JPS6148668A - Structure of multilayer bellows - Google Patents

Abstract

PURPOSE:To prevent the generation of the local contact and stress on extension and contraction of a bellows by generating the bellows interval larger than that at other parts, at the top part, bottom part, or the both parts of a multilayer bellows. CONSTITUTION:Each layer is put into closely attached state only in the parallel part 5 of a multilayer bellows, and the radius of curvature of the inner surface of an outer layer bellows 1 is made equal to the radius of curvature of the outer surface of an inner layer bellows 2, and a gap is formed between the top part and the bottom part of the stress concentration part. By closely attaching the parallel parts of the bellows and making the radius of curvature of the inner surface of the outside bellows equal to the radius of the contiguous tow bellows curvature of the outer surface of the inside bellows and forming the prescribed gaps between the layers where stress concentration is generated, the contact generated on extension and contraction at the stress concentration part is eliminated, and the difference of rigidity between at the top part and the bottom part of the layers is made min., and the stress distribution is made uniform.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a bellows having a multilayer structure, and relates to an IP! This invention relates to a bellows suitable for absorbing a large amount of expansion and contraction in j.

[Background of the invention]

BACKGROUND ART Piping in various high-temperature plants such as nuclear reactors and chemical equipment undergoes thermal expansion or contraction due to changes in the ambient temperature or changes in the temperature of the fluid flowing inside the pipe. Therefore,
Unless measures are taken to absorb the dimensional changes caused by this, excessive stress may be generated in the piping and a large load may be applied to the equipment, leading to damage to the equipment and piping. In order to avoid such problems, bent pipes or bellows type expansion joints are often used. Among these, piping routing using bent pipes requires a certain amount of space and is not practical in large-scale plants where space is limited and economic considerations are required.

Bellows type expansion joints include straight pipe type expansion joints, hinge type expansion joints, and universal type expansion joints, which are applicable to axial displacement, perpendicular displacement, angular displacement, and their combined displacements. and so on.

In addition to the above displacement conditions, the shape of the pipe is determined by the shape of the pipe, operating conditions, cycle life, load limits of the pipe and equipment, and the support structure to be used.

Furthermore, bellows type expansion pipe joints include single layer bellows type expansion pipe joints and multilayer bellows type expansion pipe joints having two or more layers. Multilayer bellows expansion joints are used to reduce stress on the bellows surface. The stress σ generated on the surface of the bellows is proportional to the plate thickness t of the bellows, and becomes σ oci ...α).

Therefore, by changing the thickness of the bellows and increasing the number of layers, the desired expansion and contraction spring constant can be obtained, and stress can be reduced. Furthermore, by providing a plurality of layers, it is possible to prevent the occurrence of penetrating cracks in the entire bellows.

The discovery of penetrating cracks is based on the fact that damage to each layer can be detected from pressure changes in the gaps between each layer.

For forming the bellows as described above, a hydropressure forming method is used as shown in FIG. Molding mold 7 divided on the outside
is installed, hydraulic pressure is introduced into the bellows blank tube 6, the hydraulic pressure inside the blank tube is increased to a predetermined pressure, and the bellows blank tube 6 is heated by the pressure.
) Let R2 come out. At this time, in order to withstand the hoop stress of the internal pressure, the part where the mold 7 is placed is bulged out, and at the same time, the bellows material tube 6 is compressed in the axial direction by the press, causing the bellows material tube 6 to expand. The portions corresponding to the protruding peaks 4 are buckled and further formed into a bellows shape. In the above-mentioned hydroforming method, the troughs 3 of the bellows 1 are guided by the molding die 7 and have an accurate radius of curvature, but the peaks 4 are expanded only by the hydraulic pressure, so the radius of curvature ρ It is considered that the trough portion 3 is not precise and the radius of curvature at the tip of the peak portion 4 is small.

The above-mentioned hydroforming method is applied not only to single-layer bellows but also to the molding of two-layer multilayer bellows consisting of an inner bellows 2 and an outer bellows 1. The multi-layered bellows 9td made in this way has peaks and valleys 3 and 4 as shown in FIG.
There is a possibility that the layers in the parallel portion 5 are in close contact with each other, and that each layer slides when the peroyuz expands and contracts, causing wear. Here, in order to analyze the contact between the two-layer bellows 9 by analytical VC, an elastic analysis was performed using the finite element method using the model shown in FIG. The bellows shape is a large diameter bellows with an inner diameter of about 1000φ. As shown in FIG. 4, one layer of the bellows is divided into 20 elements and isoparametric axisymmetric shell elements (ELEMENT No.

15). The material constant used in the analysis is Young's modulus E = 1.98 x 10'kg/power2. Poisson's ratio ν = 0.266, specific weight γ = 7.97 x 10
-'kg/kg. As a boundary condition, the lower part fixes the axial displacement and only allows the radial displacement, and the upper part applies the axial displacement and also allows the radial displacement. In this analysis, it was assumed that there was no mutual interference between the two layers.

An example of the analysis results is shown in FIG. The building is half white and 0.
The tensile displacement is 5m. The horizontal axis is the node number corresponding to FIG. 4, and the vertical axis is the meridional stress σ on the outer surface of the outer layer bellows 1.
Indicates the time. Therefore, the maximum stress occurs at the peaks and valleys, and the absolute value at these two points is approximately 8 kgf/a'', which is within the elastic range.Next, we will examine the contact state of the two-layer bellows. As shown in Fig. 5, the troughs 3 and ridges 4 are in contact with each other.In the initial state, the analysis was performed assuming that there was no interference between the two layers, but due to tensile displacement, the ridges 4 and troughs 3 came into contact. On the other hand, it has been analytically confirmed that the peak portions 4 and the valley portions 3 do not come into contact with each other during compressive displacement, and that the parallel portions 5 are likely to come into contact with each other.

As described above, when the multilayer bellows 8 expands and contracts, each part contacts and slides, and the sliding surfaces of each layer are likely to wear out due to the surface pressure generated at that time. In particular, thinning due to wear at the peaks 4 and troughs 3 where the maximum stress occurs causes stress concentration and shortens the life of the Siperose. Furthermore, since the six bellows blank tubes shown in FIG. 2 are made into a cylindrical shape by welding a flat plate, overlays remain at the welded portions. Normally, the plate thickness of the welded part t
When w is the nominal plate thickness t, tw = 1.05 t~
At 1.20t, it is thicker than other parts of the plate. Therefore, stress concentration due to wear when the bellows 8 expands and contracts tends to occur at the peaks 4 and valleys 3 that are in contact with the welded portion.

As one method for solving the above-mentioned problems, the conventional multi-layered bellows is constructed by providing spaces in each layer of the bellows 8 at equal intervals as shown in FIG. Proposed. The method for manufacturing such bellows 8 is as follows. On the outside of the cylinder that will become the innermost layer bellows, cylinders having inner cylinders that approximate the outer diameter of the cylinder are sequentially stacked to form a bellows material 6, and this bellows material 6 is placed in a bellows-shaped low-temperature mold, and the bellows is formed into a bellows material. By applying high-temperature pressure fluid into the material, it can be formed in an extremely short time. The molded bellows material 6 is then taken out from the mold and cooled to room temperature. Since the molding time of the bellows material 6 is extremely short, each cylinder is molded with a temperature difference, and the amount of shrinkage up to room temperature is different.
Microscopic voids are created between the layers. In the manner described above, a multilayer bellows 8 having voids between each layer can be manufactured. However, this molding method utilizes the heat conduction of the material, and it is difficult to obtain a uniform temperature distribution. Particularly during molding, since adjacent bellows are brought into close contact due to internal pressure, it is difficult to create a temperature difference between each layer.

Furthermore, as shown in FIG. 6, the difference in the radius of curvature between the peaks 4 and valleys 3 of the bellows in each layer is larger than that of the bellows in the close contact state shown in FIG. The rigidity is different in part 3. In the innermost layer of bellows, the stiffness of the valley portions 3 is lower than that of the peak portions 4, and in the outermost layer of bellows, the stiffness of the peak portions 4 is lower than that of the valley portions 3. For this reason, the bellows 8 with voids between the layers is more likely to cause stress concentration due to the stress distribution in the peaks 4 and valleys 3 varying greatly for the same amount of load displacement compared to the bellows 9 in a close contact state, resulting in a shortened lifespan. This may lead to

[Purpose of the invention]

It is an object of the present invention to provide a multilayer bellows that eliminates contact that occurs during expansion and contraction in stress concentration parts of the multilayer bellows, and further minimizes the difference in stiffness between the peaks and valleys of each layer to provide a uniform stress distribution. It is.

[Summary of the invention]

The present invention aims to bring the parallel parts of the bellows into close contact with each other, to ensure that the radius of curvature of the inner surface of the outer bellows of two adjacent bellows is as equal as possible to the radius of curvature of the outer surface of the inner bellows, and to create a void between each layer of the stress concentration part. By providing this, contact that occurs during expansion and contraction in stress concentration areas is eliminated, and the difference in rigidity between the peaks and valleys of each layer is minimized, resulting in a uniform stress distribution.

[Embodiments of the invention] --- Hereinafter, one embodiment of the present invention will be explained. Figure 1(a).

(b) shows a two-layer bellows, which is a type of multilayer bellows. Each layer is in close contact only at the parallel portion 5 of the bellows, and the radius of curvature of the inner surface of the outer bellows 1 is equal to the radius of curvature of the outer surface of the inner bellows 2,
In addition, voids are provided in the peaks and valleys of the stress concentration area.

The amount of voids at this time can be determined by simple calculation as follows. FIG. 7 shows a model of early release from the peak 4 to the valley 3 of the bellows 8. The radius of curvature of the bellows 8 is r1, the parallel length is t1, the moment of inertia of area is 11, and the Young's modulus is E. If axial reaction force R1 radial virtual reaction force Q and bending moment Me act at point 0, then B
,D.

The songs acting on each point of F are moments Mi, Mn, M
F is Mal = Ma R(r-1-z-)-rcosθ)
-Q r (2-sin θ)...(2) Mo=Mo R(j x+r)...-
(a) MF = MO-Rr (-Q rc of 1-sin
O5θ ・(4). Here, there is a condition that point G does not rotate. This is it Mu=R(r+-)...(6)
becomes. Next, from equations (2) to (4), the strain energy U of the curve 1 is...(7). Ca5t:gI:auo theorem, Q at 9G point
The displacement δ in the direction (radial direction) is δ=[δU/aQ)Q=0 =Rr! (r+(--1)t)/EI (8). Here, reaction force R = 0.178 (kg
f/wn), average radius of the peak r = 11.75 (
mm), E = 16200 (kgf/i2), plate thickness t = 1.5 mm = t'/12 = 0
．． 281 (Wan'), using t = 35 (w), δ
20.171 (B). Here, assuming that the center point of the parallel portion is not displaced, the radial displacement amount δ' of the valley portion 3 shown in FIG. = 几r2(r+(--1)/J/2EI ・(9).If this model is applied to the valley part 3 of the outer layer bellows 1, it will be displaced to the outside 11i1 by δ' = 0.08ytas.Next The reaction force is equal to the parallel part a1 Young's modulus E1 moment of inertia of area) I is equal, and the radius r. When applied to the valley portion 3 of the inner layer bellows 2 where (>r), then the radial displacement δ of [. ' is the same as above, δo' = Rro'('o + (21) ')/2
EI can be expressed as (10). Obviously, under the condition that the tensile displacement R is >0, the radial displacement difference Δδ between the outer layer bellows 1 and the inner layer bellows 2 becomes Δδ=δ0′−δ′〉0 (11), and they are in contact with each other. become. For example, the amount of radial displacement δ of the inner bellows 2. ' is the radius r. -13,25■(
> r = 1x, 75 degrees) and the above conditions, δ. '=0.
It will be in the 11th key. Therefore, Δδ=0.11−0.08=0.03■ (12).

The above-mentioned radial displacement amount δ due to the curve is approximately the same value as in the detailed analysis using the finite element method using isoparametric axisymmetric shell elements. In addition, in conventional multilayer bellows, the gap between the layers is 0.005 to 0.0
It is said that there is 1m + Δδ = 0 calculated above.
．． The void is smaller than 03m, and there is sufficient possibility of contact between the valleys due to expansion and contraction of each layer.

Furthermore, the amount of voids Δδ=0.03 va is as small as 0.01 when the height of the bellows is 60 m, and the change in the rigidity of the bellows due to the voids can be ignored.

As described above, the amount of voids Δδ in the valleys of the multilayer bellows 8
can be calculated using the following formula.

Here, R is the reaction force of the force applied by the unit length in the circumferential direction. .

E is the Young's modulus of the material, ■ is the moment of inertia determined by the plate thickness, a is the length of the parallel section, and r.

and r is the radius of curvature of the peak or valley of the adjacent bellows. The above calculation example is based on the valley 31 of bellows 8.
This is the case where C is applied, but it can also be applied to the mountain portion 4. In this case, using the radius of curvature r1 of the inner bellows 2, the radial displacement amount δ of the peak portion 4 is δr=f(r, "cr++<--x)'t]/2Ex
・(14) becomes. Next, using the radius of curvature r of the outer bellows 1, the radial displacement amount δ2 of the peak portion 4 is δ2=Rr2' [r2+(-1)t]/2EI
−(15). The direction of displacement at this time is that the peak portion 4 is displaced inward. Therefore, the displacement difference Δδ between the inner layer bellows 2 and the outer layer bellows 1 is Δa:δ from the relationship r2>rl.
-δ,>0 (16), which indicates that they are in contact. Therefore, the amount of voids required for non-contact can be determined using equation (13).

As described above, the amount of voids in the troughs 3 and peaks 4 of the multilayer bellows 8 to avoid contact due to expansion and contraction can be determined using equation (13).

An example of a method for forming such a bellows 8 is shown in FIG. A two-split molding die 7 is installed on the outside, and hydraulic pressure is introduced into the bellows blank tube 6 to increase the hydraulic pressure inside the blank tube to a predetermined pressure.
The bellows blank tube 6 is expanded by pressure. Further, liquid or gas is injected between the layers through the injection pipe 10Vc. The volume of liquid or gas injected at this time is the volume that can be filled in the voids in the peaks 4 or troughs 3, and molding is carried out while maintaining a balance with the internal liquid pressure. In order to withstand the hoop stress of the internal pressure, the part where the mold 7 is contained is bulged out only by the bellows material tube 6 between them, and at the same time is compressed in the axial direction by a press.
The parts of the bellows blank tube 6 that will become the bulging peaks 4 are buckled and further formed into a bellows shape. In this case, the liquid or gas injected between the inner and outer layer bellows 1 and 2 has the property of moving to the peaks and valleys 3 and 4, which are easily buckled (easily deformed). A predetermined bellows spacing can be obtained in a focused manner.

In the above embodiment, a predetermined gap is provided in the stress concentration parts of both the peak part 4 and the valley part 3, but the peak part 4, which is most likely to rupture,
Alternatively, a gap may be provided in either of the valleys 3. An embodiment in which a gap is provided in the valley portion 3 is shown in FIG.

According to an embodiment of the present invention, the parallel parts of the bellows are brought into close contact with each other, and the radius of curvature of the inner surface of the outer bellows is equal to the radius of curvature of the outer surface of the inner bellows, and the stress concentration part is By providing a predetermined gap between each layer, contact that occurs during expansion and contraction in stress concentration areas can be eliminated.
Furthermore, the difference in stiffness between the peaks and valleys of each layer is minimized, and the stress distribution is uniform.

Furthermore, the method for manufacturing the multilayer bellows according to the embodiment of the present invention is based on the conventional hydroforming method, and only requires applying a predetermined liquid or gas pressure between the layers, and can be easily manufactured using conventional bellows manufacturing equipment. Can be easily manufactured. In addition, compared to the case where the bellows has voids throughout the bellows, since there are voids only in the peaks or valleys, the volume of liquid or gas that needs to be injected between the layers is smaller, and rapid cooling is not required. , it is possible to reduce manufacturing costs.

〔Effect of the invention〕

As described above, according to the present invention, since the multilayer bellows has a shape in which each bellows has a larger spacing in the peaks, valleys, or picture parts than in other parts, the inner surface of the outer bellows and the outer surface of the inner bellows are The radius of curvature tends to be the same, and contact and local stress caused by expansion and contraction of the bellows are prevented. b) is a longitudinal cross-sectional view of the Y section in Fig. 1, Fig. 2 is a longitudinal cross-sectional view showing a conventional hydroforming method for bellows, Fig. 3 is a longitudinal cross-sectional view showing a conventional example of multilayer bellows, and Fig. 4 is a vertical cross-sectional view showing a conventional example of multilayer bellows. An analysis model diagram of a conventional two-layer bellows, Figure 5 is a stress distribution diagram of the bellows, Figure 6 is a vertical cross-sectional view of a multi-layer bellows according to another conventional example, Figure 7 is a bellows cage model, and Figure 8 is a diagram of the present invention. FIG. 9 is a vertical cross-sectional view showing an example of a manufacturing method according to an embodiment of the present invention, and FIG. 9 is a vertical cross-sectional view of a multilayer bellows according to another embodiment of the present invention.

1... Outer layer bellows, 2... Inner layer bellows, 3...
・Bellows valley, 4... Bellows peak, 5... Bellows parallel part, 6... Bellows blank tube, 7... Molding mold, 8... Multilayer bellows, 9... Multilayer bellows , 10
...Injection pipe, 11...Packing, 12...Hydraulic pressure pipe.

Claims (1)

[Claims] A structure of a multilayer bellows comprising one, two or more layers of bellows, characterized in that each bellows is provided with a larger spacing between peaks and/or valleys of the multilayer bellows, or both of them, than in other areas.