JP3917740B2 - Mold for vulcanization molding of pneumatic tires - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention provides at least a pair of circumferential grooves extending along the circumference of the tread surface of a tire, and a vulcanization molding metal for a pneumatic tire having a tread portion in which the circumferential grooves forming the pair are arranged close to each other. Regarding molds, more specifically, when unvulcanized tires are vulcanized, it is possible to prevent the occurrence of bear failures that tend to occur in narrow tread rubber portions sandwiched between pairs of circumferential grooves arranged close to each other. The present invention relates to a vulcanization mold.
[0002]
[Prior art]
In recent years, there has been a demand for diversified performance requirements (including appearance) for passenger cars or truck and bus pneumatic tires that run mainly on paved roads. To meet these requirements, there are a wide variety of tire tread patterns (tread patterns). Is also required. Among them, circumferential grooves extending along the tread (tread) circumference form a pair, and the interval between these circumferential grooves is narrow, and a convex rib extending from the groove bottom to the tread is provided in this narrow interval portion. Unique patterns are also preferred and used.
[0003]
The tread pattern grooves are formed by bones (ribs) provided in a mold for vulcanizing and molding an unvulcanized tire. Since the ribs of the mold that vulcanizes and molds the rib portion existing between the two are narrow, the vulcanized molding of the unvulcanized tire has a space that is separated by a pair of mold ribs within a narrow range. When the tread rubber member of an unvulcanized tire flows, air is trapped in this narrow space and air traps easily occur. As a result, a rubber flow failure occurs, and when the tire vulcanization molding is completed, a bare (Surface exposure of vulcanized rubber fabric) Failure is likely to occur.
[0004]
[Problems to be solved by the invention]
In order to improve the bare failure, it is a common practice to provide a so-called vent hole that opens on the inner peripheral surface between the ribs forming a pair of molds, penetrates the mold and opens on the outer surface of the mold. It is. However, the conventional vent holes are too wide to dispose of bare failures (the former), or because they are too narrow, there are too many vent hole protruding rubbers, so-called spews, and unnecessary amount of inflow rubber in the vent holes. In the actual situation, trial and error must be repeated until the optimum value of the vent hole arrangement interval is found. Moreover, the low efficiency of the trial and error described above is not suitable for the current situation, for example, if the tire size or tread pattern changes, the optimum value needs to be changed.
[0005]
Thus the invention according to claim 1 of this application relates mold comprising a rib forming a easy-to generate a bare fault a narrow spacing, without trial and error placement intervals of the vent hole as described above , yet regardless of the change in the tire size and tread pattern, to prevent the occurrence of bare failure, comprising a vent hole made in the proper arrangement does not emit excessive spew goal is to provide a vulcanization molding mold of the pneumatic tire It is.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the invention described in claim 1 of the present application includes at least a pair of circumferential grooves extending along the circumference of the tread surface of the tire, and the circumferential grooves forming the pair are arranged close to each other. In a mold for vulcanization molding of a pneumatic tire having a tread portion,
In the mold between the ribs forming a pair from the outside of the mold, the separation distance between the mold inner peripheral surfaces of the molds forming the pair of circumferential grooves forming the pair is 15 mm or less. Vent holes communicating with the peripheral surface are arranged at substantially equal intervals on the circumference of the inner peripheral surface, and the distance between adjacent vent holes is within the range of 50 to 300 mm, and the ribs forming a pair This is a mold for vulcanization molding of a pneumatic tire, in which a large number of shallow bottom narrow grooves are provided on the inner peripheral surface of the mold to pass through at least the vent hole position.
[0007]
The invention described in claim 1 is useful when applied to a mold for vulcanization molding of pneumatic tires for passenger cars or trucks and buses mainly traveling on paved road surfaces.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example of an embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a tread development view of a tread portion of a pneumatic radial tire for trucks and buses (hereinafter referred to as a tire).
2 is an enlarged partial cross-sectional view of a vulcanization mold corresponding to a part of the cross-section of the tread portion along the line II-II in FIG.
FIG. 3 is a plot diagram showing an example of the relationship between the vent hole arrangement interval of the vulcanization mold and the bear occurrence rate.
[0009]
In FIG. 1, reference numeral 2 denotes a tread surface of the tread portion 1 of the tire, and the tread portion 1 includes at least a pair (two pairs in the illustrated example) of circumferential grooves 3 and 4 extending along the circumference of the tread surface 2. In addition, circumferential grooves 5 and 6 that are not called a pair here are provided. The width in the tire rotation axis direction of the narrow rib 7 sandwiched between the pair of circumferential grooves 3 and 4 is narrow and is in the range of about 4 to 15 mm. The circumferential grooves 3 and 4 forming a pair are not only straight grooves extending along the circumference of the tread surface 2 as shown, but also a groove extending in a crank shape like the groove 5 and a zigzag bent not shown. It can be a groove and a curved groove.
[0010]
A large number of spew removal traces 8 can be seen along the circumference of the tread 2 at the center of the width of the rib 7. The spacing L of the spew marks 8 along the circumference of the tread 2 is substantially equal over the entire circumference, and the spacing L is in the range of about 50 to 300 mm, preferably in the range of 50 to 150 mm.
[0011]
The rib 7 is formed with a large number of vent ridges 9 arranged across the width direction, and the vent ridges 9 are formed at least at the position of the spew mark 8. A bent ridge 9 is formed. These vent ridges 9 are convex ridges formed by shallow bottom narrow grooves that serve to assist trap air escape provided in a tire vulcanization molding die (hereinafter abbreviated as a die).
[0012]
The tread pattern in FIG. 1 is a block pattern that mainly includes blocks 10 that are partitioned by circumferential grooves 3, 4, 5, 6, and the like and a large number of lateral grooves that communicate with each other. The block is provided with a sipe 11 having a small hole at its tip, and these small holes are not spew marks 8.
[0013]
The partial cross section of the mold 20 shown in FIG. 2 is a portion that forms a cross section along the II-II line of the tread portion 1 shown in FIG. 1, and this II-II line is on the vertical line of the tire equatorial plane (plane) E. Therefore, the plane on the partial cross section of the mold 20 is also orthogonal to the tire equatorial plane E.
[0014]
In FIG. 2, the inner peripheral surface 22 of the mold 20 forms a tread surface 2 of the tire tread portion 1, and ribs 23 projecting inward from the inner peripheral surface 22 toward the mold inward are circumferential grooves on the tread surface 2. 3 and ribs 24 form circumferential grooves 4 respectively. The mold ribs 23 and 24 make a pair in the same meaning as the circumferential grooves 3 and 4 forming the pair of the tread surface 2 of the tire tread described above. The separation distance D on the inner peripheral surface 22 between the paired mold ribs 23 and 24 is in the range of 4 to 15 mm. Here, the predetermined separation distance D and the width of the narrow rib 7 on the tread surface 2 are practically equal.
[0015]
Reference numeral 28 in FIG. 2 is a vent hole, and the vent hole 28 is a through-hole that opens to the outer surface 21 and the inner peripheral surface 22 of the mold 20 at a substantially central position of the separation distance D, respectively. The vent hole 28 is an escape hole for the air trapped between the unvulcanized tread rubber (not shown) and the ribs 23 and 24 of the mold 20 during vulcanization molding of the unvulcanized tire. Since a high pressure is applied to the inner surface of the unvulcanized tire at the time of molding, the unvulcanized tread rubber flows into the vent hole 28, which becomes spew after completion of the vulcanization molding, and the trace of this spew is the spew trace 8.
[0016]
Here, the vent holes 28 are arranged at substantially equal intervals along the circumference of the inner peripheral surface 22 of the mold 20, and the distance between the adjacent vent holes 28 at that time (the length along the circumference). Is in the range of 50 to 300 mm, preferably in the range of 50 to 150 mm. The distance between the vent holes 28 corresponds to the distance L along the circumference of the spew mark 8 on the tread surface 2.
[0017]
In addition, a large number of shallow and narrow grooves 29 are formed on the inner peripheral surface 22 between the paired mold ribs 23 and 24 at positions passing through the vent hole 28 at least across the mold inner peripheral surface 22. The groove 29 forms a vent ridge 9 in the rib 7 of the tread surface 2.
[0018]
When the unvulcanized tire is loaded into the mold 20 described above and the mold 20 is completely closed, the unvulcanized tire expands due to the high pressure acting on the inner surface thereof, and the tread rubber of the unvulcanized tire becomes the mold. 20 is pressed against the inner peripheral surface 22. In particular, the rubber flowing into the narrow region where the separation distance D between the paired mold ribs 23 and 24 is in the range of 4 to 15 mm once traps the air. It is discharged from the mold 20 to the outside.
[0019]
At that time, since trap air tends to gather at the corner where the opposing surfaces of the mold ribs 23 and 24 and the inner peripheral surface 22 intersect, a large amount of air trapped at a position corresponding to the surface of the rib 7 of the tread 2 is present. The air gathers at the corner through the shallow groove 29 and gathers the air at the corner, gathers at the shallow groove 29 communicated with the vent hole 28, and is discharged out of the mold through the vent hole 28. Therefore, the arrangement of the shallow groove narrow groove 29 further increases the discharge efficiency.
[0020]
However, if the arrangement interval of the vent holes 28 is too wide, the trap air cannot be exhausted to the outside of the mold 20 and a bare failure occurs. If it is too narrow, the occurrence of the bare failure can be prevented, but the number of spews increases. As a result, the processing man-hours of the mold 20 are unnecessarily increased, and the spew is removed in the finishing process, so that the amount of unnecessary rubber used increases.
[0021]
It was found that there is an optimum vent hole arrangement interval that can avoid the above disadvantages, and an optimization experiment was conducted there. An example is shown in FIG. Fig. 3 shows the tires for trucks and buses with a size of 11R22.5 (radial structure), and the vent holes are arranged in increments of 50 mm between 50 mm and 200 mm, and thereafter 300 mm and 400 mm. It is the figure which plotted the result of having investigated the bear generation rate (%) which generate | occur | produced when the tire addressed to 100 at the arrangement | positioning space | interval was vulcanized-molded by a circle ((circle)) mark.
[0022]
FIG. 3 shows that the bear occurrence rate is zero until the interval between the vent holes 28 is 150 mm, which is about 3% at 200 mm and about 5.3% at 300 mm. When the shallow groove narrow groove 29 (arrangement of the vent ridge 9 shown in FIG. 1) described above is provided (Δ mark), the bear generation rate is zero even at least 300 mm.
[0023]
From this, it can be seen that in the truck and bus tires having a large size, it is necessary that the arrangement interval of the vent holes 28 should be an upper limit of 300 mm. This is because when there is a variation in the vulcanization molding process, there is a possibility that a bare failure occurs when the thickness exceeds 300 mm. Therefore, the proper arrangement interval in the tire for trucks and buses is 150 to 300 mm when the above-mentioned shallow groove narrow groove 29 is provided, and is 100 to 150 mm when the shallow groove narrow groove 29 is not provided.
[0024]
On the other hand, when examining with other small size tires for passenger cars, it can be seen that if the arrangement interval of the vent holes 28 is less than 50 mm, the effect of blocking the bear will reach its peak only by increasing the spew. Again, this is not possible because both the mold processing cost and the amount of wasted rubber are increased. In FIG. 3, the case where the vent hole 28 is not provided is indicated by a cross, and in this case, bare failures occur in almost all of them.
[0025]
【The invention's effect】
According to the invention described in claim 1 of this application , even if a mold having a pair of ribs that have a narrow mutual interval and are likely to cause a bear failure is used, trial and error are applied to an appropriate interval between the vent holes. It is possible to provide a vulcanization mold for a pneumatic tire including a vent hole that is properly arranged without repeating, without increasing the number of man-hours for processing the mold, and without generating extra spew rubber.
[Brief description of the drawings]
FIG. 1 is a development view of a tread pattern of an example tire suitable for the present invention.
FIG. 2 is a partial cross-sectional view of a mold according to the present invention for vulcanizing the II-II cross section shown in FIG.
FIG. 3 is an explanatory diagram of the effect of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Tread part 2 Tread surface 3, 4 Paired circumferential groove 5, 6 Circumferential groove 7 Narrow rib 8 Spew mark 9 Bent ridge 10 Block 11 Sipe 20 Mold 21 Mold outer surface 22 Mold inner circumferential surface 23, 24 Paired mold rib 28 Vent hole 29 Shallow bottom narrow groove

Claims (1)

In a mold for vulcanization molding of a pneumatic tire comprising at least a pair of circumferential grooves extending along the circumference of the tread surface of the tire and having a tread portion in which the circumferential grooves forming the pair are arranged close to each other,
In the mold between the ribs forming a pair from the outside of the mold, the separation distance between the mold inner peripheral surfaces of the molds forming the pair of circumferential grooves forming the pair is 15 mm or less. Vent holes communicating with the peripheral surface are arranged at substantially equal intervals on the circumference of the inner peripheral surface, and the distance between adjacent vent holes is within the range of 50 to 300 mm, and the ribs forming a pair A mold for vulcanization molding of a pneumatic tire, in which a large number of shallow bottom narrow grooves are provided on the inner peripheral surface of the mold to pass through at least the vent hole position.

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