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What is a Thermoset

Thermoset plastics are synthetic materials that strengthen when heated but cannot successfully be remolded or reheated after initial heat-forming or molding. Molded thermoset components offer protection against high operating temperatures, corrosion, UV exposure, and aggressive chemicals, oils and automotive fluids. These property benefits allow thermosets to be used in a variety of aggressive and challenging end-use environments, from electrical applications to automotive powertrain and transmission components to products with outdoor exposure. Utilizing a thermoset molding process gives final parts and assemblies dimensional and chemical stability against moisture, high heat and operating temperatures, electric voltage, and chemicals or automotive fluids.

Thermoset materials that are molded include Bulk Molding Compound (BMC), Phenolic, Epoxy, and Diallyl Phthalate (DAP). Bulk Molding Compounds include unsaturated polyesters and vinyl esters. Molding wise, thermosets can be injection, compression, injection-compression, or transfer molded. The difference from molding thermosets vs engineered thermoplastics is material is molded with a hot tool or mold with thermoset materials, whereas thermoplastics are molded into a cooled mold.


Understanding Thermoset Plastics

With an array of material property benefits, molded thermoset parts are used in a variety of customer end-markets and applications that require a strong, durable material capable of withstanding aggressive elements. Thermosets will not degrade with exposure to certain chemicals, oils, and automotive fluids. In electrical applications and assemblies, thermoset parts can protect internal components with superior dielectric strength and electrical insulation. In outdoor applications, thermoset components remain durable even in wide-ranging weather conditions including exposure to heavy sunlight and UV, rain, sleet or snow. Whether a product application functions in Alaska or Arizona, thermosets remain a preferred material choice of engineers and designers for challenging applications requiring heat-stable components. Cost-wise, thermosets are competitively priced against similarly performing engineered thermoplastics, with raw materials generally priced between $1-$3.50 per lb. for thermoset molding compounds.



In scientific terms, a thermoset monomer must have three or more reactive ends, with its molecular chains crosslinking in three dimensions. Post-molding, thermosets have virtually all molecules interconnected with strong, permanent, physical bonds which are not heat reversible. Thermoplastic monomers on the other hand, only have two reactive ends for linear chain growth.




In layman terms, molding or curing a thermoset is like cooking an egg or baking a cake. Once an egg is dropped into boiling water and cooked, it cannot revert to its original physical state as a yoke. Similarly, after thermosets are molded, it cannot be ground up and reprocessed or remolded.



Benefits of Thermoset Plastics


  • Corrosion and Steam Resistant
  • Excellent Chemical and Dimensional Stability
  • Excellent Thermal Properties
  • Heat Resistant
  • High Dielectric Strength
  • High Strength-to-Weight Ratio
  • Low Creep/Shrink
  • Superior Thermal Insulation
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