Basic Knowledge of Metal Bellows Mechanical Seal

Author:Site Editor     Publish Time: 2020-12-30      Origin:Site

The metal bellows mechanical seal is a single-end, balanced, and arbitrary-rotation metal bellows seal. Since the moving ring O-ring and flexible graphite ring can not compensate, there is no resistance to the movement of the bellows, which is suitable for high temperature and high viscosity media. Please select the friction pair material and auxiliary sealing material of the bellows mechanical seal according to the actual working conditions. The metal bellows mechanical seal is suitable for high temperature and high-speed working conditions, and the use of torque transmission does not affect the bellows. No other elastic elements constitute the secondary seal, and the non-compensation ring can be assembled as required.


Main features of metal bellows mechanical seal


The function of the spring in the general mechanical seal (push ring type) is to maintain the compression and balance of the friction surface. The metal bellows mechanical seal not only acts as a spring but also has a sealed structure, so the design does not require a moving ring O-ring. Compared with ordinary mechanical seals, metal bellows seals have many advantages, which can be summarized as follows.


1. High precision

The metal bellows acts as a spring, and it is a combination of countless springs, so it solves the problem of ordinary springs deforming due to centrifugal force. It is suitable for high rotation, and the sealing surface is evenly pressed, which is good for preventing leakage.


2. Vibration resistance and excellent flexibility and indulgence

The bellows have high flexibility, so the vibration absorption effect is very good, so the ability to adapt to radial runout, axial clearance, vibration, and swing is very high to prevent leakage.


Metal bellows mechanical seals


3. Simple structure

Unlike the spring mechanical seal which is composed of many parts, the metal bellows mechanical seal has a simple structure and is easy to assemble.


4. Adapt to a variety of temperature conditions

The metal bellows have a small thermal expansion coefficient and can be used at low or high temperatures. Moreover, there is no O-ring, free from temperature restrictions and more free design.


5. Suitable for high pressure

Because the bellows themselves has a balancing effect, the sealing surface area can be set to offset the fluid pressure, reduce the friction of the sealing surface, and thereby reduce heat generation and wear. Therefore, the metal bellows mechanical seal can be used in high-pressure environments.


6. Protect the machine (no shaft sleeve is needed)

The metal bellows seal has no O-ring, so there will be no wear of the shaft or sleeve caused by the abrasion of the O-ring. It can protect the shaft, so there is no need to install a shaft sleeve.


7. Adapt to corrosive fluids

Welded bellows are made of materials such as Hastelloy 276 with high corrosion resistance, which avoids the problem of corrosion of springs and O-rings, thus achieving sealing.


8. No hanging

Using ordinary push-ring mechanical seals, a small amount of leaked fluid is solidified and deposited in the air to prevent the advance of the moving ring O-ring. Therefore, the adhesion force of the sealing end face becomes weak or disappears, resulting in leakage. On the contrary, the metal bellows mechanical seal has no O-ring. Even if there is solidification, it will not be affected, it can rotate stably, and it can also extend life.


9. Thread pumping function

The bellows itself has a screw pumping function, which can effectively deal with fluids containing solid particles and help to flush.

 

Application of metal bellows mechanical seal


Bellows mechanical seals have a wide range of applications, from low temperature to high temperature, from neutral media to corrosive media, from low speed to high speed, and from ordinary to harsh working conditions. All of these can change the elasticity of the bellows by changing the geometry of the bellows (such as inner and outer diameter, wave plate thickness and wavenumber, etc.) and the elastic modulus of the material. According to the corrosion performance of the medium, different bellows materials are selected. For example, for neutral media (oil and water, etc.) whose working pressure and temperature are not high, simple bellows made of rubber can be used for sealing. In corrosive media (acid or alkali, etc.), bellows made of PTFE can be used for sealing. At high temperatures and high speeds, welded metal bellows mechanical seals can be used.


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