O-rings , cords

Description
O-rings are closed circular rings of circular cross-section. They are made through vulcanisation from form tools as a complete ring. The sealing function of the O-ring is achieved by the deformation of the cross-section when installed and compressed in its housing.

Hardness
O-ring hardness is usually in Shore A, or IRHD. Standard is 70Sh (Shore)

Fields of application
O-rings are used predominantly for sealing non-moving machine and system components (static application) and media in liquid and gas form, e.g. flange and cover seals, threaded tube connections and the cylinder head and cylinder bottom for hydraulic cylinders. Under certain conditions it is also possible to use O-rings with reciprocating, rotating and helical movements (dynamic application).

Materials
NBR -  Good chemical resistance to mineral oils and greases, hydraulic oils H, HL, HLP, non-inflammable hydraulic pressure fluids HFA, HFB, HFC to approx. +50°C and water to max. +80°C 
FPM – Good chemical resistance to mineral oils and greases, synthetic oils and greases, engine, transmission and ATF oils to approx. +150°C, fuels, non-flammable hydraulic pressure fluids HFD, aliphatic, aromatic and chlorinated hydrocarbons, water to max. +80°C, excellent resistance to weathering, ozone and ageing, very low gas permeability (and therefore excellent for vacuum application) and resistance to a wide range of chemicals.
HNBR – HNBR is obtained by fully or partially hydrogenating NBR. It leads to considerable improvement in resistance to heat, ozone and ageing, and gives it very good mechanical properties, e.g. good resistance to wear. The media resistance compares to that of NBR. HNBR has a good resistance to some refrigerants. The temperature application range is from -30°C to +150°C.
MVQ – Good resistance to water (up to 100 °C), aliphatic engine and transmission oils, animal and plant oils and fats. VMQ is generally not resistant to fuels, aromatic mineral oils, steam (short term up to 120 °C possible), silicone oils and greases, acids and alkaline compounds.
PTFE – Nearly universal chemical resistance (aggressive acids, bases, alcohols and oils). Resistant to high and extremely low temperatures .

Housing
The installation housings (grooves) for O-rings should if possible be produced with right angles and should be processed with care. Burrs, scratches and notches should be avoided. The dimensions for the required depth and width of the groove depend on the particular application and cross-section.