FFKM O-RINGS | MATERIALS SIMPLY EXPLAINED

What are FFKM O-rings?

FFKM is currently by far the best performing O-ring material.

In contrast to all other O-ring materials, FFKM O-rings can withstand temperatures of up to +340°C. In addition, every FFKM compound is resistant to almost all chemicals. At present, the combination of these two properties is unique.

Furthermore, FFKM O-rings are even fully elastic. They can therefore be used as flange, piston or rod seals without any problems.

Feature

Value

ISO designation

FFKM

Chemical name

Perfluoro rubber

Media resistance

Almost universally resistant to media

Temperature resistance

-40°C to +340°C (depending on mixture)

Standard color

Black

Standard hardness

75 Shore A

Production

Compression molding and injection molding

Tolerances

DIN ISO 3601

Durability

13 years

Biggest disadvantage

High price

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#1 FFKM O-rings: The king of elastomers?

It is important to know that elastomer materials such as NBR, FKM or FFKM are dimensionally stable plastics. This allows them to deform elastically under tensile or compressive load and then return to their original shape.

Particularly in applications with high requirements, conventional O-ring materials such as NBR, EPDM or FKM are often no longer sufficient. Therefore, only special materials such as FFKM can be used for temperatures above +200°C and aggressive chemicals.

What are the 5 most important advantages of FFKM O-rings?
1. Almost universal media resistance
2. temperature resistance of up to +340°C
3. elastic
4. available in a variety of mixtures (compounds)
5. excellent compression set (durability)

The starting point for the correct selection of an O-ring material is always the requirements of the application. To make it easy for you, we have put together a table with the properties of the most important O-ring materials.

Material

Temperature resistance

Chemical resistance

Elasticity

NBR

-30°C to +120°C

Low

High

HNBR

-30°C to +150°C

Medium

High

EPDM

-45°C to +150°C

Medium

High

SILICONE

-60°C to +200°C

Low

High

FKM (VITON)

-25°C to +200°C

Medium

High

FEP coated

-60°C to +200°C

High

Medium

PTFE

-250°C to +250°C

High

Low

FFKM

-40°C to +340°C

High

High

In summary, FFKM is far superior to all other O-ring materials. However, there is also a catch.

This is because O-rings made of FFKM are very expensive compared to other materials. They should therefore only be used where no other O-ring material would work.

It is therefore not surprising that FFKM O-rings are predominantly used in sensitive industries such as the chemical and pharmaceutical industries.

Basically, every industry has its own requirements and demands on the FFKM material.

What are the requirements for FFKM O-rings?
1. High temperature
2.Low temperature
3. Food-safe (FDA and USP Class VI approvals)

4. high purity (semiconductor applications)
5. Decompression resistant (NOROSK M710)

In order to cover a wide range of applications, FFKM is available in a large variety of compounds. The different composition of the material can be used to adjust the temperature range, elasticity or hardness, for example.

Summary Chapter 1: FFKM basic knowledge

Eule als NH Maskottchen

FFKM O-rings are clearly superior to all other O-ring materials in terms of thermal and chemical resistance. In addition, FFKM is produced in a variety of material mixtures.

#2 Pure variety: Overview of all FFKM O-ring compounds

We have compiled tables to give you a quick overview of all FFKM mixtures. The tables are divided into the 4 main application areas.

What are the 4 main areas of application for FFKM O-rings?
1. Chemical industry
2. Food and pharmaceutical industry
3. Oil and gas industry
4. Semiconductor industry

Important note: As a reference for the various mixtures, we have used our own FFKM brand “ECOLAST®” as a reference.

FFKM O-Ringe ECOLAST

FFKM mixtures: Chemical industry

Ecolast

Color

Temperature

Hardness

Applications

Data sheet

NH5600

Black

-25°C to +270°C

60 Shore

All-rounder

View

NH5750

Black

-25°C to +270°C

75 Shore

All-rounder

View

NH5751 HT

Black

-15°C to +330°C

75 Shore

High temperature

View

NH5755 HT

Black

-15°C to +330°C

75 Shore

High temperature

View

NH5756 HT

Black

-15°C to +340°C

75 Shore

Hot water, steam

View

NH5760 LT

Black

-40°C to +250°C

75 Shore

Low temperature

View

NH5900

Black

-20°C to +270°C

90 Shore

All-rounder

View

FFKM mixtures: Food and pharmaceutical industry

Ecolast

Color

Temperature

Hardness

Applications

Data sheet

NH4600

White

-20°C to +270°C

60 Shore

All-rounder: FDA, USP Class VI, 3-A Sanitary

View

NH4700

White

-20°C to +270°C

70 Shore

All-rounder: FDA, USP Class VI, 3-A Sanitary

View

NH5700

Black

-25°C to +270°C

70 Shore

All-rounder: FDA, USP Class VI, 3-A Sanitary

View

NH4701 HT

White

-15°C to +300°C

70 Shore

High temperature: FDA, USP Class VI, 3-A Sanitary

View

NH4702 LT

White

-40°C to +250°C

70 Shore

Low temperature: FDA, USP Class VI, 3-A Sanitary

View

NH4750 HT

White

-15°C to +315°C

75 Shore

High temperature: FDA, USP Class VI, 3-A Sanitary

View

NH4800

White

-20°C to +270°C

80 Shore

All-rounder: FDA, USP Class VI, 3-A Sanitary

View

NH4801 HT

White

-15°C to +300°C

80 Shore

All-rounder: FDA, USP Class VI, 3-A Sanitary

View

FFKM mixtures: Oil and gas industry

Ecolast

Color

Temperature

Hardness

Applications

Data sheet

NH6900

Black

-15°C to +260°C

90 Shore

All-rounder

AED NORSOK M710

View

NH6901 HT

Black

-15°C to +320°C

90 Shore

All-rounder

AED NORSOK M710

View

NH6902 LT

Black

-40°C to +250°C

90 Shore

All-rounder

AED NORSOK M710

View

So you can see how many different requirements are placed on FFKM O-rings. Accordingly, there are many compounds.

At this point, we will take a very brief look at the requirements and special features of the four application areas.

1. Chemical industry
Requirement: Aggressive media meet high temperatures
Solution: Mixtures with high chemical and thermal resistance

2. Food industry
Requirement: High purity requirements and cleaning with aggressive chemicals
Solution: Mixtures with high chemical resistance and FDA approval (food)

3. Oil and gas industry
Requirement: High pressure in combination with high temperatures
Solution: Compounds with 90 Shore and against decompression resistant

4. Semiconductor industry
Requirement: Extremely high purity requirements and plasma as a medium
Solution: Mixtures that are highly pure (do not release any substances) and are plasma-resistant

We know from experience that the variety of FFKM materials can be overwhelming. We hope that the tables have given you a rough overview.

If you have any questions about selecting the right mixture for your application, you are of course welcome to contact us for advice at any time.

Summary Chapter 2: FFKM compounds

Eule als NH Maskottchen

FFKM O-rings are used in many different industries. Every industry has its own specific requirements and there are correspondingly many FFKM compounds.

#3 Why is the durability of FFKM O-rings so high?

Both the extremely high thermal and chemical resistance are due to the solid chemical structure of FFKM.

Definition of media resistance

The media resistance of a material is measured by its resistance to the effects of a chemical.

Sounds great, but what exactly does that mean?

Every elastomer (rubber) consists of so-called polymer chains. These chains consist of individual molecules. The molecules that make up the chain are decisive for the chemical resistance.

Interestingly, the name of each material tells us roughly what molecules it is made of.

Example FFKM material
The two “F’s” in FFKM stand for Fluor. Fluorine (F) forms an extremely strong bond with the base molecule carbon (C). This bond is so strong that almost no medium has a chance of attacking the FFKM material.

In comparison:
FKM (VITON) 
also consists of carbon and fluorine bonds, but unlike FFKM it is not fully saturated. As a result, FKM is significantly more susceptible than FFKM.

For those of you interested in chemistry, here is the structure of the polymer chains:

FFKM polymer chain: Only with strong fluorine bonds

Darstellung einer chemischen FFKM-Polymerkette

FKM polymer chain: With fluorine and hydrogen bonds

Darstellung einer chemischen FKM-Polymerkette

At this point, we could well imagine you asking yourself:
What is FFKM not resistant to?

Care must only be taken with 2 media if FFKM is to be used
1. Media with high fluorine content (like with like is not compatible)
2. Molten alkali metals (Caution: extremely toxic)

Otherwise, you can use FFKM materials almost without hesitation, at least as far as chemical resistance is concerned.

Summary of Chapter 3: FFKM resistance

Eule als NH Maskottchen

FFKM is almost universally resistant to media. Due to its solid chemical structure, FFKM is clearly superior to other elastomers such as NBR, EPDM and FKM.

#4 What do I need to consider when designing and installing FFKM O-rings?

The design and installation of FFKM O-rings is not much different from other elastomer materials such as NBREPDM or FKM.

As an overview, we have compiled a comparison table between FFKM and FKM with the most important design features.

Note: The data in the table refers to a flange seal.

Feature

FFKM

FKM

Grouting

12-18%

15-25%

Groove clearance after grouting

20%

20%

Max. Elongation during assembly

<50%

<50%

Max. Permanent stretching

3%

3%

Max. Permanent compression

3%

3%

Assembly grease

Mineral oil and silicone greases

Mineral oil and silicone greases

In summary, there are only differences in the desired compression.

This is due to the fact that no swelling is generally assumed with FFKM, as FFKM is almost universally resistant to media. Accordingly, the compression may also be set somewhat lower.

You can also make things very easy for yourself with assembly greases. Just like FKM O-rings, FFKM O-rings are resistant to all oils and greases. You can therefore use any grease or oil during assembly.

Otherwise, as with all elastomers, the 5 basic installation instructions apply

1. No sharp edges
2. Use suitable tools
3. Clean the groove space thoroughly before installation
4. Use suitable assembly grease
5. Observe an insertion slope of approx. 20%

Summary Chapter 4: FFKM design and installation

Eule als NH Maskottchen

FFKM O-rings are largely designed and fitted in the same way as all other O-rings. Due to its excellent durability, even less attention needs to be paid.

#5 Are there suitable alternatives to FFKM O-rings?

The direct answer: Yes, FEP coated O-rings and pure PTFE O-rings are suitable alternatives to FFKM O-rings to a certain extent.

The advantage of FEP and PTFE O-rings is that they are significantly cheaper than FFKM.

But what are the disadvantages? We can find this out with a brief comparison of the key properties.

FFKM (NH5756 HT)

FEP/SILICON

PTFE

Universally resistant

Universally resistant

Universally resistant

-15°C to +340°C

-60°C to +205°C

-250°C to +250°C

Elastic

Partially elastic

Rigid

Result: In most cases, it only makes sense to replace FFKM O-rings with FEP or PTFE O-rings if media resistance is crucial. This is because O-rings with an FEP jacket or made of pure PTFE are also almost universally resistant to media.

Important: 2 points must be observed during replacement

1.If, for example, you want to replace a 20 x 2 FFKM O-ring with an FEP or PTFE material, then the O-ring or, if applicable, the O-ring must be replaced with a new one. the groove
must be redesigned. Due to the rigidity and the higher manufacturing tolerances (FEP O-rings), the O-ring cannot simply be replaced 1:1.

2 Despite the rigidity of FEP and PTFE O-rings, installation must be possible. FEP O-rings can only be used as flange and rod seals and PTFE O-rings can even only be used as flange seals.

While FEP O-rings can at least be stretched or compressed a little, this is almost no longer possible with PTFE O-rings.

Side tip: If you place FEP O-rings in hot water at 80°C before fitting, they become slightly more elastic. This also applies to all other elastomers.

Summary Chapter 5: Alternatives to FFKM O-rings

Eule als NH Maskottchen

Yes, FEP-coated and pure PTFE O-rings are suitable alternatives to FFKM O-rings, but only if media resistance is the main factor.

#6 Interesting questions: quick and easy answers

Finally, we would like to answer a few questions that we are frequently asked in everyday life.

#6.1 What is the difference between FFKM vs. FFPM O-rings?

There is no difference. FFPM is just an outdated term. Nowadays, perfluoro rubber is abbreviated FFKM in accordance with ISO 3601. Accordingly, both abbreviations stand for the same material: perfluoro rubber.

#6.2 What is the difference between FFKM vs. FKM O-rings?

FKM stands for fluororubber and FFKM for perfluororubber. While FKM has a fluorine content of approx. 60-65%, FFKM has a fluorine content of approx. 75-85%. Accordingly, perfluoro rubber is clearly superior to normal fluoro rubber.

#6.3 What is the difference between FFKM vs. Kalrez O-rings?

FFKM is the material designation and stands for perfluoro rubber. Kalrez, on the other hand, is a trademark for FFKM O-rings from DuPont. While Kalrez was the only FFKM brand many years ago, there are now several new FFKM brands.

ECOLAST = NH O-RING
KALREZ = DuPont
SIMRIZ = Freudenberg
Chemraz = Greene Tweed

#6.4 Why is the price of FFKM O-rings so high?

This is solely due to the price of raw materials. The price per kilogram of FFKM raw material is several thousand euros. This means that FFKM is only used where it is absolutely necessary.

#6.5 How long can FFKM O-rings be stored?

FFKM O-rings have a service life of 13 years.

How long an O-ring may be stored depends on the DIN 7716 . It contains the requirements for optimum elastomer mounting.

“I am convinced that we should share our knowledge with the world. I hope I have been able to answer all your questions. If you have any further questions, please feel free to contact us at any time. We will be happy to help you.”

Picture of Luke Williams
Luke Williams

Lord of the O-rings
Author of the sealing academy

Do you have any questions on this topic? Then please contact us!

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