Material requirements for hydropneumatic seals

Hydraulic and pneumatic seals are the basic parts of the industry and the basic parts of industrial automation. They have been widely used in various industries such as industry, agriculture, aerospace, shipbuilding, metallurgy, mining, etc., and play a role in providing a power source to the system. An indispensable core element of the system.

The performance of hydraulic and pneumatic components directly reflects the level of industry and automation. Hydraulic and pneumatic components are wearing parts, and their service life directly affects the advancement, stability and long-term nature of automation and industrial machinery. These are directly related to its machining accuracy, structural rationality, material properties, and machining methods.

Sealing principle: Hydraulic pneumatic seals are divided into extrusion seals and lip seals according to their working principles. The extrusion seal relies on the compressive deformation filled in the groove to block the leakage channel and obtain the sealing effect. The lip seal also relies on the pre-compression elastic deformation of the filling groove to block the leakage channel, and under the action of the medium pressure, the lip further closes to the counterpart to enhance the blocking and sealing effect.

Material requirements for hydropneumatic seals:

Due to the performance difference of the sealing material itself, the sealing performance of the manufactured seals is also very different. Therefore, understanding the performance of the sealing material is a prerequisite for the correct design and selection of the sealing material. When selecting the sealing material, the following factors must be considered :

1. Media resistance

The degree of swelling of the material in the medium is directly related to the quality of the sealing performance, so when selecting the material for the hydropneumatic seal, the first thing to consider is whether it is compatible with the sealing medium.

2. Tensile strength

The tensile strength of the sealing material generally decreases with the increase of temperature, so the maximum operating temperature and the mechanical strength at high temperature must be considered. The tensile strength is low, and it is easy to produce stress relaxation and permanent deformation, resulting in sealing failure.

3. Wear resistance

The wear resistance of the material is an important performance of the dynamic seal. Good wear resistance means a long service life. The wear resistance of the material is closely related to the hardness of the material. The higher the hardness of the material, the more wear-resistant it is.

4. Permanent deformation

The hydropneumatic seal obtains the sealing ability by generating recoverable compression deformation in the sealing groove. Therefore, the permanent deformation of the sealing material should be small, the elasticity should be high, and the resilience should be strong. In addition, the permanent deformation of the material is related to temperature, Both low temperature and high temperature will increase permanent deformation.

5. Elasticity

Extrusion type seals obtain sealing ability by relying on the resilience generated by the sealing material itself after being pressed, while lip seals may have eccentricity, and may rely on the elasticity of the material to compensate for the lack of contact stress of the seal. Therefore, elasticity is important for seals. The sealing effect is very important.

6. Hardness

Hardness is an important indicator of the sealing material, which depends on the roughness of the sealing surface. The rough sealing surface and the hardness of the seal should be low, so that the sealing effect is good. In the part with high sealing pressure, the hardness of the seal should be increased. , to prevent excessive deformation of the seal, or even extrusion. In addition, the hardness of the material decreases with the increase of the use temperature, and the hardness is high, and the wear resistance of the material is also strong.

7. Temperature resistance

The working temperature of the seal depends on the temperature of the sealing medium and the temperature rise of the seal itself during the movement. The temperature directly affects the sealing performance. If the temperature is too high, the aging of the sealing material will be accelerated, resulting in a significant decrease in the material's elasticity and hardness. Hardening occurs; if the temperature is too low, the material will harden, lose its elasticity, and reduce the sealing performance. Therefore, materials with a wider temperature range should be selected.

8. Permeability

Permeability also has an important impact on fluid sealing, and more attention should be paid to gas sealing, especially vacuum sealing. The permeability of various rubbers varies greatly.

Influence of friction on sealing: Friction is inevitable in dynamic sealing, and the magnitude of friction is related to factors such as seal material, fluid type, fluid pressure, working temperature, speed, and surface roughness of the sealing surface. It directly affects the sealing performance and life of the seal, as follows:

1) Friction causes seal failure and reduces service life;

2) Friction reduces the output pressure;

3) Frictional heat accelerates aging of seals and reduces service life;

4) At low speed, it is easy to cause the hydraulic cylinder to crawl.