The metal bellows tube blank is made of a thin-walled stainless steel strip welded pipe, 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, as well as various fluid media such as water, oil and medicine. It plays an important role in the reciprocating motion of the pipe system, the absorption of thermal expansion, the absorption of vibration, and the adjustment of the center of the piping. The metal pressure hoses currently produced by the company are divided into two types: spiral metal hoses (S type) and ring metal hoses (type A).
First, the characteristics of metal bellows
1) High temperature resistance
Since the metal bellows seal eliminates the influence of the moving ring seal in the ordinary spring seal, the applicable medium and temperature are greatly expanded. Generally, the material of the common mechanical seal of the moving ring seal is made of organic compounds such as polytetrafluoroethylene rubber. In some media, organic compounds react chemically with the whole body. At low temperatures and higher temperatures, they change their physical properties and cause hardening to seal the seal. The bellows seal is not limited by the above factors, and is generally 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 seal failure caused by water scaling:
In many areas, due to poor water quality and high scale index, coupled with the absence of a specific softened water treatment device, many of the phenomena in the normal machine seal of the moving ring auxiliary seal due to water scaling have become a major problem.
3) Less leakage points
Both the moving ring and the static ring sealing point are metal (non-metal) gaskets sealed and connected by bolt fastening. It is difficult to find the leakage. In fact, the leakage of the bellows machine seal is only the dynamic sealing point of the friction pair. The probability is greatly reduced, and there are three main leakage channels of ordinary mechanical seals: moving ring seal ring, static ring seal ring and friction pair end face. In this leakage channel, seal leakage accounts for 40% of the total leakage due to the failure of the dynamic and static ring auxiliary seals.
4) Excellent follow-up:
Due to the fully enclosed structure of the bellows seal itself, the dynamic seal ring and the sleeve (or shaft) of the common spring seal are eliminated in the structure, so that the elastic rate of the bellows itself is fully utilized to form a specific pressure. (While the ordinary seal is due to the existence of the seal ring, it needs to absorb part of the balance force when the movable ring bushing is relatively displaced. The friction between the seal ring and the bushing (or shaft) makes it position, and the balance force is sealed. The processing precision of the ring and the limitation of heat treatment show its superior followability. In the process of use, the ordinary mechanical seal often causes the pump body to be evacuated due to various reasons such as fluctuations in the device or the operation process, and the existence of the moving ring seal at this time After the end face is opened, it cannot be reset in time, which causes the leakage of the mechanical seal, and the bellows machine seals the structure to eliminate the failure of the seal. It is almost unaffected by the pumping of the pump body, showing its good compensation and performance. Efficient pumping of light hydrocarbon pumps, decompression bottom pumps and other pumps, this feature is an important reason for the popularity of bellows seals.
5) Shock resistance and high speed
The bellows seal eliminates the dynamic ring seal to greatly reduce the vibration of the moving ring caused by the vibration of the pump body or the shaft vibration caused by the transmission of the moving ring seal ring, so that the moving ring is protected from the big influence, which is usually called a seal. Floating.
6) Remove the oil and save the cost
In ordinary mechanical seals for pumps with high temperature and impurities, due to the limitation of the use temperature of various auxiliary seals and friction pairs, the external flushing oil (sealing oil) is injected around the friction pair to lubricate and reduce the sealed chamber. The temperature establishes an adaptable environment suitable for the work of various components, but due to the large amount of waste caused by the oil sealing, the selection of the appropriate amount of bellows seal can save a lot of oil sealing funds without sealing the oil.
7) It can transmit torque itself
In the ordinary mechanical seal operation, it is necessary to add a structure for transmitting the seal. The structure is various, such as forks, pins, screws, and the use of fastening to transmit torque performance. Under normal circumstances, it can be used normally without additional twisting. Structure The simplification is carried out, the failure caused by the failure of the transmission structure is avoided, and the reliability of the machine seal is improved. When the working pressure of the bellows seal exceeds the allowable torque, the structure such as the fork is often structurally increased, and the torque resistance thereof is increased. The ability and stability play a supporting role in high-pressure high-speed sealing. The bellows seal is designed as an externally cooled or static structure, which can effectively prevent scaling. If the structural design is unreasonable or improperly applied, the bellows seal is also easy to scale, resulting in seal failure. Therefore, when using a bellows, The cooling water is used as the cooling water for the water, so that the corrugated pipe sealing working environment is greatly improved and the service life is prolonged.
Second, the application of metal bellows
The metal bellows is characterized by a corresponding displacement under pressure, axial force, lateral force or bending moment, and has pressure resistance, vacuum sealing, corrosion resistance, temperature stability and long-term service life. Therefore, it is widely used in many industrial fields. Its main application is in the following aspects.
1. Elastic sensitive components used in meters
There is a high demand for the elastic properties of bellows as an elastic sensitive element. A bellows used as an elastic sensitive element basically changes the pressure into a displacement output or a pressure into a concentrated force output. The bellows that transforms the pressure into a concentrated force output has little or no displacement, so the stress generated on the corrugation is smaller than the stress on the bellows of the output displacement, and the effect on the elastic aftereffect and hysteresis can be said to be no. Therefore, the reliability and accuracy of a meter with a force-balanced bellows as an elastic sensor can be high. This is the reason why the force balance type bellows is used as the elastic sensitive component in the measuring instrument. The bellows which changes the pressure into the displacement output will generate a large pressure on the corrugation. Attention should be paid during the design, and the elastic aftereffect and hysteresis It has a certain influence on the elasticity of the bellows.
In the instrument as a bellows for elastic sensitive components, the stiffness of the bellows should be as small as possible.
The change in volume of the inner (or external) volume during the displacement of the bellows can be used for temperature control and temperature measurement.
2. Vacuum seal for vacuum switch
The vacuum switch is a switch device for current on and off in a vacuum. Its main contact is located in the vacuum interrupter. The bellows is a key component in the vacuum interrupter. It is only possible to remove the vacuum from the vacuum bellows. The outer part of the arc uses mechanical force to move the moving contact, and keeps the vacuum interrupter housing completely sealed. Each time the vacuum switch is turned on and off, the bellows is subjected to a large displacement, and the large and frequent axial displacement easily causes the bellows to be damaged due to fatigue. The bellows is an important part of the vacuum interrupter housing. If it is damaged, the life of the vacuum interrupter is terminated by air leakage. The other parts of the vacuum interrupter are not easily damaged during normal operation, so the fatigue life of the bellows determines the mechanical life of the vacuum interrupter. In addition, the contact opening distance of the vacuum switch is equal to the actual axial displacement of the bellows. Therefore, the axial allowable displacement of the bellows determines the maximum contact opening distance that can be obtained.
The fatigue life of a bellows is related to its structure and materials used, and also to the conditions of use. The working stroke of the bellows applied to the vacuum switch has a great influence on its fatigue life. For the same bellows and the same vacuum switch, in order to obtain a long fatigue life, only the working stroke of the bellows or the contact opening distance can be reduced. Conversely, if the working stroke or contact opening distance of the bellows is increased, the fatigue life of the bellows will be greatly shortened. Therefore, the main properties of the bellows for vacuum switches are axial displacement and vacuum tightness. The vacuum switch has two working states, on or off. When it is turned on, the bellows needs to be stretched and deformed. When disconnected, the bellows is compressed and deformed. In order to ensure the service life of the vacuum switch, the bellows is stretched and compressed. Must be designed reasonably.
Both the hydroformed bellows and the welded bellows can meet the requirements of ordinary vacuum switches. In view of the manufacturing cost, the vacuum switches generally use hydraulically formed bellows. Welded bellows are only used for vacuum switches that require a particularly long service life and a large contact stroke. The bellows material is generally stainless steel 1Cr18Ni9Ti, 00Cr17Ni14Mo2, and 0Cr18Ni9.
3, for the valve as a sealed isolation component
Bellows valves, whether they are shut-off valves, throttle valves, regulating valves, or valves such as pressure reducing valves, are used as a non-filled sealed isolation element for the valve stem. During operation of the valve, the bellows is axially displaced and reset together with the valve stem, while it is also subjected to fluid pressure and is absolutely sealed. The axial displacement of the bellows is related to the diameter of the valve. For a flat-sealed shut-off valve, the working stroke of the bellows is generally 1/4 of the diameter. The axial displacement stroke of the bellows should be limited by the mechanical limit of the valve stem movement. The corrugated tube corrugation is not allowed to be plastically deformed, and the bellows is prevented from being distorted. In valves, the main performance of bellows is resistance to pressure, working displacement and fatigue life. The failure modes of the bellows are mainly fatigue cracking, stress corrosion damage and bellows instability. The factors affecting the service life of the bellows are mainly working pressure, working displacement, working temperature, fluid medium, wave structure, raw material quality, pressure shock, vibration, joint part structure and assembly quality. In the bellows valve, the bellows is the most vulnerable part. Therefore, the design and selection of the bellows is very important. If the design is unreasonable, it will cause premature failure of the valve. Bellows valves offer greater reliability and longevity than packing seal valves. It has been widely used in the nuclear industry, petroleum, chemical, pharmaceutical, aerospace and other industrial fields.
4, for metal bellows expansion joint
Metal bellows expansion joints are widely used in various piping systems to compensate for axial, lateral and angular displacements due to temperature and pressure fluctuations. The core part of the metal bellows expansion joint is a bellows, which is subjected to the pumping, lateral and angular displacement by the deformability and pressure tightness of the bellows, and is subjected to the fluid pressure of the system. The other parts are structural members, guiding, Support, connection, diversion and other functions. According to the design and use requirements, the bellows and related structural parts are welded to the different types of corrugated expansion joints in the axial, transverse and angular directions according to the required structure.
5, for metal hoses for flexible couplings
The metal hose uses its flexibility to compensate for the positional deviations caused by the installation in the piping system and to meet the requirements for the displacement of the working end and to withstand the fluid pressure of the system. The core part of the metal hose is a bellows. The ratio of the length to the inner diameter of the bellows is generally greater than 3. The wave shape is divided into a ring shape and a spiral shape, and the bending rigidity of the ring is smaller than that of the spiral shape. In order to increase the pressure bearing capacity of the metal hose, in many cases, a wire or a braided metal mesh sheath is placed over the bellows.
6, for bellows heat exchangers as heat exchange components
The bellows heat exchanger is a high-efficiency, reinforced heat exchanger that is a combination of metal forming, mechanics and heat transfer. The bellows acts as a heat exchange tube bundle to enhance heat transfer, and also acts as a heat compensation and vibration resistance. The failure modes of the bellows are mainly fatigue cracking, stress corrosion cracking and corrosion cracking. In the bellows heat exchanger, the main performance of the bellows is heat exchange efficiency, fatigue life, pressure resistance, temperature resistance, corrosion resistance, vibration resistance and thermal compensation. The heat exchange efficiency is mainly related to the waveform, and the waveform affects the forming processability of the bellows.
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