AS-C432 Customized Cartridge Mechanical Seal With Metal Bellow Design

This is metal bellow type cartridge mechanical seal made as per drawing

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Background Knowledge：

What is a high-speed mechanical seal and its characteristics
When the average linear velocity of the sealing end faces of the mechanical seal exceeds 30m/s, it is called a high-speed mechanical seal. At present, the seals of high-speed pumps and centrifugal compressors are high-speed mechanical seals. Some high-speed pumps are vertical, and rely on gear transmission to achieve high speed. Generally, it is 10,000 to 20,000 r/min, and some exceed 20,000 r/min. The shaft diameter is not very large, about ∅40mm, and the linear speed of the sealing surface is 30 ~50m/s.

There are many types of shaft seals for centrifugal compressors, and mechanical seals can be used under low pressure. The rotational speed of the centrifugal compressor is 8000~14000r/min, the shaft diameter is larger, generally above ∅100mm, and the linear speed of the friction pair of the mechanical seal is much higher than that of the high-speed pump, at 50~90m/s. Therefore, its high-speed characteristics are more prominent.

Why does the high-speed mechanical seal adopt static structures
If the high-speed mechanical seal adopts a rotary structure, the centrifugal force at high speed will affect the performance of the elastic element, making the specific pressure uneven. In addition, there are many rotating parts in the rotating structure, and dynamic balance calibration is required before installation，which is very important.On the other hand, so many rotating parts will cause the liquid medium to be violently stirred, and the power consumption will be large. At the same time, this power consumption will be manifested in the form of heat, and the next problem is that the cooler area of the sealed system needs to be increased. Based on the above three reasons, high-speed mechanical seals adopt static structures.

Why does the high-speed mechanical seal consume more power
The power consumed by each mechanical seal consists of two parts: one is the power consumed by the friction between the sealing end faces of the mechanical seal, and the other is the power consumed by stirring the liquid when the rotating parts rotate.As the speed increases, the proportion of stirring power gradually increases. For high-speed mechanical seals with a line speed of 50-90m/s, the stirring power accounts for 60%-80% of the total power.

Why high-speed mechanical seals have poor followability
In addition to high-speed rotation, the rotary face of the high-speed mechanical seal also has two kinds of motion, one is to make axial displacement with the shaft. This displacement occurs irregularly. As long as the spring force is sufficient, that is, the axial displacement is within the compensation range of the spring, it will not affect the sealing performance of the mechanical seal.

There is another kind of motion in the rotary face of the mechanical seal, which is axial vibration. Due to the manufacturing accuracy of the rotary face itself and the cumulative installation error, the rotary face has a perpendicularity error to the shaft, and the rotary face end face vibrates when it rotates.The stationary seat is in close contact with the rotary face under the action of the spring force, and the ability of the stationary seat and the rotary face to fit together during the movement is called the followability of the mechanical seal.

It is obvious that under the action of the vibration of the rotary face, the stationary seat must be pushed away by a small gap every revolution, and the stationary seat must be attached to the end face of the rotary face in time under the action of the spring force, and the frequency of the two is equal (or called"synchronization"), the followability of the mechanical seal is good and the seal leakage is small. On the contrary, it is called poor followability.

The followability of high-speed mechanical seals is poor, which is one of the reasons why its leakage is larger than that of general mechanical seals.
To be summed，the high-speed mechanical seal has the following characteristics: the sealing structure adopts multi-spring, static and balanced seal; the power consumption is relatively large, and the stirring power is greater than the friction power of the sealing end faces of the mechanical seal. In order to reduce power consumption, the width of the sealing surface of the mechanical seal is small (3mm), and the diameter of the rotating part should be reduced as much as possible: the followability of the stationary seat assembly is poor, and the leakage is large. To improve the followability, the mass of the stationary seat should be small and the Spring specific pressure should be larger; The installation requires high technical requirements, especially the verticality between the rotary face end face and the shaft is controlled within 5 μm. In addition, the technical requirements for the installation of the machine itself are relatively high. For example, the amount of shaft string is not more than 0.30mrn, the rotor balance is better, the vibration during operation is small, and the seal between the sealing box and the machine must be reliable, etc.