Service life and scrapping standard of elevator wire rope

Service life and scrapping standard of elevator wire rope

Abstract: In the elevator, the steel wire rope is an important component, it mainly plays a bearing role, and its quality will affect the safety and service life of the elevator. After the elevator has been used for a long time, the wire rope will be depleted to a certain extent. What is the service life of the elevator wire rope? Generally speaking, 3-9 years is normal, so what is the standard for scrapping the elevator wire rope? The following is an introduction to the elevator wire rope scrapping standards from the aspects of the nature and quantity of broken wires, broken wires at the rope end, local aggregation of broken wires, increase rate of broken wires, and broken strands.

 
1. Service life of elevator wire rope
The state does not expressly stipulate the service life of the elevator wire rope, which is generally between 3-9 years. If the elevator is used frequently and the maintenance is not in place, its service life will be shorter. If the elevator is used less frequently and has regular maintenance, its service life will be longer. The higher the use frequency of the elevator and the larger the load, the shorter the service life. The use frequency of the elevator in the residential building and the office building is very different. At the same time, the use environment and maintenance of the elevator also have a decisive impact on the service life. Corrosion and inadequate maintenance will also shorten the use time.

2. What is the scrap standard for elevator wire ropes?
The standard for scrapping of elevator wire ropes is applicable to the "Practical Specification for Inspection and Scrapping of Wire Ropes for Hoisting Machinery" (GB5972-86)
The nature and quantity of broken wires
The general design of the hoisting machinery does not allow the wire rope to have an infinite life.
For 6-strand and 8-strand wire ropes, wire breakage mainly occurs on the outside. This is different for wire ropes with multiple strands (a typical multi-strand structure), where most of the wire breakage occurs internally, so it is an "invisible" break.
1. Broken wire at the end of the rope
When there is a broken wire at or near the end of the rope, even a small number indicates that the stress is high at the part, which may be caused by incorrect installation of the rope end, and the cause of the damage should be identified. If the length of the rope allows, the part of the broken wire should be cut off and re-installed reasonably.
2. Local aggregation of broken wires
If the broken wires are close together to form a local cluster, the wire rope should be scrapped. If such broken wires are gathered within the rope length range of less than 6d, or are concentrated in any rope strand, then the wire rope should be scrapped even if the number of broken wires is less than the value listed in the table.
3. Increase rate of broken wires
In some occasions, fatigue is the main reason for the damage of the wire rope, and the broken wire begins to appear after a period of use, but the number of broken wires gradually increases, and the time interval becomes shorter and shorter. In this case, in order to determine the rate of increase in broken wires, the increase in broken wires should be carefully examined and recorded. Determining this "law" can be used to determine the date when the wire rope will be scrapped in the future.
4. Strand breakage
In the event of a breakage of the entire strand, the wire rope shall be scrapped.
5. Decrease in rope diameter due to damage to the rope core
When the fiber core of the wire rope is damaged or the steel core (or the inner strands in the multi-layer structure) breaks, causing the rope diameter to decrease significantly, the wire rope should be scrapped.
Minor damage, especially when the stresses in all strands are well balanced, may not be apparent by normal inspection methods. However, this situation will cause the strength of the wire rope to be greatly reduced. Therefore, when there are any signs of internal minor damage, the inside of the wire rope should be inspected to find out. Once damaged, the wire rope should be scrapped.
6. Reduced elasticity
In some cases (usually related to the working environment), the elasticity of the wire rope can be significantly reduced, and it is not safe to continue to use it. The reduction of the elasticity of the wire rope is difficult to detect. If the inspector has any doubts, he should consult the opinions of the wire rope expert. However, the reduction in elasticity is usually accompanied by the following phenomena:
a. The rope diameter is reduced;
b. Wire rope lay length elongation;
c. Due to the mutual compression of each part, there is a lack of space between the wires and between the strands;
d. A fine brown powder appears in the concave portion of the rope;
e. Although no broken wires were found, the apparent inflexibility and diameter reduction of the wire rope were much faster than those caused by wire wear alone. This situation will lead to sudden rupture under dynamic load, so it should be scrapped immediately.
7. External and internal wear
There are two situations in which wear occurs:
a. Internal wear and crater
This condition is caused by friction between the individual strands and the wires within the rope, especially when the wire rope is subjected to bending.
b. External wear
The wear of the wire surface of the outer strand of the wire rope is caused by its contact and friction with the pulley and the rope groove of the drum under pressure. This phenomenon is particularly obvious at the contact part of the wire rope and the pulley when the hoisting load accelerates and decelerates, and the outer wire is ground into a flat shape. Insufficient or incorrect lubrication, as well as the presence of dust and grit, can increase wear. Wear reduces the cross-sectional area of the wire rope and thus the strength. When the outer steel wire is worn to 40% of its diameter, the wire rope should be scrapped.
When the diameter of the wire rope is reduced by 7% or more relative to the nominal diameter, the wire rope shall be scrapped even if no broken wires are found.
8. External and internal corrosion
Corrosion is particularly prone to occur in marine or industrially polluted atmospheres. Not only does it reduce the metal area of the wire rope and thus the breaking strength, it also causes surface roughness from which cracks can develop and accelerate fatigue. Severe corrosion can also cause a reduction in the elasticity of the wire rope.
8.1. External corrosion
Corrosion of external wires can be observed with the naked eye. When there are deep pits on the surface and the steel wire is quite loose, it should be scrapped.
8.2. Internal corrosion
Internal corrosion is more difficult to detect than the external corrosion that often accompanies it. However, the following phenomena can be identified:
a. Changes in the diameter of the wire rope. The diameter of the wire rope usually becomes smaller at the bend around the pulley. However, for the wire rope in the static section, the diameter of the wire rope is often increased due to the rust on the outer 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 are any signs of internal corrosion, the wire rope should be internally inspected by a competent person. If serious internal corrosion is confirmed, the wire rope should be scrapped immediately.
9. Deformation
The loss of the normal shape of the wire rope produces a visible deformity called "deformation". This deformed part (or deformed part) can cause changes, which can lead to uneven distribution of stress inside the wire rope.
The deformation of the wire rope is distinguished from the appearance, which can be mainly divided into the following categories:
1) Wavy
The wave-shaped deformation is: the longitudinal axis of the wire rope is in the shape of a helix. This deformation does not necessarily lead to any loss of strength, but if the deformation is serious, it will produce jumping and cause irregular transmission. Over time will cause wear and wire breakage.
When there is a wave shape, within the range of the length of the wire rope not exceeding 25d, if d1≥4d/3, the wire rope should be scrapped.
where d is the nominal diameter of the wire rope; d1 is the diameter of the envelope after the wire rope is deformed.
2) Cage distortion
This deformation occurs on wire ropes with a steel core. This deformation occurs when the outer strands become disjointed or become longer than the inner strands. Cage-distorted wire ropes should be discarded immediately.
3) strand extrusion
This condition usually occurs with cage distortion. The strands are squeezed out, indicating that the wire rope is unbalanced. Wire ropes extruded from the strands should be discarded immediately.
4) Wire extrusion
This kind of deformation is that a part of the steel wire or wire bundle is arched to form a ring on the side of the wire rope that is behind the pulley groove. This deformation is often caused by shock loads. If the deformation is serious, the wire rope should be scrapped.
5) Local increase in rope diameter
The diameter of the wire rope may increase locally, and it can affect a considerable length of wire rope. The increase in rope diameter is usually related to the distortion of the rope core (such as the expansion of the fiber core due to moisture in special environments), and the inevitable result is that the outer strands are unbalanced, resulting in incorrect positioning.
Wire ropes with locally increased rope diameters should be scrapped.
9. Kink
A kink is a deformation caused by the wire rope being stretched in a loop in which it is impossible to rotate about its axis. The result is an uneven lay length that causes extra wear and, in severe cases, the wire rope will be twisted, leaving only a very small part of the wire rope strength. Severely kinked wire ropes should be discarded immediately.
The local reduction of the rope diameter and the local reduction of the wire rope diameter are often related to the fracture of the rope core. Special attention should be paid to checking whether there is such deformation at the end of the rope, and the wire rope with a serious reduction in the rope diameter should be scrapped.
10. Partially squashed
The wire rope is partially squashed due to a mechanical accident. In serious cases, the wire rope should be scrapped.
11. Bend
Bending is the angular deformation of the wire rope under external influences.
Such deformed wire ropes should be scrapped immediately.
12. Damage due to heat or arcing
When the wire rope has been subjected to special heat and its surface has an identifiable color, the wire rope should be scrapped.