What Are The Factors That Affect The Sealing Performance Of Rubber O-rings?

1. Compression permanent deformation

Another indicator for evaluating the sealing performance of O-rings is the compression set of the material. Under the action of pressure, the O-ring as an elastic element is elastically deformed, and as the pressure increases, permanent plastic deformation occurs.

2. Installation compression force

During installation, the compressive force is related to the degree of initial compression and the hardness of the material.

3. Pre-compression amount

The O-ring is installed in the groove, in order to ensure its sealing performance, an initial compression amount should be reserved. For different applications, the amount of pre-compression relative to the section diameter W is also different. Usually, it is about 15% to 30% in static seals, and about 9% to 25% in dynamic seals.

4. The hardness of the O-ring

O-ring material hardness is the most important indicator for evaluating sealing performance. The hardness determines the amount of compression of the O-ring and the maximum allowable extrusion clearance of the groove. Since the nitrile seal of Shore A70 can meet most of the conditions of use, there is no special description for the sealing material, and the nitrile rubber of Shore A70 is generally provided.

5. O-rings are used as rotary shaft seals

O-rings can also be used as rotary shaft seals for low-speed rotary motion and short operating cycles. When the peripheral speed is lower than 0.5m/s, it is necessary to consider the phenomenon that the elongated rubber ring will shrink after being heated, so the inner diameter of the sealing ring is about 2% larger than the diameter of the shaft sealed by it. After the sealing ring is installed in the groove, the sealing ring is compressed radially, and the O-ring ring forms a slight corrugation in the groove, thereby improving the lubrication condition.

6. Extrusion gap

The maximum allowable extrusion gap gmax is related to the system pressure, the diameter of the O-ring section and the hardness of the material. Generally, the higher the working pressure, the smaller the maximum allowable extrusion gap gmax. If the gap g exceeds the allowable range, the O-ring will be squeezed out and damaged.

7. Tension and compression

When the O-ring is installed in the groove, it is subject to tension or compression. Excessive values of tension and compression will result in an excessive increase or decrease in the cross section of the O-ring, since 1% stretching correspondingly reduces the cross-sectional diameter W by about 0.5%. For hole seals, the O-ring should preferably be in a stretched state, with a maximum allowable stretch of 6%; for shaft seals, the O-ring should preferably be compressed along its circumference, with a maximum allowable circumference compression of 3 %.