Textiles: spinning – twisting – and twining – Strand structure
Reexamination Certificate
1999-04-28
2001-07-17
Calvert, John J. (Department: 3741)
Textiles: spinning, twisting, and twining
Strand structure
C057S013000, C057S015000, C057S133000, C057S201000, C057S206000, C057S207000, C057S210000, C057S214000, C057S248000, C057S253000, C174S11300R
Reexamination Certificate
active
06260343
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to improved high-strength, fatigue resistant strands and wire ropes. This invention also relates to methods for making the strands and wire ropes.
2. Description of the Related Art
Strands and wire ropes are used in a wide range of applications for lifting and holding objects. For example, wire ropes are used in cranes as lifting elements and as pendants to support the boom. Most standard wire ropes comprise six outer strands surrounding a central core. Three-strand wire ropes are specifically designed to reduce rotation under load. These wire ropes have been used in tower cranes where torque generation in the ropes needs to be minimized for better rope performance.
Wire ropes are produced from various metals that can be drawn into small-diameter wire and have sufficient ductility for the forming process. Presently, high-carbon wires are used in strands and wire ropes. Other metals that are used include stainless steels, copper, aluminum and other alloys. The most commonly used materials for wire ropes are high-carbon steels and stainless steels. High-carbon steel wire ropes can be used in applications and environments in which corrosion is not a major concern. High-carbon steel wire ropes can be galvanized for corrosion resistance. In addition, high-carbon steel wire ropes can be compacted for use in applications requiring higher strength and improved crush resistance and fatigue life.
Desired properties for strands and wire ropes include high strength; high strength-to-weight ratio to reduce the weight of the wire rope having sufficient strength for a given use; high fatigue life to withstand repeated stresses; and suitable bending stiffness. In addition, reduced rotation under load is also desired for better performance.
There is a need for improved strands and wire ropes that have improved properties and can be provided in various material compositions. There is also a need for a method of making the improved strands and wire ropes.
SUMMARY OF THE INVENTION
This invention provides improved strands and wire ropes that satisfy the above needs. This invention also provides methods of making the improved strands and wire ropes. The strands and wire ropes according to exemplary embodiments of this invention provide increased strength; increased strength-to-weight ratio; increased fatigue life; suitable stiffness; corrosion resistance and rotation resistance or torque balance.
Strands according to exemplary embodiments of this invention comprise a plurality of wires in a compacted, mechanically stress relieved and thermally stress relieved condition. Compaction produces compressive residual stress in the outer wires of the strands and increases strength and fatigue life. The strands can comprise high-carbon steels, stainless steels and other suitable metals.
Strands according to exemplary embodiments of this invention comprise a plurality of thermally stress relieved stainless steel wires.
Wire ropes according to exemplary embodiments of this invention comprise a plurality of strands. The wire ropes can be in a mechanically stress relieved and thermally stress relieved condition.
The wire ropes can comprise a core and can be rotation resistant. Torque balanced wire ropes can comprise three or more strands.
Stainless steel wire ropes and high carbon steel wire ropes can be provided in a compacted mechanically stress relieved condition and, optionally, also in a thermally stress relieved condition.
The compacted stainless steel strands and wire ropes have a strength level which is comparable to the strength level of thermally stress relieved stainless steel wire ropes of the same diameter. Mechanically and thermally stress relieved stainless steel strands and wire ropes have improved mechanical properties including enhanced breaking strength as compared to compacted, but non-thermally stress relieved, stainless steel wire rope.
Exemplary embodiments of the methods of this invention comprise heating a plurality of wires to thermally stress relieve the wires; and stranding the wires to form strands. The wires are compacted during stranding to mechanically stress relieve the strands.
Exemplary embodiments of the methods of this invention can further comprise closing a plurality of strands to form a wire rope. In embodiments, the wire ropes can optionally be compacted and/or thermally stress relieved to produce finished ropes.
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“Thermomechanical Surface Hardening Raises Spring Life,” Advanced Materials & Processes 3/99, p. 17.
S. R. Bhonsle et al, “Mechanical Fatigue Properties of Stress Relieved Type 302 Stainless Steel Wire,” Journal of Materials Engineering and Performance, vol. 1, No. 3, 6/92, pp. 363-369.
Calvert John J.
Hurley Shaun R
Oliff & Berridg,e PLC
Wire Rope Corporation of America, Incorporated
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