O-rings are usually selected as large-section O-rings as much as possible. Under the same gap, the volume of the O-rings squeezed into the gap should be smaller than the maximum allowable value.

O-rings are annular rubber seals with a circular cross-section, which are mainly used for mechanical parts to prevent leakage of liquid and gaseous media under static conditions. In some cases, the O-ring can also be used as a dynamic sealing element for axial reciprocating motion and low-speed rotary motion. According to different conditions, different materials can be selected to suit it.

O-ring seals are the most common form of sealing used in fluid power systems. They work well in many fluid power systems, but they must be used with care and care. O-rings only work when they are deformed. An O-ring is shaped like an O-ring, it is installed in the seal groove and then pressed so that there is no gap in the seal groove to seal off liquid or air flow. Although this simple sealing structure works well in fluid power systems, it can only be achieved with careful design, careful selection, and proper installation.

2. Reasons and countermeasures for the failure of O-ring seals

(1) Installation damage Failure state: Part or all of the sealing ring has a neat wound.

Causes of failure: sharp edges and corners of grooves and other components, improper size of seals; too low hardness or elasticity of seals; dirt on the surface of seals. Solution: remove sharp edges and corners; make groove design more reasonable; choose seals with appropriate size; choose seals with greater elasticity and higher hardness.

(2) Curl failure state: The O-ring is obviously curled. Failure reasons: caused by installation, the movement speed is too low, the material is too hard or the elasticity is too small, the surface treatment of the O-ring is uneven, the groove size is uneven, the groove The groove surface is rough and the lubrication is insufficient. Solution: Install it correctly, select high elastic materials, properly improve the design of the groove and the surface finish, and use the support ring as much as possible.

(3) Excessive compression Failure state: The contact surface of the O-ring is flat and deformed, and may be accompanied by cracks. Failure reason: The design is unreasonable, and the deformation of the material due to heat and chemical media, or the deformation caused by excessive pressure is not considered. Solution: The design of the groove should take into account the deformation of the material due to temperature and chemical media.

(4) Permanent compressive deformation Failure state: The contact surface of the seal exhibits plane permanent deformation. Failure reasons: too high pressure; too high temperature; the material has not completed the vulcanization treatment; the permanent deformation rate of the material itself is too large; the material is excessively expanded in the chemical medium. Solution: Select materials with low deformation rate; appropriate groove design; confirm that the material is compatible with the medium.

(5) Failure state of chemical corrosion damage: chemical corrosion can cause various defects of O-ring seals, such as blistering, cracking, small holes, or discoloration, etc. Sometimes chemical corrosion can only be known by measuring its physical properties with instruments . Failure reason: The material does not match the medium or the temperature is too high. Solution: Choose a material that is more resistant to chemical media corrosion.

(6) Damage

Failure state: The O-ring seal is damaged by wear in all or part of the sealing area, and particles of material wear can be found on the sealing surface. Reasons for failure: The surface finish of the seal is not enough, the temperature is too high, the sealing environment enters into the highly abrasive sundries, the seal produces relative movement, and the surface treatment of the seal is not thorough. Solution: Improve the groove finish, choose self-lubricating materials, and clear the parts and environment that cause wear.

(7) Blasting failure state: bubbles, pits and scars appear on the surface of the O-ring; when the pressure is very high, the material absorbs the gas in the medium, and when the pressure suddenly decreases, the gas absorbed by the material runs out quickly, causing the O-ring seal Ring skin blasting. Cause of failure: The pressure changes too fast, and the hardness and elasticity of the material are too low. Solution: Choose a material with higher hardness and better elasticity to reduce the speed of decompression.

(8) Debris contamination Failure state: There are foreign objects in the section of the O-ring. Failure reason: The production process is polluted by the environment, the material is corroded or reacted, and the material is non-semiconductor industry grade material. Solution: indicate the cleanliness required for production and packaging, and strengthen environmental control during the production, transportation and use of O-rings.

(9) Hot corrosion Failure state: The high temperature contact surface of the O-ring shows radial cracks, and some materials may become soft, or the material may become shiny due to excessive temperature. Failure reasons: The material cannot withstand high temperatures, or the temperature exceeds the design temperature, or the temperature changes too quickly and frequently.