Selection of hydraulic seal materials
When selecting sealing materials, the main considerations are the working conditions and the quality of the materials used, so that the machine can work efficiently. Examples are given below.
1. Working medium
Whether the sealing medium is liquid or gas is crucial. If it's liquid, compatibility between the liquid and the material must be considered; for gas, compatibility with lubricants and greases must also be considered; and for gas and negative pressure seals, air permeability must be taken into account. Incompatibility between the sealing material and the sealing fluid can cause the seal to expand or contract, leading to malfunctions in the initial stages of use. Seal expansion increases frictional resistance and can cause the seal to roll. Seal contraction reduces preload, decreases eccentricity compensation, and ultimately leads to leakage.
2. Coefficient of friction
Sealing requires materials with specific friction and wear resistance properties; therefore, materials with a suitable coefficient of friction should be selected based on the speed of movement. To achieve sufficient service life, the wear resistance of the material must also be selected based on the speed and stroke. When low-speed performance is required, special attention should be paid to the magnitude of the material's coefficient of friction and the difference between the dynamic and static coefficients of friction.
3. Structural type
Different structural types and sealing working principles (such as extrusion type, shaft lip type or mechanical seal, etc.) will inevitably have different requirements for the elasticity, strength, deformation rate and other mechanical properties of the materials.
4. Operating Temperature
The applicable temperature ranges of various sealing rings, whether made of rubber or plastic, or mechanical seals made of graphite or metal, vary greatly. When selecting materials, it is essential to accurately determine the operating temperature of the sealing components, especially in low-temperature environments; or to control the temperature rise of components, systems, and seals based on the operating temperature range of the materials.
5. Working Pressure
Working pressure is a key operating parameter of the sealing system, and can vary between 1-400 MPa or even further. The pressure resistance of the material should be adapted to the working pressure requirements.
6. Working Environment
If the working environment is dusty, it will accelerate material wear; therefore, the material's wear resistance should be improved.
7. Vibration and Impact
If the material operates under vibration or impact conditions, it should have sufficient strength and elasticity to compensate for seal damage and insufficient contact stress caused by vibration-induced displacement.
8. Assembly Process
The assembly process of seals, and even the structure of sealing devices, is related to the deformability of materials. Generally, the assembly process should be adapted to the material properties. Where permissible, the assembly performance of the seal should be appropriately considered when selecting materials.
The above eight requirements for sealing materials are often interdependent and cannot be perfectly unified. Regarding both sealing performance and friction resistance, from a material properties perspective, pursuing one inevitably comes at the expense of the other. Therefore, a proper balance between the two performance requirements must be struck. As higher sealing requirements emerge, specialized materials must be sought based on the application conditions. Even within the same component, multiple sealing materials may need to be selected depending on the specific requirements.