Yes, it is wise to know that there are two main types of acrylic that should be differentiated. This has to do with the way the sheet material is made. The different production process means that there are important differences in material properties, application areas and fabrication possibilities.
In this article, we explain what the differences are between the two types of acrylic and when you should choose what kind of acrylic. Both types are clearly distinguished on our website and you can choose from different thicknesses, colours and surface structures for each type. The following article will help you to choose the right type of acrylic for your acrylic project!
Cast acrylic is made by allowing acrylic monomer to cure (polymerization) slowly between glass sheets or another type of mould under well-controlled conditions. Because the liquid monomer (base element) is cast between the glass sheets, it is called cast acrylic. It’s that simple. This method of polymerization gives the best quality.
Cast acrylic (sheets, tubes, blocks) has very good characteristics. An additional advantage of the casting process of acrylic is that it is flexible and it can be done in comparatively small quantities. This is efficient because the material can be made in a quantity that fits with what is needed. The cast sheets can be made very flexible in your chosen colour, thickness and surface structure. This is completely customer-specific!
When casting between two glass sheets of 2 by 3 meters, it is unavoidable that there will be some thickness tolerance in the acrylic sheet. On the other hand, the slow, smooth and carefully controlled polymerization leads to a very good quality acrylic. The material is stress-free, optically very pure, brighter than glass, durable, excellent to work with and – because it is a thermoplastic – can be bend after heating. You can order custom cast acrylic here.
Extruded acrylic is the other type. Extrusion means that a viscous rubber-like hot plastic mass from a wide injection moulding jaw. Just behind the extruding machine is a large multiple cylinder Waltz. The acrylic sheet-in-progress is calibrated and cooled using perfectly polished rollers. After the roller, there is “suddenly” a completely flat optically pure stress-free acrylic sheet XT. Anyone who has never seen an extrusion plant cannot imagine how impressive this process is. A great big machine in a warm room with overpressure, a clean room, with a lot of noise and light, a slack rubber sheet that is suddenly perfect after the roller, in a huge hall with overhead cranes and action everywhere.
The extrusion process outlined
The current quality of extruded acrylic is very good, optically pure and – that is the major advantage of the extrusion process – with negligible thickness tolerance. That is why extruded acrylic is used in many areas where the accurate fitting is important. Extruded acrylic is slightly cheaper than cast acrylic and is therefore widely used in applications where large quantities are processed, such as skylights and displays. The disadvantage of the extrusion process is that the production is not batchwise (in small quantities) as with the casting but in a continuous process. When extruding on a large 2-meter-wide extrusion line, a minimum quantity of 5,000 kg is usually required to allow the extruder to switch economically to a different colour or type. The entire machine must be cleaned! It is not possible to make a 20 mm red sheet. No, with a thickness of 8 mm you should purchase 500 m2. Then it is better to choose cast acrylic! You can order cut to size extruded acrylic via our webshop.
When complex operations are required or otherwise high demands are made, preference is therefore given to cast acrylic. This is because cast acrylic has a higher melting point than extruded. This means that it does not soften quickly. As a result, cast acrylic has slightly better mechanical properties (molecular weight), which means that it is also better machined with a cleaner surface after processing. However, vacuum forming is much easier with extruded acrylic. This is because XT is a shorter polymer and therefore has a low molecular weight. This means that extruded acrylic becomes smoother faster and is therefore very easy to vacuum form. XT, therefore, has a lower processing point than cast acrylic. Extruded acrylic is not (yet) made in thicknesses above 30 mm and wider than 2050 mm. Cast acrylic, on the other hand, is “easily” available in thicknesses of up to 400mm.
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Author: Sied Kooistra, Creative Director – founder PyraSied Xtreme Acrylic
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