Stiff engineering plastic

[GeorgeEllwood]

Hello,
I wonder if someone can help me. I'm looking for a transparent, stiff engineering plastic. This is to be a clear plate and that's going to withstand 1 bar of pressure without deforming too much.
I've based my current design on Perspex because it's readily available, the only problem is that it's modulus is only 3GPa, which means I'll need it to be 65mm thick.
Can anyone suggest something that's stiffer?
I don't want to use glass becuase I may need to machine an o-ring grove so I think I'm limited to plastics.
Any ideas greatly appreciated.
Cheers
George

 

[moltenmetal]

Your list of truly transparent rather than transluscent materials is very limited- you probably know them all already.

Could you perhaps put your o-ring on the mating part? Or maybe you could put the o-ring groove into a thinner section of acrylic (Perspex is a tradename which I presume is acrylic), with a backing/stiffening plate of either glass or quartz glass?

 

[patprimmer]

Perspex was ICIs trade name for cell cast acrylic sheet.

Cell cast acrylic has quite a high modulus for a transparent material and you would have to forego some transparency and pay a very high price to do better.

Matweb will list alternatives.

Polysulphones and polyethers might have higher moduli and transparency, but I doubt it.

Acrylic is one of very few if not the only thermoplastic that remains crystal clear at 65mm.

An alternative might also be Ally resins (CR39). I dont know its modulus nor its transparency at that thickness.

Regards
Pat
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[GeorgeEllwood]

Thanks for the tips. I think I'll stick with the perspex. Although it's thicker than I'd like and consequently heavier, in terms of availabilty, optical properties and cost it's probably the optimum choice.
Thanks
George