Steel cord for reinforcing rubber product

Abstract

A steel cord comprising a number (between 3 and 27) of element steel wires tightly twisted at a regular pitch P between 5 and 20 mm in the same direction. Each wire has a diameter d between 0.1 and 0.4 mm. At least one of the wires includes a spiral portion having a spiral pitch P1 between 0.1P and 0.7P and a spiral diameter d1 between d+2/100 mm and d+2/10 mm. At least one other wire includes a straight portion. At any cross section of the cord, 1/4 through 2/3 of the wires is/are spiral and the other wire/s is/are straight. The stretch of the cord under a load of 5 kg is between 0.10 and 0.40%. A method of producing a steel cord comprises supplying a number of element steel wires, forming at least part of at least one of the wires to be spiral, and tightly twisting the wires. An apparatus for producing a steel cord comprises feeders supported by a frame, each feeding an element steel wire along an axis, a tension device for applying a tension to the wire from at least one of the feeders, a spiral device having pins which extend across and are spaced along an axis, so that at least one of the wires from the tension device turns alternately over and under the pins, a strand device rotatable on the axis, so that the wires are twisted to form a strand, and a take-up device to take up the strand.

Dependencies are inferred from the claim text.