Metal mold for tire manufacturing

Abstract

To provide a metallic mold for manufacturing a tire, the metallic mold comprising void molding material and enabling reduction of demolding resistance of the void molding material.SOLUTION: A metallic mold 22 for manufacturing a tire comprises: a metallic mold main body 40 molding a tread surface, and a void molding material 42 which is composed of a material different from the metallic mold main body 40 and molds a void such as a sipe on the tread surface. The void molding material 42 is manufactured by metal molding using a 3D printer, and fluorine resins 52 is disposed in recesses 50 of a surface 46 having unevenness formed by metal molding.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] SUMMARY OF THE INVENTION An embodiment of the present invention relates to a tire building mold. [Background technology]

[0002] Some tires have voids such as sipes on their tread surfaces. In molds for manufacturing the tread surfaces of such tires, the void molding material for molding the voids is made of a material different from the mold body. For example, the mold body is made of a soft metal such as aluminum for lightness, while the void molding material is made of an iron-based metal for strength and other reasons.

[0003] Patent Document 1 describes that in order to improve the rigidity of the block in which the sipes are formed, a specific uneven surface is formed on the surface of the blade that molds the sipes, and that the blade can be manufactured by additive manufacturing. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-185901 Summary of the Invention [Problem to be solved by the invention]

[0005] Due to the increasing demands on tire performance, there is a trend toward more complex groove shapes being required in tire manufacturing molds. Among the elements that make up the tread design, the void molding material used to mold sipes, particularly those with a thickness of 2 mm or less, is not only press-molded from iron-based metals, but also manufactured using additive manufacturing methods, i.e., 3D printers, as described in Patent Document 1.

[0006] In tire manufacturing using such void molding materials, it is believed that the unevenness of the surface of the void molding material increases the resistance to release of the void molding material from the tire after vulcanization. In particular, in void molding materials for molding sipes with complex shapes, the increased resistance to release can lead to poor tire release, which can impair productivity.

[0007] In view of the above, an object of an embodiment of the present invention is to provide a tire manufacturing mold that can reduce the mold release resistance of a void molding material. [Means for solving the problem]

[0008] A tire manufacturing mold according to an embodiment of the present invention is a tire manufacturing mold comprising a mold body for molding the tread surface, and a void molding material made of a material different from the mold body for molding voids in the tread surface, wherein the void molding material is produced by metal molding using a 3D printer, and a fluororesin is placed in the depressions in the uneven surface formed by the metal molding.

[0009] In one embodiment, the fluororesin may be disposed in depressions on a surface formed by the metal shaping, the surface having an arithmetic mean roughness Ra of 3.0 to 7.0 μm and a skewness Rsk>0.

[0010] In one embodiment, the flat top surface may be formed by planarizing the upper portions of the protrusions among the surface irregularities formed by the metal shaping. In this case, the flat top surface may be formed by scraping off the upper portions of the protrusions formed by the metal shaping.

[0011] In one embodiment, the void molding material may have a narrowed portion between the top surface of the protrusions and the bottom of the depressions in the uneven surface.

[0012] In one embodiment, the void forming material may be made of stainless steel. [Effects of the Invention]

[0013] According to an embodiment of the present invention, it is possible to reduce the mold release resistance of the void molding material, and to reduce the occurrence of defects in demolding of the tire after vulcanization. [Brief explanation of the drawings]

[0014] [Figure 1] Half cross-section of tire vulcanizing equipment [Figure 2] 2 is a cross-sectional view of a tire manufacturing mold according to one embodiment (a cross-sectional view corresponding to line II-II in FIG. 3). [Figure 3] FIG. 1 is a partial plan view of a tire tread according to an embodiment. [Figure 4] 1 is a side view of a void molding material according to an embodiment; [Figure 5] Schematic diagram showing the cross-sectional shape of the surface of the void molding material according to the first embodiment. [Figure 6] Schematic diagram showing the cross-sectional shape of the unevenness formed by metal molding [Figure 7] An enlarged image of the surface of a void molding material produced by metal molding before resin placement. [Figure 8] Schematic diagram showing the cross-sectional shape of the surface of a void molding material according to a second embodiment. [Figure 9] FIG. 10 is a schematic diagram showing the cross-sectional shape of the void molding material produced by metal molding in the second embodiment after cutting to form a flat top surface. [Figure 10] FIG. 10 is a plan view showing the surface of the void molding material at the stage shown in FIG. [Figure 11] 10 is a schematic diagram showing the cross-sectional shape of the surface of the void molding material according to the third embodiment; [Figure 12] 10 is a schematic diagram showing the cross-sectional shape of a void molding material produced by metal molding in the third embodiment after press working is performed on the surface of the void molding material. [Figure 13] FIG. 11 is a schematic diagram showing a cross-sectional shape at the stage where cutting is performed after press working in the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment will be described with reference to the drawings.

[0016] 1 shows an example of a tire vulcanizing apparatus 10 for vulcanizing and molding a pneumatic tire. The tire vulcanizing apparatus 10 includes a vulcanizing mold 12, a container 14 to which the vulcanizing mold 12 is attached, and a bladder 16, and vulcanizes an unvulcanized tire while molding it into a predetermined shape.

[0017] The vulcanization mold 12 includes a pair of upper and lower side plates 18, 20, a plurality of sectors 22 divided in the circumferential direction, and a pair of upper and lower bead rings 24, 26, and molds the outer surface of the tire T. The sectors 22 are molds for molding the tread surface T1 of the tire T, and are divided into a plurality of sectors in the tire circumferential direction and are provided so as to be able to expand and contract in the tire radial direction.

[0018] The container 14 includes a plurality of segments 28 that hold the sectors 22, a jacket ring 30 that moves the segments 28 in the tire radial direction, and a pair of upper and lower mounting plates 32, 34. The jacket ring 30 moves up and down relative to the segments 28, thereby moving the segments 28 in the tire radial direction, thereby enabling the sectors 22 to expand and contract in the tire radial direction. The upper mounting plate 32 is configured to move up and down relative to the lower mounting plate 34 by a lifting device (not shown).

[0019] The bladder 16 is made of a toroidal elastic rubber body that can expand and contract, and is disposed on the inner surface side of the tire T. The bladder 16 is inflated by the supply of pressurized gas, thereby pressurizing the tire T from the inside.

[0020] Hereinafter, there will be described the sector 22, which is a mold for molding the tread surface T1 (i.e., the design surface of the tread) of the tire T. In the following description, the sector 22 will be referred to as a "tire manufacturing mold 22" or simply as a "mold 22."

[0021] 2, the mold 22 includes a mold body 40 for molding the tread surface T1 and a void molding material 42 for molding voids in the tread surface T1. Usually, a plurality of void molding materials 42 are cast-in into the mold body 40. Cast-in generally refers to pouring molten metal around a different material to obtain a cast product integrated with the main body, and here refers to pouring molten metal using the void molding material 42 as an insert to obtain a mold 22 in which the void molding material 42 is integrated into the mold body 40.

[0022] The mold body 40 is made of a soft metal such as aluminum or an aluminum alloy. The mold body 40 has a tread molding surface 40A for molding the tread surface T1. The tread molding surface 40A is provided with ribs 44 for molding main grooves (i.e., circumferential grooves) on the tread surface T1. The ribs 44 are convex stripes that protrude from the tread molding surface 40A and extend in the tire circumferential direction, and are formed integrally with the mold body 40.

[0023] The void molding material 42 is made of a material different from the mold body 40, and is preferably made of an iron-based metal from the viewpoint of strength, etc. More preferably, the void molding material 42 is made of stainless steel. Stainless steel has better rust resistance than iron, and also reduces adhesion to vulcanized rubber compared to iron. Even more preferably, the void molding material 42 is made of stainless steel with a nickel (Ni) content of 8% by mass or less (more preferably 5% by mass or less). A low nickel content further reduces adhesion to vulcanized rubber.

[0024] Examples of voids molded by the void molding material 42 include various recesses provided on the tread surface T1, but preferably include groove-like recesses such as sipes and narrow grooves. Here, a sipe is a cut with a groove width of 2 mm or less and is also called a kerf. A narrow groove is a groove with a narrower groove width than a main groove, for example, a groove with a groove width of 5 mm or less. The sipes and narrow grooves may extend in the tire circumferential direction or the tire width direction.

[0025] 3 is a plan view showing an example of a tread surface T1 molded by a mold 22. A plurality of main grooves T2 are provided on the tread surface T1, and a plurality of sipes T4 extending in the tire width direction are provided on ribs T3 that extend in the tire circumferential direction and are defined by the main grooves T2. The void molding material 42 in one embodiment is used to mold the sipes T4. In FIGS. 2 and 3, the symbol CL indicates the tire equatorial plane.

[0026] Note that the void molding material 42 has a plate shape when molding a groove-shaped depression. When molding the sipe T4 shown in FIG. 3, the void molding material 42 has a flat plate shape with curved portions at both longitudinal ends. The shape of the void molding material 42 is not limited thereto. For example, when the depression to be molded is linear in a plan view (opening shape), the void molding material 42 may have a flat plate shape over the entire longitudinal direction. Furthermore, when the depression to be molded has a curved linear shape in a plan view, the void molding material 42 may have a curved plate shape. When the depression to be molded has a linear shape with a bent portion in a plan view, the void molding material 42 may have a plate shape with a bent portion. When the depression to be molded has a wave-shaped shape in a plan view, the void molding material 42 may have a corrugated plate shape.

[0027] Fig. 4 is a diagram showing an example of the void molding material 42. Of the void molding material 42, the portion that protrudes from the mold body 40 and molds the voids is called a molding portion 42A, and the portion that is embedded in the mold body 40 is called an embedded portion 42B. In Fig. 4, the embedded portion 42B is shown hatched.

[0028] In this embodiment, the void molding material 42 is produced by metal molding (also called metal additive manufacturing) using a 3D printer. Metal molding is a technology for fusing and stacking metal powder layer by layer to produce a three-dimensional shape. Examples of metal molding include SLS (Selective Laser Sintering) and SLM (Selective Laser Melting), in which metal powder is selectively sintered or melted on a support plate by irradiating it with a laser beam, thereby forming the object to be molded layer by layer.

[0029] The surface 46 of the void molding material 42 produced in this manner has minute irregularities formed by metal molding. That is, as shown schematically in Fig. 6, the surface 46 of the void molding material 42 is formed into an irregular surface including a plurality of protrusions 48 and a plurality of depressions 50. Fig. 7 is an image showing the surface 46 of the void molding material 42 formed by metal molding. The whiter the color, the higher, i.e., the more protruding, and the darker the color, the lower, i.e., the more depressed.

[0030] In the first embodiment, as shown in Fig. 5, fluororesin 52 is disposed in depressions 50 in the uneven surface 46 formed by the metal molding. By disposing fluororesin 52, which is a low-friction resin, in the depressions 50 in the surface 46 of the void molding material 42 in this manner, it is possible to reduce the mold release resistance of the void molding material 42 after the tire T has been vulcanized. In addition, the surface 46 formed by metal molding has moderate unevenness, which has the advantage that the fluororesin 52 can easily bite into and fill the depressions 50. Furthermore, the fluororesin 52 not only has low frictional resistance but also has excellent heat resistance, and can withstand vulcanization temperatures (for example, 150 to 180°C).

[0031] Examples of the fluororesin 52 include polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE, CTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), perfluoroalkoxy fluororesin (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), and the like, and any one of these can be used alone or in combination of two or more.

[0032] Although there are no particular limitations on the method for disposing the fluororesin 52 in the depressions 50 on the surface 46 of the void molding material 42, a shot blasting method is preferred. By impacting fluororesin powder as a projection material against the surface 46, which has depressions and protrusions formed by metal molding, the powder enters the depressions 50, and the depressions 50 are thereby filled with the fluororesin 52.

[0033] 5, the fluororesin 52 is disposed only in the recesses 50, but as long as it is disposed in the recesses 50, it may be disposed so as to cover other portions, i.e., the protrusions 48. Furthermore, the fluororesin 52 does not necessarily have to be disposed in all the recesses 50, and as long as the effect of reducing the mold release resistance is achieved, there may be recesses 50 in which the fluororesin 52 is not disposed.

[0034] In one embodiment, the surface 46 after metal molding (before resin placement) preferably has an arithmetic mean roughness Ra of 3.0 to 7.0 μm and a positive roughness parameter skewness Rsk (Rsk>0). That is, it is preferable that the fluororesin 52 is placed in the recesses 50 of the surface 46 formed by metal molding, which has an arithmetic mean roughness Ra of 3.0 to 7.0 μm and a skewness Rsk>0. This effectively reduces the mold release resistance of the void molding material 42.

[0035] In this specification, the arithmetic mean roughness Ra and the skewness Rsk are measured in accordance with the 2001 edition of JIS B0601.

[0036] In one embodiment, the spacing G between the recesses 50 is not particularly limited and is preferably 0.2 to 1.5 mm, and more preferably 0.5 to 1.0 mm. By setting the spacing G between the recesses 50 within this range, the low-adhesion regions in which the fluororesin 52 is disposed are arranged at appropriate intervals, thereby further reducing the mold release resistance. Here, the spacing G between the recesses 50 is the spacing between the recesses 50, and is the center-to-center distance between adjacent recesses 50, 50, as shown in FIG. 5.

[0037] The surface 46 on which the fluororesin 52 is arranged may be the surface of the molded portion 42A (i.e., in the case of a plate-shaped void molded material 42, both side surfaces of the molded portion 42A), and the fluororesin 52 may or may not be applied to the surface of the embedded portion 42B.

[0038] 8 is a schematic diagram showing the cross-sectional shape of a surface 46 of a void molding material 42X according to the second embodiment. The second embodiment differs from the first embodiment in that the upper portions of the protrusions 48 are flattened to form flat top surfaces 48A.

[0039] In the second embodiment, among the unevenness of the surface 46 formed by metal molding, the upper portions (i.e., the top portions) of the protrusions 48 are flattened, that is, the top surfaces 48A of the protrusions 48 are formed as flat (smooth) surfaces. More specifically, as shown in FIG. 9 , the upper portions of the protrusions 48 are scraped off from the uneven surface formed by metal molding to flatten the upper portions, thereby forming truncated protrusions 48 with flat top surfaces 48A. Therefore, the surface 46 of the void molding material 42 is formed by the top surfaces 48A of the truncated protrusions 48 and the depressions 50. After the truncated protrusions 48 are formed in this manner, a fluororesin 52 is disposed in the depressions 50, as shown in FIG. 8 .

[0040] The method for scraping off the upper portions of the protrusions 48 is not particularly limited as long as it is possible to remove the upper portions of the protrusions 48 and form a flat surface, and cutting or grinding may be used.

[0041] FIG. 10 is a plan view showing an example of the surface 46 of the void molding material 42 after planarization processing and before the fluororesin 52 is disposed, in which recesses 50 are disposed between the top surfaces 48A of the truncated protrusions 48.

[0042] By forming the flat top surfaces 48A on the protrusions 48 and then disposing the fluororesin 52 in the depressions 50 as described above, the mold release resistance of the void molding material 42 can be more effectively reduced. The reason for this is as follows: In the early stages of tire vulcanization, when the unvulcanized rubber flows over the surface 46 of the void molding material 42, the heat received by the flat top surfaces 48A of the protrusions 48 promotes vulcanization of the extreme surface of the unvulcanized rubber. This reduces the adhesiveness of the rubber, making it less likely to penetrate into the depressions 50. Moreover, because the depressions 50 are filled with the fluororesin 52, the adhesion force in the depression 50 region can be further reduced. This allows the mold release resistance of the void molding material 42 to be significantly reduced.

[0043] In the second embodiment, the skewness Rsk of the surface 46 of the void molding material 42 at the stage when the tops of the protrusions 48 are flattened is preferably negative (Rsk<0). By making Rsk<0, the ratio between the flat top surface 48A and the recesses 50 becomes an appropriate value, and it is possible to more effectively reduce the mold release resistance of the void molding material 42. The arithmetic mean roughness Ra of the top surfaces 48A of the protrusions 48 is preferably 2.0 μm or less.

[0044] In the second embodiment, it is preferable that the major dimension 50B of the opening surface of each recess 50 is two to ten times the minor dimension 50C (see FIG. 10). By making the opening shape of the recess 50 elongated in this way, it is possible to further reduce the intrusion of rubber into the recess 50. Here, the major dimension 50B of the recess 50 refers to the vertical dimension of the rectangle 53 when the outline of the opening surface of the recess 50 is detected and the outline is inscribed and fitted into the rectangle 53, as shown in FIG. 10. The minor dimension 50C refers to the horizontal dimension of the rectangle 53.

[0045] The other configurations of the second embodiment are the same as those of the first embodiment, and therefore the description thereof will be omitted.

[0046] 11 is a schematic diagram showing the cross-sectional shape of the surface 46 of the void molding material 42Y according to the third embodiment. The third embodiment differs from the second embodiment in that a narrowed portion 54 is provided between the top surface 48A of the protrusion 48 and the bottom 50A of the recess 50 on the uneven surface 46.

[0047] Narrowed portion 54 refers to the narrowed portion where the outer shape of recess 50 first widens and then narrows from bottom 50A to top surface 48A of recess 50. As shown in Fig. 11, narrowed portion 54 is preferably provided near the opening surface of recess 50 (i.e., top surface 48A), and is preferably provided closer to the opening surface than halfway along the depth of recess 50.

[0048] The effect of reducing the mold release resistance by the fluororesin 52 depends on the surface area of ​​the fluororesin 52 placed in the recess 50, and the effect increases as the surface area increases, but it is desirable to devise a way to prevent the fluororesin 52 from peeling off. In response to this, by providing the narrowed portion 54, the fluororesin 52 placed in the recess 50 can be effectively prevented from falling off.

[0049] The void molded material 42Y having such a narrowed portion 54 can be produced as follows. The narrowed portion 54 is formed by applying pressure to the upper portion of the protrusion 48 formed by metal shaping so as to reduce its height, thereby causing plastic deformation. The upper portion of the protrusion 48 is then scraped away while leaving the narrowed portion 54, thereby forming a flat top surface 48A. Thereafter, the fluororesin 52 is placed in the recess 50. Here, the plastic deformation can be performed by performing press processing or shot peening on the uneven surface 46 formed by metal shaping.

[0050] In more detail, when press working is performed on the uneven surface 46 after metal forming shown in Fig. 6, pressure is applied to the upper parts of the protrusions 48 so as to reduce their height, and the upper parts are compressed and plastically deformed, expanding like eaves, and narrowed parts 54 are formed at the upper parts of the protrusions 48 as shown in Fig. 12. The same is true for shot peening, in which countless spheres are collided at high speed, and pressure (instantaneous pushing force caused by the collision of countless spheres) is applied to the upper parts of the protrusions 48 so as to reduce their height, and the upper parts are plastically deformed and expanding like eaves, and narrowed parts 54 are formed.

[0051] Next, the upper portion is removed by cutting or grinding or the like while leaving the narrowed portion 54, thereby forming a flat top surface 48A as shown in Fig. 13. In this way, by plastically deforming the part by pressing or the like and then removing the upper portion by cutting or the like, the desired shape having the narrowed portion 54 can be easily obtained.

[0052] 11, fluororesin 52 is then filled into recess 50. It is preferable that fluororesin 52 enters inside narrowed portion 54 (i.e., the bottom side of recess 50) and is locked by narrowed portion 54 so as not to fall out of recess 50. This makes it possible to more effectively prevent fluororesin 52 from falling out. Note that it is not necessary for the entire fluororesin 52 to be disposed inside narrowed portion 54, and a portion of it may protrude outside narrowed portion 54.

[0053] The other configurations of the third embodiment are the same as those of the second embodiment, and therefore the description thereof will be omitted.

[0054] In the second and third embodiments, when manufacturing the void-formed materials 42X, 42Y, it is preferable to reduce the hardness by performing a solution heat treatment after forming the overall shape by metal forming. This improves the workability in the above-mentioned pressing, shot peening, cutting, grinding, and other processes. After forming the surface 46 of the void-formed materials 42X, 42Y into the desired shape by these processes, it is preferable to perform an age-hardening heat treatment, which improves the strength of the uneven shape of the surface 46.

[0055] The above embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. [Explanation of symbols]

[0056] 22... Tire manufacturing mold, 40... Mold body, 42, 42X, 42Y... Void molding material, 46... Surface of void molding material, 48... Protrusion, 48A... Top surface, 50... Depression, 52... Fluorine resin, 54... Narrowed portion

Claims

1. A tire manufacturing mold comprising: a mold body for molding a tread surface; and a void molding material made of a material different from the mold body for molding voids in the tread surface, The void molding material is produced by metal molding using a 3D printer, and a fluororesin is disposed only in the depressions on the surface having irregularities formed by the metal molding. Mold for tire manufacturing.

2. 2. The tire manufacturing mold according to claim 1, wherein the fluororesin is disposed in depressions in a surface formed by the metal shaping, the surface having an arithmetic mean roughness Ra of 3.0 to 7.0 μm and a skewness Rsk>0.

3. The mold for manufacturing a tire according to claim 1 or 2, wherein the upper portions of the protrusions among the surface irregularities formed by the metal shaping are flattened to form flat top surfaces.

4. The tire manufacturing mold according to claim 3 , wherein the flat top surface is formed by scraping off an upper portion of the protrusion formed by the metal shaping.

5. 5. The tire manufacturing mold according to claim 1, wherein the void molding material has narrowed portions between top surfaces of the protrusions and bottoms of the depressions on the uneven surface, and the fluororesin disposed in the depressions is retained by the narrowed portions.

6. The mold for manufacturing a tire according to any one of claims 1 to 5, wherein the void molding material is made of stainless steel.

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