JP7797984B2 - Bellows and molds - Google Patents

Description

This disclosure relates to a bellows and a mold.

Bellows made of synthetic resin are known (for example, Patent Document 1).

Japanese Utility Model Application Publication No. 61-188090

Bellows are manufactured by blow molding. In blow molding, a thermoplastic resin material (parison) is placed in a mold, and compressed air is blown into the parison to press the resin against the mold. Bellows molded in this way have thinner peaks and thicker valleys. With conventional bellows, only the peaks deform when compressed, and when a certain amount of compression is exceeded, buckling occurs, where some of the valleys deform and move outward.

A bellows according to one aspect of the present disclosure is a bellows made of synthetic resin, and includes: a peak portion that is convex in the radial direction; a valley portion that is adjacent to the peak portion in the axial direction and concave in the radial direction; and an intermediate portion that includes a peak on the outer surface of the peak portion and a midpoint in the radial direction of the peak on the outer surface of the valley portion, wherein a first length, which is the length in the axial direction between the peak on the outer surface of the peak portion and the midpoint, is greater than a second length, which is the length in the axial direction between the peak on the outer surface of the valley portion and the midpoint.

A mold according to one aspect of the present disclosure is a mold used for blow molding a synthetic resin bellows, and includes a peak-forming portion that is concave in the radial direction for forming a convex peak of the bellows, a valley-forming portion that is convex in the radial direction and adjacent to the peak-forming portion in the axial direction for forming a concave valley of the bellows, and an intermediate-forming portion that includes an apex of the peak-forming portion and a midpoint in the radial direction of the apex of the valley-forming portion, wherein a first length, which is the length in the axial direction between the apex and the midpoint of the peak-forming portion, is greater than a second length, which is the length in the axial direction between the apex and the midpoint of the valley-forming portion.

The present disclosure can be realized not only as a bellows having the characteristic shape described above, but also as a mold used to form the characteristic shape of the bellows, or as a manufacturing method for forming the characteristic shape of the bellows.

This disclosure makes it possible to prevent buckling of the bellows when it is compressed.

FIG. 2 is a front view illustrating an example of a bellows according to an embodiment. FIG. 2 is a partially enlarged cross-sectional view showing an example of a bellows according to an embodiment. FIG. 10 is a partially enlarged cross-sectional view of a conventional bellows. FIG. 1 is a diagram showing the shape of a conventional bellows in the middle stage of compressive deformation. FIG. 1 is a diagram showing the shape of a conventional bellows at the final stage of compressive deformation. 10A and 10B are diagrams showing the shape of the bellows according to the embodiment at a point in time during compressive deformation. FIG. 10 is a diagram showing the shape of the bellows according to the embodiment at the end of compressive deformation. FIG. 10 is a diagram showing the results of a simulation of stress distribution in a conventional bellows at the initial stage of compressive deformation. FIG. 10 is a diagram showing a simulation result of stress distribution during compressive deformation in a bellows according to an embodiment. 1 is a graph showing the relationship between the maximum stress generated by compressive deformation and the amount of compression in the bellows according to the embodiment and in a conventional bellows. 10 is a graph showing the relationship between the compression load and the compression amount during compressive deformation in the bellows according to the embodiment and in a conventional bellows. 10 is a graph showing the relationship between L1/L3 and maximum stress. 10 is a graph showing the relationship between L4/L3 and maximum stress. FIG. 2 is a cross-sectional view showing an example of the configuration of a mold according to the embodiment. 10A and 10B are diagrams for explaining an example of use of a mold according to an embodiment. FIG. 2 is a partially enlarged view of a mold according to an embodiment.

Overview of the embodiments of the present disclosure
The following provides an outline of embodiments of the present disclosure.

(1) The bellows according to this embodiment is made of synthetic resin and includes: peaks that are convex in the radial direction; valleys that are adjacent to the peaks in the axial direction and are concave in the radial direction; and an intermediate portion that includes the apexes of the outer surfaces of the peaks and the midpoints in the radial direction of the apexes of the outer surfaces of the valleys. A first length, which is the length in the axial direction between the apexes of the outer surfaces of the peaks and the midpoint, is greater than a second length, which is the length in the axial direction between the apexes of the outer surfaces of the valleys and the midpoint. This increases the amount of deformation in the peaks when the bellows is compressed, making it possible to suppress buckling.

(2) In the above (1), the relationship between the first length L1 and the second length L2 may be determined by the following formula (1).
L1>L2>0.4・L1...(1)
This allows the first length L1 and the second length L2 to be set to appropriate values in order to prevent buckling from occurring when the bellows is compressed.

(3) In the above (1) or (2), the relationship between a third length L3, which is the length in the axial direction between the apex of the outer surface of the peak portion and the apex of the outer surface of the valley portion, and a fourth length L4, which is the length in the radial direction between the apex of the outer surface of the peak portion and the apex of the outer surface of the valley portion, may be defined by equation (2).
3 · L3 ≧ L4 ≧ L3 ... (2)
This allows the third length L3 and the fourth length L4 to be set appropriately in order to suppress the occurrence of buckling when the bellows is compressed.

(4) In any one of (1) to (3) above, the thickness of the valley portion may be greater than the thickness of the peak portion. This allows for a larger amount of deformation in the peak portion.

(5) In any one of (1) to (4) above, the synthetic resin may be ethylene tetrafluoroethylene copolymer (ETFE). This allows for the construction of a fluororesin bellows with excellent chemical resistance.

(6) The mold according to this embodiment is a mold used for blow molding a synthetic resin bellows, and includes a peak-forming portion that is concave in the radial direction for forming a convex peak of the bellows, a valley-forming portion that is convex in the radial direction and adjacent to the peak-forming portion in the axial direction for forming a concave valley of the bellows, and an intermediate-forming portion that includes an apex of the peak-forming portion and a midpoint in the radial direction of the apex of the valley-forming portion, wherein a first length, which is the length in the axial direction between the apex of the peak-forming portion and the midpoint, is greater than a second length, which is the length in the axial direction between the apex of the valley-forming portion and the midpoint. As a result, when a bellows manufactured by blow molding using this mold is compressed, the amount of deformation in the peaks is large, making it possible to suppress buckling.

<Details of the embodiment of the present disclosure>
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. At least some of the following preferred embodiments may be combined in any desired manner.

[1. Bellows configuration]
FIG. 1 is a front view showing an example of a bellows according to this embodiment, and FIG. 2 is a partially enlarged cross-sectional view thereof.

The bellows 10 is cylindrical overall. It includes a main body 100 made of synthetic resin and metal parts 200 provided at both ends of the main body 100 in the axial direction.

The circumferential surface of the main body 100 is formed in an accordion-like shape. That is, the main body 100 has peaks 110 and valleys 120 arranged alternately in the axial direction. The peaks 110 are convex in the radial direction, and the valleys 120 are concave in the radial direction. A linear intermediate portion 130 is provided between adjacent peaks 110 and valleys 120. The intermediate portion 130 smoothly connects the peaks 110 and valleys 120. Note that, hereinafter, the axial direction is referred to as the "X direction" and the radial direction is referred to as the "Y direction."

Referring to Figure 2, the peaks 110 are curved in an arc shape in cross section. The valleys 120 are curved in an arc shape in the opposite direction to the peaks 110 in cross section. On the other hand, the metal part 200 includes triangular peaks and triangular valleys in cross section, and is curved in a sawtooth shape (see Figure 1).

As shown in FIG. 2, the main body 100 of the bellows 10 is formed by blow molding. The main body 100 formed by blow molding has a small thickness at the peaks 110 and a large thickness at the valleys 120. The thickness of the intermediate portion 130 varies so that it is small on the outer side in the Y direction (the peaks 110 side) and large on the inner side in the Y direction (the valleys 120 side). In other words, the intermediate portion 130 has a tapered shape in which the thickness decreases as it moves outward in the Y direction.

In Figure 2, 110a is the apex of the outer surface of the peak portion 110 in the Y direction, and 120a is the apex of the outer surface of the valley portion 120 in the Y direction. 130a is the midpoint in the Y direction between the peaks 110a and 120a. The midpoint 130a is included in the intermediate portion 130. The first length L1 is the length in the X direction between the peak 110a and the midpoint 130a on the outer surface of the peak portion 110. The second length L2 is the length in the X direction between the peak 120a and the midpoint 130a on the outer surface of the valley portion 120.

In the bellows 10 according to this embodiment, the first length L1 is greater than the second length L2. The curvature (convex curvature) R1 of the outer surface of the peak portion 110 is greater than the curvature (concave curvature) R3 of the outer surface of the valley portion 120, and is greater than the curvature (convex curvature) R4 of the inner surface of the valley portion 120. Furthermore, the curvature (concave curvature) R2 of the inner surface of the peak portion 110 is greater than the curvature R3 of the outer surface of the valley portion 120, and is greater than the curvature R4 of the inner surface of the valley portion 120.

The third length L3 is the length in the X direction between the apex 110a of the outer surface of the peak 110 and the apex 120a of the outer surface of the valley 120. The fourth length L4 is the length in the Y direction between the apex 110a of the outer surface of the peak 110 and the apex 120a of the outer surface of the valley 120. In the bellows 10 according to the embodiment, the fourth length L4 is equal to or greater than the third length L3.

It is particularly desirable to use ethylene tetrafluoroethylene copolymer (ETFE) as the synthetic resin material for the bellows 10. This allows for the construction of a fluororesin bellows with excellent chemical resistance. Note that polytetrafluoroethylene (PTFE), a typical fluororesin, is not suitable for blow molding because it does not melt completely.

[2. Issues with conventional bellows]
FIG. 3 is an enlarged partial cross-sectional view of a conventional bellows.

As shown in Figure 3, in conventional bellows, the first length L1 is equal to the second length L2. The curvature (convex curvature) R1 of the outer surface of the peak portion 110 is equal to the curvature (concave curvature) R3 of the outer surface of the valley portion 120. The curvature (concave curvature) R2 of the inner surface of the peak portion 110 is smaller than the curvature R3 of the outer surface of the valley portion 120.

The inventors used the finite element method to simulate compressive deformation of a bellows in the X direction. Figures 4A and 4B show a conventional bellows under compression. Figure 5A shows the shape of the bellows in the middle stage of compressive deformation, and Figure 4B shows the shape of the bellows in the final stage of compressive deformation.

In conventional bellows, in the initial stage of deformation, the peaks 110, which have a smaller thickness, deform significantly, while the valleys 120, which have a larger thickness, hardly deform at all. In the initial stage of deformation, stress is concentrated in the peaks 110.

As the deformation progresses further, the inner surfaces of the two intermediate portions 130 sandwiching one peak 110 come into contact with each other (middle stage of deformation), as shown in Figure 4A. In the middle stage of deformation, the peak 110 does not deform, and only the valley 120 deforms.

As shown in Figure 4B, at the end of the deformation, buckling occurs, causing some of the valleys 120 to deform and move outward in the Y direction. Buckling is undesirable because it can cause damage to the bellows 10.

3. Simulation
5A and 5B are diagrams showing the bellows according to the embodiment in a compressed state. Fig. 5A shows the shape of the bellows at a point in the middle of compressive deformation, and Fig. 5B shows the shape of the bellows at the end of compressive deformation. Note that, hereinafter, the conventional bellows will also be referred to as the "conventional bellows," and the bellows according to the embodiment will also be referred to as the "improved bellows."

In the improved bellows 10, the peaks 110, which have a smaller thickness, deform significantly throughout the entire compression, while the valleys 120, which have a larger thickness, deform very little. As described above, the first length L1 of the improved bellows 10 is greater than the second length L2. Therefore, the amount of deformation in the X direction of the peaks 110 of the improved bellows 10 is greater than that of the conventional bellows. In other words, in the improved bellows 10, the same deformation as in the initial stage of deformation in the conventional bellows occurs throughout the entire compression period, and the deformation pattern does not change during the initial, middle, and final stages of compression, as in the conventional bellows. In the improved bellows 10, the compression deformation ends when the inner surfaces of the two intermediate sections 130 sandwiching one peak 110 come into contact with each other (see Figure 5B).

The shape of the improved bellows 10 at the end of compressive deformation corresponds to the shape of the conventional bellows at the middle stage of deformation. As shown in Figure 5B, the improved bellows does not buckle even at the end of compressive deformation.

Figure 6A shows the simulation results of stress distribution in a conventional bellows at the beginning of deformation, and Figure 6B shows the simulation results of stress distribution during deformation in an improved bellows.

As shown in Figure 6A, in conventional bellows, stress is concentrated at the top of the peaks 110 (areas surrounded by dashed lines in the figure). Therefore, in conventional bellows, the stress at the tops of the peaks 110 is very large.

In contrast, as shown in Figure 6B, in the improved bellows 10, strong stress occurs not only at the tops of the peaks 110 but also at the connections between the peaks 110 and the intermediate portions 130 (areas surrounded by dashed lines in the figure). Because stress is thus dispersed in the improved bellows 10, the maximum stress value is smaller than in conventional bellows.

Figures 7 and 8 are graphs comparing the simulation results of compressive deformation of the improved bellows and the conventional bellows. Figure 7 shows the relationship between the maximum stress generated in the bellows 10 and the amount of compression. In Figure 7, the vertical axis represents the maximum stress, and the horizontal axis represents the amount of compression. The location where the maximum stress occurs in the bellows 10 changes depending on the amount of compression. The maximum stress shown in Figure 7 represents the stress value at the location where the maximum stress occurs within the entire bellows.

In conventional bellows, the maximum stress increases in proportion to the amount of compression in the early stages of deformation. In conventional bellows, from the first compression amount P1, the maximum stress decreases as the amount of compression increases. This is the middle stage of deformation. Furthermore, at the second compression amount P2, the maximum stress reaches a lower limit, and thereafter the maximum stress increases rapidly as the amount of compression increases. This is the end stage of deformation, when the conventional bellows is in a buckled state.

On the other hand, for the improved bellows, the maximum stress increases in proportion to the amount of compression throughout the entire compressive deformation. For the same amount of compression, the maximum stress value for the improved bellows is smaller than the maximum stress value for the conventional bellows.

Figure 8 shows the relationship between the compressive load and compression amount applied to the bellows 10. In Figure 8, the vertical axis represents the compressive load, and the horizontal axis represents the compression amount. With conventional bellows, the compressive load gradually increases as the compression amount increases up to the first compression amount P1, but from the first compression amount P1 onwards, the compressive load increases rapidly in accordance with the compression amount. In other words, in the middle and final stages of deformation, the bellows 10 will not deform unless a large compressive load is applied.

On the other hand, with the improved bellows, the compressive load gradually increases as the amount of compression increases throughout the entire compressive deformation. In this way, the compressive load is significantly reduced with the improved bellows compared to the conventional bellows. Furthermore, the slope of the compressive load versus the amount of compression with the improved bellows is smaller than the slope of the compressive load versus the amount of compression with the conventional bellows at the initial stage of deformation.

The following table shows the results of analyzing the maximum stress values for various shapes of bellows 10. In Nos. 1 to 16, the Young's modulus of the synthetic resin material constituting the main body 100 was set to 1,000 MPa, in Nos. 17 and 19, the Young's modulus was set to 10 MPa, and in Nos. 18 and 20, the Young's modulus was set to 10,000 MPa.

Nos. 1, 5, 9, 13, 17, and 18 are the analysis results for conventional bellows. That is, for Nos. 1, 5, 9, 13, 17, and 18, L1/L3 is 0.5. That is, the first length L1 is equal to the second length L2 (see Figure 2). For No. 1, L4/L3 is 1.0, that is, the third length L3 is equal to the fourth length L4. The maximum stress value for No. 1 is 159.2 MPa. For No. 5, L4/L3 is 0.6, that is, the fourth length L4 is 0.6 times the third length L3. The maximum stress value for No. 5 is 195.7 MPa. For No. 9, L4/L3 is 2.0, that is, the fourth length L4 is twice the third length L3. No. The maximum stress value for No. 9 is 105.8 MPa. For No. 13, L4/L3 is 3.0, meaning the fourth length L4 is three times the third length L3. The maximum stress value for No. 13 is 150.4 MPa. With the exception of No. 9, the conventional bellows all have high maximum stress values of 150 or more.

Nos. 2, 3, and 4 have a different L1/L3 ratio from No. 1. In No. 2, L1/L3 is 0.4, meaning L1:L2 = 4:6. The maximum stress value for No. 2 is 117.5 MPa. In No. 3, L1/L3 is 0.3, meaning L1:L2 = 3:7. The maximum stress value for No. 3 is 123.7 MPa. In No. 4, L1/L3 is 0.2, meaning L1:L2 = 2:8. The maximum stress value for No. 4 is 195.7 MPa. As such, Nos. 2 and 3 have smaller maximum stress values than No. 1, and better results were obtained.

Nos. 6, 7, and 8 have changed L1/L3 from No. 5. Nos. 5 and 6 have high maximum stress values, and Nos. 7 and 8 were unable to create the shape.

Nos. 10, 11, and 12 have a different L1/L3 ratio from No. 9. In No. 10, L1/L3 is 0.4, meaning that L1:L2 = 4:6. The maximum stress value for No. 10 is 101.9 MPa. In No. 11, L1/L3 is 0.3, meaning that L1:L2 = 3:7. The maximum stress value for No. 11 is 104.5 MPa. In No. 12, L1/L3 is 0.2, meaning that L1:L2 = 2:8. The maximum stress value for No. 12 is 107.0 MPa. Thus, the maximum stress values for Nos. 10, 11, and 12 are less than 110 MPa. In particular, Nos. 10 and 11 have smaller maximum stress values than No. 9, and good results were obtained.

Nos. 14, 15, and 16 have a different L1/L3 ratio from No. 13. In No. 14, L1/L3 is 0.4, meaning that L1:L2 = 4:6. The maximum stress value for No. 14 is 107.0 MPa. In No. 15, L1/L3 is 0.3, meaning that L1:L2 = 3:7. The maximum stress value for No. 15 is 109.9 MPa. In No. 16, L1/L3 is 0.2, meaning that L1:L2 = 2:8. The maximum stress value for No. 16 is 105.1 MPa. As such, the maximum stress values for Nos. 14, 15, and 16 were less than 110 MPa, and good results were obtained in all cases.

In No. 17, L4/L3 is 1.0, meaning the third length L3 and the fourth length L4 are equal. The Young's modulus of No. 17 is 10 MPa, and the maximum stress value is 1.6 MPa. In No. 19, L1/L3 is changed from No. 17. In No. 19, L1/L3 is 0.4, meaning L1:L2 = 4:6. The maximum stress value of No. 19 is 1.2 MPa, an improvement over No. 19.

In No. 18, L4/L3 is 1.0, meaning the third length L3 and the fourth length L4 are equal. The Young's modulus of No. 18 is 10,000 MPa, and the maximum stress value is 1,592.0 MPa. In No. 20, L1/L3 is changed from No. 18. In No. 20, L1/L3 is 0.4, meaning L1:L2 = 4:6. The maximum stress value of No. 20 is 1,175.4 MPa, an improvement over No. 18.

Figure 9A is a graph showing the relationship between L1/L3 and maximum stress, and Figure 9B is a graph showing the relationship between L4/L3 and maximum stress. Here, bellows with L1/L3 = 0.5 and L4/L3 = 1 are taken as the reference bellows. As shown in Figure 9A, when L4/L3 = 2 and 3, the maximum stress value is lower than that of the reference bellows for all of L1/L3 = 0.2, 0.3, 0.4, and 0.5. When L4/L3 = 1, the maximum stress value is lower than that of the reference bellows for all of L1/L3 = 0.3, 0.4, and 0.5.

As shown in Figure 9B, when L1/L3 = 0.5, 0.2, the maximum stress value is lower than that of the standard bellows (L4/L3 = 1) when L4/L3 = 2, 3. When L1/L3 = 0.4, 0.3, the maximum stress value is lower than that of the standard bellows when L4/L3 = 1, 2, 3.

From the above analysis results, it has been found that it is preferable that the first length L1 and the second length L2 satisfy the following formula (1).
L1>L2>0.4・L1...(1)

Furthermore, it has been found that it is preferable that the third length L3 and the fourth length L4 satisfy the following formula (2).
3 · L3 ≧ L4 ≧ L3 ... (2)

[4. Mold]
10 is a cross-sectional view showing an example of the configuration of a mold according to an embodiment. The mold 300 is a mold for blow molding. The mold 300 includes a first mold 300a and a second mold 300b. The first mold 300a is provided with a concave cavity 301. The second mold 300b is also provided with a cavity 302 having the same shape as the first mold 300a.

Cavities 301 and 302 are used to mold the outer surface of the main body 100 of the bellows 10. When the bellows 10 is manufactured, the first mold 300a and the second mold 300b are arranged so that cavities 301 and 302 face each other, and are closed together so that cavities 301 and 302 form a single space. In other words, when the first mold 300a and the second mold 300b are closed together, cavities 301 and 302 form a cylindrical space overall that corresponds to the shape of the outer surface of the main body 100 of the bellows 10. In the following description, the axial direction of this space will be referred to as the "x-direction," and the radial direction will be referred to as the "y-direction."

Each of the cavities 301, 302 includes a peak forming portion 310, a valley forming portion 320, and an intermediate portion forming portion 330. The peak forming portion 310 is a portion for forming the convex peak portion 110 of the bellows 10 and is concave in the y direction. The valley forming portion 320 is a portion for forming the concave valley portion 120 of the bellows 10 and is convex in the y direction. The intermediate portion forming portion 330 is a portion for forming the intermediate portion 130 of the bellows 10 and is linear and inclined in the y direction.

The peak forming portions 310, valley forming portions 320, and intermediate portion forming portions 330 are each provided in a concentric semicircular shape on the first mold 300a and the second mold 300b. The peak forming portions 310 and valley forming portions 320 are provided alternately in the x direction. The intermediate portion forming portions 330 are provided between adjacent peak forming portions 310 and valley forming portions 320.

When the first mold 300a and the second mold 300b are closed together, the peak forming portion 310 of cavity 301 and the peak forming portion 310 of cavity 302 are combined to form a circular space. Similarly, the valley forming portion 320 of cavity 301 and the valley forming portion 320 of cavity 302 are combined in a circular shape, and the intermediate portion forming portion 330 of cavity 301 and the intermediate portion forming portion 330 of cavity 302 are combined in a circular shape.

Figure 11 is a diagram illustrating an example of use of a mold according to an embodiment. When manufacturing bellows 10 using mold 300, as described above, first mold 300a and second mold 300b are closed together, and a parison 400 made of thermoplastic resin is placed in the internal space. Compressed air is blown into the parison 400, pressing the resin against cavities 301 and 302 in mold 300. This transfers the shape of cavities 301 and 302 to the resin, forming main body 100.

Figure 12 is a partially enlarged view of a mold according to an embodiment. In Figure 12, 310a is the apex of the peak forming portion 310 in the y direction, and 320a is the apex of the valley forming portion 320 in the y direction. 330a is the midpoint in the y direction between the peaks 310a and 320a. The midpoint 330a is included in the intermediate portion forming portion 330. The first length L1' is the length in the x direction between the peak 310a and the midpoint 330a of the peak forming portion 310. The second length L2' is the length in the x direction between the peak 320a and the midpoint 330a of the valley forming portion 320.

In the mold 300 according to this embodiment, the first length L1' is greater than the second length L2'. The curvature (concave curvature) R1' of the peak forming portion 310 is greater than the curvature (convex curvature) R3' of the valley forming portion 320.

The third length L3' is the length in the x direction between the apex 310a of the peak forming portion 310 and the apex 320a of the valley forming portion 320. The fourth length L4' is the length in the y direction between the apex 310a of the peak forming portion 310 and the apex 320a of the valley forming portion 320. In the mold 300 according to the embodiment, the fourth length L4' is equal to or greater than the third length L3'.

It is preferable that the first length L1' and the second length L2' satisfy the following formula (3).
L1'>L2'>0.4・L1'...(3)

Furthermore, it is preferable that the third length L3' and the fourth length L4' satisfy the following formula (4).
3.L3'≧L4'≧L3'...(4)

5. Effects
The bellows 10 is made of synthetic resin. The bellows 10 includes a peak portion 110, a valley portion 120, and an intermediate portion 130. The peak portion 110 is convex in the radial direction. The valley portion 120 is adjacent to the peak portion 110 in the axial direction and is concave in the radial direction. The intermediate portion 130 includes an apex 110a on the outer surface of the peak portion 110 and a midpoint 130a in the radial direction of the apex 120a on the outer surface of the valley portion 120. A first length L1, which is the length in the axial direction between the apex 110a and the midpoint 130a on the outer surface of the peak portion 110, is longer than a second length L2, which is the length in the axial direction between the apex 120a and the midpoint 130a on the outer surface of the valley portion 120. This increases the deformation amount of the peak portion 110 when the bellows 10 is compressed, thereby suppressing buckling.

The relationship between the first length L1 and the second length L2 may be determined by equation (1).
L1>L2>0.4・L1...(1)
This allows the first length L1 and the second length L2 to be set appropriately in order to prevent buckling from occurring when the bellows 10 is compressed.

The relationship between a third length L3, which is the length in the axial direction between the apex 110a of the outer surface of the peak portion 110 and the apex 120a of the outer surface of the valley portion 120, and a fourth length L4, which is the length in the radial direction between the apex 110a of the outer surface of the peak portion 110 and the apex 120a of the outer surface of the valley portion 120, may be determined by equation (2).
3 · L3 ≧ L4 ≧ L3 ... (2)
This allows the third length L3 and the fourth length L4 to be set appropriately in order to suppress the occurrence of buckling when the bellows 10 is compressed.

The thickness of the valley portion 120 may be greater than the thickness of the peak portion 110. This allows for a greater amount of deformation in the peak portion 110.

The synthetic resin that is the material of the bellows 10 may be ethylene tetrafluoroethylene copolymer (ETFE). This allows the bellows 10 to be made of fluororesin, which has excellent chemical resistance.

The mold 300 is used for blow molding a bellows 10 made of synthetic resin. The mold 300 comprises a peak forming portion 310, a valley forming portion 320, and an intermediate portion forming portion 330. The peak forming portion 310 is a portion for forming the convex peaks 110 of the bellows 10. The peak forming portion 310 is concave in the radial direction. The valley forming portion 320 is a portion for forming the concave valleys 120 of the bellows 10. The valley forming portion 320 is adjacent to the peak forming portion 310 in the axial length direction. The valley forming portion 320 is convex in the radial direction. The intermediate portion forming portion 330 includes a midpoint 330a in the radial direction of the apex 310a of the peak forming portion 310 and the apex 320a of the valley forming portion 320. The first length L1', which is the length in the axial direction between the apex 310a and the midpoint 330a of the peak-forming portion 310, is greater than the second length L2', which is the length in the axial direction between the apex 320a and the midpoint 330a of the valley-forming portion 320. As a result, when the bellows 10 manufactured by blow molding using the mold 300 is compressed, the amount of deformation in the peak portion 110 increases, making it possible to suppress the occurrence of buckling.

[6. Supplementary Notes]
The embodiments disclosed herein are illustrative in all respects and are not restrictive. The scope of the present invention is defined by the claims rather than the above-described embodiments, and includes meanings equivalent to the claims and all modifications within the scope thereof.

REFERENCE SIGNS LIST 10 Bellows 100 Main body 110 Peak 110a Apex 120 Valley 120a Apex 130 Middle 130a Midpoint 200 Metal part 300 Mold 300a First mold 300b Second mold 301, 302 Cavity 310 Peak forming part 310a Apex 320 Valley forming part 320a Apex 330 Middle forming part 330a Midpoint 400 Parison L1 First length L2 Second length L3 Third length L4 Fourth length L1' First length L2' Second length L3' Third length L4' Fourth length P1 First compression amount P2 Second compression amount R1 to R4 Curvature R1', R2' Curvature

Claims (6)

A bellows made of synthetic resin,
a peak portion that is convex in the radial direction;
a valley portion adjacent to the peak portion in the axial direction and concave in the radial direction;
an intermediate portion including a midpoint in the radial direction of the apex of the outer surface of the peak portion and the apex of the outer surface of the valley portion;
Equipped with
a first length that is a length in the axial direction between the apex of the outer surface of each of the peaks and the midpoint is greater than a second length that is a length in the axial direction between the apex of the outer surface of each of the valleys and the midpoint;
The relationship between the first length L1 and the second length L2 is determined by Equation (1).
L1>L2>0.4・L1...(1)
Bellows. A bellows made of synthetic resin,
a peak portion that is convex in the radial direction;
a valley portion adjacent to the peak portion in the axial direction and concave in the radial direction;
an intermediate portion including a midpoint in the radial direction of the apex of the outer surface of the peak portion and the apex of the outer surface of the valley portion;
Equipped with
a first length that is a length in the axial direction between the apex of the outer surface of each of the peaks and the midpoint is greater than a second length that is a length in the axial direction between the apex of the outer surface of each of the valleys and the midpoint;
a third length L3, which is the length in the axial direction between the apexes of the outer surfaces of the peaks and the apexes of the outer surfaces of the valleys, and a fourth length L4, which is the length in the radial direction between the apexes of the outer surfaces of the peaks and the apexes of the outer surfaces of the valleys, are related by the following formula (2):
3 · L3 ≧ L4 ≧ L3 ... (2)
Bellows . The thickness of the valley portion is greater than the thickness of the peak portion.
3. A bellows according to claim 1 or 2 . The synthetic resin is ethylene tetrafluoroethylene copolymer (ETFE).
3. A bellows according to claim 1 or 2 . A mold used for blow molding a synthetic resin bellows,
a ridge-forming portion having a concave shape in a radial direction for forming a convex ridge of the bellows;
a valley-forming portion that is convex in the radial direction and adjacent to the peak-forming portion in the axial direction, for forming a concave valley portion of the bellows;
an intermediate portion forming portion including a midpoint in the radial direction of the apex of the peak portion forming portion and the apex of the valley portion forming portion;
Equipped with
a first length, which is a length in the axial direction between the apex and the midpoint of each of the peak forming portions, is greater than a second length, which is a length in the axial direction between the apex and the midpoint of each of the valley forming portions;
The relationship between the first length L1 and the second length L2 is determined by Equation (1).
L1>L2>0.4・L1...(1)
Mold. A mold used for blow molding a synthetic resin bellows,
a ridge-forming portion having a concave shape in a radial direction for forming a convex ridge of the bellows;
a valley-forming portion that is convex in the radial direction and adjacent to the peak-forming portion in the axial direction, for forming a concave valley portion of the bellows;
an intermediate portion forming portion including a midpoint in the radial direction of the apex of the peak portion forming portion and the apex of the valley portion forming portion;
Equipped with
a first length, which is a length in the axial direction between the apex and the midpoint of each of the peak forming portions, is greater than a second length, which is a length in the axial direction between the apex and the midpoint of each of the valley forming portions;
a third length L3, which is the length in the axial direction between the apexes of the outer surfaces of the peaks and the apexes of the outer surfaces of the valleys, and a fourth length L4, which is the length in the radial direction between the apexes of the outer surfaces of the peaks and the apexes of the outer surfaces of the valleys, are related by the following formula (2):
3 · L3 ≧ L4 ≧ L3 ... (2)
Mold.