JPH023501A - Pneumatic tire and forming die therefor - Google Patents

Abstract

PURPOSE:To prevent the crack of the bottom part of a traverse groove by setting the depth of a translot in a tread pattern at the specified rate for the depth of a main groove and arranging a notch set in the specified height on the block formed by these grooves. CONSTITUTION:The tread pattern of a tire 1 is formed by the numerous main grooves 2 extending in zigzags in the tire peripheral direction E, numerous traverse grooves 3, 3' crossing the space between respective adjacent main groove 2 in the radial direction and numerous blocks 5 surrounded by these respective grooves 2, 3, 3'. The optimum number of notches 4-4'' extending in the radial direction are arranged on each block 5. In said structure the depth (d) of the translot 3, 3' is set at 30-70% for the depth D of the main groove 2. The height H of the notches 4-4'' is set as to satisfy the following equation. Namely, H>=d+(0.15D). Consequently the crack of the bottom part of the translot 3, 3' is prevented.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is directed to a pneumatic tire that improves the crank resistance of the groove bottom of a lateral groove and has good traction performance even after wear, and for repeated molding. The present invention relates to a mold for forming a tire having excellent durability.

[Conventional technology]

Conventionally, when a tire is new, it has a block pattern defined by a main groove extending in the circumferential direction of the tire and a lateral groove that crosses this main groove, and after wear, it changes to a bulge pattern, which can be called a combination pattern of blocks and ribs. This tire has a block pattern that exhibits excellent heat dissipation effects, good heel and toe wear resistance, traction properties, etc. when new, and as wear progresses, the tire changes to a rib pattern. It also has the feature that it does not cause uneven wear and can ensure a long wear life. However, this tire has the drawback that the lateral grooves disappear due to wear, making it difficult to maintain traction performance.In order to improve this, the depth of the lateral grooves was increased, which caused cracks to occur at the bottom of the lateral grooves, causing the tire to lose its lateral grooves. There was a problem of shortening the lifespan of.

In order to improve the abrasion performance of this tire, especially a tire with a rib-lug pattern or a block pattern, Japanese Patent Application Laid-Open No. 18305/1983 discloses that the tread surface of the tire is formed at an angle substantially parallel to the lateral grooves over substantially the entire width of the tread surface of the tire. A tire has been proposed in which a plurality of cuts are provided that are deeper than the groove depth of the lateral groove and are inclined at an angle of 30'' to 90° with respect to the tire equator. The raw cover tire is formed using a mold with a thin plate, rather than being formed at the same time as vulcanization.
This is carved on the tread surface of a molded and vulcanized tire using a knife, and this is one of the features of this invention. However, the method of making cuts using a cutter increases the number of steps compared to forming cuts using a mold, and is disadvantageous in terms of workability and productivity. Although it is possible to form deep cuts at regular or irregular intervals in the circumferential direction of the tire and at arbitrary angles, in the case of tires that have blocks of different shapes and sizes, for example, the surface area of each block can be divided equally. It is difficult to form notches that divide the tire, or it is difficult to form notches that are bent along the tire width direction. Moreover, the notch is formed at the main groove side mouth portion of the lateral groove, and there is a drawback that cracks are likely to form in the lateral groove from the notch.

On the other hand, although it is possible to form shallow cuts using a mold equipped with a thin plate for forming cuts, it is difficult to make deep cuts (the height of the forming blade increases).
The problem is that the incision forming blade (metal plate) of the mold gradually becomes curved and deformed each time it is vulcanized due to the flow (pressure) of unvulcanized rubber during molding and vulcanization, shortening the life of the mold. was there.

[Problem to be solved by the invention]

The object of the present invention is to provide a pneumatic tire and a block (rib) with thin incisions that improve the abrasion resistance of a tire having the block/rib combination pattern and prevent the formation of cracks at the bottom of the lateral groove. It is an object of the present invention to provide a mold for molding a pneumatic tire, which is hard to cause bending of the incision molding blade and has a long life.

[Means to solve the problem]

A feature of the present invention is that it has a block pattern formed by a main groove and a lateral groove, and the groove depth d of the lateral groove is the depth D of the main groove.
3 oz, ~70X, and in which the block is provided with a notch with a height H defined by the following formula, H≧d + (0,15D), and has the block pattern as described above, and the block is a tire molding die having a notch, and a notch forming blade with a height H" defined by the following formula is radially inserted into a block forming part surrounded by groove forming ribs that form the main groove and lateral groove. This is a mold for forming a pneumatic tire provided so as to connect the main groove forming bones facing each other in the direction.

H゛ ≧d' + (0,15D') (in the above formula, D
′ indicates the height of the main groove molded bone, and d゛ indicates the height of the lateral groove molded bone).

Hereinafter, the present invention will be explained in detail based on the drawings.

FIGS. 1(a) and 1(b) respectively show the tread pattern of the tire of the present invention when it was new, and the tread portion of the tire when it was new.
FIG. 2 is a plan view showing an example of a tread pattern after 0x wear, with the direction of arrow E being the tire circumferential direction. As shown in the figure, the tire of the present invention has a plurality of main grooves 2 extending in a zigzag shape along the circumferential direction of the tire, a plurality of lateral grooves 3.3' extending in the radial direction between the main grooves 2 adjacent to each other, It has a trend pattern consisting of a large number of blocks 5 surrounded by these main grooves 2 and lateral grooves 3.3. each block 5
has a radially extending notch of 4.4'1.4"
One or more degrees are provided. These cuts 4.4° to 4° may not only connect two adjacent main grooves 2, but may also extend from the main grooves 2 to the lateral grooves 3 (not shown). Further, the depth of the lateral groove 3.3° may be constant in the width direction of the lateral groove 3.3°, but it may not be constant, for example.
3゛The groove depth at the center can be made shallow, and the groove depths on both sides (main groove 2 side) can be made deeper (in this case, the horizontal groove depth d
is the depth at the center).

For example, FIG. 2 (
In (b), if the groove depth dc at the center of the lateral groove is shallow and the groove depth de at both sides thereof is deep, when the tread surface wears out, the center of the lateral groove A portion is exposed on the surface, and the horizontal grooves on both sides change into a rig pattern that remains as branch grooves 6. In addition, Fig. 2(b) shows the first
A cross section taken along line CC (horizontal groove) in Figure (a) is shown.

In the tire of the present invention, the groove depth d of the lateral groove is the groove depth D of the main groove.
It is most effective at 30% to 70χ. In other words, the causes of cracks occurring at the bottom of the lateral groove can be broadly classified into the following two factors.

■Cracks that occur in the rising part of the horizontal groove block due to the compressive stress of the ground reaction force acting on the tread block.

■A crank that occurs at the center of the bottom of the lateral groove due to stress concentration in the lateral groove due to bending deformation of the tread that occurs at the front and rear edges of the tire.

Regarding cracks caused by factor (2), the groove depth d of the lateral grooves is made shallower (smaller) than the groove depth D of the main grooves, which is 70χ.

Although this cannot be a problem in the tire targeted by the present invention, for the crank of factor (2), the stress concentration due to bending that causes this crack is such that the groove depth d of the lateral groove is 30% of the main groove depth D. It is largest when ~70χ. By forming cuts deeper than the groove depth of the horizontal grooves in the blocks partitioned by the horizontal grooves, the bending deformation of each block row is homogenized and stress concentration is dispersed, thereby preventing the occurrence of cranking. be.

In this case, the cut formed in the block needs to have a depth greater than the depth of the lateral groove, that is, the depth H needs to be a size defined by the following formula.

H≧d + (0,15X D) Preferably, H≧d + (0,25X D) (However,
In the above formula, D is the groove depth of the main groove, and d is the groove depth of the lateral groove.

) Note that if the groove depth d of the lateral groove becomes too shallow (smaller) than 30χ of the groove depth D of the main groove, the effect of improving wear resistance will decrease, and as wear progresses, traction will decrease. This is not preferable because the performance also deteriorates.

In the present invention, the lateral groove is 3
The angle is preferably 0° or less, and the notch is also preferably arranged in the same axial direction as the lateral groove.

In addition, the cuts in the block in the present invention need to be formed during molding and vulcanization using a mold, rather than being cut with a knife or the like after tire molding and vulcanization.

In such a mold, in order to keep the thickness of the incision forming blade thin and prevent deformation during molding, the incision forming blade of a certain height must be surrounded by main groove forming bones and lateral groove forming bones. It is necessary to provide it in the block molding part. The height H' of this incision forming blade is defined by the following formula, that is, the height d of the horizontal groove forming bone plus the height D of the main groove forming bone by at least 15χ, preferably 25χ. It is necessary that the incision forming blade be provided in the radial direction so as to connect the main groove forming bones that face each other.

H゛ ≧d' + (0,15D') (in the above formula, D
゛ is the height of the main groove molded bone, d゛ is the height of the lateral groove molded bone.) Figure 3 shows an embodiment of the present invention for molding a tire with a block pattern as shown in Figure 1(a). The main parts of the mold are shown.

As shown in the figure, in the mold 10 of the present invention, the cut forming blade 14 provided in the block forming part 15 has a height Ho
is higher than the height do of the horizontal groove molded bone 13, H゛≧d'
+ (0,15D'), and when the mold is closed, the notch forming blade (
The tip of the metal plate (usually a metal plate) plunges into the tread block made of unvulcanized rubber, and the unvulcanized rubber that wraps around the tip restricts its movement and firmly fixes it, so it is not swept away by the horizontal groove forming bones. It does not deform due to the flowing unvulcanized rubber flow.

In the mold of the present invention, even if the block forming part 15 has a plurality of incision forming blades, the height thereof is similarly set higher than the height of the horizontal groove forming bone as defined by the above formula. It is necessary.

Furthermore, when molding a tire with the combination block/rib pattern of the present invention, the height do of the lateral groove molding bone is set to 30% to 702% of the height D'' of the main structural bone.

In the present invention, the thickness of the metal plate as the incision forming blade is 0.4 mm to 2.0 mm, preferably 0.6 mm.
It is preferable to set the thickness to 1.2 mm to 1.2 mm. If it is thinner than 0.4 mm, it is not desirable in terms of strength and prevention of deformation.
If it exceeds 2.0 mm, it is not preferable because it becomes difficult to ensure braking and driving performance of the tire (block), especially braking and driving performance on icy and snowy roads.

Furthermore, in order to ensure the above-mentioned braking and driving performance, the lateral groove forming rib and incision forming blade (metal plate) of the present invention are preferably 30 degrees or less, preferably 20 degrees with respect to the rotational axis of the tire.
It is desirable to place it at a shallow angle of less than 1°.

〔Example〕

EXAMPLES Hereinafter, the effects of the tire and mold of the present invention will be specifically explained with reference to Examples.

Example, conventional example 1.2.3 The height D” of the main structural bone is 19.6 m at the groove depth D of the main groove
m, the height do of the horizontal groove forming bone is the groove depth d of the horizontal groove 1).
5 mm (corresponds to 59χ of the groove depth D of the main groove), the height Ho of the incision forming blade is 4.4° of the groove depth H
is 16.5 mm 1 equation Height calculated from H≧d+(0,15D), 1). 5+ (0°15 x 19.
6) = 1). 5 + 2.94 = 14.44
mm] using a mold, the block pattern shown in Fig. 2 (a) is used, and the tire size is lo, 0OR.
2014Pl? molded tires.

As shown in Figure 3(a), the horizontal groove forming bones have different groove depths in the groove width direction, being higher at the center and lower at both ends. As the groove progresses, the groove changes into a branch groove 6 as shown in FIG. 1(b).

In addition, the above-mentioned incision forming blade is made of stainless steel (SOS
A 0.8 mm thick metal plate manufactured by A. 304) was used.

For comparison, a mold of the same standard as the mold of the previous example except that the notch forming blade was not provided, and a mold of the previous example except that the height of the notch forming blade was changed as follows. Conventional tires 1 to 3 were created using molds of the same standard.

Conventional tire 1: No notch.

Conventional tire 2: Depth of cut 4.4゛ and 4'' =
8.0III+.

Conventional tire 3: Depth of cut 4, 4゛ and 41"
1). 5mm.

These tires were left in an open air condition at 100° C. for 340 hours to thermally deteriorate the tread rubber.

Next, each of the heat-degraded tires was evaluated using a rotating drum tester to determine the running time until cranking occurred.

The evaluation conditions using the rotating drum tester are as follows.

Rim: 7.50V, Air pressure: 7.25Kg/cm
”, Load: 2700Kg, Speed: 20Km
/Time.

The evaluation results are shown in the table.

In addition, as a result of molding tires using the four types of molds mentioned above and examining the occurrence of bending of the kerf forming blade, it was found that in conventional tire 3, bending occurred in the kerf forming blade after molding 20 tires. . On the other hand, in the tire of the present invention and the conventional tire 2, the cutting blade did not bend at all and had excellent durability.

〔Effect of the invention〕

The tire of the present invention can effectively prevent the occurrence of cranks at the bottom of the horizontal grooves that partition the blocks, despite the deep cuts in the blocks, has excellent wear resistance, and has a high degree of control and control on icy and snowy roads. It is a tire that exhibits driving performance, especially a tire for heavy loads, and as a mold for such a tire, it can effectively prevent deformation during tire molding of a thin notch forming blade that is higher than the height of the horizontal groove forming bone, and after molding. Compared to making cuts with a knife,
It provides a mold with excellent workability and productivity, and a long life.

[Brief explanation of the drawing]

FIG. 1(a) is a plan view showing 16 trend patterns of the tire of the present invention when new, and FIG. 1(b) is a plan view of the tire shown in FIG. 1a after the tread surface wear has progressed (50χ). Top view showing the trend pattern, Figure 2 (a) and (b)
) is a sectional view of the lateral groove taken along line B-B and line C-C in FIG. 2...Main groove, 3.3゛...Horizontal groove, 4.41.41)
... cut, 5 ... block, lO ... mold,
13... Lateral groove forming bone, 14... Cut forming blade 14
．． 15...Block molding part. Figure 1(a)

Claims (2)

[Claims] (1) In a tire having a tread pattern consisting of a main groove extending in the tire circumferential direction, a lateral groove crossing the main groove, and a block formed by the main groove and the lateral groove, the groove depth d of the lateral groove is the same as that of the main groove. A pneumatic tire, the block having a notch having a depth of 30% to 70% of D and having a height H defined by the following formula. H≧d+(0.15D) (2) A tire molding tool that has a pattern consisting of a main groove in the tire circumferential direction, a lateral groove that crosses this main groove, and blocks separated by these main grooves and lateral grooves, and has radial cuts in the blocks. A cut-forming blade having a height H' defined by the following formula is placed in the radial direction on a block molding portion surrounded by groove-forming ribs for molding the main groove and the lateral groove, and facing each other. A pneumatic tire mold that connects the main groove molding bones. H'≧d'+(0.15D') (In the above formula, D' represents the height of the main groove molded bone, and d' represents the height of the lateral groove molded bone).