O-rings is one of the most common seals in use today. They can be used in both static and dynamic applications and offer an economic and effective sealing solution. By choosing a compound and hardness it is usually possible to find a suitable O-ring for most applications. Rubber O-rings can operate in temperatures from -55 deg C to + 320 deg C and (with backup rings) at pressures of 400 Bar. They are available in a large range of standard imperial and metric sizes The most common international standards for O-Ring dimensions, in addition to ISO 3601/1 are:-
- American Standard : AS-568
- Great Britain : BS 1806 - BS 4518,
- Germany: DIN 3771,
- Sweden: SMS 1586,
- France: NF T 47 501,
- Japan: JIS B 2401-77
CROSS SECTIONS :-
- Common metric sections include 1.0mm, 1.5mm, 2.0mm, 2.5mm 3.0mm, 3,5mm, 4.0mm, 4.5mm 5.0mm, 6.0 etc.
- Common Swedish sections include 1.6mm, 2.4mm, 5.7mm, 8.4mm
- Common French sections include 1.8mm
- Common Japanese Sections include 1.9mm, 2.7mm, 3.1mm 3.6mm,
- Common Imperial sections are 1.78mm, 2.62mm, 3.53mm, 5.33mm and 6.99mm
Common rubber compounds are available in a range of hardness grades, the most common being 70 shore (Standard Hardness), 80 shore, 90 shore (Hard) is also available, with 40/50 shore (soft) being the least popular. Fluoro elastomer (VITON) O'rings to be slightly harder with 75/80 Shore being the norm.
Most Common Materials:-
|FKM||Viton||-40 deg C + 230 deg C||High Temperature, Synthetic and hydraulic fluids, many acids and alkalis|
|FKM||Perfluoro elastomer (Viton)||-30 deg + 320 deg C||Very high temperature, Best chemical resistance of all Elastomers High performance material|
|MVQ||Silicon||-55 Deg C + 230 Deg C||High Temp Air, Water, Oxygen, alkalis and some acids Static applications only|
|NBR||Nitrile||-40 deg C + 110 Deg C||Mineral based Hydraulic and lubricating oils LPG Gas, Butane, Propane, Acetylene, Petrol, Diesel|
|EPDM||Ethylene-propylene||-55 deg C + 150 deg C||Fire resistant hydraulic fluids, Brake fluids, Hot water, Steam Not resistant to mineral oils|
|PU||Polyurethane||-30 deg + 80 deg C||Good wear and extrusion resistance Not resistant to glycol based fluids, acids or alkalis|
|PTFE||PolytetrafluoroethylenePolytetrafluoroethylene||-200 deg +260 deg C||Very good chemical resistance except liquid alkaline metals No rubber elastic properties, static applications only|
Above table is only a guide to the most common Elastomers, performance would be dependents on the particular variant of elastomer used. Chemical resistance should also be checked before use.
The correct functioning of the O-ring is dependents on both the groove size and the radial clearance. For higher pressures the o ring hardness can be increased, backup rings can be used or radial clearance should be decreased.
O-Rings Recessing Arrangement for AS-568 Series (American Standard): -
O-Rings Cross Section
All dimensions in mm.
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