I. Unreasonable design and selection
(1) According to whether there is relative motion between the two sealing surfaces, the seal is divided into static seal and dynamic seal two categories. Dynamic seal is divided into rotary dynamic seal and mobile dynamic seal according to the different direction of relative movement. In addition, the type of working medium, pressure, temperature and the relative speed of motion between the two pairs of sealed parts have different requirements for the material and structure of the seals. For example, static seal multi-purpose O-ring, gasket, sealant, etc.; Rotary dynamic seal in addition to the O-ring seal, oil seal is also widely used; Reciprocating movement is generally less use of O-ring, especially at high speed is generally not used, and the common use of lip sealing ring such as V, Y, Yx, J shape.
(2) Materials used as seals, nitrile rubber and polyurethane, can only be used in the oil temperature below 100℃; The use temperature of polypropyl resin, silicone rubber and tetrafluoroethylene is -50 ~ 225℃; Oil resistant rubber and clip fabric oil resistant rubber can be used at 120℃ for a long time. The highest pressure resistance of the rotary shaft lip seal ring is 0.4 ~ 0.7MPa, and the reciprocating lip pressure resistance is between 30 ~ 80MPa according to the different material and shape; Fluorine rubber is suitable for almost all lubricating oil, fuel oil and gasoline, while silicone rubber is not suitable for mineral oil with low benzene glue point and oil containing extreme pressure additives; Nitrile rubber is good for oil resistance, but not suitable for phosphoric acid hydraulic oil and gear oil containing extreme pressure additives; The linear speed of rotating lip seal ring and spindle contact is generally 6 ~ 12m/s, reciprocating lip rubber or cloth rubber is 0.5 ~ 1.5m/s. In addition, the hardness of rubber should change with the level of pressure and the size of the gap. When the pressure is high and the gap is large, the hardness is slightly larger, and on the contrary, it becomes smaller.
(3) The structure, size and tolerance design of the seal itself are unreasonable and do not meet the requirements of the relevant standards.
(4) Improper design of the structure size and tolerance of the sealing parts installation groove or processing does not meet the design requirements.
(5) Too high surface roughness of the shaft matching the seal will accelerate the wear of the seal; Too low, the lubrication film between the lip of the seal and the contact surface of the shaft is difficult to form, and the general roughness is appropriate between Ra0.32 and 0.16.
(6) The inner hole and stop of the bearing cover of the oil seal shall not only meet the dimensional accuracy, but also the coaxiality tolerance shall not be too large. If the coaxiality Diweiation between the oil seal and the spindle is too large, the surface of the oil seal and the spindle will produce local wear and lead to leakage.
Two. Poor assembly
(1) Without checking before installation, the seals that do not meet the requirements will be installed.
(2) The processed sealing groove is not checked during installation, and the groove has burrs, roughness, dimensional accuracy and form and position tolerance without chamfering.
(3) During installation, the installation site, tools and sealing grooves are not guaranteed to be clean, and there are iron filings and other debris in the grooves.
(4) No hydraulic oil or grease is applied to the lip of the seal during installation.
(5) Improper operation during assembly, resulting in damage to the seals. When the seals pass through threads and other easily damaged parts, they are not installed with protective sleeves or wrapped with tape, or when the seals pass through the keyway and other parts, they fail to take corresponding measures (such as filling the keyway with asbestos board or rubber) to protect them.
(6) some seals are directional, such as careless direction installed, it will not only play a sealing role, but will cause leakage.
3. Improper use and storage
(1) The oil is polluted, and the content of solid particles exceeds the standard, which leads to the deterioration of the sealing parts. Due to the presence of water in hydraulic oil, it will accelerate the wear and corrosion of components, and make the oil deteriorate, resulting in poor seal.
(2) The continued use of aging oil will corrode the seals, and the hard oxide particles will make the corroded seals wear.
(3) If the compatibility between the oil and the sealant is poor, it will accelerate the deterioration of the sealant. Hydraulic oil must be selected in accordance with the requirements of the machine instruction manual.
(4) The seals that have been used for many years have been permanently deformed or aged, but they continue to be used.
(5) improper storage. When the rubber seals are stored, the temperature in the warehouse is required to be kept between -15 and 35 degrees Celsius, the relative humidity should be kept between 50% N80%, and should avoid direct sunlight, rain and snow immersion, prohibit contact with acid and alkali, oil and organic solvents that affect the quality of rubber, and should be more than Im away from the heat source. Such as can not meet these requirements, or storage time is too long and caused by rubber aging, or because of stacking, hanging and permanent deformation, can make seal failure.

The basic principle of industrial seal selection
① Follow the working speed selection
Because of the different speed of different equipment at work, there will be differences in the selection of seals, working speed and relatively slow can not choose the same sealing product, otherwise it is easy to cause leakage. In short, following the working speed to choose can improve the efficacy of the product and reduce the adverse use process.
② Follow the working medium selection
Different equipment sealing medium is not the same, such as acid and alkaline compounds, lubricating oil, water and other media. Therefore, we should consider the compatibility of the working medium and the sealing material to avoid material selection errors, leading to the shortening of the service life of the seals.
③ Follow the operating temperature selection
Many equipment will produce a large temperature in the operation, so special attention should be paid to the selection of sealing products, according to the actual temperature to choose different s seals can avoid adverse effects in the process of use.
Follow the work pressure selection
Because the seals are applied in the internal mechanical equipment, so in the selection should follow the working pressure of the sealing chamber body to choose, the right industrial seals in order to better play its sealing role.
When choosing industrial seals, we should not only follow certain principles, but also pay attention to the quality of the seals themselves. Good seals can not only allow sealing products to effectively play a variety of different sealing roles, but also allow different equipment to be used in a stable state, without a variety of abnormalities or failures