Steel cord with adapted elongation properties

Abstract

In a tire the strength of steel cord and the resilience of rubber are a successful combination. However, in some specific areas of a tire, more elongation is expected from the steel cord, while still a sufficient degree of stiffness is expected. A steel cord is presented that has these properties. The steel cord comprises two or more steel elements that are twisted together. The steel elements comprise one or more steel filaments. In total the steel cord comprises ‘N’ filaments, each with a cross sectional area ‘A’. When the steel elements are individualised out of the steel cord they show a helix pitch length of ‘L o ’, while a single pitch has a centre line length of ‘S’. The inventive steel cord shows a ‘P’ value of at least 50 newton, wherein P=πNE (A/S) 2 . Further methods are presented to produce this steel cord.

1 - 19 . (canceled) 
     
     
         20 . A steel cord for the reinforcement of a rubber product comprising two or more steel elements twisted together, said steel elements comprising one or more steel filaments, said steel cord comprising in total ‘N’ steel filaments, each of said steel filaments having a cross sectional area ‘A’ expressed in square millimeters said steel elements have, after individualization and under a tension of half a newton per filament in said steel element, a center line, said center line having a helix shape with a helix pitch length ‘L o ’ in millimeter, wherein the length of the center line of the steel element over one pitch is ‘S’ millimeter,
 wherein 
 the quantity ‘P’ expressed newton: 
 
       
         
           
             
               P 
               = 
               
                 π 
                 ⁢ 
                 
                   
                     NE 
                     ⁡ 
                     ( 
                     
                       A 
                       S 
                     
                     ) 
                   
                   2 
                 
               
             
           
         
         is larger than 50 newton and wherein ‘E’ is the modulus of steel. 
       
     
     
         21 . The steel cord according to  claim 20 , said filaments have an equivalent diameter ‘d’ defined by ‘A=πd 2 /4’, wherein ‘S/d’ is smaller than 30. 
     
     
         22 . The steel cord according to  claim 20 , wherein the ratio ‘L o /S’ is smaller than 0.95. 
     
     
         23 . The steel cord according to  claim 20 , wherein the filaments of said steel cord, when in closed condition, have a pitch length of ‘L o ’ in millimeter, wherein the ratio ‘L o /S’ is larger than 0.98. 
     
     
         24 . The steel cord according to  claim 23 , wherein the structural elongation ‘∈ 0 ’ defined as (L o −L 0 )/L o  is larger than 3.5 per cent and smaller than 10 per cent. 
     
     
         25 . The steel cord according to  claim 20 , wherein the force at the structural elongation ‘∈ 0 ’ is larger than 50 N and smaller than 120 N. 
     
     
         26 . The steel cord according to  claim 20 , wherein the number of steel elements is two, three or four and wherein the number of steel filaments within one steel element is one, two or three. 
     
     
         27 . The steel cord according to  claim 20 , wherein the number of filaments ‘N’ is from and including 2 to 8 included. 
     
     
         28 . A method to produce a steel cord comprising the following steps:
 (a) unwinding a number of steel elements with diameter de from spools;   (b) providing a mandrel wire of diameter D;   (c) twisting said steel elements around said mandrel wire with a cord number of twists N e  per unit length in a cord twist direction thereby forming an intermediate cord;   (d) removing the mandrel wire from said intermediate cord by turning said mandrel cord out of said intermediate cord, resulting in the steel cord;   (e) winding the steel cord on a take-up spool.   
     
     
         29 . The method according to  claim 28 , wherein the intermediate cord is wound on an intermediate spool after step (c) and unwound from said intermediate spool for performing step (d). 
     
     
         30 . The method according to  claim 28 , wherein the intermediate cord is directly led from step (c) to step (d). 
     
     
         31 . The method according to  claim 28 , wherein the step of removing the mandrel wire from said intermediate cord by turning said mandrel wire out of said intermediate cord is performed by
 moving said intermediate cord linearly;   turning said mandrel wire out of said intermediate cord through a flyer relatively rotating around said intermediate cord thereby leaving the steel elements as a steel cord;   winding the mandrel wire on a driven mandrel spool;   winding said steel cord on a driven take-up spool.   
     
     
         32 . The method of  claim 31 , wherein said driven take-up spool is inside said flyer or wherein said driven mandrel spool is inside said flyer. 
     
     
         33 . The method according to  claim 28 , wherein the steel elements are steel filaments and the ratio of D/d e  is larger than or equal to 0.8 and smaller than or equal to 2. 
     
     
         34 . The method according to  claim 28 , wherein the steel element is a plurality of steel filaments and the ratio of D/d e  is larger than or equal to 0.5 and smaller than or equal to 1.2. 
     
     
         35 . The method according to  claim 28 , wherein the steel filaments in said steel elements of said intermediate cord are twisted to a steel element twist number N e  in the cord twist direction, said element twist number being larger or equal than said cord twist number Ne and wherein said cord twist number Ne is larger than 150 twists per meter. 
     
     
         36 . The method according to  claim 28 , wherein the filaments in said elements of said steel cord are twisted to an element twist number N e  in the cord direction, said element twist number being smaller than said cord twist number. 
     
     
         37 . The method according to  claim 28 , wherein said mandrel wire is one out of the group comprising: a metal wire, a steel wire, a steel cord, an organic yarn, an organic cord, an organic filament. 
     
     
         38 . The method according to  claim 28 , wherein the combination of the total number ‘N’ of steel filaments, wherein each of said steel filaments has a cross sectional area ‘A’ expressed in square millimeters said steel elements having, after individualisation and under tension of half a newton per filament in said steel element, a center line, said center line having a helix shape, wherein the length of the center line of the steel element over one pitch is ‘S’ in millimeter, is such that the quantity ‘P’ expressed in newton: 
       
         
           
             
               P 
               = 
               
                 π 
                 ⁢ 
                 
                   
                     NE 
                     ⁡ 
                     ( 
                     
                       A 
                       S 
                     
                     ) 
                   
                   2 
                 
               
             
           
         
       
       is larger than 50 newton and wherein ‘E’ is the modulus of steel.