Fatigue wire breakage (Fig. 3-1): wire breakage caused by metal fatigue when the steel wire rope passes through the pulley or drum and bears a certain number of repeated bending times under the action of allowable stress. The fracture shape is flush, like knife cutting, and only a small part is finally broken. The fatigue broken wire appears on the outer steel wire on the side with the most severe bending of the strand.

Wear and broken wire (Fig. 3-3): this kind of broken wire will appear only when the steel wire is extremely worn. The fracture shape is inclined stubble on both sides and flat fracture.

Rusted broken wire (Fig. 3-5, 3-6): this kind of broken wire will appear in the later stage of use of severely rusted steel wire rope. The fracture shape is irregular and needle tip.

Shear broken wire: a broken wire formed by the rigid breaking of a steel wire at a corner. The fracture is in shear shape.

Overload broken wire (Fig. 3-2): it is caused by the overload load or impact force of the steel wire rope, which rarely occurs in the process of normal use. The fracture shape is similar to normal tension fracture, showing cup plastic shrinkage. The damaged parts of simple overload steel wire are scattered, accompanied by impact and concentrated in one strand when bending.

Kink and broken wire (Fig. 3-4): broken wire after kink caused by relaxation of steel wire rope. The fracture is flat and smooth, like a mirror.

abrasion

The wear of steel wire rope is closely related to the thinning of rope diameter. In actual testing, the wear degree is generally measured by measuring the diameter of steel wire rope. In addition, the percentage of metal cross-sectional area loss caused by wear LMA can be measured quantitatively with the help of nondestructive testing equipment.

The rope diameter is subdivided into normal thinning and wear thinning. After the new rope is hung, usually shortly after use, the diameter becomes thinner faster. When it becomes thinner near the nominal diameter (about two weeks after the hanging rope is used, there is no wear on the surface of the steel wire rope), there is a temporary stability period. As the wear on the surface of the steel wire begins, the diameter becomes thinner gradually. The early thinning is due to the elongation caused by the twisting structure of the steel wire rope, which belongs to normal thinning. The breaking force of the steel wire rope will not be lost, but will be strengthened due to the tighter structure of the steel wire rope, which is good for use; The later thinning is caused by the wear of steel wire and the corrosion and deterioration of rope core.

There are many reasons for the thinning of wear, some of which are due to long-term mechanical wear, including the wear of steel wires on the surface of steel wire rope and between strands; Some are caused by the thinning of the rope core and local thinning (the rope core is burned by impact force or flame jet); In addition, the metal section is reduced due to local corrosion and broken wire of steel wire rope.

The mechanical wear of steel wire rope can generally be divided into: external uniform wear, deformation wear, internal wear, single-sided wear and extrusion wear. Figure 2-6 shows several cross-sectional shapes of single wire wear, and figure 2-7 shows two cross-sectional shapes of whole rope wear.

(1) External uniform wear: pure mechanical wear, which is the wear of steel wire caused by the contact between steel wire rope and pulley, drum, etc. during use. This wear is uniform under normal conditions.

(2) Deformation and wear: local wear, which is caused by the frequent chronic displacement of the steel wire rope and pulley, the violent vibration and impact of the steel wire rope on the pulley, or the rope biting phenomenon caused by the deviation of the center of the pulley and the drum. This deformation and wear deforms due to local extrusion, and the cross section of the steel wire extends into a wing shape to both sides at the extrusion. From the appearance, the width of the steel wire expands. Although the cross-sectional area of the steel wire does not change significantly, the steel wire material at the local extrusion is hardened, which is very easy to cause wire breakage.

(3) Internal wear: when the steel wire rope passes through the drum or pulley during use, all the load borne by the steel wire rope is pressed on one side of the steel wire rope. At the same time, due to the bending of the steel wire rope, the steel wire in the strand moves. At this time, the contact stress between the strands increases, resulting in local indentation (indentation) of the steel wire between adjacent strands. When repeated cyclic stretching and bending, stress concentration occurs in the deep recess and is broken. The fracture of internal worn steel wire is toothed, and the surface is smooth and concave.

(4) Single side wear: when the steel wire rope is on the pulley with unsmooth rope groove or when the pulley does not rotate, the steel wire rope runs, and the hard friction between the ground roll and the ground will also produce this kind of wear.

(5) Extrusion wear: when the steel wire rope is installed or in a loose state, it may fall outside the pulley or at the damaged rim. If it is not found in time, the friction between the steel wire rope and the damaged rim during starting will cause this kind of wear phenomenon.

rust

The corrosion of steel wire rope (rust and corrosion) is the damage phenomenon of the metal surface of steel wire rope caused by the chemical or electrochemical action of the surrounding medium. Although the steel wire rope is filled with lubricating oil during use, the surface water can quickly penetrate into the internal gap along the capillary formed between the single wires of the steel wire rope. Due to the coverage of the outer lubricating oil and oil sludge, the water infiltrated into the steel wire rope is not easy to dry and remains in the rope core, thus corroding the interior of the rope; In addition, the corrosive substances contained in water or gas in the service environment will also aggravate the corrosion of steel wire rope. It can be found by artificially observing the external corrosion of the steel wire rope, while the internal corrosion is difficult to find and evaluate. However, the nondestructive testing of the steel wire rope can meet the requirements of detecting the internal and external corrosion, judge the percentage LMA of metal cross-sectional area loss caused by corrosion, and then evaluate the percentage of breaking force loss caused by corrosion. In practice, the influence of corrosion on the mechanical properties of steel wire rope is far more than that of wire breakage and wear.

Typical corrosion defects of steel wire rope

Obvious corrosion of inner steel wire after strand splitting

After strand removal, the rope core is completely dry and free of grease, losing its support and lubrication

deformation

The deformation caused by the wire rope losing its normal shape becomes "deformation", which will lead to uneven stress distribution in the wire rope.

(1) Wavy

The wavy shape makes the longitudinal axis of the steel wire rope take on the shape of spiral line no matter in the state of bearing or unloading. This deformation does not necessarily lead to the loss of strength, but when the deformation is serious, it may lead to runout and irregular transmission of steel wire rope. After long-term operation, it will cause increased wear and wire breakage.

Wavy deformation

(2) Cage distortion

Basket or cage distortion also becomes "Birdcage" and "lantern", which is the result of different lengths of rope core and outer strand. For example, when the steel wire rope is wound into the pulley or drum at a large deflection angle, it first contacts the rim of the pulley or the tip of the drum rope groove, and then rolls down and falls into the bottom of the rope groove. This characteristic causes the looseness of the outer strand to be greater than that of the core, resulting in a length difference between the strand and the core.

When the steel wire rope bypasses the "dense pulley", that is, the pulley with too small groove radius, the steel wire rope is compressed to reduce the rope diameter and increase the length of the steel wire rope at the same time. If the length of the outer layer of the rope strand compressed and elongated is greater than the length of the steel wire rope core compressed and elongated, in this case, the length difference between the steel wire rope strand and the rope core will be formed again.

In both cases, the pulley and drum can shift the loose outer strand and concentrate the length difference at a certain position in the wire rope winding system, resulting in basket or cage distortion.

Cage distortion

(3) Extrusion / twisting of rope core or strand

This imbalance phenomenon of steel wire rope is characterized by the extrusion (uplift) of the rope core between the outer strands (the center of the steel wire rope for the anti rotation steel wire rope), or a special type of basket or cage distortion of the extrusion (uplift) of the rope core in the outer strands or strands of the steel wire rope.

Strand extrusion / twisting

(4) Steel wire extrusion

Steel wire extrusion is the deformation of some steel wires or steel wire bundles arched on the side of the steel wire back to the pulley groove to form a ring.

The internal strand of anti rotation steel wire rope protrudes

(5) Local increase of rope diameter

The diameter of the steel wire rope increases locally and can affect a considerable length of steel wire rope. This situation is usually related to the distortion of the rope core (for example, in a special environment, the fiber core expands due to moisture). As a result, the force on the outer strand is unbalanced, resulting in the dislocation of the rope strand.

Due to the twist and deformation of the rope core, the local rope diameter increases

(6) Local flattening

The wire rope partially flattened through the pulley will be damaged quickly, which will appear as broken wire and may damage the pulley pad.

Local flattening

(7) Kink

Kink is caused by a tightened wire rope which is not allowed to revolve around its axis, resulting in a deformation. The result is that excessive uneven wear is caused by uneven twisting, and the wire rope will distort seriously, so that only a minimal strength exists.

Kink deformation