HOW PLASTIC SHEET, ROD, & TUBE ARE MADE
Of course, Shakespeare’s Othello n’r dreamt of casting pearl finish sheet out of methyl methacrylate (acrylic). So, what exactly is cast material versus extruded?
The Extrusion Process
Similar to what you did with plasticine as a child, you push squishy plastic through a die and out comes a continuous flow. That squishy plastic is just resin that’s been superheated to its melting point.
For plastic profile extrusions, it’s an imperfect and somewhat uncontrollable science due to the fact that once the plastic leaves the extruding machine and hits the air it rapidly cools and, depending on factors such as humidity and air quality, that batch is probably very unique in that those conditions will never be able to be reproduced exactly. The rule of thumb is order what you need now because no one can guarantee an EXACT match – probably close, but not exact – on the next run.
Plastic sheet extrusion on the other hand is far more advanced with respects to control of the final product. Continuous manufacturing processes ensure that batch after batch meets a pre-defined standard of quality.
Some materials, such as acetal/Delrin, need to be anealed – the material is bathed in hot oil after it’s extruded to relieve the stress caused by the inside cooling at a different rate then the outside. If this process isn’t done properly then bubbles will form inside the material (called perosity) rendering it useless and a potential hazard to someone cutting it.
The Casting Process
Casting, on the other hand, is much like making icecubes – you pour liquid monomer into a containment system (mold), add a catalyst to affect a chemical reaction, and bim! bam! shamalam! you have cast acrylic.
A Cast Acrylic Figurine
You can cast just about any shape or size and layer the process so you can insert things into the acrylic, functionally preserving them for eternity – an award, money, collectible.
Thicker Guages & More Colours
Traditional plastic sheet is cast between two panes of glass and then cured in a big oven. More modern techniques allow for a continuous manufacturing process. Cast acrylic sheet is about 1.6 to 2 x the price of extruded acrylic due to the amount of handling and process involved in producing it.
Optically-perfect Cast Acrylic Tube
Cast tubing is optically pure, beyond that of glass, and can take days to cure rotating round and round – hence a price tag 10x or more than that of extruded tubing. For outside diameters exceeding 4″ cast is the best solution because at that thickness, extruded material tends to warp with very visible extrusion lines.
For acrylic, the casting process allows more flexiblity in the molecular structure of the product too. Cast acrylic has a more brilliant pallet of colours to choose from, glowing edges, and unique light transmission properties.
Florescent Edge Acrylic
NOTE: Exotic acrylic products usually require a minimum purchase volume (10 sheets or more). Not everything is available for sale in single sheets.
Are There Other Processes?
There’s compression molding, blow molding, rotational molding, injection molding… lots of neat things to explore in other articles.
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Warehoused Plastic Sales has partnered with the best manufacturers in the world to deliver a consistent, reliable partner. If you have concern about the products you buy from us then please ask and we’ll provide manufacturers’ certificates of compliance which will identify the source of resin and the international standards by which the material can be compared.