Bellows for the hottest corrugated compensator

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Bellows for bellows compensator

in recent years, a new product derived from metal hose ----- thin-walled bellows compensator. Its main component is also bellows

like metal hose, it is also an important part of modern large-scale pipeline system. Because it has just come to the fore, at present, there is no very mature experience and independent and complete theory. Here, just a brief introduction to some of the information we have learned

the influence of ripple number and waveform on displacement performance

there are many ripple forms of bellows. In practical engineering applications, different waveforms must be selected according to different applications to maximize its compensation effect

material of bellows

as mentioned earlier, people can make bellows from various metal materials. For the bellows used as compensator, although its design idea and process conditions are different from those used as the body of metal hose, the views of various countries on the selection of its materials are relatively consistent

most of the materials used in various countries are chromium molybdenum and chromium nickel stainless steel. Because these materials have good physical, chemical and mechanical properties, and can meet the requirements of general engineering, at present, we also use chromium molybdenum and chromium nickel stainless steel to make bellows

bellows with small diameter are usually processed with thin-walled seamless pipes; Bellows with large diameter are usually welded into cylinders with thin-walled plates, and then processed; The inner and outer layers of corrugated pipes with large or medium diameter in the form of multi-layer structure are thin-walled seamless pipes or welded cylinders made of thin-walled plates, and several layers between them are multi-layer cylinders made of thin-walled plates with seams and no welding

when using materials, in order to prevent the weld from near eutectic corrosion, post weld heat treatment can be carried out. Its specification is to heat to 1080~1150c and water quench. At the same time, the material should not be used at 450~800c. If the bellows is made of materials, it can be used for a long time at -196~+600c without post weld heat treatment

determination of geometric parameters of bellows

the principle of determining geometric parameters of bellows varies according to their use conditions. In the case of a given inner diameter, the first thing to consider is the ratio C of the outer diameter to the inner diameter of the bellows. The maximum C value of Japanese Fuji deep groove bellows is 1. 85. The maximum C value of the British HydroFlex deep wave corrugated tube is 1. 84. The General Administration of instrumentation industry of China stipulates that the C value of deep wave corrugated tube is 1. 6~2。 Between 0; The C value of shallow wave bellows is 1. Less than 6. These are for the bellows making sensing elements. Neither copy nor misappropriate. For bellows used as compensator with a diameter of 40~400 mm, the value of C can only be controlled at 1. 12~1。 42 range

generally speaking, the determination of C value should increase with the increase of inner diameter D value, because the bearing capacity of bellows decreases with the increase of D value and C value. Therefore, in order to obtain the required bearing capacity and other related performance, when D duty increases to a certain value, C value should decrease with the increase of D value. The outer diameter is the derived parameter, which is calculated after the D value and C value are determined

wave distance refers to the distance between two adjacent waves. The wave distance increases with the increase of the outer diameter of the bellows, and its percentage in the outer diameter of the bellows decreases with the increase of the outer diameter. Therefore, according to the statistical results of relevant foreign materials, some books and periodicals recommend that the wave distance be determined according to a certain percentage of the outer diameter of the bellows (that is, the wave distance t is 8-12% of the outer diameter d). We believe that this percentage is inappropriate for bellows used as compensator. Because the determination of the wave distance of the bellows is not only related to the outer diameter of the bellows, but also to the inner diameter and wall thickness of the bellows. Under certain conditions, in order to ensure good compensation performance, it is necessary to strictly control the band width h of two mutually parallel circular diaphragms connecting the crest semicircular arc and the trough semicircular arc

experiments show that this width should not be less than the sum of the two radii of the crest semicircle arc and the trough semicircle arc, otherwise, the compensation may depend on the change of the radius of the crest semicircle arc or the trough semicircle arc. In this way, the bellows working under the stress state of metamaterial yield limit is inevitable, which is neither safe nor reliable

of course, the ring width of the ring diaphragm should not be too large for three reasons:

① it is difficult to process and mold manufacturing; ② Low bearing capacity, easy to lose stability; ③ Narrow application range and small displacement compensation

therefore, we stipulate that the specific range of wave distance t must be controlled between 2/3~1 times the wave height

the test results show that when the ratio of the inner radius of the semicircular arc of the wave crest to the radius of the semicircular arc of the wave trough is 1, the longitudinal stiffness and stress of the bellows are the minimum; Fyodor Sheff will just become the mainstream of the power battery industry in a certain period of time in the future; On May 27, the degree theory proved that the "U" shaped bellows has the best sensitivity. We believe that this is the common feature of all thin-walled bellows. Therefore, to study the bellows used as a compensator, we should derive the formula of the radius of the peak semicircle arc and the radius of the trough semicircle arc and the ripple width B on the basis of determining the wave distance t as

calculation of the wall thickness of the bellows

the remarkable feature of the thin-walled bellows compensator is the wall thickness. The degree of wall thickness is proportional to the diameter. The maximum ratio of wall thickness to diameter of bellows with a drift diameter of 40~400 mm shall not be greater than 1/200~1/150. In general, there are:

the formula does not give the pipe wall thickness δ Does it mean that it is allowed to be arbitrarily small? The smaller the wall thickness of the bellows, the greater the displacement compensation, and the better the elasticity. However, the smaller the wall thickness of the bellows, the lower its critical load and the limited working pressure. Therefore, the wall thickness of bellows δ The value cannot be arbitrarily small, but it should be limited, that is, it must be based on engineering practicality

as we all know, the stress on the axial section of thin-walled pressure pipes is the product of the total load on the area composed of diameter and axial length and twice the pipe wall thickness and its axial length. If these shortcomings are not eliminated:

however, the radial stiffness of thin-walled bellows is much larger than that of general thin-walled smooth pipes. At the same time, the actual axial length of the former is much larger than that of the latter when compared with the same force value point on the dial of the tensile testing machine and the standard tensile sample. As mentioned above, the ratio of outer diameter to inner diameter of bellows is c=1. 12~1。 42; The wave distance t value is between 2/3~1 times the wave height. Therefore, it can be deduced that the ratio of the effective ripple length to the actual unfolding length of all ripples is 0. 389~0。 280

strengthening measures for bellows

from the test results, it is necessary to use testing equipment to test whether the external wall insulation material is qualified. The bellows used as compensator, which is made of thin-walled plates welded into cylinders, has relatively high weld strength, and the weld strength is generally greater than or equal to 0 of the base metal strength. 8 times. For some specimens with no or few welding defects, their ratio is equal to 1. Can we use this as a basis to give a certain safety factor in the occasion of high working pressure? No

The structural characteristics of the bellows show that their radial stiffness is much higher than that of the blank, while their axial stiffness is much lower than that of the blank. In the working state with large load, although its strength is sufficient and its radial stiffness is surplus, the axial stiffness may not meet the requirements of use. In Chapter 3 3. In Section 4, we have analyzed the stability of bellows: instability is the precursor of failure. From the critical load formula of bellows, it can be seen that there are three methods to improve the stability of bellows:

① increase the thickness of pipe wall; ② Reduce the ratio of outer diameter to inner diameter; ③ Reduce the number of effective ripples and expand its slenderness ratio

however, by excessively increasing the thickness of the pipe wall and reducing the ratio of the outer diameter to the inner diameter, the rigidity is increased, but the flexibility is reduced, which is not in line with the relevant provisions of the thin-walled corrugated compensator; Excessively reducing the number of effective ripples and expanding its slenderness ratio make it unable to meet the use requirements of a certain amount of compensation. In this way, we are forced to consider external factors, that is, to improve the stability of bellows used as compensator by using inner bushing, outer sheath, trough reinforcing ring or composite structure

all compensators with inner bushing or outer sheath structure are generally used as axial compensation of pipes instead of bearing lateral and angular displacement due to small radial clearance. The displacement compensation amount of axial, transverse and angular directions of corrugated compensator with trough reinforcing ring structure shall be calculated according to its specific geometric dimensions

when the waveform of the bellows is as shown in the figure, one end of the inner bushing is fixedly connected with the thick wall smooth pipe at one end of the bellows compensator, and the other end is in a free state. The relative displacement of the free end to the compensation must be greater than the rated compensation, which is generally controlled at 1. 2~1。 5 times. Similarly, when the waveform of the bellows is as shown in the figure, the normal position of the free end of the inner bushing should be 1/2 of the axial length of the thick wall smooth pipe

the structural design of bellows with outer sheath is the same as above. In order to grasp the waveform changes at any time, an oval hole can be machined on the outer sheath as an observation window

the section of the trough stiffening ring must be designed as "" shape to ensure the displacement characteristics of the bellows, and its geometric size should be determined according to the requirements of waveform and compensation. Take it as a half ring, and the bolts with large diameter can be screwed; For small diameter, the half ring can be integrated with an elastic snap ring

like the outer sheath, the trough reinforcing rings are on the outer surface of the bellows. They are different from the lining and do not contact with the working medium. Therefore, it is not necessarily made of stainless steel. From the perspective of some foreign products, they are mostly made of cast iron, carbon steel, aluminum alloy and other materials

the so-called composite structure is to arrange two bellows on the same compensator. They are connected in series with a short thick wall smooth pipe, and their maximum displacement is controlled by a pull rod, hinge or special outer sheath. In this way, when the radial contour size is unchanged and the axial length is slightly longer, it is very convenient to obtain a compensation amount equivalent to two or several times the general compensation amount. It does not reduce the number of effective corrugations of each section of bellows, nor expand its slenderness ratio. However, it also meets the requirements of large compensation and does not produce instability. This is another way to strengthen from the outside. (end)

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