O-rings

O-rings made of PTFE are used mainly in the chemical industry, pharmaceutics and in medical engineering as static seals in flange connections, caps, etc. Due their good chemical resistance they are compatible with most liquids and chemicals. Exceptions are liquid alkali metals and some fluorine compounds. Furthermore, they are physiologically safe and sterilizable.

Other advantages are their wide operating temperature range from approx. -200 °C to +260 °C and their stick-slip free running capability. Since they are machine cut, they can be manufactured up to a diameter of 1.000 mm in all dimensions.

Application range

Pressure: ≤150 bar; Temperature: -200°C to +210°C

Application media

Universally applicable (exceptions are with molten alkali metals and fluorine compounds)

Materials

Materials Typical properties Operating conditions
CCN-01 (PTFE pure) low gas permeability, universal chemical resistance, good reverse bending strength standard material, for food environments
CCN-02 (PTFE modified) very low gas permeability, universal chemical resistance for enhanced requirements on gas tightness and surface finish
PTFE conductive static dissipative properties for ATEX requirements (hazard ex. zones)

Construction information

The expansion and compression of PTFE O-rings is only limitedly possible. Due to their low elasticity, the selected size of the PTFE O-ring must be the same as the nominal cross-section to be sealed. They should be installed only in easy-to-reach split grooves.

Installation recommendations for an axial static installation.

O-ring Groove dimensions
Ring cross section

d2

Groove width

B5 + 0,1

Groove depth

T3 + 0,05

Radius
R1
1,50 1,70 1,30 0,20
1,60 1,80 1,40 0,30
1,78 – 1,80 2,00 1,60 0,40
2,00 2,20 1,80 0,50
2,40 2,60 2,15 0,50
2,50 2,80 2,25 0,50
2,62 – 2,65 2,90 2,35 0,60
3,00 3,30 2,70 0,80
3,10 3,40 2,80 0,80
3,53 – 3,55 3,90 3,15 1,00
4,00 4,40 3,60 1,00
5,00 5,50 4,50 1,00
5,30 – 5,33 5,90 4,80 1,20
5,70 6,30 5,10 1,20
6,00 6,60 5,60 1,20
7,00 7,70 6,30 1,50
8,00 8,80 7,20 1,50
8,40 9,20 7,55 2,00

Slit PTFE O-rings

Since PTFE O-rings are harder than elastomer O-rings, they require higher contact pressures. This can be countered to a certain extent by using slit ring designs. The O-ring must always be installed in such a way that the pressure of the medium causes the slit to expand.

Design I – axial plunge cut, inside

Design A – axial plunge cut, outside

Design M – radial plunge cut

Design SA – plunge cut 45° offset, inside

Design SA – 45° plunge cut, outside

FEP-encapsulated O-rings

Depending on the application temperature range and medium, FEP-encapsulated O-rings have an elastic core made of either FKM or VMQ. Due to the very high chemical resistance of the FEP envelope, the core material is protected against attack by the medium. (Please find the material overview at the end of this page.)

O-rings are therefore ideal for very high chemical and thermal stresses and present, at the same time, the properties of customary elastomers. Mounting requires special care since FEP is limitedly expandable and compressible. Its flexibility can be increased when heated up to 80 °C to 100 °C in hot water or oil.

Application range

Temperature: -55°C to +200°C (depending on the core material)

Elastomer-O-rings

Elastomer O-rings are universal seals with many advantages. A high sealing effect and small installation space requirement combined with low twisting forces distinguishes this type of seal. It is used mainly in static applications. An elastomer O-ring is suitable for use as a dynamic seal or in linear and rotary motions only to a limited extent.

Elastomer O-rings are ideally suited for large pressures and high thermal stresses. They show minimal abrasion wear and have a high service life. These low-priced seals are available in various shore hardness grades and for many media.

In case of poor lubrication stick-slip effects may occur. After long standstill periods there is a risk of adhesion and gap extrusion is also possible.

O-ring cross sections d2 as per standard

Standard / Regulations Cross sections, Cross section diameter (d2) of O-rings in mm
International standard ISO 3601-1 1,00 1,50
5,00
2,00
5,50
2,50
6,00
3,00
7,00
3,50
8,00
4,00
10,00
4,50
12,00
Internationale Norm ISO 3601-1 1,80 2,65 3,55 5,30 7,00
Swedish standard ISO 1586 1.60 1,60 2,40 3,00 5,70 8,40
French standard NFT47-501 1.90 1,90 2,70 3,60 5,33 6,99
Japanese standard JIS B 2401 1,90 2,40 3,10 3,50 5,70 8,40
American standard AS 568 A

Britsh standard ISO 1806

1,78 2,62 3,53 5,33 6,99
American standard AS 568 A series 990 1,02
2,08
1,42
2,20
1,63
2,46
1,83
2,95
1,98
3,00
Special dimensions Customer-specific O-rings Further cross sections on request.

O-ring materials overview

Standard materials

ISO 1629 designation Base elastomer Trade name Properties
NBR Nitrile butadiene rubber Chemigum®, BunaN®,
Nipol N®, Krynac®,
Paracryl®, Perbunan
N®, Hycar®, Elaprim®
-25° to +100 °CA synthetic rubber with outstanding resistance to fuels, oils, hydraulic oils, lubricating greases and other aliphatic hydrocarbons. Has good physical properties such as high abrasion resistance and stability and good temperature resistance.
EPDM EPDM Ethylene propylene diene rubber Buna AP®, Dutral®,
Epcar®, Keltan®,
Nordel®, Royalene®,
Vistalon®
-40° to +140°C

Very good ozone, aging and weather resistance, also hot water and steam resistant. Resistance to cold is good compared to other synthetic rubbers. Shows strong swelling behavior in aliphatic, aromatic and chlorinated hydrocarbons.

VMQ VMQ Vinyl methyl rubber / Silicone Silopren® -50° to +210 °C
Very good temperature resistance. Oil resistance is similar to NBR, though its good physical and mechanical properties are not reached.Not suited for permanent use in hot water or steam.
FKM Fluoroelastomer Viton®, Fluorel®,
Technoflon®
-20° to +200 °C

Very good resistance to the effects of mineral oils, aliphatic and aromatic hydrocarbons as well as chlorinated hydrocarbons, concentrated and diluted acids and weak alkaline solutions. High mechanical values, very low gas permeability as well as excellent resistance to aging, very good compression set values.

Special materials (a selection)

ISO 1629 designation Base elastomer Trade name Properties
FEPM FEPM Tetrafluoroethylene propylene rubber Aflas® -30° to + 200 °C
Peroxide cross-linked TFE elastomer, high resistance to a number of specific media and chemicals such as e.g. hot water, steam, acids, bases, ammonia, bleaching substances, acidic gases (H2S) and oils as well as amines, doped engine and transmission oils, brake fluids and oxidized media.
FFKM FFKM Perfluoroelastomers Kalrez®, ZALAK®,
PAROFLUOR®,
CHEMRAZ®, SIMRIZ®
-15° to + 270 °C
Perfluoroelastomers combine the properties of elastomers with the almost universal chemical and temperature resistance of PTFE. The application of this extremely expensive material is economical only in very few cases.
FVMQ FVMQ Fluorosilicone FSE®, Silastic®,
Sylon®
-45° bis + 175 °C
Better resistance to oils, fuels and solvents (in particular aromatic and chlorinated hydrocarbons and ethanol) compared to MVQ. For applications with high requirements (wide temperature range together with an aggressive media environment), e.g. seals in automobile fuel systems, in the aerospace and also chemical industry.
HNBR HNBR Hydrogenated nitrile butadiene rubber Therban®, Zetpol® -15° to + 150 °C
High mechanical resistance, improved abrasion resistance and low compression set. Media resistance is comparable to that of NBR combined with an increased resistance to steam.

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