AS-B445 welded metal bellow mechanical seal

S-B445 welded metal bellow mechanical seal is part of cartridge seal which can be used as bolier seal

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Background Knowledge:

Mechanical seals are widely used in rotary equipment such as pumps and stirred tanks. Due to its simple structure, low price and convenient use, the conventional spring-type mechanical seals basically cover the working conditions when temperatures are under -15 ~ 150 ℃; if the materials are allowed to be cooled, when between 150 ~ 200 ℃.

The bellows mechanical seals are widely used in the conditions when temperatures are above 200 ℃ or below - 50 ℃.
The reason for this is that under high (low) temperatures, the auxiliary sealing rings of the spring-type mechanical seals will fail. For example, the auxiliary sealing rings made of rubber will age at high temperature and brittle at low temperature;The tetrafluoroethylene auxiliary sealing ring undergoes thermal deformation at high temperature and cold flow at low temperature, so metal bellows mechanical seals have to be used at extreme temperatures.

In fact, the metal bellows mechanical seal has no auxiliary dynamic sealing ring. Compared with the spring-type mechanical seal, the leakage point is reduced, the reliability is significantly improved, and the advantage of being used as a shaft seal is obvious. However, the manufacturing cost of bellows mechanical seals is relatively high. Due to economic factors, the application of metal bellows mechanical seals is limited to high temperature or low temperature working conditions, and the advantages of high reliability are not fully exerted. In recent years, the manufacturing technology of metal bellows has developed rapidly, and many domestic manufacturers are able to manufacture them. Therefore, the price of metal bellows mechanical seals has dropped, which also promotes the use of metal bellows mechanical seals under normal temperature conditions.

Let's talk about what are the advantages of welded metal bellows mechanical seals compared to other types of mechanical seals in detail：
For mechanical seals used in rotating equipment, if leakage is too large, they will be unusable and must be repaired or replaced. Therefore, for the purpose of long-term stable operation of the equipments, the selection of mechanical seals should take reliability as primary indicator, and at the same time refers to their prices. Generally speaking, performances of welded metal bellow mechanical seals are much more reliable in use than other types of mechanical seals.The main factors considered are as follows：
1. The force on the sealing end face of the bellows mechanical seal is relatively uniform;
2. The followability of the bellows mechanical seal is good, and it can to e certain degree make up for the end face clearance (generally it is required to be less than 1μm，and caused by deflection of the rotating shaft, equipment vibration, coaxiality error between the rotary face& stationary seat and the shaft sleeve, etc.), thereby reducing possible leakage of the mechanical seal;
3. Compared with the large spring type mechanical seal, the bellows mechanical seal is less affected by the surface corrosion of the shaft sleeve;
4. The stationary seat of the bellows mechanical seal is fastened on the mechanical seal gland with bolts while most of the stationary seats of spring-type mechanical seals basically rely on the excessive cooperation between the O-ring and the mechanical seal gland, as well as the fluid pressure and the action of the outer spring to seal.The sealing effect of the stationary seat ot latter type is affected by the matching size and corrosion degree of the gland sealing surface, which means poor sealing effect.
In a word,though prices of welded metal bellows mechanical seals are relatively high, but it is much more economical to use welded bellows mechanical seals for most equipments in terms of unit cost of equipment operation cycle.