Static Seals

Static seals are universal sealing elements that impress with easy installation, small footprint and versatile application is the reason why they are used very frequently. ttv ensures that these seemingly simple parts are still produced with the utmost care.

ttv seals are distinguished by the highest technical quality standards and the best materials, as a specialist in sealing technology, we know, the seemingly simple parts need to be.

Catalogue
O- and X-Rings
Technical informations O- and X-Rings
O-Ring Tolerances DIN 3771
Instructions for storing elastomers
Data Sheet
O- and X-Rings

O-Rings

General

An O-Ring is a circumferentially closed, ring-shaped sealing element, which prevents unwanted discharge or loss of media. It requires little installation area and can be easily mounted. Therefore, the O-Ring is the most widely used seal. Other advantages are its functional reliability and very cost-effective manufacturing.

Description

ttv O-Rings are manufactured and controlled in accordance to DIN 3601 (formerly 3771). They are produced seamlessly in a heated injection or compression mould by vulcanization. As for the material variations of elastomer materials are used.

The designation of the O-Ring is composed of three elements:
» d1 = Dimensions of the inner diameter (mm)
» d2 = Cord thickness (mm)
» Material designation and its hardness (elasticity)

Working principle

The O-Ring marks a strikingly simple form and reliable function. The sealing action of the O-Ring is formed by the deformation of its cross-section d2 in a groove.

Thereby, the sealing gap at the groove base and the contact or sealing surface is sealed. As a result a surface pressure is generated, which makes the sealing effect possible. The maximum deformation of the O-Ring cross section depends mainly on the depth of the groove. With the right groove design and material selection, a dynamic or static seal can then be employed within the temperature limits of the material.

In the operating state the pressure of the medium increases the deformation and therefore its sealing function. If this pressure drops to „zero“, then the deformation is close to reaching installation condition once more.

Important advise

The cord diameter d2 must always be greater than the installation area.

The compression is specified as a percentage. Designated as pressing is that percentage of the cord diameter d2, by which it is compressed in the installation state. The compression is consequently directly related to the depth of the groove. Equal percentage of compression force and increase deformation in accordance with the increasing cord strength d2. To compensate for this, the percentage of the compression will be reduced with increasing cord diameter.

Existing pressure can be advantageous for the sealing. This is additionally deforming the O-Ring; the pressure will be supported in in some areas. Pressure bears down on the O-Ring on the pressure-remote groove side. In order to avoid gap migration at the O-Ring, this should be kept to a minimum. For a radial sealing tolerance of H8 / f7 is anticipated, for an axial sealing it is H11 / h11.

If this cannot be ensured, or high pressures are to be expected, a high material hardness of the O-Ring should be chosen. Otherwise, a gap migration?/?extrusion may occur resulting in the destruction of the O-Ring.

Applications

O-Rings can be applied in two areas:
» static sealing in resting machine parts
» dynamic sealing in moving machine parts

Static sealing
O-Rings are very suitable for the sealing of machine elements, which do not move comparatively to each other. Here, with O-Rings pressures up to 1000 bar are sealed, as long as the installation area is carried out properly, the application and critical design areas are accurate and correct material has been selected (Additional Backup-Rings are to be used if in doubt).

Dynamic sealing
In dynamic applications, O-Rings are used successfully as a sealing element. Here, however, more likely at lower pressures, velocities or in small installation areas. Because it comes to frictional resistance with e.g. the movement in hydraulic or pneumatic components, a smaller compression of the O-Ring is selected as for static sealing. To prevent friction or premature wear of the O-Ring caused by dry running, good lubrication should always be guaranteed.

For the translational (back-and-forth) motion and for spiral motion the installation areas are the same. In the application fields of hydraulics and pneumatics, however, they differ in air pressure and lubrication conditions.

Materials

The primary criterion for selection of materials comes down to the operating temperature and the media resistance. Since they contribute towards the life of the seal, the mechanical properties of an elastomeric composition need to be taken into account.

The ttv resistance guide gives information on the chemical resistance of different materials. Technical rubber materials are subject to an exact recipe. In comparison of all the media to be sealed containing mixed components, the polymer is in relation to its chemical resistance the weakest of the components. The selection of the right material is dependent on the right choice of the base polymer. In practice, further recipe-related influences in accordance to the nature and amount of the plasticisers and fillers, would decisively alter the characteristics.

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

IngredientPercentage
Rubber (polymer)40
Fillers35
Plasticisers20
Auxiliary processing means1.3
Durability means 1.3
Activators1
Cross-linking agents0.7
Catalysts0.7
Mix components of a sample recipe

Temperature and environment

Main materialsTemperature-resistancerange
Nitril NBR-30°C+120°CHydraulic oil, grease, hydrocarbons, oils, lubricants, vegetable oil, water, butane, compressed air
HNBR-35°C+150°COzone, UV, hot water, sulphurous oils
Chloropren CR-40°C+120°CAir, 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°CFood resistant (when peroxide cross-linked): water, beverages, use with inflammable liquids, vapour, diverse acids, caustic soda, glycols, ozone, hot water
Silikon VMQ-60°C+225°CLow and high temperatures, air, oxygen, inert gas, low concentrated bases and acids, ozone
Fluorenkohlenstoff FKM-15°C+240°CGood oil resistance, hydraulic liquids, solvents, use with inflammable oils and chemicals, ozone
PTFE-150°C+260°CExcellent chemical resistance, electric insulator, low friction coefficient

 

 

 

Other materials and mixtures upon request.

 

 

Surface-treated O-Rings

Since elastomeric materials typically point out "anti-sliding“ and "sticky“ surfaces, it is often necessary to improve the coefficient of friction of an O-Ring. Various methods can reduce slip friction and for easier assembly and even achieve a lifetime extension.

Type of treatmentDescriptionColour/Aspect
Short termSiliconisationA silicone film is sprayed onto the parts to be treatedGlossy, greasily, transparent
Intensification of slidingAdding a molybdenum disulfide coating Molybdenum powder coating by tumblingSilver-like
Long termTalcum powder coatingTalcum powder coating by tumblingDry, white
PTFE powder coatingPTFE powder coating by tumblingDry, white


Even better friction reduction over a long period can be achieved by intensifying sliding additives in elastomer compositions, such as molybdenum disulfide (MoS2) or PTFE.

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 advise

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.


Backup-Rings


General

The main function of a Backup-Ring is to prevent gap migration under pressure with large gaps. The Backup-Ring prevents this consistently and thus a rapid O-Ring destruction.

Installation

Installation is simple and fast. The Backup-Ring is fitted at low pressure side. In case of a double-acting seal two Backup-Rings can be installed on both sides.

Advantages of this assembly

The life of the seal is extended. The costs of the sealing system are low: it allows more tolerance of parts to be sealed, thereby reducing the processing cost.

Operation conditions Temperatures of:
–20 °C to +200 °C with FPM
–30 °C to +120 °C with NBR

PTFE Backup-Ring

The function of a PTFE Backup-Ring is similar to that of a Backup-Ring of NBR, but it has a wider range of applications:
Temperatures of –150 °C to +250 °C


X-Rings

Description

X-Rings are double sealing four-lobe seals that are characterised by their square profile. The X-Ring is defined by its inner diameter d1 and its cord thickness d2.

 

Mode of action

The X-Ring is symmetrically shaped. It can adapt to every situation and withstand stress in any direction (radial, axial). The grouting increases dependent on the pressure. At high pressure should use Backup-Rings.

Advantages

No risk of torsion and a low friction coefficient:
» by lubricious materials
» by low bias
» through fat reserves between the lips

A better seal (in relation to an O-Ring) is mainly caused by a duplicate contact. Due its geometry the X-Ring can be used in dynamic applications with rotating movements (1m?/?s).

X-Rings in dynamic applications

The main advantage of the X-Ring is its high stability in dynamic applications where O-Rings provide a low performance.

X-Rings have four lips, which result in greater sealing surface. The four-lip seal was developed to achieve an improved lubrication of the seal and to avoid a rolling of the seal or spiral errors.

In contrast to O-Rings, which can roll in the groove and can cause a rotation, X-Rings will slide easily on. Also in regards to spiral errors X-Rings are much more resistant.

Standards and Approvals

As it is the case with O-Rings, most X-Rings are produced in accordance for American Produced standards with inch sizes and AS numbers.

The dimensions of the X-Ring in accordance with the American standard AS568 and the associated O-Ring numbers. Compared to the grooves for O-Rings the standard grooves for X-Rings are deeper. For groove dimensions for X-Rings, there is a greater scope available, since X-Rings needs less pressure and can compensate for this. That means less friction and therefore less wear of the seal.


END-CAPS AND USIT-RINGS

ttv End-Caps are used to seal holes and boreholes in housings or apertures for shaft and axis inputs. As a specialist in sealing and bearing technology, we also offer perfect solutions for these technical requirements.

Whether you require standard End-Caps, whole or partially gummed variants or custom designed, we use the latest technology and the best materials.

ttv Usit-Rings are offered as standard screw gasket seal in carbon steel or stainless steel and in NBR/FPM/EPDM. Our varied supply of rubber body designs ensure your application.

It secures the function and longevity of your machine using End-Caps and Usit-Rings from ttv.


End-Caps

Type VK

End-Caps consist of a metal-component (deep-drawing sheet metal) and of a rubber sleeve on the outside. They are used to close apertures and core drilling holes. In engineering they often replace terminal flanges or lids.

In accordance with DIN 3760 the End-Caps have an excess on the outer diameter corresponding with size, so that the prefabricated plummer block-gasket sealing-drillings and press fit is achieved.

Advantages of the End-Cap
• compensation of thermal expansion
• no risk of frictional corrosion
• effective airtight protection against grease or dirt
• mounting possibilities for split casings
• low-cost static sealing

Catalogue End-Caps
and Usit-Rings
Data Sheet End-Caps

Type VK H+H

As an alternative to the standard End-Cap there is the „half and half” End-Cap, which is only partly rubberized on the outer sheath.

Special advantages of this new development
• good static sealing (no pop-out effect)
• non-positive fit to the case drilling
• good thermal conduction
• higher pressure stability

Additionally we offer a variety of special solutions, such as with a hole or a vent hole.

Material choice at a glance

End-Caps

Raw materialDesignationTemperature range
Nitrile butadiene rubberNBR 70-30°c+100°C
Fluoric rubberFPM 70-20°c+180°C

USIT-RINGS

Usit-Rings are commonly referred to as screw gasket seals or flange connection seals. They consist of a flat, metallic disc and a rubber bulge on the inside or outside. The metallic disc is available in both steel and stainless steel, the rubber seal can be delivered in either NBR or even Viton.

Our range of dimensions offers both metric as well as inch sizes.

Catalogue End-Caps
and Usit-Rings
Dimensions
Usit-Rings
Data Sheet Usit-Rings

Material choice at a glance

USIT-RINGS

Raw materialDesignationTemperature range
Nitrile butadiene rubberNBR 70-30°c+100°C
Fluoric rubberFPM 70-20°c+180°C
Ethylen-Propylen-Dien-RubberEPDM 70-40°c+150°C
SteelAISI 1020
Stainless steelAISI 304 / ASI 316