Tire molding mold and tire manufacturing method

Abstract

To provide a tire molding die that can reduce the driving force necessary for driving a segment at an initial stage of tire release, and a tire production method.SOLUTION: The present invention provides: a tire molding die 1 provided with an annular tread molding part 20 divided into a plurality of segments 21 arranged side by side in the circumferential direction, the tire molding die comprising: a turning shaft 5 perpendicular to each of the movement direction of the segments 21 and the axial line of the tread molding part 20; a base member 6 supporting the segments 21 rotatably about the turning shaft 5; and an external force application mechanism 30 that, when the tread molding part 20 is opened, applies an external force to the segments 21 to turn the segments 21 in a direction in which the axially other ends of the segments 21 move radially outward about the turning shaft 5; and a tire production method using the die.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a tire molding mold and a tire manufacturing method. [Background technology]

[0002] Conventionally, as a tire molding mold used when manufacturing a tire by vulcanizing and molding an unvulcanized raw tire, there has been known a tire molding mold in which a circular tread molding portion (tread mold) that molds the tire tread is divided into a plurality of segments arranged in the circumferential direction, and each segment is configured to open and close by moving in the radial direction (for example, see Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2000-326332 A [Patent Document 2] JP 2000-334740 A [Patent Document 3] JP 2009-149079 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the above-mentioned conventional tire molding molds and tire manufacturing methods, when the tire is released from the tread molding section after vulcanization molding, each segment moves radially outward while maintaining its orientation relative to the tire tread. This causes the entire tread design surface that forms the tread of the segment to simultaneously peel off from the tread, resulting in a problem in that a large driving force is required to drive the segments in the initial stage of tire release.

[0005] The present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to provide a tire molding mold and a tire manufacturing method that can reduce the driving force required to drive the segments in the early stage of tire demolding. [Means for solving the problem]

[0006] The tire molding die of the present invention is a tire molding die having an annular tread molding section divided into a plurality of segments arranged in a circumferential direction, and used for vulcanizing and molding an unvulcanized raw tire into a tire, the tire molding die having a rotation shaft provided on one end side of the segment in the axial direction of the tread molding section, the rotation shaft being perpendicular to both the moving direction of the segment and the axis of the tread molding section, a base member supported by a guide rail and movable in a radial direction centered on the axis, and supporting the rotation shaft to support the segment so that it can rotate freely around the rotation shaft, and an external force imparting mechanism that imparts an external force to the segment when the tread molding section is opened, for rotating the segment in a direction in which the other end side of the segment in the axial direction moves radially outward around the rotation shaft, the external force imparting mechanism being A shaft body is fixed to the upper surface of the base member in a vertical position extending in the up-down direction, inserted into a hole formed in the segment, a flange portion is provided at the upper end of the shaft body and disposed in the hole, and the flange portion is disposed in a compressed state between the bottom wall of the hole and the bottom wall of the hole. A spring force is applied to the segment as an external force. It is a compression coil spring. Rotation spring member and The present invention is characterized in that it is equipped with:

[0008] In one embodiment, the tire molding mold of the present invention can be configured to include an outer ring that is disposed radially outward of the segments and is movable between a holding position that holds the segments in a specified position and a release position that allows the segments to rotate radially outward about the rotation axis.

[0009] In one embodiment, the tire molding die of the present invention has a guide rail that supports the base member so as to be freely movable in the radial direction of the tread molding portion, and a slide spring member that urges the base member toward the radially outward direction of the tread molding portion, and the segments can be configured to move radially outward while rotating about the rotation axis.

[0010] In one embodiment, the tire molding mold of the present invention can be configured such that, when the tread molding section is opened after the tire has been vulcanized and molded, the first segment rotates about the first pivot axis, and then the second segment rotates about the second pivot axis.

[0011] The tire manufacturing method of the present invention is a tire manufacturing method for manufacturing a tire by vulcanizing and molding an unvulcanized raw tire using a tire molding die having an annular tread molding portion divided into a plurality of segments arranged in a circumferential direction, and when the tread molding portion is opened after the tire has been vulcanized and molded, an external force is applied to the segment by an external force application mechanism, so that the tire is released from the tread molding portion while rotating the segment about a rotation axis provided on one end side of the segment in the axial direction of the tread molding portion, the rotation axis being perpendicular to both the moving direction of the segment and the axis of the tread molding portion, and the tire molding die is a tire molding die that is supported by guide rails and movable in a radial direction about the axis, and includes a base member that supports the segment so as to be rotatable about the rotation axis by supporting the rotation axis, and the external force application mechanism is A shaft body is fixed to the upper surface of the base member in a vertical position extending in the up-down direction, inserted into a hole formed in the segment, a flange portion is provided at the upper end of the shaft body and disposed in the hole, and the flange portion is disposed in a compressed state between the bottom wall of the hole and the bottom wall of the hole. A spring force is applied to the segment as an external force. It is a compression coil spring. Rotation spring member and The present invention is characterized in that the device is equipped with the following. Effect of the Invention

[0012] According to the present invention, it is possible to provide a tire molding die and a tire manufacturing method that are capable of reducing the driving force required to drive the segments in the initial stage of tire demolding. [Brief description of the drawings]

[0013] [Figure 1] 1 is a cross-sectional front view of a tire molding mold according to an embodiment of the present invention. FIG. [Diagram 2] 2 is a cross-sectional view of the tread molding portion shown in FIG. 1 in a plan view. [Diagram 3] FIG. 2 is an enlarged cross-sectional view of a main part of the tire molding die shown in FIG. 1 in detail. [Figure 4] 4 is an enlarged cross-sectional view of a main part of one segment shown in FIG. 3 in detail. FIG. [Diagram 5] FIG. 2 is a cross-sectional plan view showing a state of a main part of a tire molding die at the initial stage of tire release. [Figure 6] FIG. 6 is a cross-sectional plan view showing a state of a main part of the tire molding die when tire release has progressed further from the state shown in FIG. 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] A tire molding die and a tire manufacturing method according to an embodiment of the present invention will now be described in detail with reference to the drawings, in which the same reference numerals are used to designate common members and parts in the various drawings.

[0015] A tire molding mold 1 according to one embodiment of the present invention shown in FIG. 1 is used for manufacturing a tire 2 by molding a raw tire made mainly of unvulcanized (before vulcanization) synthetic rubber into a predetermined shape while vulcanizing it.

[0016] The tire 2 is a hollow tire made mainly of synthetic rubber, having a pair of sidewalls 2a, 2b and a tread 2c, and formed into a shape with a space therein that is filled with a gas such as air or nitrogen.

[0017] The tire molding die 1 includes a sidewall molding portion 10 and a tread molding portion 20 .

[0018] The sidewall molding portion 10 can be configured, for example, to include a circular lower sidewall molding portion 11 fixed to the upper surface of the lower container 3, and a circular upper sidewall molding portion 12 fixed to the lower surface of the upper container 4.

[0019] The sidewall molding section 10 can place (store) an annular tire 2 or raw tire between the lower sidewall molding section 11 and the upper sidewall molding section 12 in a position in which the central axis of the tire 2 or raw tire is coaxial with the central axis O of the sidewall molding section 10. The lower sidewall molding section 11 has an annular, upwardly facing lower sidewall design surface 11a centered on the central axis O, and the lower sidewall design surface 11a can mold the outer surface of one sidewall 2a of the tire 2 or raw tire (the side facing downward in FIG. 1). Similarly, the upper sidewall molding section 12 has an annular, downwardly facing upper sidewall design surface 12a centered on the central axis O, and the upper sidewall design surface 12a can mold the outer surface of the other sidewall 2b of the tire 2 or raw tire (the side facing upward in FIG. 1). The sidewall molding section 10 is opened by moving the upper container 4 relatively upward (in the direction in which the two move away from each other along the central axis of the tire 2) from the position shown in Fig. 1 with respect to the lower container 3, and the tire 2 is released from the sidewall molding section 10. Meanwhile, by moving the upper container 4 downward to the original position shown in Fig. 1, the sidewall molding section 10 is closed from the open state to a state in which the tire 2 or the raw tire can be molded.

[0020] The configuration of the sidewall molding portion 10 can be appropriately changed, for example, so that the lower container 3 moves downward relative to the upper container 4 to open the sidewall molding portion 10.

[0021] The tread molding portion 20 has an annular shape coaxial with the sidewall molding portion 10, and is disposed adjacent to the radially outer sides of the lower sidewall molding portion 11 and the upper sidewall molding portion 12. An inner peripheral surface of the tread molding portion 20 facing radially inward forms a tread design surface 20a that molds the outer peripheral surface of the tread 2c of the tire 2.

[0022] As shown in Fig. 2, the tread molding portion 20 is divided into a plurality of segments 21 arranged in the circumferential direction. Each of the segments 21 has an arc shape in a plan view, and is combined in the circumferential direction to constitute the tread molding portion 20 as a ring-shaped mold as a whole. In this embodiment, the tread molding portion 20 is divided into nine segments 21 having the same circumferential length. The number of divisions of the tread molding portion 20 in the circumferential direction is preferably 7 to 13, but is not limited to this and can be changed as appropriate.

[0023] As shown in FIG. 3, in this embodiment, each of the plurality of segments 21 constituting the tread molding portion 20 has a holder 22 and a design surface divided mold portion 23.

[0024] The holder 22 can be formed by cutting a block of metal such as low carbon steel.

[0025] The design surface divided mold part 23 is a part that constitutes the tread design surface 20a that molds the tread 2c of the tire 2, and is arc-shaped in a plan view, with the surface facing radially inward constituting a part that is divided in the circumferential direction of the tread design surface 20a. The design surface divided mold part 23 is disposed radially inside the corresponding holder 22 and is fixed to the holder 22 using a fixing member such as a bolt (not shown).

[0026] The design surface divided mold section 23 may be configured such that the tread design surface 20a is provided with a plurality of protrusions 24 that protrude radially from the tread design surface 20a toward the radially inward direction. The plurality of protrusions 24 are used to form grooves or sipes that form a tread pattern in the tread 2c of the tire 2 during vulcanization molding. The plurality of protrusions 24 may be of various shapes or large (length) sizes corresponding to the tread pattern, such as those that extend in the tire width direction or those that extend in the tire circumferential direction. Note that the tread design surface 20a may not be provided with the protrusions 24.

[0027] The design surface divided mold part 23 is preferably formed by casting a metal material with high thermal conductivity, such as an aluminum alloy. In this case, for example, a rib-shaped or blade-shaped protrusion 24 made of steel may be integrally formed with the design surface divided mold part 23 when the design surface divided mold part 23 is cast.

[0028] 3, each segment 21 is provided with a rotation shaft 5 at one end side in the axial direction of the tread molding portion 20 (the lower end side in the case shown in FIG. 3), the rotation shaft 5 being perpendicular to both the moving direction (radial direction) of the segment 21 and the axis of the tread molding portion 20. In this embodiment, the rotation shaft 5 is disposed at the lower end side portion of the holder 22.

[0029] An individual base member 6 corresponding to the segment 21 is disposed below each segment 21. The base member 6 supports the rotation shaft 5, thereby supporting the segment 21 so as to be rotatable about the rotation shaft 5. In other words, the segment 21 is rotatable about the rotation shaft 5 relative to the base member 6.

[0030] After the tire 2 is vulcanized with each segment 21 in a specified position, the tread molding section 20 can be opened so as to release the tread 2c from the tread design surface 20a by rotating each segment 21 radially outward from the specified position around the pivot axis 5.

[0031] In this embodiment, the base member 6 is supported by a guide rail 25 that is supported by the lower container 3 and the lower sidewall molding portion 11 and extends along the radial direction of the segment 21, and is capable of moving in the radial direction centered on the axis (central axis O) of the tread molding portion 20. In addition, slide spring members 26 are disposed between the base member 6 and the lower sidewall molding portion 11, and each segment 21 is biased radially outward by the corresponding slide spring member 26. When the base member 6 moves in the radial direction, the segment 21 supported thereby also moves in the radial direction together with the base member 6.

[0032] Between each segment 21 and the base member 6 corresponding to that segment 21, an external force imparting mechanism 30 is provided which imparts an external force to the segment 21 in a direction in which the upper end side of the segment 21 moves radially outward around the pivot axis 5 when the tread molding section 20 is opened after the tire 2 has been vulcanized and molded.

[0033] In this embodiment, the external force exerting mechanism 30 is configured to include a rotation spring member 31 that exerts a spring force as an external force on the segment 21 .

[0034] More specifically, as shown in Fig. 4, the external force imparting mechanism 30 includes a shaft 32 fixed to the upper surface of the base member 6 in a vertical position extending in the up-down direction. The shaft 32 is inserted into a hole 22a provided in a holder 22 constituting the segment 21, and a flange 33 provided at the upper end of the shaft 32 is disposed in the hole 22a. The rotation spring member 31 is a compression coil spring, and is disposed in a compressed state between the flange 33 and the bottom wall of the hole 22a. As a result, an external force is applied from the external force imparting mechanism 30 to the segment 21 in a direction in which the upper end side of the segment 21 moves radially outward around the rotation shaft 5.

[0035] As shown in Figures 1, 3, and 4, an outer ring 7 is disposed on the radial outside of each segment 21 in order to hold the segment 21 at a specified position against the external force applied by the external force application mechanism 30. The outer ring 7 is fixed to the upper container 4 via the upper sidewall molding part 12, and can move vertically relative to the segment 21 supported by the lower container 3 or the base member 6 together with the upper container 4. The specified position is a position where the segment 21 is in an attitude where the tread design surface 20a provided on the design surface division mold part 23 is continuously connected to the tread design surfaces 20a provided on the design surface division mold parts 23 of the other segments 21 along the circumferential direction.

[0036] The outer ring 7 has a tapered surface 7a on its inner peripheral surface facing inward in the radial direction, the tapered surface 7a being inclined so that the outer diameter gradually decreases toward the upper side. On the other hand, each segment 21 has a tapered surface 21a on its outer peripheral surface facing outward in the radial direction, the tapered surface 21a being inclined so that the outer diameter gradually decreases toward the upper side. In this embodiment, the tapered surface 21a is provided on the outer peripheral surface of the holder 22. When the outer ring 7 is in the holding position shown in Figs. 1 and 3, the tapered surface 7a abuts against the tapered surface 21a of the segment 21 to hold the segment 21 at a specified position. In addition, when the upper container 4 moves upward to open the tread molding section 20, the outer ring 7 can move together with the upper container 4 to a release position that is above the holding position.

[0037] The tire molding mold 1 is disposed inside the green tire and is provided with a bladder 8 that expands when pressurized steam is supplied thereto. The tire molding mold 1 also includes a heater (not shown) for heating the sidewall molding portion 10 and the tread molding portion 20. The heater can be installed at an appropriate location.

[0038] Next, a method for producing a tire 2 having a predetermined shape by vulcanizing a green tire using the tire molding mold 1 having the above-mentioned configuration, that is, a tire manufacturing method according to one embodiment of the present invention, will be described.

[0039] First, the sidewall molding section 10 and the tread molding section 20 are opened and a green tire is placed inside the tire molding die 1, and then the sidewall molding section 10 and the tread molding section 20 are closed.

[0040] Next, pressurized steam is supplied to the bladder 8 placed inside the green tire to expand the bladder 8, and both sidewalls of the green tire are pressed against the lower sidewall design surface 11a and the upper sidewall design surface 12a of the sidewall molding portion 10, respectively, and the tread is pressed against the tread design surface 20a of the tread molding portion 20. Then, in this state, the sidewall molding portion 10 and the tread molding portion 20 are heated by a heater, and the synthetic rubber that constitutes the green tire is vulcanized by the heat, and molded into a tire 2 of a predetermined shape.

[0041] After the molding of the tire 2 is completed, the sidewall molding section 10 and the tread molding section 20 are opened, and the molded tire 2 is taken out.

[0042] Here, after the tire 2 has been vulcanized and molded, in order to open the tread molding section 20, the outer ring 7 moves upward from the holding position to the release position with respect to each segment 21. As shown in FIG. 5, the segments 21 are permitted to rotate radially outward around the pivot axis 5, and the segments 21 are driven by an external force applied by the external force application mechanism 30 to spontaneously rotate (pan action) radially outward from a specified position around the pivot axis 5.

[0043] In this way, in the tire manufacturing method using the tire molding die 1 of the present embodiment, after the tire 2 is vulcanized and molded, when the tread molding section 20 is opened, the external force applying mechanism 30 applies an external force to the segment 21, so that the segment 21 can be rotated about the rotation shaft 5 provided at one end side (lower end side) of the segment 21 while releasing the tire 2 from the tread molding section 20. As a result, the tread 2c of the tire 2 is gradually released from one end side (upper end side in FIG. 5) of the design surface divided mold section 23 in the width direction of the tire 2 before the other end side (lower end side in FIG. 5), and outside air is gradually introduced between the tread 2c and the tread design surface 20a from the one end side, thereby reducing the release resistance of the tread 2c of the tire 2 from the tread design surface 20a in the early stage of the release of the tire 2. Therefore, at the initial stage of demolding of the tire 2, the force required to release the tread 2c of the tire 2 from the tread design surface 20a is reduced, and the tire 2 can be reliably released from the tread molding portion 20 by the external force applied by the external force application mechanism 30. Also, since the driving force applied to the segment 21 can be reduced when demolding the tire 2, the external force application mechanism 30 can be made smaller, and the manufacturing cost can be reduced. Furthermore, since the demolding resistance of the tread 2c of the tire 2 from the tread design surface 20a can be reduced, the occurrence of residual strain (permanent deformation) in the tire 2 after demolding can be suppressed, and the initial performance of the tire 2 can be improved.

[0044] Furthermore, when the tire 2 is released from the tread molding portion 20, each of the design surface divided mold portions 23 rotates about the rotation axis 5, thereby reducing the undercut resistance that the protrusions 24 generate against the tread 2c of the tire 2, and further reducing the driving force required to drive the segments 21 in the initial stage of releasing the tire 2. Furthermore, when the tire 2 is released from the tread molding portion 20, it is possible to prevent the undercut resistance from becoming excessively large, thereby preventing defects such as permanent deformation of the tread 2c of the tire 2 after molding and damage to the protrusions 24.

[0045] Furthermore, the tire molding die 1 of this embodiment has a guide rail 25 that supports the base member 6 so as to be freely movable in the radial direction of the tread molding portion 20, and a sliding spring member 26 that urges the base member 6 radially outward from the tread molding portion 20. When the outer ring 7 moves to the release position, as shown in FIG. 6, the segment 21 spontaneously rotates radially outward from a specified position about the pivot axis 5 due to the external force applied by the external force application mechanism 30, while being urged by the sliding spring member 26 to move radially outward together with the base member 6 along the guide rail 25. As a result, for example, in cases where the protrusion 24 on the tread design surface 20a has a high protruding height, such as when molding large tires used for construction vehicles, the undercut resistance that occurs when the protrusion 24 contacts the tread 2c of the tire 2 when the segment 21 is rotated around the pivot axis 5 can be reduced, and the segment 21 can be moved to a position where the protrusion 24 does not get in the way when the tire 2 is released from the mold, making it easier to release the tire 2 from the mold.

[0046] Furthermore, in the tire molding die 1 of this embodiment, the external force imparting mechanism 30 is configured to include a pivoting spring member 31 that imparts a spring force as an external force to the segment 21, thereby simplifying the configuration of the external force imparting mechanism 30 and further reducing the manufacturing costs of the tire 2.

[0047] In addition, the external force exerting mechanism 30 is not limited to a configuration including a pivoting spring member 31 that exerts a spring force as an external force on the segment 21, but can also be configured to exert an external force on the segment 21 by a driving source such as an air cylinder.

[0048] Furthermore, the tire molding mold 1 of this embodiment is configured with an outer ring 7 that is positioned radially outward of the segment 21 and is movable between a holding position that holds the segment 21 in a specified position and a release position that allows the segment 21 to rotate radially outward around the pivot axis 5, thereby simplifying the opening and closing mechanism of the segment 21 and further reducing the manufacturing costs of the tire 2.

[0049] The tire molding die 1 of this embodiment can be configured such that, when the tread molding section 20 is opened after the tire 2 is vulcanized, one segment (first segment) 21 of the plurality of segments 21 rotates radially outward around the rotation axis 5 (first rotation axis), and then another segment (second segment) 21 of the plurality of segments 21 rotates radially outward around the rotation axis (second rotation axis) 5. That is, the plurality of segments 21 can be configured to rotate in sequence with a time difference for each segment 21. In this case, after one segment 21 rotates radially outward around the rotation axis 5, the segment 21 adjacent to that segment 21 rotates radially outward around the rotation axis 5, and then the segment 21 adjacent to that segment 21 rotates radially outward around the rotation axis 5, so that the segments 21 rotate radially outward around the rotation axis 5 in sequence in the circumferential direction. With this configuration, in the early stage of demolding of the tire 2, the tread 2c is demolded in the circumferential direction from a portion of the tread design surface 20a, so that the tread 2c of the tire 2 can be demolded from the tread design surface 20a with a smaller driving force.

[0050] The present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made without departing from the spirit and scope of the present invention.

[0051] For example, in the above embodiment, a holder 22 is provided on each segment 21, the design surface divided mold part 23 is fixed to the holder 22, and the holder 22 is supported so as to be freely rotatable on the base member 6 by the pivot shaft 5; however, it is also possible to configure the design surface divided mold part 23 to be supported on the base member 6 by the pivot shaft 5 without providing the holder 22.

[0052] Also, the tread molding portion 20 may be configured so that the base member 6 cannot move in the radial direction, and the tread molding portion 20 is opened and closed only by the rotational movement of the segments 21 about the rotation shaft 5 . [Explanation of symbols]

[0053] 1: tire molding die, 2: tire, 2a: sidewall, 2b: sidewall, 2c: tread, 3: lower container, 4: upper container, 5: pivot, 6: base member, 7: outer ring, 7a: tapered surface, 8: bladder, 10: sidewall molding portion, 11: lower sidewall molding portion, 11a: lower sidewall design surface, 12: upper sidewall molding portion, 12a: upper sidewall design surface, 20: tread molding portion, 20a: tread design surface, 21: segment, 21a: tapered surface, 22: holder, 22a: hole portion, 23: design surface division die portion, 24: protrusion, 25: guide rail, 26: slide spring member, 30: external force imparting mechanism, 31: pivot spring member, 32: shaft body, 33: flange portion

Claims

1. A tire molding die for vulcanizing and molding an unvulcanized raw tire into a tire, the tire molding die comprising an annular tread molding portion divided into a plurality of segments arranged in a circumferential direction, a rotation axis provided on one end side of the segment in a direction of an axis of the tread molding portion, the rotation axis being perpendicular to both the moving direction of the segment and the axis of the tread molding portion; a base member supported by a guide rail and movable in a radial direction around the axis line, and supporting the rotation shaft to support the segment so as to be rotatable around the rotation shaft; an external force applying mechanism that applies an external force to the segment in a direction in which the other end side of the segment in the axial direction moves radially outward around the pivot shaft when the tread molding portion is opened, a tire molding mold, characterized in that the external force imparting mechanism comprises: a shaft fixed to the upper surface of the base member in a vertical position extending in the up-down direction, and inserted into a hole formed in the segment; a flange provided at the upper end of the shaft and positioned in the hole; and a rotation spring member which is a compression coil spring positioned in a compressed state between the flange and a bottom wall of the hole to impart a spring force as an external force to the segment.

2. 2. The tire molding mold according to claim 1, further comprising an outer ring disposed radially outward of the segments and movable between a holding position in which the segments are held in a specified position and a release position in which the segments are allowed to rotate radially outward about the rotation axis.

3. a guide rail that supports the base member so as to be movable in a radial direction of the tread molding portion; a slide spring member that biases the base member toward the radially outer side of the tread molding portion, 3. The tire mold according to claim 1, wherein the segments are configured to move radially outward while rotating about the rotation axis.

4. 4. The tire molding mold according to claim 1, wherein, when the tread molding section is opened after the tire has been vulcanized and molded, the first segment rotates about the first rotation axis, and then the second segment rotates about the second rotation axis.

5. A tire manufacturing method for manufacturing a tire by vulcanizing and molding an unvulcanized raw tire using a tire molding die having an annular tread molding portion divided into a plurality of segments arranged in a circumferential direction, comprising the steps of: When the tread molding section is opened after the tire is vulcanized and molded, an external force is applied to the segment by an external force application mechanism, whereby the tire is released from the tread molding section while rotating the segment about a rotation axis provided on one end side of the segment in the axial direction of the tread molding section, the rotation axis being perpendicular to both the moving direction of the segment and the axis of the tread molding section; a tire molding die including a base member supported by guide rails and movable in a radial direction around the axis, and supporting the pivot shaft to support the segments so that they can rotate freely around the pivot shaft; and an external force applying mechanism including a shaft fixed to the upper surface of the base member in a vertical position extending in the up-down direction and inserted into a hole formed in the segment, a flange provided at the upper end of the shaft and positioned in the hole, and a rotation spring member which is a compression coil spring positioned in a compressed state between the flange and a bottom wall of the hole to apply a spring force as an external force to the segment.

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