Vent plug, tire vulcanization mold, and tire manufacturing method

Abstract

To provide a vent plug that can maintain an exhaust function in an event of rubber biting, a tire vulcanizing mold and a method for manufacturing a tire.SOLUTION: A vent plug 2 comprises: a cylindrical housing 3 having an exhaust path therein; a stem 4 that is inserted to the housing 3; and a spring that energizes the stem 4 toward a cavity side so as to open the exhaust path. The housing 3 comprises: an annular top surface 31; a tapered surface 32 decreasing a diameter from the top surface 31 toward a side opposite to the cavity; and a cylindrical surface 33 extending along an axial direction AD of the housing 3 from the tapered surface 32 toward the side opposite to the cavity. A protrusion 36 is provided on a ridge line RL between the tapered surface 32 and the cylindrical surface 33.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] Tire curing molds are provided with numerous exhaust holes on the molding surface that forms the outer surface of the tire. These allow air to escape between the tire's outer surface and the molding surface during curing, reducing the occurrence of dents known as bare holes. Vent plugs are sometimes installed in the exhaust holes to prevent the formation of rubber protrusions known as spews. Known examples of vent plugs include spring vents, as disclosed in Patent Document 1.

[0003] The vent plug 92 shown in Figure 11 is a spring vent that includes a cylindrical housing 93 with an exhaust passage 91 inside, a stem 94 inserted into the housing 93, and a spring 95 that biases the stem 94. The vent plug 92 opens when the spring 95 biases the stem 94 toward the cavity (see Figure 11), and closes when the outer surface of the tire presses down on the stem 94. Therefore, the vent plug transitions from the open state to the closed state when it comes into contact with the tire, and returns from the closed state to the open state due to the operation of the spring 95 when the tire leaves.

[0004] However, if rubber entrapment occurs, the vent plug 92 will be prevented from returning to the open state, as shown in Figure 12. Rubber entrapment is a phenomenon in which unvulcanized rubber R, which has flowed in from the side (the left side in Figure 11) before the stem 94 is fully pushed down, enters the exhaust path 91 and becomes entangled with the spring 95. In a vent plug 92 with rubber entrapment, the operation of the spring 95 is prevented by the unvulcanized rubber R, causing the stem 94 to become stuck to the housing 93. If this causes the vent plug 92 to lose its exhaust function, bare spots will easily occur on the outer surface of the vulcanized tire. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2017-113895 Summary of the Invention [Problem to be solved by the invention]

[0006] The present disclosure has been made in consideration of the above-described circumstances, and its purpose is to provide a vent plug, a tire vulcanization mold, and a tire manufacturing method that can maintain exhaust function when rubber jamming occurs. [Means for solving the problem]

[0007] The vent plug of the present disclosure is a vent plug attached to an exhaust hole opening on the molding surface of a tire vulcanization mold, a cylindrical housing having an exhaust passage therein; a stem that is inserted into the housing and serves as a valve body for opening and closing the exhaust passage; and a biasing member that biases the stem toward a cavity side so as to open the exhaust passage, the housing has an annular top surface facing the cavity, a tapered surface that decreases in diameter from the top surface toward the opposite side to the cavity, and a cylindrical surface that extends from the tapered surface toward the opposite side to the cavity along the axial direction of the housing, A protrusion is provided on the ridgeline between the tapered surface and the cylindrical surface, on the cylindrical surface, or on a side surface portion of the stem that faces the ridgeline or the cylindrical surface in the closed state.

[0008] Another vent plug of the present disclosure is a vent plug attached to an exhaust hole opening on a molding surface of a tire vulcanization mold, a cylindrical housing having an exhaust passage therein; a stem that is inserted into the housing and serves as a valve body for opening and closing the exhaust passage; and a biasing member that biases the stem toward a cavity side so as to open the exhaust passage, the housing has an annular top surface facing the cavity, a tapered surface that decreases in diameter from the top surface toward the opposite side to the cavity, and a cylindrical surface that extends from the tapered surface toward the opposite side to the cavity along the axial direction of the housing, a protrusion is provided on the tapered surface or on a side surface portion of the stem that faces the tapered surface in a closed state, A slit is formed extending from the ridge between the tapered surface and the cylindrical surface toward the side opposite the cavity.

[0009] The tire vulcanizing mold of the present disclosure includes the molding surface that contacts the outer surface of the tire set in the cavity, and the above-mentioned vent plug attached to the exhaust hole that opens on the molding surface.

[0010] The tire manufacturing method of the present disclosure includes the steps of setting an unvulcanized tire in a cavity of a tire vulcanization mold equipped with the above-mentioned vent plug, and applying heat and pressure to the unvulcanized tire to vulcanize it. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view schematically illustrating an example of a tire vulcanization mold according to the present disclosure. [Figure 2] FIG. 1 is a cross-sectional view schematically showing a vent plug in an open state according to a first embodiment; [Figure 3] Cross-sectional view of Figure 2 taken along the arrow XX [Figure 4] FIG. 1 is a cross-sectional view schematically showing a vent plug in a closed state according to a first embodiment; [Figure 5] 1A and 1B are cross-sectional views showing a main part of a vent plug in a closed state and a rubber-engaged state, respectively, in a first embodiment; [Figure 6] FIG. 10 is a cross-sectional view of a main part showing a vent plug in a closed state according to a modification of the first embodiment. [Figure 7] FIG. 10 is a vertical cross-sectional view showing a vent plug in a closed state according to a second embodiment. [Figure 8] FIG. 10 is a cross-sectional view of a main part of the vent plug in a state where a rubber is engaged in the vent plug according to the second embodiment; [Figure 9]FIG. 10 is a vertical cross-sectional view showing a vent plug in a closed state according to a third embodiment. [Figure 10] FIG. 10 is a cross-sectional view of a main part of the vent plug in a state where a rubber is engaged in the vent plug according to the third embodiment. [Figure 11] FIG. 1 is a cross-sectional view showing a conventional vent plug in an open state. [Figure 12] A cross-sectional view of the vent plug of Figure 11 with rubber jamming [Figure 13] (A) AA cross-sectional view and (B) BB cross-sectional view of Figure 12 DETAILED DESCRIPTION OF THE INVENTION

[0012] An embodiment of the vent plug of the present disclosure will be described with reference to the drawings.

[0013] [First embodiment] First, a first embodiment of a vent plug of the present disclosure will be described with reference to Figures 1 to 6. Figure 1 shows a cross section of a tire vulcanization mold 10 (hereinafter, may be simply referred to as "mold 10") along a tire meridian cross section. This mold 10 is in a closed state. A tire T is set with the tire axial direction facing up and down. In Figure 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. Figure 2 shows an enlarged view of a main part of Figure 1, with the upper direction being the inner side in the tire radial direction and the lower direction being the outer side in the tire radial direction. Figure 3 is a cross section taken along arrow XX in Figure 2.

[0014] The mold 10 includes a cavity 15 in which the tire T is set, and a molding surface 1 that comes into contact with the outer surface of the tire T set in the cavity 15. The molding surface 1 is provided with an exhaust hole 16 that connects the inside of the mold 10 (i.e., the cavity 15) with the outside. During vulcanization molding, air is discharged between the outer surface of the tire T and the molding surface 1 through the exhaust hole 16. As shown enlarged in FIG. 2, a vent plug 2 is attached to the exhaust hole 16 that opens on the molding surface 1. The vent plug 2 is a spring vent.

[0015] An example of the material for the forming surface 1 is an aluminum material. This aluminum material is a concept that includes not only pure aluminum-based materials but also aluminum alloys, such as Al-Cu-based, Al-Mg-based, Al-Mg-Si-based, Al-Zn-Mg-based, Al-Mn-based, and Al-Si-based materials. 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 these may be made of the same metal or different metals.

[0016] The mold 10 includes a tread mold 11 for molding the tire tread, side molds 12 and 13 for molding the tire sidewalls, and bead rings 14 and 14 into which the tire bead portions are fitted. The molding surface 1 includes the inner surface of the tread mold 11 and the inner surfaces of the side molds 12 and 13. Although not shown, the inner surface of the tread mold 11 has projections and depressions for forming the tire tread pattern. While FIG. 1 depicts only one exhaust hole 16 opening on the inner surface of the tread mold 11, in reality, many exhaust holes opening on the inner surfaces of the tread mold 11 and the side molds 12 and 13 are provided.

[0017] The vent plugs 2 are attached to exhaust holes 16 that open on the inner surface of the tread mold 11 that serves as the molding surface 1, but instead of or in addition to this, they can also be attached to exhaust holes that open on the inner surfaces of the side molds 12 and / or side molds 13. Also, in this embodiment, the mold 10 has a structure that includes the tread mold 11 and a pair of side molds 12, 13, but is not limited to this, and for example, the mold structure may be such that the tread mold is divided into two parts, upper and lower, at the center.

[0018] As shown in FIG. 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 spring 5 that serves as a biasing member that biases the stem 4 toward the cavity side D1 (the tire radially inward in FIG. 2) to open the exhaust passage 21. For convenience of illustration, the stem 4 and spring 5 are shown as viewed from the front (the same applies to other figures). In this embodiment, an example is shown in which the biasing member is a coil-shaped spring 5, but the biasing member is not limited to this and may be a structure that uses, for example, a leaf spring.

[0019] The housing 3 is press-fit into the exhaust hole 16 by an interference fit. The housing 3 has an annular top surface 31 facing the cavity 15, a tapered surface 32 that decreases in diameter from the top surface 31 toward the anti-cavity side D2 (the tire radial outer side 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. The axial direction AD coincides with the axial direction of the exhaust hole 16 and the stem 4. The top surface 31 is disposed flush with (i.e., on the same plane as) the molding surface 1, but is not limited to this. A through hole 34 and an inner flange-shaped support portion 35 are provided at the end of the housing 3 farther from the cavity 15.

[0020] The stem 4 has 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 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 this stopper 43. The stopper 43 can pass through the through-hole 34 by elastically deforming to close the slit 44. In this embodiment, the stem 4 has a flange 45 that closes the inlet of the exhaust path 21 in the closed state (see FIGS. 4 and 5(A)).

[0021] The body 41 has 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 G1 through which air can pass is formed between the first body 41a and the cylindrical surface 33 surrounding it (see FIG. 5). The outer diameter of the second body 41b is smaller than the outer diameter of the first body 41a. A gap in which a spring 5 can be disposed is formed between the second body 41b and the cylindrical surface 33 surrounding it. The spring 5 is inserted into the second body 41b.

[0022] The head 42 is formed in a truncated cone shape with a diameter that decreases toward the opposite cavity side D2. The head 42 has a tapered side surface that corresponds to the tapered surface 32. In this embodiment, a gap G2 is formed between the head 42 in the closed state and the tapered surface 32 that surrounds it (see FIG. 5). The spring 5 is interposed between the first body 41a and the support portion 35 and biases the stem 4 so as to push it up.

[0023] In Figure 2, the spring 5 pushes up on the stem 4, opening the exhaust passage 21 and keeping the vent plug 2 in an open state. While the vent plug 2 is in an open state, the air inside the cavity 15 is discharged to the outside of the mold 10 through the exhaust passage 21 as the outer surface of the tire approaches the molding 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 between the tapered surface 32 and the head 42, through the gap between the cylindrical surface 33 and the first body 41a, and then through the gap between the cylindrical surface 33 and the second body 41b.

[0024] In FIG. 4, the tire outer surface Ts presses down on the stem 4, closing the exhaust passage 21 and placing the vent plug 2 in a closed state. In this embodiment, the entrance to the exhaust passage 21 is closed by the flange 45 of the stem 4. When the stem 4 is pressed down against the biasing force of the spring 5, the flange 45 comes into contact with the top surface 31 and closes the entrance to the exhaust passage 21. Therefore, in this embodiment, the top surface 31 serves as the valve seat. The flange 45 is formed in an annular shape around the axis of the housing 3. When the tire outer surface Ts separates from the molding surface 1 after vulcanization molding is completed, the spring 5 presses up the stem 4, returning it to the open state shown in FIG. 2.

[0025] During the vulcanization molding process, unvulcanized rubber that has entered the exhaust passage 21 may become entangled with the spring 5, causing rubber jamming. If this causes the exhaust function of the vent plug 2 to be lost, bare spots may easily form on the outer surface of the vulcanization-molded tire. Therefore, in the first embodiment, a protrusion 36 is provided on the ridge line RL between the tapered surface 32 and the cylindrical surface 33 so that exhaust function can be maintained even if rubber jamming occurs. The protrusion 36 protrudes further toward the cavity side D1 than the tapered surface 32 and further toward the stem 4 than the cylindrical surface 33. In this embodiment, such a protrusion is not provided on the portion of the tapered surface 32 that is away from the ridge line RL toward the cavity side D1, or on the portion of the cylindrical surface 33 that is away from the ridge line RL toward the anti-cavity side D2.

[0026] Here, the state of the vent plug when rubber jamming occurs will be described with reference to Figures 12 and 13. Figures 13(A) and 13(B) are cross-sectional views taken along the lines AA and BB in Figure 12, respectively. As described above, unvulcanized rubber R (see Figure 11) has flowed from the side into the exhaust path 91 and become entangled with the spring 95. With respect to the flow direction of the unvulcanized rubber R, the left side of the drawing is the upstream side, and the right side of the drawing is the downstream side. The unvulcanized rubber R that has entered the exhaust path 91 causes the stem 94 to adhere to the housing 93 before it is fully pushed down.

[0027] In a vent plug 92 with rubber jamming, the stem 94 is eccentric downstream relative to the housing 93. This is because the unvulcanized rubber R pushes the stem 94 downstream while entering the exhaust passage 91. The upstream portion of the gap between the housing 93 and the stem 94 widens as the stem 94 becomes eccentric downstream, and is almost completely blocked by the unvulcanized rubber R that has entered there. The downstream portion of the gap is also almost completely blocked by the eccentric stem 94 coming into contact with the inner surface of the housing 93. When the exhaust passage 91 is substantially blocked in this way, the vent plug 92 loses its exhaust function.

[0028] In contrast, with the vent plug 2 of this embodiment, when unvulcanized rubber pushes the stem 4 downstream, the protrusion 36 interposed between the housing 3 and the stem 4 maintains a gap therebetween, leaving the exhaust path 21 at least partially open, as shown in FIG. 5(B). Specifically, the upstream portion of the gap between the housing 3 and the stem 4 does not expand significantly, preventing excessive intrusion of unvulcanized rubber, while the downstream portion of the gap maintains gaps G1 and G2, allowing air to pass through. As a result, the exhaust function can be maintained even when rubber is trapped.

[0029] As described above, the vent plug 2 of the first embodiment is intended to ensure the gaps G1 and G2 by the protrusion 36 provided on the ridge line RL. However, because the protrusion 36 is provided on the ridge line RL, the tapered surface 32 cannot be used as a valve seat. Therefore, in this vent plug 2, as shown in FIG. 5(A), a flange 45 is provided on the stem 4 that can close the entrance to the exhaust passage 21 with the top surface 31 serving as a valve seat.

[0030] As shown in FIG. 3, the protrusions 36 are provided at multiple locations around the axis of the housing 3, with gaps between them. The protrusions 36 are preferably provided at three or more locations around the circumference, more preferably at four or more locations, and even more preferably at eight or more locations. In this embodiment, the protrusions 36 have a shape that extends in the circumferential direction, but this is not limited to this. Furthermore, if the protrusions 36 are angular, they may get caught on the stem 4 when raised or lowered. Therefore, it is preferable that the shape of the protrusions 36 in a plan view as shown in FIG. 3 be a rounded shape such as a (curved) semi-elliptical shape so as not to impair the mobility of the stem 4.

[0031] The protrusion 36 has a substantially semicircular outline when viewed from the side as shown in FIG. 5. A cross section of the protrusion 36 cut along a plane passing through the central axis of the housing 3 also has a substantially semicircular outline. This shape of the protrusion 36 is effective in preventing the protrusion 36 from getting caught on the stem 4 as it repeatedly moves up and down, and in preventing the mobility of the stem 4 from being impaired. However, the shape of the protrusion is not limited to this. The protrusion amount of the protrusion 36 relative to the tapered surface 32 is, for example, 0.01 to 0.03 mm. The protrusion amount of the protrusion 36 relative to the cylindrical surface 33 is, for example, 0.01 to 0.03 mm.

[0032] The method for providing the protrusions 36 is not particularly limited. Therefore, for example, the protrusions 36 may be provided by cutting a ring-shaped member that is attached to the inside of the housing 3 by welding or the like. The protrusions 36 may be made from a member separate from the housing 3 in this way, or may be provided integrally with the housing 3.

[0033] In this embodiment, an example has been shown in which the protrusion 36 is provided on the ridge line RL. However, instead of or in addition to this, a protrusion may be provided on a side portion of the stem 4 that faces the ridge line RL in the closed state. In this case, the side portion of the stem 4 on which the protrusion is provided is a portion that includes the vicinity of the boundary between the head 42 and the first body 41a (see FIG. 5(A)). However, it is preferable that the protrusion be provided on the housing 3 as in the above-described embodiment. The reason for this is that if the stem is replaced with a normal stem that does not have a protrusion during maintenance work after rubber jamming occurs, the effect of maintaining the above-described exhaust function can be obtained thereafter.

[0034] In the present embodiment, the stem 4 has a flange 45 that abuts against the top surface 31 to close the entrance of the exhaust passage 21 when the stem 4 is pushed down against the biasing force of the spring 5, but this is not limiting. Therefore, as shown in FIG. 6, the stem 4 may have a structure that does not have such a flange 45. In this case, a minute clearance C is set at the entrance of the gap between the housing 3 and the stem 4 so that air can be exhausted while preventing unvulcanized rubber from entering the exhaust passage 21. The size of the clearance C is, for example, 0.01 to 0.03 mm.

[0035] A tire manufacturing method using a mold 10 equipped with a vent plug 2 includes the steps of setting an unvulcanized tire in the cavity 15 of the mold 10 and applying heat and pressure to the unvulcanized tire to vulcanize it. The tire expands and deforms due to the expansion of a rubber bag called a bladder, and its outer surface presses against the molding surface 1. During this process, air between the tire and the molding surface 1 is discharged to the outside through the exhaust path 21 of the vent plug 2. At this time, the space inside the exhaust hole 16 may be suctioned with a suction machine to improve exhaust performance. Even if rubber jamming occurs during repeated tire vulcanization molding, the exhaust function of the vent plug 2 can be maintained as described above, thereby reducing the occurrence of bare holes.

[0036] [Second embodiment] Next, a second embodiment of a vent plug of the present disclosure will be described with reference to Figures 7 and 8. Other than the configuration described below, the second embodiment can be configured similarly to the first embodiment, and therefore the following description will omit commonalities and focus mainly on differences. Components already described in the first embodiment will be assigned the same reference numerals, and redundant description will be omitted.

[0037] In the vent plug 2α shown in Figures 7 and 8, a protrusion 37 is provided on the cylindrical surface 33. The protrusion 37 is located closer to the cavity D1 than the spring 5. The protrusion 37 is located closer to the cavity D2 than the ridge line RL. No such protrusions are provided on the ridge line RL or the tapered surface 32. The protrusions 37 are provided at multiple locations in the circumferential direction around the axis of the housing 3, with gaps between them. With this configuration, when unvulcanized rubber pushes the stem 4 downstream (to the right in the drawing), the protrusions 37 ensure a gap between the housing 3 and the stem 4, as shown in Figure 8. This allows the exhaust function to be maintained even if rubber jamming occurs. The protrusion 37 may also be provided on the side of the stem 4 that faces the cylindrical surface 33 in the closed state.

[0038] In a normal operating state where no rubber is trapped, the vent plug 2α is in a closed state as the tire outer surface Ts presses down on the stem 4, as shown in Figure 7, and returns to an open state when the outer surface Ts separates from the molding surface 1. In the closed state, the head 42 comes into contact with the tapered surface 32, thereby closing the exhaust passage 21. In this way, with the vent plug 2α, the tapered surface 32 can be used as a valve seat to close the entrance to the exhaust passage 21, so there is no need to provide the stem 4 with a flange that seats on the top surface 31 of the housing 3. However, there is no problem if the flange 45 employed in the first embodiment is provided on the stem 4 of the vent plug 2α.

[0039] [Third embodiment] Next, a third embodiment of a vent plug of the present disclosure will be described with reference to Figures 9 and 10. Other than the configuration described below, the third embodiment can be configured similarly to the first embodiment, and therefore the following description will omit commonalities and focus mainly on differences. Components already described in the first embodiment will be assigned the same reference numerals, and redundant description will be omitted.

[0040] In the vent plug 2β shown in Figures 9 and 10, a protrusion 38 is provided on the tapered surface 32. The protrusion 38 is located closer to the cavity D1 than the ridge line RL. No such protrusion is provided on the ridge line RL or the cylindrical surface 33. With this configuration, when the unvulcanized rubber pushes the stem 4 downstream (to the right in the drawings), the eccentric stem 4 comes into contact with the inner surface (cylindrical surface 33) of the housing 3, as shown in Figure 10. Furthermore, unvulcanized rubber (not shown in Figure 10) may enter the gap between the housing 3 and the stem 4 on the upstream side, potentially causing the exhaust path 21 to become substantially blocked.

[0041] Therefore, in the third embodiment, slits 39 are formed that extend from the ridge line RL between the tapered surface 32 and the cylindrical surface 33 toward the anti-cavity side D2. The slits 39 are formed in the cylindrical surface 33 of the housing 3. The slits 39 are formed at multiple locations in the circumferential direction around the axis of the housing 3. The slits 39 connect the gap between the head 42 and the tapered surface 32, which is secured by the protrusion 38, to the gap between the body 4 (the second body 41b) and the cylindrical surface 33. This keeps the exhaust path 21 at least partially open, and the exhaust function can be maintained even if rubber jamming occurs.

[0042] In a normal operating state where no rubber is trapped, the vent plug 2β is closed as the tire's outer surface Ts presses down on the stem 4, as shown in FIG. 9, and returns to an open state when the outer surface Ts separates from the molding surface 1. As with the example in FIG. 6, a small clearance is provided at the entrance to the gap between the housing 3 and the stem 4 so that air can be discharged while preventing unvulcanized rubber from entering the exhaust passage 21. The size of the clearance is, for example, 0.01 to 0.03 mm. As with the example in FIG. 5, the stem 4 of the vent plug 2β can also be provided with a flange that seats on the top surface 31 of the housing 3.

[0043] As described above, the vent plug 2, 2α of the present disclosure is a vent plug that is attached to the exhaust hole 16 that opens on the molding surface 1 of the tire vulcanization mold 10, and 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 spring 5 that serves as a biasing member that biases the stem 4 toward the cavity side D1 to open the exhaust passage 21. The housing 3 has an annular top surface 31 that faces the cavity 15, a tapered surface 32 that decreases in diameter from the top surface 31 toward the anti-cavity side D2, 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. Protrusions 36, 37 are provided on the ridge line RL between the tapered surface 32 and the cylindrical surface 33, on the cylindrical surface 33, or on a side surface portion of the stem 4 that faces the ridge line RL or the cylindrical surface 33 in the closed state.

[0044] With this configuration, when the stem 4 is pushed downstream by unvulcanized rubber flowing in from the side, the projections 36, 37 interposed between the stem 4 and the housing 3 ensure a gap between them, leaving the exhaust path 21 at least partially open. Therefore, the exhaust function can be maintained even if rubber gets stuck.

[0045] Another vent plug 2β of the present disclosure is a vent plug that is attached to an exhaust hole 16 that opens on the molding surface 1 of a tire vulcanization mold 10. The vent plug 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 spring 5 that serves as a biasing member that biases the stem 4 toward the cavity side D1 to open the exhaust passage 21. The housing 3 has an annular top surface 31 that faces the cavity 15, a tapered surface 32 that decreases in diameter from the top surface 31 toward the anti-cavity side D2, 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. A protrusion 38 is provided on the tapered surface 32 or on a side surface of the stem 4 that faces the tapered surface 32 in the closed state, and a slit 39 is formed that extends from a ridge line RL between the tapered surface 32 and the cylindrical surface 33 toward the anti-cavity side D2.

[0046] With this configuration, when the stem 4 is pushed downstream by unvulcanized rubber flowing from the side, the protrusion 38 and slit 39 interposed between the stem 4 and the housing 3 keep the exhaust path 21 at least partially open. Therefore, the exhaust function can be maintained even if rubber gets stuck.

[0047] The stem 4 may have a flange 45 that abuts against the top surface 31 to close the inlet of the exhaust passage 21 when the stem 4 is pushed down against the biasing force of the spring 5. This allows the inlet of the exhaust passage 21 to be properly closed in the closed state even if the tapered surface 32 cannot be used as a valve seat. Even if the tapered surface 32 can be used as a valve seat, it is acceptable to provide such a flange 45 on the stem 4.

[0048] From the viewpoint of ensuring a gap between the stem 4 and the housing 3 regardless of the direction in which the unvulcanized rubber flows (i.e., the direction in which the stem 4 is pushed), it is preferable that the protrusions 36 be provided at three or more locations in the circumferential direction around the axis of the housing 3. This makes it possible to more reliably maintain the exhaust function of the vent plug 2 in the event of rubber jamming. The same applies to the protrusion 37 of the vent plug 2α and the protrusion 38 and slit 39 of the vent plug 2β.

[0049] The tire vulcanizing mold 10 of the present disclosure includes a molding surface 1 that contacts the outer surface of a tire T set in a cavity 15, and a vent plug 2 (or vent plug 2α or vent plug 2β) attached to an exhaust hole 16 that opens on the molding surface 1. With this configuration, when rubber jamming occurs, a gap is secured between the stem 4 and the housing 3 as described above, thereby maintaining the exhaust function.

[0050] The tire vulcanizing mold 10 of the present disclosure is equivalent to a normal tire vulcanizing mold, except that the vent plug 2 (or vent plug 2α or vent plug 2β) attached to the exhaust hole 16 is configured as described above, and any of the conventionally known shapes, materials, mechanisms, etc. can be adopted.

[0051] The tire manufacturing method of the present disclosure includes the steps of setting an unvulcanized tire in the cavity 15 of a tire vulcanization mold 10 equipped with a vent plug 2 (or vent plug 2α or vent plug 2β), and applying heat and pressure to the unvulcanized tire to vulcanize it. According to this method, even if rubber jamming occurs, a gap can be secured between the stem 4 and the housing 3 as described above, thereby maintaining the exhaust function.

[0052] The tire manufacturing method of the present disclosure is the same as a normal tire manufacturing method, except that the vent plug 2 (or vent plug 2α or vent plug 2β) as described above is attached to the exhaust hole 16 of the tire vulcanization mold 10, and any of the conventionally known processes and vulcanization conditions can be adopted.

[0053] Although the embodiments of the present disclosure have been described above, it should be understood that the specific configurations are not limited to these embodiments. The scope of the present disclosure is not limited to the above-described embodiments, but is indicated by the claims, and further includes all modifications within the meaning and scope equivalent to the claims.

[0054] The vent plug, tire vulcanization mold, and tire manufacturing method of the present disclosure are not limited to the above-described embodiments, and various improvements and modifications are possible without departing from the spirit thereof. Furthermore, the configurations employed in the first to third embodiments described above can be combined in any desired manner. [Explanation of symbols]

[0055] 1 Molding surface 2 vent plugs 3. Housing 4 Stem 5. Spring (an example of a biasing member) 10 Tire curing mold 15 Cavity 16 Exhaust vent 21 Exhaust duct 31 Top surface 32 Tapered surface 33 Cylindrical Surface 36 Protrusion 37 Protrusion 38 Protrusion 39 Slit 41 Body 42 heads 45 Tsuba

Claims

1. A vent plug attached to an exhaust hole opening on the molding surface of a tire vulcanization mold, a cylindrical housing having an exhaust passage therein; a stem that is inserted into the housing and serves as a valve body for opening and closing the exhaust passage; and a biasing member that biases the stem toward a cavity side so as to open the exhaust passage, the housing has an annular top surface facing the cavity, a tapered surface that decreases in diameter from the top surface toward the opposite side to the cavity, and a cylindrical surface that extends from the tapered surface toward the opposite side to the cavity along the axial direction of the housing, a protrusion having a substantially semicircular outline in a vertical cross section provided on a ridgeline between the tapered surface and the cylindrical surface.

2. A vent plug attached to an exhaust hole opening on the molding surface of a tire vulcanization mold, a cylindrical housing having an exhaust passage therein; a stem that is inserted into the housing and serves as a valve body for opening and closing the exhaust passage; and a biasing member that biases the stem toward a cavity side so as to open the exhaust passage, the housing has an annular top surface facing the cavity, a tapered surface that decreases in diameter from the top surface toward the opposite side to the cavity, and a cylindrical surface that extends from the tapered surface toward the opposite side to the cavity along the axial direction of the housing, a protrusion is provided on a side surface portion of the stem that faces a ridge line between the tapered surface and the cylindrical surface in a closed state, The stem has a columnar body and a head integrally connected to the body, the body includes a first body connected to a side of the head opposite the cavity, and a second body connected to a side of the first body opposite the cavity; The outer diameter of the second body is smaller than the outer diameter of the first body, The second body is inserted into a coil spring as the biasing member, a lower end of the first body positioned on the opposite side of the cavity from the protrusion, the lower end of the first body restricting the position of the upper end of the spring;

3. A vent plug attached to an exhaust hole opening on the molding surface of a tire vulcanization mold, a cylindrical housing having an exhaust passage therein; a stem that is inserted into the housing and serves as a valve body for opening and closing the exhaust passage; and a biasing member that biases the stem toward a cavity side so as to open the exhaust passage, the housing has an annular top surface facing the cavity, a tapered surface that decreases in diameter from the top surface toward the opposite side to the cavity, and a cylindrical surface that extends from the tapered surface toward the opposite side to the cavity along the axial direction of the housing, a protrusion having a substantially semicircular outline in a vertical cross section is provided on the tapered surface or on a side surface portion of the stem that faces the tapered surface in a closed state, a slit extending from the ridge line between the tapered surface and the cylindrical surface toward the side opposite the cavity is formed.

4. 4. The vent plug according to claim 1, wherein the stem has a flange that abuts against the top surface to close the inlet of the exhaust passage when the stem is pushed down against the biasing force of the biasing member.

5. The vent plug according to any one of claims 1 to 4, wherein the protrusions are provided at three or more locations in a circumferential direction around the axis of the housing.

6. A tire vulcanizing mold comprising: the molding surface that contacts the outer surface of the tire set in the cavity; and the vent plug according to any one of claims 1 to 5 that is attached to the exhaust hole that opens on the molding surface.

7. A method for manufacturing a tire, comprising the steps of setting an unvulcanized tire in a cavity of a tire vulcanization mold equipped with the vent plug according to any one of claims 1 to 5, and applying heat and pressure to the unvulcanized tire to vulcanize it.

Images