JP2023088030A - Low cover molding apparatus and tire manufacturing method - Google Patents

Abstract

To reduce low cover defect.SOLUTION: A low cover molding apparatus 1 disclosed herein includes: a pair of drums 10 provided axially apart; a bead holding part 30 provided on each of the pair of drums 10; a turn-up bladder 40 arranged axially outside a cylindrical part 50 relative to the bead holding part 30 of the pair of drums 10; and a gap adjusting mechanism 20 for adjusting an axial gap between the pair of drums 10. The turn-up bladder 40 is configured to fold back an axially outer part 50b of the cylindrical part 50 beyond a bead 54 so as to wrap around the bead 54 by bulging outward from the axial bead holding part 30 of the cylindrical part 50. The turn-up bladder 40 has an uneven surface at least in part of a portion of the cylindrical part 50 that hits an axially outer part 50b rather than the bead 54.SELECTED DRAWING: Figure 2

Description

TECHNICAL FIELD The present disclosure relates to a raw cover forming apparatus and a tire manufacturing method.

Japanese Patent Laying-Open No. 2018-114646 discloses a molding device for molding a low cover. A raw cover is a tire before vulcanization, and a tire is manufactured by being vulcanized in a mold. The raw cover is formed by folding back the end of a cylindrical part containing a rubber sheet with a turn-up bladder. The molding apparatus disclosed in the publication includes a shaping drum that supports a cylindrical part from the inside, and a pair of turn-up bladders that expand when filled with gas. The shaping drum has a pair of work drums. These work drums are spaced apart axially. Each work drum has a hold ring that holds a bead, a grip plate that secures the end of the turn-up bladder, and a support cylinder that extends axially outward from the grip plate and supports the turn-up bladder before expansion. and The turn-up bladder has a projection projecting radially outward while being supported by the support cylinder. When the bead is fitted to the cylindrical part and held by the hold ring, when the turn-up bladder is expanded, the projection presses the tip of the bead from the outside of the cylindrical part. Such a forming apparatus is said to prevent the formation of air pockets at the tip portion of the bead, thereby improving the quality of the tire.

JP 2018-114646 A

By the way, in the study of the low cover forming apparatus, the present inventor found a phenomenon that the cylindrical parts of the low cover adhere to the low cover forming apparatus during forming, thereby causing defects in the low cover. Therefore, the present inventor wishes to reduce the occurrence of such low cover defects.

The raw cover molding apparatus disclosed herein is provided at axially separated positions, and cylindrical parts forming the inner layer of the raw cover including the inner liner, carcass ply and sidewall rubber are formed along the outer peripheral surface. and a pair of drums provided on each of the pair of drums, respectively, and held at predetermined positions inside the cylindrical parts from both ends in the axial direction. turn-up bladders arranged axially outside the cylindrical parts relative to the bead holding portions of the pair of drums; and a gap adjusting mechanism for adjusting the axial gap between the pair of drums. there is The turn-up bladder expands outside the bead holding portion in the axial direction of the cylindrical part, thereby folding back the portion of the cylindrical part axially outside the bead so as to involve the bead. The turn-up bladder has unevenness on at least a part of the surface of the portion of the cylindrical part that is axially outside the bead.
According to the raw cover molding apparatus having such a configuration, defects in the raw cover are reduced.

FIG. 1 is a cross-sectional view of a raw cover forming apparatus 1. FIG. FIG. 2 is a cross-sectional view of the raw cover forming apparatus 1. As shown in FIG. FIG. 3 is a plan view of the turn-up bladder 40. FIG. FIG. 4 is a cross-sectional view of turn-up bladder 40. As shown in FIG. FIG. 5 is a plan view of the turn-up bladder 40A. FIG. 6 is a cross-sectional view of turn-up bladder 40A.

An embodiment of the present disclosure will be described below based on the drawings. Note that the present disclosure is not limited to the following embodiments. Each drawing is schematically drawn and does not necessarily reflect the real thing. Each drawing only shows an example and does not limit the present disclosure unless otherwise specified. Further, members and portions that perform the same functions are given the same reference numerals as appropriate, and overlapping descriptions are omitted.

1 and 2 are sectional views of the raw cover forming apparatus 1. FIG. FIG. 1 shows a state in which a cylindrical part 50 is attached to the raw cover forming apparatus 1 before the raw cover is formed. FIG. 2 shows a state in which the turn-up bladder 40 is inflated and the cylindrical part 50 is folded back. 2, hatching of the turn-up bladder 40, the cylindrical part 50, and the low cover 60 is omitted. In FIG. 2, the drum 10 and the structure of the bead holding portion 30 provided on the drum 10 are integrally shown.

<Low cover 60>
A raw cover is an unvulcanized tire before vulcanization molding, and is also called a raw tire. A raw cover is a cylindrical member in which an unvulcanized sidewall rubber or tread rubber is bonded to a base material such as a bead or carcass ply. The raw cover 60 includes a pair of bead portions 61, a pair of sidewall portions 62, and a tread portion 63, as shown in FIG. The bead portions 61 are formed on both peripheral edge portions of the low cover 60 . The sidewall portion 62 is formed radially outward from the bead portion 61 . The radially outer end of the sidewall portion 62 is also referred to as a shoulder portion 62a. The tread portion 63 is formed so as to connect the sidewall portions 62 . The inner surface of the raw cover includes, for example, an inner liner 51 and a carcass ply 52 .

When molding the raw cover 60, a cylindrical part 50 including an inner liner 51, a carcass ply 52, and sidewall rubbers 53 is prepared. The cylindrical part 50 is a cylindrical member forming the inner layer of the raw cover. The inner liner 51 constitutes the inner surface of the cylindrical part 50 . A carcass ply 52 is arranged outside the inner liner 51 . The carcass ply 52 is formed axially longer than the inner liner 51 . The sidewall rubber 53 constitutes both axial ends of the cylindrical part 50 . The sidewall rubber 53 partially overlaps the end of the carcass ply 52 .

A bead 54 is attached to the cylindrical part 50 when the raw cover 60 is molded. The cylindrical part 50 is inserted through a cylindrical tread member 55 . When the raw cover 60 is molded, a tread member 55 including a tread rubber and a belt is press-fitted to the central portion 50 a of the cylindrical part 50 on the inner side in the axial direction.

When the raw cover 60 is molded, the outer portion 50b of the cylindrical part 50 that is axially outside the bead 54 is rolled up with the bead 54 as a starting point. At the same time, the cylindrical part 50 is inflated from the inside and pressed against the tread portion from the inside. Thus, the raw cover is molded. A raw cover forming apparatus 1 for forming such a raw cover will be described below.

<Low cover molding device 1>
The raw cover forming apparatus 1 forms the raw cover 60 described above. As shown in FIG. 1 , the raw cover forming apparatus 1 includes a pair of drums 10 , a gap adjusting mechanism 20 , a bead holding section 30 and a turn-up bladder 40 .

<Drum 10>
The drum 10 supports the cylindrical part 50 from inside. A sheet-like inner liner, a carcass ply, and a pair of sidewall portions are wound around the drum 10 . For example, an inner liner is wrapped around the drum 10 to form a cylindrical inner liner. Next, a carcass ply is wound around the outer surface of the inner liner to form a cylindrical carcass ply on the outside of the cylindrical inner liner. Axially outward from the ends of the cylindrical inner liner and carcass ply, the drum 10 is wrapped with sidewalls to form a pair of cylindrical sidewalls. Thereby, cylindrical parts 50 are formed along the outer peripheral surfaces of the pair of drums. The pair of drums 10 are provided at axially separated positions.

The drum 10 has a body 11 , a grip plate 13 , a support cylinder 14 and a guide plate 15 . A bead holding portion 30 is provided on the drum 10 . The body portion 11 has a cylindrical shape. Body 11 supports various configurations of drum 10 . A screw shaft 21 , which will be described later, is inserted through the trunk portion 11 . A pair of drums 10 are connected to the same screw shaft 21 through the body portion 11 .

A grip plate 13 and a guide plate 15 are attached to the outer peripheral surface of the body portion 11 . In the axial direction of the barrel 11, the grip plate 13 is attached to the outside and the guide plate 15 is attached to the inside. The grip plate 13 and the guide plate 15 are each formed in a substantially disc shape. A cylindrical support cylinder 14 extends axially outward from the radially outer end of the grip plate 13 . A space is formed on the radially inner side of the guide plate 15 on the axially outer side. The grip plate 13 and the guide plate 15 are attached with a gap in the axial direction. A bead holding portion 30 is provided between the grip plate 13 and the guide plate 15 .

<Bead holding portion 30>
The bead holding portion 30 is a portion that holds the bead 54 via the cylindrical part 50 . When the cylindrical part 50 is set on the drum 10 , the beads 54 are conveyed inward from both axial ends of the cylindrical part 50 . The beads 54 are attached to predetermined positions of the cylindrical part 50 . The bead holding portions 30 are provided on each of the pair of drums 10 . The bead retainer 30 has a piston ring 31 and a lock segment 32 . The lock segment 32 is a ring-shaped member. The lock segment 32 is pressed against the inner peripheral surface of the cylindrical part 50 by expanding radially outward. A part of the outer peripheral surface of the lock segment 32 is pressed against the position where the bead 54 of the cylindrical part 50 is mounted. The lock segment 32 is provided with an elastic ring 32a at a portion pressed against the position.

The lock segment 32 has an inclined surface 32b on its axially inner side. The inclined surface 32b is formed radially outward from the inner side. A piston ring 31 is provided between the inclined surface 32 b of the lock segment 32 and the space formed inside the guide plate 15 . The piston ring 31 is formed in an annular shape. The piston ring 31 is provided axially outwardly with an inclined surface 31 a corresponding to the inclined surface 32 b of the lock segment 32 . The piston ring 31 is configured to be axially driven by a driving device (not shown). When the piston ring 31 is driven axially outward, the slanted surface 32b of the lock segment 32 slides against the slanted surface 31a of the piston ring 31 . Lock segment 32 moves radially outward. As a result, the bead holding portion 30 is pressed against the cylindrical part 50 to hold the bead 54 .

<Gap adjustment mechanism 20>
The gap adjusting mechanism 20 adjusts the gap between the pair of drums 10 in the axial direction. When molding the raw cover 60 , the gap adjusting mechanism 20 expands the cylindrical part 50 radially outward while narrowing the gap between the pair of drums 10 . In this embodiment, the gap adjusting mechanism 20 is composed of a screw shaft 21, a screw hole 22 formed in the body portion 11, and a motor 23. As shown in FIG. The screw shaft 21 is provided with a male thread on its outer peripheral surface. Both ends of the screw shaft 21 are supported by bearings 24 . A motor 23 is connected to one end of the screw shaft 21 . The screw shaft 21 is inserted through the cylindrical body portion 11 . A threaded hole 22 through which a threaded shaft 21 is inserted is formed in the body 11 . The screw hole 22 penetrates the body portion 11 in the axial direction. A female thread corresponding to the outer peripheral surface of the screw shaft 21 is formed in the screw hole 22 . The threaded hole 22 and the threaded shaft 21 are engaged.

The screw shaft 21 is rotated by a motor 23 connected to one end. The barrel portion 11 is configured to move in the axial direction of the screw shaft 21 in conjunction with the rotation of the screw shaft 21 by engaging the screw hole 22 with the screw shaft 21 . In this embodiment, the male threads of the screw shaft 21 are oppositely wound on one side of the body section 11 and on the other side of the body section 11 . Therefore, by changing the direction of rotation of the motor 23, the interval between the drums 10 can be widened or narrowed.

<Turn-up bladder 40>
The turn-up bladder 40 is a member for folding back the end of the cylindrical part 50 when molding the raw cover. The turn-up bladder 40 is arranged axially outside the bead holding portion 30 . The turn-up bladder 40 is made of rubber and formed in a tubular shape that continues in the circumferential direction of the grip plate 13 . The turn-up bladder 40 is supported by a support portion 13 a provided on the outer peripheral surface of the grip plate 13 . The support portion 13 a is continuously provided in the circumferential direction of the grip plate 13 . The support portions 13a are provided on the inner and outer sides of the cylindrical part 50 in the axial direction, and support the inner and outer ends of the turn-up bladder 40, respectively. A hole (not shown) is formed in the grip plate 13 between the inner and outer pointing portions 13a. It is configured such that the inside can be filled with gas through the hole. Before being filled with gas, the turn-up bladder 40 is folded and tilted outward in the axial direction. The turn-up bladder 40 before being filled with gas is arranged on the outer peripheral surface of the support cylinder 14 (see FIG. 1). A cylindrical tread member 55 is set radially outwardly of the cylindrical part 50 when molding the raw cover. Although illustration is omitted here, the inner diameter of the tread member 55 set here is larger than the outer diameter of the cylindrical part 50, and a required gap is formed between the cylindrical part 50 and the tread member 55. .

At least a part of the surface of the cylindrical part 50 of the turn-up bladder 40 that contacts the outer portion (outer portion 50b) of the bead 54 in the axial direction has unevenness. In this embodiment, the surface of the portion of the turn-up bladder 40 that contacts the outer portion 50b of the cylindrical part 50 has a plurality of recesses.

A plurality of depressions formed on the surface of the turn-up bladder 40 are formed by a surface layer 41 having an uneven shape. In this embodiment, a sheet forming the surface layer 41 is attached to the turn-up bladder 40 . The surface layer 41 is provided at a portion of the cylindrical part 50 that is axially outside the bead 54 (outer portion 50 b ). The surface layer 41 is formed on part of the surface of the bladder rubber 40a. As shown in FIG. 1, the surface layer 41 is provided on the radially outer surface when the turn-up bladder 40 is folded. The surface layer 41 is made of rubber. Surface layer 41 follows the expansion and contraction of turn-up bladder 40 .

FIG. 3 is a plan view of the turn-up bladder 40. FIG. FIG. 4 is a cross-sectional view of turn-up bladder 40. As shown in FIG. FIG. 4 shows a cross section along the direction in which the holes 41a of the surface layer 41 are arranged. As shown in FIGS. 3 and 4, the sheet forming the surface layer 41 is formed with a plurality of holes 41a. The hole 41 a penetrates the surface layer 41 . The turn-up bladder 40 has unevenness formed by the surface layer 41 and the holes 41 a of the surface layer 41 . Although not particularly limited, in this embodiment, the hole 41a has a circular shape with a diameter of 5 mm. The holes 41a are formed at regular intervals in a first direction and in a second direction orthogonal to the first direction. In this embodiment, the interval between holes 41a is set to 10 mm.

Although not particularly limited, in this embodiment, the thickness of the surface layer 41 is equal to or less than the thickness of the bladder rubber 40a. Therefore, the flexibility of the portion of the turn-up bladder 40 where the surface layer 41 is provided is less likely to decrease. As a result, variations in the pressure with which the surface layer 41 is pressed against the outer portion 50b of the cylindrical part 50 can be reduced.

In this embodiment, as shown in FIG. 2, the turn-up bladder 40 is filled with gas while the gap between the drums 10 is narrowed by the gap adjusting mechanism 20 . As a result, the cylindrical part 50 flexes in the radial direction with respect to the drum 10 , and the turn-up bladder 40 swells outside the bead holding portion 30 in the axial direction of the cylindrical part 50 . At this time, the tread member 55 presses the central portion 50 a of the cylindrical part 50 that bends in the radial direction with respect to the drum 10 . Further, when the turn-up bladder 40 expands, the outer portion 50b of the cylindrical part 50 is folded back so as to involve the bead 54, and is pressed against the central portion 50a of the cylindrical part 50 that is bent in the outer diameter direction with respect to the drum 10. be done. As a result, the outer portion 50b (mainly the sidewall rubber 53 in this embodiment) of the cylindrical part 50 is pressed against a portion of the central portion 50a. Thereby, the low cover 60 is molded.

In this embodiment, a pressing member 16 is provided to press the inflated turn-up bladder 40 from the outside in the axial direction. The pressing members 16 are provided on both sides in the axial direction. The pressing member 16 has a disk-shaped pressing surface that contacts the turn-up bladder 40 . When the turn-up bladder 40 is inflated, the pressing member 16 moves inward from both axial ends to press the turn-up bladder 40 against the cylindrical part 50 . The action by which the outer portion 50b of the cylindrical part 50 is folded back is appropriately referred to as "turn-up".

By the way, since the surface of the cylindrical part 50 is composed of a rubber sheet before vulcanization, it may be highly adhesive. The turn-up bladder 40 is also made of rubber. Therefore, when the turn-up bladder 40 is pressed against the cylindrical part 50 during molding, the turn-up bladder 40 and the cylindrical part 50 may adhere. According to the findings of the present inventor, for example, when the outer portion 50b of the cylindrical part 50 is thin, when the turn-up bladder 40 is contracted after molding, part of the cylindrical part 50 remains attached to the turn-up bladder 40. sell. As a result, there is a concern that a defect such as part of the low cover 60 being peeled off or cut may occur. Such defects are likely to occur particularly at the shoulder portion 62a (end portion of the cylindrical part 50) of the low cover 60 where the thickness is reduced. In addition, regardless of the thickness of the cylindrical part 50, there is a concern that air may enter between the turn-up bladder 40 and the cylindrical part 50, and the side wall portion 62 of the molded low cover 60 may be roughened. Due to the high adhesion strength between the turn-up bladder 40 and the cylindrical part 50, there is a concern that the molded low cover 60 may be defective. Defects in the raw cover 60 can affect the appearance quality of the tire after vulcanization molding.

In the above-described embodiment, the turn-up bladder 40 has irregularities in the portion of the cylindrical part 50 that contacts the portion (outer portion 50b) axially outside the bead 54 . Therefore, the contact area between the turn-up bladder 40 and the cylindrical part 50 is reduced. As a result, even when the turn-up bladder 40 is pressed against the cylindrical part 50, the turn-up bladder 40 and the cylindrical part 50 are less likely to come into excessive contact. As a result, the occurrence of defects in the low cover 60 due to the adhesion of the cylindrical part 50 to the turn-up bladder 40 is suppressed.

In the above-described embodiment, the sheet forming the surface layer 41 is attached to the portion of the turn-up bladder 40 that is axially outside the bead 54 of the cylindrical part 50 (the outer portion 50b). With this configuration, the strength of the portion of the turn-up bladder 40 that contacts the outer portion 50b is improved, and the outer portion 50b is strongly suppressed. As a result, turn-up failure due to poor adhesion is less likely to occur.

In the embodiment described above, the sheet is formed with a plurality of holes 41a. With such a configuration, the turn-up bladder 40 is easily inflated and easily conforms to the shape of the cylindrical part 50 . This makes it easy to stably mold the low cover 60 while suppressing the occurrence of defects.

Note that the configuration of the turn-up bladder is not limited to such a form as long as the surface of the turn-up bladder that contacts the outer portion 50b is formed with an uneven shape. FIG. 5 is a plan view of the turn-up bladder 40A. FIG. 6 is a cross-sectional view of turn-up bladder 40A. FIG. 6 shows a cross section across the ridge 42 of the turnup bladder 40A. As shown in FIGS. 5 and 6, a plurality of ridges 42 are formed on the turn-up bladder 40A. The ridge 42 is formed on the surface of the portion of the turn-up bladder 40</b>A that contacts the outer portion 50 b of the cylindrical part 50 . In this embodiment, the ridge 42 protrudes from the outer surface 40A1 of the turnup bladder 40A. Although not particularly limited, in this embodiment, the ridges 42 are elongated with a height of 2 mm and a width of 1 mm. The multiple ridges 42 extend in the same direction. The direction in which the protrusion 42 extends is not particularly limited. The ridge 42 may extend along the axial direction of the cylindrical part 50 or may be inclined with respect to the axial direction. The interval between the plurality of protrusions 42 is set to 10 mm. Even when such a turn-up bladder 40A is used, the contact area between the turn-up bladder 40A and the cylindrical part 50 is reduced. As a result, the occurrence of defects in the low cover 60 is suppressed. In addition, the form of the protrusion 42 is not limited to the form mentioned above. For example, the turn-up bladder 40A may have multiple ridges 42 extending in different directions. The ridges 42 extending in different directions may intersect.

Further, the turn-up bladder may have a fine uneven surface. A portion of the turn-up bladder 40 that contacts the outer portion 50b may have a rougher surface than other portions. Although not particularly limited, for example, the surface of the turn-up bladder 40A may be textured. The contact area between the turn-up bladder 40 and the cylindrical part 50 is reduced by roughening the surface of the portion that contacts the outer portion 50b in at least a portion of the portion that contacts the outer portion 50b. As a result, the occurrence of defects in the low cover 60 is suppressed.

Various descriptions have been made above regarding the raw cover molding apparatus disclosed herein. However, the raw cover forming apparatus disclosed herein is not limited to the above-described embodiments and modifications unless otherwise specified. In addition, various configurations of the embodiments and modified examples can be appropriately combined as long as they do not hinder each other. This specification includes the following disclosure, which is not limited to the embodiments described above. For example, the irregularities on the surface of the turn-up bladder are not limited to those formed by the above-described dents, ridges, and roughening of the surface. The unevenness on the surface of the turn-up bladder may be formed, for example, in the shape of projections. The side surfaces of the unevenness may be curved or flat. The irregularities on the surface of the turn-up bladder may be formed over the entire portion that is brought into contact with the outer portion of the cylindrical part, or may be formed partially. In addition, unevenness may be formed on the portion of the turn-up bladder that is not brought into contact with the outer portion of the cylindrical part.

The present disclosure (1) is a pair of cylindrical parts that are provided axially apart and that form an inner layer of a low cover including an inner liner, a carcass ply, and a sidewall rubber along the outer peripheral surface. a drum and
A bead that is provided on each of the pair of drums and is attached at a predetermined position inside from both ends in the axial direction of the cylindrical part so that the inner peripheral surface of the cylindrical part is pressed against the bead to hold the bead. a holding part;
turn-up bladders arranged axially outside the cylindrical parts relative to the bead holding portions of the pair of drums;
A gap adjusting mechanism for adjusting the gap in the axial direction of the pair of drums,
The turn-up bladder expands outside the bead holding portion in the axial direction of the cylindrical part, so that the portion of the cylindrical part axially outside the bead is folded back so as to involve the bead. is composed of
The turn-up bladder is a raw cover molding apparatus having unevenness on at least a part of the surface of a portion of the cylindrical part that contacts the axially outer portion of the bead.

The present disclosure (2) is the raw cover molding apparatus according to the present disclosure (1). In the present disclosure (2), the surface of the portion of the turn-up bladder that contacts the portion axially outside the bead of the cylindrical part has a plurality of recesses.

The present disclosure (3) is the raw cover forming apparatus according to the present disclosure (1). In the present disclosure (3), the surface of the portion of the turn-up bladder that contacts the portion axially outside the bead of the cylindrical part is provided with a plurality of raised ridges.

The present disclosure (4) is the raw cover molding apparatus according to the present disclosure (1). In the present disclosure (4), at least part of the surface of the portion of the turn-up bladder that contacts the portion of the cylindrical part axially outside the bead is rougher than the other portion.

This disclosure (5) is a raw cover molding apparatus in any combination with any of this disclosure (1)-(4). In the present disclosure (5), a sheet forming a surface layer is adhered to a portion of the turn-up bladder that is axially outside the bead of the cylindrical part.

The present disclosure (6) is the raw cover forming apparatus according to the present disclosure (5). In the present disclosure (6), the sheet is formed with a plurality of holes.

The present disclosure (7) is a method for manufacturing a tire, in which a raw cover forming an inner layer of the raw cover is formed using the raw cover molding apparatus described in any one of the present disclosure (1) to (6). is.

1 Raw cover forming device 10 Drum 11 Body portion 13 Grip plate 13a Support portion 14 Support cylinder 15 Guide plate 16 Pressing member 20 Spacing adjustment mechanism 21 Screw shaft 22 Screw hole 23 Motor 24 Bearing 30 Bead holding portion 31 Piston ring 31a Inclined surface 32 Lock Segment 32a Elastic ring 31b Inclined surface 40, 40A Turn-up bladder 40a Bladder rubber 41 Surface layer 41a Hole 42 Ridge 50 Cylindrical part 50a Central part 50b Outer part 51 Inner liner 52 Carcass ply 53 Side wall rubber 54 Bead 55 Tread member 60 Low cover 61 Bead portion 62 Sidewall portion 62a Shoulder portion 63 Tread portion

Claims (7)

a pair of drums, which are provided axially apart from each other and have cylindrical parts formed along the outer peripheral surface thereof, which constitute the inner layer of the raw cover including the inner liner, the carcass ply, and the sidewall rubber;
A bead that is provided on each of the pair of drums and is attached at a predetermined position inside from both ends in the axial direction of the cylindrical part so that the inner peripheral surface of the cylindrical part is pressed against the bead to hold the bead. a holding part;
turn-up bladders arranged axially outside the cylindrical parts relative to the bead holding portions of the pair of drums;
A gap adjusting mechanism for adjusting the gap in the axial direction of the pair of drums,
The turn-up bladder expands outside the bead holding portion in the axial direction of the cylindrical part, so that the portion of the cylindrical part axially outside the bead is folded back so as to involve the bead. is composed of
The turn-up bladder has irregularities on at least part of a surface of a portion of the cylindrical part which is axially outward of the bead. 2. The raw cover molding apparatus according to claim 1, wherein a surface of a portion of said turn-up bladder that contacts a portion of said cylindrical part axially outside said bead has a plurality of recesses. 2. The raw cover molding apparatus according to claim 1, wherein a surface of a portion of said turn-up bladder that contacts a portion of said cylindrical part axially outside said bead is provided with a plurality of raised ridges. 2. The raw cover forming apparatus according to claim 1, wherein at least a portion of the surface of the portion of the turn-up bladder that contacts the portion of the cylindrical part axially outside the bead is rougher than the other portion. . 5. The sheet according to any one of claims 1 to 4, wherein a sheet forming a surface layer is attached to a portion of the turn-up bladder that is axially outside the bead of the cylindrical part. Raw cover molding apparatus as described. 6. The raw cover forming apparatus according to claim 5, wherein said sheet has a plurality of holes formed therein. A tire manufacturing method comprising molding a raw cover forming an inner layer of the raw cover using the raw cover molding apparatus according to any one of claims 1 to 6.

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