Tire molding die and method of manufacturing tire molding die

Abstract

To provide a tire molding die capable of suppressing dislodging of a vent plug, and a method for manufacturing the tire molding die.SOLUTION: There is provided a tire molding die, comprising: a tire forming surface; and an exhaust hole that opens at the tire forming surface and that is for inserting a vent plug, wherein the exhaust hole has three or more projections protruding toward the center of the hole, the three or more protrusions are substantially and evenly spaced along the circumferential direction of the exhaust hole; and tip portions of the protrusions are rounded or flat when viewed from the central axial direction of the exhaust hole.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE This disclosure relates to tire molding molds and methods of manufacturing tire molding molds. [Background technology]

[0002] A tire molding die is provided with many exhaust holes on the tire forming surface that forms the outer surface of the tire. The exhaust holes allow air to be discharged between the tire outer surface and the tire forming surface during vulcanization molding through the inside and outside of the die, thereby preventing the occurrence of dents called bare marks. During vulcanization molding, rubber on the outer surface of the tire flows into the exhaust holes. As a result, many rubber protrusions called spews are formed on the outer surface of the vulcanized tire. In response to this, a method is known in which vent plugs are fitted into the exhaust holes to suppress the formation of spews. For example, a vent piece as disclosed in Patent Document 1 is known as a vent plug.

[0003] The vent plug is fitted into the exhaust hole while crushing the entire circumference of the exhaust hole by an interference fit. This causes a large resistance to fitting the vent plug into the exhaust hole, and the vent plug may be fitted at an angle to the exhaust hole or with its central axis misaligned with the central axis of the exhaust hole. If the vent plug is not fitted properly, there is a risk that the tire will get caught on the vent plug when the vulcanized tire is removed from the tire mold, causing the vent plug to come out. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-44749 A Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present disclosure is to provide a tire molding die and a method for manufacturing a tire molding die that can suppress the dislodging of a vent plug. [Means for solving the problem]

[0006] The tire molding mold of the present disclosure comprises a tire forming surface and an exhaust hole that opens at the tire forming surface and into which a vent plug is fitted, the exhaust hole having three or more protrusions that protrude toward a center of the exhaust hole, the three or more protrusions being substantially evenly arranged along the circumferential direction of the exhaust hole, and the tips of the protrusions being rounded or flat when viewed from the central axial direction of the exhaust hole.

[0007] The manufacturing method of a tire molding mold disclosed herein includes an exhaust hole forming step of forming an exhaust hole in a tire forming surface, and an insertion step of inserting a vent plug into the exhaust hole, wherein the exhaust hole has three or more protrusions protruding toward a center of the exhaust hole, the three or more protrusions being substantially evenly arranged along the circumferential direction of the exhaust hole, and the tips of the protrusions are rounded or flat when viewed from the central axial direction of the exhaust hole. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view showing a tire molding die according to a first embodiment. [Diagram 2] Enlarged view of area II in Figure 1 showing the vent plug [Diagram 3] FIG. 3 is a cross-sectional view corresponding to FIG. 2 , illustrating an exhaust hole of the tire molding die according to the embodiment before a vent plug is fitted therein. [Figure 4] Cross-sectional view of line IV-IV in Figure 3 [Diagram 5] FIG. 5 is a cross-sectional view corresponding to FIG. 4, showing a modified example of the exhaust hole. [Figure 6] FIG. 5 is a cross-sectional view corresponding to FIG. 2, showing an exhaust hole of a tire molding die according to a second embodiment before a vent plug is fitted therein; [Figure 7] Flowchart showing an example of a method for manufacturing a tire mold [Figure 8] FIG. 5 is a cross-sectional view corresponding to FIG. 4 and showing another modified example of the exhaust hole. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] [Tire molding mold] (First embodiment) First, an example of the configuration of a tire molding die 100 according to the first embodiment will be described with reference to Fig. 1. Note that in each figure (as well as Figs. 2 to 8), the dimensional ratios in the drawing do not necessarily match the actual dimensional ratios, and the dimensional ratios between the drawings do not necessarily match either.

[0010] Fig. 1 shows a cross section of a tire molding die 100 (hereinafter, may be simply referred to as "die 100") along a tire meridian cross section. The die 100 shown in Fig. 1 is in a closed state. A tire T is set with the tire axial direction facing up and down. In Fig. 1, the left direction is the outer side in the tire radial direction, and the right direction is the inner side in the tire radial direction.

[0011] The mold 100 includes a cavity 15 in which the tire T is set, a tire forming surface 1 that contacts the outer surface of the tire T set in the cavity 15, and an exhaust hole 6 for fitting (attaching) a vent plug 2. The exhaust hole 6 opens at the tire forming surface 1 and connects the inside (i.e., the cavity 15) of the mold 100 to the outside. During vulcanization molding, air is exhausted through the exhaust hole 6 between the outer surface of the tire T and the tire forming surface 1.

[0012] The material of the die 100 is preferably a metal having high electrical conductivity. An example of the material of the die 100 is an aluminum material. The aluminum material is a concept that includes not only pure aluminum-based materials but also aluminum alloys, such as Al-Cu-based, Al-Mg-based, Al-Mg-Si-based, Al-Zn-Mg-based, Al-Mn-based, and Al-Si-based materials. The housing 3 and stem 4 that constitute the vent plug 2, which will be described later, are preferably made of a steel material such as stainless steel or S45C, and may be made of the same metal or different metals.

[0013] The mold 100 includes a tread mold 11 for forming the tread of the tire T, side molds 12, 13 for forming the sidewalls of the tire T, and bead rings 14, 14 into which the bead portions of the tire T are fitted. The tire forming surface 1 includes the inner surface of the tread mold 11 and the inner surfaces of the side molds 12, 13. Although not shown, the inner surface of the tread mold 11 is provided with projections and recesses for forming the tread pattern of the tire T. Although only one exhaust hole 6 opening on the inner surface of the tread mold 11 is depicted in FIG. 1, in reality, a large number of exhaust holes opening on the inner surfaces of the tread mold 11 and the side molds 12, 13 are provided. In addition, although FIG. 1 shows an example in which the exhaust hole 6 extends linearly, the exhaust hole 6 may extend in a curved manner.

[0014] The vent plugs 2 are fitted (attached) to exhaust holes 6 opening on the inner surface of the tread mold 11 serving as the tire forming surface 1, but instead of or in addition to this, it is also possible to fit (attach) them to exhaust holes opening on the inner surfaces of the side molds 12 and / or side molds 13. Also, in this embodiment, a structure is shown in which the mold 100 includes the tread mold 11 and a pair of side molds 12, 13, but this is not limited thereto, and for example, a mold structure in which the tread mold is divided into two parts, upper and lower, at the center thereof may also be used.

[0015] Fig. 2 is an enlarged view of region II in Fig. 1. In Fig. 2, the upper direction is the inner side in the tire radial direction, and the lower direction is the outer side in the tire radial direction. Fig. 2 shows an example in which the vent plug 2 is a spring vent, but is not limited to this. The vent plug 2 may be a cylindrical vent piece or the like.

[0016] 2, the vent plug 2 includes a cylindrical housing 3 having an exhaust passage 21 therein, a stem 4 that is inserted into the housing 3 and serves as a valve body for opening and closing the exhaust passage 21, and a biasing member 5 that biases the stem 4 toward the cavity side D1 (the inner side in the tire radial direction in FIG. 2). For convenience of illustration, the stem 4 and the biasing member 5 are drawn as viewed from the front.

[0017] The housing 3 is fitted (press-fitted) along the central axis Ca of the vent hole 6 by an interference fit. The housing 3 has an annular top surface 31 facing the cavity 15, a tapered surface 32 that reduces in diameter from the top surface 31 toward the anti-cavity side D2 (the tire radial outside in FIG. 2), and a cylindrical surface 33 that extends from the tapered surface 32 toward the anti-cavity side D2 along the axial direction AD of the housing 3 (vent plug 2). The axial direction AD coincides with the central axial direction of the stem 4 and the central axis Ca of the vent hole 6. The top surface 31 is disposed, for example, flush with the tire forming surface 1 (i.e., on the same plane).

[0018] The end of the housing 3 away from the cavity 15 is provided with a through hole 34, an inner brim-shaped support portion 35, and a tapered surface 37 that expands in diameter from the bottom surface 36 of the housing 3 toward the cavity side D1 (the inner side in the tire radial direction in Figure 2).

[0019] The stem 4 includes a columnar body 41 and a head 42 integrally connected to the body 41. The body 41 is formed in a cylindrical shape extending in the axial direction AD as a whole. A stopper 43 having a diameter larger than that of the through hole 34 is provided at the end of the body 41 farther from the cavity 15. The stem 4 does not come out of the housing 3 due to the action of the stopper 43.

[0020] The body 41 includes a first body 41a connected to the anti-cavity side D2 of the head 42, and a second body 41b connected to the anti-cavity side D2 of the first body 41a. The outer diameter of the first body 41a is smaller than the inner diameter of the cylindrical surface 33. A gap through which air can pass is formed between the first body 41a and the cylindrical surface 33 surrounding it. The outer diameter of the second body 41b is smaller than the outer diameter of the first body 41a. A gap through which the biasing member 5 can be disposed is formed between the second body 41b and the cylindrical surface 33 surrounding it. The second body 41b is inserted into the biasing member 5.

[0021] The head 42 is formed in a truncated cone shape that tapers toward the anti-cavity side D2. The head 42 has a tapered side surface that corresponds to the tapered surface 32. A gap G1 is formed between the head 42 and the tapered surface 32 that surrounds it.

[0022] The biasing member 5 is interposed between the first body 41a and the support portion 35, and biases (pushes up) the stem 4 so as to open the exhaust path 21. The biasing member 5 is, for example, a coil spring.

[0023] 2, the biasing member 5 pushes up the stem 4, thereby opening the exhaust passage 21 and the vent plug 2 is in an open state. While the vent plug 2 is in an open state, the air in the cavity 15 is discharged to the outside of the mold 100 through the exhaust passage 21 as the outer surface of the tire approaches the tire forming surface 1. The exhaust passage 21 is formed by the gap between the housing 3 and the stem 4. More specifically, the exhaust passage 21 is formed so as to pass from the gap G1 between the tapered surface 32 and the head 42, through the gap between the cylindrical surface 33 and the first body 41a, and through the gap between the cylindrical surface 33 and the second body 41b.

[0024] Fig. 3 is a cross-sectional view corresponding to Fig. 2, showing the exhaust hole 6 of the tire molding mold 100 according to the first embodiment before the vent plug 2 is fitted in. Fig. 4 is a cross-sectional view taken along line IV-IV in Fig. 3. In Fig. 3, the vent plug 2 is depicted as seen from the front.

[0025] As shown in Figures 3 and 4, the exhaust hole 6 has a plurality of protrusions 61 that protrude toward the center of the hole. With this configuration, the vent plug 2 is fitted into the exhaust hole 6 while the protrusions 61 are crushed in the initial stage of fitting. This reduces the fitting resistance of the vent plug 2 and makes it easier to fit the vent plug 2 along the central axis Ca of the exhaust hole 6 compared to when the vent plug 2 is fitted into an exhaust hole that does not have the protrusions 61. As the fitting of the vent plug 2 progresses, the entire circumference of the exhaust hole 6 is crushed while it is fitted, but by fitting the vent plug 2 along the central axis Ca of the exhaust hole 6 in the initial stage of fitting, the fitting pressure applied to the outer periphery of the vent plug 2 (housing 3) becomes constant, and it becomes easier to fit the vent plug 2 along the central axis Ca of the exhaust hole 6 even after the initial stage of fitting.

[0026] Three or more protrusions 61 are provided. As a result, the vent plug 2 comes into contact with three protrusions 61, and the stability of the posture of the vent plug 2 during fitting can be improved. Although an example in which five protrusions 61 are provided is shown in Figs. 3 and 4, the present invention is not limited to this. For example, as shown in Figs. 5(a) to (e), three to eight protrusions 61 may be provided. The number of protrusions 61 may be four or more, five or more, six or more, seven or more, or eight or more. Furthermore, Figs. 5(a) to (e) show an example in which eight or less protrusions 61 are provided, but the present invention is not limited to this. The number of protrusions 61 may be nine or more.

[0027] As shown in Fig. 4, the protrusions 61 are disposed substantially evenly along the circumferential direction CD of the exhaust hole 6. With such a configuration, it becomes easier to align the central axis of the vent plug 2 with the central axis Ca of the exhaust hole 6 and fit it in. "Substantially evenly" means that the difference between the maximum and minimum values ​​of the arrangement angles θi of the protrusions 61 is within 10% (preferably within 5%) of the maximum value. The arrangement angle θi is the angle between adjacent imaginary lines drawn connecting the center (or any point) of the protrusions 61 in the circumferential direction CD and the central axis Ca of the exhaust hole 6.

[0028] The tip of the projection 61 is rounded or flat when viewed from the central axis Ca of the exhaust hole 6. With this configuration, the stability of the posture of the vent plug 2 when the vent plug 2 is brought into contact with the tip of the projection 61 can be increased compared to when the tip of the projection 61 is sharp. This is because when the tip of the projection 61 is sharp, the tip of the projection is easily crushed, causing variation in the amount of crushing of each projection, and making it difficult to stabilize the posture of the vent plug 2 at the initial stage of fitting. This makes it easier to fit the vent plug 2 along the central axis Ca of the exhaust hole 6. As a result, the fitting state of the vent plug 2 can be improved and the vent plug 2 can be prevented from coming off. In addition, the fitting error of the vent plug 2 can be prevented, and deformation of the vent plug 2 due to the fitting error can be prevented. It is preferable that the tip of the projection 61 is a surface when viewed from the central axis Ca of the exhaust hole 6.

[0029] 4 shows an example in which the tip of the protrusion 61 is rounded when viewed from the direction of the central axis Ca. In this example, the tip of the protrusion 61 is curved so as to be convex toward the central axis Ca of the exhaust hole 6. Note that, as shown in FIG. 5(f), the tip of the protrusion 61 may be flat when viewed from the direction of the central axis Ca of the exhaust hole 6.

[0030] 4, the cross-sectional shape of the protrusions 61 is, for example, an arch shape. The cross-sectional shape of the exhaust hole 6 including the protrusions 61 is, for example, a gear shape. It is preferable that the shapes of all the protrusions 61 are substantially the same.

[0031] The protrusion 61 preferably has a shape along the circumferential direction CD of the exhaust hole 6. The protrusion amount Pa of the protrusion 61 is preferably 40% or less of the diameter Dh of the exhaust hole 6, and more preferably 20% or less. This makes it possible to suppress the occurrence of a gap between the vent plug 2 and the exhaust hole 6 after the vent plug 2 is fitted. The protrusion amount Pa of the protrusion 61 is preferably 1.0 mm or less. In this embodiment, the protrusion amount Pa is substantially constant along the central axis Ca (see FIG. 3), but is not limited to this.

[0032] It is preferable that the cross-sectional area of ​​the exhaust hole 6 including the protrusion 61 is substantially the same as the cross-sectional area of ​​a conventional exhaust hole not having the protrusion 61. This makes the crushing amount of the exhaust hole 6 when the vent plug 2 is fitted substantially the same as the crushing amount of a conventional exhaust hole, and the fitting strength between the vent plug 2 and the exhaust hole 6 can be made close to the conventional fitting strength. In addition, since the diameter Dh of the exhaust hole 6 is larger than the diameter of a conventional exhaust hole by providing the protrusion 61, a gap is more likely to occur between the vent plug 2 and the exhaust hole 6 than in a conventional exhaust hole when the fitting state of the vent plug 2 is poor, and it becomes easier to judge the fitting state of the vent plug 2. Specifically, when a gap occurs between the vent plug 2 and the exhaust hole 6, it can be judged that the fitting state of the vent plug 2 is poor. The cross-sectional area (diameter Dh) of the exhaust hole 6 is appropriately set according to the diameter of the vent plug 2 to be fitted.

[0033] The diameter of an imaginary circle Vc that is in contact with the tip of each protrusion 61 is greater than the outer diameter of the bottom surface 36 of the housing 3. The length L1 of the protrusion 61 along the central axis Ca is, for example, substantially the same as the length in the axial direction AD of the housing 3. Note that the length L1 of the protrusion 61 may be shorter or longer than the length of the housing 3.

[0034] The protrusions 61 are preferably arranged at intervals from one another in the circumferential direction CD of the exhaust hole 6. That is, it is preferable that a gap is provided between the protrusions 61, 61. With such a configuration, the protrusions 61 are more easily crushed than when the protrusions 61 are arranged without any intervals, and the vent plug 2 is more easily fitted along the central axis Ca of the exhaust hole 6. This improves the fitted state of the vent plug 2 and suppresses the vent plug 2 from coming off. "At intervals" means that the protrusions 61 are not in contact with other protrusions 61 adjacent to them. It is preferable that the arrangement intervals of the protrusions 61 are substantially the same. Note that the above is not limited, and the protrusions 61 may be arranged without any intervals.

[0035] As shown in FIG. 3, the protrusion 61 is provided at a position where the vent plug 2 is fitted. The protrusion 61 is provided at a position where it comes into contact with the tapered surface 37 before the outer periphery of the exhaust hole 6 when the vent plug 2 is fitted. That is, the protrusion 61 is provided near the tire forming surface 1. The distance along the central axis Ca between the tire forming surface 1 and the cavity 15 side end face of the protrusion 61 is shorter than the length of the axial direction AD of the tapered surface 37. In this embodiment, the cavity 15 side end face of the protrusion 61 is disposed so as to be substantially flush with the tire forming surface 1 (i.e., on the same plane), but is not limited thereto. The cavity 15 side end face of the protrusion 61 may be provided with an inclined surface inclined in the same direction as the tapered surface 37.

[0036] Second embodiment Next, a tire molding die 100 according to a second embodiment will be described with reference to Fig. 6. Since the second embodiment can be configured similarly to the first embodiment except for the configuration described below, the common points will be omitted and differences will be mainly described. The same reference numerals will be used to designate components already described in the first embodiment, and duplicated explanations will be omitted. Fig. 6 is a cross-sectional view corresponding to Fig. 2, showing the exhaust hole 6 of the tire molding die 100 according to the second embodiment before the vent plug 2 is fitted.

[0037] As shown in Fig. 6, a plurality of protrusions 61 are provided along the central axis Ca. Fig. 6 shows an example in which three of each of the protrusions 61 arranged along the circumferential direction CD of the exhaust hole 6 are provided along the central axis Ca, but this is not limited to this. The protrusions 61 are arranged at intervals in the axial direction AD. The number of each protrusion 61 in the direction of the central axis Ca (axial direction AD) may be different.

[0038] It is preferable that the volume of the region Ap in which the protrusion 61 is provided in the exhaust hole 6 be substantially the same as the volume of a region corresponding to the region Ap in a conventional exhaust hole that does not have the protrusion 61.

[0039] The protrusion 61 has a protrusion amount Pa that gradually increases with increasing distance from the tire forming surface 1. That is, the protrusion 61 is formed in a wedge shape in vertical cross section. With such a configuration, the fitting pressure of the vent plug 2 is locally increased, making it difficult for the vent plug 2 to come out. FIG. 6 shows an example in which the protrusion amount Pa gradually increases quadratically with increasing distance from the tire forming surface 1, but this is not limited to this. For example, the protrusion amount Pa may gradually increase linearly with increasing distance from the tire forming surface 1.

[0040] [Manufacturing method of tire molding mold] Next, an example of a method for manufacturing a tire molding die will be described with reference to Figures 3, 6 and 7. Figure 7 is a flow chart showing an example of the method for manufacturing a tire molding die.

[0041] As shown in FIG. 7, the manufacturing method for a tire molding mold includes an vent hole forming step ST1 of forming an vent hole in the tire forming surface, and an insertion step ST2 of inserting a vent plug into the vent hole.

[0042] In the exhaust hole forming step ST1, it is preferable to form the protrusion 61 shown in Fig. 3 by electrical discharge machining. This method makes it easier to form the protrusion 61 in the exhaust hole 6 than by cutting. The electrical discharge machining is preferably performed using a die-sinking electrical discharge machine that does not rotate an electrical discharge machining electrode (e.g., made of brass). However, this is not limited to the above, and the protrusion 61 may be formed by cutting. Also, the protrusion 61 may be formed by electrical discharge machining, and the other parts of the exhaust hole 6 may be formed by cutting.

[0043] In the exhaust hole of the tire molding die according to the first embodiment, as shown in Fig. 3, when the electric discharge electrode EL (see Fig. 6) is moved along the central axis Ca of the exhaust hole 6 (axial direction AD), the feed speed of the electric discharge electrode EL and the voltage applied thereto are kept substantially constant to form the protrusion 61. According to this method, it is possible to form the protrusion 61 whose protrusion amount Pa is substantially constant along the central axis Ca.

[0044] 6, in the exhaust hole of the tire molding die according to the second embodiment, the feed speed of the electric discharge electrode EL or the voltage applied thereto is changed when the electric discharge electrode EL is moved in the direction of the central axis Ca of the exhaust hole 6 (axial direction AD), thereby forming a protrusion 61 whose protrusion amount Pa gradually increases with increasing distance from the tire forming surface 1. According to this method, it is possible to easily form the protrusion 61 whose protrusion amount Pa gradually increases with increasing distance from the tire forming surface 1. Note that the protrusion 61 may also be formed by changing the feed speed of the electric discharge electrode and the voltage applied thereto.

[0045] When the feed speed of the electric discharge electrode is changed to form the protrusion 61, a constant feed speed (first feed speed) is used in a first region A1 of the exhaust hole 6 that does not include the protrusion 61. In a second region A2 where the protrusion amount Pa of the protrusion 61 gradually increases, the feed speed is gradually accelerated to a speed (second feed speed) faster than the first feed speed. In a third region A3 where the protrusion amount Pa of the protrusion 61 gradually decreases, the feed speed is gradually decelerated to the same speed as the first feed speed (third feed speed). When the feed speed of the electric discharge electrode is changed, it is preferable that the voltage applied to the electric discharge electrode is substantially constant.

[0046] When the voltage applied to the electric discharge electrode is changed to form the protrusions 61, the voltage is constant in the first region A1 (first voltage). In the second region A2, the voltage is gradually decreased to a voltage smaller than the first voltage (second voltage). In the third region A3, the voltage is gradually increased to the same voltage as the first voltage (third voltage). When the voltage applied to the electric discharge electrode is changed, it is preferable that the feed speed of the electric discharge electrode is substantially constant.

[0047] 7, the tapered surface 37 (or a surface equivalent thereto) shown in FIG. 3 is brought into contact with the protrusion 61, and then the vent plug 2 is fitted into the exhaust hole 6. This makes it easier to fit the vent plug 2 along the central axis Ca of the exhaust hole 6. The vent plug 2 is fitted by hitting it with a hammer, for example.

[0048] In the fitting step, when fitting the vent plug 2 into the exhaust hole 6, it is preferable to fit the vent plug 2 while visually checking the amount of crushing of each protrusion 61. In this way, by fitting the vent plug 2 so that the amount of crushing of each protrusion 61 is constant, it becomes easier to align the central axis of the vent plug 2 with the central axis Ca of the exhaust hole 6.

[0049] [1] As described above, the tire molding mold 100 disclosed herein comprises a tire forming surface 1 and an exhaust hole 6 that opens at the tire forming surface 1 and into which a vent plug 2 is inserted, the exhaust hole 6 comprises three or more protrusions 61 that protrude toward the center of the hole, the three or more protrusions 61 are substantially evenly arranged along the circumferential direction CD of the exhaust hole 6, and the tips of the protrusions 61 are rounded or flat when viewed from the direction of the central axis Ca of the exhaust hole 6.

[0050] According to this configuration, the vent plug 2 is fitted into the exhaust hole 6 while crushing the projection 61 at the initial stage of fitting. As a result, the fitting resistance of the vent plug 2 is smaller than when the vent plug 2 is fitted into an exhaust hole that does not have the projection 61, and the vent plug 2 can be easily fitted along the central axis Ca of the exhaust hole 6. In addition, since three or more projections 61 are arranged substantially evenly along the circumferential direction CD of the exhaust hole 6, the vent plug 2 can be easily fitted into the exhaust hole 6 with its central axis aligned with the central axis Ca of the exhaust hole 6. Furthermore, since the tip of the projection 61 is rounded or flat when viewed from the central axis Ca of the exhaust hole 6, the stability of the posture of the vent plug 2 when the vent plug 2 is brought into contact with the tip of the projection 61 can be increased compared to when the tip of the projection 61 is sharp. This makes it even easier to fit the vent plug 2 along the central axis Ca of the exhaust hole 6. As a result, the fitted state of the vent plug 2 is improved, and the vent plug 2 can be prevented from coming off.

[0051] [2] With regard to the tire molding die 100 described above in [1], it is preferable that three or more protrusions 61 are arranged at intervals from each other in the circumferential direction CD of the exhaust hole 6.

[0052] With this configuration, the protrusions 61 are more easily crushed than when the protrusions 61 are arranged with no space between them, making it easier to fit the vent plug 2 along the central axis Ca of the exhaust hole 6. This improves the fitted state of the vent plug 2 and makes it possible to prevent the vent plug 2 from coming off.

[0053] [3] With respect to the tire molding die 100 of the above [1] or [2], the protrusion 61 may be configured so that the protrusion amount Pa gradually increases with increasing distance from the tire forming surface 1.

[0054] According to such a configuration, the fitting pressure of the vent plug 2 is locally increased, making the vent plug 2 less likely to come out.

[0055] [4] The manufacturing method of the tire molding mold 100 disclosed herein includes an exhaust hole forming process ST1, in which an exhaust hole 6 is formed in the tire forming surface 1, and an insertion process ST2, in which a vent plug 2 is inserted into the exhaust hole 6, wherein the exhaust hole 6 has three or more protrusions 61 protruding toward a center of the exhaust hole 6, the three or more protrusions 61 being substantially evenly arranged along the circumferential direction CD of the exhaust hole 6, and the tips of the protrusions 61 are rounded or flat when viewed from the direction of the central axis Ca of the exhaust hole 6.

[0056] According to this method, the insertion resistance of the vent plug 2 is smaller than when the vent plug 2 is inserted into an exhaust hole that does not have a protrusion 61, and the vent plug 2 can be easily inserted along the central axis Ca of the exhaust hole 6. In addition, since three or more protrusions 61 are arranged substantially evenly along the circumferential direction CD of the exhaust hole 6, the vent plug 2 can be easily inserted with its central axis aligned with the central axis Ca of the exhaust hole 6. Furthermore, since the tip of the protrusion 61 is rounded or flat when viewed from the central axis Ca of the exhaust hole 6, the stability of the posture of the vent plug 2 when the vent plug 2 is brought into contact with the tip of the protrusion 61 can be increased compared to when the tip of the protrusion 61 is sharp. This makes it even easier to insert the vent plug 2 along the central axis Ca of the exhaust hole 6. As a result, the inserted state of the vent plug 2 is improved, and the vent plug 2 can be prevented from coming off.

[0057] [5] With regard to the manufacturing method of the tire molding die 100 described above in [4], it is preferable that the three or more protrusions 61 are arranged at intervals from each other in the circumferential direction CD of the vent hole 6.

[0058] According to this method, the projections 61 are more easily crushed than when the projections 61 are arranged with no space between them, and the vent plug 2 is more easily fitted along the central axis Ca of the exhaust hole 6. This improves the fitted state of the vent plug 2 and makes it possible to prevent the vent plug 2 from coming off.

[0059] [6] With regard to the above-mentioned method [4] or [5] for manufacturing the tire molding die 100, in the vent hole forming step ST1, it is preferable to form the projections 61 by electric discharge machining.

[0060] According to this method, it becomes easy to form the protrusion 61 on the exhaust hole 6.

[0061] [7] With regard to the manufacturing method of the tire molding die 100 described above in [6], in the vent hole forming step ST1, a preferred method is to form a protrusion 61 whose protrusion amount Pa gradually increases with distance from the tire forming surface 1 by changing the feed speed of the electric discharge electrode EL or the voltage applied thereto when moving the electric discharge electrode EL in the direction of the central axis Ca of the vent hole 6 (axial direction AD).

[0062] According to this method, it is easier to form the protrusion 61 in the vent hole 6 whose protrusion amount Pa gradually increases with increasing distance from the tire forming surface 1 than in the case of cutting work.

[0063] The tire molding die 100 and the manufacturing method of the tire molding die 100 are not limited to the configurations of the above-mentioned embodiment, and are not limited to the above-mentioned effects. Furthermore, the tire molding die 100 and the manufacturing method of the tire molding die 100 can naturally be modified in various ways without departing from the gist of the present invention. For example, it is of course possible to arbitrarily select one or more of the configurations, methods, etc. related to the various modified examples described below and adopt them in the configurations, methods, etc. related to the above-mentioned embodiment.

[0064] In the above embodiment, the cross-sectional shape of the protrusion 61 is an arch shape, but is not limited to this. For example, as shown in Fig. 8, the cross-sectional shape of the protrusion 61 may be substantially trapezoidal. In this example, the tip of the protrusion 61 is rounded when viewed from the direction of the central axis Ca of the exhaust hole 6. The tip of the protrusion 61 is curved so as to be convex in the direction away from the central axis Ca. The cross-sectional shape of the protrusion 61 may be, for example, a polygonal shape (excluding a triangular shape). [Explanation of symbols]

[0065] Reference Signs List 1... tire forming surface, 2... vent plug, 21... exhaust passage, 3... housing, 31... top surface, 32... tapered surface, 33... cylindrical surface, 34... through hole, 35... support portion, 36... bottom surface, 37... tapered surface, 4... stem, 41... body, 41a... first body, 41b... second body, 42... head, 43... stopper, 5... biasing member, 6... exhaust hole, 61... projection, 11... tread mold, 12... side mold, 13... side mold, 14... bead ring, 15... cavity, 100... tire molding die, CD... circumferential direction, Ca... central axis, Pa... protrusion amount, T... tire, EL... electric discharge machining electrode

Claims

1. A tire forming surface; an exhaust hole that opens on the tire forming surface and into which a vent plug is fitted, The exhaust hole has three or more projections protruding toward the center of the hole, the three or more protrusions are substantially evenly spaced along a circumferential direction of the exhaust hole; A tire molding die, wherein a tip of the protrusion is rounded or flat when viewed from the central axial direction of the exhaust hole.

2. The tire mold according to claim 1 , wherein the three or more protrusions are spaced apart from one another in the circumferential direction.

3. 3. The tire molding die according to claim 1, wherein the projections increase in amount of projection with increasing distance from the tire forming surface.

4. an exhaust hole forming step of forming an exhaust hole on a tire forming surface; and a fitting step of fitting a vent plug into the exhaust hole, The exhaust hole has three or more projections protruding toward the center of the hole, the three or more protrusions are substantially evenly spaced along a circumferential direction of the exhaust hole; A method for manufacturing a tire molding mold, wherein a tip of the protrusion is rounded or flat when viewed from the central axial direction of the exhaust hole.

5. The method for manufacturing a tire molding mold according to claim 4 , wherein the three or more protrusions are arranged at intervals from one another in the circumferential direction.

6. The method for manufacturing a tire molding die according to claim 4 or 5, wherein in the vent hole forming step, the protrusions are formed by electric discharge machining.

7. 7. The method for manufacturing a tire molding die according to claim 6, wherein in the vent hole forming step, a feed speed of the electric discharge electrode or a voltage applied thereto is changed when the electric discharge electrode is moved in an axial direction of the vent hole, thereby forming the protrusion whose protrusion amount gradually increases with distance from the tire forming surface.

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