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Factors to consider when choosing an O - ring

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Update time : 2020-12-08 09:31:04

Working medium and working conditions

When selecting o-ring material, the compatibility with working medium should be considered first.The working conditions such as pressure, temperature, continuous working time and operating cycle of the sealing place shall also be considered.When used in rotary applications, the temperature rise due to friction heat must be considered.Different sealing material, its physical and chemical properties are different.

Seal form

 

According to load type can be divided into static seal and dynamic seal;According to sealing purpose, it can be divided into hole seal, shaft seal and rotary shaft seal.According to its installation form can be divided into radial installation and axial installation.For radial installation, the deviation between the inner diameter of the O-ring and the sealed diameter d2 shall be as small as possible for shaft seals;For hole seals, the bore diameter should be equal to or slightly less than the trench diameter D1.

When installing axial, consider the direction of pressure.Internal.When the force is applied, the outer diameter of the O-ring should be about 1 ~ 2% larger than the outer diameter d3 of the trench.When the external pressure is applied, the inner diameter of the O-ring should be about 1 ~ 3% smaller than that of the trench inner diameter D4.

Other factors affecting sealing performance

Hardness of O-ring

The hardness of O-ring material is the most important index to evaluate the sealing performance.Hardness determines the compression amount of the O-ring and the maximum groove

Allowed extrusion clearance.As shaw A70's ding Qing seal can meet most of the conditions of use, so the sealing material is not special

In particular, butadiene rubber of Shaw A70 is generally available.

(2) Extrusion clearance

The maximum allowable extrusion clearance is related to the system pressure, o-ring section diameter and the hardness of the material.Generally, the higher the working pressure is, the smaller the value of the maximum allowable extrusion clearance is.If the clearance exceeds the allowed range, the O-ring will be extruded and damaged.

 

(3) Compression permanent deformation

Another index to evaluate the sealing performance of O-ring is the compression permanent deformation of the material.Under the action of pressure, the O-ring, as an elastic element, produces elastic deformation, and with the increase of pressure, permanent plastic deformation will occur.Compression permanent deformation D can be determined by the following formula:

 

Where: B0 - original thickness (section diameter W), B1 - Thickness under compression.

In general, to prevent permanent plastic deformation, the maximum allowable compression of the O-ring is approximately 30% in a static seal and 20% in a dynamic seal.

Table: Recommended values for o-ring compression of partial line diameter

Section diameter of O-ring

(mm) 1.9 + / - 0.08 to 2.4 + / - 0.09 3.1 + 3.5 + / - 0.11 5.7 0.1 8.6 0.14 mm + / - 0.16

Cylindrical dynamic

Seal or

Maximum static seal

(%) 24 20 20 17 15 12

The minimum

(%) 15 12 12 9 8 7

 

Plane of the static

Seal the biggest

(%) 30 29 27 26 22 20

 

22 22 18 18 16

, precompression quantity

The O-ring is installed in the groove and an initial amount of compression should be reserved to ensure its sealing performance.For different application fields

The amount of precompression relative to section diameter W is also different.

In general, about 15% ~ 30% in static seal, and about 9% ~ 25% in dynamic seal.Specific can consult below chart to undertake choosing.

(5) Stretching and compression

The O-ring shall be stretched or compressed when installed in the groove.If the value of stretching and compression is too large, the o-ring section will be excessively increased or decreased, because 1% of stretching will correspondingly reduce the section diameter W by about 0.5%.For the hole seal, the O-ring should be in the best stretching state, the maximum allowable stretching amount is 6%;For shaft seals, the O-ring is best compressed in the direction of its perimeter, with a maximum allowable perimeter compression of 3%.

6, O ring as a rotary shaft seal

The O-ring can also be used as a rotary shaft seal for low speed rotary motion and short operating cycle.When the circumferential speed is lower than 0.5m/s, the phenomenon that the elongated rubber ring will shrink when heated should be considered. Therefore, the inner diameter of the sealing ring should be about 2% larger than the axial diameter sealed by it.The placement of the seal ring in the groove results in radial compression of the seal ring, and the O-ring forms a trace ripple in the groove, thus improving lubrication conditions.

Installation of compression force

During installation, the compression force is related to the degree of initial compression and the hardness of the material.The relationship between the unit compression force per centimeter on the seal circumference and the section diameter is shown below to estimate the total force required to install the O-ring.