FKM 70A
Hardness band
EN FPM · also Fluorel, Fluoroelastomer
70A = 70 Shore A
Most common O-ring hardness: good sealing conformance and low compression load for static and dynamic sealing at low to medium pressure, with 11 MPa tensile and 250% elongation.
Values for the 70A condition
Other FKM grades and fills
FKM is listed in 6 conditions; see the grade overview at FKM.
Compare all 6 grades and fillsHide
| Grade · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness |
|---|---|---|---|---|---|
70AThis page 70 Shore A | Most common O-ring hardness: good sealing conformance and low compression load for static and dynamic sealing at low to medium pressure, with 11 MPa tensile and 250% elongation. | — | 11 | 250 | 22 Shore D |
Low-temperature | Specify the perfluoromethylvinyl ether low-temperature type (GLT/GFLT class) for aerospace and cold-region fuel and driveline seals: Tg drops to −30 to −40 °C while oil and heat resistance is retained. | — | 12 | 220 | 25 Shore D |
80 Shore A | Use this medium hardness for medium- to high-pressure seals or groove designs needing extrusion resistance; conformance is lower than 70 Shore A and elongation falls to 180%. | — | 13 | 180 | 28 Shore D |
Peroxide-cured | Substitute peroxide cure with bromine/iodine cure sites for the bisphenol type when service involves hot water, steam or inorganic acids and better hydrolysis resistance is required. | — | 14 | 190 | 25 Shore D |
90 Shore A | Pick for high-pressure hydraulic and downhole seals and back-up rings where gap extrusion resistance governs; sealing conformance and low-temperature recovery are poorer, elongation 130%. | — | 15 | 130 | 38 Shore D |
70% | Choose the peroxide-cured terpolymer with about 70% fluorine for chemical and fuel-system seals exposed to methanol/ethanol fuels, acids, hot water or temperatures up to 230 °C. | — | 16 | 180 | 78 Shore A |
What is FKM 70A?
FKM 70A is FKM heat treated to 70A — most common O-ring hardness: good sealing conformance and low compression load for static and dynamic sealing at low to medium pressure, with 11 MPa tensile and 250% elongation. FKM 70A has a tensile strength of 11 MPa (1.6 ksi), weaker than 78% of polymer grades. Elongation at break is 250% and the elastic modulus is 0.01 GPa (8.7×10⁻⁴ Msi). FKM 70A has a density of 1.82 g/cm³ (0.0658 lb/in³), heavier than 96% of polymer grades. Its glass-transition temperature is -20°C (-4 °F).
Advantages
- Good corrosion resistance — 95/100, better than 97% of polymer grades
- Good UV / weathering resistance — 95/100, better than 95% of polymer grades
- High service temperature — 200°C (392 °F), better than 87% of polymer grades
- Ductile — tolerates forming and impact — 250%, better than 79% of polymer grades
Limitations
- High mold shrinkage — 3.2%, worse than 98% of polymer grades
- Difficult to machine — 20/100, worse than 97% of polymer grades
- Heavy — 1.82 g/cm³ (0.0658 lb/in³), worse than 96% of polymer grades
- High embodied carbon — 12 kg CO₂/kg, worse than 91% of polymer grades
- Low stiffness — 0.01 GPa (8.7×10⁻⁴ Msi), worse than 86% of polymer grades
FKM 70A properties
Typical room-temperature values for FKM 70A; 14 are specific to this condition. Other listed values are FKM reference data and may not represent this condition. Bars are the position among polymer grades.
Physical3
FKM 70A has a density of 1.82 g/cm³ (0.0658 lb/in³), heavier than 96% of polymer grades. Its glass-transition temperature is -20°C (-4 °F).
Mechanical7
FKM 70A has a tensile strength of 11 MPa (1.6 ksi), weaker than 78% of polymer grades. Elongation at break is 250% and the elastic modulus is 0.01 GPa (8.7×10⁻⁴ Msi).
Thermal8
FKM 70A is rated for continuous service to 200°C (392 °F). It conducts heat at 0.2 W/m·K (0.116 BTU/hr·ft·°F), worse than 56% of polymer grades. Thermal expansion is 160 µm/m·K (88.9 µin/in·°F).
Electrical5
FKM 70A is an electrical insulator with a dielectric strength of 16 kV/mm (406.4 V/mil) and a resistivity of 2×10¹¹ Ω·m.
Chemical & Environmental3
Corrosion resistance is excellent (95/100), better than 97% of polymer grades. UV resistance is excellent.
Sustainability4
Producing a kilogram of FKM 70A takes about 200 MJ of energy and emits 12 kg of CO₂ — more than 89% of polymer grades. Typical recycled content is 0%.
Manufacturability4
FKM 70A's machinability is poor (20/100, worse than 97% of polymer grades).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with FKM 70A
Is FKM easy to machine?
Not suited to conventional cutting; seals are compression or injection molded and deflashed by cryogenic tumbling. If machining is unavoidable, turn pre-cured blanks with very sharp tools at low speed and cool the part thoroughly.
Can FKM be welded?
Not heat weldable; splice joints with uncured gum stock vulcanized in place, or bond with fluoroelastomer-specific adhesives applied over the matching primer.
Can FKM be formed, bent or molded?
Compression, transfer or injection molded with a press cure at 175–190 °C, followed by a 200–230 °C post-cure for 16–24 h to lower compression set and drive off volatiles.
What surface finishes work on FKM?
Surfaces can be graphite, PTFE or silicone coated to cut friction and installation stiction; bonding to metal inserts requires plasma or chemical pretreatment plus a fluoroelastomer-specific primer.
FKM chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| vinylidene fluoride (VDF, )main-chain monomer | 45 – 70 | 60 |
| hexafluoropropylene (HFP, )provides amorphous elasticity | 25 – 45 | 40 |
| tetrafluoroethylene (TFE, )added in terpolymer (high-fluorine); 0 in standard dipolymer | 0 – 30 | 0 |
| fluorine contentmass fraction of fluorine in the polymer | 65 – 70 | 66 |
| carbon black (N990/N550 )share in the compound (about 20-30 phr) | 10 – 30 | 20 |
| curative + Ca(OH)2 / MgObisphenol AF + phosphonium salt or peroxide/TAIC system | 3 – 10 | 6 |
FKM 70A — frequently asked
What is FKM 70A used for?
FKM 70A is typically used for fuel system O-rings, rotary shaft oil seals, engine and transmission gaskets, chemical pump diaphragms, valve stem seals and aerospace hydraulic seals. In short: high-temp chemical fluoroelastomer.
What is the tensile strength of FKM 70A?
FKM 70A has a typical tensile strength of 11 MPa (1.6 ksi) — weaker than 78% of polymer grades. Strength varies by condition: see the 6 listed tempers.
Is FKM 70A easy to machine?
Not especially — machinability is rated poor (20/100, worse than 97% of polymer grades). Not suited to conventional cutting; seals are compression or injection molded and deflashed by cryogenic tumbling. If machining is unavoidable, turn pre-cured blanks with very sharp tools at low speed and cool the part thoroughly.
Can FKM 70A be welded?
Not heat weldable; splice joints with uncured gum stock vulcanized in place, or bond with fluoroelastomer-specific adhesives applied over the matching primer.
What surface finishes work on FKM 70A?
Surfaces can be graphite, PTFE or silicone coated to cut friction and installation stiction; bonding to metal inserts requires plasma or chemical pretreatment plus a fluoroelastomer-specific primer.
Can FKM 70A be formed, bent or molded?
Compression, transfer or injection molded with a press cure at 175–190 °C, followed by a 200–230 °C post-cure for 16–24 h to lower compression set and drive off volatiles.
What is the maximum service temperature of FKM 70A?
FKM 70A is rated for continuous use to about 200°C (392 °F), and briefly to 275°C. Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Can FabDigit make parts in FKM 70A?
Yes — FKM 70A is available for injection molding; every part is priced by an engineer rather than instantly. Upload a STEP file to get a price and a DFM check.
Sources
- ASTM D1418 — Rubber and Rubber Latices Nomenclature (FKM) — ASTM (2022)
- ASTM D2000 — Classification System for Rubber Products in Automotive Applications — ASTM (2020)
- Viton™ Fluoroelastomer Product & Chemical Resistance Guides — Chemours / DuPont (2023)
- Tecnoflon® FKM Product Selection Guide — Solvay Specialty Polymers (2022)
- Engineered Materials Handbook Vol.2 — Engineering Plastics & Elastomers — ASM International (1988)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.