The filling material located at the center of the steel wire rope for support and cushioning. The filling material located at the center of the rope strand that plays the same role is called the strand core. Rope (strand) cores are divided into two categories: fiber rope (strand) cores and metal rope (strand) cores.

The core of the rope (strand) plays a role in supporting the outer rope strand (steel wire) and maintaining the integrity of the shape of the steel wire rope (strand) during the twisting and use of the steel wire rope and strand; The fiber rope core also plays a role in increasing softness, oil storage, rust prevention, and lubrication to reduce wear. When the steel wire rope is subjected to impact and vibration, the compressed fiber rope (strand) core can play a buffering role due to its elasticity, but it will reduce the actual bearing capacity. In addition to the above functions, the metal rope core can also enhance the load-bearing capacity of the steel wire rope. The core of the fiber rope (strand) should have resistance to compression. When the wire rope is in working condition and the radial pressure of the strand (wire) on it reaches 147MPa, radial flattening deformation should not occur. Otherwise, the contact stress at the contact between adjacent strands increases, causing premature wear of the wire and even early fracture. The core of the rope (strand) should have small moisture absorption and good wear resistance, otherwise it will increase its moisture content, cause corrosion of the internal steel wire, exacerbate the brittleness of the steel wire, and reduce the tensile strength of the steel wire rope.

The metal rope core can increase the strength of the steel wire rope and has its own high-temperature and compressive resistance. However, steel wire ropes with metal cores have poor bending ability and high stiffness, making them suitable for use in ship tensioning masts, suspension bridges, salt wells, and other places. Double twisted metal core has bending performance and can be used in lifting machinery that can withstand extrusion and impact loads, such as car cranes, electric shovels, etc.

Rope core - classification and use

Rope cores are divided into four types based on material: metal core, natural organic fiber core, mineral core, and synthetic fiber core. Rope cores made of different materials have different characteristics and are suitable for different purposes.

(1) Metal rope core. When the ratio of the breaking force of the entire steel wire rope to the load it bears is small (but greater than 4), the pressure of the strand rope on the rope core is greater than 147MPa, or when the steel wire rope is used in high temperature and with significant load changes, a metal rope core should be used. The metal rope core is made by twisting steel wires like strands. The metal core of the rope strand is generally a single steel wire, which can also be tightly wound into a spring using a steel wire coated with a layer of polyamide resin (Kaplon) on the outer surface or a steel wire filled with dry oil as the steel core. It is called a spring metal core. The metal core used for circular strand point contact wire rope (see circular strand wire rope) is the same as that of ordinary single stranded wire rope (rope strand); The metal core of wire contact wire rope is mostly 7 × Double twisted steel wire rope with a structure of 7 (see Steel Wire Rope). In recent years, in order to improve the working conditions of rope strands in steel wire ropes, 6 has been used instead × Steel wire rope with a structure of 7.

(2) Natural organic fiber rope (strand) core. The materials used to make natural organic fiber cores can be divided into hard fibers, such as sisal hemp, manila hemp, and banana hemp; Soft fibers such as jute and cotton yarn. Hard fibers are good natural organic rope core materials, with lower moisture absorption compared to soft fibers, and higher compressive, tensile, and wear resistance. The natural organic fiber rope core is suitable for manufacturing lifting steel wire ropes. The moisture content of natural organic rope (strand) core should be less than 2%, and the content of acid, alkali, and salt should be less than 0.03%. In order to improve its wear resistance and tensile performance, the organic rope (strand) core adopts a small lay distance and needs to be tightly twisted.

The natural organic fiber core material used in Chinese steel wire ropes is mostly jute, with four specifications of hemp yarn: 1.7, 1.4, 1.3, and 1.0mm; Most of them use left twist, but some also use right twist (see wire rope twist method).

(3) Mineral rope core. Made of asbestos, it is resistant to high temperatures and has high softness, but low strength. Steel wire ropes made from mineral rope cores are often used in high-temperature working environments.

(4) Synthetic fiber core. Polyamide (nylon), polyethylene L vinylon, polypropylene and other fibers can all be used as rope (strand) core materials. Compared with natural fiber core, it has high wear resistance and extrusion resistance, and is made of even rope (strand) core with uniform diameter, stable rope diameter, solid texture and light specific gravity; And it has advantages such as strong adsorption to oil, but low softening point and melting point, and poor heat resistance. Synthetic fiber cores also have unique advantages, such as resistance to corrosion by acids, alkalis, salts, and hydrogen sulfide, and stable performance in the temperature range of 46 to 150 ℃. With the development of the chemical synthetic fiber industry, especially after the emergence of polypropylene fibers in the 1950s, synthetic fibers gradually replaced natural organic fibers as rope (strand) cores. Steel wire ropes for fishing and salt wells, as well as some special-shaped strand steel wire ropes, are often made of synthetic fibers to make cable (strand) cores.