Shaping drum for crown reinforcement plies

Abstract

A drum ( 1 ) of variable diameter of generally cylindrical form, intended for the assembly of the belt plies and profiled elements constituting the crown of a tyre, comprising a set of first holding means ( 3 ) arranged circumferentially at the equator of the drum and suitable for making that part of the ply arranged level with these means adhere to the surface of the drum, and characterised in that it comprises a set of second holding means ( 4 ) suitable for making that part of the ply placed level with said second means alternately adhere to or slide freely on the drum, and which are arranged circumferentially and axially on either side of said equator over the entire surface of said drum ( 1 ).

1 . A drum ( 1 ) of variable diameter of generally cylindrical form, intended for assembly of the belt plies (N 1 , N 2 ) and profiled elements constituting the crown of a tyre, comprising a set of first holding means ( 3 ) arranged circumferentially at the equator of the drum EE′ and suitable for making that part of the ply (N 1 ) arranged level with these means adhere to the drum, and characterised in that it comprises a set of second holding means ( 4 ) suitable for making that part of the ply placed level with said second means alternately adhere to or slide freely on the drum, and which are arranged circumferentially and axially on either side of the equator EE′ over the entire surface of said drum ( 1 ).  
   
   
       2 . A drum according to  claim 1 , in which the first means ( 3 ) are formed by pneumatic valves opening on to the outer surface of said drum ( 1 ) and connected to a vacuum connection.  
   
   
       3 . A drum according to  claim 1 , in which the first means ( 3 ) are formed by electromagnets.  
   
   
       4 . A drum according to  claim 1 , in which the second means ( 4 ) are formed by pneumatic valves opening on to the outer surface of said drum which are able to be connected alternately to a vacuum connection or to a pipe supplying pressurised air.  
   
   
       5 . A drum according to  claim 1 , formed by assembling a given number of radially mobile elements ( 2 ), on which said first means ( 3 ) are placed axially in the middle of said element and said second means ( 4 ) are placed axially on either side of said first means ( 3 ).  
   
   
       6 . A process for assembling a tyre, comprising a separate step of producing the crown of said tyre on a drum of variable diameter ( 1 ) of generally cylindrical form, said drum comprising a set of first holding means ( 3 ) arranged circumferentially at the equator EE′ of said drum and suitable for making that part of the ply arranged level with these means adhere to the drum ( 1 ) and comprising a set of second holding means ( 4 ) suitable for making that part of the ply placed level with said second means ( 4 ) alternately adhere to or slide freely on the drum, and which are arranged circumferentially and axially on either side of the equator EE′ over the entire surface of said drum ( 1 ), 
 characterised in that it comprises the following steps:    positioning the drum ( 1 ) at a first diameter D 1 , 
 depositing a first crown belt ply N 1  composed of reinforcement cables coated in a rubber mix forming a given angle α1 with the circumferential direction, by activating the first and second means so as to make the entire ply adhere to the surface of the drum,  
 depositing a second crown belt ply N 2  composed of reinforcement cables coated in a rubber mix forming a given angle α2 of opposite sign to the angle α1 with the circumferential direction,  
 making the second ply N 2  adhere to the first ply N 1 ,  
 while keeping the first means ( 3 ) in the preceding configuration, activating the second means ( 4 ) so as to permit sliding of the first ply level with said second means ( 4 ),  
 positioning the drum at a second diameter D 2  greater than the first diameter D 1 ,  
 activating the second means ( 4 ) so as to make the ply adhere to the surface of the drum,  
 depositing the other plies and the other profiled products constituting the crown of the tyre,  
 gripping the crown thus produced with a transfer ring and depositing the crown on a tyre blank of toroidal form.  
   
   
   
       7 . An assembly process according to  claim 6 , in which the shaping ratio, which is equal to the ratio between the second diameter D 2  and the first diameter D 1 , is of between 1.03 and 1.5.  
   
   
       8 . An assembly process according to  claim 7 , in which the angle formed with the circumferential direction by a cable at its two ends is greater than the angle formed with the circumferential direction by the same cable in its central part.  
   
   
       9 . An assembly process according to  claim 8 , in which the angle formed with the circumferential direction by a cable at its two ends is greater by 2° to 15° than the angle formed with the circumferential direction by the same cable in its central part.