Mold for vulcanizing a tire having a specified belt profile in the absence of load and inflating pressure

Abstract

A mold for tire vulcanization that includes axially opposite sidewalls and a tread band molded with a raised pattern formed with at least one circumferential groove. The mold has a pair of axially opposite cheeks corresponding to the sidewalls of the tire and a matrix interposed between the cheeks, which corresponds to the tread band. The matrix has a plurality of ribs projecting in a raised configuration from a bottom surface. The sectional profile of the bottom surface comprises two distinct concave side portions and the sectional profile of the surface tangent to the ridge of the ribs in the area included between the side portions has a convexity directed radially inwardly.

1 . A tire for motor-vehicle wheels ( 1 ) comprising a toric carcass ( 2 ) provided with axially opposite sidewalls and beads for anchoring of said tire to a corresponding mounting rim, a tread band disposed crown-wise to said carcass and a belt structure ( 6 ) interposed between said carcass and tread band, axially extended in a continuous manner between said sidewalls, said tread band being moulded with a raised pattern having at least one circumferential groove ( 11 ), characterized in that, in the absence of load and inflating pressure, said belt structure, seen in right section in the plane containing the tire axis, has 
 an axial profile comprising three distinct portions, two side portions referred to as first ( 14 ) and second ( 15 ) portions, and one central portion ( 16 ) respectively, said central portion being interposed between said side portions in register with said circumferential groove ( 11 ),    said side portions being concave at a radially internal position, in which the concavity is defined for each portion by a respective centre and a respective radius of curvature,    said central portion being concave at a radially external position, in which the depth of said outer concavity is capable of being cancelled under the effect of the normal inflating pressure of the tire.    
     
     
         2 . A tire as claimed in  claim 1 , characterized in that the concavity centre of said central portion lies in the centre line plane of said groove ( 11 ) which is coincident with the equatorial plane of the tire.  
     
     
         3 . A tire as claimed in  claim 2 , characterized in that the depth of said concavity is defined by the following relation: 
       S=R 1 −R 0   
       wherein: 
 R 1  corresponds to the radius of a known tire, substantially identical in its structure and size with said tire, the belt structure of which, under any condition and seen in axial cross section, exhibits a continuously concave profile in a radially internal position, measured along the equatorial plane of the tire, when the tire is mounted to the respective rim and inflated to the normal running pressure;  
 R 0  corresponds to the radius of the same known tire, still measured along the equatorial plane of the tire, under non-working conditions.  
 
     
     
         4 . A tire as claimed in  claim 2 , characterized in that the radii of curvature of said concave side portions are substantially identical with each other and have a value included between 120 and 500 mm.  
     
     
         5 . A tire as claimed in  claim 2 , characterized in that the radius of curvature of said central concave portion is of a value included between 20 and 150 mm.  
     
     
         6 . A tire as claimed in  claim 2 , characterized in that the thickness of said tread band at the equatorial plane is included between 1 and 3.5 mm.  
     
     
         7 . A tire as claimed in  claim 2 , characterized in that the ratio of said groove ( 11 ) depth to the thickness of the underlying tread band portion is included between 2 and 10.  
     
     
         8 . A tire as claimed in  claim 1 , characterized in that the width of said groove ( 11 ) is included between 10% and 18% of the width of said tread band.  
     
     
         9 . A tire as claimed in  claim 1 , characterized in that said groove ( 11 ) is comprised, at the inside thereof, of reinforcing means for said tread band.  
     
     
         10 . A tire as claimed in  claim 9 , characterized in that said groove ( 11 ) comprises at least one rib ( 17 ) extending in cantilevered fashion from the bottom.  
     
     
         11 . A tire as claimed in  claim 10 , characterized in that said rib ( 17 ) is located at the centre line plane of said groove ( 11 ) and is circumferentially continuous.  
     
     
         12 . A tire as claimed in  claim 11 , characterized in that the ratio of said groove depth to the height of said rib is included between 1.75 and 6.5.  
     
     
         13 . A tire as claimed in  claim 10 , characterized in that the head ( 17   a ) of said rib is made of a coloured blend, for aesthetic and/or safety purposes, for signalling beginning of the aquaplaning danger and/or the maximum admissible limit for tread wear.  
     
     
         14 . A process for manufacturing a tire comprising a toric carcass ( 2 ) provided with axially opposite sidewalls and beads for anchoring of said tire to a corresponding mounting rim, a tread band disposed crown-wise to said carcass and a belt structure ( 6 ) interposed between said carcass and tread band, axially extending in a continuous manner between said sidewalls, said tread band being moulded with a raised pattern provided with at least one circumferential groove ( 11 ), said process comprising the step of disposing the green tire, in a toric conformation, in a vulcanization mould for achievement of its final moulded configuration by means of a heat treatment and with the use of fluid under pressure, characterized by utilizing a mould forcing said belt structure to take a moulded configuration; the profile of said moulded configuration, seen in cross section in the plane containing the tire axis, comprises: 
 three distinct portions, i.e. two side portions, respectively referred to as first ( 14 ) and second ( 15 ) portions, and one third portion ( 16 ), the central one, interposed between said side portions in register with said circumferential groove ( 11 ),    said side portions being concave in a radially internal position, in which the concavity is defined for each portion by a respective centre and a respective radius of curvature,    said central portion being concave in a radially external position, the depth of said radially external portion being capable of being cancelled under the effect of the normal inflating pressure of the tire.    
     
     
         15 . A mould for tire vulcanization comprising axially opposite sidewalls and a tread band moulded with a raised pattern formed with at least one circumferential groove ( 11 ), said mould comprising a pair of axially opposite cheeks corresponding to the sidewalls of said tire and a matrix interposed between said cheeks, corresponding to said tread band, said matrix being provided with a plurality of ribs projecting in a raised configuration from a bottom surface for forming said pattern, characterized in that, in a plane containing the mould axis, 
 the sectional profile of said bottom surface comprises two distinct concave side portions, in which the concavity is defined for each portion by a respective centre and a respective radius of curvature,    the sectional profile of the surface tangent to the ridge of said ribs in the area included between said side portions has a convexity directed radially inwardly.