First chapter
2.5 standard of discarding
The properties and quantity of 2.5.1 broken wire
The overall design of hoisting machinery does not allow wire rope to have an infinite life span.
For wire rope with 6 strands and 8 strands, broken wire mainly occurs in appearance. For multi-layer rope strands, the wire ropes (typical multiply structures) are different, and most of this wire rope broken wire occurs inside, and thus is “invisible” fracture.
When combined with factors from 2.5.2 to 2.5.11, it can be applied to various kinds of wire ropes.
Broken wire at the end of 2.5.2 rope
When the wire ends or near the wire is broken, even if the number is very small, it indicates that the stress is very high. It may be caused by the incorrect installation of the rope end, and the cause of the damage should be found. If the rope length is allowed, the location of the broken wire should be cut off and installed again.
Local aggregation of 2.5.3 broken wire
If the broken wires are close together to form local aggregation, the wire rope should be scrapped. If the broken wire is within the length of less than 6D or concentrated in any rope, the wire rope should be scrapped even if the number of broken wires is less than that of the list.
The increase rate of 2.5.4 broken wire
In some situations, fatigue is the main cause of wire rope damage, and the broken wire begins to appear only after a period of use, but the number of broken wire increases gradually, and its time interval is shorter and shorter. In this case, in order to determine the increase rate of broken wire, careful inspection and recording of wire breakage should be made. Identifying this “rule” can be used to determine the date of the wire rope being scrapped in the future.
2.5.5 strand break
If the strand breaks, the wire rope should be scrapped.
The decrease of the rope diameter caused by the damage of the cord core in 2.5.6
When the fiber core of the wire rope is damaged or the inner strand of the steel core (or the inner strand of the multi-layer structure is broken), the rope diameter is significantly reduced, and the wire rope should be scrapped.
Small damage, especially when the stress of all strands is in good balance, may not be obvious by the usual test method. However, this situation will cause the strength of the wire rope to be greatly reduced. Therefore, any signs of internal minor damage should be inspected inside the wire rope to be identified. Once the damage is confirmed, the wire rope should be scrapped.
2.5.7 elasticity reduction
In some cases (usually related to the working environment), the elasticity of the wire rope will be significantly reduced, and it will be unsafe to continue using it.
It is difficult to detect the elasticity of the wire rope. If the inspector has any doubts, he should consult the expert of wire rope. However, the reduction of elasticity is usually accompanied by the following phenomena:
The diameter of A. rope is reduced.
The distance of the B. wire rope is elongated.
C. because the parts are tightly pressed between each other, there is no gap between the wire and strand.
There is a fine brown powder in the D. rope.
Although no broken wire was found in E., the wire rope was obviously not easy to bend and the diameter decreased, which was much faster than that caused by steel wire wear. This situation will cause sudden rupture under the action of dynamic load, so it should be scrapped immediately.
External and internal wear of 2.5.8
Two cases of abrasion are produced:
Internal wear and pressure pits in a.
This is due to the friction between the strand and wire in the rope, especially when the wire rope is bent.
External wear of B.
The wear of steel wire on the outer surface of wire rope is caused by the contact friction between the rope and groove of the pulley and the drum under pressure. During the acceleration and deceleration motion, the contact between the wire rope and the pulley is very obvious, and the outer steel wire is grind into a plane shape.
Inadequate lubrication or incorrect lubrication and dust and sand still increase wear.
Wear reduces the sectional area of the wire rope and reduces the strength. When the outer steel wire reaches 40% of its diameter, the wire rope should be scrapped.
When the diameter of the wire rope is reduced by 7% or more than the nominal diameter, even if no broken wire is found, the wire rope should be scrapped.
External and internal corrosion of 2.5.9
Corrosion is especially prone to occur in marine or industrial polluted atmospheres. It not only reduces the metal area of the wire rope, thereby reducing the breaking strength, but also causes rough surface and starts developing cracks and accelerates fatigue. Serious corrosion will also cause the elasticity of wire rope to decrease.
External corrosion of 2.5.9.1
The corrosion of the external steel wire can be observed by the naked eye. When a deep pit appears on the surface and the steel wire is quite loose, it should be scrapped.
Internal corrosion of 2.5.9.2
Internal corrosion is more difficult to detect than external corrosion often accompanied by it. However, the following phenomena can be identified:
The change of the diameter of the A. wire rope. The diameter of the wire rope in the bending part around the pulley is usually smaller. But for the static steel wire rope, the diameter of the wire rope often increases due to the rust accumulation on the outer strands.
The gap between outer strand of B. wire rope decreases, and wire breaking between outer strand often occurs.
If there is any sign of internal corrosion, the supervisor should conduct internal inspection of the wire ropes. If there is serious internal corrosion, the wire rope should be scrapped immediately.
2.5.10 deformation
The wire rope loses its normal shape and produces visible deformities. This deformation part (or shape part) may cause changes, which will lead to uneven stress distribution inside the wire rope.
The deformation of wire rope can be distinguished from appearance.
2.5.10.1 wave shape
The deformation of the wave is: the longitudinal axis of the wire rope forms a spiral shape. This deformation does not necessarily lead to any loss of strength, but if the deformation is serious, it will cause beating and cause irregular transmission. Long time will cause wear and disconnect.
When the wave shape occurs, the length of the wire rope is not more than 25d.