TWI770326B - A composite tube - Google Patents

Abstract

A composite tube includes: a tubular pipe body; an overlaying layer composed of a resin material, being tubular and covering the periphery of the pipe body, in which an annular mountain portion outwardly protruded towards a radial direction and an annular valley portion recessed on the outside of the radial direction are formed alternately in an axial direction of the pipe body so as to contract along the axial direction in a bellows shape; and retaining mechanisms extendedly disposed along either the peripheral direction or axial direction of the overlaying layer and separated along by the other in a plural manner with an interval so that the pipe body is retained within the overlaying layer.

Description

Composite pipe

The present disclosure relates to a composite pipe.

Conventionally, a composite pipe formed by overlapping a pipe body in a plurality of layers has been known. For example, Japanese Patent Laid-Open No. 2013-231490 describes a composite pipe in which a protective layer is formed between a pipe body and a holding layer covering the periphery of the pipe body.

The composite pipe system disclosed in Japanese Patent Application Laid-Open No. 2013-231490 is provided with a protective layer to hold the pipe body inside the holding layer. In addition, the inner peripheral surface of the protective layer is provided with concavities and convexities, so as to reduce the frictional resistance between the outer peripheral surface of the pipe body and the protective layer. Thereby, when the holding layer and the protective layer are pulled toward the axial direction of the pipe body in order to connect the pipe body to the pipe joint, the ends of the pipe body are easily exposed. However, since the protective layer covers the outer peripheral surface of the tube body, it becomes an impedance when the holding layer expands and contracts, and it may be difficult to expand and contract.

The present disclosure provides a composite pipe capable of keeping the pipe body inside the coating layer and making the coating layer easy to expand and contract.

The composite pipe system of the first aspect has: a tubular pipe body; a coating layer composed of a resin material is tubular and covers the outer periphery of the pipe body, and is alternately formed in the axial direction of the pipe body: radially outward A convex annular mountain portion; and a concave annular valley portion on the radially outer side to form a bellows-like shape that can be retracted in the axial direction; and a holding mechanism, along the circumferential direction or Any one of the axial directions is extended and arranged along the other in plural at intervals, so as to keep the pipe body inside the coating layer.

According to the composite pipe of the first aspect, the pipe system is held inside the coating layer by the holding mechanism. The holding mechanisms are extended along the circumferential direction of the coating layer, and are arranged in plural at intervals along the axial direction. Alternatively, they may be extended along the axial direction of the coating layer, and may be arranged in plural at intervals along the circumferential direction.

Therefore, compared to a retaining mechanism that would extend both in the peripheral and axial directions of the coating (in other words, a retaining mechanism covering the outer periphery of the tube), the friction between the tube and the retaining mechanism, or There will be less friction between the cladding and the retaining mechanism. Therefore, the coating layer can be easily stretched and contracted in the axial direction.

The composite pipe of the second aspect is in the composite pipe of the first aspect, and the holding mechanism is a diameter-reduced portion in which the valley portion protrudes radially inward.

In the composite pipe of the second aspect, the valley portion of the coating layer protrudes radially inward, and a diameter-reduced portion is formed. Then, the tube body is held inside the coating layer by the reduced diameter portion. The diameter-reduced portion can act in the axial direction along with the expansion and contraction of the coating layer. Moreover, the diameter-reduced part is arrange|positioned at intervals along the axial direction. Therefore, the contact area between the coating layer and the tube body will be smaller, and the frictional force will be smaller. Thereby, the covering layer can be easily stretched.

The composite pipe of the third aspect is in the composite pipe of the first aspect, and the holding mechanism is an elastic body arranged in the axial direction between the valley portion and the pipe body.

The composite pipe of the third aspect is tied between the valley portion of the coating layer and the pipe body, and an elastic body is arranged along the axial direction. Moreover, this elastic body is arrange|positioned at intervals along the peripheral direction. Therefore, the contact area between the coating layer and the elastomer will be smaller, and the frictional force will be smaller. Thereby, the covering layer can be easily stretched.

The composite pipe of the fourth aspect is in the composite pipe of the first aspect, and the elastic system is formed into a wave shape with amplitude in the peripheral direction of the coating layer.

In the composite pipe of the fourth aspect, the elastic body extending along the axial direction of the coating layer has an amplitude in the peripheral direction of the coating layer. Therefore, the elastic body is easily deformed in the axial direction. In this way, the covering layer can be more easily stretched.

According to the present disclosure, it is possible to provide a composite pipe capable of keeping the pipe body inside the coating layer and making the coating layer easy to expand and contract.

10‧‧‧Composite pipe

12‧‧‧Pipe body

12A‧‧‧Outer surface

14‧‧‧Interlayer

20‧‧‧Coating

22‧‧‧Yamabe

22A‧‧‧Outside Wall

22B‧‧‧Sidewall

22C‧‧‧External bending part

24‧‧‧Tanibe

24A‧‧‧Inner Wall

24B‧‧‧Sidewall

24C‧‧‧Inner bend

26‧‧‧Reduced diameter

26A‧‧‧Inner side wall

30‧‧‧Elastomer

40‧‧‧Elastomer

H1‧‧‧Thickness

H2‧‧‧Thickness

L1‧‧‧Length

L2‧‧‧Length

M‧‧‧Middle

R‧‧‧Radial

△R‧‧‧Radius difference

S‧‧‧axial

V‧‧‧Air Storage

FIG. 1 is a perspective view showing a composite pipe according to an embodiment of the present disclosure.

FIG. 2 is a longitudinal sectional view showing a composite pipe according to an embodiment of the present disclosure.

3 is a partial enlarged view of a longitudinal section of a composite pipe according to an embodiment of the present disclosure.

4A is a perspective view showing a modification of the holding mechanism in the composite pipe according to the embodiment of the present disclosure.

FIG. 4B is a perspective view showing a state in which the pipe end of the composite pipe of FIG. 4A is exposed.

FIG. 4C is a perspective view showing a state in which the elastic body is also shortened and deformed along with the shortening and deformation of the coating layer.

FIG. 5 is a longitudinal sectional view showing a state in which the end of the tube body of the composite tube according to the embodiment of the present disclosure is exposed.

FIG. 6 is a diagram showing the process of shortening and deforming the cladding layer in the longitudinal section of FIG. 3 .

FIG. 7 is a diagram showing a state in which the coating layer is shortened and deformed in the longitudinal section of FIG. 3 .

FIG. 8 is a perspective view showing a state in which the pipe body end of the composite pipe according to the embodiment of the present disclosure is exposed.

9A is a perspective view showing a modification of the holding mechanism in the composite pipe according to the embodiment of the present disclosure.

FIG. 9B is a perspective view showing a state in which the end of the tube body of the composite tube of FIG. 9A is exposed.

9C is a perspective view showing a state in which the elastic body is also shortened and deformed along with the shortening and deformation of the coating layer.

Fig. 10 is a longitudinal sectional view showing a composite pipe according to a comparative example.

Hereinafter, an exemplary embodiment of the composite pipe related to the present disclosure will be described in detail with reference to the drawings. Components denoted by the same symbols in the respective drawings represent the same components. In addition, each component is not limited to one, and may exist in plural. In addition, description may be abbreviate|omitted about the structure and code|symbol which are repeated in embodiment demonstrated below. In addition, the present disclosure is not limited to the following embodiments, and can be implemented by adding appropriate changes within the scope of the purpose of the present disclosure.

The term "process" in this specification does not refer only to an independent process, and even if it is not clearly distinguishable from other processes, the process is included in this term as long as its purpose can be achieved. In this specification, the amount of each component in the composition represents the total amount of the plural substances present in the composition unless otherwise specified, when the substances corresponding to each component are present in the composition in plural. The so-called "main component" in this description refers to the component with the highest mass-based content in the mixture, unless otherwise specified.

<Composite tube>

The composite pipe system related to the present disclosure has: a tubular pipe body; a coating layer, which is tubular and covers the outer periphery of the pipe body; and a holding mechanism, which keeps the pipe body inside the coating layer. The pipe system is made of resin material. The coating layer is made of resin material. In addition, the shape of the tube body is formed by alternately forming an annular mountain portion that becomes convex toward the radially outer side and an annular valley portion that becomes a concave shape toward the radially outer side, forming a bellows shape. The outer circumference is guided and can be shortened axially. The retention mechanism is integrally formed with the coating.

Next, an example will be given to describe the form of the composite pipe used in the present disclosure based on the drawings. The composite pipe 10 according to the present embodiment shown in FIG. 1 includes a pipe body 12 and a coating layer 20 .

(tube body)

The tube body 12 is tubular, and is a resin tube made of a resin material. Examples of resins of resin materials include polyolefins such as polybutene, polyethylene, cross-linked polyethylene, polypropylene, and vinyl chloride, and the resin may be used alone or in combination of two or more. Among them, polybutene is suitably used, and polybutene is preferably contained as a main component, for example, in the form of 85 mass % contained in the resin material constituting the pipe body. In addition, the resin material constituting the pipe body may contain other additives.

The diameter (ie, the outer diameter) of the pipe body 12 is not particularly limited, and can be, for example, in the range of 10 mm or more and 100 mm or less, preferably 12 mm or more and 35 mm or less. In addition, the thickness of the pipe body 12 is not particularly limited, and may be, for example, 1.0 mm or more and 5.0 mm or less, preferably 1.4 mm or more and 3.2 mm or less.

(coating layer)

The coating layer 20 is tubular and covers the outer periphery of the tubular body 12 . The covering layer 20 is made of resin material. Examples of resins constituting the covering layer 20 include polyolefins such as polybutene, polyethylene, cross-linked polyethylene, and polypropylene, and vinyl chloride, and may be used alone or in combination of two or more. Among them, low-density polyethylene is suitably used, and preferably low-density polyethylene is contained as a main component, for example, in the form of 80% by mass or more in the resin material constituting the coating layer, more preferably Contains more than 90% by mass.

In addition, the MFR (Melt Flow Rate) of the resin used is preferably 0.25 or more, more preferably 0.3 or more, and most preferably 0.4 or more and 1.2 or less. By making MFR 1.2 or less, it becomes difficult to generate|occur|produce a burr. When the MFR is larger than 1.2, the molten resin can easily flow into the parting surface of the mold for forming the coating layer 20, and burrs are easily generated. In addition, the resin material constituting the coating layer may contain other additives.

As shown in FIG. 2 , the cladding layer 20 is in accordion shape, and in the axial direction S of the tube body 12 , an annular mountain portion 22 that is convex toward the radially outer side and a concave shape toward the radially outer side are alternately and continuously formed. The annular valley 24. The mountain portion 22 is arranged on the outer side in the radial direction R than the valley portion 24 . As shown in FIG. 3 , when the radially outermost portion of the coating layer 20 is defined as the outer side wall 22A, and the radially innermost portion is defined as the inner sidewall 24A, the radially outermost portion can be The middle portion M of the wall 22A and the inner side wall 24A is defined as a boundary, the radially outer side is defined as the peak portion 22 , and the radially inner side is defined as the valley portion 24 .

The mountain portion 22 has an outer side wall 22A extending in the axial direction S (see FIG. 2 ) and a side wall 22B extending in the radial direction R from both ends of the outer side wall 22A. An outer curved portion 22C is formed between the outer side wall 22A and the side wall 22B. The valley portion 24 has an inner side wall 24A extending in the axial direction S and side walls 24B extending along the radial direction R from both ends of the inner side wall 24A. An inner curved portion 24C is formed between the inner side wall 24A and the side wall 24B.

In addition, although not particularly limited, the length L1 of the axial direction S of the mountain portion 22 is preferably set to be longer than the length L2 of the axial direction S of the valley portion 24 . The length L1 is preferably 1.2 times or more of the length L2 in order to ensure the ease of deformation of the outer side wall 22A during the shortening deformation described below.

Also, the length L2 is preferably 0.8 mm or more. When the length L2 is less than 0.8 mm, the width of the valley portion of the mold for manufacturing the cladding layer 20 will be too small. As a result, when the coating layer 20 is manufactured, after the resin constituting the coating layer 20 is extruded, when the resin is formed with concavities and convexities by a mold, the portion corresponding to the valley of the resin mold is changed. Thin and easily damaged. Therefore, it is difficult to form the cladding layer 20 . On the other hand, the length L1 is preferably not more than 5 times the length L2. This is because the flexibility of the composite pipe 10 can be maintained by making the length L1 equal to or less than five times the length L2. Moreover, when the length L1 is too long, when laying the composite pipe 10, the contact area with the ground may become large, which may make construction difficult.

In addition, as shown in FIG. 3 , the length L1 is the distance between the outer sides of the axial direction S of the surface viewed from the outer side of the radial direction R of the coating layer 20 in the portion intersecting with the middle portion M of the coating layer 20 (also That is, the distance between the surface on one side in the axial direction S and the surface on the other side in the axial direction S of the portion that becomes convex on the outer side in the radial direction R of the coating layer 20 ). In addition, the length L2 is the distance between the outer side of the axial direction S of the surface viewed from the inner side of the radial direction R of the coating layer 20 in the portion intersecting with the middle portion M of the coating layer 20 (that is, in the coating layer 20 The distance between the surface on one side in the axial direction S and the surface on the other side in the axial direction S of the portion where the inner side in the radial direction R becomes convex).

The thickness of the coating layer 20 is preferably 0.1 mm or more at the thinnest part and 0.4 mm or less at the thickest part in order to shorten the coating layer 20 . The thickness H1 of the outer side wall 22A is thinner than that of the inner side wall 24A. In order to ensure the ease of deformation of the outer side wall 22A during the shortening deformation described below, the thickness H1 is preferably 0.9 times or less of the thickness H2.

The radius difference ΔR between the mountain portion 22 and the valley portion 24 on the outer surface is preferably less than 800% of the thickness of the coating layer 20 on average. If the radius difference ΔR is too large, even if the portion of the mountain portion 22 along the axial direction S is not deformed, it is difficult to cause the valley portion 24 to bulge radially outward when shortening, or to prevent the adjacent mountain portions 22 from being separated from each other. It is in a deformed state of being distorted by approaching it. When the radius difference ΔR is equal to or less than 800% of the average thickness of the coating layer 20 , in order to suppress the above-mentioned deformed state, the axial length S of the peaks 22 is preferably longer than the axial length of the valleys 24 . Moreover, it is more preferable that the radius difference ΔR is equal to or less than 600% of the thickness of the coating layer 20 on average.

The diameter of the coating layer 20 (ie, the outermost outer diameter) is not particularly limited, and can be, for example, in the range of 13 mm or more and 130 mm or less.

(holding mechanism)

As shown in FIG. 2 , the coating layer 20 is partially formed with a diameter-reduced portion 26 serving as a holding mechanism for holding the pipe body 12 . The reduced diameter portion 26 is an annular support body formed by the valley portion 24 protruding radially inward, and is extended along the peripheral direction of the coating layer 20 . The diameter-reduced portions 26 are provided in plural at intervals along the axial direction of the coating layer 20 . In the present embodiment, for example, the three valleys 24 of the non-diameter-reduced portion 26 and one diameter-reduced portion 26 are arranged alternately and continuously in the axial direction.

As shown in FIG. 3 , the radius of the inner side wall 26A of the reduced diameter portion 26 is approximately the same as the radius of the outer peripheral surface 12A of the pipe body 12 . In this way, the tube body 12 is held inside the coating layer 20 by the reduced diameter portion 26 . In addition, the aspect of "substantially coincident" includes the radius of the inner side wall 26A of the diameter-reduced portion 26 deformed radially outward and the radius of the outer peripheral surface 12A of the pipe body 12 as shown by the two-dot chain line in FIG. 3 . will be consistent. In addition, the radius of the inner side wall 26A of the reduced diameter portion 26 is slightly larger than the radius of the outer peripheral surface 12A of the pipe body 12 , and a gap is formed between the inner side wall 26A and the outer peripheral surface 12A.

(function)

When the composite pipe 10 according to this embodiment is connected to the joint, a force in the direction of exposing the pipe body 12 acts on the coating layer 20 in the state shown in FIG. 2 , and the coating layer 20 is shortened in the axial direction S . As a result, as shown in FIG. 5 , the coating layer 20 at one end is kept in a state in which the tube body 12 is held by the diameter-reduced portion 26 , and moves in a direction in which the tube body 12 is exposed.

In this way, according to the composite pipe 10 of the present embodiment, the pipe body 10 is held inside the coating layer 20 by the diameter-reduced portion 26 . The diameter-reduced portion 26 is extended along the peripheral direction of the coating layer 20 . Therefore, the pipe body 12 can be surely held. By holding the pipe body 12 , even in the case of a water hammer phenomenon caused by, for example, the liquid flowing inside the pipe body 12 , the pipe body 12 can be restrained from vibrating and the generation of noise can be restrained.

In addition, the reduced diameter portion 26 can act in the axial direction along with the expansion and contraction of the coating layer 20 . Since the diameter-reduced portions 26 are arranged at intervals along the axial direction, the contact area with the tube body 12 is small. Therefore, the covering layer 20 can be easily stretched.

On the other hand, for example, the holding mechanism (intermediate layer 14 ) according to the comparative example shown in FIG. 10 is extended along both the circumferential direction and the axial direction of the coating layer 20 . In other words, the intermediate layer 14 covers the entire outer circumference of the tube body 12 . Therefore, the contact area between the intermediate layer 14 and the tube body 12 is larger than the contact area between the diameter-reduced portion 26 and the tube body 12 in this embodiment. Therefore, in the comparative example, when the coating layer 20 is stretched and contracted, a relatively large frictional force acts between the tube body 12 and the intermediate layer 14, which may become a resistance force. In addition, since the intermediate layer 14 is disposed on the entire outer circumference of the tube body 12, the rigidity is high when it is about to be shortened in the axial direction, so it is difficult to deform, and the coating layer 20 may be difficult to expand and contract.

Moreover, according to the composite pipe 10 concerning this embodiment, as shown in FIG. 3, the diameter reducing part 26 is formed so that the valley part 24 may protrude radially inward. Therefore, an air storage portion V is formed between the inner side wall 24A of the valley portion 24 and the outer peripheral surface 12A of the pipe body 12 . In other words, the tube body 12 is covered by the air storage portion V. As shown in FIG. Therefore, the thermal insulation of the pipe body 12 can be ensured.

In addition, in the outer side wall 22A of the mountain portion 22 and the inner side wall 24A of the valley portion 24, preferably, the length L1 of the axial direction S is longer than the length L2, and the thickness H1 is thinner than the thickness H2. Therefore, the outer side wall 22A is deformed more easily than the inner side wall 24A, and as shown in FIG. 6 , it is deformed by bulging outward in the radial direction. Next, as shown in FIG. 7 , the outer curved portion 22C of the mountain portion 22 and the inner curved portion 24C of the valley portion 24 are deformed so that the adjacent mountain portions 22 come close to each other.

In this way, as shown in FIG. 5 , one end of the coating layer 20 can more easily move in the direction of exposing the tube body 12 . In this way, when the cladding layer 20 is shortened, the outer side wall 22A will be deformed by bulging. Thereby, even if the bending angle or thickness of the coating layer 20 is slightly uneven, the valley portion 24 can be prevented from bulging radially outward, or the adjacent mountain portions 22 can be prevented from approaching each other and becoming distorted. deformed state. In this way, the appearance of the cladding layer 20 after being shortened can be suppressed from deteriorating.

In addition, in this embodiment, although the thickness H1 of the outer side wall 22A is made thinner than the thickness H2 of the inner side wall 24A, the thickness H1 may be the same as the thickness H2.

In addition, in this embodiment, although the outer side wall 22A is made into a substantially linear shape along the axial direction S, it may be an arc shape that bulges radially outward. Further, the inner side wall 24A may be in an arc shape bulging radially inward. Still further, the inner side wall 26A of the diameter-reduced portion 26 may have a shape that bulges radially inward. In this way, the covering layer 20 can be more easily stretched.

Moreover, in this embodiment, the diameter-reduced part 26 which deforms the valley part 24 of the coating layer 20 is used as a holding means for holding the pipe body 12 inside the coating layer 20 . In this way, by integrating the holding mechanism with the cladding layer 20, the number of components is reduced. Thereby, the composite pipe can be easily manufactured.

In addition, the holding mechanism may be formed separately from the cladding layer 20 . For example, as shown in FIG. 4A , a resin-made elastic body 30 formed in a rod shape (eg, a column shape) may be arranged between the coating layer 20 and the tube body 12 . The elastic bodies 30 are extended along the axial direction of the coating layer 20 , and are arranged in plural at intervals along the circumferential direction of the coating layer 20 . In the present embodiment, a total of four are arranged at intervals of approximately 90 degrees along the peripheral direction, but any number of them may be arranged. For example, a total of three may be arranged at intervals of approximately 120 degrees. However, in order to ensure the retention force of the tube body 12, preferably three or more elastic bodies 30 are provided.

The elastic body 30 is sandwiched between the outer peripheral surface 12A of the tube body 12 and the inner side wall 24A of the valley portion 24 of the coating layer 20 . Thereby, the tube body 12 is held inside the coating layer 20 .

Examples of resins constituting the elastomer 30 include polyurethane, polystyrene, polyethylene, polypropylene, EPDM rubber, silicone rubber, and mixtures of these resins, among which silicone rubber is preferred. Alternatively, a spring coil or the like that can expand and contract along the axial direction of the coating layer 20 can also be used. In addition, in the present embodiment, the elastic body 30 is a rubber tube made of ethylene propylene rubber.

According to the composite tube using the elastic body 30 , the rod-shaped elastic body 30 is extended between the covering layer 20 and the tube body 12 along the axial direction of the covering layer 20 . Therefore, in the case where the covering layer 20 is to be stretched, compared with the comparative example in which the intermediate layer 14 such as shown in FIG. The friction generated between 30 will be less. Therefore, as shown in FIG. 4B , the covering layer 20 can be easily stretched.

In addition, in the case where the elastic body 30 is fixed to the inner side wall 24A of the valley portion 24 of the covering layer 20 , as shown in FIG. 4C , the elastic body 30 is elastically deformed along with the expansion and contraction of the covering layer 20 . Case. Even in this case, compared with the comparative example of FIG. 10 , since the frictional force generated between the elastic body 30 and the tube body 12 is smaller, the coating layer 20 can be easily stretched.

Furthermore, as shown in FIG. 9A , a resin-made elastic body 40 formed in a wave shape may be arranged between the coating layer 20 and the tube body 12 . The elastic body 40 is extended along the axial direction of the coating layer 20 , has an amplitude in the peripheral direction, and is formed in a wave shape. In addition, the elastic bodies 40 are arranged in plural at intervals along the circumferential direction of the coating layer 20 . In this embodiment, a total of four are arranged at intervals of approximately 90 degrees along the peripheral direction. In addition, as the resin constituting the elastic body 40, the same resin as the resin constituting the elastic body 30 can be used.

According to the composite pipe provided with the elastic body 40, when the coating layer 20 is to be stretched and contracted, compared with the comparative example in which the intermediate layer 14 is provided between the coating layer 20 and the pipe body 12 as shown in FIG. The frictional force generated between the layer 20 and the elastomer 40 will be less. Therefore, as shown in FIG. 9B , the covering layer 20 can be easily stretched.

Furthermore, as shown in FIG. 9C , the elastic body 40 may be elastically deformed in accordance with the expansion and contraction of the coating layer 20 . Even in this case, compared with the comparative example of FIG. 10 , since the frictional force generated between the elastic body 40 and the tube body 12 is smaller, the coating layer 20 can be easily stretched. Further, since the elastic body 40 itself can be deformed at intervals of waves in the axial direction, the coating layer 20 is more easily deformed.

10‧‧‧Composite pipe

12‧‧‧Pipe body

20‧‧‧Coating

22‧‧‧Yamabe

24‧‧‧Tanibe

26‧‧‧Reduced diameter

S‧‧‧axial

Claims (2)

A composite tube is provided with: a tubular tube body; a coating layer composed of a resin material is tubular and covers the outer periphery of the tube body, and is alternately formed in the axial direction of the tube body: An annular mountain portion; and a concave annular valley portion on the radially outer side, which becomes a bellows shape that can be retracted in the axial direction; and a holding mechanism, which is along the circumferential direction or axial direction of the coating layer. Either one is extended and arranged along the other in plural at intervals, so as to hold the pipe body inside the coating layer; the holding mechanism enables the valley to protrude radially inward. Reduced diameter. A composite tube is provided with: a tubular tube body; a coating layer composed of a resin material is tubular and covers the outer periphery of the tube body, and is alternately formed in the axial direction of the tube body: An annular mountain portion; and a concave annular valley portion on the radially outer side, which becomes a bellows shape that can be retracted in the axial direction; and a holding mechanism, which is along the circumferential direction or axial direction of the coating layer. Either one is extended and arranged along the other at intervals to keep the pipe body inside the coating layer; the holding mechanism is connected to the edge between the valley and the pipe body. The elastic body is arranged in the axial direction; the elastic system is formed in a wave shape with amplitude in the peripheral direction of the coating layer.

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