Patent Publication Number: US-2011070325-A1

Title: Multiple-preformer die of extrusion mold for tire treads

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an extrusion mold for tire treads that extrudes an assembly of semi-finished tires, for example, a cap tread, a wing tread and a sub tread, in a process of manufacturing a tire and, more particularly, to a multiple-preformer die of an extrusion mold for tire treads that has an improved structure including preformers and rubber flow-paths in the preformers so as to allow the use of final dies of various standards and to facilitate adjustment of a boundary surface between respective tread rubbers. 
     2. Description of the Related Art 
     In an extrusion process for manufacturing a tire, a compounded rubber produced by a refining process is sequentially supplied to an extruder through a break-down roll and a warming roll and an extrudate having a constant shape according to a fabrication specification is finally ejected through a regulated preformer die of the extruder. Here, treads of the extrudate include a cap tread, a wing tread, a sub tread, and the like. 
     A conventional preformer die of an extrusion mold for tire treads is generally classified into a pressure type and an overlapping piece type. 
     Referring to  FIG. 5 , the pressure type preformer die includes first and second preformer die holders  103 ,  104 , first upper and lower preformers  101  and  102  mounted to the first preformer die-holder  103 , second upper and lower  105   a  and  105   b  mounted between the first and second preformer die-holders  103  and  104 , and a final die  106  mounted to the second preformer die-holder  104 . 
     Reference number  107  indicates a flow-path for the wing tread. 
     Since the preformers have a retractably insertable cassette type structure and are inserted into the preformer die-holders, the conventional preformer die employs final dies of multiple standards to allow rapid substitution of the final die of various standards, but suffers difficulty in adjustment of a boundary surface between the respective tread rubbers. 
     Referring to  FIG. 6 , the overlapping piece type preformer die includes a preformer die-holder  210 , which has a wing tread flow-path  202 , a cap tread flow-path  203  and a sub tread flow-path  204  defined therein, and a final die  205  mounted to the preformer die-holder  201 . Accordingly, the overlapping piece type preformer die allows easy adjustment of the boundary surface between the respective tread rubbers, but requires substitution of the preformer die-holder for substitution of the final die, so that it is impossible to employ final dies of various standards or it takes long time to replace the final die, thereby causing inconvenience. 
     SUMMARY OF THE INVENTION 
     The present invention is conceived to solve the problems of the related art, and an aspect of the invention is to provide a multiple-preformer die of an extrusion mold for tire treads which can realize the advantages of the pressure type preformer die allowing the use of final dies of various standards and the overlapping piece type preformer die allowing easy adjustment of a boundary surface between respective tread rubbers. 
     In accordance with an aspect of the invention, a multiple-preformer die of an extrusion mold for tire treads includes a first preformer die-holder having a wing tread flow-path, a cap tread flow-path and a sub tread flow-path, a second preformer die-holder, and a final die inserted into the second preformer die-holder and ejecting an extrudate. The improvement includes a middle upper preformer die and a middle lower preformer die interposed between the first and second preformer die-holders to be brought into contact with the final die. The middle upper preformer die is formed with a wing tread-connecting guide groove and a cap tread-connecting guide groove communicating with the wing tread flow-path and the cap tread flow-path of the first preformer die-holder, respectively. The middle lower preformer die is formed with a sub tread-connecting guide groove communicating with the sub tread flow-path of the first preformer die-holder. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features and advantages of the invention will become apparent from the following detailed description in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a coupled sectional view of a multiple-preformer die of an extrusion mold for tire treads in accordance with one embodiment of the present invention; 
         FIG. 2  is an enlarged front view of middle upper and lower preformer dies of  FIG. 1 ; 
         FIG. 3  is a coupled sectional view of a double-preformer die of an extrusion mold for tire treads in accordance with another embodiment of the present invention; 
         FIG. 4  is an enlarged front view of middle upper and lower preformer dies of  FIG. 3 ; 
         FIG. 5  is a coupled sectional view of a conventional pressure type preformer die of an extrusion mold; and 
         FIG. 6  is a coupled sectional view of a conventional overlapping piece type preformer die of an extrusion mold. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of the invention will now be described in detail with reference to the accompanying drawings. 
       FIGS. 1 and 2  illustrate a multiple-preformer die of an extrusion mold for tire treads in accordance with one embodiment of the invention, in which  FIG. 1  is a coupled sectional view and  FIG. 2  is an enlarged front view of an upper preformer die and a lower preformer of  FIG. 1 . 
     The present invention relates to a preformer die of an extruder for treads in a process of manufacturing a tire. The terms of the treads will now be defined before the description of the invention. 
     Herein, a wing tread refers to a component of a tread that is located at a boundary surface between a cap tread and a side wall of the tread to improve crack resistance and adhesive properties between the cap tread and the side wall. 
     The cap tread is a rubber layer on a portion of the tire that will be brought into contact with the road surface, and a sub tread is a rubber layer between an inner cord layer and the cap tread. 
     According to one embodiment of the invention, a preformer die of an extrusion mold for tire treads includes a first preformer die-holder  4  having a wing tread flow-path  1 , a cap tread flow-path  2  and a sub tread flow-path  3  formed therein, a second preformer die-holder  6 , and a final die  5  inserted into the second preformer die-holder  6  and ejecting an extrudate. Further, the preformer die includes a middle upper preformer die  7   a  and a middle lower preformer die  7   b  interposed between the first and second preformer die-holders  4  and  6  to be brought into contact with the final die  5 . The middle upper preformer die  7   a  is formed with a wing tread-connecting guide groove  1   a  and a cap tread-connecting guide groove  2   a  that communicate with the wing tread flow-path  1  and the cap tread flow-path  2  of the first preformer die-holder  4 , respectively. The middle lower preformer die  7   b  is formed with a sub tread-connecting guide groove  3   a  that communicates with the sub tread flow-path  3  of the first preformer die-holder  4 . 
     In this embodiment, the middle upper and lower preformer dies  7   a  and  7   b  have a retractably insertable cassette type structure and are mounted between the first preformer die-holder  4 , which has the wing tread flow-path  1 , the cap tread flow-path  2  and the sub tread flow-path  3  therein, and the second preformer die-holder  6 . Further, the final die  5  is inserted into the second preformer die-holder  6  and finally mounted to the middle upper and lower preformer dies  7   a  and  7   b  to be in contact with each other. 
     As shown in  FIG. 2 , the middle upper preformer die  7   a  is formed with the wing tread-connecting guide groove  1   a  and the cap tread-connecting guide groove  2   a , and the middle lower preformer die  7   b  is formed with the sub tread-connecting guide groove  3   a.    
     Therefore, according to this embodiment, a rubber flow from the first preformer die-holder  4  is forcibly distributed from a start portion of the first preformer die-holder  4  to a start portion of the second preformer die holder  6  to form the wing tread, cap tread and sub tread as in the conventional overlapping piece type, thereby allowing easier adjustment of a boundary surface between the respective tread rubbers than in the conventional pressure type. Further, the middle upper and lower preformer dies  7   a  and  7   b  have a retractably insertable cassette type structure and are mounted to the second preformer die-holder  6  as in the conventional pressure type, thereby enabling rapid substitution of final dies of various standards. 
     Specifically, the middle upper preformer die  7   a  of the retractably insertable cassette type structure is formed with the wing tread-connecting guide groove  1   a  and the cap tread-connecting guide groove  2   a  so that a distance between the opposite wing tread-connecting guide grooves  1   a  and a horizontal length of the cap tread-connecting guide groove  2   a  are adjusted to large, medium and small sizes corresponding to the standard of the final die  5 , and the middle lower preformer die  7   b  of the retractably insertable cassette type structure is formed at a starting point thereof with the sub tread-connecting guide groove  3   a  so that a horizontal length of the sub tread-connecting guide groove  3   a  is adjusted to large, medium and small sizes corresponding to the standard of the final die  5 . 
       FIGS. 3 and 4  illustrate a preformer die of an extrusion mold for tire treads in accordance with another embodiment. In this embodiment, the sub tread-connecting guide groove  3   a  of the middle lower preformer die  7   b  extends to an end point of the middle lower preformer die  7   b  and a start point of the final die  5 . 
     Accordingly, in the preformer die according to this embodiment shown in  FIGS. 3 and 4 , the middle lower preformer die  7   b  has a retractably insertable cassette type structure and allows a horizontal length of the sub tread-connecting guide groove  3   a  to be adjusted so as to have large, medium and small sizes corresponding to the standard of the final die  5 . 
     In the multiple-preformer die according to the embodiments, the upper and lower preformers have a retractably insertable cassette structure and are configured to allow replacement with preformers of large, medium and small sizes according to the standard of the final dies, so that final dies of various standards can be used (advantage of the pressure type preformer die), a boundary surface between the respective tread rubbers can be easily adjusted (advantage of the overlapping piece type preformer die), and back pressure acing on the preformer is significantly lowered as compared with the related art. 
     Although some embodiments have been provided to illustrate the invention in conjunction with the drawings, it will be apparent to those skilled in the art that the embodiments are given by way of illustration only, and that various modifications, changes, alterations, and equivalent embodiments can be made without departing from the spirit and scope of the invention. The scope of the invention should be limited only by the accompanying claims.