pipe joint

Abstract

The pipe joint 1 has an inner ring 4 having a bulging portion 6 pressed into the front end portion of a pipe 8, a joint body 2 pressing the end portion of the inner ring 4 into the inner periphery and having an outer threaded portion 2b on the outer periphery, and a union nut 3 having an inner threaded portion 3a fastened to the outer threaded portion 2b and pressing the inner threaded portion 3a to the outer threaded portion 2b to press the front end portion of the pipe 8. The bulging portion 6 has a front end tapered portion 13 generating a surface pressure with the pipe 8 by the pressing of the union nut 3. The outer peripheral surface 15 of the front end tapered portion 13 has a concave curved portion 15a formed in a concave curved shape in a cross-sectional view in the axial direction.

Description

Technical Field

[0001] This invention relates to a pipe fitting. Background Technology

[0002] In manufacturing processes across various technological fields such as semiconductor manufacturing, medical / pharmaceutical manufacturing, and food processing / chemical industries, pipe fittings made of synthetic resin are used as connection structures to connect flow paths formed in pipes and fluid devices in piping routes that supply fluids such as pharmaceutical solutions, high-purity liquids, ultrapure water, or cleaning solutions. One known pipe fitting structure includes: an inner ring mounted on the inner circumference of the front end of the pipe; a cylindrical fitting body mounted on the outer circumference of the front end of the pipe; and a connecting nut mounted on the outer circumference of the fitting body (see, for example, Patent Document 1).

[0003] The inner ring has: a cylindrical main body; a bulge that protrudes radially outward from one axial end of the main body; and a sealing portion formed at the other axial end of the main body. A fluid flow path is formed inside the inner ring. The bulge of the inner ring is pressed into the front end of the pipe, thereby expanding the diameter of the front end of the pipe. Regarding the pipe nut, the outer circumferential surface of the pipe, which has expanded in diameter due to the bulge of the inner ring, is pressed using the pushing force when installed on the connector body. As a result, the sealing portion of the inner ring can apply pressure to the sealing groove formed in the connector body and can prevent the pipe from being pulled out. Furthermore, a surface pressure is generated between the pipe and the bulge, thus suppressing fluid leakage from between the pipe and the bulge.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2018-168947 Summary of the Invention

[0005] If the pipe is pressed down using the pushing force of the connecting nut, the inner circumferential surface of the pipe comes into contact with the outer circumferential surface of the bulge of the inner ring over a large axial area. Therefore, the area of ​​surface pressure generated between the pipe and the bulge reaches a large axial range. Consequently, there is a problem that, in order to ensure the surface pressure required to suppress fluid leakage between the pipe and the bulge, the tightening torque of the connecting nut needs to be increased, resulting in poor workability.

[0006] The present invention was made in view of this situation, and its object is to provide a pipe fitting that can ensure the required surface pressure between the bulge of the inner ring and the pipe even without increasing the tightening torque of the pipe nut.

[0007] (1) The pipe fitting of the present invention comprises: an inner ring having a bulge that is formed radially outward on one axial side and pressed into the front end of a pipe; a fitting body having the end of the inner ring on the other axial side pressed inward with the bulge pressed into the front end of the pipe, and having an external thread on the outer periphery; and a pipe nut having an internal thread that is fastened to the external thread, and the internal thread is fastened to the external thread to press the front end of the pipe on the other axial side, the bulge having a front end tapering portion that tapers towards one axial side from its midpoint in the axial direction, and a surface pressure is generated between the pipe and the pipe by the pressing of the pipe nut, the outer peripheral surface of the front end tapering portion having a concave curved surface that is formed as a concave curved surface when viewed in axial cross section.

[0008] According to the pipe fitting of the present invention, a concave curved surface is formed on the outer peripheral surface of the tapered front end of the bulge of the inner ring. Therefore, when the pipe is pressed against the pipe by the connecting nut, it is difficult for the pipe to contact the bottom portion of the concave curved surface. As a result, the axial range of the surface pressure generated between the tapered front end of the bulge and the pipe is narrower than currently available, thus increasing the surface pressure generated between the tapered front end of the bulge and the pipe compared to current methods. Therefore, even without increasing the tightening torque of the connecting nut, the required surface pressure between the bulge of the inner ring and the pipe can be ensured. Consequently, fluid leakage from the bulge and the pipe to the outside can be suppressed.

[0009] (2) Preferably, the concave curved surface is formed along the entire axial length of the outer peripheral surface of the front end tapering portion.

[0010] In this case, the axial range of the surface pressure generated between the front end of the bulge and the tube can be further narrowed, thus further increasing the surface pressure generated between the front end of the bulge and the tube.

[0011] (3) Preferably, the outer peripheral surface of the front end tapering has a convex curved surface that is formed on the axial side further from the concave curved surface when viewed in axial cross section.

[0012] In this case, compared to case (2) above, the radial thickness of the end further axially than the concave curved surface of the front taper can be increased. As a result, the strength of the end of the front taper is increased, and even when the front taper is pressed using a connecting nut and via a pipe, it is possible to prevent the end of the front taper from tilting radially inward. Consequently, the flow of fluid within the inner ring can be prevented from being obstructed by the front taper of the bulge.

[0013] (4) According to another viewpoint of the present invention, the pipe fitting has: an inner ring having a bulge that is formed radially outward on one axial side and pressed into the front end of the pipe; a fitting body having the end of the inner ring on the other axial side pressed into the inner circumference while the bulge is pressed into the front end of the pipe, and having an external thread on the outer circumference; and a pipe nut having an internal thread that is fastened to the external thread, and the internal thread is fastened to the external thread to press the front end of the pipe to the other axial side, the bulge having a front end tapering that tapers from its axial midpoint toward one axial side, and a surface pressure is generated between the front end tapering and the pipe by the pressing of the pipe nut, the diameter D of the axial end of the outer circumferential surface of the front end tapering and the inner diameter d of the non-deformable portion of the pipe that does not deform even when the bulge is pressed in satisfy the relationship 1.0d≤D≤1.4d.

[0014] According to the pipe fitting of the present invention, the diameter D of the axial end of the outer peripheral surface of the tapered portion of the inner ring's bulge satisfies the relationship D ≤ 1.4d with the inner diameter d of the non-deformable portion of the pipe, thus the tightening torque of the connecting nut will not increase. Furthermore, the diameter D of the axial end of the outer peripheral surface of the tapered portion satisfies the relationship 1.0d ≤ D with the inner diameter d of the non-deformable portion of the pipe, thus ensuring the required surface pressure between the bulge of the inner ring and the pipe even without increasing the tightening torque of the connecting nut. As a result, fluid leakage from the bulge to the outside between the bulge and the pipe can be suppressed.

[0015] The effects of the invention

[0016] According to the present invention, even without increasing the tightening torque of the connecting nut, the required surface pressure between the bulge of the inner ring and the tube can be ensured. Attached Figure Description

[0017] Figure 1 This is an axial cross-sectional view of the pipe fitting according to the first embodiment of the present invention.

[0018] Figure 2 This is a cross-sectional view showing the axial direction of the inner ring of the pipe fitting.

[0019] Figure 3 This refers to the bulging portion of the inner ring. Figure 2 Enlarged cross-sectional view of the main part.

[0020] Figure 4 It is a cross-sectional view showing the contact state between the tapered front end of the bulge and the tube.

[0021] Figure 5 It is a cross-sectional view showing the state in which the front end tapering of the bulge is tilted radially inward.

[0022] Figure 6 This is an enlarged cross-sectional view showing the bulge of the inner ring of the pipe fitting according to the second embodiment of the present invention.

[0023] Figure 7 This is a cross-sectional view showing the contact state between the tapered front end of the bulge in the second embodiment and the tube.

[0024] Figure 8 This is an enlarged cross-sectional view showing the axial direction near the bulge of the inner ring of the pipe fitting according to the third embodiment of the present invention.

[0025] Figure 9 This is an enlarged axial cross-sectional view showing a modified example of the bulge portion of the inner ring in the third embodiment. Detailed Implementation

[0026] Next, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

[0027] [First Implementation]

[0028] Figure 1 This is an axial cross-sectional view showing the pipe fitting according to the first embodiment of the present invention. Figure 1 In this embodiment, the pipe fitting 1 is used, for example, for a piping path for supplying a chemical solution (fluid) in a semiconductor manufacturing apparatus. The pipe fitting 1 has a fitting body 2, a connecting nut 3, and an inner ring 4. Hereinafter, for convenience, in this embodiment, [the following will be described as follows]. Figure 1 The left side is called the axial side. Figure 1 The right side is called the other side of the axis ( Figures 2-9 Same here).

[0029] The inner ring 4 is formed into a cylindrical shape, for example, from a synthetic resin material such as polyvinyl chloride (PVC), polypropylene (PP), polyethylene (PE), or fluoropolymer (perfluoroalkane (PFA), polytetrafluoroethylene (PTFE), or polyvinylidene fluoride (PVDF)).

[0030] The inner ring 4 has: a main body 5, which is cylindrical; a bulge 6, which is formed on one axial side of the main body 5; and a sealing part 7, which is formed on the other axial side of the main body 5. Fluid flow paths 4a are formed radially inside the main body 5, the bulge 6, and the sealing part 7 of the inner ring 4. The fluid flow paths 4a connect the flow path 8a formed inside the pipe 8 with the flow path 2c formed inside the connector body 2.

[0031] The bulge 6 is formed on one axial side of the main body 5, protruding radially outward. The bulge 6 is pressed into the front end of the tube 8 made of synthetic resin (PFA, etc.), thereby expanding the diameter of the front end of the tube 8. The bulge 6 will be described in detail later. The sealing part 7 has an annular primary sealing part 7a and a cylindrical secondary sealing part 7b.

[0032] The primary sealing portion 7a is formed to protrude radially inward from the other axial end of the main body 5 towards the other axial side. The outer peripheral surface of the primary sealing portion 7a is formed to gradually narrow from one axial end towards the other axial end. The primary sealing portion 7a is pressed into the primary sealing groove 2d of the connector body 2 (described later). The secondary sealing portion 7b is formed to protrude radially outward from the other axial end of the main body 5 towards the other axial side. The secondary sealing portion 7b is pressed into the secondary sealing groove 2e of the connector body 2 (described later).

[0033] The connector body 2 is formed into a cylindrical shape from a synthetic resin material such as PVC, PP, PE, or fluoropolymer (PFA, PTFE, etc.). The inner diameter of the connector body 2 is set to be approximately the same as the inner diameter of the inner ring 4 in a manner that does not impede the movement of the liquid. A socket portion 2a is formed at one axial end of the connector body 2. The sealing portion 7 (the other axial end) of the inner ring 4, which is pressed into the front end of the pipe 8, is pressed into the inner circumference of the socket portion 2a. Thus, one axial end of the connector body 2 is mounted on the outer circumference of the front end of the pipe 8. An external thread portion 2b is formed on the outer circumference of the socket portion 2a.

[0034] The connector body 2 has an annular primary sealing groove 2d and an annular secondary sealing groove 2e, which are formed radially inward compared to the socket portion 2a. The primary sealing groove 2d is formed radially inward on the connector body 2 in a tapered shape, gradually narrowing from one axial end to the other. The secondary sealing groove 2e is formed radially outward on the connector body 2 compared to the primary sealing groove 2d.

[0035] The connecting nut 3 is formed into a cylindrical shape, for example, from a synthetic resin material such as PVC, PP, PE, or fluoropolymer (PFA, PTFE, etc.). The connecting nut 3 has: an internal thread portion 3a, which is formed on the inner circumference on the other side of the axial direction; and a pressing portion 3b, which is formed protruding radially inward on one side of the axial direction.

[0036] The internal thread 3a of the pipe nut 3 is fastened to the external thread 2b of the connector body 2. This fastening installs the pipe nut 3 onto the connector body 2, and the corner portion 3c formed at the other axial end of the pressing portion 3b presses the expanded diameter portion 8b of the pipe 8, which is enlarged due to the bulge 6 of the inner ring 4, towards the other axial side. Furthermore, in this embodiment, the portion of the pressing portion 3b that presses the pipe 8 is not limited to the corner portion 3c. For example, a chamfered portion can be formed at the other axial end of the pressing portion 3b instead of the corner portion 3c, and the pipe 8 can be pressed using this chamfered portion.

[0037] Based on the above structure, if the internal thread 3a of the connecting nut 3 is tightened to the external thread 2b of the connector body 2, the primary sealing part 7a and the secondary sealing part 7b of the inner ring 4 are pressed into the primary sealing groove 2d and the secondary sealing groove 2e of the connector body 2, respectively. This ensures the sealing performance of the connection between the inner ring 4 and the connector body 2. Furthermore, the corner portion 3c of the connecting nut 3 presses the enlarged diameter portion 8b of the pipe 8 axially to the other side, preventing the pipe 8 from being pulled out.

[0038] Figure 2 This is a cross-sectional view showing the axial direction of the inner ring 4. Figure 1 and Figure 2 In the inner ring 4, the bulging portion 6 has: a maximum thickness portion 11, which has the greatest radial thickness; a base end portion 12, which is formed on the other side of the axial direction of the maximum thickness portion 11; and a front end tapering portion 13, which is formed on one side of the axial direction of the maximum thickness portion 11.

[0039] The maximum thickness portion 11 is formed over a predetermined length along the axial direction. The outer peripheral surface of the base end portion 12 is formed to gradually narrow in diameter from the other axial end of the maximum thickness portion 11 toward the other axial side. Thus, the base end portion 12 is formed to gradually decrease in thickness radially from the other axial end of the maximum thickness portion 11 toward the other axial side. The other axial end of the base end portion 12 is connected to the main body portion 5. Furthermore, in Figure 2 When viewed in cross-section, the outer peripheral surface of the base end 12 is inclined in a planar shape, but it can also be inclined in a curved shape.

[0040] The inner circumferential surface 14 of the front tapering portion 13 is formed to gradually increase in diameter from the other side of the axial direction toward one end of the axial direction. The outer circumferential surface 15 of the front tapering portion 13 is formed to gradually decrease in diameter from one end of the axial direction of the maximum thickness portion 11 toward one side of the axial direction. Thus, the front tapering portion 13 is formed to gradually decrease in thickness radially from the middle of the axial direction of the bulging portion 6 toward one side of the axial direction, i.e., front tapering. Between the outer circumferential surface 15 of the front tapering portion 13 and the inner circumferential surface of the diameter-expanding portion 8b of the tube 8, the corner portion 3c of the connecting nut 3 is used to press the diameter-expanding portion 8b to generate surface pressure.

[0041] Figure 3 It represents the bulging part 6 of the inner ring 4. Figure 2The enlarged cross-sectional view of the main part. The outer peripheral surface 15 of the front end tapering portion 13 of the bulging portion 6 has a concave curved surface 15a formed in a radially inward concave manner. The concave curved surface 15a is formed, for example, in a concave arc shape. In this embodiment, the concave curved surface 15a is formed along the entire axial length of the outer peripheral surface 15 of the front end tapering portion 13.

[0042] As described above, a concave curved surface 15a is formed on the outer peripheral surface 15 of the tapered portion 13 at the front end of the bulge 6 of the inner ring 4, therefore, as Figure 4 As shown, when the expanded diameter portion 8b of the tube 8 is pressed axially to the other side by the connecting nut 3 (not shown), the inner circumferential surface of the tube 8 is difficult to contact the bottom portion 15a1 of the concave curved portion 15a. Therefore, the axial range of the surface pressure generated between the front end tapering portion 13 of the bulge 6 and the tube 8 is narrower than currently, thus allowing for a higher surface pressure generated between the front end tapering portion 13 of the bulge 6 and the tube 8. Therefore, even without increasing the tightening torque of the connecting nut 3, the required surface pressure between the bulge 6 of the inner ring 4 and the tube 8 can be ensured. As a result, leakage of the liquid medicine flowing in the fluid flow path 4a of the inner ring 4 from the bulge 6 to the outside can be suppressed.

[0043] Furthermore, since the concave curved surface 15a is formed along the entire axial length of the outer peripheral surface 15 of the front end taper 13, compared to the case where the concave curved surface 15a is only formed on a portion of the axial length of the outer peripheral surface 15 of the front end taper 13, the axial range of the surface pressure generated between the front end taper 13 of the bulge 6 and the tube 8 can be further reduced. Therefore, the surface pressure generated between the front end taper 13 of the bulge 6 and the tube 8 can be further increased.

[0044] However, in this embodiment, the radial thickness of the front end (axial end) of the front tapering portion 13 is relatively small. Therefore, when the front tapering portion 13 is pressed using the connecting nut 3 through the pipe 8, such as Figure 5 As shown, the front end of the tapered section 13 tends to tilt radially inward (towards the fluid flow path 4a), and the tube 8 is not coplanar with the inner circumferential surface 14. If this causes the front end of the tapered section 13 to tilt, the flow of the liquid medicine in the fluid flow path 4a of the inner ring 4 may be obstructed by the front end of the tapered section 13. Therefore, in the second embodiment described later, a structure is provided to suppress the tilting of the front end of the tapered section 13.

[0045] [Second Implementation]

[0046] Figure 6 This is an enlarged cross-sectional view showing the axial direction of the bulge 6 of the inner ring 4 of the pipe connector 1 according to the second embodiment of the present invention. In the second embodiment, the shape of the outer peripheral surface 15 of the front end tapering portion 13 of the bulge 6 is different from that in the first embodiment. The differences will be explained below.

[0047] The outer peripheral surface 15 of the tapered front end 13 of the bulge 6 has: a concave curved surface 15a, which is formed in a concave curved surface in a radially inward manner; and a convex curved surface 15b, which is formed in a convex curved surface in a radially outward manner at a position further axially than the concave curved surface 15a. The concave curved surface 15a is, for example, formed in a concave arc shape. The convex curved surface 15b is, for example, formed in a convex arc shape.

[0048] A concave curved surface 15a is formed between the other axial end and the midpoint of one axial side of the outer peripheral surface 15. A convex curved surface 15b is formed between the midpoint and one axial end of the outer peripheral surface 15. Thus, on the outer peripheral surface 15 of the front end taper 13, the concave curved surface 15a and the convex curved surface 15b are continuously formed in the axial direction, with the convex curved surface 15b formed at the front end of the front end taper 13. The other structures of the second embodiment are the same as those of the first embodiment, therefore the same reference numerals are used and their descriptions are omitted.

[0049] As described above, in the pipe connector 1 of the second embodiment, a concave curved surface 15a is also formed on the outer peripheral surface 15 of the tapered portion 13 at the front end of the bulge 6 of the inner ring 4, therefore, as Figure 7 As shown, when the expanded diameter portion 8b of the tube 8 is pressed axially to the other side by the connecting nut 3 (not shown), the inner circumferential surface of the tube 8 is difficult to contact the bottom portion 15a1 of the concave curved portion 15a. Therefore, the axial range of surface pressure generated between the front end taper 13 of the bulge 6 and the tube 8 is narrower than currently, thus allowing for a higher surface pressure generated between the front end taper 13 of the bulge 6 and the tube 8. Therefore, even without increasing the tightening torque of the connecting nut 3, the required surface pressure between the bulge 6 of the inner ring 4 and the tube 8 can be ensured. As a result, leakage of the liquid medicine flowing in the fluid flow path 4a of the inner ring 4 from the bulge 6 to the outside can be suppressed.

[0050] Furthermore, a convex curved surface 15b is formed on the outer peripheral surface 15 of the front end taper 13, further axially than the concave curved surface 15a. Therefore, compared to the first embodiment, the radial thickness of the front end portion of the front end taper 13 can be increased. Consequently, the strength of the front end portion of the front end taper 13 is increased, so even when the front end taper 13 is pressed using the connecting nut 3 via the pipe 8, it can still maintain its strength as in the first embodiment (see [reference]). Figure 5 This prevents the front end of the tapered section 13 from tilting significantly inward in a radially inward direction. As a result, the flow of the liquid medicine in the fluid flow path 4a of the inner ring 4 is prevented from being obstructed by the front tapered section 13 of the bulge 6.

[0051] [Third Implementation]

[0052] Figure 8This is an enlarged cross-sectional view showing the axial direction near the bulge 6 of the inner ring 4 of the pipe connector 1 according to the third embodiment of the present invention. In the third embodiment, the shape of the front end taper 13 of the bulge 6 is different from that in the first embodiment. The differences will be explained below.

[0053] The tapered portion 13 at the front end of the bulge 6 is shorter in the axial direction compared to the tapered portion 13 at the front end of the bulge 6 in the first embodiment. A flat surface 16 extending radially is formed at one axial end of the tapered portion 13. The flat surface 16 extends radially inward from one axial end 15c of the outer peripheral surface 15 of the tapered portion 13 and connects to one axial end of the inner peripheral surface 14 of the tapered portion 13.

[0054] The outer peripheral surface 15 of the front tapering portion 13 and its entire axial length are formed into a convex curved surface (e.g., a convex arc). The diameter D of one axial end 15c of the outer peripheral surface 15 of the front tapering portion 13 and the inner diameter d of the non-deformable portion 8c of the tube 8 are set to satisfy the relationship 1.0d≤D≤1.4d. The non-deformable portion 8c in the tube 8 is the part that does not deform even when the bulge 6 of the inner ring 4 is pressed into the front end of the tube 8.

[0055] The value D is set to ≤ 1.4d because if the diameter D of the axial end 15c exceeds 1.4d, the tightening torque of the connecting nut 3 increases due to the pressing force generated axially by the corner 3c of the connecting nut 3 across the entire flat surface 16. The value 1.0d ≤ D is set because if the diameter D of the axial end 15c is less than 1.0d, the axial range of the surface pressure generated between the front end tapering 13 of the bulge 6 and the tube 8 becomes longer, making it impossible to ensure the required surface pressure between the bulge 6 and the tube 8. The other structures of the third embodiment are the same as those of the first embodiment; therefore, the same reference numerals are used and their descriptions are omitted.

[0056] Furthermore, a flat surface 16 is formed at one axial end of the front tapering portion 13, but it can also be formed into a shape other than a flat surface (e.g., a conical surface).

[0057] Furthermore, the shape of the outer peripheral surface 15 of the front end tapering 13 is not limited to a convex curved surface; for example, it can be as follows: Figure 9 The shape shown is planar.

[0058] As described above, according to the pipe connector 1 of the third embodiment, the diameter D of the axial end 15c of the outer peripheral surface 15 of the tapered portion 13 at the front end of the inner ring 4 satisfies the relationship D ≤ 1.4d with the inner diameter d of the non-deformable portion 8c of the pipe 8, so the tightening torque of the connecting nut 3 will not increase. Furthermore, the diameter D of the axial end 15c of the outer peripheral surface 15 of the tapered portion 13 satisfies the relationship 1.0d ≤ D with the inner diameter d of the non-deformable portion 8c of the pipe 8, so even without increasing the tightening torque of the connecting nut 3, the required surface pressure between the bulge 6 of the inner ring 4 and the pipe 8 can be ensured. As a result, leakage of the liquid medicine flowing in the fluid flow path 4a of the inner ring 4 from the bulge 6 to the outside can be suppressed.

[0059] [other]

[0060] In addition to semiconductor manufacturing equipment, the connectors of the present invention can also be used in the fields of liquid crystal / organic EL, medical / pharmaceutical, or automotive-related fields.

[0061] It should be understood that the embodiments disclosed herein are illustrative in all respects and are not restrictive. The scope of the invention is not as described above, but is indicated by the claims and is intended to include all modifications equivalent to or within the scope of the claims.

[0062] Explanation of the label

[0063] 1 pipe fitting

[0064] 2. Connector body

[0065] 2b External Thread Section

[0066] 3-Pipe Nut

[0067] 3a Internal thread section

[0068] 3c corner

[0069] 4 Inner Ring

[0070] 6. Drum Exit

[0071] 8 tubes

[0072] 8c Non-deformable part

[0073] 13 Front-end tapering

[0074] 15 outer perimeter

[0075] 15a concave face

[0076] 15b Convex Face

[0077] 15c axial end

Claims

1. A pipe fitting, wherein, The pipe fitting has the following features: The inner ring has a bulge that is formed radially outward on one axial side and pressed into the front end of the tube; The connector body, wherein the bulge is pressed into the front end of the tube, presses the end of the inner ring on the opposite axial side inward circumferentially, and has an external thread on the outer circumference; and A pipe-connecting nut has an internal thread portion that is fastened to the external thread portion, and the internal thread portion is fastened to the external thread portion to press the front end of the pipe axially to the other side. The bulge has a front end that tapers from its midpoint toward one side in the axial direction, and the tapering front end generates surface pressure with the pipe when pressed by the connecting nut. The outer peripheral surface of the tapered front end has a concave curved surface that is concave when viewed in axial cross-section, and a convex curved surface that is convex on the axial side further than the concave curved surface. The convex curved surface is formed at the front end of the front tapering portion.

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