the flow thro' device is quite small (60mm x 90mm), I had to restrict the width of the gasket. Is there a good way of estimating the minimum "no leak" width?
thanks philip
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Philip wrote:

Add a tracer dye to the working fluid and observe the penetration into the joint.
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Philip wrote:

You would want the contact thickness to be several time the "wavelength" of the surface roughness features.
In other words, you don't want the surface asperities and gouges widths to be of the order of the contact thickness.
Further refinements of the idea would be based on the depth/height of the surface asperities and gouges.
There are certain gouge and asperity geometries that would be particularly hard to seal, if you apply your mind and think about what making a surface seal involves.
Jim
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1. what is the PH value require? 2. what is the working temperature? room temperature? 3. what processing method will you use, injection moulding? 4. what is the compression set require? 5. what color of the material, or transparent? 6. any criterial you haven't mention, pls state clearly.
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