Application of silicon carbide sealing material

Application of silicon carbide sealing material

Due to its excellent mechanical properties, corrosion resistance, and good tribological properties, silicon carbide materials are gradually developed and applied in many fields as sealing materials. According to the characteristics of the application, it can be attributed to the mechanical seal under the following six working conditions.

1 Silicon carbide is used in mechanical seals with high sealing medium pressure

When the mechanical seal works under high pressure, the sealing face needs to bear a great load, which requires that the sealing material must have high strength and stiffness, otherwise, the sealing face will be deformed due to pressure, resulting in leakage or rapid wear , failing the mechanical seal. Silicon carbide material is a kind of material with high strength, high stiffness, and high elastic modulus. It is not easy to deform under high pressure. At the same time, the compressive strength of silicon carbide is very high . For example, the flexural strength of atmospheric sintered silicon carbide is 410 MPa, while the compressive strength is more than 2800 MPa, which is 7 times the flexural strength. It can bear high-end stress and meet the application requirements.


2 Application of silicon carbide in high speed mechanical seal

In the high-speed working state, due to the high linear speed, the heating, wear, and vibration of the friction pair will be an important problem to face in the working process. Therefore, it is required that the material used as a rotary seal should have high strength and low density. In this way, the centrifugal force generated by the rotating ring during high-speed operation is small, and the vibration and deflection caused are also small, to maintain the stable fit of the sealing end face. The density of silicon carbide is much smaller than that of cemented carbide used for sealing and has a high elastic modulus, which ensures that the silicon carbide sealing end face is not easy to produce deformation and vibration under high-speed working conditions, and maintains the silicon carbide sealing end face stable fit of the end face. Due to its low density, good thermal performance, and low friction coefficient, silicon carbide has obvious advantages in high-speed rotating sealing materials, so it is widely used in me mechanical seal hard rings.

At present, the product of the pressure (P) of the sealing fluid and the average sliding speed (V) between the sealing surfaces (i.e. PV value) is usually used as the index of the working capacity of the mechanical seal to measure the limit value of the mechanical seal. With the development of technology, the PV value of mechanical seals continues to increase, so the requirements for sealing auxiliary materials are higher and higher. Due to the excellent performance of silicon carbide ceramic materials, it has attracted more and more attention in the sealing industry. With the wide application of silicon carbide sealing materials, the high-precision processing of silicon carbide has also developed rapidly, It can make the roughness of the sealing end face in tens of nanometers or even several nanometers, avoiding the pear cutting effect of the sealing pair due to the local bulge of the end face, ensure the stable fitting of the sealing surface, and improve the service life of the mecha nical seal.

3 Application of silicon carbide in high-temperature mechanical seal

High temperature is easy to cause the performance change of friction materials, deforms the sealing face, reduces the hardness, and reduces the service life of the mechanical seal. Therefore, the thermal deformation, high-temperature strength and wear resistance of high-temperature sealing materials are the key to be considered when selecting sealing materials. Silicon carbide has high high-temperature strength. For example, the bending strength of hot-pressed silicon carbide at 1600 ℃ is the same as that at room temperature, so there will be no high-temperature creep phenomenon similar to metal. Due to the self-lubricating effect of silicon carbide ceramics, there will be no adhesive wear when rotating between two ends. Therefore, silicon carbide can be used for mechanical seals under high-temperature working conditions.

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4 Application of silicon carbide in the mechanical seal of corrosive medium

For mechanical seals used in corrosive media, corrosive wear is the main form of failure of friction materials. This corrosive effect is very strong, which will directly or quickly cause a change in sealing performance. Therefore, the selection of sealing auxiliary materials should be carried out according to the characteristics of the sealing medium. Silicon carbide has good chemical stability and strong corrosion-resistance, so it can be used in a variety of corrosive acid and alkaline media.

5 Silicon carbide is used in mechanical seals containing solid particles

In the practical application of mechanical seal, the sealed fluid often contains solid particles, such as wastewater to be treated, seawater in some sea areas, some chemical solutions that are easy to crystallize, etc. these liquids contain hard particles and are easy to deposit on the end face of friction pair when the mechanical seal device works. These particles not only cause serious particle wear on the sealing face but also cause local heating on the sealing face and cause thermal cracking. Therefore, hard and hard matching is required when selecting sealing pair materials. Due to the characteristics of high hardness, wear-resistance, and heat crack resistance, silicon carbide as one or two end face materials of mechanical sealing pair becomes an ideal choice under such working conditions. However, when selecting hard and hard matching, it is not necessary to choose two materials with high hardness at will, and there must be a certain hardness difference between sealing pair mate rials, The effect of dealing with the same material is not good. When selecting the sealing material for the marine centrifugal seawater pump, Wu rendering and others first selected the reaction sintered silicon carbide self matching, and the effect was poor. Later, the effect was greatly improved by selecting hot-pressed sintered silicon carbide and atmospheric pressure sintered silicon carbide.

6 Application of silicon carbide in dry friction mechanical seal

Under normal circumstances, the mechanical seal does not want dry friction, but it cannot be completely avoided in some cases. For example, due to the increase of fluid force and the reduction of clearance on the mechanical seal surface, the dry friction will begin to occur due to the contact of the micro convex body on the sealing surface, the temperature rise, or other reasons; In addition, semi-dry friction or dry friction will occur briefly when most seals are started and stopped. Due to the dry friction of the sealing surface, the friction coefficient and wear will increase, resulting in the burning loss or thermal stress cracking of the sealing ring, resulting in leakage. Therefore, the sealing materials are required to have high-temperature resistance and good tribological properties. When the temperature of silicon carbide is higher than that of silicon carbide when the temperature of silicon carbide is lower than that of silicon carbide when the temperature of silicon carbide is lower than that of silicon carbide when the temperature of silicon carbide is higher than that of silicon carbide when the temperature of silicon carbide is lower than that of silicon carbide when the temperature of silicon carbide is lower than that of silicon carbide when the temperature of silicon carbide Silicon carbide is higher than that of silicon carbide when the temperature of silicon carbide is lower than that of silicon carbide when the temperature of silicon carbide is higher than 600 ℃. Therefore, it can be seen that silicon carbide has good adhesion and wear resistance. Even under special working conditions, silicon carbide can fully meet the needs of work.

Due to its excellent performance, silicon carbide material can be used as sealing material under the conditions of high PV value, strong corrosion, high temperature, dry friction, and containing solid particles. However, because silicon carbide is a ceramic material, its brittleness limits its wider application in the sealing industry. Therefore, some experts and scholars at home and abroad are committed to the toughening technology and high-precision processing technology of silicon carbide, to promote the further development and wider application of silicon carbide materials.Read more: Suconvey Silicone Rubber