Three-Layer Steel Cord that is Rubberized in Situ and has a 3+M+N Structure
Metal cord with three layers (C 1 +C 2 +C 3 ) of 3+M+N construction, rubberized in situ, comprising a first layer or central layer (C 1 ) comprised of three wires of diameter d1 assembled in a helix at a pitch p 1, around which central layer there are wound in a helix at a pitch p 2, in a second layer (C 2 ), M wires of diameter d 2, around which second layer there are wound in a helix at a pitch p 3, in a third layer (C 3 ), N wires of diameter d3. The cord has the following characteristics (d 1, d 2, d 3, p 1, p 2 and p 3 being expressed in mm): 0.08≦d 1 ≦0.50; 0.08≦d 2 ≦0.50; 0.08≦d 3 ≦0.50; 3<p 1 <50; 6<p 2 <50; 9<p 3 <50; over any 3 cm length of cord. A rubber composition called “filling rubber” is present in the central channel delimited by the three wires of the first layer (C 1 ) and in each of the capillaries delimited by, on the one hand, the three wires of the first layer (C 1 ) and the M wires of the second layer (C 2 ), and on the other hand the M wires of the second layer (C 2 ) and the N wires of the third layer (C 3 ). The content of filling rubber in the cord is comprised between 10 and 50 mg per gram of cord.
1 . Metal A metal cord with three layers of 3+M+N construction, rubberized in situ, comprising a first layer or central layer comprised of three wires of diameter d 1 assembled in a helix at a pitch p 1 , around which central layer there are wound in a helix at a pitch p 2 , in a second layer, M wires of diameter d 2 , around which second layer there are wound in a helix at a pitch p 3 , in a third layer, N wires of diameter d 3 , wherein the cord it has the following characteristics (d 1 , d 2 , d 3 , p 1 , p 2 and p 3 being expressed in mm):
0.08≦d 1 ≦0.50;
0.08≦d 2 ≦0.50;
0.08≦d 3 ≦0.50;
3<p 1 <50;
6<p 2 <50;
9<p 3 <50;
over any 3 cm length of cord, a rubber composition called “filling rubber” is present in the central channel delimited by the three wires of the first layer (C 1 ) and in each of the capillaries delimited by, on the one hand, the three wires of the first layer (C 1 ) and the M wires of the second layer (C 2 ), and on the other hand the M wires of the second layer (C 2 ) and the N wires of the third layer (C 3 );
the content of filling rubber in the cord is comprised between 10 and 50 mg per gram of cord.
2 . The cord according to claim 1 , wherein the rubber of the filling rubber is a diene elastomer.
3 . The cord according to claim 2 , wherein the diene elastomer is chosen from the group consisting of polybutadienes, natural rubber, synthetic polyisoprenes, copolymers of butadiene, copolymers of isoprene, and blends of these elastomers.
4 . The cord according to claim 3 , wherein the diene elastomer is an isoprene elastomer.
5 . The cord according claim 1 , in which wherein the following characteristics are satisfied (with p 1 , p 2 , p 3 being expressed in mm):
3<p 1 <30;
6<p 2 <30;
9<p 3 <30.
6 . The cord according to claim 1 , wherein:
p 1 ≦p 2 ≦p 3 .
7 . The cord according to claim 1 , wherein the following characteristics are satisfied (with d 1 , d 2 , d 3 being in mm):
0.10≦d 1 ≦0.40;
0.10≦d 2 ≦0.40;
0.10≦d 3 ≦0.40.
8 . The cord according to claim 1 , wherein the 3, M and N wires of the first, second and third layers are wound in the same direction of twisting.
9 . The cord according to claim 1 , wherein d 1 =d 2 =d 3 .
10 . The cord according to claim 1 , wherein p 2 =p 3 .
11 . The cord according to claim 1 , wherein which the second layer comprises 6 to 12 wires, and the third layer comprises 12 to 18 wires.
12 . The cord according to claim 11 , in which wherein the second layer (C 2 ) comprises 8 or 9 wires and the third layer comprises 14 or 15 wires.
13 . The cord according to claim 1 , wherein the third layer is a saturated layer.
14 . The cord according to claim 1 , wherein the content of filling rubber is comprised between 15 and 45 mg.
15 . The cord according to claim 1 , wherein, in an air permeability test, it has an average air flow rate of less than 2 cm3/min.
16 . The cord according to claim 15 , wherein, in the air permeability test, it has an air flow rate less than or at the most equal to 0.2 cm3/min.
17 . A method of manufacturing a cord according to claim 1 , comprising the following steps:
a first step of assembling by twisting the three wires of the first layer to form, at a first point called “first assembling point” the first layer or central layer;
a second assembling step by twisting the M wires around the central layer to form, at a second point called “second assembling point” an intermediate cord called “core strand” of 2+M construction;
downstream of the first assembling point, a sheathing step in which the central layer and/or the core strand is/are sheathed with a filling rubber in the uncured state, this sheathing being conducted either upstream or downstream or both upstream and downstream of the second assembling point;
followed by a third assembling step by twisting or cabling the N wires around the core strand thus sheathed;
then a final twist-balancing step.
18 . A multi strand rope at least one of the strands of which is a cord according to claim 1 .
19 . (canceled)
20 . (canceled)
21 . A tire comprising a cord according to claim 1 .
22 . The tire according to claim 21 , said tire being a tire of an industrial vehicle.
23 . The tire according to claim 21 , the cord being present in the carcass reinforcement or the crown reinforcement of the tire.
24 . The cord according to claim 3 , wherein the diene elastomer is natural rubber.
24 . The cord according to claim 1 , wherein the content of filling rubber is comprised between 15 and 45 mg.