O型圈及其槽设计
Design of O type sealing ring and its groove
The O ring seal is a typical extrusion seal. The compression ratio and stretch of the section diameter of O ring are the main contents of sealing design, which are important for sealing performance and service life. The O ring is usually installed in the sealing groove to seal. The good sealing effect of O shape seal ring depends largely on the proper matching of the size of the O ring and the groove size, forming a reasonable sealing ring, the amount of compression and the amount of tension. Sealing device design, processing, if the O ring compression is too small, it will cause leakage; too much compression will lead to O ring rubber stress relaxation caused by leakage. Similarly, excessive stretching in the work of the O ring will also accelerate aging and cause leakage. The standards of the countries all over the world have strict regulations.
1, O ring seal design principles
1) compression ratio
Compression rate W pass is usually expressed in the lower form:
W= (do-h) /do%
Section diameter of do - O - ring in free form (mm)
H -- the distance between the bottom of the O ring groove and the sealed surface, that is, the height of the cross section (mm) after the compression of the O ring.
When choosing the compression ratio of O ring, we should consider the following three aspects:
A. should have enough sealed contact area
B. the friction is as small as possible
C. avoid permanent deformation as much as possible.
From these factors, it is not difficult to find that they are contradictory to each other. The greater compression ratio leads to greater contact pressure, but excessive compression will undoubtedly increase sliding friction and permanent deformation. The compression rate is too small, it may be due to the sealing groove of coaxial error and O ring error does not meet the requirements, the loss of part of the volume of compression caused by leakage. Therefore, in choosing the compression ratio of the
O ring, the factors to be weighed are weighed. Generally, the compression rate of the static seal is greater than that of the dynamic seal, but the extreme value should be less than 30% (as opposed to the rubber material). Otherwise, the compressive stress is obviously relaxed and will cause excessive permanent deformation, which is especially severe in the high temperature condition.
The compression rate of W selection should consider the use condition of the sealing O ring, a dynamic or static seal static seal; it can be divided into radial and axial seal seal; radial seal (or cylindrical sealing) leakage clearance is the radial clearance, axial seal (or plane static seal) leakage gap is the
axial clearance. Axial seal according to the pressure medium acting on the inner diameter or outer diameter of the O ring, and divided into two conditions, internal pressure and external pressure, the internal pressure increases the tensile, external pressure to reduce the initial stretch of the O ring. The different forms of static seal, the sealing medium on the O - shaped coil direction of force is different, so the design of pre stress is also different. For dynamic seals, it is necessary to distinguish whether it is reciprocating motion or rotary motion seal. 1., static seal: cylindrical static sealing device and reciprocating type sealing device, generally take W=10%~15%; flat sealing device, take W=15%~30%. 2. for dynamic seal, can be divided into three cases: A. reciprocating seals, usually take W=10%~15%.
B. rotational motion seal must consider Joule heating effect when choosing compression ratio. Generally speaking, the inner diameter of O ring used in rotary motion is larger than that of shaft, and the compression rate of 3%~5% is W=3%~8%. C. low friction motion uses O ring. In order to reduce the friction resistance, the smaller compression ratio is generally chosen, that is, W=5%~8%.
Besides,
Also consider the expansion of the rubber material caused by the medium and temperature. Generally, the maximum expansion rate allowed outside a given compressive deformation is 15%, beyond this range, indicating that the material is not suitable for use and should be replaced by a O ring of other materials or a given rate of compression deformation. The specific values of compression deformation, under normal circumstances, all countries in accordance with their own experience in the
development of standards or recommended values.
stretch up high2) tensile quantity
Generally, the O ring has a certain amount of tension when it is loaded into the sealing groove. Different from the compression ratio, the amount of tensile has great influence on the sealing performa
nce and service life of O ring. A large amount of tensile will not only lead to the difficult installation of O ring, but also reduce the compression ratio due to the change of section diameter do, so as to cause leakage. The tensile amount alpha can be expressed in the lower form:
Alpha = (d+do) / (d1+do)
Type
D - shaft diameter (mm);
D1 - the inner diameter of the O ring (mm);
Sectional diameter of do - O - ring (mm).
3) contact width
After the O ring is loaded into the sealing groove, its cross section produces compression deformation. The width of the contact width and the deformation of the shaft and O ring sealing performance and service life, its value is too small will make the sealing of the affected; too large increase friction, friction heat, influence of O ring life.
The width BO (mm) after the deformation of the O shape ring is related to the compression ratio W of the O ring and the sectional diameter dO, and can be calculated by the lower form
BO={1/ (1-W) -0.6W}dO (W take 10%~40%)
The width of the contact surface B (mm) of the O - shaped ring and the shaft also depends on W and dO:
B= (4W2+0.34W+0.31) dO (W take 10%~40%)
The O ring seals with higher friction limits such as pneumatic seals and hydraulic servo control elements can be used to estimate the friction force.
2, O ring design
The vast majority of O rings are made of synthetic rubber. The size of O - shaped rings of synthetic rubber is determined by international standards (ISO3601/1), national standards and organizational standards. Some countries, such as O ring size series is divided into P series (Sports), G series (fixed), V series (vacuum) and ISO series (general industrial use) four series. The diameter, section diameter, size and tolerance of O rings in our country are stipulated by GB/T34542.1 - 1992. The seali
ng reliability of the seal depends mainly on the amount of compression of the O ring. In general, the amount of compression is very small, only a dozen microns to tens of microns, which requires the size of the O ring tolerance is very high accuracy. Therefore, the O ring needs to be machined with

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