Hydraulic oil for hydraulic transmission system as a working medium, from the energy transfer, conversion and control role, but also plays a hydraulic system of various components of lubrication, corrosion, rust and cooling and so on. The seals in the hydraulic system act to prevent fluid from leaking from the bonding surface, maintaining pressure, maintaining energy transfer or switching.
Hydraulic oil for hydraulic transmission system as a working medium, from the energy transfer, conversion and control role, but also plays a hydraulic system of various components of lubrication, corrosion, rust and cooling and so on. The seals in the hydraulic system act to prevent fluid from leaking from the bonding surface, maintaining pressure, maintaining energy transfer or switching.
At present, most of the sealing materials used at home and abroad is a polymer elastomer, some special conditions are also used in various types of plastic and metal. But no matter what kind of material, should have the following properties:
1, with a certain mechanical and physical properties: such as tensile strength, tensile strength, elongation;
2, a certain degree of flexibility, the right hardness, and a small compression set;
3, adapt to the working medium, not easy to produce swelling, decomposition, hardening;
4, wear resistance, a certain anti-tear performance;
5, with high temperature, low temperature aging properties.
However, none of the sealing materials described above includes all of the above properties, and it is necessary to select a suitable sealing material in accordance with the working environment such as temperature, pressure, medium, and movement pattern, and to meet certain requirements by formulating the formulation of the material. Or more than two kinds of material composite or combination of structures in the form of their respective strengths, to achieve a more comprehensive effect.
The formation of sealing effect: dynamic seal is divided into non-contact seal and contact seal. Non-contact seal is mainly a variety of mechanical seals, such as: graphite packing ring, floating ring seal, etc .; rubber and plastic composite seals and rubber seals are sealed contact with the sealed cavity in the preloading force, Blocking the leakage path to obtain the sealing effect. Hydraulic system seals are mostly static seal (end seal), reciprocating seal (piston, piston rod seal) and rotary seal.
Factors affecting the sealing effect: the choice of sealing structure and oil film formation, pressure, temperature, material compatibility, dynamic sealing the surface of the material, hardness, geometry, surface finish.
Seal material and hydraulic oil (liquid) compatibility:
One of the sources of particle contamination of hydraulic oil is the "debris" or "debris" that the seal material does not correspond to the hydraulic fluid. Seal due to "swollen" damage to the "debris" or "extracted" out of the unbound inorganic and filled with reinforcing materials, the seal damage and failure, while the formation of oil pollution caused by hydraulic Oil deterioration that failure.
In the hydraulic system, the vane pump is widely used, and the wear problem becomes prominent when the working pressure is greater than 6.9 MPa. Therefore, an antiwear agent is used in the hydraulic oil. To meet the hydraulic system near the high temperature heat source and the open flame, Fuel phosphate, water-glycol hydraulic fluids, oil-in-water and water-in-oil emulsions. Anti-rust and other types of compound additives for different uses of hydraulic oil (liquid) variety.For example: anti-wear hydraulic oil compound type of zinc-free type (no ash type) Anti-wear hydraulic oil compound, is the use of hydrocarbon sulfide, phosphate, phosphite, etc., as well as sulfur, phosphorus and nitrogen three elements of SPN extreme pressure anti-wear agent.In extreme pressure industrial gear oil, But also to PS-based extreme pressure agent.
The reason for the "swelling" or "extraction" of the seals is that the various chemical elements contained in the additive in the hydraulic fluid and their concentrations have different effects on the different sealing materials according to the principle of "similarity and compatibility". (P) element concentration in the gear oil of ShellOmala320 gear oil and ShellOmala460 is around 300ppm, so the nitrile rubber has polarity because of containing acrylic nitrile group, and has excellent properties of the sealing material, for example: ShellOmala320 gear oil and ShellOmala460 gear oil Of the oil resistance, but not suitable for the type of oil medium conditions.
With the continuous development of hydraulic oil (oil) varieties, to improve the oil (liquid) performance of the various anti-wear, extreme pressure additives, metal deactivators, demulsifiers and anti-foam additives, the impact of sealing materials Need to be verified through experiments.