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RS NBR 70

Description
Product group: RS cord

Materials:
NBR, NB 70
FKM,  FP 75
EPDM (peroxide-cured), EP 70
VMQ, SI 60

Colour:
NBR 70, black
FKM 75, black
EPDM 70, black
VMQ 60, red-brown

Tolerances:
NBR, ISO 3302-1 E1
FKM, ISO 3302-1 E1
EPDM, ISO 3302-1 E1
VMQ, ISO 3302-1 E2

Operational application limits
Temperature NBR: -30 °C to +100 °C
Temperature FKM: -15 °C to +200 °C
Temperature EPDM 70: -55 °C to +150 °C
Temperature VMQ 60: -55 °C to +200 °C

Function
Cords are extruded as open-ended billets of circular cross-section (like an O-ring). The cord achieves its sealing effect by the deformation of its cross-section once installed, on being compressed within the installation housing. Under operational conditions, the pressure exerted by the medium reinforces the sealing function.

Applications
The primary application for cords is as the basic material for joined O-rings. They are similar to the O-ring in the way they are handled and applied. They are used as static seals, e.g. for sealing larger pipe unions and as cover seals in container construction. Cords are frequently used for on-site repairs, being joined together to provide the "customized" dimensions.

The process of end-joining cords to form a joined O-ring can be undertaken using cyano-acrylate or 2-component adhesives. However, for applications in seawater or other more demanding applications, bonding by means of an end-vulcanisation process is required.

Suitability for specific media
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

FKM
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.

EPDM
Good resistance to hot water and steam, detergents, caustic potash solutions, silicone oil and greases, many polar solvents, and many diluted acids and chemicals, along with a high level of ozone resistance. EPDM materials are totally unsuitable for use with all mineral oil products (lubricants, fuels).

VMQ
Good resistance to water (up to 100 °C), aliphatic engine and transmission oils, animal and plant oils and fats. Our material is applicable for food contact, reference tests according to FDA (21 CFR § 177.2600) and LFGB recommendation XV (EC 1935/2004). 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.

Production of joined RSR O-rings
The normal procedure is to first cut the cords to length and then bond them using a cyano-acrylate adhesive (e.g. Loctite 406 ®). The operational temperature limit is approx. 80 °C.

With EPDM, VMQ and FKM cords, in certain circumstances the use of a special primer (e.g. Loctite 770 ®) may also be required. Ensure that the manufacturer's product information and safety instructions are observed.

Before bonding, both ends to be joined should be roughened with a fine sandpaper and cleared of any grease using a suitable cleaning agent (e.g. Aceton ®). The two ends should not be under any pressure during the bonding process. Then check that the joint has cured completely through. The end-joined cord must not be stretched at its joint. The joint created displays a distinctly lesser degree of bending elasticity than the cord itself.

Installation
Avoid damaging the O-ring during installation, as this will cause leakage. Observe the following:
-  The end-joined O-ring must not be stretched over the joint and the rest of the O-ring must not be expanded to its elongation limit.
-  Edges must be burr-free, radii and angles applied smoothly.
-  Dust, dirt, metal chips and other particles must be removed.
-  Tips of screws and installation housings for other sealing and guiding elements should be covered by an assembly sleeve.
-  A suitable grease to be applied to the assembly surfaces and O-rings.
-  Elastomer materials are made smoother if they are heated in oil or hot water to approx. 80 °C. This makes it easier to stretch the O-ring for assembly.
-  Any assembly tools used, such as expansion mandrels or sleeves, should be made of a soft material (e.g. POM) and not have any sharp edges.
-  The cord or joined O-ring should not be rolled over assembly surfaces. Ensure it is not twisted as it slots into the groove.