Advantages of metal bellows mechanical seal

Advantages of metal bellows mechanical seal




2020-09-18 09:27





In recent years, metal bellows manufacturing technology has developed rapidly, and many domestic manufacturers can produce and manufacture. Therefore, the price of metal bellows mechanical seals has dropped, which also promotes the use of metal bellows mechanical seals under normal temperature conditions. Applications. The author has achieved good results in using metal bellows mechanical seals in different normal temperature occasions, and believes that the application of metal bellows mechanical seals in some special working conditions is worth promoting. For the shaft seal, given that the working temperature of the pump is less than 150°C, the general idea is to use back-to-back double-end spring mechanical seals, and pressurized methanol to flush Plan53. The flushing pressure is 0.05MPa higher than the pump seal chamber pressure, and 0.2MPa higher than the pump inlet pressure. Based on this, the double-end seal of the auxiliary impeller (the inner mechanical seal adopts a metal bellows mechanical seal, and the outer adopts a balanced spring mechanical seal) is used as the shaft seal, and the structure is shown in Figure 5. The basic idea is: use the centrifugal action of the auxiliary impeller to make solid sodium methoxide particles leave the sealing chamber to purify the sealing chamber; at the same time, the auxiliary impeller can also reduce the pressure of the sealing chamber by 0.15MPa to create a good working environment for the mechanical seal. In this way, the flushing pressure is only 0.05MPa higher than the pump inlet pressure.

In the actual use process, we found that the ambient temperature has a great influence on the working state of the pump, the pump often appears to be pumped out, and the life of the mechanical seal is usually only about 2 months. The failure of the shaft seal is that the surface of the friction pair is burnt and blackened, and a layer of white self-polymer is attached to the outer surface of the shaft sleeve exposed to the medium. The O-ring of the mechanical seal is wrapped and stuck by the self-polymer. If the O-ring slides on the shaft sleeve, the mechanical seal must be replaced as a whole every time the shaft seal fails to be repaired. After the device was started, the problem could not be solved even though it was overhauled several times.

Since the metal bellows mechanical seal has no auxiliary dynamic sealing ring, the leakage points are reduced and the reliability is relatively improved. Changing the traditional concept and using metal bellows mechanical seals in some specific normal temperature media can achieve satisfactory sealing effects. When the cost performance is better than the spring mechanical seal, it is worthwhile to promote the use of metal bellows mechanical seals.
The metal bellows tube blank is made of thin-walled stainless steel strip welded pipe with wave processing, which is flexible and has good temperature and pressure resistance. It is suitable for the transportation of various industrial gases such as air and steam, and various fluid media such as water, oil, and medicine. It plays an important role in the reciprocating motion of the piping system, absorption of thermal expansion systems, vibration absorption, and center adjustment of piping. The metal pressure-resistant hose currently produced by our company is divided into two types: spiral metal hose (S type) and ring type metal hose (A type).

First, the characteristics of metal bellows

1) High temperature resistance

Because the metal bellows seal cancels the influence of the dynamic ring seal in the ordinary spring seal, the applicable medium and temperature are greatly expanded. Usually, the material of the dynamic ring seal of the ordinary mechanical seal is mostly organic compounds such as polytetrafluoroethylene rubber. These In some mediums, organic compounds will react with the whole body of the medium. At low temperature and high temperature, it will change its physical properties, harden and make the seal invalid. The bellows seal is not limited by the above factors, and is usually suitable for benzene , ketones, olefins, alkanes, and general oils, acids, alkali salts and many other media, the temperature range can also be -250-400, of course, this also requires strict material selection welding and thermal repair of metal bellows.

2) Design a certain structure to reduce the sealing failure caused by water scaling:

In many areas, due to poor water quality, high scaling index, and no specific softening water treatment device, the phenomenon of failure of the auxiliary seal ring of the moving ring in ordinary mechanical seals due to water scaling has become a persistent problem.

3) Less leakage points

The sealing points of the dynamic ring and the static ring are both metal (non-metallic) gaskets for sealing and connection through bolt fastening, so it is difficult to find leakage. In fact, the leakage of the bellows mechanical seal is only the dynamic sealing point of the friction pair, which is undoubtedly The probability is greatly reduced, and there are three main leakage channels of ordinary mechanical seals: dynamic ring seal ring, static ring seal ring and friction pair end face. In this leakage channel, the sealing leakage due to the failure of the auxiliary sealing ring of the dynamic and static rings accounts for 40% of the total leakage.

4) Excellent followability:



Due to the fully enclosed structure of the bellows seal itself, the structure eliminates the necessary dynamic and static rings and the dynamic seal ring of the shaft sleeve (or shaft) in the ordinary spring seal, so that the elastic rate of the bellows itself is fully utilized to form a specific pressure. (Due to the existence of the sealing ring, the ordinary seal needs to consume part of the balance force when the relative displacement of the moving ring sleeve occurs. The friction between the seal ring and the shaft sleeve (or shaft) makes it in place, and the size of the balance force is affected by the seal. The processing size accuracy of the ring and the limitation of heat treatment show its superior followability. During use, ordinary mechanical seals often cause the pump body to evacuate due to various reasons such as device fluctuations or operating processes. At this time, the existence of the dynamic ring seal ring After the end face is opened, it cannot be reset in time, resulting in the leakage of the mechanical seal, and the bellows mechanical seal eliminates this way of seal failure in structure. It is almost not affected by pumping out of the pump body, showing its good compensation and performance. It is outstanding in pumps such as light hydrocarbon pumps that are easy to evacuate, vacuum tower bottom pumps, etc. This feature is an important reason for the popularization of bellows seals.