O-rings are the most popular seals used in hydraulic, pneumatic components and system devices, and are widely used in various sealing occasions.
O-rings can be used as sealing elements as well as force-applying elements for hydraulic sliding seals and dust rings. Under specified temperatures, pressures, and different liquid and gas media, these products can act as seals in a static or moving state. It can be said that in the industrial field, whether it is a single seal for repair and maintenance, or in applications such as aerospace, automotive industry, and general industry, O-rings are almost everywhere.
Product features and applications:
O-rings have many advantages:
(1) Suitable for a variety of sealing forms, including static sealing and dynamic sealing.
(2) Suitable for a variety of motion modes, such as rotational motion, axial reciprocating motion or combined motion.
(3) Suitable for a variety of different sealing media, including oil, water, gas, chemical media or other mixed media;
(4) The cross-sectional structure is extremely simple, and it has a self-sealing effect, reliable sealing performance, compact structure, and easy assembly and disassembly;
(5) There are many types of materials;
(6) Low cost;
(7) The dynamic friction resistance is relatively small.
The list of O-ring standards is shown in the table below:
| Table 1-1 List of O-ring standards | |||||||
| Standard | O-ring cross-sectional diameter d2 |
 |
|||||
| American Standard AS 568 British Standard BS 1516 |
1.7 8 |
2.62 | 3.53 | 5.33 | 6.99 | - | |
| Japanese Standard JIS B 2401 | 1.9 | 2.4 | 3.1 | 3.5 | 5.7 | 8.4 | |
| International Standard IS0 3601/1 German Standard DIN 3771/1 Chinese Standard GB 3452.1 | 1.8 | 2.65 | 3.55 | 5.30 | 7.00 | - | |
| Chinese Standard GB1235 | 1.9 | 2.4 | 3.1 | 3.5 | 5.7 | 8.6 | |
| Preferred metric sizes | 1.0 | 1.5 | 2.0 | 2.5 | 3.0 | 3.5 | |
| 4.0 | 4.5 | 5.0 | 5.5 | 6.0 | 7.0 | ||
| 8.0 | 10.0 | 12.0 | - | - | - | ||
| American Standard AS 568 (900 Series) |
1.0 2 |
1.42 | 1.63 | 1.83 | 1.98 | 2.08 | |
|
2.2 1 |
2.46 | 2.95 | 3.00 | - | - | ||
Sealing mechanism
The O-ring is an automatic two-way sealing element. During installation, its radial and axial pre-compression determines the initial sealing ability of the O-ring itself, which increases with the increase of system pressure.
(1) Uncompressed state
(2) Compressed state without pressure
(3) Pressure
Performance parameters
Table 1-2 O-ring performance parameters
| Standard | Static seal | Dynamic seal |
| Work Pressure | Without retaining ring, the maximum can reach 20MPa; With retaining ring, the maximum can reach 40MPa: With special retaining ring, the maximum can reach 200MPa | Without retaining ring, the maximum pressure can reach 5MPa; with retaining ring, higher pressure |
| Speed | Reciprocating 0.5m/s max, rotating 2m/s max | |
| Temperature | General occasions: -30~+110, special occasions: -60~+250, rotating occasions: -30~+80 | |
| Medium | See (Material Properties Table) | |
O-ring selection
1. Working medium and working conditions
When selecting the O-ring material, the compatibility with the working medium must be considered first, and the working conditions such as the pressure, temperature, continuous working time, and operation cycle of the sealing part must also be considered. If it is used in a rotating situation, the temperature rise caused by frictional heat must be considered. Different sealing materials have different physical and chemical properties, please refer to the "Material Properties Table" for details.
2. Seal type and installation groove size
(1) According to the sealing form, it can be divided into: static seal (seal without relative motion between adjacent surfaces) and dynamic seal (seal with reciprocating motion between sealed parts);
(2) According to the purpose of sealing, it can be divided into: hole seal, shaft seal and rotary seal;
(3) According to the installation form, it can be divided into: axial installation (its cross section is axially deformed after installation) and radial installation (its cross section is radially deformed after installation).
①Axial static seal
Table 1-3 Axial static seal installation groove dimensions
| O-ring wire diameter d2 | Groove depth W+0.05 | Groove width L+0.25 | O-ring wire diameter d2 | Groove depth W+0.05 | Groove width L+0.25 | O-ring wire diameter d2 | Groove depth W+0.05 | Groove width L+0.25 |
| 1 | 0.7 | 1.4 | 2.7 | 2.1 | 3.8 | 5.7 | 4.6 | 7.6 |
| 1.2 | 0.9 | 1.6 | 2.8 | 2.1 | 4 | 6 | 4.8 | 8.1 |
| 1.25 | 0.9 | 1.7 | 3 | 2.3 | 4.1 | 6.5 | 5.3 | 8.6 |
| 1.3 | 1 | 1.7 | 3.1 | 2.4 | 4.2 | 6.99 | 5.7 | 9.7 |
| 1.5 | 1.1 | 2.1 | 3.5 | 2.7 | 4.8 | 7 | 5.7 | 9.7 |
| 1.6 | 1.2 | 2.2 | 3.53 | 2.7 | 4.9 | 7.5 | 6.2 | 10.1 |
| 1.78 | 1.3 | 2.5 | 3.55 | 2.7 | 5 | 8 | 6.6 | 10.7 |
| 1.8 | 1.3 | 2.6 | 3.6 | 2.8 | 5.1 | 8.4 | 7.1 | 11.1 |
| 1.9 | 1.4 | 2.7 | 3.7 | 2.9 | 5.2 | 8.5 | 7.2 | 11.3 |
| 2 | 1.5 | 2.8 | 4 | 3.1 | 5.5 | 9 | 7.6 | 12 |
| 2.2 | 1.6 | 3.1 | 4.3 | 3.3 | 5.9 | 9.5 | 8.1 | 12.5 |
| 2.4 | 1.8 | 3.3 | 4.5 | 3.5 | 6.1 | 10 | 8.5 | 13.6 |
| 2.5 | 1.9 | 3.5 | 5 | 4 | 6.7 | 10.5 | 8.9 | 14 |
| 2.6 | 2 | 3.6 | 5.3 | 4.2 | 7.2 | 11 | 9.4 | 14.7 |
| 2.62 | 2 | 3.7 | 5.33 | 4.2 | 7.3 | 12 | 10.4 | 15.7 |
| 2.65 | 2 | 3.8 | 5.5 | 4.5 | 7.4 | 15 | 13.2 | 19.4 |
②Radial static seal
Radial hole seal: The installation groove is on the shaft, and the inner diameter of the O-ring is equal to or slightly smaller than the groove bottom diameter d.
Radial shaft seal: The installation groove is in the hole, and the inner diameter of the O-ring and the sealed shaft diameter d are as close as possible.
| Table 1-4 Dimensions of radial static seal installation groove | |||||||||||
| O-ring wire diameter d2 | Groove depth W+0.05 | Groove width L±0.25 | C | O-ring wire diameter d2 | Groove depth W+0.05 | Groove width L±0.25 | C | O-ring wire diameter d2 | Groove depth W+0.05 | Groove width L±0.25 | C |
| 1 | 0.75 | 1.3 | 1.2 | 2.7 | 2.1 | 3.6 | 2 | 5.7 | 4.6 | 7.6 | 3.5 |
| 1.2 | 0.9 | 1.6 | 1.2 | 2.8 | 2.2 | 3.7 | 2 | 6 | 4.9 | 7.9 | 3.5 |
| 1.25 | 0.9 | 1.7 | 1.2 | 3 | 2.3 | 3.9 | 2.5 | 6.5 | 5.4 | 8.4 | 4 |
| 1.3 | 1 | 1.7 | 1.2 | 3.1 | 2.4 | 4 | 2.5 | 6.99 | 5.8 | 9.2 | 4 |
| 1.5 | 1.1 | 2 | 1.5 | 3.5 | 2.7 | 4.6 | 2.5 | 7 | 5.8 | 9.3 | 4 |
| 1.6 | 1.2 | 2.1 | 1.5 | 3.53 | 2.7 | 4.7 | 2.5 | 7.5 | 6.3 | 9.8 | 4 |
| 1.78 | 1.3 | 2.4 | 1.5 | 3.55 | 2.8 | 4.7 | 2.5 | 8 | 6.7 | 10.5 | 4 |
| 1.8 | 1.3 | 2.4 | 1.5 | 3.6 | 2.8 | 4.8 | 2.5 | 8.4 | 7.1 | 10.9 | 4.5 |
| 1.9 | 1.4 | 2.5 | 1.5 | 3.7 | 2.9 | 4.9 | 2.5 | 8.5 | 7.2 | 11 | 4.5 |
| 2 | 1.5 | 2.6 | 2 | 4 | 3.2 | 5.2 | 3 | 9 | 7.7 | 11.7 | 4.5 |
| 2.2 | 1.7 | 3 | 2 | 4.3 | 3.4 | 5.6 | 3 | 9.5 | 8.2 | 12.3 | 4.5 |
| 2.4 | 1.8 | 3.2 | 2 | 4.5 | 3.6 | 5.8 | 3 | 10 | 8.6 | 13 | 5 |
| 2.5 | 1.9 | 3.3 | 2 | 5 | 4 | 6.5 | 3 | 10.5 | 9 | 13.8 | 5 |
| 2.6 | 2 | 3.4 | 2 | 5.3 | 4.3 | 7 | 3 | 11 | 9.5 | 14.3 | 5 |
| 2.62 | 2 | 3.5 | 2 | 5.33 | 4.3 | 7.1 | 3.5 | 12 | 10.5 | 15.6 | 5 |
| 2.65 | 2 | 3.6 | 2 | 5.5 | 4.5 | 7.2 | 3.5 | 15 | 13.2 | 19.2 | 5 |
③Vacuum seal (static seal)
Vacuum packaging is an O-ring seal under special circumstances, and the pressure of the sealed system is lower than 1 standard atmosphere (101.325kpa).
Its application and installation groove size requirements are as follows:
a. The installation groove space is almost 100% filled with the volume of the O-ring after deformation, which can increase the contact area and prolong the diffusion time through the elastomer.
b. The compression deformation of the O-ring cross section is about 30%.
c. Vacuum grease should be used (to reduce leakage).
d. The surface roughness of each surface of the installation groove should be considered higher than the requirements of hydraulic static seals, and the percentage of contact range ftp should be greater than 50%.
e. The O-ring should be made of materials that are compatible with gas, low permeability and low compression deformation. Here, we recommend the use of fluororubber.
④Radial hydraulic dynamic seal
Since the O-ring will be displaced during movement, its application is limited to lower pressure (without retaining ring) and speed (reciprocating motion = 0.5m/s; rotary motion = 2.0m/s).
3. Hardness factor
The hardness of the O-ring material is one of the important indicators for evaluating the sealing performance. The hardness of the O-ring determines the compression of the O-ring and the maximum allowable extrusion gap of the groove. Generally, the nitrile rubber of Shore A70 is provided, which can meet most of the use conditions.
4. Extrusion gap
The maximum allowable extrusion gap g max is related to the system pressure, the cross-sectional diameter of the O-ring, and the hardness of the material. Generally, the higher the working pressure, the smaller the maximum allowable extrusion gap g max. If the gap g exceeds the allowable range, it will cause the O-ring to be extruded or even damaged.
It is recommended to use a retaining ring in radial dynamic seals, which can prevent the O-ring from being squeezed into the radial gap and also increase the working pressure. When the pressure exceeds 5MPa and the inner diameter is >50mm, and the pressure is greater than 10MPa and the inner diameter is <50mm, it is recommended to use a retaining ring.
For static sealing applications, it is recommended to match H7/g6.
5. Tensile and Compression Rates
When the O-ring is installed in the groove, it will be stretched and compressed to a certain extent. If the stretching and compression values are too large, the cross section of the O-ring will be excessively enlarged or reduced. In order not to affect its sealing effect, it is recommended to strictly follow the following two points:
(1) For radial hole sealing: The O-ring is preferably in a stretched state (i.e. d>d2), and the maximum allowable stretching rate is 6%, because a 1% stretching will correspondingly reduce the cross-sectional diameter W by 0.5%.
Elongation = (d-2/d2) × 100% ＜6%
In the equation: d-the bottom diameter of the mounting groove in the radial hole seal
d2-the inner diameter of the O-ring
(2) For radial shaft seals, the O-ring is preferably compressed along its circumference (i.e. D1>D), and the maximum allowable circumference compression rate is 3%.
Compression ratio = (D1-D)/D1×100% ＜3%
In the equation: D1-outer diameter of O-ring
D-bottom diameter of mounting groove in radial shaft seal
6. O-rings are used as rotating shaft seals
O-rings can also be used as seals for low-speed rotation and short-cycle rotating shafts. When the circumferential speed is lower than 0.5m/s, the O-ring selection can be based on normal design standards; when the circumferential speed is higher than 0.5m/s, it is necessary to consider the phenomenon that the elongated rubber ring will shrink after being heated (Joule heat phenomenon), so the inner diameter of the sealing ring is selected to be about 2% larger than the diameter of the sealed shaft, and the above phenomenon can be avoided. After the O-ring is installed in the groove, it is radially compressed to form a fine corrugation, thereby improving the lubrication conditions.
7. Installation compression force
During installation, the compression force is related to the degree of initial compression and the hardness of the material. The figure shows the relationship between the unit compression force and the cross-sectional diameter per centimeter of the seal circumference, which is used to estimate the size of the compression force when installing the O-ring.
Local structure design
Because the O-ring will be squeezed during installation, in order to avoid serious damage, the hole end or shaft end must be processed into a 15°~20° chamfer, and the edges must be rounded and burrs removed. If the O-ring is to pass through a transverse hole during installation, the transition hole must also be chamfered or rounded.
Hole chamfer
Shaft chamfer
Chamfering/rounding of transition holes
Table 1-10 Minimum chamfer length Cmin
| Section diameter W | ≤1.78, 1.80 | ≤2.62, 2.65 | ≤3.53, 3.55 | ≤5.30, 5.33 | ≤7.00 | >8.40 | |
| Minimum chamfer length Cmin | 15° | 2.5 | 3.0 | 3.5 | 4.0 | 5.0 | 6.0 |
|
|
20° | 2.0 | 2.5 | 3.0 | 3.5 | 4.0 | 4.5 |
Chamfer surface roughness: Rz≤4.0μm Ra≤0.8μm
Permissible deviations of shape and surface defects
We classify the shapes and surface defects of O-rings into two categories: N and S.
(1) N: represents our standard quality, which can fully meet high quality requirements and daily applications.
(2) S: suitable for occasions with very high requirements for shape and surface defects, usually requiring large production and high cost.
Mold misalignment d
Mold splitting flash h
Mold splitting shrinkage
Excessive trimming
Flow marks
Other defects
| Table 1-8 O-ring shape and surface defects | ||||
| Defects | Category | Permissible deviation of section W | ||
| ≤2.65 | >2.65 | |||
| Error modulus | Width h | N | 0.06 | 0.12 |
| Flash amount | Width h | S | 0.05 | 0.09 |
| Parting shrinkage | Width h | N | 0.1 ·W | 0.1 ·W |
| Width h | 0.05 | 0.09 | ||
| Width h | S | 0.05 ·W | 0.05 ·W | |
| Width h | 0.05 | 0.09 | ||
| Excessive trimming width (excess trimming is allowed, but it must be within the deviation range of the cross section and the surface must be kept smooth) | Width h | N | 0.4 | 1.2 |
| Width h | S | 0.4 | 0.7 | |
| Flow marks (circumferential direction) | Thickness a | N | 0.1 · ID | 0.1 · ID |
| Depth f | 0.03 | 0.06 | ||
| Thickness a | S | 0.05 · ID | 0.05 · ID | |
| Depth f | 0.03 | 0.06 | ||
| Other defects | Thickness a | N | 0.3 ·W | 0.3 ·W |
| Depth f | 0.05 | 0.09 | ||
| Thickness a | S | 0.1 ·W | 0.1 ·W | |
| Depth f | 0.03 | 0.06 | ||
| Surface roughness | μm | N | 10 | 16 |
| μm | S | 5 | 6 | |
| Noise | / | N | Allow | |
| / | S | Allow | ||
Storage Guide
In order to avoid the physical and chemical properties of O-rings caused by long-term storage, a reasonable storage environment is necessary to ensure that the O-rings are not affected during long-term storage.
During storage, the following points should be observed:
(1) The storage environment must be dry, dust-free and well ventilated;
(2) The temperature should be above +15℃ but not exceed +20℃;
(3) Store in hollow packaging bags as much as possible, and avoid ingredients that damage the material of the O-ring;
(4) Avoid direct sunlight in the storage environment and keep away from ultraviolet light sources;
(5) When storing, the O-rings should be in a stress-free state, that is, not stretched, not compressed, and not deformed:
(6) It is forbidden to tie with string or hang on metal parts.
Address
No.1 Ruichen Road, Dongliuting Industrial Park, Chengyang District, Qingdao City, Shandong Province, China
Tel
Internal pressure: The outer diameter of the O-ring and the outer diameter of the groove D should be basically close to or greater than 1~3%.
External pressure: The inner diameter of the O-ring should be close to or slightly smaller than the inner diameter d of the groove, but not less than 6%.
