O-RING

The O-rings (or more synthetically OR) are toroidal shaped sealing elements with a circular cross-section; generally their dimensional definition is given by the inner diameter and the diameter of the cross-section. The O-rings can be used as static or dynamic seals and are normally installed inside hollow seats with a rectangular section.

O-rings are undoubtedly the most widespread and used type of seal : simple and symmetrical shape, ease of manufacture, cost-effectiveness, low design costs, warranty single sealing or double-acting, small size and ease of installation have promoted their use in all industrial and non-industrial applications.

O-Ring, OR in NBR, OR in HNBR, OR in CR, OR in KFM, O-Ring in PFTE Vergine

LIMA manufactures and markets O-rings in NBR, HNBR, FKM, FFKM, polyamide, EPDM, silicone, PTFE, PCTFE, polyurethane and PEEK

The O-ring choice, both in terms of size and in terms of material, is related to factors like the working temperature of the sealing area, the working pressure (fluid hammer), the chemical aggressiveness of the fluid and the abrasion degree of the containment surfaces.

PRINCIPLE OF OPERATION

First Step

The tightness is achieved when the O-ring is compressed between the two surfaces. The higher the pressure, the more the o-ring pushes against the sealing surfaces

Second Step

Through pressure, the O-ring starts to get deformed against the sealing walls in proportion to the exerted pressure.

Third Step

With increasing pressure, the O-ring tends to get extruded in the coupling backlash and get deformed irreversibly

Fourth Step

To avoid extrusion phenomena, back-up rings are usually mounted on the side opposite to the pressure direction.

TECHNICAL PRECAUTIONS

Any minimum damage compromises the sealing function of the O-ring. Thus, it  is critically  important to adopt every precaution to ensure the integrity of the seal, which may get damaged  by sharp edges, threads or machining burrs. Also dust, machining waste, dirt and other impurities must never come into contact with the O-ring.

Both the seal and the housing shall be manufactured observing scrupulously the indicated tolerances: the backlash is decisive for the effectiveness of the seal and for the duration of the life of the O-ring. To assure  functionality of the O-rings it is recommended to store them in a place away from UV radiation, air and atmospheric agents, with humidity at 70% and at a temperature of 10-20 ° C. The O-rings shall not be unnecessarily pulled, loaded, hung or folded.

TRADITIONAL MATERIALS

Many elastomeric materials and certain thermoplastics are used for the production of O-rings. The choice of the suitable material depends on parameters like the materia resistance to the fluid to be contained, the permanent deformation, the hardness in relation to the backlashes, the resistance to high and low temperatures.

Here are the most commonly used materials and their characteristics.

NBR

Suitable for contact with oils, vegetable and animal fats, flameproof liquids, silicone based oils and greases, salt solutions, aliphatic hydrocarbons, glycol, air, and water up to 80 ° C. Ideal for hydraulic and pneumatic systems, pumps, equipments, machinery in general.

HNBR

Suitable for contact with oils, vegetable and animal fats, flameproof liquids, silicone based oils and greases, salt solutions, aliphatic hydrocarbons, glycol, air, and water up to 80 ° C. Ideal for the motor industry.

CR

Suitable for contact with alkali, alcohol, ozone, glycol, coolants; It has high resistance to aging and weathering, and low resistance to grease and mineral oils. Ideal for refrigerators, compressors, buildings external equipment.

FKM

Suitable for contact with petrol, diesel, mineral oils and fats, silicone oils and greases, phosphates-based flameproof liquids, acids, alkalis, aliphatic, aromatic and chlorinated hydrocarbons. Ideal for vacuum applications.

FFKM

Suitable for contact with most fluids and chemicals, similar to PTFE, has excellent chemical resistance and excellent resistance to high temperatures, even above 300°C. Ideal for chemical equipments and in any environment with high temperatures and aggressive substances.

EPDM

Suitable for contact with organic and inorganic acids and bases, phosphates-based explosion protection  liquids, hot water, steam, detergents, brake fluids, engine coolants, ketones, alcohol; resistant to aging and weathering, it does not resist to oils and mineral greases. Ideal for nuclear equipment, fittings, pumps, brake circuits.

FPM

Suitable for contact with aliphatic hydrocarbons, oils, various non-flammable hydraulic fluids; It is resistant to heat and chemicals. Ideal for chemical equipment, hydraulic equipment with non-flammable fluids and for vacuum pumps.

MVQ

Suitable for contact with ozone, oxygen, inert gases at high temperatures, ultraviolet rays, hot air, and animal and vegetable fats and oils, brake fluids, aliphatic oils for engines and transmissions; It has low resistance to mineral oils and excellent resistance to aging. Ideal for chemical equipment, machinery for the food industry, packaging and bottling.

MVFQ

Suitable for contact with aromatic fuels, lubricants, hot air, ozone, oils and oxygen. Ideal for chemical equipment, machinery for the food industry, machinery for the sector of packaging and bottling and for aerospace applications.

PUR

Suitable for contact with mineral oils and greases, oxygen, ozone; not resistant to water above 50 ° C, esters, aliphatic hydrocarbons, aromatic and chlorinated hydrocarbons, concentrated acids and alkaline solutions; It is high wear resistant. Ideal for hydraulic and pneumatic systems with high dynamic loads.

PTFE virgin

Suitable for contact with most fluids and chemical substances, except for the alkali metals and some fluorine-based compounds. Ideal for petrochemical, food, pharmaceutical, medical applications (where the chemical resistance of normal elastomeric O-ring is not sufficient).

SPECIAL MATERIALS

There are also special materials ideal for critical applications such as cryogenics, medical instrumentation, aeronautics, painting, the food processing and beverages, electrical equipment, and petrochemical plants.

They include PEEK, polyamides (especially PA 6 + molybdenum sulfide and Devlon), PCTFE and modified PTFE and PTFE loaded with glass or carbon graphite.

O-Ring in PTFE

In addition, the elastomeric O-rings can be encapsulated with a FEP or PFA coating to ensure maximum performance. The FEP / PFA coating guarantees a high degree of resistance to breakage, a low coefficient of friction, chemical inertness and therefore the possibility of application in the food, chemical, medical and pharmaceutical industry.

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