Excerpted from "Practical Specification for Inspection and Retirement of Steel Wire Ropes for Hoisting Machinery" (GB5972-86)
The overall design of the hoisting machinery does not allow the rope to have an infinitely long life.
For 6- and 8-strand wire ropes, the broken wire mainly occurs on the outside. The wire ropes (typically multi-stranded structures) of the multi-layer strands are different. Most of these wire rope breaks occur internally and are therefore "invisible" fractures.
The following table considers these factors, so it is applicable to wire ropes of various constructions when considered in combination with the factors in paragraphs 2.5.2 to 2.5.11.
2.5.2 Broken wire at the end of the rope
When a broken wire occurs at or near the rope end, even if the number is small, it indicates that the stress is high in the part, which may be caused by incorrect installation of the rope end, and the cause of the damage should be ascertained. If the length of the rope is allowed, cut the broken wire and re-install it properly.
2.5.3 Local aggregation of broken wires
If the broken wires are close together to form a local gather, the wire rope should be scrapped. If the broken wire gathers within the rope length of less than 6d, or is concentrated in any of the strands, the wire rope should be scrapped even if the number of broken wires is less than the value listed.
2.5.4 Increase rate of broken wire
In some applications, fatigue is the main cause of wire rope damage. Broken wire begins to appear after a period of use, but the number of broken wires increases gradually, and the time interval becomes shorter and shorter. In this case, in order to determine the rate of increase of the broken wire, the increase in broken wire should be carefully checked and recorded. It was found that this "law" can be used to determine the date of future scrapping of the wire rope.
2.5.5 Strand break
If a break in the entire strand occurs, the wire rope should be scrapped.
2.5.6 Reduced rope diameter due to damage to the core
When the fiber core of the wire rope is damaged or the steel core (or internal strands in the multilayer structure) is broken and the rope diameter is significantly reduced, the wire rope should be scrapped.
Minor damage, especially when the stresses in all strands are well balanced, may not be apparent with the usual test methods. However, this situation can 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 for identification. Once the damage is confirmed, the wire rope should be scrapped.
2.5.7 Reduction in elasticity
In some cases (usually related to the working environment), the elasticity of the wire rope is significantly reduced and it is unsafe to continue using it.
The reduction in the elasticity of the wire rope is difficult to detect. If the inspector has any doubts, the wire rope expert should be consulted. However, the reduction in elasticity is usually accompanied by the following phenomena:
a. rope diameter reduction
b. wire rope pitch elongation
c. Since the parts are pressed against each other, there is no gap between the wires and between the strands
d. Subtle brown powder appears in the strand recess
e. Although no broken wires were found, the wire ropes were significantly less susceptible to bending and the diameter reduction was much faster than simply due to wire wear. This situation can lead to sudden breakage under dynamic load, so it should be immediately scrapped.
2.5.8 External and internal wear
Two situations that cause wear:
a. internal wear and pressure pit
This situation is caused by friction between the individual strands in the rope and the steel wire, 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 due to the frictional contact of the pulley and the rope groove of the drum under pressure. This phenomenon is particularly noticeable when the wire rope is in contact with the pulley during the acceleration and deceleration movement, and the outer wire is ground into a flat shape.
Insufficient lubrication, or incorrect lubrication, and the presence of dust and sand can exacerbate wear.
The wear reduces the sectional area of ​​the wire rope and thus the strength. When the outer 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 with respect to the nominal diameter, the wire rope should be scrapped even if no broken wire is found.
2.5.9 External and internal corrosion
Corrosion is particularly prone to occur in marine or industrially polluted atmospheres. It not only reduces the metal area of ​​the wire rope, but also reduces the breaking strength, and will also cause the surface to be rough and develop cracks from it to accelerate fatigue. Severe corrosion can also cause a decrease in the elasticity of the wire rope.
2.5.9.1 External corrosion
Corrosion of the outer wire can be observed with the naked eye. When there is a deep pit on the surface, the wire should be scrapped when it is quite slack.
2.5.9.2 Internal corrosion
Internal corrosion is more difficult to find than external corrosion that often occurs with it. However, the following phenomena are available for identification:
a. Change in wire rope diameter. The diameter of the wire rope is usually small at the bend of the winding around the pulley. However, for the wire rope of the stationary section, the diameter of the wire rope is often increased due to the rust accumulation of the outer strand.
b. The gap between the outer strands of the wire rope is reduced, and often accompanied by broken wires between the outer strands.
If there is any indication of internal corrosion, the wire rope should be internally inspected by the supervisor. If serious internal corrosion is confirmed, the wire rope should be immediately scrapped.
2.5.10 deformation
The loss of the normal shape of the wire rope creates a visible deformity called "deformation". This deformation (or deformed part) may cause a change, which may result in uneven stress distribution inside the wire rope.
The deformation of the wire rope is distinguished from the appearance, and can be divided into the following types:
2.5.10.1 Wave shape
The undulating deformation is that the longitudinal axis of the wire rope is in the shape of a spiral. This deformation does not necessarily result in any loss of strength, but if the deformation is severe, it will cause an impulsive transmission caused by the beating. Long time will cause wear and broken wires.
When the wave shape appears, if the length of the wire rope does not exceed 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 deformation of the wire rope.
2.5.10.2 Cage Distortion
This deformation occurs on a steel cord with a steel core. This deformation occurs when the outer strands are disjointed or become longer than the inner strands. Cage-distorted wire ropes should be scrapped immediately.
2.5.10.3 Strand extrusion
This condition is usually accompanied by cage distortion. The strands are squeezed out to indicate that the wire rope is unbalanced. The wire rope extruded from the strands should be immediately scrapped.
2.5.10.4 Steel wire extrusion
Such deformation is that a part of the steel wire or the wire bundle is arched on the side of the wire rope carrying the pulley groove to form a ring shape. This deformation is often caused by an impact load. If such deformation is severe, the wire rope should be scrapped.
2.5.10.5 Local increase in rope diameter
The diameter of the wire rope may increase locally and can affect a relatively long length of wire rope. The increase in rope diameter is usually related to the distortion of the core (for example, in a special environment, the fiber core expands due to moisture), and the inevitable result is that the outer strands are unbalanced and the positioning is incorrect.
Wire ropes with a severely increased rope diameter should be scrapped.
2.5.10.6 Kink
Kinking is a deformation caused by the wire rope being looped in the event that it is impossible to rotate about its axis. The result is an uneven wear and tear that causes extra wear and tear. In severe cases, the wire rope will be distorted, leaving only a very small portion of the wire rope strength.
Severely twisted wire ropes should be scrapped immediately.
2.5.10.7 Local reduction of rope diameter
The local reduction in the diameter of the wire rope is often related to the breakage of the core. Special inspection should be carried out to see if there is such a deformation at the end of the rope.
Wire ropes with a severely reduced rope diameter should be scrapped.
2.5.10.8 part is flattened
The flattening of the wire rope is caused by a mechanical accident. In severe cases, the wire rope should be scrapped.
2.5.10.9 Bending
Bending is the angular deformation caused by the wire rope under the influence of the outside world.
This deformed wire rope should be scrapped immediately.
2.5.11 Damage caused by heat or arc
The wire rope shall be scrapped when it is subjected to a special thermal force and its appearance has a recognizable color.
(1) There are two methods for connecting steel wire ropes: small connection method and large connection method. The small connection method is in the joint range, the strands of the two ropes are put together, so the rope head becomes thicker and its joint length is shorter. The large connection method removes the strands of the two rope heads by half, and then inserts the two rope heads together, and the joint length is long. The rope which is taken out by this method, the thickness of the rope remains unchanged. The position of the joint is not visible on the surface. When the wire rope is used as a sling, it needs to be manually inserted to become a sling, commonly known as a small connection method. The wire rope insertion method can be generally divided into five types: one into one plugging method, one into two plugging method, one into three plugging method, one in four and one in five plugging method. The most common one is the one-in-three-plug method, and the one-in-three-plug method is mostly used for the summary of the wire rope.
(2) When the wire rope is braided and fixed, the length of the braiding shall not be less than 20 times the diameter of the steel wire rope, not shorter than 0.3 m. The thin steel wire shall be bundled in the braided part.
(3) When the steel wire rope is fixed by the rope card, the number shall not be less than three, and the last one shall not be less than 0.14 meters from the rope head. The rope clamp plate shall be on the side of the force-receiving "U"-shaped bolts at the end of the wire rope, and shall not be crossed in the forward or reverse direction. The clip should be tightened so that the height of the two ropes is flattened by about 1/3. After the rope card is fixed, it should be tightened again after the wire rope is stressed. Rope card matching table:
Wire rope diameter mm 10 10~20 21~26 28~36 36~40
Minimum number of rope cards (3) 5 4 5 6 7
Rope card spacing mm 80 140 160 220 240
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