COMPACTED STEEL STRAND WITH CLADDED CORE

Abstract

A steel strand (10) comprises a steel core wire (12). This steel core wire (12) is surrounded by steel layer wires (14) that are twisted around the steel core wire (12). The steel core wire (12) is covered with a thick corrosion resistant core coating (16) provided by strip cladding or by metal extrusion. The steel layer wires (14) are covered with a thin corrosion resistant layer coating (18) provided by a hot dip operation or by an electroplating or chemical plating process. The steel strand (10) is compacted so that said steel layer wires (14) have a non-circular cross-section and that the thick corrosion resistant core coating fills the interstices between the steel core wire (12) and the steel layer wires (14) in order to give the steel strand (10) an improved corrosion resistance and increased lifetime.

Claims

1. A steel strand comprising a steel core wire, said steel core wire surrounded by steel layer wires that are twisted around said steel core wire, said steel core wire covered with a corrosion resistant core coating provided by strip cladding or by metal extrusion, said steel layer wires covered with a corrosion resistant layer coating provided by a hot dip operation or by an electroplating or chemical plating process, said steel strand being compacted so that said steel layer wires have a non-circular cross-section and that said corrosion resistant core coating fills the interstices between the steel core wire and the steel layer wires.

2. The steel strand according to claim 1, wherein said corrosion resistant core coating is of aluminium or an aluminium alloy.

3. The steel strand according to claim 1, where said corrosion resistant core coating has a weight ranging from 400 g/m.sup.2 to 2500 g/m.sup.2.

4. The steel strand according to claim 1, wherein said corrosion resistant layer coating is of zinc or a zinc alloy.

5. The steel strand according to claim 4, wherein said corrosion resistant layer coating has a weight ranging from 150 g/m.sup.2 to 450 g/m.sup.2.

6. The steel strand according to claim 4, wherein said corrosion resistant layer coating is a zinc aluminium alloy.

7. The steel strand according to claim 6, wherein said corrosion resistant layer coating is a zinc aluminium magnesium alloy.

8. The steel strand according to claim 1, wherein said steel strand has an outer diameter ranging from 10.0 mm to 30.0 mm.

9. The steel strand according to claim 1, wherein said steel strand is in a stress-relieved state.

10. Use of the steel strand according to claim 1 as a pre-tensioned strand.

11. Use of the steel strand according to claim 1 as a post-tensioned strand.

Description

BRIEF DESCRIPTION OF FIGURE IN THE DRAWING

[0033] FIG. 1 shows a cross-section of a steel strand according to a first aspect of the present invention.

MODE(S) FOR CARRYING OUT THE INVENTION

[0034] FIG. 1 shows a cross-section of a steel strand 10. The steel strand 10 has a steel core wire 12 and six steel layer wires 14 that are twisted around the steel core wire 12. The steel core wire 12 is provided with an aluminium strip clad core coating 16. The steel layer wires 14 are provided with a zinc aluminium magnesium layer coating 18.

[0035] The steel strand 10 is compacted so that the steel layer wires 14 obtain a trapezium-like cross-section. The steel layer wires 14 form a closed layer around the steel core wire 12 and push the aluminium strip clad core coating 16 to flow and fill the interstices between the steel core wire 12 and the steel layer wires 14.

[0036] The aluminium strip clad core coating 16 fills all interstices and holes inside the steel strand and prevents moisture from penetrating inside the steel strand 10. At the same time the aluminium strip clad core coating 16 gives corrosion resistance to steel core wire 12.

[0037] The zinc aluminium magnesium layer coating 18 gives corrosion resistance to the steel layer wires 14.

[0038] A steel strand according to the invention can be made along following lines.

[0039] The composition of the starting material (wire rod) is usually a micro-alloyed high-carbon composition as follows: (all percentages being percentages by weight): [0040] a carbon content (% C) ranging from 0.50% to 1.20%, e.g. 0.60% to is 1.0%; [0041] a manganese content (% Mn) ranging from 0.10% to 1.0%, e.g. from 0.20% to 0.80%; [0042] a silicon content (% Si) ranging from 0.10% to 1.50%, e.g. from 0.15% to 0.70%; [0043] a sulphur content (% S) below 0.03%, e.g. below 0.01%; [0044] a phosphorus content (% P) below 0.03%, e.g. below 0.01%. [0045] Micro-alloying elements such as chromium, vanadium, aluminium or nickel may or may not be present in amounts up to 0.50%.

[0046] Starting from wire rod, the steel core wire is drawn until an intermediate steel wire diameter. An aluminium strip is formed and welded or extruded around the steel wire and the thus formed composite is further drawn until a final diameter.

[0047] Starting also from wire rod, the steel layer wires are drawn until an intermediate steel wire diameter. The steel layer wires are then guided through a hot dip bath of zinc-aluminium-magnesium. The thus coated steel layer wires are then further drawn until their final wire diameter.

[0048] The steel layer wires are twisted around the steel core wire with the aluminium strip to form a non-compacted steel strand. Thereafter, the steel strand is finally subjected to a compacting treatment.

[0049] Examples of a 1+6 steel strand (6 steel layer wires): [0050] diameters of the steel core wire resp. (steel only): 2.64 mm, 5.60 mm, 6.50 mm; [0051] diameters of the steel core wire with aluminium strip: 3.00 mm, 6.35 mm, 8.07 mm; [0052] diameters of the coated and drawn steel layer wires: 2.53 mm, 5.60 mm, 6.46 mm; [0053] diameter of the compacted steel strand: 7.0 mm, 15.2 mm, 18.0 mm.

[0054] The compacted steel rope according to the invention is preferably subjected to a stress-relieving treatment in order to lower the relaxation and to improve the straightness. A suitable temperature for carrying out such a stress-relieving treatment is 380 C.

[0055] The compacted steel rope according to the invention can obtain following tensile strength grades: 1700 MPa, 1860 MPa, 1960 MPa and 2060 MPa.

LIST OF REFERENCE NUMBERS

[0056] 10 Steel strand [0057] 12 Steel core wire [0058] 14 Steel layer wire [0059] 16 Thick corrosion resistant core coating [0060] 18 Thin corrosion resistant layer coating