| Operating temperature | Continuous service commonly ranges from approximately −20°C to +200°C, depending on formulation. Some specialized grades extend toward +230°C. | Standard FKM for general high-temperature sealing; specialized high-temperature formulations for prolonged exposure above +200°C. | Expose finished parts at the maximum continuous temperature and measure hardness, tensile strength, elongation, mass, and compression set. | Maximum temperature is compound- and exposure-time-dependent; short-term peak temperature should not be treated as continuous service temperature. |
| Low-temperature flexibility | Required flexibility may be below −20°C, especially in outdoor, aerospace, mobile, and cold-start applications. | Low-Temperature FKM formulations or modified fluorinated elastomers; consider an alternative elastomer if deep-flexibility is the primary requirement. | Use ASTM D1329/TR test methods, brittleness testing where relevant, and dynamic sealing tests at the minimum operating temperature. | Higher fluorine content generally improves fluid resistance but can reduce low-temperature flexibility. |
| Fuel and hydrocarbon resistance | Resistance to gasoline, diesel, lubricants, hydraulic fluids, and many mineral-oil-based media is commonly required. | General-purpose FKM is often suitable; select a fuel-optimized formulation for aggressive fuel blends or long-term immersion. | Immersion testing using the actual fluid or the applicable reference fluid; record volume change, hardness change, tensile retention, and visual damage. | Compatibility can change with fuel oxygenates, additives, temperature, pressure, and exposure duration. |
| Chemical compatibility | Resistance may be needed against acids, solvents, aromatic compounds, cleaning agents, or process chemicals. | Choose the formulation according to the exact chemical, concentration, temperature, and exposure mode rather than fluorine content alone. | Perform ASTM D471 immersion testing or an equivalent procedure with the production compound and actual chemical mixture. | FKM is not universally resistant to strong bases, hot steam, hot water, amines, and certain polar solvents. |
| Compression set | Low permanent deformation is important for static seals, especially at elevated temperature. Target values must be defined for the application and test condition. | Use a properly post-cured FKM compound with a cure system selected for the temperature and sealing geometry. | Measure according to ASTM D395, Method B, at the specified temperature and duration; test production-size parts when possible. | Compression-set results from different temperatures, durations, and specimen geometries are not directly interchangeable. |
| Gas and vapor permeation | Low permeation may be required for fuel vapor, refrigerant, vacuum, or emissions-control applications. | Higher-fluorine or low-permeation formulations may reduce transport through the seal; geometry and surface finish remain critical. | Use application-specific permeation testing, helium leak testing, or the relevant regulatory test protocol. | Permeation depends on pressure differential, temperature, seal thickness, compound, and time; hardness alone is not a reliable predictor. |
| Dynamic sealing and friction | Reciprocating or rotary seals require controlled friction, wear resistance, extrusion resistance, and adequate lubrication. | Select a dynamic-sealing formulation and optimize hardness, surface finish, lubrication, and gland design together. | Run representative pressure-speed-temperature endurance tests and inspect wear, leakage, friction, and surface damage. | Static material-screening data cannot reliably predict dynamic seal life. |
| Hardness and extrusion control | Common seal hardness selections are often within approximately 70–90 Shore A, subject to pressure, gap, and installation requirements. | Use softer compounds for conformity and lower installation force; use harder compounds or anti-extrusion measures for higher pressure and clearance gaps. | Measure hardness under ASTM D2240 and conduct pressure-cycle tests using the actual gland dimensions. | Hardness is not a substitute for correct gland design, tolerances, backup rings, and surface finish. |
| Electrical and plasma environment | Applications may require controlled outgassing, low particle generation, or resistance to plasma and cleaning cycles. | Use a formulation qualified for the specific vacuum, plasma, cleaning chemistry, and contamination limits. | Conduct outgassing, particle, weight-loss, dimensional, and repeated cleaning-cycle tests in the application environment. | Conventional industrial FKM should not be assumed suitable for high-purity or plasma processes without qualification. |
| Regulatory and material compliance | Requirements may include restricted-substance control, food-contact suitability, potable-water contact, automotive specifications, or aerospace qualification. | Select a compound with documented compliance for the exact market, application, and processing condition. | Review the current declaration, formulation restrictions, lot traceability, and independent laboratory reports where required. | Compliance is compound-specific and may vary by color, cure system, production site, and product thickness. |
| Manufacturing and quality consistency | Stable hardness, dimensions, cure state, surface condition, and batch-to-batch performance are essential for reliable sealing. | Choose a compound supported by a controlled specification, defined cure conditions, and repeatable production capability. | Audit incoming material controls, first-article inspection, capability data, dimensional inspection, and lot-level test records. | A laboratory sample that passes testing may still fail if processing, storage, or dimensional controls are inadequate. |
