Requirements for High Temperature Mechanical Seals

When the working temperature of the mechanical seal exceeds 80 ℃, it is used as a high-temperature mechanical seal. At high temperature, the main problems of the seal are as follows: the liquid vaporization of the sealing end face, the thermal stress and thermal variation of the friction pair, and the assembly and insert may If it is improperly loosened, the aging, cracking, bonding and elasticity of the auxiliary sealing ring caused by high temperature will disappear, the fatigue and strength of the spring will be reduced, and the corrosion and wear of the material will be accelerated.

1. High temperature mechanical seals use high temperature resistant sealing materials

At high temperature, the temperature resistance of high-temperature mechanical sealing materials is particularly important. Reasonable selection of sealing materials can make mechanical seals of general structure still suitable for high-temperature working conditions, simplify procedures and save costs.

2. The high temperature mechanical seal adopts the sealing structure combining metal bellows type mechanical seal and ordinary mechanical seal

From the perspective of heat resistance, the auxiliary seal ring is the weakest link in the mechanical seal. When the temperature exceeds 80 °C, ordinary rubber is no longer suitable, and when the temperature exceeds 230~250 °C, PTFE cannot be used. In addition, the spring can become blocked due to the deposition of lysates from high temperature, flammable media. Therefore, when the temperature exceeds 220 °C, a metal bellows type mechanical seal should be used, or a sealing structure combining metal bellows and ordinary mechanical seals should be used.

3. Cooling measures taken by high temperature mechanical seals

At high temperature, in order to make the high-temperature mechanical seal operate reliably, the mechanical seal should be cooled as much as possible, and it is necessary to avoid working in a dry friction state. The temperature in the sealing gap must be kept below the vaporization temperature of the sealing fluid. The cooling measure is to control the temperature of the seal. Commonly used temperature controls include flushing, blocking, and strengthening liquid circulation. At high temperatures, the following measures can also be used:

(1) Diphy1 (a mixture of diphenyl and diphenyl oxide) is used as the blocking liquid, which is a cold and pressureless heat exchange agent (the blocking liquid is conveyed by the pump-effect screw).

(2) At ultra-high temperature or when there is no suitable liquid, nitrogen and argon can also be introduced to prevent oxidation caused by air.

4. The problem of high temperature mechanical seal inlaid friction pair

The sealing ring inlay is to make full use of the characteristics of the end face material and the base material to improve the use value of the material. Generally, the hot inlay method is used for high temperature sealing. However, due to the difference in thermal expansion coefficient between the end-face wear-resistant material and the base material, the friction ring will loosen and fall off when used at high temperatures. Therefore, special attention should be paid to the temperature used for the friction ring of the mosaic structure. The reason for the looseness and falling off of the hot insert structure is not only related to the operating temperature, but also related to the size of the shaft diameter.

5. Allowable clearance between friction pair ring and shaft of high temperature mechanical seal

Under high temperature conditions, due to the difference in thermal expansion coefficient between the friction pair ring and the shaft, the gap between the friction pair ring and the shaft will approach zero, resulting in the disappearance of the friction pair ring's floating and sealing failure. Therefore, the mechanical seal for high temperature must be designed reasonably and correctly to select the gap between the friction pair ring and the shaft.

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