Process for the manufacture of two-wheeled-vehicle tires and tires obtained thereby

Abstract

A process for the manufacture of tire for high speed two-wheeled vehicles comprising making a cylindrical sleeve, attaching annular bead wires to the axial ends of said sleeve and shaping the sleeve into a toroidal configuration. A belt structure made of coils of cords is applied to the crown of said toroidal configuration. The belt is reinforced with HE cords which can be deformed to enable the tire carcass to be so largely expanded into the sold to achieve completely molding of a tread band.

1 . In a process for the manufacture of tires for vehicle wheels comprising the following steps: 
 manufacturing a tire carcass in the form of a cylindrical sleeve, by producing a tubular element of rubberized fabric reinforced with cords disposed substantially parallel to the axis of said sleeve and folding back the ends of the cords of said tubular element each about at least an annular metal bead core which is circumferentially inextensible, said bead cores lying in planes perpendicular to the sleeve axis;    toroidally shaping said tubular element by radially expanding the sleeve wall and moving said bead cores close to each other in an axial direction, so that a first toroidal configuration is achieved;    assembling a belt structure to said toroidally-shaped carcass, which belt structure comprises coils of cords oriented in a substantially circumferential direction and disposed in side by side relation' and    superposing a tread band on said belt at a radially outer position thereof;    introducing the thus assembled tire into a vulcanization mold;    closing said mold and expanding the carcass radially outwardly against the mold surface, so that it reaches its final toroidal configuration, so as to achieve the molding of the tread band; and    vulcanizing said carcass,    the improvement comprising: 
 making said belt of high-elongation cords, said cords having in their load-elongation diagram, a curvilinear portion mutually connecting two substantially rectilinear lengths of different inclination relative to the axes of said diagram, and  
 moving said annular bead cores coaxially toward each other during the toroidal shaping of said tubular element until a mutual axial distance between the bead cores is reached which corresponds to an intermediate toroidal configuration of smaller diameter than that of said first toroidal configuration and has a deviation of predetermined value from said final toroidal conformation, the value of the axial distance between said annular bead cores being proportional to the load-elongation diagram of said belt cords, so that the expansion of said carcass in said mold to the final toroidal configuration puts said belt cords in a tensile preloading condition corresponding to a point of said load-elongation diagram located within said curvilinear portion.  
   
     
     
         2 . A process according to  claim 1 , including forming said belt by the use of rubberized metal cords oriented in the same manner and having an ultimate elongation of between 4% and 8%.  
     
     
         3 . A process according to  claim 1 , in which said belt is made by wrapping at least one strip of rubberized fabric reinforced with said high-elongation cords around said carcass, overlapping the ends of said strips over a portion not lower than 20 mm in length.  
     
     
         4 . A process according to  claim 1 , in which said belt is made by wrapping a single high-elongation cord continuously and repeatedly around said carcass and extending in an axial direction from one axial end of said carcass to the other.  
     
     
         5 . A process according to  claim 1 , in which said belt is made by helically wrapping a tape of rubberized fabric comprising two to ten high-elongation cords around said carcass, proceeding in an axial direction from one end of the carcass to the other.  
     
     
         6 . A process according to  claim 4 , in which the helically wrapping of said metal high-elongation cords so as to make said belt is carried but by simultaneously proceeding from the middle towards both axial ends of the carcass.  
     
     
         7 . A process according to  claim 5 , in which the helically wrapping of said metal high-elongation cords so as to make said belt is carried out by simultaneously proceeding from the middle towards both axial ends of the carcass.  
     
     
         8 . In a tire for two-wheeled vehicles comprising 
 a carcass of toroidal form having a strong transverse convexity, having one crown portion and two sidewalls terminating in beads for anchoring to a corresponding mounting rim,    a tread band located on said crown and having a convexity ratio in the range of 0.15 to 0.45, and an annular, circumferentially inextensible reinforcement structure interposed between said carcass and tread band, said annular reinforcement structure comprising a plurality of cord coils disposed in axial side-by-side relation and extending from one axial end of said structure to the other at an angle almost of zero value relative to the equatorial plane or the tire,    the improvement comprising said reinforcement cords being of a high-elongation type having a load-elongation diagram with a curvilinear portion connecting two substantially rectilinear lengths to each other, said lengths having a different sloping, said cords in a vulcanized but not inflated and not loaded tire being in a tensile preloading condition corresponding to a point of said diagram located within said curvilinear portion.    
     
     
         9 . A tire according to  claim 8 , in which said reinforcement cords are metal cords oriented in the same manner and having an ultimate elongation in the range of 4% to 8%.  
     
     
         10 . A tire according to  claim 8 , in which said reinforcement cords are disposed at a density of between 25 to 150 cords/dm.  
     
     
         11 . A tire according to  claim 8 , in which said reinforcement cords are axially distributed in said belt structure in an uneven manner.  
     
     
         12 . A tire according to  claim 8 , in which the difference between the values of the drift thrust measured on a tire rotating in either of the two rotational directions, is lower than 15% of the maximum value of said drift thrusts.  
     
     
         13 . A tire according to  claim 9 , in which said metal cords oriented in the same manner and of the high elongation type are formed with 1 to 4 strands, each strand in turn preferably comprising 1 to 7 elementary wires, of a diameter in the range of 0.1 to 0.50 mm.