Candidate List Duty Triggers in Component Level Imports
Candidate List duties trigger when any discrete component article exceeds 0.1 percent SVHC by weight, regardless of aggregate assembly mass.
Fluoroelastomer
Meaning
Fluorinated synthetic polymers exhibit heat resistance and chemical inertness under harsh operating environments. Raw compound grades of fluoroelastomer feature high fluorine content along polymer backbones, enabling compression moulding or transfer moulding of O-rings and dynamic shaft seals. The application boundary excludes extreme sub-zero flexible applications where low-temperature glass transition causes elastomeric embrittlement and seal failure.
Chemical Resistance
Strong carbon-fluorine bonds prevent chemical attack by aggressive fuels, synthetic oils, and aromatic solvents. Seals manufactured from fluoroelastomer maintain sealing force and volumetric stability when exposed to harsh engine lubricants at elevated temperatures. Contact with molten alkali metals or specialized amine compounds degrades the polymer network, leading to swelling and rapid seal degradation.
Moulding Rheology
High raw polymer viscosity requires precise mold heating and cavity venting to ensure complete cavity filling. Processing raw fluoroelastomer stock involves vulcanization crosslinking under heat and pressure, requiring controlled cure cycles to prevent scorched compound defects. Post-cure baking operations drive off residual volatile crosslinking agents and stabilize physical properties.
Compression Recovery
Permanent deformation resistance determines seal longevity under continuous mechanical stress. Compounding fluoroelastomer with bisphenol or peroxide curing systems improves recovery after prolonged compression at elevated temperatures. Proper mold geometry design compensates for thermal expansion and crosslinking shrinkage during vulcanization.