Vent piece, tire vulcanization mold, and tire manufacturing method

Abstract

To provide a vent piece that reduces spew pull-out resistance and prevents tire adhesion during demolding, a tire vulcanization mold, and a tire manufacturing method.SOLUTION: Provided is a vent piece, which is a cylindrical vent piece 2 that is fitted into an exhaust hole 16 that opens on a molding surface 1 of a tire vulcanization mold and has an exhaust path 21 inside, and has a contraction part 26 that reduces the cross-sectional area of the exhaust path 21, and a front end part 27 located on the side opposite to the molding surface from the contraction part 26, and in which the cross-sectional area of the exhaust path 21 at the contraction part 26 is smaller than the cross-sectional area of the exhaust path 21 at the front end part 27 and is 70% or more of the cross-sectional area thereof.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a cylindrical vent piece that is attached to an exhaust hole on the molding surface of a tire vulcanizing mold, a tire vulcanizing mold with the vent piece attached, and a tire manufacturing method using the same. [Background technology]

[0002] A tire vulcanization mold has many exhaust holes on the molding surface that molds the outer surface of the tire. During vulcanization, air between the tire's outer surface and the molding surface is discharged through the exhaust holes, and rubber that flows into the exhaust holes forms rubber protrusions called spews on the tire's outer surface. As described in Patent Documents 1 to 3, it is known to attach cylindrical vent pieces to the exhaust holes for the purpose of adjusting the size of the spews, etc.

[0003] After vulcanization molding is complete, when removing the vulcanized tire from the mold, the tire may adhere to the mold and prevent smooth removal. The main cause of this tire adhesion during demolding is the spew's resistance to removal from the vent piece. If the tire adheres to the vent piece during demolding due to the spew's resistance to removal, the spew may break unintentionally, which is known as spew breakage. Spew breakage can cause the vent piece to become clogged with the separated spew, hindering air from escaping. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-30402 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-105126 [Patent Document 3] Japanese Patent Publication No. 2020-82646 Summary of the Invention [Problem to be solved by the invention]

[0005] The present disclosure has been made in consideration of the above-described circumstances, and an object of the present disclosure is to provide a vent piece, a tire vulcanization mold, and a tire manufacturing method that can reduce the spew removal resistance and suppress adhesion of the tire during demolding. [Means for solving the problem]

[0006] The vent piece of the present disclosure is attached to an exhaust hole that opens on the molding surface of a tire vulcanization mold, is a cylindrical vent piece having an exhaust passage therein, and has a constricted portion that reduces the cross-sectional area of ​​the exhaust passage, and a front end portion that is located on the side opposite the molding surface from the constricted portion. The cross-sectional area of ​​the exhaust passage at the constricted portion is smaller than the cross-sectional area of ​​the exhaust passage at the front end portion and is 70% or more of that cross-sectional area.

[0007] The tire vulcanizing mold of the present disclosure includes the molding surface that contacts the outer surface of the tire set in the cavity, and the above-mentioned vent piece attached to the exhaust hole that opens on the molding surface.

[0008] The tire manufacturing method of the present disclosure includes the steps of setting an unvulcanized tire in a cavity of a tire vulcanization mold equipped with the above-described vent piece, and applying heat and pressure to the tire to vulcanize it. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view schematically illustrating an example of a tire vulcanization mold according to the present disclosure. [Figure 2] 1 is a cross-sectional view showing a ventlid according to a first embodiment; [Figure 3] 1A is an external side view showing the ventlid of the first embodiment, and FIG. 1B is a cross-sectional view taken along the arrow aa. [Figure 4] FIG. 10 is a diagram schematically illustrating the effects of the vent piece of the present disclosure. [Figure 5] 1A is an external side view, FIG. 1B is a cross-sectional view taken along the arrow bb, and FIG. 1C is a cross-sectional view taken along the arrow cc, showing a modified example of the ventlid in the first embodiment. [Figure 6]1A is an external side view of a ventlid according to a second embodiment, FIG. 1B is a cross-sectional view taken along the arrow dd, and FIG. 1C is a cross-sectional view taken along the arrow ee. [Figure 7] 10A is an external side view of a ventlid according to a third embodiment, FIG. 10B is a cross-sectional view taken along the arrow ff, and FIG. 10C is a cross-sectional view taken along the arrow gg. [Figure 8] 10A is an external side view of a ventlid according to a fourth embodiment, FIG. 10B is a cross-sectional view taken along the arrow hh, and FIG. 10C is a cross-sectional view taken along the arrow ii. [Figure 9] 10A is an external side view, FIG. 10B is a cross-sectional view taken along the arrow jj, and FIG. 10C is a cross-sectional view taken along the arrow kk, showing a modified example of the ventlid in the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Embodiments of the present disclosure will be described with reference to the drawings.

[0011] [Tire curing mold] FIG. 1 shows a cross section of a tire curing mold 10 (hereinafter, may be simply referred to as "mold 10") along the tire meridian cross section. This mold 10 is in a closed state. A tire T is set with its axial direction facing up and down. In FIG. 1, the left side is the outer side in the tire radial direction, and the right side is the inner side in the tire radial direction.

[0012] The mold 10 includes a cavity 15 in which the tire T is set, and a molding surface 1 that comes into contact with the outer surface of the tire T set in the cavity 15. The molding surface 1 is provided with an exhaust hole 16 that connects the inside of the mold 10 (i.e., the cavity 15) to the outside. During vulcanization molding, air is discharged between the outer surface of the tire T and the molding surface 1 through the exhaust hole 16. A vent piece 2 is attached to the exhaust hole 16.

[0013] An example of the material for the forming surface 1 is an aluminum material. This aluminum material is a concept that includes not only pure aluminum-based materials but also aluminum alloys, such as Al-Cu-based, Al-Mg-based, Al-Mg-Si-based, Al-Zn-Mg-based, Al-Mn-based, and Al-Si-based materials. An example of the material for the ventlid 2 is a steel material such as stainless steel or S45C.

[0014] The mold 10 includes a tread mold 11 for molding the tire tread, side molds 12 and 13 for molding the tire sidewalls, and bead rings 14 and 14 into which the tire bead portions are fitted. The molding surface 1 includes the inner surface of the tread mold 11 and the inner surfaces of the side molds 12 and 13. Although not shown, the inner surface of the tread mold 11 has projections and depressions for forming the tire tread pattern. While FIG. 1 depicts only one exhaust hole 16 opening on the inner surface of the tread mold 11, in reality, many exhaust holes opening on the inner surfaces of the tread mold 11 and the side molds 12 and 13 are provided.

[0015] The vent piece 2 is attached to an exhaust hole 16 that opens on the molding surface 1. In FIG. 1, it is attached to the exhaust hole 16 on the inner surface of the tread mold 11, but instead of or in addition to this, it is also possible to attach it to an exhaust hole that opens on the inner surface of the side mold 12 and / or side mold 13. Also, in this embodiment, the mold 10 has a structure including the tread mold 11 and a pair of side molds 12, 13, but this is not limited to this, and for example, a mold structure in which the tread mold is divided into two, upper and lower, at the center may also be used.

[0016] [First embodiment of vent piece] A first embodiment of the ventpiece of the present disclosure will be described with reference to Figures 2 to 5. In the example shown in Figure 2, a ventpiece 2a, which is one form of ventpiece 2, is attached to an exhaust hole 16. In Figure 2, the downward direction is the molding surface side (cavity side), and the upward direction is the opposite molding surface side (opposite cavity side). The ventpiece 2a is formed in a cylindrical shape with an exhaust passage 21 therein. The exhaust passage 21 is formed by a through-hole that penetrates the ventpiece 2a in the longitudinal direction LD. Figure 3 shows (A) an external side view of the ventpiece 2a, and (B) a cross-sectional view taken along the arrow aa.

[0017] The vent piece 2a is attached to the exhaust hole 16 by an interference fit. In the area where the vent piece 2a is attached, the inner surface of the exhaust hole 16 is formed by a cylindrical surface extending with a constant diameter from the molding surface 1 toward the opposite molding surface. The longitudinal direction LD of the vent piece 2a coincides with the axial direction of the exhaust hole 16. The vent piece 2a has an inner surface 22 facing the exhaust passage 21, an outer peripheral surface 23 in contact with the inner surface of the exhaust hole 16, an end surface 24 on the molding surface side, and an end surface 25 on the opposite molding surface side. The vent piece 2a has a constant outer diameter along the longitudinal direction LD, but is not limited to this. Although not employed in this embodiment, a counterbore may be provided on the end surface 24 on the molding surface side to prevent spew breakage.

[0018] As shown in FIG. 2 , the ventlid 2a has a constricted portion 26 that reduces the cross-sectional area of ​​the exhaust passage 21, and a front end portion 27 located on the side opposite the molding surface from the constricted portion 26. At the front end portion 27, the exhaust passage 21 extends with a constant diameter from the constricted portion 26 toward the side opposite the molding surface. Furthermore, the ventlid 2a of this embodiment has a rear end portion 28 located on the molding surface side from the constricted portion 26. At the rear end portion 28, the exhaust passage 21 extends with a constant diameter from the constricted portion 26 toward the molding surface. The cross-sectional area of ​​the exhaust passage 21 is smallest at the constricted portion 26. The cross-sectional area of ​​the exhaust passage 21 refers to the cross-sectional area when cut by a plane perpendicular to the center line CL of the exhaust passage 21. The cross-sectional area Ax of the exhaust passage 21 at the constricted portion 26 is smaller than the cross-sectional area Ay of the exhaust passage 21 at the front end portion 27 and is set to be 70% or more of the cross-sectional area Ay.

[0019] Fig. 4 is a diagram schematically showing the action and effect of this vent piece 2a. Similar action and effect are also achieved by vent pieces 2b to 2d in other embodiments described later. First, during vulcanization molding, air between the outer surface of the tire T and the molding surface 1 is discharged through the exhaust path 21. At the same time, as shown in Fig. 4(A), the rubber that has flowed into the exhaust path 21 forms a spew S on the outer surface of the tire T. The rubber that forms the spew S passes through the constricted portion 26 and reaches the front end 27, and the tip of the spew S is positioned on the side away from the molding surface relative to the constricted portion 26.

[0020] Next, when the tire T is demolded after vulcanization, a force is applied to pull the spew S out of the vent piece 2a as the outer surface of the tire T is pulled away from the molding surface 1. At this time, as shown in Fig. 4(B), the tip of the spew S temporarily gets caught in the narrowed portion 26, and the pulled spew S is stretched and thinned, causing the spew S to peel off from the inner circumferential surface 22 of the vent piece 2a (particularly the rear end 28). Thereafter, as shown in Fig. 4(C), the tip of the spew S is further pulled and passes through the narrowed portion 26, allowing the spew S to be smoothly pulled out of the vent piece 2a.

[0021] Setting the cross-sectional area Ax of the exhaust passage 21 at the constricted portion 26 to 70% or more of the cross-sectional area Ay of the exhaust passage 21 at the front end 27 is useful for causing the tip of the spew S to bend over the constricted portion 26 and then pass through (i.e., for transitioning from the state of FIG. 4(B) to the state of FIG. 4(C)). If this ratio falls below 70% and the difference between the cross-sectional area Ax and the cross-sectional area Ay becomes large, the tip of the spew S, which is pulled further, may be torn off by the constricted portion 26, and the torn pieces may hinder the discharge of air. As described above, this vent piece 2a reduces the resistance to the spew S being removed, thereby preventing the tire from adhering to the tire during demolding.

[0022] The ratio (Ax / Ay) of the cross-sectional area Ax to the cross-sectional area Ay is preferably 75% or more, more preferably 80% or more. In order to hook the tip of the spew S on the constricted portion 26, the ratio (Ax / Ay) is preferably 95% or less, more preferably 90% or less. The cross-sectional area Ax is, for example, 1 to 2.2 mm 2 The cross-sectional area Ay is, for example, 1.4 to 3.1 mm 2 When the cross-sectional area of ​​the exhaust passage 21 at the constricted portion 26 changes in the longitudinal direction LD, the minimum value is adopted as the cross-sectional area Ax. When the cross-sectional area of ​​the exhaust passage 21 at the front end portion 27 changes in the longitudinal direction LD, the maximum value is adopted as the cross-sectional area Ay.

[0023] The constricted portion 26 is not formed in the exhaust hole 16 itself, but in the vent piece 2a attached to the exhaust hole 16. Because the vent piece 2a is press-fit into the exhaust hole 16, the relative position of the constricted portion 26 with respect to the molding surface 1 does not change. Repeated vulcanization molding tends to cause dirt to accumulate inside the exhaust path 21, particularly around the constricted portion 26, but this can be addressed by removing and cleaning the vent piece 2a or by replacing the vent piece 2a.

[0024] The length L from the end face 24 on the molding surface side to the tapered portion 26 is preferably 30 to 80% of the length FL of the entire ventlid. If this is 30% or more, the length of the spew S arranged at the front end portion 27 becomes appropriately short, which is convenient for reducing the resistance to removal of the spew S. From this perspective, the length L is more preferably 40% or more of the length FL, and even more preferably 45% or more. Furthermore, if this is 80% or less, it becomes easier to ensure that the spew S reaches the front end portion 27, and it is possible to appropriately form a spew S with a tip portion of an appropriate size for hooking onto the tapered portion 26. From this perspective, the length L is more preferably 60% or less of the length FL, and even more preferably 55% or less.

[0025] In order to reduce the resistance to removal of the spew S, the length L is preferably 3 mm or more, more preferably 4 mm or more, and even more preferably 4.5 mm or more. The length L is measured based on the position at which the cross-sectional area of ​​the exhaust passage 21 in the constricted portion 26 is smallest. As in the examples in Figures 5 and 6 described below, if the position at which the cross-sectional area of ​​the exhaust passage 21 in the constricted portion 26 is smallest extends in the longitudinal direction LD, the length L is determined based on the end of that position on the side opposite the molding surface. The length FL of a ventlid used in molding passenger car tires is, for example, 10 to 15 mm.

[0026] 2 and 3, the ventlid 2 (ventlid 2a) of this embodiment has a slot 31 that opens on the outer peripheral surface 23 and communicates with the exhaust passage 21, and an insert member 32 inserted into the slot 31. A portion of the insert member 32 inserted into the slot 31 protrudes toward the exhaust passage 21, thereby forming the throttled portion 26. With this configuration, the ventlid 2a having the throttled portion 26 can be manufactured by relatively simple processing. In this embodiment, a pair of slots 31 are formed on either side of the center line CL of the exhaust passage 21, and the insert member 32 is formed by a pair of members that are inserted into each of the slots.

[0027] In this embodiment, the slot 31 includes a pair of circular holes 31a positioned on either side of the center line CL of the exhaust passage 21, and the insertion member 32 is formed in the shape of a round rod to be inserted into the pair of circular holes 31a. The pair of circular holes 31a extend parallel to each other and are skewed relative to the center line CL. As shown in FIG. 3, a portion of the insertion member 32 inserted into the circular hole 31a protrudes from the inner circumferential surface 22 and enters the exhaust passage 21, thereby reducing the cross-sectional area of ​​the exhaust passage 21. With this configuration, the rounded constricted portion 26 is formed as shown in FIG. 2, which makes it easy for the tip of the spew S to pass through the constricted portion 26.

[0028] The insertion member 32, which is formed in a round bar shape, may be inserted into the round hole 31a so as to be rotatable. This configuration is convenient for the tip of the spew S to pass through the drawn portion 26. However, in order to temporarily hook the tip of the spew S on the drawn portion 26 and extend the spew S, it is preferable that the insertion member 32 is fitted into the round hole 31a to an extent that there is appropriate resistance when rotating. The insertion member 32 may also be configured not to rotate with respect to the slot 31. The slot 31 is not limited to the round hole 31a, and the insertion member 32 may be formed in a bar shape other than a round bar (for example, a square bar).

[0029] The corners of the constricted portion 26 on the side opposite the molding surface are preferably rounded or obtuse-angled. This configuration reduces resistance when the tip of the spew S passes through the constricted portion 26, allowing the spew S to be pulled out more smoothly from the ventlid 2a. In this embodiment, the corners of the constricted portion 26 on the side opposite the molding surface are rounded. It is also possible to adopt a shape that combines a rounded shape with an obtuse-angled shape. As shown in Figure 2, in a cross section cut along a plane including the center line CL, the inner circumferential surface of the exhaust passage 21 at the constricted portion 26 is semicircular or semielliptical, and does not have any acute angles.

[0030] The shape of the insert member 32 is not limited to a rod shape, and the same goes for the shape of the slot 31. Therefore, for example, the constricted portion 26 may be formed with a structure as shown in FIG. 5. In a modified example of the ventlid 2a shown in FIG. 5, the slot 31 includes a pair of slits 31b positioned on either side of the center line CL of the exhaust passage 21, and the insert member 32 is formed in a plate shape to be inserted into the pair of slits 31b. In this example, the corners on the side opposite the molded surface of the constricted portion 26 are right-angled. A more preferable form can be achieved by making this a rounded or obtuse-angled shape.

[0031] [Second embodiment of vent piece] Next, a second embodiment of the ventlid of the present disclosure will be described with reference to Fig. 6. A ventlid 2b as the second embodiment can be configured similarly to the ventlid 2a as the first embodiment, except for the configuration described below, so commonalities will be omitted and differences will be mainly described. Components already described in the first embodiment will be assigned the same reference numerals, and duplicate explanations will be omitted.

[0032] As shown in Fig. 6, ventpiece 2b, which is one form of ventpiece 2, has a constricted portion 26 that reduces the cross-sectional area of ​​exhaust passage 21, and a front end portion 27 that is located on the side away from the molding surface than constricted portion 26. Ventpiece 2b also has a rear end portion 28 that is located on the molding surface side than constricted portion 26. The cross-sectional area Ax of exhaust passage 21 at constricted portion 26 is smaller than the cross-sectional area Ay of exhaust passage 21 at the front end portion 27 and is 70% or more of the cross-sectional area Ay.

[0033] The ventlid 2b is divided into multiple members including a cylindrical member 41 (first cylindrical member) including the end face 24 on the side opposite to the molding surface, a cylindrical member 42 (second cylindrical member) including the end face 25 on the molding surface side, and a cylindrical member 43 (third cylindrical member) that is disposed between the cylindrical members 41 and 42 and has the constricted portion 26 formed therein. Each of the cylindrical members 41 to 43 has a simple shape, and the ventlid 2b is formed as a single cylindrical body by connecting them in the longitudinal direction LD. With this configuration, the ventlid 2b having the constricted portion 26 can be produced by a relatively simple process.

[0034] The inner diameter of the cylindrical member 43 is smaller than the inner diameters of the cylindrical members 41 and 42. Therefore, the inner circumferential surface of the exhaust passage 21 in the cylindrical member 43 is shaped to protrude toward the center line CL, thereby forming the throttled portion 26. As shown in FIG. 6(B), the inner circumferential surface of the exhaust passage 21 at the throttled portion 26 protrudes in an annular (ring-like) shape around the center line CL of the exhaust passage 21. With the throttled portion 26 having such a shape, the tip of the spew S is stably caught, allowing the spew S to be pulled in a balanced manner and stretched well. However, the shape is not limited to this, and the inner circumferential surface of the exhaust passage 21 at the throttled portion 26 may have the shape shown in the first embodiment.

[0035] As shown in FIG. 6(C), in a cross section cut along a plane including the center line CL, the inner circumferential surface of the exhaust passage 21 in the constricted portion 26 is trapezoidal and does not have any acute angles. The corners of the constricted portion 26 on the side opposite the molding surface are obtuse-angled. As a modification, it is possible to form the inner circumferential surface of the exhaust passage 21 in the constricted portion 26 into a semicircular or semielliptical shape. In this case, the corners of the constricted portion 26 on the side opposite the molding surface are rounded.

[0036] When attaching the ventlid 2b to the exhaust hole 16 (not shown in FIG. 6), the tubular members 41 to 43 may be bonded together to form a single unit before attachment. However, they may also be attached as separate members without being bonded. In this case, by sequentially press-fitting the separate tubular members 41 to 43 into the exhaust hole 16, they are connected inside the exhaust hole 16 to form the ventlid 2b as a single cylindrical body.

[0037] [Third embodiment of vent piece] Next, a third embodiment of the ventlid of the present disclosure will be described with reference to Fig. 7. A ventlid 2c as the third embodiment can be configured similarly to the ventlid 2a as the first embodiment, except for the configuration described below, so commonalities will be omitted and differences will be mainly described. Components already described in the first embodiment will be assigned the same reference numerals, and duplicate explanations will be omitted.

[0038] 7, ventpiece 2c, which is one form of ventpiece 2, has a constricted portion 26 that reduces the cross-sectional area of ​​the exhaust passage 21, and a front end portion 27 that is located on the side away from the molding surface than the constricted portion 26. Ventpiece 2c also has a rear end portion 28 that is located on the molding surface side than the constricted portion 26. The cross-sectional area Ax of the exhaust passage 21 at the constricted portion 26 is smaller than the cross-sectional area Ay of the exhaust passage 21 at the front end portion 27 and is 70% or more of the cross-sectional area Ay.

[0039] The ventlid 2c has constricted portions 51 at multiple locations in the circumferential direction (two locations in this embodiment). At the constricted portions 51, the outer peripheral surface 23 is recessed and the inner peripheral surface 22 protrudes toward the center line CL, thereby forming the constricted portions 26. The constricted portions 26 can be formed by applying a local force to the outer peripheral surface 23 using a tool such as pliers or a punch, thereby plastically deforming required portions of the ventlid 2c. Therefore, the number of parts is small, and the ventlid 2c having the constricted portions 26 can be produced by relatively simple and inexpensive processing.

[0040] As shown in Figure 7(C), in a cross section cut along a plane including the center line CL, the inner circumferential surface of the exhaust passage 21 at the constricted portion 26 has a semicircular or semi-elliptical shape and does not have any acute angles. The corners of the constricted portion 26 on the side opposite the molding surface are rounded. The constricted portion 51 needs to be provided in at least one location in the circumferential direction, and may be provided in three or more locations. The constricted portion 51 may be provided so that the inner circumferential surface of the exhaust passage 21 protrudes in an annular (ring-shaped) shape around the center line CL.

[0041] [Fourth embodiment of vent piece] Next, a fourth embodiment of the ventlid of the present disclosure will be described with reference to Figures 8 and 9. A ventlid 2d as the fourth embodiment can be configured similarly to the ventlid 2a as the first embodiment, except for the configuration described below, so commonalities will be omitted and differences will be mainly described. Configurations already described in the first embodiment will be assigned the same reference numerals, and duplicate explanations will be omitted.

[0042] 8, ventpiece 2d, which is one form of ventpiece 2, has a constricted portion 26 that reduces the cross-sectional area of ​​the exhaust passage 21, and a front end portion 27 that is located on the side away from the molding surface than the constricted portion 26. Ventpiece 2c further has a rear end portion 28 that is located on the molding surface side than the constricted portion 26. The cross-sectional area Ax of the exhaust passage 21 at the constricted portion 26 is smaller than the cross-sectional area Ay of the exhaust passage 21 at the front end portion 27 and is 70% or more of the cross-sectional area Ay.

[0043] In the ventlid 2d of Fig. 8, the exhaust passage 21 at the front end 27 is tapered, with the diameter gradually increasing toward the side away from the molding surface. In this example, the cross-sectional area of ​​the exhaust passage 21 at the front end 27 changes in the longitudinal direction LD, so the cross-sectional area of ​​the exhaust passage 21 at the end face 25, where the cross-sectional area is maximum, is used as the cross-sectional area Ay. In addition, the exhaust passage 21 at the rear end 28 is tapered, with the diameter gradually increasing toward the molding surface. However, as in the modified example shown in Fig. 9, it is also possible to form the inner surface of the exhaust hole 16 at the rear end 28 as a cylindrical surface extending with a constant diameter.

[0044] Since the inner diameter of the narrowed portion 26 is smaller than the inner diameter of the front end portion 27, the inner peripheral surface of the exhaust passage 21 at the narrowed portion 26 is shaped to protrude toward the center line CL. )of As described above, the inner peripheral surface of the exhaust passage 21 at the constricted portion 26 protrudes in an annular (ring-like) shape around the center line CL of the exhaust passage 21. With the constricted portion 26 having such a shape, the tip of the spew S is stably caught, and the spew S can be pulled in a well-balanced manner to be stretched well. 9(B), the inner peripheral surface of the exhaust passage 21 at the first portion 29 protrudes in an annular (ring-like) shape around the center line CL of the exhaust passage 21. With the first portion 29 having such a shape, the tip of the spew S is stably caught, and the spew S can be pulled in a balanced manner to be stretched well.

[0045] [Tire manufacturing method] A tire manufacturing method using a mold 10 equipped with a vent piece 2 includes the steps of setting an unvulcanized tire T in a cavity 15 of the mold 10 and applying heat and pressure to the tire T to vulcanize it. The tire T expands and deforms due to the expansion of a rubber bag called a bladder, and its outer surface presses against the molding surface 1. During this process, air between the tire and the molding surface 1 is discharged to the outside through the exhaust path 21 of the vent piece 2. As described above, when demolding, the removal resistance of the spew S can be reduced, thereby suppressing tire adhesion.

[0046] [1] As described above, the vent piece 2 of the present disclosure is attached to the exhaust hole 16 opening on the molding surface 1 of the tire vulcanizing mold 10, and is a cylindrical vent piece 2 having an exhaust passage 21 therein, and has a constricted portion 26 that reduces the cross-sectional area of ​​the exhaust passage 21, and a front end portion 27 that is located on the opposite molding surface side from the constricted portion 26, and the cross-sectional area Ax of the exhaust passage 21 at the constricted portion 26 is smaller than the cross-sectional area Ay of the exhaust passage 21 at the front end portion 27 and is 70% or more of the cross-sectional area Ay.

[0047] According to this configuration, the tip of the spew S gets caught in the narrowed portion 26 during demolding, and the pulled spew S stretches and becomes thinner, allowing the spew S to smoothly peel off from the ventlid 2. As a result, the resistance to removal of the spew S is reduced, making it possible to prevent the spew S from adhering to the tire during demolding. Furthermore, by setting the cross-sectional area Ax to 70% or more of the cross-sectional area Ay, the tip of the pulled spew S can more easily pass through the narrowed portion 26, allowing the spew S to be smoothly pulled out of the ventlid 2.

[0048] [2] The ventlid 2 of [1] above may be a ventlid 2a having a slot 31 that opens on the outer peripheral surface 23 and communicates with the exhaust passage 21, and an insert member 32 inserted into the slot 31, with a portion of the insert member 32 inserted into the slot 31 protruding toward the exhaust passage 21, thereby forming the throttled portion 26. With this configuration, the ventlid 2a having the throttled portion 26 can be produced by a relatively simple process.

[0049] [3] In the ventpiece 2 (ventpiece 2a) of [2] above, the slot 31 preferably includes a pair of round holes 31a positioned on either side of the center line CL of the exhaust passage 21, and the insertion member 32 is preferably formed in the shape of a pair of round rods to be inserted into the pair of round holes 31a. With this configuration, the rounded constricted portion 26 is formed, which makes it easy for the tip of the spew S to pass through the constricted portion 26.

[0050] [4] The ventlid 2 of [1] above may be a ventlid 2b that is divided into multiple members including a tubular member 41 (first tubular member) including the end face 24 on the side opposite to the molding surface, a tubular member 42 (second tubular member) including the end face 25 on the molding surface side, and a tubular member 43 (third tubular member) that is disposed between the tubular members 41 and 42 and has the constricted portion 26 formed therein. With this configuration, the ventlid 2b having the constricted portion 26 can be produced by a relatively simple process.

[0051] [5] In the ventpiece 2 of any one of the above [1] to [4], the length L from the end face 24 on the molding surface side to the tapered portion 26 is preferably 30 to 80% of the overall length FL of the ventpiece. This appropriately shortens the length of the spew S located at the front end 27, which is convenient for reducing the resistance to removal of the spew S. It also makes it easier to reliably allow the spew S to reach the front end 27, and allows the spew S to be appropriately formed with a tip of an appropriate size for hooking onto the tapered portion 26.

[0052] [6] In the ventlid 2 of any one of the above [1] to [5], it is preferable that the corners of the constricted portion 26 on the side opposite to the molding surface have at least one of a rounded shape and an obtuse angle shape. This configuration makes it easy for the tip of the spew S to pass through the constricted portion 26.

[0053] [7] The tire vulcanizing mold 10 of the present disclosure includes a molding surface 1 that contacts the outer surface of a tire T set in a cavity 15, and one of the vent pieces 2 [1] to [6] above that is attached to an exhaust hole 16 that opens on the molding surface 1. This configuration reduces the resistance to removal of the spew S, thereby preventing the tire from adhering to the mold when it is removed.

[0054] The tire vulcanizing mold 10 of the present disclosure is equivalent to a normal tire vulcanizing mold, except that the vent piece 2 attached to the exhaust hole 16 is configured as described above, and any of the conventionally known shapes, materials, mechanisms, etc. can be adopted.

[0055] [8] The tire manufacturing method of the present disclosure includes the steps of setting an unvulcanized tire T in the cavity 15 of a tire vulcanizing mold 10 equipped with any one of the vent pieces 2 described above [1] to [6], and applying heat and pressure to the tire T to vulcanize it. This method reduces the pull-out resistance of the spew S, thereby preventing the tire from adhering to one another when demolded.

[0056] The tire manufacturing method of the present disclosure is the same as a normal tire manufacturing method, except that the vent piece 2 as described above is attached to the exhaust hole 16 of the tire vulcanization mold 10, and any of the conventionally known steps and vulcanization conditions can be adopted.

[0057] Although the embodiments of the present disclosure have been described above, it should be understood that the specific configurations are not limited to these embodiments. The scope of the present disclosure is not limited to the above-described embodiments, but is indicated by the claims, and further includes all modifications within the meaning and scope equivalent to the claims.

[0058] The ventlid, tire vulcanization mold, and tire manufacturing method of the present disclosure are not limited to the above-described embodiments, and various improvements and modifications are possible without departing from the spirit thereof. Furthermore, the configurations employed in the first to fourth embodiments described above can be adopted in any combination. For example, while adopting a structure in which a constricted portion is formed by an insert member as in the first embodiment, the ventlid may have a divided structure as in the second embodiment. [Explanation of symbols]

[0059] 1 Molding surface 2 Vent Pieces 2a Vent piece (first embodiment) 2b Vent piece (second embodiment) 2c Vent piece (third embodiment) 2d Vent piece (fourth embodiment) 10 Tire curing mold 16 Exhaust vent 21 Exhaust duct 22 Inner surface 23 Outer surface 24 End face on the molding surface side 25 End face on the opposite side of the forming surface 26 Constriction section 27 Front end 31 slots 31a Round hole 32 Insert 41 first cylindrical member 42 second cylindrical member 43 Third cylindrical member

Claims

1. A cylindrical vent piece that is attached to an exhaust hole that opens on the molding surface of a tire vulcanization mold and has an exhaust path therein, a drawing portion disposed at a position spaced from the end face on the molding surface side toward the side opposite the molding surface, and a front end portion disposed on the side opposite the molding surface with respect to the drawing portion, a minimum cross-sectional area of ​​the exhaust passage at the narrowed portion is smaller than a minimum cross-sectional area of ​​the exhaust passage at the front end portion and is 70% or more of a maximum cross-sectional area of ​​the exhaust passage at the front end portion, a slot that opens on an outer peripheral surface and communicates with the exhaust passage, and an insertion member that is inserted into the slot; A vent piece in which a portion of the insertion member inserted into the slot protrudes toward the exhaust path, thereby forming the constricted portion.

2. The slot includes a pair of circular holes positioned on either side of a centerline of the exhaust passage, The ventlid according to claim 1, wherein the insertion members are formed in the shape of a pair of round rods that are inserted into the pair of round holes.

3. A cylindrical vent piece that is attached to an exhaust hole that opens on the molding surface of a tire vulcanization mold and has an exhaust path therein, a drawing portion disposed at a position spaced from the end face on the molding surface side toward the side opposite the molding surface, and a front end portion disposed on the side opposite the molding surface with respect to the drawing portion, a minimum cross-sectional area of ​​the exhaust passage at the narrowed portion is smaller than a minimum cross-sectional area of ​​the exhaust passage at the front end portion and is 70% or more of a maximum cross-sectional area of ​​the exhaust passage at the front end portion, A vent piece divided into multiple members including a first tubular member including an end face on the side opposite to the molding surface, a second tubular member including an end face on the molding surface side, and a third tubular member disposed between the first and second tubular members and having the constricted portion formed therein.

4. A cylindrical vent piece that is attached to an exhaust hole that opens on the molding surface of a tire vulcanization mold and has an exhaust path therein, the die has a drawn portion disposed at a position spaced from the end face on the molding surface side toward the side opposite the molding surface, a front end portion located on the side opposite the molding surface side relative to the drawn portion, and a rear end portion located on the molding surface side relative to the drawn portion, The cross-sectional area of ​​the exhaust passage is smallest at the constricted portion, the exhaust passage at the rear end portion extends from the narrowed portion toward the molding surface side with a constant diameter, A vent piece wherein the minimum cross-sectional area of ​​the exhaust passage at the constricted portion is smaller than the minimum cross-sectional area of ​​the exhaust passage at the front end portion and is 70% or more of the maximum cross-sectional area of ​​the exhaust passage at the front end portion.

5. A cylindrical vent piece that is attached to an exhaust hole that opens on the molding surface of a tire vulcanization mold and has an exhaust path therein, a drawing portion disposed at a position spaced from the end face on the molding surface side toward the side opposite the molding surface, and a front end portion disposed on the side opposite the molding surface with respect to the drawing portion, the exhaust passage at the front end portion extends from the constricted portion toward the side opposite the molding surface with a constant diameter, A vent piece wherein the minimum cross-sectional area of ​​the exhaust passage at the constricted portion is smaller than the minimum cross-sectional area of ​​the exhaust passage at the front end portion and is 70% or more of the maximum cross-sectional area of ​​the exhaust passage at the front end portion.

6. A cylindrical vent piece that is attached to an exhaust hole that opens on the molding surface of a tire vulcanization mold and has an exhaust path therein, a drawing portion disposed at a position spaced from the end face on the molding surface side toward the side opposite the molding surface, and a front end portion disposed on the side opposite the molding surface with respect to the drawing portion, the minimum cross-sectional area of ​​the exhaust passage at the throttle portion is 1 to 2.2 mm 2 ; A vent piece wherein the minimum cross-sectional area of ​​the exhaust passage at the constricted portion is smaller than the minimum cross-sectional area of ​​the exhaust passage at the front end portion and is 70% or more of the maximum cross-sectional area of ​​the exhaust passage at the front end portion.

7. A cylindrical vent piece that is attached to an exhaust hole that opens on the molding surface of a tire vulcanization mold and has an exhaust path therein, a first portion disposed at a position spaced from the end face on the molding surface side toward the side opposite the molding surface, a front end portion located on the side opposite the molding surface from the first portion, and a rear end portion located on the molding surface side from the first portion; The cross-sectional area of ​​the exhaust passage is smallest at the first portion, the exhaust passage at the rear end portion extends from the first portion toward the molding surface side with a constant diameter, A vent piece, wherein the minimum cross-sectional area of ​​the exhaust passage in the first portion is smaller than the minimum cross-sectional area of ​​the exhaust passage at the front end portion and is 70% or more of the maximum cross-sectional area of ​​the exhaust passage at the front end portion.

8. A tire vulcanizing mold comprising: the molding surface that contacts the outer surface of a tire set in a cavity; and the vent piece according to any one of claims 1 to 7 that is attached to the exhaust hole that opens on the molding surface.

9. A method for manufacturing a tire, comprising the steps of setting an unvulcanized tire in a cavity of a tire vulcanizing mold equipped with the vent piece according to any one of claims 1 to 7, and applying heat and pressure to the tire to vulcanize it.

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