JP7187325B2 - Tire mold and tire manufacturing method - Google Patents

Description

The present invention relates to tire molds and tire manufacturing methods.

To vulcanize and mold a pneumatic tire, an unvulcanized tire is set in a tire mold, a rubber bag called a bladder is inflated, and the unvulcanized tire is pressed against the tire mold from the inside of the tire and held at a high temperature. It is done by

Patent Literature 1 discloses a bead ring, which is one of the constituent members of a tire mold. The bead ring consists of an upper bead ring and a lower bead ring that are arranged apart in the vertical direction and are in contact with a pair of bead portions of the tire from outside in the tire width direction. It is disclosed to mold the bead portion of the.

Patent Literature 2 discloses that the tip shape of the bead portion is precisely defined because the bead portion is a region fitted to the rim.

The shape of a conventional bead ring will be described with reference to FIG. In FIG. 3, a portion of the bead ring 50, a bead portion 30 in contact with the bead ring 50, a portion of the bladder 6 inflated toward the inner surface of the tire, and a portion of the lower side plate 8 include the tire rotation axis. It is represented by a meridional section. The bead portion 30 includes a bead toe 31 , a bead heel 32 and a bead core 33 . The shape of bead toe 31 and bead heel 32 is defined by the shape of bead ring 50 .

The bead ring 50 includes a bead heel molding surface and a bead toe molding surface that contact the bead portion 30, and a bladder contact surface that contacts the bladder 6 that presses the tire from the inside. In a meridian cross section including the tire rotation axis, the bead heel molding surface appears as a bead heel contour line 51, the bead toe molding surface as a bead toe contour line 52, and the bladder contact surface as a bladder contour line 53, respectively. The bead heel contour 51 is connected to the bead toe contour 52 and the bead toe contour 52 is connected to the bladder contour 53 .

The bead toe profile 52 has two curved sections, a curved section 54 connected to the bead heel profile 51 and a curved section 55 connected to the bladder profile 53 .

By the way, the surface of the bladder 6 is provided with a groove called a bladder groove for releasing air remaining between the unvulcanized tire and the bladder 6 to the outside. During vulcanization molding, the rubber of the tire inner surface 34 enters the grooves 61 after the air is discharged to the outside through the grooves 61 . As a result, linear raised portions called groove lines are formed on the tire inner surface 34 after vulcanization molding.

FIG. 4(a) is a perspective view including a cross section of the bead portion 30 (a meridional cross section including the tire rotation axis) and the tire inner surface 34 in the vulcanized tire. In the figure, a cross section of the bead portion 30 shows a bead core 33, a bead toe 31 and a bead heel 32. As shown in FIG. A large number of groove lines 35 are formed on the tire inner surface 34 . The groove line 35 reaches the tip of the bead toe 31 . Although the figure shows a cross section of the tire for convenience of explanation, the product tire is, of course, an annular body without a cross section.

FIG. 4(b) shows a view seen from the A direction in FIG. 4(a), that is, from the tire outer surface side. When viewed from the tire outer surface side, the groove line 35 reaching the tip of the bead toe 31 appears to protrude. The groove line 35 that protrudes from the tire outer surface side is referred to as a protruding portion 35a. The protrusion 35a impairs the appearance of the tire.

Therefore, after vulcanization molding, the operator cuts off the protruding portion 35a together with the tip of the bead toe. For example, the cutting tool and the tire are relatively moved along the cutting line C1 shown in FIG. 4 to cut the bead toe tip side from the cutting line C1. As a result, the protruding portion 35a of the groove line 35 is removed to improve the appearance.

However, the cutting line C1 is close to the tip of the bead toe 31 and cuts a thin rubber region in the tire width direction. Such a thin rubber region has a low stiffness, so the rubber tends to flex and escape from the cutting edge of the cutting tool. In this case, there is a risk that the cutting edge will deviate from the cutting line C1 and the cutting of the protruding portion 35a will be insufficient, and complicated work will be required to cut off the protruding portion 35a. On the other hand, if more rubber than desired is removed in an attempt to prevent the rubber from bending, the dimensional range will be exceeded and a defect will occur.

In this way, cutting the tip of the bead toe 31 while keeping it within a specified size range is a highly technically difficult and inefficient task that requires a lot of work time. Furthermore, there is concern about the occurrence of defects due to such a cutting process.

JP 2018-089827 A JP-A-9-020110

SUMMARY OF THE INVENTION An object of the present invention is to improve the efficiency of the cutting process for cutting the bead toe tip including the protruding portion of the groove line, and to suppress the occurrence of defects due to the cutting process.

The tire mold of the present invention has the following characteristics. That is, an upper bead ring and a lower bead ring are arranged separately in the vertical direction, and the upper bead ring and the lower bead ring respectively form a bead heel molding surface and a bead toe molding surface in contact with the bead portion of the tire. and a bladder contact surface with which a bladder that presses the tire from the inner surface side contacts, and at least one of the upper bead ring and the lower bead ring, in a meridional cross section including the tire rotation axis, the bead heel molding surface is As the bead heel contour line, the bead toe forming surface appears as a bead toe contour line, and the bladder contact surface appears as a bladder contour line, respectively. and a third curved portion, wherein the first curved portion is connected to the bead heel contour line, the second curved portion is located radially inward of the first curved portion, and the third curved portion is It is connected to the bladder contour line and positioned radially inward of the second curved portion.

According to the present invention having the above configuration, the thickness of the rubber at the cutting portion of the bead toe tip including the overhanging portion of the groove line is ensured. can be suppressed.

Further, in the tire mold, an angle formed between a first straight line portion connecting the second curved portion and the third curved portion and a straight line parallel to the tire rotation axis is 30 degrees or more and 60 degrees or less. may be provided.

Furthermore, in the tire mold, the radius of curvature of the third curved portion may be smaller than the radius of curvature of the second curved portion.

Further, in the tire mold, the bead toe profile includes one or more additional curved sections between the second curved section and the third curved section, and the additional curved section is aligned with the bladder profile. A configuration may be provided in which the closer the curved portion, the more inward the tire radial direction.

In the tire manufacturing method of the present invention, an unvulcanized tire is placed on the inner surface side of the tire mold, the unvulcanized tire is pressed against the tire mold by the bladder to be vulcanized, and after vulcanization and molding A groove line formed in the tire and protruding inward in the tire radial direction is cut off together with the bead toe tip of the bead portion.

1 is a meridian half-sectional view showing an example of a tire mold according to the present invention; FIG. (a) Enlarged view of B section in FIG. 1, (b) Enlarged view of D section in FIG. Meridian sectional view showing essential parts of a conventional tire mold (a) Perspective view showing a bead portion of a tire, (b) A view in the direction of arrow A in FIG. 4(a)

An example of a tire mold used for vulcanization molding will be described with reference to FIG. In FIG. 1 a meridional half-section view of the tire mold 1 is shown together with the bladder 6 and the tire 3 . The tire mold 1 includes a tread ring 2 for molding the tread portion of the tire 3, an upper side plate 7 and a lower side plate 8 for molding the sidewall portion of the tire 3, and an upper bead ring for molding the bead portion of the tire 3. 9 and lower bead ring 10 . The upper bead ring 9 and the lower bead ring 10 are located inside the upper side plate 7 and the lower side plate 8 in the width direction of the tire, respectively, and are spaced apart from each other in the vertical direction. In FIG. 1, an unvulcanized tire 3 is arranged on the inner surface side of a tire mold 1, and a bladder 6 arranged on the inner surface side of the tire 3 is inflated to press the tire 3 from the inner surface side for vulcanization molding. situation is shown. The tread ring 2 is divided into a plurality of sectors along the tire radial direction.

FIG. 2(a) is an enlarged view of part B in FIG. The shape of the lower bead ring 10 will be described with reference to FIG. 2(a). In FIG. 2( a ), a portion of the lower bead ring 10 , the bead portion 20 , a portion of the bladder 6 inflated toward the inner surface of the tire, and a portion of the lower side plate 8 include the tire rotation axis. It is represented by a meridional section. The bead portion 20 includes a bead toe 21 , a bead heel 22 and a bead core 23 . The shape of the bead toe 21 and bead heel 22 is defined by the shape of the lower bead ring 10 .

The lower bead ring 10 includes a bead heel molding surface and a bead toe molding surface that come into contact with the bead portion 20, and a bladder contact surface that comes into contact with the bladder 6 that presses the tire 3 from the inside. In a meridian cross section including the tire rotation axis, the bead heel molding surface appears as a bead heel contour line 11, the bead toe molding surface as a bead toe contour line 12, and the bladder contact surface as a bladder contour line 13, respectively. The bead heel contour 11 is connected to the bead toe contour 12 and the bead toe contour 12 is connected to the bladder contour 13 .

FIG.2(b) is an enlarged view of the D section in Fig.2 (a). In FIG. 2(b), for convenience of explanation, slanted lines representing cross sections are omitted. In the present embodiment, the bead heel contour line 11 is formed by a line segment including an arc centered on the cavity side (inside the contour line in the tire width direction). The bladder contour line 13 extends along the tire radial direction.

The bead toe profile 12 has three curved portions. A curved portion represents a continuous arc on the contour line. In the present embodiment, the three curved portions are all arcs having a specific center of curvature and radius of curvature inside the contour in the tire radial direction. A first curved portion 14, a second curved portion 15 and a third curved portion 16 are provided in order from the bead heel.

The first curved portion 14 is connected to the bead heel contour line 11 at one end and to the second curved portion 15 at the other end. The curvature radius RA of the first curved portion 14 is larger than the curvature radius RB of the second curved portion 15 and the curvature radius RC of the third curved portion 16 .
The second curved portion 15 is located between the first curved portion 14 and the third curved portion 16 on the bead toe contour line 12 and located radially inward of the first curved portion 14 . The second curved portion 15 is connected to the third curved portion 16 via the first straight portion 17 . The first linear portion 17 is inclined inward in the tire width direction toward the inner side in the tire radial direction.
A third curved portion 16 is located at the other end of the bead toe contour 12 and is connected to the bladder contour 13 . The second curved portion 15 is located inside the first curved portion 14 in the tire radial direction, and the third curved portion 16 is located inside the second curved portion 15 in the tire radial direction.

As a result, a space surrounded by the second curved portion 15, the third curved portion 16 and the bladder 6 is formed at the tip of the bead toe, which is not originally required in the bead toe. When the rubber enters this space, a skirt-like rubber portion is formed at the tip of the bead toe, protruding inward in the tire radial direction and continuously extending in the tire circumferential direction.

The bead portion 20 after vulcanization molding has a protruding portion where the groove line 25 reaching the tip of the bead toe 21 protrudes from the outside of the tire. Therefore, the protruding portion is cut together with the skirt-like rubber portion. In the cutting step, the skirt-like rubber is cut along the tire circumferential direction. A cut portion of the skirt-like rubber is shown as a cutting line C2 in FIG. 2(b), for example.

The cutting line C2 is an extension line of the first curved portion 14 extending from the other end connected to the second curved portion 15, and forms an angle θ1 with a straight line parallel to the tire rotation axis. The angle θ1 is, for example, 10 degrees or more and less than 30 degrees, and more preferably 15 degrees or more and less than 20 degrees. Since the resection line C2 is longer than the conventional resection line C1, it is possible to ensure a sufficient thickness of the rubber at the resection location. If the rubber at the cut portion is thick, the rigidity is high, so the rubber bends from the cutting edge of the cutting tool and becomes difficult to escape, making it easier to cut into a desired shape. As a result, the technical difficulty of excision can be reduced, and the working time can be shortened and the efficiency of the work can be improved. Furthermore, it is possible to suppress the occurrence of tire defects due to the cutting process.

The resection line C2 shown above and in FIG. 2 is an example of a resection location, and is not limited to this. The excision point should be set so that it is longer than the excision line C1, the protruding part of the bladder line is difficult to see from the tire outer surface side, and the tip of the bead toe after excision can be kept within the specified size range. .

The position and shape of the curved portion are preferably set so that the angle θ2 formed between the first straight portion 17 and a straight line parallel to the tire rotation axis is 30 degrees or more and 60 degrees or less, more preferably 45 degrees. It should be set to ±5 degrees. If the angle θ2 is too small, when the bladder 6 is inflated and inserted, the bladder 6 may be caught by the third curved portion 16 and rub against the third curved portion 16, which may damage the bladder 6, which is not preferable. If the angle θ2 is too large, it will be difficult to ensure the thickness of the rubber at the cut portion.

In other embodiments, bead toe profile 12 may include one or more additional curved portions between second curved portion 15 and third curved portion 16 . Here, since the tip of the bead toe 21 has a shape in which the thickness in the tire width direction gradually decreases as it approaches the tip, the additional curved portion is positioned more inward in the tire radial direction as the curved portion is closer to the bladder contour line 13 . It is preferable to provide the additional curved portion in order to reduce the bending of the third curved portion and suppress damage to the bladder 6 while ensuring the thickness of the rubber at the cut portion.

When the radius of curvature RC of the third curved portion 16 is smaller than the radius of curvature RB of the second curved portion 15, it is easy to ensure the thickness of the rubber at the cut portion.

Although the lower bead ring 10 has been described above, the same contour shape can be applied to the upper bead ring 9 as well. The upper bead ring 9 may have the same shape as the lower bead ring 10 or may have a different shape.

The above embodiment shows a segmented type tire mold that includes a tread ring configured with a plurality of sectors and a pair of upper and lower side plates that are in contact with the ends of the tread ring in the tire width direction. may be a so-called two-piece mold in which the is incorporated inside a pair of upper and lower back metals in the tire radial direction.

The present invention is by no means limited to the above-described embodiments, and various improvements and modifications are possible without departing from the scope of the present invention.

Reference Signs List 1 Tire mold 2 Tread ring 6 Bladder 7 Upper side plate 8 Lower side plate 9 Upper bead rings 10, 100 Lower bead rings 11, 51 Bead heel contour lines 12, 52 Bead toe contour line 13 , 53... Bladder outline 14... First curved part 15... Second curved part 16... Third curved part 17... First straight part 20... Bead part 21... Bead toe 22, 32... Bead heel 23, 33... Bead core 24, 34 ... Tire inner surface 25, 35 ... Groove line 35a ... Protruding portion 61 ... Groove

Claims (4)

comprising an upper bead ring and a lower bead ring spaced apart in the vertical direction,
The upper bead ring and the lower bead ring each include a bead heel molding surface and a bead toe molding surface that contact the bead portion of the tire, and a bladder contact surface that contacts the bladder that presses the tire from the inside,
In at least one of the upper bead ring and the lower bead ring, in a meridian cross section containing the tire rotation axis, the bead heel molding surface is a bead heel contour line, the bead toe molding surface is a bead toe contour line, and the bladder contact surface is a bladder contact surface. appear as outlines, respectively,
The bead toe contour line has a first curved portion, a second curved portion and a third curved portion in order from the bead heel,
the first curved portion is connected to the bead heel profile;
The second curved portion is positioned radially inward of the first curved portion,
The third curved portion is connected to the bladder contour line and positioned radially inward of the second curved portion ,
One or more additional curved portions are provided between the second curved portion and the third curved portion, and the additional curved portion is positioned more inward in the tire radial direction as the curved portion is closer to the bladder contour line. A tire mold characterized by : 2. The invention according to claim 1, wherein an angle formed between a first straight portion connecting said second curved portion and said third curved portion and a straight line parallel to the tire rotation axis is 30 degrees or more and 60 degrees or less. tire mold. 3. The tire mold of claim 1 or 2, wherein the radius of curvature of said third curved portion is less than the radius of curvature of said second curved portion. An unvulcanized tire is placed in the tire mold according to any one of claims 1 to 3 , and the bladder is used to press the unvulcanized tire against the tire mold to vulcanize and mold,
A method for manufacturing a tire, wherein a protruding portion of a groove line formed in a tire after vulcanization molding and protruding radially inward of the tire is cut off together with the bead toe tip of the bead portion.

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