Vacuum applications and Material

In vacuum applications the material's permeability makes point contacts unusable.Instead, a higher installation force is used and the ring fills the entire groove.Additionally,round retaining rings are used to prevent excessive deformation of the retaining ring.Because the rings experience [colloquial] ambient pressure and gas partial pressure only at the seal, their gradient will be steep near the seal and shallow overall (compared to contact stress.The gradient is reversed (see Vacuum Flange #KF.2FQF.) High vacuum systems Torr use copper or nickel O-rings.Additionally, vacuum systems that must be submerged in liquid nitrogen use indium O-rings, Because rubber becomes hard and brittle at low temperatures.

High temperature applications

In some high temperature applications,O-rings may need to be installed in tangential compression to compensate for the high joule effect.

Sizes 

O-rings come in a variety of sizes.Society of Automotive Engineers (SAE) Aerospace Standard 568 (AS568) specifies the inside diameter, cross-section, tolerances, and size identification code (dash) gaskets for O-ring and straight thread fitting bosses used in sealing applications.British Standard (BS), ie imperial or metric sizes.Typical dimensions for o-rings are inner dimension (id), outer dimension (od) and thickness/cross section (cs).Metric O-rings are usually defined by inside dimension x cross section.Typical Part Number for Metric O-Rings ID x CS [Material and Shore Durometer] 2x1N70 = Defines this O-ring as 2mm id and 1mm cross section, made of 70Sh of Nitrile.BS O-rings are defined by a standard reference.The Guinness World Record for the world's largest O-ring was achieved by Trelleborg Sealing Solutions Tewkesbury in collaboration with 20 students from Tewkesbury School.The O-ring was once completed and placed around medieval Tewkesbury Abbey and has a circumference of 364 meters (1,194 ft), an internal diameter of approximately 116 meters (381 ft), and a cross-section of 7.2 mm (0.28 in).

Material

• O-ring selection is based on chemical compatibility, application temperature,seal pressure, lubrication requirements,durometer, size and cost.

• Synthetic Rubber Thermoset:

• Butadiene rubber (BR)

• Butyl Rubber (IIR)

• Chlorosulfonated polyethylene (CSM)

• Epichlorohydrin Rubber (ECH, ECO)

• Ethylene Propylene Diene Rubber (EPDM): Good resistance to hot water and steam,detergents, caustic potash solutions, sodium hydroxide solutions,silicone oils and greases,many polar solvents and many diluted acids and chemicals.Specially formulated for use with glycol-based brake fluids.Not suitable for use with mineral oil products: lubricants,oils or fuels.Peroxide cured compounds are suitable for higher temperatures.

• Ethylene Propylene Rubber (EPR)

• Viton (FKM): Known for its very high resistance to heat and many chemicals.Other key benefits include excellent resistance to aging and ozone,very low gas permeability and the fact that the materials are self-extinguishing.Standard FKM materials have excellent resistance to mineral oils and greases, aliphatic, aromatic and chlorinated hydrocarbons,fuels, non-flammable hydraulic fluids (HFD) and many organic solvents and chemicals.Generally not resistant to hot water, steam, polar solvents, glycol-based brake fluids and low molecular weight organic acids.In addition to the standard FKM materials, a number of specialty materials with different monomer compositions and fluorine content (65% to 71%) are available that offer improved chemical or temperature resistance and/or better low temperature performance.

• Nitrile (NBR, HNBR, HSN, Buna-N): A common material for O-rings because of its good mechanical properties, resistance to lubricants and greases, and relatively low cost.The physical and chemical resistance of NBR materials depends on the acrylonitrile (ACN) content of the base polymer: low content ensures good flexibility at low temperatures, but limited resistance to oils and fuels.With the increase of ACN content, the low-temperature flexibility decreased and the oil and fuel resistance improved.The physical and chemical resistance of NBR materials are also affected by the polymer curing system.Peroxide cured materials have improved physical properties, chemical resistance and thermal performance compared to sulfur donor cured materials.Standard grades of NBR are generally resistant to mineral oil-based lubricants and greases, many grades of hydraulic fluids, aliphatic hydrocarbons, silicone oils and greases, and water up to approximately 176 °F (80 °C).NBR is generally not resistant to aromatic and chlorinated hydrocarbons, fuels with high aromatic content, polar solvents, glycol-based brake fluids and non-flammable hydraulic fluids (HFD).NBR also has low ozone resistance,weather resistance and aging resistance.HNBR has considerable improvement in heat resistance, ozone resistance and aging resistance, and endows it with good mechanical properties.

• Perfluoroelastomer (FFKM)

• Polyacrylate rubber (ACM)

• Polychloroprene (Neoprene) (CR)

• Polyisoprene (IR)

• Polysulfide Rubber (PSR)

• Polytetrafluoroethylene (PTFE)

• Sanifluor (FEPM)

Silicone Rubber (SiR):Known for its ability to be used over a wide temperature range and its excellent resistance to ozone, weathering and aging.Silicones have poor physical properties compared to most other sealing elastomers.In general, silicone materials are not harmful to physiology and are therefore widely used in the food and pharmaceutical industries.Standard silicones are resistant to water up to 212 °F (100 °C),aliphatic engine and transmission fluids, and animal and vegetable oils and fats.Silicones are generally not resistant to fuels, aromatic mineral oils,steam (possibly up to 248 °F (120 °C) for short periods),silicone oils and greases, acids or bases.Fluorosilicone elastomers are more resistant to oils and fuels.The temperature range of the application is more restricted.

• Styrene Butadiene Rubber (SBR)

• Thermoplastics:

• Thermoplastic Elastomer (TPE) Styrene

• Thermoplastic Polyolefin (TPO) LDPE, HDPE, LLDPE, ULDPE

Thermoplastic Polyurethane (TPU) Polyethers, Polyesters: Polyurethanes differ from traditional elastomers because they have better mechanical properties.In particular they have high abrasion, abrasion and crush resistance, high tensile strength and excellent tear resistance.Polyurethanes are generally resistant to aging and ozone, mineral oils and greases, silicone oils and greases, nonflammable hydraulic fluids HFA and HFB, water up to 122 °F (50 °C), and aliphatic hydrocarbons.

• Thermoplastic ether ester elastomer (TEEE) copolyesters

• Thermoplastic polyamide (PEBA) polyamide

• Melt Processable Rubber (MPR)

• Thermoplastic Vulcanizate (TPV).