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Technical Library / Seals and Gaskets

In the area of vacuum technology mainly elastomer gaskets are used for ISO-KF (small flange) and ISO-K (clamped flange) joints. When subjected to pressure or tensile loads they can be reversibly deformed whereby the total volume remains unchanged. Generally Viton© or Perbunan© are used since the permeability of these materials for gases is low. For special applications also other sealing materials as well as various metal gaskets can be supplied.

Name FPM NBR PTFE EPDM VMQ FFPM
Chemical Name Flour rubber Acryl Nitril Butadien rubber Poly Tetra Flour Ethylen Ethylen Propylen Dien rubber Silicone rubber Perflouro rubber
Sustainable Heat Exposure -20 - 200°C -25 - 120°C -200 -200°C -40 - 140°C -55 - 200°C -30 - 320°C


Areas of application

FPM: Well resistant to mineral oil, petrol, water, acids and weak alkaline solutions. Not resistant to polar solvents like, for example, acetone, low molecular organic acids (formic acid and ethanoic acid), ammonia gas and super heated steam.

NBR: Resistant to mineral oil, petrol, water, acids and weak alkaline solutions. Not resistant to polar solvents like, for example, chlorinated hydrocarbons, aromatic compounds like, for example, benzene, esters and ketones. Moderately resistant to ozone and environmental influences.

PTFE: Universally resistant to almost all media except fluorine gas under pressure. Since Teflon is not elastic like rubber, special clamping rings which generate very high pressing forces should be used in the case of KF joints.

EPDM: Highly resistant to hot water and steam up to 130°C, well resistant to chemicals and also media which have an oxidising effect. Not resistant to mineral oil, animal and plant oils, petrol, aromatic and chlorinated hydrocarbons.

VMQ: Excellent temperature resistance (for water vapour up to 120 °C). Resistant to mineral oil. Not resistant against petrol, chlorinated and aromatic hydrocarbons, acids and alkalis. Permeation is relatively high.

FFPM: In regards to media and temperature resistance FFPM exceeds FPM. FFPM is used if highest requirements need to be met, in the semiconductor industry, for example.

Other materials available upon request.

 

Metall Gaskets and Seals

If in certain applications special requirements like, for example, low permeation, good resistance to chemicals, resistance to high temperatures or pressures below 10-7 mbar can no longer be fulfilled using elastomer gaskets, then metal gaskets will have to be used. For ISO-KF and ISO-K joints various types of metal gaskets have been developed, and for the UHV range even special so called ConFlat (CF) flanges with metal gaskets.

In comparison with elastomers, metals require much higher forces for their deformation. Thus on the one hand flanges made of stainless steel should be used and on the other hand in the case of ISO-KF joints special clamping rings or clamping chains should be used instead of the standard clamping rings.


Al knife edge seal with clamping chain 		During assembly Aluminum knife edge seals are subjected to such high pressures that they are irreversibly deformed. During assembly they adapt themselves to the contour of the flange thereby equalising any slight roughness owing to production con­straints. The remaining amount of elastic de­for­mation is such that thermally induced contrac­tions and flowing of the sealing material can be compensated. Aluminium gaskets can be used at temperatures up to 200 °C.
Helicoflex©-Gaskets consist of an elastic Nimonic spring and an inner jacket of Inconel and a soft outer jacket usually of aluminium. Within the spring a stainless steel spacing ring prevents excessive deformation of the spring. The entire arrangement is supported and guided by an Inconel centering ring. Since the spring is elastically compressed, this type of metal seal can be reused several times. The operating temperature range spans -272 to 280°C, when using an outer jacket made of nickel the range even extends to 600°C. The maximum permissible overpressure is 60 bar at room temperature and 20 bar at 200°C.
Helicoflex©
In the CF / UHV range mostly gaskets made of OFHC (oxygen free high conductivity) copper are used. A description of the UHV sealing system is provided on the first pages detailing our range of UHV products.