JP2019077108A - Tire manufacturing method - Google Patents

Abstract

To provide a bladder free of burrs on its molding surface and a method of manufacturing a tire using this bladder.SOLUTION: A method of manufacturing a tire includes a low cover charging process in which a low cover is inserted into a tire mold, and a low cover pressing and heating process in which the low cover is pressurized and heated by the tire mold and a bladder. The bladder 69 has a molding surface 82 that abuts on the low cover and on which a burr 80 is not formed. The burr 80 is formed on a back surface 84. A method of manufacturing the bladder 69 includes a bladder forming process in which the bladder 69 is formed from a slab, and a reverse process in which an outer peripheral surface 76 of the bladder 69 is formed to an inner peripheral surface, and an inner peripheral surface 78 of the bladder 69 is formed to an outer peripheral surface.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a method of manufacturing a tire.

  JP 2008-12751 A discloses a bladder and a method of manufacturing a tire using the bladder. The tire is obtained by vulcanizing an unvulcanized low cover in a mold in a vulcanization step. In this vulcanization process, the raw cover is pressed and heated between the molding surface of the bladder and the cavity surface of the mold. This pressurization and heating produces a tire from the low cover. The surface of the tire is molded by the molding surface of the bladder and the cavity surface of the mold.

  The bladder is molded using a bladder mold. In molding with this bladder mold, burrs are generated on the molding surface of the bladder. The burrs are removed after molding. Man-hours occur for this removal process. Also. The burr removal process may damage the molding surface of the bladder. JP-A-2016-37034 discloses a method of manufacturing a bladder in which the occurrence of burrs is reduced. According to the method of manufacturing the bladder, the number of steps for removing burrs is reduced. Damage to the molding surface of the bladder can be suppressed.

JP, 2008-12751, A JP, 2016-37034, A

  However, the above-described bladder manufacturing method can not completely eliminate the burr removal process. Even with this manufacturing method, man-hours for removing the burrs occur. In addition, this burr removal process may cause the durability of the bladder to be impaired.

  An object of the present invention is to provide a bladder free of burrs on its molding surface and a method of manufacturing a tire using the bladder.

  The method for manufacturing a tire according to the present invention comprises a low cover loading step of loading a low cover into a tire mold, and a low cover pressing and heating step of pressing and heating the low cover by the tire mold and the bladder. The bladder includes a molding surface that abuts on the low cover and does not form a burr.

  In this tire manufacturing method, the bladder is formed by extruding a slab from the cavity surface forming the forming outer peripheral surface of the bladder into the cavity. Preferably, the molding inner peripheral surface behind the molding outer peripheral surface is the molding surface, and the molding outer peripheral surface is the rear surface of the molding surface.

The method of manufacturing a bladder according to the present invention is
A bladder forming process in which a slab is pressurized and heated by a bladder mold, and a bladder is formed from the slab;
And the front and back turning step in which the molding outer peripheral surface of the bladder is an inner peripheral surface and the molding inner peripheral surface of the bladder is an outer peripheral surface.
By this method, a bladder is obtained which is used in a vulcanization step of molding a tire from a low cover.

  Preferably, the bladder mold includes an upper mold and a lower mold for molding the outer peripheral surface, and a core for molding the inner peripheral surface. The core is provided with a core molding surface for molding the molding inner circumferential surface. A vent line forming portion is formed on the core molding surface.

  Preferably, the vent line forming portion may extend obliquely with respect to the equatorial plane of the core. The angle θ between the vent line forming portion and the equatorial plane is 55 ° or more and 65 ° or less.

  Preferably, the temperature of the bladder is set to 80 ° C. or more in the front and back turning step.

  Preferably, in the bladder molding step, the temperature of the bladder is higher than 80 ° C. The turn over step is performed before the temperature of the bladder drops below 80 ° C. from the temperature in the bladder molding step.

  In the tire manufacturing method according to the present invention, the bladder has burrs formed on the back surface, and no burrs are formed on the molding surface. The molding surface of the bladder abuts against the low cover to cure the tire. The bladder according to the present invention does not require burr removal processing. This bladder does not impair the durability of the bladder due to the removal of burrs.

FIG. 1 is a cross-sectional view of a portion of a bladder manufacturing apparatus according to an embodiment of the present invention. FIG. 2 is a development of the core molding surface of the bladder manufacturing apparatus of FIG. 3 (a) is an explanatory view showing a use state of the bladder manufacturing apparatus of FIG. 1, and FIG. 3 (b) is an explanatory view showing another use state of the bladder manufacturing apparatus of FIG. FIG. 4 is an explanatory view showing still another use state of the bladder manufacturing apparatus of FIG. 5 (a) is an explanatory view showing still another use condition of the bladder manufacturing apparatus of FIG. 1, and FIG. 5 (b) is an explanation showing still another use condition of the bladder manufacturing apparatus of FIG. FIG. 6 (a) is an explanatory view of a method of manufacturing a bladder using the bladder manufacturing apparatus of FIG. 1, and FIG. 6 (b) is another explanatory view of a method of manufacturing a bladder using the bladder manufacturing apparatus of FIG. is there.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the drawings as appropriate.

  A bladder manufacturing device 2 is shown in FIG. The bladder manufacturing apparatus 2 includes a mold 9 including an upper mold 4, a lower mold 6 and a core 8, an upper core lifting unit 10, a lower core lifting unit 12, a base member 14, and a lower mold lifting unit 16. Is equipped. The left-right direction in FIG. 1 is the radial direction of the mold 9, and the direction perpendicular to the paper is the circumferential direction. The vertical direction in FIG. 1 is also the axial direction of the mold 9.

  The upper mold 4 includes an upper cavity surface 18, a contact surface 19, a recess 20 as a fitting portion, a sliding surface 21, an upper slab land 22, and a heating chamber 24. The upper cavity surface 18 is formed by a part of the inner peripheral surface of the upper mold 4. The abutment surface 19 is located radially inward of the upper cavity surface 18. The abutment surface 19 is a downward surface. The recess 20 is located radially inward of the abutment surface 19. The recess 20 is recessed upward. The recess 20 is provided with a tapered surface 20a. The tapered surface 20a is inclined radially inward from the lower side to the upper side. The sliding surface 21 is formed by a part of the outer peripheral surface of the upper mold 4. The upper slab land 22 is located at the lower end portion of the upper mold 4 in the vertical direction. The upper slab land 22 is provided with the upper slab land surface 26 facing downward. The radially inner end of the upper slab land surface 26 is continuous with the upper cavity surface 18. The radially outer end of the upper slab land surface 26 is continuous with the sliding surface 21.

  The lower mold 6 includes a lower cavity surface 28, an abutting surface 29, a recess 30 as a fitting portion, a sliding surface 31, a lower slab land 32, and a heating chamber 34. The lower cavity surface 28 is formed by a part of the inner peripheral surface of the lower mold 4. The abutment surface 29 is located radially inward of the lower cavity surface 28. The contact surface 29 is an upward surface. The recess 30 is located radially inward of the abutment surface 29. The recess 30 is recessed downward. The recess 30 has a tapered surface 30a. The tapered surface 30a is inclined radially inward from the upper side to the lower side. The sliding surface 31 is formed by a part of the inner peripheral surface of the lower mold 4. The sliding surface 31 is formed above the lower cavity surface 28 in the vertical direction. The lower slab land 32 is located below the sliding surface 31 in the vertical direction. The lower slab land 32 is provided with a lower slab land surface 36 facing upward. The lower slab land surface 36 is located between the lower cavity surface 28 and the sliding surface 31. The radially inner end of the lower slab land surface 36 is continuous with the lower cavity surface 28. The radially outer end of the lower slab land surface 36 is continuous with the sliding surface 31.

  The core 8 includes an upper core 38 and a lower core 40. The upper core 38 includes an upper core molding surface 42, an upper abutment surface 44, a lower abutment surface 46, a convex portion 48 as an upper fitting portion, and a convex portion 50 as a lower fitting portion.

  The upper core molding surface 42 is formed on the outer peripheral surface of the upper core 38 and the upper end surface facing upward. The upper abutment surface 44 is formed on the upper end surface of the upper core 38. The upper abutment surface 44 is continuous with the radially inner end of the upper core molding surface 42. The convex portion 48 is located radially inward of the upper abutment surface 44. The convex portion 48 protrudes upward from the upper abutment surface 44. The convex portion 48 includes a tapered surface 48 a. The tapered surface 48a is inclined radially inward from the lower side to the upper side. The lower abutment surface 46 is formed on the lower end surface of the upper core 38 in the downward direction. The lower abutment surface 46 extends radially inward from the lower end of the upper core molding surface 42. The protrusion 50 is located radially inward of the lower abutment surface 46. The protrusion 50 protrudes downward from the lower contact surface 46. The convex part 50 is provided with the taper surface 50a. The tapered surface 50a is inclined radially inward from the upper side to the lower side.

  The lower core 40 includes a lower core molding surface 52, an upper abutment surface 54, a lower abutment surface 56, a concave portion 58 as an upper fitting portion, and a convex portion 60 as a lower mating portion.

  The lower core molding surface 52 is formed on the outer peripheral surface of the lower core 40. The upper abutment surface 54 is formed on the upper end surface of the lower core 40 facing upward. The upper abutment surface 54 extends radially inward from the upper end of the lower core molding surface 52. The recess 58 is located radially inward of the upper abutment surface 54. The recess 58 is recessed downward from the upper abutment surface 54. The recess 58 has a tapered surface 58a. The tapered surface 58a is inclined radially inward from the upper side to the lower side. The lower abutment surface 56 is a downward surface. The lower abutment surface 56 extends radially inward continuously with the lower core molding surface 52. The convex portion 60 is located radially inward of the lower abutment surface 56. The convex portion 60 protrudes downward from the lower abutment surface 56. The convex part 60 is provided with the taper surface 60a. The tapered surface 60a is inclined radially inward from the upper side to the lower side.

  In FIG. 1, the sliding surface 21 of the upper mold 4 and the sliding surface 31 of the lower mold 6 are slidably fitted. The upper slab land surface 26 of the upper mold 4 and the lower slab land surface 36 of the lower mold 6 are in contact with each other. The convex portion 48 of the upper core 38 and the concave portion 20 of the upper mold 4 are fitted. The tapered surface 48a is in contact with the tapered surface 20a. The upper contact surface 44 of the upper core 38 and the contact surface 19 of the upper mold 4 are in contact with each other. The convex portion 50 of the upper core 38 and the concave portion 58 of the lower core 40 are fitted. The tapered surface 50a and the tapered surface 58a are in contact with each other. The lower abutment surface 46 of the upper core 38 abuts on the upper abutment surface 54 of the lower core 40. The convex portion 60 of the lower core 40 and the concave portion 30 of the lower mold 6 are fitted. The tapered surface 60a and the tapered surface 30a are in contact with each other. The lower abutment surface 56 of the lower core 40 abuts on the abutment surface 29 of the lower mold 6.

  The base member 14 is located above the upper mold 4. The upper mold 4 is fixed to the base member 14. The lower mold lifting unit 16 is located below the lower mold 6. The lower mold lifting unit 16 movably supports the lower mold 6 in the vertical direction. The upper core lifting unit 10 is located above the upper core 38. The upper core lifting unit 10 is supported so that the upper core 38 can be moved in the vertical direction. The lower core lifting unit 12 is located below the lower core 40. The lower core lifting unit 12 supports the lower core 40 so as to be movable in the vertical direction.

  In the bladder manufacturing device 2, the upper mold 4, the lower mold 6, the upper core 38 and the lower core 40 form a cavity 62. The upper cavity surface 18 of the upper mold 4 and the lower cavity surface 28 of the lower mold 6 form a cavity surface 64.

  A portion of the core molding surface 66 of the core 8 is shown in FIG. The vertical direction in FIG. 2 is the axial direction, the horizontal direction in FIG. 2 is the circumferential direction, and the direction perpendicular to the paper is the radial direction. The core molding surface 66 is formed of the upper core molding surface 42 of the upper core 38 and the lower core molding surface 52 of the lower core 40. The alternate long and short dash line CL in FIG. 2 represents the equatorial plane.

  A plurality of vent line forming portions 68 are formed on the core molding surface 66. Each of the vent line forming portions 68 protrudes outward in the half direction. The vent line forming portion 68 extends from one end to the other end of the core molding surface 66 in the axial direction, in other words, from the upper end in the vertical direction to the lower end. The vent line forming portion 68 is inclined with respect to the equatorial plane. The dashed-dotted line L1 of FIG. 2 represents the center line of the vent line forming portion 68. A double arrow θ represents an inclination angle between the vent line forming portion 68 and the equatorial plane.

  With reference to FIGS. 3 to 6, the bladder manufacturing apparatus 2 is used to explain a method of manufacturing the bladder. The method of manufacturing the bladder includes a slab charging step, a bladder molding step, a mold opening step, a bladder removing step, and a surface turning step.

  In the slab charging step, as shown in FIG. 3A, the mold 9 of the bladder manufacturing apparatus 2 is in the open state. The lower mold 6 is separated downward from the upper mold 4. The lower core 40 is separated downward from the upper core 38. The upper mold 4 is heated by passing a heating medium through the heating chamber 24. The lower mold 6 is heated by passing a heating medium through the heating chamber 34. Here, although an example in which the upper mold 4 and the lower mold 6 are heated by the heating medium is described, the invention is not limited thereto. The bladder manufacturing device 2 may include other heating devices for heating the upper mold 4 and the lower mold 6. Further, although not shown, the upper core 38 and the lower core 40 may also be heated by the heating device.

  The slab S (see FIG. 3 (b)) is placed on the lower slab land surface 36 of the lower mold 6. The slab S is made of rubber. The upper core 38 is lowered toward the lower mold 6 on which the slab S is placed. The lowered upper core 38 abuts on the lower core 40. The convex portion 50 of the upper core 38 and the concave portion 58 of the lower core 40 are fitted. The lower abutment surface 46 of the upper core 38 abuts on the upper abutment surface 54 of the lower core 40. Thus, the state shown in FIG. 3 (b) is obtained.

  In the bladder molding process, the lower mold 6, the upper core 38 and the lower core 40 rise toward the upper mold 4. The lower slab land 32 of the lower mold 6 rises toward the slab land 22 of the upper mold 4. The sliding surface 21 of the upper mold 4 slides on the sliding surface 31 of the lower mold 6. The upper slab land surface 26 and the lower slab land surface 36 press the slab S from above and below. The slab S is pressurized and heated to be extruded into the cavity 62. As shown in FIG. 4, a slab S is vulcanized into the bladder 69 in the cavity 62.

  The bladder 69 includes a main body 70, a locking portion 72 continuous with the upper end of the main body 70, and a locking portion 74 continuous with the lower end of the main body 70. The outer peripheral surface 76 of the main body 70 is formed by the upper cavity surface 18 of the upper mold 4 and the lower cavity surface 28 of the lower mold 6. The molding inner circumferential surface 78 of the main body 70 is molded by the upper core molding surface 42 of the upper core 38 and the lower core molding surface 52 of the lower core 40. A vent line is formed on the forming inner circumferential surface 78 by the vent line forming portion 68. The locking portion 72 is formed by the upper cavity surface 18 and the upper core molding surface 42. The locking portion 74 is formed by the lower cavity surface 28 and the lower core molding surface 52.

  In the mold opening process, as shown in FIG. 5A, the lower mold 6, the upper core 38 and the lower core 40 are separated from the upper mold 4. A burr 80 is formed on the molding outer peripheral surface 76 of the bladder 69. The burrs 80 are formed by pushing the slab S into the cavity 62 from between the upper slab land surface 26 and the lower slab land surface 36. The burrs 80 are rubbers protruding radially outward from the outer circumferential surface 76. The burrs 80 are formed along the boundary between the upper mold 4 and the lower mold 6.

  In the bladder removal step, the upper core 38 is removed from the bladder 69 as shown in FIG. 5 (b). Although not shown, the lower core 40 is raised with respect to the lower mold 6. The bladder 69 is removed from between the lower mold 6 and the lower core 40. In this manner, the bladder 69 is pulled out of the mold 9. The removed bladder 69 is shown in FIG. 6 (a).

  In the front and back turning process, the molding outer peripheral surface 76 and the molding inner peripheral surface 78 of the bladder 69 are turned over. As shown in FIG. 6 (b), the molding inner circumferential surface 78 is the outer circumferential surface of the bladder 69, and the molding outer circumferential surface 76 is the inner circumferential surface. The molding inner circumferential surface 78 forms a molding surface 82 of the bladder 69. A vent line is formed on the molding surface 82. The molding outer peripheral surface 76 forms the back surface 84 of the molding surface 82. The burrs 80 project radially inward from the back surface 84. In this way, a bladder 69 is obtained.

  In this manufacturing method, the burrs 80 may not be particularly subjected to removal processing such as cutting and polishing, but may be removed. In the present invention, in addition to the burrs 80 formed in the bladder molding process, the burrs after the burrs 80 have been removed are referred to as burrs.

  A method of manufacturing a tire using the bladder 69 will be described. The tire manufacturing method comprises a preforming step and a vulcanization step. In this preforming step, the members forming the respective portions of the tire are combined to form a low cover. In the vulcanization step, the low cover is vulcanized to obtain a tire from the low cover. In this vulcanization process, a vulcanizing apparatus provided with a mold and a bladder 69 is used. The vulcanization process includes a low cover charging process, a mold closing process, a heating and pressing process, a mold opening process, and a removal process.

  In the charging step, the low cover is set on the tire mold. The medium is filled in the bladder 69 and the bladder 69 is expanded. A bladder 69 abuts the inner surface of the low cover. In the mold closing step, the tire mold is closed. In the heating and pressurizing step, the raw cover is heated and pressurized in the tire mold. The low cover is vulcanized to obtain a tire from the low cover. The surface of the tire is formed by the cavity surface of the tire mold and the forming surface 82 of the bladder 69. In the mold opening process, the tire mold is opened. In the removal step, the tire is removed from the opened tire mold.

  In this tire manufacturing method, the tire is vulcanized and formed by the tire mold and the bladder 69. The forming surface 82 of the bladder 69 forms the inner circumferential surface of the tire. In the bladder 69, a burr 80 is formed on the back surface 84. The burr 80 is not formed on the molding surface 82.

  In this tire manufacturing method, no burrs 80 are formed on the molding surface 82, so no marks of the burrs 80 are formed on the inner circumferential surface of the tire. The tire manufacturing method contributes to the improvement of the quality of the tire. In addition, it is not necessary to cut off the burrs 80 of the bladder 69. The processing of the burrs 80 does not impair the durability of the bladder 69. The tire manufacturing method contributes to the improvement of the durability of the bladder.

  In the bladder manufacturing method, a vent line forming portion 68 is formed on the upper core molding surface 42 and the lower core molding surface 52. Thereby, a vent line is formed on the molding inner peripheral surface 78 of the bladder 69, that is, on the molding surface 82 of the bladder 69. The tire manufacturing method using the bladder 69 is excellent in the air dischargeability on the inner peripheral surface of the tire. The manufacturing method of this bladder contributes to the improvement of the quality of the tire.

  The bladder 69 having a large inclination angle of the vent line with respect to the equatorial plane contributes to the improvement of the air discharging property in the tire vulcanization process. From this viewpoint, the inclination angle θ of the vent line forming portion 68 is preferably 55 ° or more. On the other hand, the bladder 69 having an excessively large inclination angle of the vent line impairs the air dischargeability in the tire vulcanization process. In addition, the durability of the bladder 69 is impaired. From these viewpoints, the inclination angle θ of the vent line forming portion 68 is preferably 65 ° or less.

  In the front and back turning process, the high temperature bladder 69 can easily turn over the front and back. Moreover, the damage to the bladder 69 is reduced by turning over the front and back. From this point of view, the temperature of the bladder 69 is preferably 80 ° C. or more, more preferably 120 ° C. or more.

  In this bladder manufacturing method, the heating temperature is raised to above 80 ° C. in the bladder molding process. Preferably, the front and back is turned over before the temperature of the bladder is less than 80 ° C. in the front and back turning process. This eliminates the need to heat the bladder 69 in the face-to-face turning process.

  Hereinafter, the effects of the present invention will be clarified by examples, but the present invention should not be interpreted in a limited manner based on the description of the examples.

Example 1
The bladder was manufactured by the manufacturing method according to FIGS. 1 to 6. The temperature of the bladder was 120 ° C. in the process of turning over.

Comparative Example 1
The bladder was manufactured in a conventional bladder manufacturing method. This manufacturing method does not include the inside-out process. The burrs on the molding surface of the bladder were cut off and the burrs after cutting off were buffed.

[Example 2-5]
A bladder was manufactured in the same manner as in Example 1 except that the temperature of the bladder in the front and back turning step was as shown in Table 1.

[Rubber hardness]
The hardness of each bladder was measured in the front-to-back process. The hardness was measured at the temperature of the front and back turning process, respectively. The hardness of this bladder is JIS-A hardness. This hardness is measured by a durometer of type A in accordance with the definition of "JIS-K6253". This hardness is measured by pressing a durometer of type A against the surface of the bladder. In Comparative Example 1, the hardness of the bladder was measured in the same manner as in Example 1 except that the temperature was 25 ° C. The results are shown in Table 1 below.

[Workability]
The workability was evaluated in the process of turning over. The evaluation of this workability is evaluated in three stages of easy, normal and difficult, and the result is expressed by an index. The larger the index, the easier and preferred.

[durability]
The tire was manufactured repeatedly and the durability of the bladder was evaluated. The results are shown in Table 1 below. The evaluation result is represented by an index where Comparative Example 1 is 100. The larger the index, the better the durability. The larger the index, the better.

Defect rate
The appearance of the inner circumferential surface of the tire manufactured by each bladder was inspected. It was inspected for the appearance defect of a bear etc. on the inner skin of a tire. Here, for relative comparative evaluation, evaluations were made including fine items that would not cause any problems as normal products and those that could be corrected. The results are shown in Table 1 below. The evaluation result is represented by an index where Comparative Example 1 is 100. The smaller the index is, the less the appearance defect. The smaller the index, the better.

[Example 6]
The inclination angle θ of the bent line forming portion of the core was set to 60 °, and the bladder was manufactured by the manufacturing method of the bladder according to FIGS. 1 to 6. A tire was manufactured using this bladder.

Comparative Example 2
The bladder manufactured by the conventional manufacturing method was prepared. In this manufacturing method, the vent line forming portion was not formed in the core. Vent line moldings were formed on the cavity surfaces of the upper mold and the lower mold. The inclination angle θ of the bent line forming portion was 65 °.

[Example 7-10]
A tire was manufactured in the same manner as Example 1, except that the inclination angle θ of the bent line forming portion of the core was changed.

  The durability and the percent defective were evaluated in the same manner as in Example 1-5 and Comparative Example 1. The results are shown in Table 2 below. The evaluation result is represented by an index where Comparative Example 2 is 100. The larger the durability index, the better the durability. The larger the index, the better. As the defect rate index is smaller, the appearance defect is less. The smaller the index, the better.

  As shown in Tables 1 and 2, in the manufacturing method of the example, the evaluation is higher than the manufacturing method of the comparative example. The superiority of the present invention is clear from the evaluation results.

  The method described above can be widely applied to a method of manufacturing a bladder used to mold a tire.

2 ... bladder manufacturing device 4 ... upper mold 6 ... lower mold 8 ... core 9 ... mold 18 ... upper cavity surface 22 ... upper slab land 26 ... upper Slab land surface 28 · · · lower cavity surface 32 · · · lower slab land 36 · · · lower slab land surface 38 · · · upper core 40 · · · lower core 42 · · · upper core molding surface 52 · · · lower Core molding surface 62 ... cavity 64 ... cavity surface 66 ... core molding surface 68 ... vent line molding portion 69 ... bladder 76 ... molding outer peripheral surface 78 ... molding inner peripheral surface 80 ... Burr 82 ... Molding surface 84 ... Back surface

Claims (7)

A low cover loading step in which a low cover is loaded into a tire mold;
And a low cover pressing and heating process in which the low cover is pressurized and heated by the tire mold and the bladder.
A method of manufacturing a tire, wherein the bladder includes a molding surface that abuts on the low cover and does not have burrs. A slab is extruded from the cavity surface, which the bladder forms on the molded outer peripheral surface of the bladder, into a cavity;
The method for manufacturing a tire according to claim 1, wherein a molding inner peripheral surface behind the molding outer peripheral surface is the molding surface, and the molding outer peripheral surface is the rear surface of the molding surface. A method of manufacturing a bladder used in a vulcanization process of forming a tire from a low cover, comprising:
A bladder forming process in which a slab is pressurized and heated by a bladder mold, and a bladder is formed from the slab;
And b) turning the inner peripheral surface of the bladder into an inner peripheral surface and the inner peripheral surface of the bladder into an outer peripheral surface. The bladder mold includes an upper mold and a lower mold for molding the outer peripheral surface, and a core for molding the inner peripheral surface;
The core is provided with a core molding surface for molding the molding inner circumferential surface;
The method for manufacturing a bladder according to claim 3, wherein a vent line forming portion is formed on the core molding surface. The vent line forming portion extends obliquely with respect to the equatorial plane of the core;
The method according to claim 4, wherein an angle θ between the vent line forming portion and the equatorial plane is 55 ° or more and 65 ° or less.   The method for producing a bladder according to any one of claims 3 to 5, wherein the temperature of the bladder is set to 80 ° C or higher in the front and back turning step. In the bladder molding process, the temperature of the bladder is higher than 80.degree. C.,
7. A method according to claim 6, wherein the step of turning over is performed before the temperature of the bladder drops below 80 DEG C. from the temperature of the bladder molding step.

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