What factors of hydraulic oil affect the performance of seals?

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Hydraulic oil is used in hydraulic transmission systems as a working medium, serving to transfer and convert energy as well as to control operations. It also performs functions such as lubricating the various components within the hydraulic system, preventing corrosion and rust, and providing cooling. Seals in hydraulic systems serve to prevent fluid from leaking between mating surfaces, maintain pressure, and ensure the transfer or conversion of energy. At present, most of the sealing materials used domestically and internationally are polymer elastomers; under certain special conditions, plastics and various metals are also utilized. But regardless of the type of material, it should possess the following properties: 1. Certain mechanical and physical properties: such as tensile strength, strength at a fixed elongation, and elongation rate ； 2. It has a certain degree of elasticity, appropriate hardness, and minimal permanent compression deformation ； 3. Suitable for the working medium, and does not easily suffer from swelling, decomposition, or hardening ； 4. Wear-resistant, with certain tear resistance ； 5. It possesses aging resistance to high and low temperatures. However, no sealing material possesses all of the aforementioned properties; it is necessary to select an appropriate sealing material based on the working environment, such as temperature, pressure, the medium involved, and the mode of movement, and to formulate the material composition accordingly to meet specific requirements. Alternatively, more than two materials can be used in a form that meets certain requirements or in a combined structure, allowing each material to utilize its strengths and achieving a more comprehensive result. Formation of the sealing effect: Dynamic seals are divided into non-contact seals and contact seals. Non-contact sealing mainly refers to various mechanical seals, such as graphite packing rings, floating ring seals, etc ； Both rubber-plastic composite seals and rubber-plastic combined seals belong to contact seals; they achieve a sealing effect by blocking the leakage paths through the pre-compression force applied within the sealing chamber. Seals used in hydraulic systems include static seals (face seals), reciprocating motion seals (piston and piston rod seals), and rotary seals. Factors affecting the sealing performance include: the selection of the sealing structure and oil film formation, pressure, temperature, material compatibility; the material, hardness, and shape of the working surfaces in contact in dynamic seals; as well as surface finish. Several common sealing materials with excellent resistance to media include: Nitrile rubber, silicone rubber, fluororubber, EPDM rubber, polytetrafluoroethylene, polyurethane rubber, and acrylate rubber. IV. The effect of hydraulic oil on the performance of seals. Seal theory posits that there is a complete lubrication film between a dynamically flexible seal and its mating surface. Under normal conditions, it is this lubricating film that helps achieve sealing and extend the lifespan of the seal. In hydraulic systems, the effect of hydraulic oil on the sealing performance of seals is influenced by various factors. These include the compatibility between the fluid and the sealing material, the viscosity of the oil, how viscosity changes with temperature, the speed of reciprocating (rotating) motion, pressure, as well as the material, hardness, geometric shape, and surface finish of the shafts, cylinder barrels, or piston rods. Additionally, the structure of the seals itself also affects the formation of the lubrication film and its properties, all of which influence the sealing effect. Generally speaking, forming a continuous lubricating film can achieve an ideal sealing effect. When the system’s speed is too high, it hinders the formation of a continuous lubricating film, leading to an increase in frictional heat. If this heat exceeds the temperature tolerance of the sealing material, it results in damage to the seal. When the pressure is too high, it not only affects the formation of the oil film but also exerts a \"pushing\" effect on rubber and plastic seals; this issue can generally be addressed by using retaining rings. Alternatively, choosing a PTFE composite seal structure with a low friction coefficient and good self-lubricating properties will facilitate lubrication between the frictioning surfaces of the cover and umbrella, making it suitable for sealing cylinder pistons and piston rods in applications involving high and low speeds of reciprocating motion as well as high-pressure systems.