1. Field of the Invention
The present invention relates to a strip wind construction method of forming a rubber member for a tire by spirally winding a rubber strip, and more particularly to a manufacturing method of a rubber member for a tire which can reduce a air remnant in the rubber member.
2. Description of the Related Art
There has been considered to form a rubber member in each of positions of tire, such as a tread rubber, a side wall rubber or the like by spirally winding a rubber strip made of a material corresponding to a demand characteristic of the rubber member. By the strip wind construction method, a mouth piece of a nozzle and a labor hour of a management can be reduced in comparison with an conventional extrusion molding method of continuously extruding from a mouth piece in a predetermined finish cross sectional shape. Further, it is possible to use a compact rubber extruding machine, and it is possible to achieve a large item small scale production. As mentioned above, the strip wind construction method (STW method) can improve a productivity.
However, in the STW method mentioned above, since the rubber strip is spirally wound, an air reservoir tends to be generated due to a step in a side edge of the rubber strip or the like. This is because the adjacent rubber strips are wound astride the step in the side edge of the previously wound rubber strip. There is an increased risk that the air reservoir is generated between a wound body such as a drum or the like, and a rubber layer spirally wound in an outer side in a radial direction thereof, or between the inner and outer rubber layers in the radial direction in comparison with the conventional one mouth method. Accordingly, Japanese Published patent application 2000-254980 proposes a rubber strip provided with thin lug portions in both side edges, in a rubber strip.
In the proposed structure mentioned above, since both the side edges are provided with the thin step, in the case of forming a diagonal side edge portion, a thickness of an edge step is reduced in comparison with a thickness of a base portion. And an error in an outer peripheral edge between a finish cross sectional shape and an outline shape is reduced. Further, it is possible to achieve an effect to reduce a winding number by the thick base portion. However, it becomes necessary to hold specialized mouth pieces for the extruding machine, and a productivity tends to be lowered.
On the other hand, in the STW method, it is necessary to expel the air between the layers so as to prevent the air reservoir from being generated. Accordingly, a degree of adhesion is increased by pressing a roller to the spirally wound rubber layer or a previously wound rubber layer. Therefore, there is employed a straight bar-shaped pressing roller RT having a length more than a length of the rubber member to be formed or a half length, for example, as shown in
However, there is a case to form a tread rubber having bulge portions a protruding to an outer side in a radial direction in both side shoulder portions, for example, as shown in
Further,
As a result of making a study of the formation of the rubber member with a high precision and with no air reservoir in accordance with the STW method, there is conceived that it is preferable to execute a pressing as uniform as possible and set the thickness about a half height of each of the rubber members G without making the thickness too large, in order to obtain a preferable rubber member. Accordingly, it is possible to effectively transmit the pressing force by the pressing roller RT to an entire thickness of each of the layers. Further, there is conceived that it is preferable to spirally wind an entire length by dividing in a length direction in place of continuously winding the entire length in the tire axial direction.
Accordingly, an object of the present invention is to provide a manufacturing method of a rubber member for a tire which can reduce an air reservoir and can improve a junction between the rubber strip even in the case of using a rubber strip having a rectangular cross section in an STW method.
In accordance with the present invention, there is provided a manufacturing method of a rubber member for a tire constituted by a plurality of rubber layers overlapping in inner and outer sides in a radial direction, by spirally winding a ribbon-shaped unvulcanized rubber strip around a cylindrical wound body while moving in an axial direction, wherein the rubber member includes an inner first layer and a second layer. The first layer is formed by spirally winding the rubber strip from a starting point corresponding to a reference position of any one of a center position of the wound body and a side edge to the other reference position in an axial direction, in a half region between the center position and an side edge in a tire axial direction of a winding region. And the second layer is formed by folding back from the other reference position corresponding to the starting point of the first layer. The reference positions are set at a line-symmetrical position with respect to the center position.
A compounded rubber of a plurality of rubber layers can be identical. The structure can be made such that the first layer is wound from the reference point that is the starting point corresponding to the outer edge in the tire axial direction in the winding region to the reference point that is the center position, and the second layer is formed by being folded back at the center position so as to be wound to the outer edge in the tire axial direction. Further, the structure can be made such that the rubber member is a tread rubber, the first layer is constituted by a rubber layer having a flat thickness, and second layer is spirally wound in such a shape as to apply a similar thickness change to a shape of the tread rubber member in a green tire.
The rubber strip can be pressed by using a pressing roller which is movable close to and away from the wound body in parallel and is in a long straight rod shape having a uniform diameter, at a time of winding.
As mentioned above, in the present invention, in the STW method, the rubber strip is symmetrically reciprocated in the half region between the center position of the wound body and the outer edge in the tire axial direction of the wound body. Accordingly, the first layer and the second layer are formed in the inner and outer sides. Therefore, even in the case of using the pressing roller above described, it is easy to press as an approximately line-symmetrical shape at the center position. Accordingly, it is possible to obtain the rubber member which is good in a shape balance. Further, since the rubber member comprises the first and second layer, the first layer in the inner side in the radial direction can be efficiently pressed over an entire thickness. It is possible to suppress generation of an air reservoir on the basis of an air vent. Further, it is possible to improve an adhesion between the rubber strips, and is possible to mold the rubber member which is good in a uniformity, a durability and a dimensional precision.
Since the rubber strip is pressed in the long straight rod shape having the uniform diameter and by using the pressing roller RT which is movable close to or away from the wound body in parallel, it is possible to make a surface shape of the rubber member after being spirally wound smoother in comparison with the case of being pressed by a thin disc shaped roller, and it is possible to improve a quality of the rubber member by uniformizing the press-down force.
A description will be given of an embodiment in accordance with the present invention with reference to the accompanying drawings.
However, the present invention can be adopted to a side wall rubber G2 arranged in a side wall portion 3 and forming a tire outer surface, an inner liner rubber G3 arranged in an inner side of a carcass 6 and surrounding a tire inner cavity H, a clinch rubber G4 arranged in a bead portion 4 and preventing a rim displacement, a belt cushion rubber G5 arranged in both ends of a belt 7 and between the both ends and the carcass 6 and protecting an outer end of the belt, and the like. Further, it is possible to include a bead apex rubber G6 extending to an outer side in a radial direction from a bead core 5 of the bead portion 4 as the rubber member G. In this case, in the present embodiment, a band 10 is arranged in an upper surface in a radial direction of the belt 7. The band 10 is formed by spirally winding a band-like ply formed by embedding a plurality of cords in a topping rubber, for example, around an entire surface of an outer periphery of the belt 7, and preferably at a uniform thickness. Accordingly, it is possible to prevent the belt 7 from lifting up, and a tread reinforcing layer is structured in cooperation with the belt 7.
Further, in the present embodiment, the wound body P (shown in
In this case, the band 10 is preferably fitted to a concavity provided in the outer peripheral surface 14A of the former 14. Accordingly, the band 10 becomes flush with the outer peripheral surface 14A corresponding to the protruding portion 14Aa. Further, a surface-finish is applied to the protruding portion 14Aa for increasing an adhesion property with the rubber strip T and preventing a displacement of a winding start end so as to smoothen a winding work.
The pressing roller RT is formed in a straight rod shape of a uniform diameter at a length of a half or more than a half of the wound body P, in the present embodiment. Further, facing inner ends of the respective pressing rollers RT are arranged at a center position Tc of the wound body P so as to be coincided in a circumferential direction. Further, the pressing roller RT constitutes a part of a pressing apparatus (not shown) which controls an actuation of the pressing roller RT. The pressing roller RT moves close to and away from the former 14 while keeping a parallel state to the former 14 and without moving in an axial direction. It is possible to align thicknesses of the wound rubber members G by the close moving, the air vent is achieved by the pressing, and it is possible to preferably press the rubber strip T uniformly so as to connect each other. In this case, the pressing roller RT is positioned in a downstream side of each of the applicators 16a,16b and can press the rubber member G formed by winding the rubber strip T fed from the applicators 16a, 16b.
The rubber strip T is formed in a ribbon shape made of an unvulcanized rubber as exemplified in
Further, taking into consideration factors such as a low heat generation property, a grip performance, an abrasion resistance service life and the like as the tread rubber G1, a rubber composition, JISA hardness, a complex elastic modulus (E*) and a tangent of the loss angle (tan δ) are selected in an optimum manner. In this case, a silica can be employed as a rubber filler in addition to the carbon black. The silica compounded rubber in which the silica is compounded can improve a wet grip performance, and can reduce a rolling resistance on a dry road surface. However, an electric resistance is increased. Accordingly, in order to suppress the increase of the electric resistance, it is preferable to set a conductive coat on the rubber strip T, for example, at least one surface thereof so as to make a rim conductive from a tread ground surface TS.
A half region Lh is defined as a portion between a center position Tc of the wound body P, and one outer edge Te in the tire axial direction of a winding region around which the rubber strip T is wound (a forming region of the winding body). Further, the center position Tc or each of the outer edges Te is defined as reference positions p and p. Actually, “center position Tc” and “outer edge Te” include “vicinity” allowing a length in the tire axial direction equal to or less than about 5% of the half region, from each of the positions, in this specification.
In the present invention, the tread rubber G1 is structured such that the rubber strip T is spirally wound from a starting point corresponding to one of the reference positions p and p constituted by the center position Tc or the outer edge Te, to the other reference position p (the outer edge Te or the center position Tc) in the axial direction, as shown in
Next, a second layer 12 is formed by folding back from the starting point of the corresponding to each of the other reference positions(the starting position of the first layer 11) to the other in the axial direction.
Further, a description will be given of a case shown in
Further, each of the first layers 11 in both sides is formed in a flat shape in which a rubber height is almost constant in an upper surface 11S. Accordingly, the roller height Hr of the pressing roller RT, which is minimum value Hr1m in the starting point, is increased in accordance with forming the outer surface of the buttress portion 2A (the upper side of the side wall portion 2). After that, the pressing roller RT can press the rubber strip continuously wound while keeping the state of a rubber height Hr1M of the first layer 11. The first layer 11 of the rubber height Hr1M becomes approximately line-symmetrical around the center position Tc. Even when the upper surface 11S is swell (expanding shape) in which the rubber height Ht is increased toward the center position Tc, the pressing roller RT can follow.
Further, the second layers 12A and 12B (called as the second layer 12 in conjunction) are formed on the first layers 11A and 11B folding back the rubber strip T at the center position Tc toward the other reference point p, that is, the outer edge Te after forming the turbulent and asymmetrical portion in which the rubber strips T overlap, as mentioned above, at the fold-back portion. The second layer 12 is relatively thin in the center region, and the height is increased little by little toward the outer edge Te. Accordingly, there is formed the bulge portion a in which the upper surface 12S bulges gradually to each of the shoulder portion side, and there is formed a concave shape in which the center region is depressed.
Accordingly, in the pressing roller RT mentioned above, the starting point in the second layer 12 exists in the center position Tc, as shown in
As mentioned above, the first layer 11 has a half thickness and a pressing effect is larger, in comparison with the structure in which the entire thickness is formed by one spiral winding. Accordingly, it is possible to properly bond the rubber strips T to each other. Also, it is possible to uniformly press in the entire length, and it is possible to reduced the air reservoir. Further, the second layer 12 has a half thickness of the conventional single layer tread rubber G, it is possible to efficiently extrude the air and connect between the rubber strips T by pressing.
In this embodiment, the upper surface 11S in each of the first layers 11 in both sides is structured such that a rubber height is a minimum height Hr1m at the center position Tc forming the starting point, and the rubber height is gradually increased toward the outer edge Te. Accordingly, it is formed as a concave shape in which the bulge portion a near the outer edge Te comes to the maximum height H1rM. The height Hr of the pressing roller RT is increased from the state of the minimum roller height Hr1m toward the outer edge Te in accordance with the outer surface of the bulge portion a, as shown in
As described above, the pressing roller RT can press the rubber strip T at a time of the winding in which the upper surface 11S is formed in the concave shape, and the entire shape is approximately line-symmetrical around the center position Tc. In the case of the upper surface 11S being flat, the pressing roller RT can easily press the winding body in the entire length range.
The second layers 12A and 12B (called as the second layer 12 in conjunction) are formed on the first layers 11A and 11B by being folded back at the outer edge Te. The second layer 12 is folded back toward the reference point p of the center position Tc. The second layer 12 is made relatively thicker in the center region between the buttress 2A and 2A, so as to compensate the structure in which the upper surface 11S of the first layer 11 is formed concave. Accordingly, the pressing roller RT is maintained at the roll height Hr2M of the upper surface 12S of the second layer 12. Therefore, the entire rubber thickness comes to the uniform thickness over the entire of the half length Lh, that is, the upper surface 12S of the second layer 12 is formed flat.
The pressing roller RT exists at the maximum roller height Hr1M of the first layer 11 at the starting point (the winding start) of the second layer 12, as shown in
The base portion 13A is formed on the basis of each of the embodiments mentioned above. In
Further, the case that the starting point of the first layer 11 is set to the outer edge Te is shown by a broken arrow. At this time, it reaches the outer edge Te of the second layer 12 after being folded back at the center position Tc, and the base portion 13A is constituted. Further, the additional layer 13B forming the bulge portion a of the shoulder portion is formed by folding back at the outer edge Te, for example, by one layer thickness and may be thereafter repeated at a plurality of times.
As mentioned above, in the case shown in
The description is given above of the embodiments in accordance with the present invention, however, the present invention can be applied to the other rubber strips having the other cross sectional shapes than the rectangular shape in correspondence to the performance demanded for the tire. Further, various materials can be employed as the rubber strip. The present invention is particularly preferable for the pneumatic tire for the passenger car, however, it goes without saying that the present invention can be applied to various tires such as tires for a motor cycle, a truck, a bus and the like, in addition to the tire for the passenger car.
There is manufactured a tread rubber G1 of a pneumatic radial tire for a passenger car on the basis of a tire size of 215/45ZR17 and a specification shown in Table 1. A test is executed about a performance thereof. In this case, a rubber strip is set to be identical. Results thereof are shown in Table 1. In the tested specification, FIGS. 2 and 3 are set to an example 1,
Twenty tires are manufactured for each of the tires, and a uniformity is measured. The uniformity is measured as a radial force variation (RFV) on the basis of a uniformity test condition of JASO C607:2000. An evaluated speed is set to 10 km/h. Results are expressed by an average (N) of twenty tires, and the smaller the numerical value is, the better the result is.
Number | Date | Country | Kind |
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2005-380591 | Dec 2005 | JP | national |