JPH0733022B2 - Pneumatic tire manufacturing method and vulcanization mold used therefor - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for manufacturing a pneumatic tire that reduces tire noise when a tire is new, and a vulcanization molding die used therefor.

[Prior art]

The tread portion of the tire is provided with a complicated tread pattern formed by combining a plurality of grooves. To vulcanize and mold a tire having such a complicated tread pattern, a large number of vent holes (air vent holes) are provided in a portion corresponding to the tread surface of the mold, whereby the mold and the tire rubber are The appearance failure (referred to as a light) due to the accumulation of air between them is prevented from occurring. For this reason, a burr is formed in the vent hole portion of the tire released from the mold after the vulcanization molding, and the burr is trimmed (cut off) to be a final product. However, even if the burr is trimmed, it is difficult to completely remove it, and in general, the root of about 1 to 2 mm is left unremoved to form many protrusions on the tread surface.

However, according to the study by the present inventors, it was found that the trim residue of the burr formed in a convex shape on the tread surface has a great influence on the noise when the tire is new. The remaining convex portion of the trim cannot be completely erased after traveling a few hundred kilometers from a new tire, and it has an effect on noise, and in some cases, it has an adverse effect even after traveling 1000 to 2000 km. I knew there was something.

As a countermeasure for this, it is necessary to trim the burr to the extent that it does not affect noise, but to do this, it is necessary to work with considerable caution, and it takes a lot of time and productivity is reduced. It is not practical because it will decrease and industrial production will increase the cost. Further, a vulcanizing apparatus that does not form a burr in the belt hole has been considered, but such an apparatus has not yet been put into practical use at present.

Therefore, as a result of diligent study on reducing tire noise on the premise that the residual trim of the vent hole exists, the present inventor has found that the tire noise is proportional to the volume of the convex portion of the residual trim. It has been found that it is effective to reduce the tire noise if the value is reduced.
However, if the volume of the vent hole is simply reduced, the original exhaust capacity of the vent hole will be reduced and a vulcanization failure (light) will occur, or the vent will break in the vent hole, resulting in cutting of burrs. However, problems such as remaining in the vent hole will occur.

[Object of the Invention]

An object of the present invention is to provide a method for manufacturing a pneumatic tire capable of molding a tire that reduces tire noise when a tire is new while maintaining the original exhaust function of the mold vent hole, and a vulcanization molding mold used therefor. To provide.

[Structure of Invention]

In the method for manufacturing a pneumatic tire according to the present invention, which achieves the above object, the vent hole diameter a of the tread portion is 0.8 to 1.5 m.
m, the counterbore diameter b is 3.0 mm or less, the counterbore height h ₁ is 2.5 mm or more, and the counterbore taper angle α is 15 ° or more and less than 45 ° after vulcanizing and molding the tire, and then molding it in the vent hole It is characterized by trimming burrs.

The vulcanization molding die used in this manufacturing method has a vent hole diameter a of the tread portion of 0.8 to 1.5 mm and a counterbore diameter b.
Is 3.0 mm or less, the counterbore height h ₁ is 2.5 mm or more, and the counterbore taper angle α is 15 ° or more and less than 45 °.

There are various causes of tire noise, but one of the major causes is vibration generated when the rubber of each part of the tread is deformed when the tire rotates and is released at a dash at the end of touchdown (when kicking out). (Self-excited vibration). Therefore, the reason why the trim residual convex portion of the vent hole burr affects the tire noise is that the presence of the trim residual convex portion in the tread portion causes the trim residual convex portion when the tread portion is deformed as described above. It is presumed that this is because the ground contact pressure at the point becomes higher and the rubber deformation around it becomes larger than that at other portions without the convex portion. It is presumed that the larger the volume of the remaining trim convex portion, the higher the rigidity of the trim residual convex portion, and thus the greater the deformation of the surrounding rubber, the greater the noise generation.

FIG. 4 is a cross-sectional view of a vent hole portion of a conventional vulcanization molding die in which a burr that causes such noise is formed. The diameter a of the vent hole 2 of the mold 1 is preferably as large as possible in order to provide sufficient exhaust capacity. However, if it is too large, the flow rate of rubber during vulcanization becomes too large and the tire internal structure is deformed. Therefore, the thickness of about 1.5 mm has been conventionally used. Further, when the vulcanized tire is released from the mold 1, a counterbore 2z is formed at the root of the venthole in order to prevent cutting of burrs at the venthole 2, and the counterbore diameter b is about 4
The counterbore taper angle α is about 45 °, and the counterbore height h ₁ is about ₁ to 2 mm. Since the burr trim residue formed by such a conventional vent hole has high rigidity, the deformation of the surrounding rubber becomes large as described above,
It was a cause of worsening tire noise.

The present invention has found from the various findings described above an optimum vent hole shape that reduces the rigidity of the trim remaining convex portion of the burr without impairing the original function of the vent hole. The shape is a vent hole 2 having a counterbore 2z shaped substantially as shown in FIG.
Compared with the conventional one in the figure, the vent hole diameter a as a whole
And the counterbore diameter b is small, and the counterbore height is
h ₁ is high, and the spot facing taper angle α is small.

More specifically, as described above, the vent hole diameter a
0.8-1.5 mm, counterbore diameter b is 3.0 mm or less, counterbore height h ₁
Is 2.5 mm or more and the counterbore taper angle α is 15 ° or more and less than 45 °.

FIG. 3 shows the results of tire noise experiments conducted to find the upper limit of the counterbore diameter b described above. In this experiment, the vent hole diameter a was 1.5 mm and the counterbore taper angle α was 45.
Each of the four types of dies (tire size: 175 / 70SR13) was fixed as the same size as the conventional one, and the counterbore diameter b was changed to each of 5 mm, 4 mm, 3 mm, and 2 mm (tire size: 175 / 70SR13). Burrs are trimmed for each of the tires vulcanized and molded from the mold, and the height h ₂ after trimming is set to the same 1.5 mm, and the results of noise measurement are plotted. Further, the tread patterns of the respective tires were all designed as shown in FIG. 2 so that the trim residual convex portions 20 of burrs were respectively formed on the block row II and the block row III of the shoulder portion.

The noise measurement conditions are as follows: rim 5-J × 13, air pressure 2.
The noise was 0 kgf / cm ² , the load was 300 kg, and the sound pressure level of 100 to 2000 Hz was shown as the average value of the speed of 60 to 100 km / h. As is clear from the results shown in FIG. 3, the noise reduction is remarkable when the counterbore diameter b of the vent hole is 3 mm or less.

On the other hand, as the counterbore diameter b is made smaller, the root strength of the vent becomes insufficient, and vent cut (burr cut) is more likely to occur. At the same time, since the inlet (root) of the vent hole is narrowed, the flow resistance of the rubber is increased, and the effect of preventing vulcanization failure (light) is diminished.

In the present invention, as a countermeasure against this, the counterbore height h ₁ is made larger than that of the conventional _one , and even if the counterbore diameter b is reduced, the volume of the vent hole root portion is increased to maintain a good rubber flow. Moreover, it was designed so that the vent would not run out. That is, it was found that the counterbore height h ₁ for this purpose should be 2.5 mm or more.

However, in this case, if the counterbore taper angle α is smaller than 15 °,
Since the root angle of the vent hole becomes too sharp, vent breakage easily occurs. Therefore, the counterbore angle α
Must be above 15 °. In order to increase the counterbore taper angle α, it is necessary to reduce the vent hole diameter a, but if the vent hole diameter a is too small, the exhaust function of the vent hole will be deteriorated or venting will occur, so 0.8 Must be in the range of ~ 1.5mm.

A tire vulcanized and molded with a mold having a vent hole as described above is released from the mold and then trimmed with a burr corresponding to the vent hole to obtain a trim as shown in FIG. 2, for example. A tread pattern product in which the remaining convex portions 20 are present. At this time, the height h ₂ of the trim residual convex portion 20 is preferably at least 2.0 mm or less. That is, it is preferable to trim at a position lower than the counterbore height h ₁ (see FIG. 1).

〔Example〕

The tread portion has a block pattern as shown in FIG. 2, and the vent hole diameter a, counterbore diameter b, counterbore height h ₁ , and counterbore taper angle α of the tread portion are shown in Table 1, respectively.
As shown in Fig. 5, five different types of molds (molds according to the present invention, comparative molds 1, 2 and 3 excluding the conditions of the present invention, and conventional molds according to Fig. 4) were manufactured. Then, the tire was vulcanized and molded by each mold. Table 2 shows the occurrence of light and the occurrence of vent breakage during the vulcanization molding.

Further, the vent hole burrs after mold release were trimmed to a height of about 1.5 mm for each of the five types of tires obtained by vulcanization molding using each mold. Each of these tires was subjected to a noise test under the same test conditions used in the experiment shown in FIG. 3 described above. As a result, the noise results shown in Table 2 were obtained. The noise in the table is shown in sound pressure level dB.

From Table 2 described above, the tires obtained by the molds of the present invention and the comparative molds 1, 2, and 3 have improved noise due to the residual burr trim, as compared with the tires obtained from the conventional molds. I understand. However, among the tires with improved noise, the tires with the molds of Comparisons 1, 2, and 3 have improved noise, but the diameter a related to the shape of the vent hole, the counterbore diameter b, the counterbore height h ₁ , It can be seen that any of the counterbore taper angles α is out of the condition of the present invention, so that light is generated during vulcanization molding or vent is cut off, and the vent hole does not fulfill its original normal function.

〔The invention's effect〕

As described above, the pneumatic tire obtained by the present invention can reduce the rigidity of the trim residual convex portion of the vent hole burr, thereby reducing the tire noise generated by the trim residual convex portion at the time of new article. You can

Further, according to the vulcanization molding die of the present invention, a tire with reduced tire noise can be manufactured without impairing the original function of the vent hole.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a vent hole portion of a vulcanization molding die used for manufacturing a pneumatic tire of the present invention, and FIG. 2 is a plan view showing a tread pattern of a tire obtained by the present invention, FIG. 3 is a graph showing the relationship between the counterbore diameter of the vent hole and the sound pressure level, and FIG. 4 is a vertical sectional view of the vent hole portion of the conventional mold. 1 ... Mold, 2 ... Bent hole, 2z ... Counterbore, 20 ...
… Trim remaining convex part.

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Claims (3)

[Claims] 1. The diameter a of the vent hole in the tread portion is 0.8 to
1.5 mm, counterbore diameter b is 3.0 mm or less, counterbore height h ₁ is 2.5 mm
As described above, the method for producing a pneumatic tire is characterized by vulcanizing and molding a tire with a mold having a counterbore taper angle α of 15 ° or more and smaller than 45 °, and then trimming the burr formed in the vent hole. 2. The method for manufacturing a pneumatic tire according to claim 1, wherein the height of the burr after trimming is 2.0 mm or less. 3. The diameter a of the vent hole in the tread portion is 0.8 to
1.5 mm, counterbore diameter b is 3.0 mm or less, counterbore height h ₁ is 2.5 mm
As described above, the mold for vulcanization molding of a pneumatic tire, which has a counterbore taper angle α of 15 ° or more and less than 45 °.