(1) Introduction of oil seal
Oil seals are mainly used to seal oil seals in rotary motion. Most of the main oil seals are equipped with springs as the main source of seal contact pressure. Due to the metal spring's resistance, fatigue resistance (long-term use without stress attenuation), and its good adjustability (spring length adjustment), and because the oil seal lip is not directly installed in the groove like the "O" ring It is connected to the skeleton through a certain flexible waist, so that it has a certain adaptability (that is, the machining accuracy does not need to be as high as the "O" shape, allowing a certain degree of eccentricity). The new oil seal is widely used in general After continuous research, new oil seals with long life and high speed are also being developed.
(2) Principle of oil seal sealing
1. The theory of boundary lubrication: that is, when the oil package is assembled to the working state, an oil film is formed between the contact surface of the lip and the shaft. The thickness of the oil film changes with the magnitude of the radial force. When the thickness of the oil film is within a quiet range (The average thickness is about 2.5, and the fluctuation is about 20-50%, the thickness varies with the type of oil), and the sealing effect can be obtained. This oil film is called "boundary oil film". It is related to the adsorption capacity. Once a leak, it means that the boundary oil film is destroyed, forming a fluid oil film or dry friction (which eventually leads to a fluid oil film). In general, the sharp distribution of the contact pressure is more conducive to sealing, (see figure)
2. Surface tension sealing theory: It is believed that on the contact surface, the oil film has a certain thickness without leakage, which is the result of the surface tension of the oil film. (pictured)
There is a closed oil film (about 0.003 mm thick) under the lip. On the one hand, it plays a lubricating role. On the other hand, the thickness of the oil film is just to form a meniscus on the atmospheric side of the lip. As long as this meniscus exists, the surface tension According to this theory, the worse the "lubrication" of the oil to the surface to be sealed, the greater the contact width of the contact surface. The greater the pressure difference of the oil, the easier the effect of surface tension to obtain the seal , But in fact, for the general shape of the oil seal, the large contact width is detrimental to the seal. This is due to the influence of machining accuracy factors, the larger the contact width, the more severe the friction, and the reason why it is difficult to maintain the oil film.