FFKM O-rings: the highest-performance O-ring material
FFKM O-rings combine two properties that no other elastomer offers at the same time: nearly universal resistance to media and an operating temperature of up to +340 °C. Here you can read why this is the case, how FFKM differs from FKM, and which ECOLAST compound is right for your sealing application.
- FFKM is the most chemical- and temperature-resistant elastic sealing material: In our tool, it exhibits excellent resistance in 407 out of 430 media.
- Operating range: −40 to +340 °C, depending on the mixture; standard types: −25 to +270 °C; in steam: up to 210–270 °C, depending on the type.
- Fully elastic, unlike PTFE or FEP, and therefore suitable for use as a flange, piston, and rod seal.
- The only real drawback is the price. FFKM is worth it in situations where other materials fail due to temperature or the medium.
- NH O-RINGs are available as ECOLAST in ten compounds, with over 5,000 sizes in stock and no minimum order quantity.
What is FFKM?
FFKM is the abbreviation for perfluoroelastomer, also known as perfluoroelastomer. It refers to a fully fluorinated synthetic rubber that is primarily used for high-performance seals: FFKM seals, such as O-rings, provide a seal where other elastomers fail. The older designation FFPM refers to the same material; today, the abbreviation FFKM is commonly used.
The key difference lies in the chemical structure. FFKM consists almost entirely of carbon-fluorine bonds, one of the strongest bonds in organic chemistry. As a result, even aggressive media have little effect on the material. FKM, on the other hand, is only partially fluorinated and still contains hydrogen in its chain, which makes it more susceptible to damage. The diagram above illustrates the difference. Unlike PTFE, FFKM remains a true elastomer with elastic recovery.
Key Features
Our FFKM tool has been rated "excellent" by the media. Not recommended for use with elemental fluorine only.
Depending on the mixture, standard types: −25 to +270 °C.
Unlike PTFE or FEP, it is therefore used as a flange, piston, and rod seal.
Depending on the mixture, most types are 75 Shore A.
Depending on the mixture; Regulation (EC) No. 1935/2004 applies to all mixtures.
You can check specific media in the Media Compatibility Tool. The only significant drawback is the price: Perfluoroelastomer is very costly to manufacture, and the raw material costs many times more than common materials. FFKM is worth the investment wherever no other material meets the requirements and where reliability and service life are critical.
Comparison of Temperature Ranges
Among elastic sealing materials, FFKM covers the widest range of continuous operating temperatures. The chart compares our four material families with the two common elastomers, EPDM and NBR:
The article “O-Ring Materials” provides a direct comparison of all materials; for more information on heat resistance, see “Heat-Resistant O-Rings.”
Why is FFKM virtually universally resistant?
The name of every elastomer material reveals what it is made of. The two “F”s in FFKM stand for fluorine. Fluorine forms an exceptionally stable bond with carbon. Since FFKM is fully fluorinated, media can hardly find a point of attack. Our tool shows what that means in numbers:
The few exceptions
Hot Water and Steam
In hot water and steam, the limit is lower than the air temperature and depends heavily on the mixture. The NH5755 HT is designed for steam:
| Material | Hot water | Steam |
|---|---|---|
| ECOLAST NH5755 HT | up to 270 °C | up to 270 °C |
| ECOLAST NH5751 HT | up to 230 °C | up to 230 °C |
| ECOLAST NH5750 | up to 210 °C | up to 210 °C |
| Peroxide-cured EPDM, Comparison | up to 170 °C | up to 170 °C |
| FKM | Not recommended | up to 120 °C |
Based on NH O-RING's experience; no liability assumed; test in individual cases. Comparison of all materials: O-rings for hot water.
FFKM vs. FKM: A Direct Comparison
FKM is the proven standard for demanding applications. FFKM takes it a significant step further:
| Characteristic | FKM | FFKM |
|---|---|---|
| Fluorination | Partial, with hydrogen | completely |
| Media:excellentTool, 430 media items | 250 (58%) | 407 (95%) |
| Not recommended | 98 media | 1 medium, elemental fluorine |
| Air Temperature | −25/+200 °C, FKM EX40 −40/+225 °C | −40/+340 °C depending on the type |
| Hot Water and Steam | Hot water not recommended; steam up to 120 °C | up to 210–270 °C depending on the model |
| Price level | medium | high |
| Typical Applications | Industry, oils, fuels | Chemicals, Pharmaceuticals, Semiconductors, Steam |
FKM cost-effectively covers a wide range of industrial applications. FFKM is the material of choice when temperatures and media conditions reach their limits. Learn more in the article “FKM O-Rings.”
FFKM, ECOLAST, and Kalrez: Materials and Brands
FFKM is the material designation. In addition, there are several brand names for perfluoroelastomer from various manufacturers:
For many years, Kalrez was the best-known FFKM brand. Today, high-performance alternatives are available. With ECOLAST, you can get FFKM O-rings in ten compounds, in over 5,000 sizes available from stock, and with no minimum order quantities.
ECOLAST Guide to Other Designations
Do you have a request that includes a compound designation from another manufacturer? The overview lists ECOLAST compounds with similar primary applications and is intended solely as a non-binding starting point for your discussion with us.
| ECOLAST | Kalrez® | Chemraz® | Perlast® | Isolast® |
|---|---|---|---|---|
| NH4700 | 6221 | 514 | G74S | J9516 |
| NH5750 | 6375, 6230 | 505, 605 | G80A, G70A | J9503, J9515 |
| NH5751 HT | 4079 | 615, 555 | G75B | J8325 |
| NH5755 HT | 1050 LF | 551 | N/A | N/A |
| NH5756 HT | 7075 | N/A | N/A | N/A |
| NH5760 LT | 0040 | 564 LT | G75LT | J9523 |
| NH5901 HT | 7090 | 600 | G90A | J9512 |
ECOLAST: Our FFKM Compounds
FFKM is not available in just one type. Its composition can be specifically tailored to meet specific temperature ranges, hardness requirements, and certifications. Our ECOLAST product line covers the most common application requirements. Select your requirement:
The white blends NH4700 and NH7700 are designed for food, pharmaceutical, and hygiene applications. All test results are listed in the data sheets; you can find an overview of the product line on the ECOLAST page.
Technical Specifications at a Glance
The values are taken from the ECOLAST data sheets and have been tested in accordance with ASTM. The hardness is given as a rounded nominal value:
| Compound | Shore A hardness | Tensile Strength MPa | Elongation at Break % | DVR % | TR-10 °C |
|---|---|---|---|---|---|
| NH4700 | 70 | 13 | 130 | 24 | −2 |
| NH7700 | 70 | 12.5 | 135 | 23 | −2 |
| NH5750 | 75 | 18 | 145 | 18.5 | −4 |
| NH7750 | 75 | 17 | 155 | 18 | −4 |
| NH5751 HT | 75 | 17.8 | 152 | 19.5 | −4 |
| NH7751 HT | 75 | 17 | 165 | 18.5 | −4 |
| NH5755 HT | 75 | 16.4 | 155 | 20 | −4 |
| NH5756 HT | 75 | 10.3 | 140 | 14 | −1 |
| NH5760 LT | 75 | 16.7 | 257 | 30 | −30 |
| NH5901 HT | 90 | 20.6 | 110 | 18 | −4 |
DVR = permanent set according to ASTM D395 B, 70 h at 200 °C. Tensile strength and elongation at break according to ASTM D412, TR-10 according to ASTM D1329, hardness according to ASTM D2240. Manufacturing-related variations are possible; the respective data sheet is authoritative. For FKM, our data sheets specify the compression set after 22 h at 200 °C; please compare only values tested under the same conditions.
What is an FFKM compound made of?
An FFKM compound is more than just the base polymer. It is the interaction of several components that determines the temperature range, hardness, approval status, and compression set:
- Base polymer (perfluoroelastomer): a fully fluorinated rubber. It provides virtually universal chemical resistance.
- Cross-linking system: plays a key role in determining the upper temperature limit and the compression set. Special cross-linking agents enable high-temperature grades capable of withstanding temperatures up to +330 °C or +340 °C.
- Fillers: enhance mechanical properties. The black grades use carbon black, while the white food- and pharmaceutical-grade types, NH4700 and NH7700, use light-colored, food-grade fillers. This also explains their higher density of 2.41 g/cm³ compared to 1.98 g/cm³ for NH5750.
- Pigments: determine the color; for example, white is used for visual inspection in food production.
| Component | Function | Proportion |
|---|---|---|
| FFKM base polymer: a terpolymer of TFE, PMVE, and a cure-site monomer | Fully fluorinated backbone provides universal resistance | 100 phr80–85% |
| Filler: carbon black for black types; light-colored or mineral fillers for high-purity types | Reinforcement, determines hardness | 10–20 phr12–18% |
| Crosslinking system: peroxide with a coagent, or triazine via nitrile cure sites | forms a thermally very stable network | 2–5 phr2–4% |
Typical guidelines for a standard black FFKM compound. The proportion is given in phr (parts by weight per 100 parts of rubber); the approximate percentage by weight is listed below. High-purity semiconductor and pharmaceutical grades are manufactured using special, often fully fluorinated fillers or without any filler at all to prevent the presence of particles and metal ions. Specific formulations vary by manufacturer.
For the NH5750, NH7750, NH5751 HT, and NH7751 HT, the FFKM content is listed in the data sheet: 80–85% FFKM, determined in the laboratory by thermogravimetry (TGA) in accordance with ISO 11358-1. This value includes FFKM along with the incorporated cross-linking agent. We would be happy to discuss directly with you which compound is best suited for your application.
Typical applications
Design and Installation
FFKM O-rings are generally installed in the same way as other elastomers, with one exception: the groove is slightly deeper, and the compression is slightly less.
static; 15–30% for other elastomers . Dynamic : 6–20% for all.
Static; the groove width remains as shown in the table.
Most types are suitable, except for fluorinated ones.
At high temperatures, the ring requires more space to accommodate thermal expansion; therefore, keep the fill ratio well below 85%. FFKM is more sensitive to mechanical stress than other elastomers: Deburr edges, provide insertion chamfers, and install the ring carefully. Determine groove dimensions and tolerances using the O-ring groove calculation and O-ring tolerances; all guidelines are provided in the article “O-Ring Design.”
Are there any alternatives to FFKM?
If chemical resistance is the primary concern rather than full elasticity, FEP-coated O-rings and PTFE O-rings are a more cost-effective option. Both are also virtually universally resistant, but significantly stiffer, so the installation space must be suitable:
Frequently Asked Questions
What does FFKM stand for?
What is the difference between FFKM and FFPM?
What is the difference between FFKM and FKM?
What is the difference between FFKM and Kalrez?
What temperature range do FFKM O-rings cover?
Why are FFKM O-rings so expensive?
How long can FFKM O-rings be stored?
How hot can steam be for FFKM O-rings?
