Layered steel cord

A steel cord for use in high-duty rubber tires, comprising 27 steel filaments assembled into a compact layered 3+9+15 cord structure having, in cross-section, a 3-filament core surrounded by two concentric steel wire layers comprising an outermost layer of 15 steel wires and a second outermost layer of 9 wires, said layers being formed by one of either a series of consecutive twisting steps or by forming a single twisted bundle of 27 wires in a single machine run, said wires being comprised of hard drawn pearlitic carbon steel wires having from about 0.7% to about 0.9% by weight carbon, a diameter of from about 0.1 to about 0.4 mm, and a tensile strength of at least about 2800 N/mm.sup.2 ;

• the wires in said outermost layer being covered with a rubber adherent brass alloy containing from about 60% to about 70% by weight copper;
• and
• the wires of said second outermost layer being covered with a corrosion resistant zinc coating, in an amount effective to significantly enhance cord endurance, adhesion retention and related tire life by the combined effect of an increased rubber penetration and of suppressing unexpected local brittle wire breaks, premature cord corrosion and fatigue cracking.

A multistep process for producing a rubber adherable multilayer steel cord, comprising:

• assembling at least one corrosion resistant steel wire layer around a steel wire core, said corrosion resistant layer comprising a plurality of steel wires, each said wire being covered with a corrosion resistant metal coating selected from the group consisting of zinc and a zinc alloy containing at least about 50% by weight zinc;
• and
• assembling an outermost steel wire layer over said at least one corrosion resistant layer, said outermost layer being covered with a brass coating having a thickness of from about 0.05 .mu.m to about 0.50 .mu.m, said brass coating being rubber adherable and containing copper in an amount of more than about 55% by weight.

A rubber adherable multilayer steel cord having an improved capacity to reinforce vulcanizable rubber products and to withstand premature corrosion fatigue, cracking and cord/rubber debonding in harsh service conditions, said cord comprising a core and a plurality of steel wires with a tensile strength in excess of about 2200 N/mm.sup.2 twisted together to form a cord construction having N wire layers consecutively arranged around said core with N being an integer of not less than 2, said wire layers having each a thickness of essentially one wire diameter and forming a regular geometrical wire packing of desired shape and compactness, the wires of the cord surface (Nth) layer being covered by a 0.05 to 0.50 .mu.m thick brass coating of a rubber adherable composition containing more than 55% copper, the wires of the (N-1th) layer inwardly adjacent said surface layer being covered by a protective coating.

A high-performance steel cord for use in high-duty rubber tires, in particular truck tires, comprising 27 steel filaments assembled into a compact layered (3+9+15) cord structure featuring in cross-section a 3-filaments core surrounded by two concentric rings comprising respectively 9 and 15 filaments, said filaments comprising hard drawn pearlitic carbon steel wires of 0.7 to 0.9% C, having a diameter ranging from 0.1 to 0.4 mm and a tensile strength of at least 2800 N/mm.sup.2, wherein the 15 exterior wires are covered with a rubber adherent brass alloy containing from 60 to 70% of copper, and wherein the 9 wires forming a continuous ring between the core and the external brassed layer are covered with a corrosion resistant zinc coating, effective to significantly enhance cord endurance, adhesion retention and related tire life by the combined effect of suppressing unexpected local brittle wire breaks, premature cord corrosion fatigue cracking and of an increased rubber penetration.