Viton FKM properties
Commercial names and designation
Section titled “Commercial names and designation”FKM is a family of fluoroelastomers defined by ASTM D1418 and ISO 1629. Its designation comes from the German Fluorkautschukmaterial (fluorinated rubber material). The best-known commercial name is Viton (originally developed by DuPont and now owned by Chemours). Other manufacturers market equivalent products under brands such as Dai-El (Daikin), Dyneon (3M), Tecnoflon (Solvay) or Fluonox (Gujarat Fluorochemicals). All FKMs contain vinylidene fluoride (VDF) as the base monomer, combined with other comonomers to adjust performance. They are the commercial elastomers with the highest thermal and chemical resistance, surpassed only by perfluoroelastomers (FFKM).
Chemical composition
Section titled “Chemical composition”FKM is a fluorinated copolymer or terpolymer. The basic composition (Type 1) is a copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) with a fluorine content near 66 % by weight. Terpolymers (Type 2) incorporate tetrafluoroethylene (TFE), reaching between 68 % and 69 % fluorine, which improves chemical and thermal resistance. Low-temperature grades (Type 3) replace HFP with perfluoromethyl vinyl ether (PMVE), with a fluorine content between 62 % and 68 % and a minimum service temperature of –50 °C. There are also special types with propylene (Type 4) or ethylene (Type 5) to resist bases and hydrogen sulfide. The following table summarizes the main types.
| FKM Type | Main Comonomers | Fluorine content (% by weight) | Main contribution |
|---|---|---|---|
| Type 1 | VDF + HFP | ~66 | General purpose |
| Type 2 | VDF + HFP + TFE | 68 – 69 | Higher chemical and thermal resistance |
| Type 3 | VDF + TFE + PMVE | 62 – 68 | Low-temperature flexibility (–50 °C) |
| Type 4 | Propylene + TFE + VDF | ~67 | Resistance to bases |
| Type 5 | VDF + HFP + TFE + PMVE + Ethylene | Variable | Resistance to H₂S and high temperatures |
Mechanical properties
Section titled “Mechanical properties”The mechanical properties given correspond to a general-purpose FKM (Type 1) vulcanized, tested at 23 °C. The tensile strength is 9 MPa. Molded parts have a Shore A hardness of 75. Elongation at break reaches 200 % and tear resistance is 10 N/mm. Compression set after 24 h at 175 °C is 43 %.
| Property | SI Value | Imperial Value | Standard / Conditions |
|---|---|---|---|
| Tensile strength | 9 MPa | 1305 psi | ASTM D412, 23 °C |
| Elongation at break | 200 % | 200 % | ASTM D412 |
| Shore A hardness | 75 A | 75 A | ASTM D2240 |
| Tear resistance | 10 N/mm | 57 lbf/in | ASTM D624 |
| Compression set (24 h / 175 °C) | 43 % | 43 % | ASTM D395 |
Physical properties
Section titled “Physical properties”The density of FKM is 2.0 g/cm³ (2000 kg/m³ or 124.9 lb/ft³), notably higher than that of most conventional elastomers. The material is self-extinguishing (does not propagate flame) and has excellent resistance to ultraviolet radiation and weathering. It is black in most commercial formulations.
| Property | SI Value | Imperial Value |
|---|---|---|
| Density | 2.0 g/cm³ | 124.9 lb/ft³ |
| Flammability | Self-extinguishing | Self-extinguishing |
| UV / weathering resistance | Excellent | Excellent |
Thermal properties
Section titled “Thermal properties”The coefficient of linear thermal expansion of FKM is 160 × 10⁻⁶ K⁻¹, high compared to metals but typical of fluorinated elastomers. Thermal conductivity at 23 °C is 0.2 W/(m·K). The minimum working temperature in continuous service is –10 °C for standard types, while low-temperature grades (Type 3) can go down to –50 °C. The maximum continuous service temperature is 220 °C, with intermittent peaks up to 300 °C in the absence of severe mechanical stress.
| Property | SI Value | Imperial Value |
|---|---|---|
| Coefficient of linear thermal expansion | 160 × 10⁻⁶ K⁻¹ | 89 × 10⁻⁶ °F⁻¹ |
| Thermal conductivity (23 °C) | 0.2 W/(m·K) | 1.39 Btu·in/(h·ft²·°F) |
| Minimum service temperature (standard) | –10 °C | 14 °F |
| Minimum service temperature (low temp.) | –50 °C | –58 °F |
| Maximum continuous temperature | 220 °C | 428 °F |
| Maximum intermittent temperature | 300 °C | 572 °F |
Electrical properties
Section titled “Electrical properties”FKM is not a high-performance electrical insulator, as its dielectric constant at 1 kHz is 10.5 and its dissipation factor reaches 0.034. However, it offers a dielectric strength of 20 kV/mm and a volume resistivity of 2 × 10¹³ Ω·cm (2 × 10¹¹ Ω·m). These values are suitable for applications requiring chemical and thermal resistance rather than high-quality electrical insulation.
| Property | SI Value | Imperial Value | Conditions |
|---|---|---|---|
| Dielectric constant (εᵣ) | 10.5 | 10.5 | 1 kHz |
| Dissipation factor (tan δ) | 0.034 | 0.034 | 1 kHz |
| Dielectric strength | 20 kV/mm | 500 V/mil | – |
| Volume resistivity | 2 × 10¹³ Ω·cm | 7.9 × 10¹² Ω·in | – |
Chemical resistance
Section titled “Chemical resistance”FKM offers outstanding chemical resistance against oils, greases, aromatic hydrocarbons, concentrated and dilute acids, and halogens. However, it is attacked by ketones and some polar esters. It exhibits good to fair behavior towards alcohols and alkalis, depending on the exact formulation.
| Chemical medium | Resistance |
|---|---|
| Concentrated acids | Good |
| Dilute acids | Good |
| Alkalis | Good – Fair |
| Alcohols | Good – Fair |
| Aromatic hydrocarbons | Good – Fair |
| Oils and greases | Good |
| Halogens | Good |
| Ketones | Poor |
Applications
Section titled “Applications”FKM fluoroelastomers are used in sectors where high temperatures, contact with aggressive fluids, and durable sealing requirements are combined. The main applications include:
- Automotive: O-rings, crankshaft seals, injector seals, and gaskets in fuel and exhaust systems.
- Aerospace industry: Seals in hydraulic and fuel systems operating at extreme temperatures.
- Oil and gas: Packings, linings, and components exposed to crude oil, sour gas (H₂S), and drilling fluids.
- Chemical processing: Flange gaskets, valve diaphragms, pipe linings, and flexible hoses in contact with acids, bases, and solvents.
- Semiconductor manufacturing: Seals in plasma environments and high-purity chemicals.
- General industrial equipment: Rollers, extruded profiles, and seals in furnaces, heat exchangers, and food processing machinery.
Comparison with other elastomers
Section titled “Comparison with other elastomers”Compared to other elastomers, FKM stands out for its temperature and chemical resistance, although it is more costly and has limited low-temperature flexibility in its standard versions. The following table compares typical values of FKM with nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), silicone (VMQ), and chloroprene (CR).
| Property | FKM | NBR | HNBR | Silicone (VMQ) | Chloroprene (CR) |
|---|---|---|---|---|---|
| Max. continuous temperature (°C) | 220 | 120 | 150 | 230 | 120 |
| Min. temperature (°C) | –10 to –50 | –30 | –30 | –55 | –40 |
| Oil resistance | Excellent | Excellent | Excellent | Fair | Good |
| Acid resistance | Good | Fair | Good | Fair | Fair |
| Weather resistance | Excellent | Poor | Poor | Excellent | Good |
| Ketone resistance | Poor | Fair | Fair | Good | Poor |
| Relative cost | High | Low | Medium | Medium | Low |
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the maximum working temperature of Viton FKM?
Section titled “What is the maximum working temperature of Viton FKM?”The maximum working temperature in continuous service for FKM is 220 °C, and it can withstand peaks of 300 °C under intermittent conditions without mechanical load.
What is the chemical resistance of Viton against ketones?
Section titled “What is the chemical resistance of Viton against ketones?”FKM has poor resistance against ketones such as acetone or methyl ethyl ketone; these solvents cause swelling and degradation of the material.
What is the density of Viton FKM?
Section titled “What is the density of Viton FKM?”The typical density of FKM is 2.0 g/cm³ (2000 kg/m³), approximately twice that of many non-fluorinated elastomers.
What is the typical Shore A hardness of FKM?
Section titled “What is the typical Shore A hardness of FKM?”The most common hardness value for general-purpose FKM compounds is Shore A75, with formulations available from 55 to 90 Shore A.
What is the tensile strength of FKM?
Section titled “What is the tensile strength of FKM?”The tensile strength of a standard FKM is 9 MPa, equivalent to 1305 psi.
Which type of FKM offers the best low-temperature flexibility?
Section titled “Which type of FKM offers the best low-temperature flexibility?”Type 3 FKMs, which incorporate perfluoromethyl vinyl ether (PMVE), achieve a minimum service temperature of –50 °C, compared to –10 °C for standard types.
References
Section titled “References”- azom.com: https://www.azom.com/article.aspx?ArticleID=1991
- engineeringtoolbox.com: https://www.engineeringtoolbox.com/chemical-resistance-rubbers-elastomers-d_1425.html
- steelnumber.com: https://www.steelnumber.com/en/steel_composition_eu.php?name_id=331