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Content

            1. Description de produit
                        Matériel/température
            2. Charte de taille
                        Impérial (ISO 3601)
                        Métrique (JIS B 2401, DIN 3771)
            3. Design de joints-toriques
                        O-Ring Cross-Section
                        O-Ring Gland Types
                        I.D. Stretch/ O.D. Interference
                        Reduction in Cross-Section
                        Compression
                        Gland Fill
                        Extrusion Gap
                                 Limits for Extrusion


 

Le joint torique est le phoque le plus largement utilisé dans l'histoire en raison de sa simplicité, son faible coût, facilité d'installation et faible encombrement. Joints toriques sont conçus pour les applications statiques et dynamiques. Une rainure bien conçu joint torique permet à l'O-ring pour être pressé diamétralement out-of-tour avant même l'application d'une pression. Les joints toriques par la distorsion de son composé élastique souple pour combler le trajet de fuite.



Profils de produit

 Material
Temperature Range
 Nitrile
-40°C/-40°F
to
120°C/248°F
 Low Temp. Nitrile
-55°C/-67°F
to
120°C/248°F
 Hydrogenated Nitrile
-40°C/-40°F
to
150°C/302°F
 Viton™ (Fluorocarbon)
-25°C/-13°F
to
204°C/399°F
 PTFE
-200°C/-328°F
to
250°C/482°F
 Aflas™
0°C/32°F
to
230°C/446°F
 Neoprene
-45°C/-49°F
to
135°C/275°F
 EPDM
-54°C/-65.2°F
to
150°C/302°F
 Perfluoroelastomer
-15°C/5°F
to
300°C/572°F
 Silicone
-55°C/-67°F
to
230°C/446°F
 Fluorosilicone
-55°C/-67°F
to
200°C/392°F
Joint-torique Joint-torique carré Joint Quad
Imperial (ISO 3601/AS-568) O-Ring Size Charts
Metric (JIS B 2401, DIN 3771) O-Ring Size Charts







O-Ring Cross Section

The I.D. and O.D. of an O-ring gland is primarily influenced by diameter of the mating surface of the rod or piston and bore. Although the cross-section of the O-ring is seen as fairly arbitrary, there are some distinct advantages to either a larger or smaller cross-section O-ring. Listed below are the advantages of small cross-sections and the advantages of large cross-sections:


Advantages of Smaller Cross-Section
Advantages of Larger Cross-Section

•   More compact
•   Lighter weight
•   Less expensive; especially for higher cost     elastomers like FKM or fluorosilicone
•   Less machining required for machined     grooves since grooves are smaller
•   More resistant to explosive decompression

•   Less prone to compression set
•   Less volume swell in liquid on a percentage basis
•   Allows for larger tolerance while still maintaining     acceptable compression squeeze and compression     ratio over full stack-up range
•   Less prone to leakage due to contamination; dirt,
    lint, scratches, etc.




O-Ring Gland Types

O-rings are primarily used to prevent the loss of a fluid or gas. However, O-rings can be used as dust seals, drive belts or on rotating shafts. Most O-ring seals can be classified into one of the three arrangements shown below.


Piston Configuration
 
Rod Configuration
 
Face Type Configuration





I.D Stretch/O.D. Interference

For hydraulic and pneumatic piston sealing applications

The O-ring inside diameter (I.D.) should be stretched between 2% and 5% for dynamic applications and 2% and 8% for static applications. For O-rings with an inside diameter smaller than 20 mm, this is not always possible which can result in a wider range of stretch. To minimize this range and the maximum stretch, it is necessary to minimize the tolerance of the piston gland diameter, and have a less stringent requirement for the minimum O-ring stretch. In dynamic applications, it is important to keep the maximum stretch to 5% or less to avoid detrimental effects on sealing performance.

For hydraulic and pneumatic rod sealing applications
The O-ring's outside diameter (O.D.) should be at least equal to or larger than the rod gland diameter to give interference on the O-ring's outside diameter (O.D.). The O-ring's outside diameter (O.D.) should not exceed 3% of the rod gland diameter for O-rings with an inside diameter (I.D.) greater than 250 mm, or 5% for O-rings with an inside diameter (I.D.) smaller than 250 mm. For O-rings with an inside diameter (I.D.) smaller than 20 mm, this is not always possible due to tolerance issues, which can result in a greater O-ring outside diameter (O.D.) interference.

O-Ring
 
Piston
 
Rod






Reduction in Cross Section

If the I.D. of the O-ring is stretched, the cross-section of the O-ring will decrease. The following table gives the O-ring cross-sections that result from various percentages of I.D. stretch.

O-RingSeries
Original O-Ring C/S
Reduced O-Ring C/S at % ID Stretch (Inch/mm)
Inch
mm
1%
2%
3%
4%
5%
000
0.070
1.78
0.069/1.76
0.069/1.74
0.068/1.73
0.068/1.71
0.068/1.69
100
0.103
2.62
0.102/2.59
0.101/2.57
0.100/2.54
0.100/2.52
0.100/2.49
200
0.139
3.53
0.138/3.49
0.137/3.46
0.136/3.42
0.135/3.39
0.134/3.35
300
0.210
5.33
0.208/5.28
0.206/5.22
0.205/5.17
0.204/5.12
0.203/5.06
400
0.275
6.99
0.272/6.92
0.270/6.85
0.268/6.78
0.267/6.71
0.266/6.64




Compression

The difference between the original O-ring cross-section and the final O-ring cross-section once installed is known as the compression squeeze.




This can usually be expressed as a percentage: O-ring C/S Squeeze (%) =
Compression Squeeze C/S
x 100




Gland Fill

The gland fill is the percentage of the gland that is occupied by the O-ring. It is calculated by dividing the cross-sectional area (CSA) of the O-ring by the cross-sectional area of the gland.

  Area of a circle = πr2 and r =
d2
, where d = diameter (C/S) and π = pi (3.14159)

  Therefore, O-ring CSA = π
 




Gland CSA = D x w*


Gland Fill (%) =
O-ring CSAGland CSA
x 100




* Effect of gland angle and extrusion gap not addressed.


It is important to consider the groove fill or occupancy of the installed O-ring to avoid detrimental effects on radial sealing performance. Groove fill of the installed O-ring should not be more than 85 % to allow for possible O-ring thermal expansion, volume swell due to fluid exposure and effects of tolerances.

Volume change is the increase or decrease of the volume of an elastomer after it has been in contact with a fluid, measured in percent (%). For static O-ring applications volume swell up to 30 % can usually be tolerated. For dynamic applications, 10 or 15 % swell is a reasonable maximum unless special provisions are made in the gland design itself. This is a general rule and there may occasionally be exceptions.

It is also important to note there are significant differences in the coefficients of thermal expansion between the O-ring material and the groove materials. Elastomers can have coefficients of thermal expansion 7 to 20 times higher than that of metal, such as steel.



Extrusion Gap

Extrusion is a concern for radial seals where there is gap between the piston and the bore for a piston type seal or between the rod and the bore for a rod type seal. It is not typically a concern for face type seals where the metal parts to be sealed are in contact line-to-line. The issue is that at higher pressures and especially for softer O-ring elastomers, the O-ring can be forced by the pressure into the small gap between the piston (or rod) and the bore. Unless the bore and the piston (or rod) are ensured to remain concentric by the hardware, we have to assume that entire possible gap can shift to one side (see diagram below).

 Piston Type Seal
Radial Extrusion Gap =

Bore Ø- Piston Ø

2
Rod Type Seal
Radial Extrusion Gap =

Bore Ø- Piston Ø

2
 


 
 




Limites pour l'extrusion


Il y a différentes façon d’empêcher l’extrusion du joint torique. L’une d’elles consiste simplement à accroître l’indice de duromètre du joint torique. Cependant, plus vous hausser l’indice du duromètre, moins le joint torique sera malléable. Une autre option serait d’utiliser des dispositifs anti-extrusion. Il existe de minces anneaux fabriqués d’un matériau plastique dur comme le PTFE, le nylon, et le PEEK. Une fois en place, ces anneaux ne laissent essentiellement aucun espace de jeu.

Réduire le dégagement indiqué de 60 % lorsque des élastomères de silicone ou de fluorisilicone sont utilisés