Scrapping and replacement of wire rope

The overall design of the hoisting machinery does not allow the wire rope to have an unlimited life.

For 6-strand and 8-strand wire ropes, wire breakage mainly occurs on the surface. The wire rope with multiple strands (typical multi strand structure) is different. This kind of wire rope breaks mostly in the interior, so it is "invisible" fracture.

The following table takes these factors into account. Therefore, when combined with the factors in 2.5.2~2.5.11, it is applicable to wire ropes of various structures.

Broken wire at rope end

When the wire breaks at or near the rope end, even if the number is small, it indicates that the stress at this part is very high, which may be caused by incorrect installation of the rope end. Find out the cause of the damage. If the rope length is allowed, the broken part shall be cut off and re installed reasonably.

Local aggregation of broken wires

If the broken wires form local aggregation closely together, the wire rope shall be scrapped. If such broken wires are gathered within the rope length of less than 6d, or concentrated in any rope strand, the wire rope shall be scrapped even if the number of broken wires is less than the value listed in the table.

Increase rate of broken wire

In some applications, fatigue is the main cause of wire rope damage, and wire breakage starts after a period of use, but the number of broken wires increases gradually, and the time interval is shorter and shorter. In this case, in order to determine the increase rate of broken wires, carefully inspect and record the increase of broken wires. This "rule" can be used to determine the future scrap date of wire rope.

Broken strands

If the whole strand breaks, the wire rope shall be scrapped.

Reduction of rope diameter due to damage of rope core

When the fiber core of the wire rope is damaged or the steel core (or the internal strand in the multi-layer structure) is broken, resulting in significant reduction of the rope diameter, the wire rope shall be scrapped.

Minor damage, especially when the stress in all strands is in good balance, may not be obvious with the usual inspection method. However, this situation will cause the strength of wire rope to be greatly reduced. Therefore, if there is any sign of minor internal damage, the interior of the wire rope should be inspected to find out. Once it is proved to be damaged, the wire rope shall be scrapped.

Decreased elasticity

In some cases (usually related to the working environment), the elasticity of wire rope will be significantly reduced, and it is unsafe to continue to use it.

It is difficult to detect the decrease of the elasticity of the wire rope. If the inspector has any doubt, he should consult the wire rope experts. However, the decrease in elasticity is usually accompanied by the following phenomena:

a. Rope diameter reduction

b. Wire rope lay extension

c. Due to the mutual compression of various parts, there is no gap between steel wires and strands

d. Fine brown powder appears in the rope strand recess

e. Although no broken wire is found, the steel wire rope is obviously not easy to bend and its diameter decreases much faster than that simply caused by steel wire wear. This situation will cause sudden fracture under dynamic load, so it should be scrapped immediately.

External and internal wear

Two conditions causing wear:

a. Internal wear and indentation

This situation is caused by the friction between each strand and the steel wire in the rope, especially when the steel wire rope is subjected to bending.

b. External wear

The wear of the steel wire surface of the outer rope strand of the steel wire rope is caused by its contact friction with the groove of the pulley and the drum under the pressure. This phenomenon is particularly obvious at the contact part between the steel wire rope and the pulley when the lifting load accelerates and decelerates, and the external steel wire is ground into a flat shape.

Insufficient lubrication, incorrect lubrication and the presence of dust and sand particles will aggravate wear.

The abrasion reduces the sectional area of the wire rope and thus the strength. When the outer steel wire is worn to 40% of its diameter, the steel wire rope shall be scrapped.

When the wire rope diameter decreases by 7% or more relative to the nominal diameter, the wire rope shall be scrapped even if no broken wire is found.

External and internal corrosion

Corrosion is particularly prone to occur in marine or industrial polluted atmosphere. It not only reduces the metal area of the wire rope and thus reduces the breaking strength, but also causes the surface roughness and the development of cracks from it to accelerate fatigue. Serious corrosion will also cause the decrease of the elasticity of the wire rope.

External corrosion: the corrosion of external steel wire can be observed with naked eyes. When there are deep pits on the surface and the steel wire is quite loose, it shall be scrapped.

Internal corrosion: internal corrosion is more difficult to find than external corrosion that often accompanies it. However, the following phenomena can be identified:

a. Change of wire rope diameter. The diameter of the wire rope at the bending part around the pulley usually becomes smaller. But for the steel wire rope in the static section, the diameter of the steel wire rope is often increased due to the rust deposit on the outer rope strand.

b. The gap between the outer strands of the wire rope is reduced, which is often accompanied by broken wires between the outer strands.

If there is any sign of internal corrosion, the wire rope shall be inspected internally by a competent person. If serious internal corrosion is confirmed, the wire rope shall be scrapped immediately.

Deformation: visible deformation caused by the loss of normal shape of the wire rope is called "deformation". Such deformed parts (or deformed parts) may cause changes, which will lead to uneven stress distribution inside the wire rope. The deformation of wire rope can be divided into the following types from the appearance:

The wavy deformation is that the longitudinal axis of the wire rope is in a spiral shape. This kind of deformation does not necessarily lead to any loss of strength, but if the deformation is serious, it will cause jumping and irregular transmission. Long time will cause wear and breakage.

In case of wave, the wire rope shall be scrapped if d1 ≥ 4d/3 within the range of 25d.

Where, d is the nominal diameter of wire rope; D1 is the envelope diameter of the deformed wire rope.

Cage distortion: This deformation occurs on the wire rope with steel core. This deformation occurs when the outer strand is disconnected or becomes longer than the inner strand. Wire ropes with cage distortion shall be scrapped immediately.

Strand extrusion: This condition is usually accompanied by cage distortion. The rope strand is extruded, indicating that the wire rope is unbalanced. The steel wire rope extruded from the rope strand shall be scrapped immediately.

Steel wire extrusion: this deformation refers to that a part of steel wire or steel wire bundle arches at the side of the steel wire rope against the pulley groove to form a ring. This deformation is often caused by impact loads. If such deformation is serious, the wire rope shall be scrapped.

Local increase of rope diameter: the diameter of steel wire rope may increase locally and can affect a quite long section of steel wire rope. The increase of rope diameter is usually related to the distortion of the rope core (for example, in a special environment, the fiber core expands due to moisture). The inevitable result is that the outer rope strand is unbalanced, resulting in incorrect positioning. The wire rope with seriously increased rope diameter shall be scrapped.

Twist: Twist is a deformation caused by the wire rope being tensioned when it is looped and cannot rotate around its axis. The result is that the uneven lay distance will cause extra wear, and in severe cases, the wire rope will twist, leaving only a small part of the wire rope strength. The seriously twisted wire rope shall be scrapped immediately.

Local reduction of rope diameter: the local reduction of wire rope diameter is often related to the fracture of rope core. The rope end shall be carefully inspected for such deformation. The wire rope whose rope diameter is seriously reduced locally shall be scrapped.

Partial flattening: the flattening of steel wire rope is caused by mechanical accident. If it is serious, the wire rope shall be scrapped.

Bending: bending is the angular deformation caused by the external influence of the wire rope. Such deformed wire rope shall be scrapped immediately.

Damage caused by heat or electric arc: the wire rope shall be scrapped when its appearance appears recognizable color under the action of special heat.

（1） There are two connection methods of wire rope: small connection method and large connection method. The small joint method is within the joint range, where the strands of two ropes are joined together, so the rope head becomes thicker and its joint length is shorter. The big joint method is to cut half of the strands of the two rope ends, and then insert the two rope ends together. Its joint length is long. The thickness of the rope connected by this method remains unchanged, and the joint position can not be seen on the surface. When wire rope is used as sling, it can only be used as sling after manual splicing, commonly known as small splicing method. The wire rope insertion methods can generally be divided into five types: one in one insertion, one in two insertion, one in three insertion, one in four and one in five insertion. The most commonly used method is the one in three splicing method, and the one in five splicing method is mostly used for wire rope summary

（2） When the steel wire rope is spliced and fixed, the spliced length shall not be less than 20 times the diameter of the steel wire rope, and shall not be less than 0.3m. The spliced part shall be bound with fine steel wire.

（3） When the steel wire rope is fixed with rope clips, the number shall not be less than 3, and the distance from the last clip to the rope head shall not be less than 0.14m. The rope clamp plate shall be on the stressed side, and the "U" shaped bolt shall be at the end of the wire rope, and shall not be crossed in the positive and negative directions. The clamp shall be tightened to make the diameter of the two ropes flatten by about 1/3. After the rope clamp is fixed, it shall be fastened again after the wire rope is stressed. Rope clip matching table:

Diameter of steel wire rope mm1010~2021~2628~3636~40 Minimum number of rope clamps (piece) 34567

Rope clamp spacing mm8014016020240