O-Rings
Available in all dimensions, materials and variants

ttv offers you the full range of O-rings in all desired dimensions, materials and variants. Due to their circular cross-section, O-rings can seal both axially and radially. The sealing pressure of the O-rings results from the superposition of the precompression and the system pressure to be sealed. Our team is always available to answer your questions about the use of O-rings.

Overview

ProfilE Design Material Hardness (Shore A) Color Temperature (°C)/temporarily
O-Ring NBR 70 black -30 to +100 / +120
O-Ring NBR 80 black -30 to +100 / +120
O-Ring NBR 90 black -30 to +100 / +120
O-Ring HNBR 70 black -30 to +130 / +150
O-Ring FKM 70 brown -20 to +200
O-Ring FKM 75 brown -20 to +200
O-Ring FKM 80 brown -20 to +200
O-Ring FKM 90 brown -20 to +200
O-Ring FKM FEP-encapsulated transparent/brown -20 to +200
O-Ring EPDM 70 black -40 to +110 / +130
O-Ring EPDM perox. cross-linking 70 black -40 to +150 / +170
O-Ring VMQ 70 red -50 to +200
O-Ring VMQ FEP-encapsulated transparent/red -50 to +200
O-Ring PTFE white -200 bis +260

O-rings from ttv are manufactured and inspected according to the new DIN 3601-1 (formerly 3771). They are manufactured by vulcanisation in heated injection or compression moulds in an impact- and seamless manner. Different elastomer materials are predominantly used as the material. These can be made of nitrile NBR, HNBR, chloroprene CR, ethylene-propylene-diene rubber EPDM, silicone VMQ, fluorocarbon FKM or PTFE.

The designation of the O-ring consists of three elements:

  • d1 = inner diameter (mm)
  • d2 =cord thickness  (mm)
  • Material designation and its hardness (elasticity) 

The primary criteria for material selection are the operating temperature and media resistance. Since they are also decisive for the service life of the seal, the mechanical values of an elastomer compound must also be taken into account.

The ttv resistance list provides information on the media resistance of the different materials. Technical rubber materials are subject to an exact formulation. In a comparison of the media to be sealed of all contained compound components, the polymer is the weakest component in terms of chemical resistance. The selection of the right material is therefore often limited to the correct choice of the base polymer. In practice, other formulation-related influences such as the type and quantity of plasticisers and fillers used can decisively change the properties.

Polymer compatibility alone is no guarantee for reliable sealing, but it is an important prerequisite.

 
Ingredient Percentage%
Rubber (polymer) 40
Fillers 35
Plasticisers 20
Auxiliary processing means 1,3
Durability means 1,3
Activators 1
Cross-linking agents 0,7
Catalysts 0,7


Mix components of a sample recipe

main Materials Temperature-resistance Range
Nitril NBR -30°C  +120°C Hydraulic oil, grease, hydrocarbons, oils, lubricants, vegetable oil, water, butane, compressed air
HNBR -35°C +150°C Ozone, UV, hot water, sulphurous oils
Chloropren CR -40°C +120°C Air, ozone, water up to 80 °C, vegetable oils, oxygen, caustic soda, fatty alcohol, chlorine, refrigerant gas, alimentary applications, CO2
Ethylen / Propylen EP -45°C +110°C Food resistant (when peroxide cross-linked): water, beverages, use with inflammable liquids, vapour, diverse acids, caustic soda, glycols, ozone, hot water
Silicone VMQ -60°C +225°C Low and high temperatures, air, oxygen, inert gas, low concentrated bases and acids, ozone
Fluorocarbon FKM -15°C +240°C Good oil resistance, hydraulic liquids, solvents, use with inflammable oils and chemicals, ozone
PTFE -150°C +260°C Excellent chemical resistance, electric insulator, low friction coefficient


Other materials and mictures upon request.

The O-ring as a sealing rubber convinces with its impressively simple shape as well as its reliable function. The sealing effect of the O-ring is created by the deformation of its cross-section d2 in a groove.

This closes the sealing gap at the base of the groove and at the contact or sealing surface. Thus a surface pressure is generated which makes a sealing effect possible. The maximum deformation of the O-ring cross-section depends essentially on the groove depth.

With the correct groove design and material selection, a seal can be used dynamically as well as statically, within the temperature limits of the material.

 

Due to the small space requirement, the simple assembly and the wide range of applications, these sealing rubbers of different materials, such as NBR, FKM or PTFE, are probably the most universal solutions among the seals.

In the operating state, the pressure of the medium increases the deformation and thus the sealing function. When this pressure drops to "zero", the deformation almost returns to the installed condition.

To a certain extent, sealing rings can be replaced or stretched during installation without impairing the sealing function. However, the compression of the sealing ring should not exceed 4%. Otherwise it may warp in the groove. 

The expansion in relation to the inner diameter should not exceed 5% when installed. Otherwise there may be a disproportionate reduction in cross-section and thus a severe flattening at the inner jacket. According to Guldin's rule, 1% elongation of the inner diameter results in 0.5% reduction of the shear thickness.

Further important information on O-rings can be found here.

Important note

The cord thickness D2 must always be greater than the installation space.

The compression is given as a percentage value. The compression is defined as the percentage of the cord thickness d2 by which it is compressed in the installed condition. The compression is therefore directly related to the groove depth. With the same percentage compression, the deformation forces increase with increasing cord thickness d2. To compensate for this, the percentage compression is reduced with increasing cord diameter. 

Existing pressure can be advantageous for sealing. This additionally compresses the O-ring, the pressure effect is supported in certain areas. Pressure presses the O-ring against the groove side facing away from the pressure. To avoid gap migration of the O-ring, it should be kept as small as possible. For radial sealing, a tolerance of H8 / f7 should be provided, for axial sealing H11 / h11.

If this cannot be ensured or if high pressures are to be expected, a material hardness as high as possible should be selected for the O-ring. Otherwise, gap migration / extrusion and thus destruction of the O-ring may occur.

O-rings are used in two areas of application:
  • static sealing for stationary machine parts
  • Dynamic sealing for moving machine parts

Static sealing
O-rings are very well suited for sealing machine elements that do not move relative to each other. Pressures of up to 1000 bar can be sealed with O-rings, provided that the installation space is properly designed, the application is structurally correct and the correct material has been selected (in case of doubt, additional back-up rings should be used).

Dynamic sealing
O-rings are successfully used as sealing elements in dynamic applications. Here, however, they tend to be used at lower pressures and speeds or in small installation spaces. Since frictional resistance occurs during movement, for example in hydraulic or pneumatic components, a smaller compression of the O-ring is selected than for static sealing. To prevent friction losses or premature wear of the O-ring due to dry running, good lubrication should always be ensured.

The installation spaces are the same for translatory (reciprocating) movement and for helical movement. In the application fields of hydraulics and pneumatics, however, they differ due to the different pressure ratios and lubrication conditions.

Since elastomer materials typically have "gripping" and "adhering" surfaces, it is often necessary to improve the coefficient of friction of an O-ring. By means of various slide intensification processes, a reduction in friction can be achieved for ease of assembly through to service life extension.

PFEIL OBEN typ of treatment description colour/ Aspect
Short term Siliconisation A silicone film is sprayed onto the parts to be treated Glossy, greasily, transparent
Intensification of sliding molybdenum disulfide coating Molybdenum powder coating by tumbling Silver-like
Long term Talkumierung Talcum powder coating by tumbling Trocken, weiß
Pfeil unten PTFE powder coating PTFE powder coating by tumbling Dry, white
O-Rings under pressure
The tendency to extrusion / gap migration mostly depends on the gap measure within the machine parts. The gap is dependant on the processing, manufacturing procedure and tolerance.


Important note

It is advisable to implement the clearance as small as possible. A larger seal clearance can result in the destruction of the O-Ring by gap migration.
O-Rings with a hardness of 90 Shore A allow for a slightly larger gap than standard-O-Rings in 70 Shore A.

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