Service Performance and Sealing Mechanism of Hydraulic Rubber Seals
As core basic components of mechanical products, hydraulic rubber seals are crucial guarantees for the normal operation of hydraulic systems. They are required in almost all hydraulic equipment and widely used in various fields such as automobiles, motorcycles, construction machinery, and general machinery. Their core function is to prevent the leakage of working medium (liquid) in the hydraulic system, and at the same time block the intrusion of external air, dust and other pollutants into the system and components, avoid oil pollution, thereby ensuring the operating efficiency and working performance of hydraulic products and extending the service life of equipment.
To ensure the stable and reliable operation of the hydraulic system, the use of hydraulic rubber seals must meet the following core performance requirements:
1. Minimal leakage: Hydraulic seals shall have excellent sealing performance, with leakage controlled within a very small range, and the sealing performance shall automatically enhance with the increase of hydraulic oil pressure; even under harsh working conditions such as high pressure and high temperature, the leakage shall not increase significantly to ensure the stability of system pressure.
2. Good compatibility: Since hydraulic seals are long-term immersed in hydraulic oil, they are prone to physical and chemical changes such as swelling, dissolution, embrittlement or hardening, leading to the failure of sealing function. Therefore, it is required that the seals have good compatibility with the contacted hydraulic oil (working medium) and can work stably for a long time without abnormal deterioration.
3. Low frictional resistance: To avoid or suppress adverse phenomena such as low-pressure crawling and operation jamming of hydraulic equipment, hydraulic seals shall have low static and dynamic frictional resistance, and the friction coefficient shall remain stable, so as to reduce the power loss of the system and ensure the smooth operation of the equipment.
4. Long service life: Hydraulic seals shall have excellent elasticity, heat resistance, cold resistance, pressure resistance, wear resistance, as well as a certain degree of physical and mechanical strength, which can adapt to the long-term test of complex working conditions, extend the replacement cycle, and reduce the equipment maintenance cost.
Sealing Mechanism of Hydraulic Rubber Seals
According to the different sealing working conditions, sealing can be divided into two categories: static sealing and dynamic sealing. Among them, static sealing mainly includes three forms: gasket sealing, sealant sealing and direct contact sealing, which are suitable for scenarios where there is no relative movement between sealing surfaces; dynamic sealing can be divided into two basic types: rotary sealing and reciprocating sealing, which are suitable for working conditions where there is relative movement between sealing surfaces.
The sealing mechanism of hydraulic rubber seals mainly involves two core links: one is cavity sealing, whose core is to ensure the accurate positioning of the outer edge (static component) of the seal in the installation cavity, preventing the medium from leaking from the fit gap between the seal and the cavity; the other is dynamic sealing, that is, the contact sealing between the sealing lip and the surface of the rotating shaft, which is the key for the seal to realize the core sealing function and directly determines the quality of the sealing effect.
The sealing mechanism of the contact area of the seal lip is of decisive significance for the exertion of its sealing function. The sealing effect mainly depends on three key factors: the structural design of the sealing lip, the structural characteristics of the elastic material, and the roughness of the rotating shaft surface. The combined effect of the radial force of the sealing lip, the design of the lip angle, and the design of the distance between the lip tip and the spring center will form an asymmetrically distributed contact pressure in the contact area between the sealing lip and the shaft surface——the contact pressure on the oil side is the largest and shows a steep upward trend, while the contact pressure on the air side decays slowly at a small angle.
Under the action of interference fit (the inner diameter of the sealing lip in the free state is designed to be slightly smaller than the diameter of the shaft), this asymmetrically distributed contact pressure, combined with the circular hoop force generated by the rotation of the rotating shaft, will cause structural elastic deformation in the contact area of the sealing lip. This deformation structure of the sealing elastomer is gradually formed during the running-in period of the oil seal, which plays a decisive role in the sealing performance. Therefore, the hydraulic rubber seal needs a running-in period before being put into formal use to ensure the stability of the deformation structure. In addition, the combined effect of the rotation of the shaft and the spiral line on the surface of the sealing lip will make this deformation structure produce a pumping effect towards the oil side, further enhancing the sealing effect.
The frictional characteristics of the sliding surface of the seal lip are mainly determined by the viscosity and sliding speed of the working medium. Under normal working conditions, a uniform oil film will be formed on the sliding surface. The mutual sliding between the seal and the rotating shaft is carried out under the lubrication state separated by the oil film, thereby effectively reducing friction and wear. On the sliding contact surface of the seal, the oil will form a circular flow of "atmospheric side → oil side → atmospheric side". A good lubrication state can effectively inhibit the aggravation of wear, thereby avoiding leakage. It can be seen that accurately controlling the performance of the seal lip material and the shape of the lip structure, and then regulating the lubrication characteristics and sealing mechanism of the seal, is the key to ensuring the sealing effect and service life of the hydraulic rubber seal.