Source：Jiangyin Eternal Heavy Industry Co.,Ltd. Release time：2021-08-30 14:48:39 Author：696
Hydraulic oil is used as a working medium in the hydraulic transmission system, which plays the role of energy transmission, conversion and control. It also plays the role of lubrication, corrosion prevention, rust prevention and cooling of various components in the hydraulic system. The seals in the hydraulic system play a role in preventing fluid leakage from the joint surfaces, maintaining pressure, and maintaining energy transfer or conversion.
At present, most of the sealing materials used at home and abroad are polymer elastomers, and under some special conditions, plastics and various metals are also used. But no matter what kind of material it belongs to, it should have the following properties:
1. It has certain mechanical and physical properties: such as tensile strength, fixed elongation strength, elongation;
2. It has a certain degree of elasticity, appropriate hardness, and small compression and permanent deformation;
3. It is compatible with the working medium and is not easy to swell, decompose and harden;
4. Abrasion resistance and a certain degree of tear resistance
5. It has high temperature and low temperature aging performance.
However, no sealing material includes all the above-mentioned properties. It is necessary to select a suitable sealing material according to the working conditions, and to meet certain requirements by formulating a material matching formula.
1. Compatibility of sealing material and hydraulic oil:
Vane pumps are widely used in hydraulic systems. When the working pressure is greater than 6.9MPa, the wear problem becomes prominent. Therefore, anti-wear agents are used in hydraulic oils. With the continuous research and development of hydraulic oil varieties, various additives have been added to improve oil performance
The reason for the "swelling" or "extraction" of the seal is that the various chemical elements contained in the additives in the hydraulic oil and their concentrations, based on the principle of "similar compatibility", have different effects on different sealing materials.
2. Testing and evaluation of oil resistance performance of sealing materials:
The oil-resistant performance of rubber material seals generally uses standard test oil. The seal is immersed under the temperature conditions and test time specified in the test standard, and its performance is evaluated by comparing the test values before and after the immersion.
3. The influence of hydraulic oil on the performance of seals:
The sealing theory believes that there is a complete lubricating film between a dynamic flexible seal and its mating surface. Under normal conditions, it is this layer of lubricating film to achieve the purpose of sealing and prolong the life of the seal.
In the hydraulic system, the influence of hydraulic oil on the sealing performance of the seals, in addition to the compatibility of the medium and the sealing material, the viscosity of the oil, the change in viscosity with temperature, and the speed of movement, etc., will all affect the formation of the lubricating film and the characteristics of the film. All affect the sealing effect.
Generally speaking, forming a continuous lubricating film can achieve an ideal sealing effect.
When the system movement speed is too high, it affects the formation of a continuous lubricating film, which will cause frictional heat to increase, and the temperature resistance range of the sealing material will be exceeded, which will cause the damage of the seal. When the pressure is too high, in addition to affecting the formation of the oil film, it will also have a "squeeze gap" effect on the rubber and plastic seals. Generally, a "retaining ring" can be used to improve it.
Reasonable selection of seals, correct installation, use and maintenance of seals according to the system operating conditions are the keys to obtaining effective sealing effects, reliability and service life.