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 various media and very high temperature resistance. They provide a reliable seal where NBR, EPDM, or FKM have long since failed.
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 as a high-performance sealing material. The older designation FFPM refers to the same material; today, the abbreviation FFKM is commonly used.
The key lies in its 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 (fluorinated rubber), on the other hand, is only partially fluorinated and still contains hydrogen in its molecule, which makes it more susceptible to damage.
Key Features
- Nearly universal chemical resistance: resistant to the vast majority of acids, alkalis, solvents, fuels, oils, and hot steam. Check specific substances using the chemical resistance tool.
- Temperature resistance: from −40 °C to +340 °C, depending on the mixture.
- Fully elastic: Unlike PTFE- or FEP-coated O-rings, FFKM remains elastic and is suitable for use as a flange, piston, and rod seal.
- Hardness: 70 to 90 Shore A, depending on the mixture.
- Approvals: Depending on the blend, FDA, USP Class VI, 3-A, and EC 1935/2004 for food, pharmaceutical, and hygiene applications.
- Shelf life: 15 years when stored properly in accordance with DIN 7716.
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.
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.
There are only a few exceptions you should be aware of:
- Media with a high fluorine content, such as elemental fluorine (like attacks like).
- Molten alkali metals.
In almost all other cases, FFKM can be used without any chemical concerns.
FFKM vs. FKM: A Direct Comparison
FKM (often known by the brand name Viton) is the proven standard for demanding applications. FFKM takes it a significant step further.
| Characteristic | FKM | FFKM |
|---|---|---|
| Fluoridation | Partially | completely |
| Media resistance | Very good, with some exceptions | nearly universal |
| Temperature | up to approx. +225 °C | up to approx. +340 °C |
| Price level | medium | high |
| Typical Applications | Industry, Standard | Chemical, pharmaceutical, semiconductor |
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:
- ECOLAST® is our own brand of FFKM (NH O-RING)
- Kalrez® is DuPont's FFKM brand
- Simriz® is a product of Freudenberg
- Chemraz® is manufactured by Greene Tweed
For many years, Kalrez was the best-known FFKM brand. Today, high-performance alternatives are available. With ECOLAST, you get FFKM O-rings of European brand quality, in over 5,000 sizes available from stock, and with no minimum order quantities.
ECOLAST: Our FFKM Compounds
FFKM is not available in just one type. Its composition can be specifically tailored to meet specific requirements for temperature range, hardness, and certifications. Our ECOLAST product line covers the most common application requirements:
| Mixture | Temperature | Hardness | Profile / Certification |
|---|---|---|---|
| NH4700 (white) | −20/+270 °C | 70 Shore A | FDA, USP Class VI, 3-A |
| NH7700 (white) | −20/+270 °C | 70 Shore A | FDA, USP Class VI |
| NH5750 | −25/+270 °C | 75 Shore A | Standard, FDA |
| NH7750 | −25/+270 °C | 75 Shore A | Standard |
| NH5751 HT | −15/+330 °C | 75 Shore A | High temperature |
| NH7751 HT | −15/+330 °C | 75 Shore A | High temperature |
| NH5755 HT | −15/+330 °C | 75 Shore A | Steam and hot water |
| NH5756 HT | −15/+340 °C | 75 Shore A | High temperature +340 |
| NH5760 LT | −40/+270 °C | 75 Shore A | Low temperature −40 |
| NH5901 HT | −15/+320 °C | 90 Shore A | Oil and gas, high pressure |
The white blends NH4700 and NH7700 are designed for food, pharmaceutical, and hygiene applications. All test results can be found on the ECOLAST website and in the data sheets.
Technical Specifications at a Glance
The following values are taken from the ECOLAST data sheets and have been tested in accordance with ASTM. Hardness is specified as a rounded nominal value; the compression set applies to 70 h at 200 °C.
| Mixture | Hardness s Shore A | 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 = Compression Set (70 h / 200 °C). Tensile strength and elongation at break per ASTM D412, compression set per ASTM D395 B (70 h / 200 °C), TR-10 per ASTM D1329, hardness per ASTM D2240. Manufacturing-related variations are possible; the respective data sheet is authoritative.
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 rely on light-colored, food-grade fillers. This also explains the higher density of 2.41 g/cm³ compared to 1.98 g/cm³ for the standard black grades.
- Pigments: determine the color; for example, white is used for visual inspection in food production.
The exact formulation and polymer content for each blend are manufacturer-specific and will be disclosed upon request. We would be happy to discuss with you directly which blend is best suited for your application.
Typical applications
Design and Installation
FFKM O-rings should generally be sized in the same way as other elastomers. You can easily determine groove dimensions and tolerances using the O-ring groove calculator and O-ring tolerances. Since FFKM hardly swells at all, the compression can generally be slightly lower. Virtually any oil or grease is suitable as an assembly lubricant, since FFKM is resistant to oils and greases.
Are there any alternatives to FFKM?
If media resistance is the primary concern rather than full elasticity, FEP-coated O-rings and PTFE O-rings are a more cost-effective option. Both also offer nearly universal resistance. Important: These materials are significantly stiffer. The installation space must be appropriately designed; FEP is suitable only as a flange and rod seal, while PTFE is suitable exclusively as a flange seal.
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?
