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What are the considerations for choosing an O-ring?

2024-06-29 18:37:35

In the use of O-rings, specific working conditions and conditions of use need to be considered. Temperature and pressure will have effects and losses on the O-ring seal. Therefore, the following 5 points need to be considered in the use of O-ring rubber seals:

1. Working medium and working conditions;

2. The compatibility of the product with the working medium, and then consider the pressure, temperature, continuous working time, operating cycle and other conditions at the seal, and the temperature rise caused by friction heat also needs to be considered in rotating occasions;

3. Seal form: When the shaft seal is installed radially, the deviation between the inner diameter of the O-ring and the diameter to be sealed should be as small as possible; for the hole seal, the inner diameter should be equal to or slightly smaller than the groove diameter. When installing axially, the pressure direction should also be considered. When the internal pressure is used, the outer diameter of the O-ring should be about 1%~2% larger than the outer diameter of the groove. When the outer diameter is under pressure, the inner diameter of the O-ring should be about smaller than the groove1%~3%.

4. Other factors affecting sealing performance

1) Hardness: Determine the compression amount of the O-ring and the maximum allowable extrusion gap of the groove;

2) Extrusion gap: system pressure, O-ring section diameter and material hardness are related.

3) Compression permanent deformation: In the case of pressure, in order to prevent permanent plastic deformation. The maximum compression allowed by the O-ring is about 30% in static seals and about 20% in dynamic seals.

4) Pre-compression amount: In order to ensure the tightness in the groove of the O-ring, an initial compression amount should be reserved. The pre-compression amount relative to the section diameter is usually about 15%~30% in the static seal. It is about 9% ~25% in the dynamic seal.

5) Tension and compression: For the hole seal, the O-ring is in a stretched state, and the maximum allowable stretch is 6%. For the shaft seal, the O-ring is compressed along the circumference direction, and the maximum allowable circumference compression is 3%.

5. The O-ring is used for low-speed rotary motion and a rotary shaft seal with a short operating cycle. When the peripheral speed is lower than 0.5m/s, the selection of the O-ring can be based on normal design standards; when the peripheral speed is greater than 0.5m/s , It is necessary to consider the phenomenon that the elongated rubber ring shrinks after being heated, and the sealing ring should be selected so that the inner diameter is about 2% larger than the diameter of the sealed shaft.