Tire vulcanization mold and tire manufacturing method using the same

Abstract

To provide a tire vulcanization mold that can effectively suppress clogging of vent hole due to spew, and to provide a tire manufacturing method using the same.SOLUTION: In a tire vulcanization mold 10 having a molding surface 31 for molding tire outer surface and a vent hole 32 opened in the molding surface 31, a valve 33 having a structure that can be opened and closed by the flow of air in the vent hole 32 is arranged at a position on the depth side of the vent hole 32 where the spew S formed inside the vent hole 32 cannot reach. An unvulcanized tire T is placed inside the tire vulcanization mold 10, and vulcanization is performed while pressurizing the tire T from the inside.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a tire vulcanizing mold equipped with vent holes and a tire manufacturing method using the same, and more specifically to a tire vulcanizing mold that makes it possible to effectively suppress clogging of the vent holes due to spew, and a tire manufacturing method using the same. [Background technology]

[0002] In the manufacturing process of pneumatic tires, an unvulcanized tire is placed inside a tire curing mold and heated while being pressurized from the inside by a bladder to vulcanize the tire. If air remains between the molding surface of the tire curing mold and the unvulcanized tire, this residual air can cause tire surface damage. To prevent such tire surface damage, tire curing molds are provided with multiple vent holes that open to the molding surface for air release.

[0003] However, if at least a portion of the spews (beard-like rubber pieces) formed in the vent holes during vulcanization remain in the vent holes when the tire is demolded and clog the vent holes, air cannot be bled through the vent holes during the next vulcanization, resulting in damage to the tire surface in that area. Furthermore, if the vent holes become clogged with spews, tire production must be temporarily stopped to clean the vent holes, which significantly reduces tire productivity.

[0004] Therefore, in order to prevent clogging of the vent holes, it has been proposed to provide non-through vent holes that do not communicate with the outside of the mold (see, for example, Patent Documents 1 and 2). However, because non-through vent holes do not inherently have the function of discharging air, they have the disadvantage of not being able to fully ensure the effect of preventing tire surface damage caused by residual air.

[0005] Another proposed structure involves installing a vent piece with an air hole inside the vent hole and an elastic member that elastically closes the air hole, allowing air to escape through the gap between the vent piece and the elastic member while blocking the rubber with the elastic member (see, for example, Patent Document 3). Similarly, another proposed structure involves installing a valve member near the entrance of the vent hole to prevent the rubber from leaking out (see, for example, Patent Document 4). However, in both cases, the elastic member or valve member must be installed near the entrance of the vent hole to shorten the spew. In such locations, the pressure of the rubber flowing into the vent hole during vulcanization is high, making it easy for the rubber to flow into the gap between the elastic member or valve member, which can result in a deterioration of the valve function. This has the disadvantage of requiring frequent cleaning and replacement of the elastic member or valve member.

[0006] Furthermore, a structure has been proposed in which a valve such as a solenoid valve is installed in the flow path of the vent hole and opened and closed by an external signal, thereby ensuring the ability to discharge residual air while suppressing the formation of spew (see, for example, Patent Document 5). However, this requires a complex mechanism, which has the disadvantage of increasing equipment and maintenance costs. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 9-94830 [Patent Document 2] Patent No. 6495239 [Patent Document 3] Patent No. 5227266 [Patent Document 4] Patent No. 6880817 [Patent Document 5] Japanese Patent Application Laid-Open No. 2014-87958 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a tire vulcanization mold that can effectively prevent clogging of vent holes due to spew, and a tire manufacturing method using the same. [Means for solving the problem]

[0009] In order to achieve the above object, the tire vulcanizing mold of the present invention is characterized in that, in the tire vulcanizing mold having a molding surface for molding the outer surface of the tire and a vent hole opening onto the molding surface, a valve having a structure that can be opened and closed by the air flow within the vent hole is disposed at the back side of the vent hole in a position that cannot be reached by the spew formed within the vent hole.

[0010] The tire manufacturing method of the present invention is characterized in that an unvulcanized tire is placed inside the tire vulcanization mold described above, and the tire is vulcanized while being pressed against the molding surface. [Effects of the Invention]

[0011] As a result of extensive research into tire curing molds equipped with vent holes, the present inventors discovered that when vulcanization is repeatedly performed using such a tire curing mold, dirt gradually accumulates near the tip of the spew formed in the vent hole, causing the tip of the spew to break due to the accumulation of dirt. Furthermore, upon investigating the physical properties of the spew, they found that the pressure in the vent hole gradually decreases from the base to the tip, and that the tip of the spew is heated at a pressure close to atmospheric pressure, causing significant foaming. They also found that the density of the rubber at the tip of the spew decreases, and that its breaking strength also decreases, making it more susceptible to the accumulation of dirt and spew breakage. In light of this situation, the present inventors discovered that vent hole clogging can be effectively prevented by suppressing rubber foaming at the tip of the spew, leading to the present invention.

[0012] Specifically, in a tire vulcanization mold having a molding surface for molding the tire outer surface and a vent hole opening to the molding surface, a valve is disposed at the rear of the vent hole, out of the reach of the spew formed in the vent hole, and is structured to be openable and closable by the air flow through the vent hole. By closing the valve with the air flow during vulcanization, the pressure in the space formed between the rubber flowing into the vent hole and the valve is maintained, thereby suppressing rubber foaming at the tip of the spew. This prevents dirt from accumulating near the tip of the spew formed in the vent hole and prevents breakage of the tip of the spew due to such deposits. This effectively prevents clogging of the vent hole due to the spew. As a result, tire surface damage caused by residual air is prevented, and tire productivity is improved by reducing the frequency of vent hole cleaning.

[0013] According to the present invention, the vent hole is connected to the outside of the mold, so the residual air exhaust performance can be sufficiently ensured. Furthermore, the valve is disposed at the back of the vent hole in a position where the spew cannot reach, so rubber does not enter the gap of the valve, and the frequency of replacement and cleaning can be reduced. Furthermore, because the valve has a structure that can be opened and closed by the air flow in the vent hole, no complicated mechanism is required, and there is no increase in equipment costs or maintenance costs.

[0014] In the present invention, the valve is preferably located at a position 150% to 200% of the average length of the spew formed in the vent hole from the molding surface. Alternatively, the valve is preferably located 18 mm to 30 mm from the molding surface along the axial direction of the vent hole. By locating the valve at a position that is an appropriate distance from the molding surface of the vent hole in this way, contact between the rubber flowing into the vent hole and the valve is reliably avoided, while ensuring pressure in the space formed between the rubber flowing into the vent hole and the valve, suppressing foaming of the rubber at the tip of the spew and effectively suppressing clogging of the vent hole by the spew.

[0015] In the present invention, it is preferable to provide a vent piece that includes at least a portion of the vent hole and is separable from the main body of the mold. By employing a vent piece that is separable from the main body of the mold, a valve can be easily disposed in relation to the vent hole. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a meridian cross-sectional view showing a tire vulcanizing apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing a vent hole portion of the tire vulcanizing mold according to the present invention. [Figure 3] 3A and 3B are cross-sectional views showing the operation of a valve in a tire vulcanizing mold according to the present invention, in which (a) and (b) are cross-sectional views showing the operation of the valve at each stage. [Figure 4] 1 is a graph showing the relationship between the length of the spew formed in the vent hole and the growth rate of the spew in the tire manufacturing method according to the present invention. [Figure 5] 10 is a graph showing the relationship between the compression length of the space formed between the rubber flowing into the vent hole and the valve and the generated pressure in the tire manufacturing method according to the present invention. [Figure 6] FIG. 1 is a cross-sectional view showing a spew formed in a conventional vent hole. [Figure 7] 1A to 1C show the mechanism by which clogging occurs in a conventional vent hole, with (a) to (c) being cross-sectional views showing the state of the vent hole at each stage. DETAILED DESCRIPTION OF THE INVENTION

[0017] The configuration of the present invention will be described in detail below with reference to the accompanying drawings. Fig. 1 shows a tire vulcanizing apparatus according to an embodiment of the present invention, Fig. 2 shows the vent hole portion of a tire vulcanizing mold according to the present invention, and Fig. 3 shows the operating state of the valve in the tire vulcanizing mold according to the present invention.

[0018] 1, this tire vulcanizing apparatus includes a tire vulcanizing mold (hereinafter referred to as "mold") 10 that molds the outer surface of a pneumatic tire T, and a cylindrical bladder 20 that is inserted inside the pneumatic tire T. In addition, this tire vulcanizing apparatus includes a heating and pressurizing medium supply means (not shown) for supplying a heating and pressurizing medium such as steam to the inside of the bladder 20, and a heating means (not shown) for heating the mold 10.

[0019] The mold 10 is composed of a lower side plate 11 and an upper side plate 12 for molding the sidewall portions of the pneumatic tire T, a lower bead ring 13 and an upper bead ring 14 for molding the bead portions of the pneumatic tire T, and a plurality of sectors 15 for molding the tread portion of the pneumatic tire T, and the pneumatic tire T is vulcanized and molded inside the mold 10. Note that the structure of the mold 10 is not particularly limited, and in addition to a sectional type mold as shown in the figure, a two-split type mold can also be used.

[0020] The lower end of the bladder 20 is held between the lower bead ring 13 and the lower clamp ring 21, and the upper end of the bladder 20 is held between the upper clamp ring 22 and the auxiliary ring 23. In the vulcanized state shown in Fig. 1, the bladder 20 is in a state of expanding radially outward of the pneumatic tire T, but when the pneumatic tire T is removed from the mold 10 after vulcanization, the upper clamp ring 22 moves upward, and the bladder 20 is removed from the inside of the pneumatic tire T.

[0021] In the tire vulcanization apparatus described above, as shown in FIGS. 1 and 2 , the mold 10 has a molding surface 31 that molds the outer surface of the tire and vent holes 32 that open to the molding surface 31. One end of the vent holes 32 opens to the molding surface 31, while the other end communicates with the outside of the mold 10. While FIG. 1 depicts a structure in which the vent holes 32 are formed in the sectors 15 that constitute the mold 10, the vent holes 32 can also be formed in the lower side plate 11, the upper side plate 12, the lower bead ring 13, or the upper bead ring 14, and multiple vent holes 32 can be disposed throughout the mold 10. The mold 10 has a main body 10A and a vent piece 10B that encompasses at least a portion of the vent holes 32 and is separable from the main body 10A of the mold 10. The vent piece 10B is configured to be detachable from the main body 10A of the mold 10.

[0022] 2, in the mold 10, a valve 33 having a structure that can be opened and closed by the air flow in the vent hole 32 is disposed at the back side of the vent hole 32, in a position that cannot be reached by the spew S formed in the vent hole 32. More specifically, the valve 33 is comprised of an outer cylinder 33A that is fitted into the vent hole 32 and has a valve seat on the molding surface 31 side, a valve element 33B inserted inside the outer cylinder 33A, and a spring member 33C (e.g., a coil spring) that urges the valve element 33B in a direction away from the valve seat of the outer cylinder 33A. The valve seat of outer cylinder 33A is inclined at an angle of 45° to 80°, more preferably at an angle of 60° to 80°, relative to the axial direction of vent hole 32, and even more preferably is curved so as to be convex toward molding surface 31. The gap between valve element 33B and the valve seat of outer cylinder 33A is set in the range of 0.05 mm to 0.2 mm, more preferably in the range of 0.05 mm to 0.1 mm. The spring constant of spring member 33C is set in the range of 0.3 N / mm to 1.3 N / mm, more preferably in the range of 0.3 N / mm to 0.6 N / mm.

[0023] When vulcanizing a pneumatic tire T using the above-mentioned tire vulcanizing apparatus, an unvulcanized pneumatic tire T is placed inside the mold 10, a bladder 20 is inserted inside the pneumatic tire T, and a heating and pressurizing medium is introduced into the bladder 20 while the mold 10 is heated from the outside, thereby vulcanizing the pneumatic tire T while pressurizing the pneumatic tire T toward the molding surface 31.

[0024] During this vulcanization process, air remaining between the molding surface 31 of the mold 10 and the unvulcanized pneumatic tire T is discharged to the outside of the mold 10 through the vent holes 32. Then, as shown in FIGS. 3(a) and 3(b), the unvulcanized rubber G that constitutes the pneumatic tire T enters the vent holes 32, and spews S are formed in the vent holes 32. When the vulcanized pneumatic tire T is removed from the mold 10, the spews S are pulled out through the vent holes 32. Then, the spews S are cut off as necessary.

[0025] Here, the mechanism by which clogging occurs in conventional vent holes will be explained in detail using Figure 6 and Figures 7(a) to 7(c). According to the findings of the present inventors, as shown in Figure 6, in a conventional vent hole 32, the pressure gradually decreases from the base of the spew S toward the tip, and the tip of the spew S is heated under conditions close to atmospheric pressure, causing significant foaming. This foaming is caused not only by the foaming agent contained in the rubber but also by moisture, etc. As a result, the density of the rubber at the tip of the spew S decreases, and the breaking strength also decreases, which makes it more susceptible to the accumulation of dirt and the spew S breaking.

[0026] If the vulcanization process is repeated under these conditions, as shown in Fig. 7(a), dirt accumulates near the tip of the spew S formed in the vent hole 32 of the mold 10, and deposit X gradually grows. Then, as shown in Fig. 7(b), unvulcanized rubber G enters the vent hole 32 during vulcanization and reaches a position beyond the deposit X. Then, as shown in Fig. 7(c), when the spew S is pulled out after vulcanization, the tip of the spew S, which has become integrated with the deposit X, breaks off and blocks the vent hole 32.

[0027] In contrast, in the mold 10 described above, a valve 33 that can be opened and closed by the air flow in the vent hole 32 is disposed at the back of the vent hole 32, out of the reach of the spew S formed in the vent hole 32. Therefore, as shown in FIG. 3( a), the valve 33 is closed by the air flow during vulcanization. As shown in FIG. 3( b), a pressure P is maintained in the space formed between the unvulcanized rubber G flowing into the vent hole 32 and the valve 33, thereby suppressing foaming of the rubber G at the tip of the spew S. The air flow required to close the valve 33 may be generated in the vent hole 32 by the inflow of the rubber G, or it may be generated intentionally by a suction device or the like installed outside the mold 10. By suppressing foaming of the rubber G at the tip of the spew S in this way, it is possible to prevent dirt from accumulating near the tip of the spew S formed in the vent hole 32 and prevent the tip of the spew S from breaking due to the deposit X. This effectively prevents clogging of the vent holes 32 by the spew S. As a result, tire surface damage caused by residual air is prevented, and the frequency of cleaning the vent holes 32 is reduced, improving the productivity of the pneumatic tire T.

[0028] Furthermore, according to the above-described mold 10, the vent hole 32 communicates with the outside of the mold 10, thereby ensuring sufficient performance in exhausting residual air. Furthermore, the valve 33 is disposed at the back of the vent hole 32, in a position where the spew S cannot reach, so that rubber G does not flow into the gap of the valve 33, thereby reducing the frequency of replacement and cleaning. Furthermore, because the valve 33 has a structure that can be opened and closed by the air flow inside the vent hole 32, no complicated mechanism is required, and there is no increase in equipment costs or maintenance costs.

[0029] The mold 10 described above includes the vent piece 10B that encompasses at least a portion of the vent hole 32 and is separable from the main body 10A of the mold 10, so that the valve 33 can be easily disposed in the vent hole 32. That is, because the valve 33 is disposed at the back side of the vent hole 32, the valve 33 can be inserted into the vent hole 32 while the vent piece 10B is in a standalone state, and the vent piece 10B equipped with the valve 33 can be attached to the main body 10A. Alternatively, with the vent piece 10B removed, the valve 33 can be inserted into the vent hole 32 in the main body 10A of the mold 10, and the vent piece 10B equipped with the valve 33 can be attached to the main body 10A.

[0030] In the mold 10, the valve 33 is preferably positioned at a distance from the molding surface 31 that is 150% to 200% of the average length L of the spew S formed within the vent hole 32. In other words, when the valve 33 is closed, the distance Y from the molding surface 31 to the closing surface of the valve 33 is preferably 150% to 200% of the average length L of the spew S. The average length L of the spew S may be determined through a preliminary vulcanization test or may be estimated from rubber properties (viscosity and vulcanization rate). For example, the valve 33 is preferably positioned at a distance of 18 mm to 30 mm from the molding surface 31 along the axial direction of the vent hole 32. In other words, when the valve 33 is closed, the distance Y from the molding surface 31 to the closing surface of the valve 33 is preferably 18 mm to 30 mm along the axial direction of the vent hole 32.

[0031] By positioning the valve 33 at a suitable distance from the molding surface 31 of the vent hole 32 in this manner, contact between the rubber G flowing into the vent hole 32 and the valve 33 is reliably avoided, while ensuring pressure P in the space formed between the rubber G flowing into the vent hole 32 and the valve 33, suppressing foaming of the rubber G at the tip of the spew S and effectively suppressing clogging of the vent hole 32 by the spew S. If the valve 33 is too close to the molding surface 31, the rubber G will easily flow into the valve 33. Conversely, if the valve 33 is too far from the molding surface, it will be difficult to ensure pressure P in the space formed between the rubber G flowing into the vent hole 32 and the valve 33. In order to suppress foaming of the rubber G at the tip of the spew S, the pressure P in the space formed between the rubber G flowing into the vent hole 32 and the valve 33 needs to be, for example, 0.1 MPa or higher.

[0032] FIG. 4 shows the relationship between the length of the spew formed in the vent hole and the growth rate of the spew in the tire manufacturing method according to the present invention. In FIG. 4, the solid line indicates the case without a valve, and the dashed line indicates the case with a valve. As shown in FIG. 4, for example, without a valve (solid line), the growth rate of the spew S formed in the vent hole 32 reaches a maximum when the length of the spew S is approximately 2 mm, and the length of the spew S becomes approximately 15 mm. On the other hand, with a valve (dashed line), when the growth rate of the spew S increases, the valve 33 closes, and the pressure P formed in the space between the rubber G flowing into the vent hole 32 and the valve 33 increases, shortening the length of the spew S to approximately 13 mm. As can be seen from this, the air flow generated by the rubber G flowing into the vent hole 32 can be used to open and close the valve 33. In addition, when opening and closing the valve 33 by creating an air flow from outside the mold 10, the structure is designed so that the valve 33 will not close due to the air flow generated by the flow of rubber G into the vent hole 32, and an air flow for closing the valve 33 can be created within the vent hole 32 by suction from the outside.

[0033] FIG. 5 shows the relationship between the compression length of the space formed between the rubber G flowing into the vent hole and the valve in the tire manufacturing method according to the present invention and the generated pressure. This relationship is for a vent hole with a diameter of 1 mm, where the valve 33 is positioned 25 mm from the molding surface along the axial direction of the vent hole (a position 150% of the average vent length). As shown in FIG. 5, as the compression length of the space formed between the rubber G flowing into the vent hole 32 and the valve 33, i.e., the stroke of the portion compressed between the valve 33 and the rubber G after the valve 33 closes, increases, the pressure P increases accordingly. As can be seen from FIG. 5, by ensuring that the compression length of the space formed between the rubber G flowing into the vent hole 32 and the valve 33 is 12 mm or more, a pressure P of 0.1 MPa or more can be ensured. [Example]

[0034] When vulcanizing pneumatic tires, tire vulcanization molds were used that differed only in the structure of the vent holes.

[0035] In the conventional example, a tire vulcanizing mold was used that had many vent holes opening onto the molding surface. In the comparative example, a tire vulcanizing mold was used that had many vent holes opening onto the molding surface, with valves disposed near the entrance of each vent hole in a position reachable by the spew. In the working example, a tire vulcanizing mold was used that had many vent holes opening onto the molding surface, with valves disposed at the back of each vent hole in a position out of reach of the spew, with a structure that allows them to be opened and closed by the air flow within the vent hole. In the comparative example and working example, the valves were disposed 2 mm and 25 mm, respectively, from the molding surface along the axial direction of the vent hole.

[0036] Using the tire curing mold described above, pneumatic tires were repeatedly cured, and the number of curing cycles required before cleaning work was required due to clogging of the vent holes or valves was investigated, and the results are shown in Table 1. The number of curing cycles is expressed as an index, with the conventional example being set at 100. A higher index value means less clogging of the vent holes and valves.

[0037] [Table 1]

[0038] As can be seen from Table 1, when the tire curing mold of the Example was used, clogging of the vent holes due to spew was effectively suppressed compared to the Conventional Example, and the number of curing cycles before cleaning work was increased. On the other hand, when the tire curing mold of the Comparative Example was used, rubber flowed into the gap in the valve, causing clogging of the valve, and cleaning work was required. [Explanation of symbols]

[0039] 10 Tire curing mold 10A main unit 10B Vent Piece 20 Bladder 31 Molding surface 32 Vent Hole 33 Valve 33A Outer barrel 33B Valve body 33C Spring material T Pneumatic tire S Spew

Claims

1. A tire vulcanizing mold having a molding surface for molding the outer surface of a tire and a vent hole opening onto the molding surface, characterized in that a valve having a structure that can be opened and closed by the air flow within the vent hole is disposed at the back side of the vent hole in a position that cannot be reached by a spew formed within the vent hole.

2. 2. The tire vulcanization mold according to claim 1, wherein the valve is positioned at a position 150% to 200% of the average length of the spew formed in the vent hole from the molding surface.

3. 2. The tire vulcanization mold according to claim 1, wherein the valve is disposed at a position 18 mm to 30 mm from the molding surface along the axial direction of the vent hole.

4. 4. The tire vulcanization mold according to claim 1, further comprising a vent piece that includes at least a portion of the vent hole and is separable from the mold body.

5. A method for manufacturing a tire, comprising: placing an unvulcanized tire inside the tire vulcanization mold according to any one of claims 1 to 4; and vulcanizing the tire while pressing the tire against the molding surface.

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