Metal mold for tire manufacturing

Abstract

To provide a metallic mold for manufacturing a tire, the metallic mold comprising a void molding material and enabling the demolding resistance of the void molding material to be reduced.SOLUTION: A metallic mold 22 for manufacturing a tire comprises a metallic mold main body 40 for molding a tread surface, and a void molding material 42 which is composed of a material different from the mold main body 40 and molds a void such as a sipe in the tread surface. The void molding material 42 is manufactured by metal molding by a 3D printer, and in unevenness of a surface 46 formed by metal molding, an upper portion of a projection 48 is flattened and a flat top face 48A is formed.SELECTED DRAWING: Figure 8

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 the tops of the protrusions among the surface irregularities formed by the metal molding are flattened to form a flat top surface.

[0009] In one embodiment, the surface formed by the metal shaping has an arithmetic mean roughness Ra of 3.0 to 7.0 μm and a skewness Rsk>0, and the surface may be flattened to have a skewness Rsk<0.

[0010] In one embodiment, the flat top surface may be formed by scraping off the upper portion of the protrusion formed by the metal shaping.

[0011] In one embodiment, the void molding material may have a narrowed portion between the flat top surface of the protrusion and the bottom of the depression. In this case, the narrowed portion may be formed by applying pressure to the upper portion of the protrusion formed by metal shaping so as to reduce its height, thereby causing plastic deformation, and the flat top surface may be formed by further scraping off the upper portion of the protrusion while leaving the narrowed portion.

[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 showing the surface of a void-molded material produced by metal molding before flattening. [Figure 8] FIG. 1 is a plan view showing the surface of a void molding material according to a first embodiment; [Figure 9] Schematic diagram showing the cross-sectional shape of the surface of a void molding material according to a second embodiment. [Figure 10] Schematic diagram showing the cross-sectional shape of the void molding material produced by metal molding in the second embodiment after press working is performed on the surface. DETAILED DESCRIPTION OF THE INVENTION

[0015] The inventors focused on the surface properties of the void-molded material in order to reduce the mold release resistance of the void-molded material, and discovered that a surface with a moderate dimple-like unevenness is more desirable than the smooth surface obtained by press-molding rolled steel with an arithmetic mean roughness Ra of 1.0 μm.

[0016] Specifically, on the smooth surface obtained by press molding rolled steel, the unvulcanized rubber is vulcanized in a state of intimate contact over the entire surface, and the contact area between the vulcanized rubber and the void molding material is large, resulting in high mold release resistance. Therefore, in order to reduce the mold release resistance, it is desirable to reduce the contact area, and for this purpose, it is considered to provide minute irregularities on the surface of the void molding material.

[0017] When void molding material is produced by metal molding using a 3D printer, minute irregularities are formed on the surface of the void molding material due to the metal molding. However, if void molding material with such an irregular surface is used as is for vulcanization molding, unvulcanized rubber will enter the depressions and harden, resulting in high mold release resistance.

[0018] Therefore, we decided to adopt a measure to flatten the tops of the protrusions among the surface irregularities. As a result, the surface of the void molding material is formed by the flattened top surfaces of the protrusions and the depressions. In this case, when the unvulcanized rubber flows over the surface of the void molding material in the early stages of vulcanization, the flat top surfaces of the protrusions absorb heat, accelerating the vulcanization of the extreme surface of the unvulcanized rubber, reducing its stickiness and making it less likely to penetrate into the depressions. As a result, the adhesion force in the depression areas is reduced, and the mold release resistance can be reduced.

[0019] Hereinafter, an embodiment will be described with reference to the drawings.

[0020] 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.

[0021] 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.

[0022] 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).

[0023] 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.

[0024] 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."

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] In this embodiment, among the irregularities on the surface 46 formed by the metal shaping, the upper portions (i.e., the top portions) of the protrusions 48 are flattened to form flat top surfaces 48A as shown in Fig. 5. That is, the top surfaces 48A of the protrusions 48 are formed as flat surfaces (smooth surfaces).

[0035] In the first embodiment, the upper portions of the protrusions 48 are scraped off to flatten the uneven surface formed by metal molding, 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 recesses 50. 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. FIG. 8 is a plan view showing an example of the surface 46 after planarization, in which recesses 50 are arranged between the top surfaces 48A of the truncated protrusions 48.

[0036] As a result, in the early stages of vulcanization of the tire, when the unvulcanized rubber flows over the surface 46 of the void molding material 42, vulcanization of the extreme surface of the unvulcanized rubber is accelerated by heat received by the flat top surfaces 48A of the protrusions 48. This reduces the adhesiveness of the rubber and makes it difficult for the rubber to enter the depressions 50, thereby reducing the adhesion of the vulcanized rubber and reducing mold release resistance.

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

[0038] In one embodiment, the surface 46 after metal molding (before planarization) preferably has an arithmetic mean roughness Ra of 3.0 to 7.0 μm and a positive roughness parameter skewness Rsk (Rsk>0). Furthermore, the tops of the protrusions 48 are preferably flattened so that the skewness Rsk of the product shape of the void molding material 42 is negative (Rsk<0). By achieving such a surface 46 with Rsk<0, the ratio of the flat top surface 48A to the recesses 50 becomes an appropriate value, and the mold release resistance of the void molding material 42 can be more effectively reduced. The arithmetic mean roughness Ra of the top surfaces 48A of the protrusions 48 is not particularly limited, but is preferably 2.0 μm or less.

[0039] Here, the arithmetic mean roughness Ra and the skewness Rsk are measured in accordance with the 2001 edition of JIS B0601.

[0040] In the product shape of the void molding material 42, 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. By making the opening shape of the recess 50 long and narrow 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 52 when the outline of the opening surface of the recess 50 is detected and the outline is inscribed and fitted into the rectangle 52, as shown in FIG. 8. The minor dimension 50C refers to the horizontal dimension of the rectangle 52.

[0041] Furthermore, in the product shape of the void molding material 42, the spacing G between the recesses 50 is not particularly limited, and is preferably, for example, 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, low-adhesion regions due to the recesses 50 are arranged at appropriate intervals between the top surfaces 48A that have high adhesion to the vulcanized rubber, thereby further reducing the mold release resistance. Here, the spacing G between the recesses 50 is the arrangement interval between the recesses 50, and is the center-to-center distance between adjacent recesses 50, 50 as shown in FIG. 6.

[0042] 9 is a schematic diagram showing the cross-sectional shape of the surface 46 of the void molding material 42X according to the second embodiment. The second embodiment differs from the first embodiment in that a narrowed portion 54 is provided between the flat top surface 48A of the protrusion 48 and the bottom 50A of the recess 50.

[0043] The narrowed portion 54 refers to the narrowed portion where the outer shape of the recess 50 first widens and then narrows from the bottom 50A to the top surface 48A of the recess 50. As shown in Fig. 9, the narrowed portion 54 is preferably provided near the opening surface of the recess 50 (i.e., the top surface 48A), and is preferably provided closer to the opening surface than halfway through the depth of the recess 50. By providing the narrowed portion 54 in the void molding material 42X in this way, it is possible to more effectively prevent the rubber from entering the recess 50.

[0044] The void molding material 42X having the narrowed portion 54 as described above 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, and then the upper portion of the protrusion 48 is scraped away while leaving the narrowed portion 54, thereby forming a flat top surface 48A. Here, the plastic deformation can be performed by subjecting the uneven surface 46 formed by metal shaping to press working or shot peening.

[0045] 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. 10. 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.

[0046] Next, the upper part 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. 9. In this way, by plastically deforming the material by press working or the like and then removing the upper part by cutting or the like, the void molding material 42X having the narrowed portion 54 can be easily obtained.

[0047] The other configurations of the second embodiment are the same as those of the first embodiment, and therefore the description thereof will be omitted.

[0048] In this embodiment, when manufacturing the void-molded materials 42, 42Y, it is preferable to reduce the hardness by performing a solution heat treatment after forming the overall shape by metal molding. This improves the workability in the above-mentioned pressing, shot peening, cutting, grinding, and other processes. After forming the surface 46 of the void-molded materials 42, 42X 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.

[0049] 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]

[0050] 22... Tire manufacturing mold, 40... Mold body, 42, 42X... Void molding material, 46... Surface of void molding material, 48... Protrusion, 48A... Top surface, 50... Recess, 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 the tops of the protrusions among the surface irregularities formed by the metal molding are flattened to form a flat top surface, and the surface skewness is Rsk<0. Mold for tire manufacturing.

2. 2. The tire manufacturing mold according to claim 1, wherein a surface formed by the metal shaping has an arithmetic mean roughness Ra of 3.0 to 7.0 μm and a skewness Rsk>0, and the surface is flattened to have a skewness Rsk<0.

3. The tire manufacturing mold according to claim 1 or 2, wherein the flat top surface is formed by scraping off an upper portion of the protrusion formed by the metal shaping.

4. The mold for manufacturing a tire according to any one of claims 1 to 3, wherein the void molding material has a narrowed portion between the flat top surface of the protrusion and the bottom of the depression.

5. 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 the upper parts of the protrusions among the surface irregularities formed by the metal molding are flattened to form a flat top surface, the void molding material has a narrowed portion between the flat top surface of the protrusion and the bottom of the depression; The narrowed portion is formed by applying pressure to the upper portion of the protrusion formed by the metal shaping so as to reduce its height, thereby causing plastic deformation, and the flat top surface is formed by further scraping away the upper portion of the protrusion while leaving the narrowed portion.

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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