Corrosion resistant spiral steel filament and steel cord made therefrom

• US 5,806,296 A
• Filed: 05/23/1996
• Issued: 09/15/1998
• Est. Priority Date: 05/26/1995
• Status: Expired due to Term

• Current Assignee: Bridgestone Corporation
• Original Assignee: Bridgestone Metalpha Corporation (Bridgestone Corporation)
• Inventors: Kaneko, Yoshikazu, Obana, Naohiko
• Primary Examiner(s): STRYJEWSKI, WILLIAM T
• Application Number:
  US08/652,082
• Time in Patent Office: 845 Days
• Field of Search: 57/902, 57/206, 57/212, 57/213, 57/216, 57/236, 57/237, 57/9, 57/311
• US Class Current: 57/206
• CPC Class Codes: D07B 1/062 the reinforcing cords being characterised by the strand configuration
• CPC Class Codes: D07B 1/0626 the reinforcing cords consisting of three core wires or filaments and at least one layer of outer wires or filaments, i.e. a 3+N configuration
• CPC Class Codes: D07B 1/0633 having a multiple-layer configuration
• CPC Class Codes: D07B 1/0646 comprising longitudinally preformed wires
• CPC Class Codes: D07B 2201/2021 characterised by their longitudinal shape
• CPC Class Codes: D07B 2201/2023 with core
• CPC Class Codes: D07B 2201/2029 Open winding
• CPC Class Codes: D07B 2201/203 Cylinder winding, i.e. S/Z or Z/S
• CPC Class Codes: D07B 2201/2031 Different twist pitch
• CPC Class Codes: D07B 2201/2032 compared with the core
• CPC Class Codes: D07B 2205/3057 having a high carbon content, e.g. greater than 0,8 percent respectively SHT or UHT wires
• CPC Class Codes: D07B 2207/4072 Means for mechanically reducing serpentining or mechanically killing of rope
• CPC Class Codes: D07B 2801/10 Smallest filamentary entity of a rope or strand, i.e. wire, filament, fiber or yarn
• CPC Class Codes: D07B 5/12 of low twist or low tension by processes comprising setting or straightening treatments

Abstract

A steel cord intended for use to reinforce rubber products is produced by drawing, into a steel filament of 0.10 to 0.40 mm in diameter and more than 3,000 N/mm² in strength, a wire rod having a carbon content of more than 0.70% by weight, and twisting a plurality of such steel filaments together. Also a pneumatic tire is provided which employs in at least a portion of a reinforcing member thereof the steel cord improved in corrosion resistance and having an R₁ /R₀ ration×100 which is less than 100, where R₀ is the radius of spiral curvature of the spiraled steel filament resulting from untwisting said steel cord and R₁ is the radius of spiral curvature of said steel filament of which the surface layer inside the spiral is removed by dissolving.

Claims

1. A steel cord intended for use to reinforce rubber products, comprising:

a plurality of steel filaments each of which is about 0.10 to about 0.40 mm in diameter and being more than about 3,000 N/mm² in strength each of said plurality of filaments being pre-formed by drawing a wire rod having a carbon content of more that about 0.70% by weight, said plurality of steel filaments being twisted together to form a steel cord structure defined by a plurality of spiraled steel filaments each having a spiral curvature;

said steel cord structure having an R₁ /R₀ ration×

100 which is less than 100, a value of said R₁ /R₀ ration×

100 which is established by a test performed on a sample of said steel cord, and in which R₀ is the radius of spiral curvature of a one of said plurality of spiraled steel filaments which is removed from said steel cord structure in performing said test, and R₁ is the radius of spiral curvature of said one of said plurality of spiraled steel filaments of which a surface layer inside the spiral is removed by dissolving.

2. A steel cord as set forth in claim 1, wherein said value of said R₁ /R₀ ration×

100 is based upon test removal of said surface layer in an amount ranging from the surface of said steel filament to a depth equivalent to 5% of the filament diameter.

3. A steel cord as set forth in claim 1, wherein said value of said R₁ /R₀ ratio×

100 is based upon test removal of said surface layer in an amount ranging from the surface of said steel filament to a depth equivalent to 10% of the filament diameter.

4. A two-layer twisted steel cord, comprising:

an "M+N" configuration comprising a number M, where M ranges from 1 to 4, OF steel filaments forming together a core of said steel cord and a number N, where N ranges from M+2 to M+5, of steel filaments forming together a sheath of said steel cord, or a three-layer twisted steel cord having an "M+N+P" configuration further comprising a number P, where P ranges from N+2 to N+5, of steel filaments wound on the outer circumference of said two-layer twisted steel cord, each of said steel filaments having a carbon content of more than about 0.70% by weight, a diameter of about 0.15 to about 0.25 mm and a tensile strength ranging from about 3,400 to about 3,900 N/mm² ;

the mean value of spacings between adjacent steel filaments of said sheath being more than about 0.02 mm and less than about 1.5 times larger than the steel filament diameter;

said steel filaments of said sheath being performed at a rate of about 80 to about 110%;

each of said steel filaments having one of a residual stress in a surface layer inside of a spiral structure thereof that is no greater than zero, and an R₁ /R₀ ratio×

100 which is less than 100, a value of said R₁ /R₀ ratio×

100 which is established by a test performed on a sample of said steel cord, and in which R₀ is the radius of spiral curvature of a one of said plurality of spiraled steel filaments which is removed from said steel cord structure in performing said test, and R₁ is the radius of spiral curvature of said one of said plurality of spiraled steel filaments of which a surface layer inside the spiral is removed by dissolving.

5. A steel cord as set forth in claim 4, wherein said value of said R₁ /R₀ ratio×

100 is based upon test removal of said surface layer in an amount ranging from the surface of a one of said steel filaments to a depth equivalent to 5% of the filament diameter.

6. A steel cord as set forth in claim 4, wherein said value of said R₁ /R₀ ratio×

100 is based upon test removal of said surface layer in an amount ranging from the surface of a one of said steel filaments to a depth equivalent to 10% of the filament diameter.

7. A steel cord as set forth in any one of claims 4 through 6, wherein said carbon content of said steel filament is 0.7 to 0.85% by weight.

8. A steel cord as set forth in any one of claims 4 through 6, wherein the diameter of the steel cord is dependent upon the diameter of the steel filament and configuration of the steel cord, selected to meet the following relation:

space="preserve" listing-type="equation">(50Y/X)-1.1≦

D≦

(50Y/X)-0.6

where D is the diameter of the steel cord;

X is a breaking strength per unit width of a composite before formation of a tire having rubber and a rubberized steel cord; and

Y is a breaking strength per unit width of the steel cord.

9. A steel cord as set forth in any one of claims 4 through 6, wherein the diameter of the steel cord is dependent upon the diameter of the steel filament and configuration of the steel cord, selected to meet the following relation:

space="preserve" listing-type="equation">(50Y/X)-0.9≦

D≦

(50Y/X)-0.6

where D is the diameter of the steel cord;

X is a breaking strength per unit width of a composite before formation of a tire having rubber and a rubberized steel cord; and

Y is a breaking strength per unit width of the steel cord.