Damage And Prevention Of Crane Vulnerable Parts——Wire Rope

Damage and Prevention of Crane Vulnerable Parts——Wire Rope
 

Steel wire rope is a flexible force transmission component commonly used in machinery. As far as the steel wire rope used on cranes is concerned, there are many specifications and varieties, and the use is relatively complicated. In recent years, special and major lifting machinery accidents caused by this have occurred from time to time.
 

Let's talk about the prevention and treatment methods from the damage types of several crane wire ropes.
 

 

1. Wear and tear
 

Abrasion is the most common damage phenomenon of wire ropes, generally divided into three types: external wear, deformation wear and internal wear.
 

① External wear lubrication
 

During the use of the steel wire rope, its outer circumference contacts with the surface of the pulley groove, drum wall, hook head and other objects, which causes external wear, and the rope diameter will become thinner, and the thin steel wire on the outer peripheral surface will be ground flat, so that the cross-sectional area of the steel wire bearing the load will be reduced. The breaking load of the wire rope is also reduced accordingly.
 

Single-week wear is more serious than full-circle wear, and single-week wear should be changed to full-week uniform wear as much as possible, and uniform wear should be achieved within the entire length of the wire rope. If the head is changed in the middle of use, the service life of the wire rope can be extended by 30% to 40%.
 

② Deformation wear
 

The surface damage of the wire rope due to vibration and collision is a local wear phenomenon.
 

For example, the wire rope on the surface of the drum is hit by other objects, the hoisting wire rope is entangled with each other, or the phenomenon of biting the rope due to the deflection of the pulley and the center of the drum will cause deformation and wear of the wire rope.
 

③ Internal wear
 

During use, due to the bending of the steel wire rope, the internal thin steel wires interact to produce slippage, the contact stress between strands increases, and the steel wires between adjacent strands produce local indentations and deep depressions. When repeated cyclic stretching and bending Sometimes in the deep recess, stress concentration occurs and it breaks, which constitutes internal wear.
 

Usually, the pressure on the surface of the thin steel wire is proportional to the pressure on the steel wire rope. Under the same tension, the pressure per unit area is also different due to the different compression areas.
 

From the perspective of surface pressure wear, it is more beneficial to use line contact than point contact for steel wire ropes, and it is more beneficial to use surface contact than line contact. Therefore, choosing wire ropes with line contact or surface contact is an effective way to reduce internal wear.
 

In addition, the degree of bending and the speed of movement of the wire rope have an impact on its internal wear.
 

 

2. Fatigue
 

During use, the steel wire rope mainly bears bending fatigue and fatigue caused by stretching, twisting and vibration.
 

① Bending fatigue lubrication
 

When the steel wire rope is bent countless times and repeatedly goes around the pulley or the drum, the steel wire will be fatigued, the toughness will be reduced, and the wire will eventually break.
 

Fatigue broken wires generally appear on the outer steel wire on the side with the most severe bending degree of the strands. Usually, the appearance of fatigue broken wires means that the steel wire rope is close to the end of use.
 

② Fatigue caused by stretching, twisting and vibration
 

The changing tensile stress of the crane-bundled steel wire rope at the beginning and end of starting and braking, before and after bearing the load will cause metal fatigue. In addition, the steel wire rope is often subjected to twisting and vibration, which is also the cause of fatigue.
 

The principle of fatigue damage is that under the action of variable stress, initial cracks are formed on the surface of thin steel wire due to various slips, and the crack tip is repeatedly plastically deformed and expanded until it breaks under the action of shear stress.
 

The fractures of broken wires caused by fatigue are generally flat, and most of them appear on the surface steel wires, which are very regular.
 

The main ways to prevent fatigue damage:
 

One is to increase the diameter of the reel and pulley as much as possible if conditions permit;
 

The second is to avoid reverse bending of the wire rope when arranging the pulley layout. The test shows that the damage of reverse bending is about 2 times that of bending in the same direction;
 

The third is to choose steel wire ropes with good structure as far as possible, such as WS, TX and other wire contact wire ropes.
 

 

3. Rust
 

Steel wire ropes are generally used in the open air, and they are corroded by the sun and rain, especially in harmful gases and harsh environments.
 

Due to the difference in oxygen affinity on the surface of the damaged steel wire rope, a large number of small batteries are formed, resulting in many circular corrosion pits and gradually deepening. These pits become the source of stress concentration points and fatigue cracks.
 

At the same time, corrosion reduces the cross-sectional area of the wire rope, reducing its elasticity and ability to withstand impact.
 

There are two ways to prevent wire rope corrosion damage:
 

One is to apply oil frequently;
 

Second, special steel wire ropes such as galvanized and aluminum-plated steel wire ropes can be selected for steel wire ropes that are used in harsh environments and relatively less in motion, because zinc hydroxide and aluminum hydroxide films will be formed on their surfaces in the atmosphere, thereby effectively preventing corrosion.
 

 

4. Deformation
 

Many broken rope accidents are caused by the fact that the steel wire rope has been deformed and damaged in advance but has not caused sufficient recurrence, resulting in catastrophe. The main reasons for the deformation are as follows.
 

① Trauma
 

Trauma is caused by abnormal contact between the wire rope and other equipment during operation.
 

The most obvious trauma is that the steel wire rope slides in the pulley and jumps out of the baffle on the drum. As a result, tens of meters or even hundreds of meters of steel wire rope are scrapped due to partial crushing.
 

The key to preventing trauma is to improve the crane equipment. The pulley should be equipped with a reliable anti-skid groove retaining ring. The gap between the retaining ring and the outer ring of the pulley should not be greater than 1/5 of the diameter of the wire rope. The jump-out baffle was crushed when it was wound tightly.
 

② crush
 

After the steel wire rope is wound up on the reel, it will roll over each other, which is easy to cause crushing phenomenon, and there will be a creaking sound during operation, and there will be traces of broken wires and flattening in some parts.
 

The preventive measure is to select the deflection angle between the pulley and the reel according to the design specifications, and if necessary, install a rope puller or a rope pressing device in the hoisting mechanism.
 

③ kink
 

The permanent deformation of the steel wire rope after local twisting is called kink, and the direction of twist is consistent with the direction of rotation of the steel wire rope, which is called positive kink, otherwise it is called negative kink.
 

Ordinary steel wire ropes have self-rotation. If tension is applied to the ends of the strands without binding, the strands will rotate in the direction of reverse twist, which is an internal factor causing kinks.
 

Prevent kinks by taking the following measures:
 

One is to use non-rotating wire ropes on important lifting equipment;
 

The second is to set the rotor at the free end of the wire rope;
 

The third is to stop the operation immediately if there are signs of kinking, and release the recovery.
 

 

5. Bite the rope
 

The rope biting phenomenon of the wire rope generally occurs on the hoist drum with multi-layer winding, especially the hoisting drum with double-layer winding with grooves.
 

It is difficult to completely eliminate the rope-biting phenomenon of multi-layer winding reels, but some measures can be taken to reduce its adverse effects, such as the correct selection of the axial displacement direction of the steel wire rope during the winding process has a great relationship with whether the second-layer steel wire rope has a rope-biting phenomenon. big.
 

According to the characteristics that the first few coils of steel wire rope on the reel are not often used but indispensable, these coils of steel wire rope can be wound on one side of the drum, and the heavy-duty section with frequent work can be wound in a single layer, which is extremely Greatly improves the contact condition of the wire rope and also eliminates the phenomenon of rope biting.
 

For the multi-layer winding steel wire rope, the method of regular truncation can also be adopted, that is, the new steel wire rope is consciously lengthened for 2 to 3 turns, and then half a turn is periodically cut off from the end of the rope according to the situation, so as to avoid the wire rope from being broken at the node. Damage too fast.
 

In addition, according to the loading situation of the whole steel wire rope on the drum, the variable section drum is used, which can prolong the service life of the steel wire rope by 4 to 5 times.
 

6. Overload
 

The wire rope will elongate slightly as the load increases, and the wire rope may break when the load exceeds the elastic limit.
 

The fracture of the wire rope broken due to overload is loose. Most of the fracture positions of the 6 strands of wire rope are not together, and the rope core is exposed. This is the characteristic of the wire rope breaking due to overload.
 

In order to prevent the wire rope from being overloaded, the following measures should be taken:
 

① Correctly select the safety factor, and strive to reduce the influence of loads other than static load on the wire rope, such as reducing the bending load by increasing the diameter of the pulley and the drum, reducing the dynamic load by improving the driver's operating level and improving the performance of the crane, and adjusting the pulley The shape of the groove and supplementary lubricating oil to reduce frictional resistance, etc.;
 

②Strictly abide by the safety operation rules and prevent artificial overloading;
 

③ Install a load indicator or overload limiter or alarm on the overhead crane to forecast the overload phenomenon.
 

In addition to the above six basic damage types, high temperature radiation, performance indicators, diameter and twisting form of the wire rope will all affect its life.