A typical tire has a plurality of rubber components and a plurality of reinforcing components chiefly constituted by cords. As illustrated in FIG. 9, a typical example of the tire includes an inner liner 1, a tread 2, side walls 3, rim strips or chafers 4, under-belt pads 5, and other components, all of which are built by rubber materials having required characteristics. These rubber components are combined with a carcass layer 6 and a belt layer 7 as reinforcing components including cords to become a tire T. FIG. 8 illustrates an example of respective disassembled components of a tire.
FIG. 8 shows the inner liner 1, a tread base 2a and a tread cap 2b constituting the tread 2, the side walls 3, the chafers 4, and the under-belt pads 5 laminated under both side ends of the belt, all of which are built by rubber materials having predetermined characteristics. The carcass layer 6 has first and second carcass plies 6a and 6b, and the belt layer 7 has a plurality of belts 7a and 7b. Each of bead members 8 has a bead core 8a made of wire or the like and a bead filler 8b made of rubber attached to the outer circumference of the bead core 8a. A squeegee 10 as a rubber layer laminated on the inner ply, tapes between plies 6c, belt edge tapes 7c are all made of rubber materials. A spiral tape 9 contains fiber cords.
A double-stage building method is known as a method for building this type of tire. According to this method, the inner liner, the carcass ply and other components are affixed on an expansive and contractive band drum, and the beads and sides are built by a primary building drum to build a green case. The green case is shifted to a secondary building drum which modifies shaping to build the green case into a toroidal shape, onto which the belt, the tread rubber and other components are affixed to build a green tire. In addition, a single-stage building method which uses a single building drum swinging between the position at which both the band building and primary building are executed and the secondary building position is known.
When the tire components in the respective processes are affixed and built at a different building position for each of the primary building step and the secondary building step in the double-stage building method, longer building cycle time is required and therefore improvement of productivity is difficult to achieve.
As a technique for overcoming these drawbacks, a system which uses a plurality of movable building drums to build a green tire has been proposed. In this system, the movable building drums are shifted to predetermined building positions. Predetermined components such as an inner liner or other rubber components or carcass plies are supplied to build a green case in a primary building step, and rubber components such as a belt and a tread are supplied to build a green tire in a secondary building step.
The system which shifts the building drums to execute the double-stage building method requires a complicated and large-scale structure and a large installation and operation space. Moreover, preparatory processes need to be performed for both the rubber components such as the inner liner and the tread and the reinforcing members such as the carcass and the belt before they are supplied for formation. Furthermore, the system requires a wide space for storing various types of plenty of components to facilitate arrangement switching at the time of size change of the tire.
Recently, such a technique has been proposed which builds rubber components having predetermined cross sections by overlapping and spirally winding unvulcanized rubber strips formed by extrusion into ribbon shapes on a building drum (see Patent Reference Nos. 1 through 4 shown below, for example).
According to the technique which builds the rubber components constituting the tire by winding the rubber strips discussed above, the rubber volume considerably differs depending on the types of rubber components. For example, the rubber volume of the components such as the tread and the side walls is relatively large, and the rubber volume of the components such as the under-belt pads and the chafers is relatively small. The rubber components having large rubber volume requires longer time for winding.
In formation of the tire, therefore, the arrangement of the building positions of the respective rubber components is an important factor associated with time required for winding of the respective rubber components. When the building time is not equalized for each of the primary and secondary building steps, loss time is produced in the building cycle.
According to the method disclosed in the Patent Reference No. 1, for example, a breaker corresponding to the belt and the tread are sequentially laminated at a position for building the final shape in the secondary building step. Thus, the side walls are built by winding rubber strips at a position for building the green case in the primary building step. However, since the under-belt pads are also built by winding rubber strips at the position for building the green case, the building cycle in the primary building step takes longer time as the rubber volume of the side walls increases. In this case, there is a possibility that prolongation of the entire building cycle time occurs.
Patent Reference No. 1: JP-B-6-51367
Patent Reference No. 2: JP-A-9-29858
Patent Reference No. 3: JP-A-2002-178415
Patent Reference No. 4: JP-A-2002-205512