Steel cord for rubber reinforcement

Abstract

A steel cord for rubber reinforcement that has a construction with an outer layer and an inner strand surrounded by and adjacent to the outer layer, the inner strand having at least one steel filament with a number of N.sub.1 and an average diameter of d.sub.1 expressed in mm, the outer layer having steel filaments with a number of N.sub.2 and an average diameter of d.sub.2 expressed in mm. The inner strand has a torque T.sub.1 and the outer layer has a torque T.sub.2, the relation between T.sub.1 and T.sub.2 is defined. By doing this, the tip rise problem of the rubber ply reinforced by steel cords is reduced.

Claims

1. A steel cord, said steel cord having a construction comprising an outer layer and an inner strand surrounded by and adjacent to said outer layer, said inner strand comprising at least one steel filament with a number of N.sub.1, said at least one steel filament of said inner strand having an average diameter of d.sub.1 expressed in mm, said outer layer comprising steel filaments with a number of N.sub.2, said steel filaments of said outter layer having an average diameter of d.sub.2 expressed in mm, wherein said inner strand has a torque T.sub.1, said outer layer has a torque T.sub.2, T.sub.1 and T.sub.2 satisfy the following formulas:
T.sub.1=GRT.sub.1.sup.2D.sub.1.sup.2d.sub.1.sup.2N.sub.1/16000,
T.sub.2=GRT.sub.2.sup.2(D.sub.1.sup.2+D.sub.2.sup.2)d.sub.2.sup.2N.sub.2/16000,
|T.sub.1+T.sub.2|<60, wherein, D.sub.1 is the theoretical diameter of the inner strand while D.sub.2 is the theoretical diameter of the steel cord, D.sub.1 and D.sub.2 are expressed in mm, RT.sub.1 is the residual torsion of the inner strand while RT.sub.2 is the residual torsion of the outer layer expressed in the number of turns per meter in + if in clockwise direction or if in anticlockwise direction, G is 80000 N/mm.sup.2, and the absolute value of RT.sub.2 is less than 2 turns per meter and no less than 0.05 turns per meter, and the absolute value of RT.sub.1 is no less than 0.05 turns per meter.

2. The steel cord as claimed in claim 1, wherein T.sub.1 and T.sub.2 satisfy, |T.sub.1+T.sub.2|<50.

3. The steel cord as claimed in claim 2, wherein T.sub.1 and T.sub.2 satisfy, T.sub.1+T.sub.2|<40.

4. The steel cord as claimed in claim 1, wherein the absolute value of RT.sub.1 is no less than 0.1 turns per meter.

5. The steel cord as claimed in claim 1, wherein the absolute value of RT.sub.2 is less than 2 turns per meter and no less than 0.1 turns per meter.

6. The steel cord as claimed in claim 1, wherein RT.sub.1 and RT.sub.2 satisfy, |RT.sub.1+RT.sub.2|<4.

7. The steel cord as claimed in claim 1, wherein said steel cord has a two layers construction, N.sub.1 is 1, 2, 3 or 4, the calculation formula of D.sub.2 is: D.sub.2=D.sub.1+2xd.sub.2; and the calculation formula of D.sub.1 is: when N.sub.1 is 1, D.sub.1=d.sub.1, or when N.sub.1 is 2, D.sub.1=2xd.sub.1, or when N.sub.1 is 3, D.sub.1=2.155xd.sub.1, or when N.sub.1 is 4, D.sub.1=2.414xd.sub.1.

8. The steel cord as claimed in claim 1, wherein said steel cord has a three layers construction, wherein the inner strand comprises an intermediate layer and a core layer surrounded by said intermediate layer, said core layer comprises at least one steel filament with a number of N.sub.c and with an average diameter of d.sub.c, said intermediate layer comprises steel filaments with an average diameter of d.sub.m, the calculation formula of D.sub.2 is: D.sub.2=D.sub.1+2xd.sub.2; and the calculation formula of D.sub.1 is: when N.sub.c is 1, D.sub.1=d.sub.c+2xd.sub.m, or when N.sub.c is 2, D.sub.1=2xd.sub.c+2xd.sub.m, or when N.sub.c is 3, D.sub.1=2.155xd.sub.c+2xd.sub.m, or when N.sub.c is 4, D.sub.1=2.414xd.sub.c+2xd.sub.m.

9. The steel cord as claimed in claim 1, wherein said inner strand and said outer layer individually have a twist pitch of less than 40 mm.

10. The steel cord as claimed in claim 1, wherein each steel filament of said steel cord has a tensile strength TS in MPa satisfying, TS4000-2000 x d, d is corresponding to the diameter of each steel filament in mm respectively.

11. The steel cord as claimed in claim 10, wherein TS4100-2000xd.

12. The steel cord as claimed in claim 1, wherein said steel cord has a construction of 1+3, 1+4, 1+5, 1+6, 1+7, 2+2, 2+3, 2+4, 2+5, 2+5 cc, 2+6, 2+7, 2+7 cc, 2+8, 3+2, 3+3, 3+6, 3+8, 3+8 cc, 3+9, 3+9 cc, 4+3, 4+6, 1+3+8, 1+4+8 cc, 1+4+9, 1+5+10, 1+5+10 cc, 1+6+11, 1+6+12, 1+6+12 cc, 2+5+10, 2+6+12, 3+8+13, 3+9+15 or 4+10+16.

13. A tire comprising at least one belt layer, at least one carcass layer, at least one tread layer and a pair of bead portions, wherein said belt layer and/or said carcass layer comprises at least one steel cord as claimed in claim 1.

Description

BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS

(1) FIG. 1 describes the measurement of the tip rise of rubber ply.

(2) FIGS. 2a-2b describe the measurement of the residual torsion.

MODE(S) FOR CARRYING OUT THE INVENTION

(3) The steel filaments for steel cord are made from a wire rod.

(4) The wire rod is firstly cleaned by mechanical descaling and/or by chemical pickling in a H.sub.2SO.sub.4 or HCl solution in order to remove the oxides present on the surface. The wire rod is then rinsed in water and is dried. The dried wire rod is then subjected to a first series of dry drawing operations in order to reduce the diameter until a first intermediate diameter.

(5) At this first intermediate diameter, e.g., at about 3.0 to 3.5 mm, the dry drawn steel filament is subjected to a first intermediate heat treatment, called patenting. Patenting means first austenitizing until a temperature of about 1000 C. followed by a transformation phase from austenite to pearlite at a temperature of about 600-650 C. The steel filament is then ready for further mechanical deformation.

(6) Thereafter the steel filament is further dry drawn from the first intermediate diameter until a second intermediate diameter in a second number of diameter reduction steps. The second diameter typically ranges from 1.0 mm to 2.5 mm.

(7) At this second intermediate diameter, the steel filament is subjected to a second patenting treatment, i.e., austenitizing again at a temperature of about 1000 C. and thereafter quenching at a temperature of 600 to 650 C. to allow for transformation to pearlite.

(8) If the total reduction in the first and second dry drawing step is not too big a direct drawing operation can be done from wire rod till second intermediate diameter.

(9) After this second patenting treatment, the steel filament is usually provided with a brass coating: copper is plated on the steel filament and zinc is plated on the copper. A thermo-diffusion treatment is applied to form the brass coating. Alternatively, the steel filament can be provided with a ternary alloy coating, including copper, zinc and a third alloy of cobalt, titanium, nickel, iron, or other known metal.

(10) The brass-coated or the ternary alloy coated steel filament is then subjected to a final series of cross-section reductions by means of wet drawing machines. The final product is a steel filament with a carbon content higher than 0.70 percent by weight, or no less than 0.80 percent by weight, or even higher than 0.90 percent by weight, with a tensile strength (TS) typically above 3000 MPa and adapted for the reinforcement of rubber products.

(11) Steel filaments adapted for the reinforcement of tires typically have a final diameter ranging from 0.05 mm to 0.60 mm, e.g., from 0.10 mm to 0.40 mm. Examples of wire diameters are 0.10 mm, 0.12 mm, 0.15 mm, 0.175 mm, 0.18 mm, 0.20 mm, 0.22 mm, 0.245 mm, 0.28 mm, 0.30 mm, 0.32 mm, 0.35 mm, 0.38 mm, 0.40 mm. Better that the diameter the steel filament is in the range of 0.10 mm-0.50 mm.

(12) A number of steel filaments are twisted by the existing steel cord making process, i.e., cabling or bunching process, to form a steel cord having a construction comprising an outer layer and an inner strand surrounded by and adjacent to the outer layer.

(13) Based on the construction of the steel cord, the torque of the inner strand, the torque of the outer layer, the residual torsion of the inner strand and the residual torsion of the outer layer are set according to the invention formula. The pre-determined residual torsion of the inner strand and the pre-determined residual torsion of the outer layer can be realized by the existing method for residual torsion control, for example using false twister or straightener after twisting.

(14) Table 1 summarize the performance of the inventions and the references.

(15) TABLE-US-00001 TABLE 1 Invention 1 Invention 2 Invention 3 Invention 4 Invention 5 Reference 1 Reference 2 Construction 3 + 8 3 + 8 2 + 7 3 + 9 + 15 1 + 6 3 + 9 3 + 8 d.sub.c (mm) 0.20 d.sub.m (mm) 0.20 d.sub.1 (mm) 0.33 0.36 0.33 0.20 0.33 0.34 0.35 d.sub.2 (mm) 0.33 0.30 0.33 0.20 0.33 0.315 0.35 N.sub.c 3 N.sub.1 3 3 2 12 1 3 3 N.sub.2 8 8 7 15 6 9 8 D.sub.1 (mm) 0.71 0.78 0.66 0.83 0.33 0.73 0.75 D.sub.2 (mm) 1.37 1.38 1.32 1.23 0.99 1.36 1.45 Twist pitch of 10 10 8 12.5 >300 mm 10 10 inner strand (mm) Twist pitch of 20 20 16 15 16 20 20 outer layer (mm) RT.sub.1 (turns/m) +1.40 +2.00 +2.00 1.55 +2.00 +2.50 4.25 RT.sub.2 (turns/m) 0.40 0.75 0.75 0.25 0.75 0.95 0.95 Cord residual 0 0 0 0 0 0 0 torsion (turns/m) |RT.sub.1 + RT.sub.2| 1 1.25 1.25 1.8 1.25 1.55 3.3 (turns/m) T.sub.1 (N .Math. mm) +11.4 +23.1 +9.4 25.4 +1.2 +23 43.8 T.sub.2 (N .Math. mm) 41.0 66.5 61.4 16.3 26.3 100.2 +123.3 |T.sub.1 + T.sub.2| 29.6 43.4 52 41.7 25.1 77.2 79.5 (N .Math. mm) Tip rise value 3 5 8 5 2 25 30 (mm)

(16) All the steel filaments of the steel cords in above table have a TS4100-2000xd, d is the diameter of the individual steel filament.

(17) FIG. 1 shows the measurement of tip rise value. The small piece 100 cut from a rubber ply which is embedded with steel cords 110 has a determined length, width and thickness. The thickness of the rubber ply can be set according to the application mode of the steel cord in the tire, for example, the thickness of the rubber ply is the diameter of the steel cord plus 1.1 mm, and while the width and the length of the rubber ply both are 1 meter. Two of the four corners 105 of the small piece 100 rise. The value T are measured from the thickness direction of the small piece. The bigger one of the two T values of the two rising corners 105 is the tip rise value of the rubber ply. If the tip rise value is more than 10 mm, it is deemed as the occurrence of tip rise problem.

(18) The measurement methods of steel filament diameter and the residual torsion of the steel cord are clearly described in GB/T.sub.33159-2016.

(19) The residual torsion of the inner strand and the residual torsion of the outer layer are measured as follows: a) prepare a steel cord sample with a length of about 1.2 m by fusing to make sure the two ends of steel cord sample (the first end and the second end) are not flared, prepare a rack installed with two clamps (the first clamp and the second clamp), the two clamps are laid at the same horizontal level with a distance of 1 m; b) clamp the steel cord sample by the first clamp and the second clamp, the first clamp is close to the first end of steel cord sample, and the length from the first end of steel cord sample to the first clamp is about 5 cm to 7 cm (the reversed length of steel cord); c) open the first clamp to release the residual torsion of the steel cord sample, and then bend the steel cord sample upwards from the portion to be clamped at the first clamp to make the reversed length of steel cord almost perpendicular to the horizontal level (the bent portion); make sure that the bending operation doesn't generate any torsion to the steel cord sample otherwise release the newly generated torsion; d) cut the first end and peel the steel filaments of the outer layer along the length of the bent portion until the portion of the steel cord sample clamped by the second clamp; clamp the inner strand by the first clamp when the peeling of the steel filaments of the outer layer is sufficient to allow such operation; make sure that the bent portion of the outer layer and the bent portion of the inner strand separately as a group are always perpendicular to the horizontal level during the peeling operation; e) release the bent portion of the outer layer and obverse and record the number of turns of the bent portion of the outer layer, and this is the residual torsion of the outer layer RT.sub.2; and then release the bent portion of the inner strand and obverse and record the number of turns of the bent portion of the inner strand, and this is the residual torsion of the inner strand RT.sub.1, the record of the residual torsion is in units of 0.05 turns/m (corresponding to 18 of turning degree) and in + if in clockwise direction or if in anticlockwise direction, the observation is done when facing the turning of the bent portion in the direction towards to the second clamp. FIG. 2a-2b shows the examples of residual torsion, FIG. 2a shows the examples of the residual torsion 0.05, 0.25, 0.5, 0.75 and 1.0 in anticlockwise direction, FIG. 2b shows the examples of residual torsion 0.15, 0.25, 0.5, 0.75 and 1.0 in clockwise direction.

(20) From Table 1, it is clear that the invention steel cords have no tip rise problem and have better performance on tip rise compared with the reference steel cords.