Cast / Extruded Acrylic

[Rodney Gold]

Cast is a long polymer acrylic and extruded is a short chain polymer – Cast is made between 2 sheets of glass and is allowed to “set” and extruded is rolled between polished rollers and is “set” when it comes out of em (Very simply put)
The differences that affect us as signmakers are this
1) Cast expands uniformly over length and breadth and extruded expands mainly in the direction it was rolled (so if you cut a piece for a long lightbox , you must compensate for this expansion)
2) Cast is MUCH less prone to stress when working with it and is substantially better in terms of developing stress fractures
3) Cast varys in thicknes by as much as +20 to -20% over a sheet (Ie 3mm can be 2.4mm to 3.6mm over the sheet) whereas extruded varys but 1% or even less
4) Cast comes in more colours , but is more expensive generally than extruded.
5) Cast laser engraves and cnc machines better than extruded , tho extruded is better to laser cut. Cast is STRONGER than extruded .
6) Any process that generates heat in extruded (even saw cutting) puts incredible stress into the material , any solvent based glueing process thereafter is almost guaranteed to stress crack the product (unless you destress the material by leaving it in an oven at 70 degrees c for 1 hr per mm of thickness) – even being near solvents (like aceton , meths etc) can lead to stress cracking. The problem with stress cracking is that sometimes it can appear weeks and months after shipping the product to the customer.
If you have 2 pieces of acrylic and dont know which is which , light a small piece of offcut . cast burns with a crackly flame and wont drip molten flaming balls , extruded burns with a silent flame and will drip flaming globs. (so dont use extruded where there are strict fire laws or fire hazards)
There are some other technical differences in respect of impact strength , uv resistance , temp the pruduct breaks down at etc

[Kev]

Rodney
Thank you very much

Cheers
kev