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Talking about the reasons for the failure of seals and the basic principles of industrial seal selection

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• 1. Unreasonable design selection

        (1) Seals are classified into static seals and dynamic seals according to whether there is relative movement between the two joint surfaces to be sealed. Dynamic seals are divided into rotary dynamic seals and mobile dynamic seals according to different directions of relative movement. In addition, the type of working medium, pressure, temperature, and the relative speed of movement between the two pairs of seals have different requirements for the material and structure of the seal. For example, static seals mostly use O-rings, various gaskets, sealants, etc.; in addition to O-rings for rotary dynamic seals, oil seals are also widely used; for reciprocating motion, O-rings are generally less used, especially at high speeds. Generally not used, but lip-shaped sealing rings such as V-shaped, Y-shaped, Yx-shaped, J-shaped, etc. are commonly used.

        (2) Nitrile rubber and polyurethane used as seals can only be used at oil temperatures below 100°C; while polypropylene rubber, silicone rubber and tetrafluoroethylene can be used at temperatures of -50 to 225°C; oil resistance Rubber and oil resistant rubber with interlocking fabric can be used for a long time at 120℃. The maximum pressure resistance of the rotary shaft lip seal ring is 0.4～0.7MPa, and the pressure resistance of the reciprocating lip type is between 30 and 80MPa depending on the material and shape. Fluorine rubber is suitable for almost all lubricating oil, fuel oil and gasoline. Rubber is not suitable for mineral oils with low benzene point and oils containing extreme pressure additives; nitrile rubber has good oil resistance, but it is not suitable for phosphate-based hydraulic oils and gear oils containing extreme pressure additives; rotating lip seals The linear velocity in contact with the main shaft is generally 6-12m/s, and the reciprocating lip rubber or cloth rubber is 0.5-1.5m/s. In addition, the hardness of the rubber should vary with the pressure and the size of the gap. When the pressure is high and the gap is large, the hardness is slightly greater, and vice versa.

        (3) The structure, size and tolerance design of the seal itself is unreasonable and does not meet the requirements of relevant standards.

        (4) The structural dimensions and tolerances of the seal installation groove are improperly designed or the processing does not meet the design requirements.

        (5) If the surface roughness of the shaft matched with the seal is too high, it will accelerate the wear of the seal; if it is too low, it is difficult to form a lubricating film between the lip of the seal and the contact surface of the shaft. Generally, the roughness is between Ra0.32～0.16 Time is appropriate.

        (6) The inner hole and stop of the bearing cap with the oil seal must not only meet the requirements for dimensional accuracy, but also the coaxiality tolerance must not be too large. If the coaxial deviation of the oil seal and the spindle is too large, the oil seal and the spindle surface will be partially Wear and cause leakage.

        2. Poor assembly

        (1) The seals that did not meet the requirements were installed without inspection before installation.

        (2) The machined sealing groove was not inspected during installation, and the groove was not chamfered with burrs, roughness, dimensional accuracy, and geometric tolerances that did not meet the requirements.

        (3) Failure to ensure the cleanliness of the installation site, tools and sealing grooves during installation, and iron filings and other debris in the grooves.

        (4) No hydraulic oil or grease was applied to the lips of the seal during installation.

        (5) Improper operation during assembly can cause damage to the seal. When the seal passes through the thread and other easily damaged parts, it is installed without a protective cover or covered with tape, or when the seal passes through the keyway, etc. Corresponding measures (such as filling the keyway with asbestos board or rubber) provide protection.

        (6) Some seals are directional. If the direction is inadvertently installed, it will not only fail to seal, but will cause leakage.

        3. Improper use and storage

        (1) The oil is contaminated, and the content of solid particles exceeds the standard, which leads to increased seal wear. Due to the presence of water in the hydraulic oil, it will accelerate the wear and corrosion of components, and degrade the oil, resulting in poor sealing.

        (2) Continued use of aging oil will corrode the seals, and the hard oxide particles in it will wear out the corroded seals.

        (3) If the oil used has poor compatibility with the seal rubber material, it will accelerate the deterioration of the rubber material. The hydraulic oil must be selected according to the requirements of the machine manual.

        (4) Some of the seals that have been used for many years have undergone permanent deformation or aging, but continue to be used.

        (5) Improper storage. When rubber seals are stored, the temperature in the warehouse should be kept between -15-35°C, the relative humidity should be kept between 50% and 80%, and direct sunlight, rain and snow immersion, and acid and alkali, oils should be avoided. Contact with organic solvents and other substances that affect the quality of rubber, and the distance from the heat source should be more than Im. If these requirements are not met, or the storage time is too long and the rubber is aging, or permanent deformation due to stacking or hanging, etc., the seal can be invalidated.

  
  

        The basic principles of industrial seal selection

        ① Follow the working speed selection

        Due to the different working speeds of different equipment, there will be differences in the selection of seals. Fast and relatively slow working speeds cannot choose the same sealing product, otherwise it will easily cause leakage. In short, following the work speed to choose can improve the efficacy of the product and reduce the defects in the use process.

        ②Follow the selection of working medium

        Different equipment sealing media are not the same, such as acid-base compounds, lubricating oil, water and other media. Therefore, it is necessary to consider the compatibility of the working medium and the sealing material to avoid material selection errors, which will shorten the service life of the seal.

        ③Follow the working temperature selection

        A lot of equipment will produce a large temperature during operation, so special attention should be paid when selecting sealing products. According to the actual temperature, choosing different s seals can avoid adverse effects during use.

        ④ Follow the working pressure selection

        Because the seals are all used inside the mechanical equipment, the working pressure in the sealed cavity should be followed when selecting, and the appropriate industrial seals can better play its sealing role.

        When choosing industrial seals, not only must follow certain principles, but also pay attention to the quality of the seal itself. A good seal not only allows the sealing product to effectively perform various sealing functions, but also allows different equipment to be used in a stable state without various abnormalities or failures.

  
  

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