Castable urethanes are elastomers that contain urethane carbamate links, are processed in liquid form, and are extremely well-suited for casting. Although they vary widely in terms of hardness and chemical composition, castable urethanes as a whole offer exceptional physical characteristics including high abrasion, chemical resistance, tensile strength and load bearing capabilities.
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Castable urethanes offer many advantages over other materials types. For instance, castable urethanes offer increased noise reduction, impact resistance, durability and flexibility versus metal; increased elastic memory, resilience, radiation resistance and lower tooling costs than plastics; and increased colorability, oil resistance and a broader hardness range than rubbers. As thermosetting elastomers, castable urethanes have a wide range of applications and are used in varied industries including: automotive and aviation, for parts such as flares, wheel chocks and spoilers; industrial manufacturing, for conveying system liners, hopper liners, transport rollers and agitator blades; furniture, for headboards, drawer fronts and holding fixtures; and retail, for point of purchase (POP) displays. Additional characteristics of castable urethanes include good insulating properties, high moisture-resistance, long service life, suitable for sanitary applications and resistant to cold flow. However, the negative of castable urethane is that it has an unpleasant smell that does not go away after fabrication.
There are two main types of castable urethanes: polyether-based elastomers and polyester-based elastomers. The two types differ in terms of characteristics, which allow one type to be better-suited for an application versus the other, as well as chemical make-up. As an example, for the soft segment, polyether urethanes will commonly use polytetramethyleneether glycol (PTMEG) or polypropylene glycol (PPG); while polyester urethanes will often use polyethylene adipate (PEA) with the addition of different polyesters to achieve certain characteristics. As for the differing characteristics, polyether urethanes have advantages such as superior hydrolytic stability, low boiling points, low chemical reactivity and excellent dynamic performance; polyester urethanes, however, offer benefits such as high oil resistance, high thermal stability, excellent physical properties and superior toughness. Since the raw materials of castable urethane exist in liquid form, they are easy to mix and measure for the casting process, which may be open or closed. To begin casting, the castable urethane is poured into an open cavity at low pressure, where it undergoes elevated temperatures in order to be cured. The application of pressure is not required to mold the shape, the heat is enough. During closed urethane casting processes such as reaction injection molding (RIM), the castable urethane is injected into the closed cavity through small holes. This process is typically much quicker than open casting, and can take as little as sixty seconds.
