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whats the difference between these two materials?

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Post Wed Oct 15, 2003 5:43 pm

whats the difference between these two materials?

Can anyone tell me the difference between perspex cast acrylic sheet and plain film extruded acrylic sheet?

I'm fairly new to this game and wondered why there was such a price difference between them.

Many Thanks

Dave Arch
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Post Wed Oct 15, 2003 8:28 pm

Cast is liquid methylacrilate that is poured between 2 sheets of glass seperated by a rubber gasket to make the thickness. This is then autoclaved for days to cur , the material is made of long polymer chains and the chains rea rando , thus the material is more resistant to stress than extruded and epands uniformly acroos width and breadth.

Extruded is the same , however the methylacrilate is mixed with a hardner and extruded out of a slit and then rolled between polished steel rollers to give the surface sheen,
This is a short chain material and is thus far more stressed especially if worked , heated , bent or subject to solvent attack - it crazes easily. It stretches more along the direction its extruded and is far better in respect of thickness tolerances. A lot cheaper to make and used where structural integrity is not required.
The way to test to see which is which is to burn a piece , cast burns with a crackly flame and doesnt drip molten flaming globs , extruded does drip and burns with a silent flame.
For a laser , extruded cuts eaiser and doesnt frost when engraved. , it also engraves with a cutter with a "clear" cut.
We work almost exclusively in Cast despite the + and - 10-15% thickness tolerance except in short term or non critical items.
There are also other grades like a UHI (Ultra high impact) which is basically an extruded with a "rubberiser" thus it doesnt shatter and can be bent without snapping on thin sections , we make a lot of bookmarks where the "tounge" of the bookmark is required to flex often.
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Post Thu Oct 16, 2003 8:58 am

Thanks for that, I now know which I will use and when.

Cheers
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Post Sat Oct 25, 2003 9:22 am

Just to make the above a bit simpler, being a fabricator we use cast almost all the time, from sign panels to flat cut lettering built up lettering to acrylic display stands its all from cast...

When someone comes in with a piece of extruded, work stops and we all stare at the guy untill he goes away..............

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