O-ring
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DIN ISO 3601 |
|---|---|
| Area | Fluid technology |
| title | O-rings - Part 1: Inner diameter, cord thickness, tolerances and designation; Part 2: Installation spaces for general applications; Part 3: shape and surface deviations; Part 4: support rings |
| Latest edition | 8.2010 |
| ISO | - |
O-rings are ring-shaped sealing elements . The name is derived from the round (O-shaped) cross-section of the ring.
O-rings are standardized according to ISO 3601 , this standard is valid in Germany as DIN ISO 3601. The DIN standard DIN 3771 was valid in Germany until August 2010 . In the GDR was O-ring ( TGL 6365) (commonly known as zero-ring) is the common term for this sealing element.
The size of O-rings is given as the inside diameter × the cord diameter.
Manufacturing
Due to their relatively simple shape, O-rings are easy to manufacture industrially. Preferably finds the injection molding (injection molding) application, at lower quantities or extremely expensive types of rubber the O-rings by means of compression molding made (compression molding). Depending on the area of application and requirements (e.g. resistance to oils, fats, acids, heat, vacuum tightness), different materials are used, e.g. B. different types of rubber , perfluorinated rubber (FFKM or FFPM), polyethylene (PE) or polytetrafluoroethylene (PTFE). Metal is also rarely used (e.g. reactor seals in nuclear power plants or in hot runner systems ).
Mode of action
Due to its circular cross-section, an O-ring can seal axially and / or radially. The initial tightness is achieved by pressing the rubber body during installation (in the radial and / or in the axial direction). The sealing pressure results from the superposition of the pre-pressure (through the installation) and the system pressure to be sealed. In the sealing joint there is therefore always a sealing pressure that is higher than the pressure to be sealed by the amount of pre-pressing. Therefore, very high pressures can be sealed.
A dynamic use, such as B. takes place in single-lever mixers , is only useful when the load is low. It mainly depends on the speed with which z. B. a piston is moved, and the system pressure. O-rings can also be used with slowly rotating spindles and shafts.
Incorrectly used O-rings led to the Challenger disaster in 1986 .
application
The sealing type of the O-ring has great, diverse potential uses, u. a. The sealing element is used in automotive or mechanical engineering. They can be found in practically every area of industry, e.g. B. O-rings are also installed in every common household single-lever mixer (faucet). Usually the O-ring is present in static seals, a distinction must be made between radial-static and axial-static seals. The former include, among other things, the application in cylinders or pipes, the axial use in flanges , plates and closures.
O-rings are often used in the piercing scene to hold larger diameter jewelry in place for widened piercings .
Nitrile rubber ( acrylonitrile butadiene rubber or Nitrile Butadiene Rubber , NBR ) is the standard material for hydraulic and pneumatic applications.
O-rings made of ethylene-propylene rubber or ethylene-propylene-diene rubber (EPDM) are predominantly used for press fittings in heating and sanitary installations , which are generally up to 130 °, depending on the application also up to 150 ° or in exceptional cases up to 200 ° C are temperature resistant. Since even higher temperatures can occur in solar installations , O-rings made of fluorinated rubber ( FKM ) are used in the particularly stressed areas , which are usually colored blue or green to distinguish them. Rings for gas installations are colored yellow accordingly.
Standard dimensions
O-rings are dimensioned with "inside diameter × cord thickness", for example 10 × 1.0 mm.
O-rings are usually manufactured in various standard sizes. Cord thicknesses (diameter of the round cross section) of 0.35 mm for very filigree applications up to 40 mm or more are possible. One of the smallest known O-rings is used in Swiss watch production and has the dimensions 0.70 × 0.20 mm. Depending on the application, the inner diameter can be up to several meters (e.g. seals in sewer pipes or pipe constructions). The largest O-rings include seals for space telescopes or nuclear reactors with internal diameters over 10 meters.
DIN 3771-1: 1984-12 specifies a typical cord thickness of 1.8 mm for rings with an inner diameter of 1.8 to 17 mm. The inner diameters are staggered depending on the application, e.g. B. 6.0 / 6.3 / 6.7 / 6.9 / 7.1 / 7.5 mm. In the range from 14 to 38.7 mm, the typical cord thickness is 2.65 mm, in the range from 18 to 200 mm it is 3.55 mm, etc., up to 670 × 7 mm. Rings with z. B. 14/15/17 mm are available in cord sizes 1.8 or 2.65 mm according to the standard.
lubrication
When using O-rings with constantly moving parts, the service life can be significantly extended through lubrication.
Occasionally, a lubricant in finely divided form is added to the starting material during the production of the sealing ring, which when used can reach the stressed surface through pores in the material structure. Alternatively, special abrasion-resistant layers can be applied to the finished rings, which ensure lubrication for a certain period of time. Otherwise, a lubricant should be applied to the O-ring and to the workpiece sliding along the ring during assembly and should be renewed later at appropriate maintenance intervals. For this purpose, special assembly greases are offered that are compatible with most of the sealing materials used.
In general, fluorocarbon rubber (FKM, Viton ), perfluorinated rubber ( FFPM / FFKM), acrylonitrile butadiene rubber (NBR) and hydrogenated acrylonitrile butadiene rubber (HNBR) can be used with most common lubricants.
O-rings made of EPDM are sensitive to mineral oil and synthetic lubricants , including petroleum jelly and paraffin (oil) as well as all traditionally used lubricating oils and greases.
Silicone oils and greases are incompatible with O-rings made of silicone rubber ( Liquid Silicone Rubber - LSR , VMQ ).
Specifically, lubricants containing mineral oil and synthetic lubricants with acrylonitrile butadiene rubber (NBR), hydrogenated acrylonitrile butadiene rubber (HNBR), polyester urethane rubber (AU), ACM ( polyacrylate rubber ), fluorine vinyl methyl silicone Rubber (FVMQ), TFE / PTFE , fluorinated rubber FKM, perfluorinated rubber FFKM and ETP and, with restrictions, for chloroprene rubber (CR) and vinyl methyl silicone rubber (VMQ). Use with EPDM is only possible in exceptional cases. Natural rubber (NR) is completely incompatible.
Silicone grease and oil can be used for NR, EPDM, NBR, HNBR, CR, AU, ACM, FVMQ, FKM, FFKM and ETP; for VMQ only in exceptional cases.
TFE / P can be used with lubricants containing mineral oils. Insufficient information is available for other agents.
Material compatibility with fats and oils
Animal fats are compatible with NBR, HNBR, AU, ACM, FVMQ, FKM, FFKM and ETP, as well as with restrictions EPDM, CR and VMQ, but not with NR.
Vegetable oils contain many different ingredients, so that general statements can hardly be made. Only FKM, FFKM and ETP are compatible with most oils. NBR, HNBR, FVMQ can be used with many oils, but only to a limited extent with some. ACM is only compatible with some oils and VMQ, EPDM and CR are only compatible with a few oils. NR is generally incompatible. Some oils such as castor oil ( castor oil ) is compatible with almost all materials. These details only concern the resistance of the sealing ring material and do not allow any statements about food compatibility.
Fatty acids can be used with FKM, FFKM and ETP, and with restrictions also with NBR, HNBR and CR. Use with EPDM and VMQ is not recommended and can be completely ruled out with NR.
Web links
- Properties and resistances of the materials for O-rings (PDF; 578 kB)
- Parker O-Ring manual (PDF; 214 pages; 10.6 MB)
- O-ring 1x1 from C. Otto Gehrckens (PDF; 1.3 MB)