Analysis on the deformation of steel wire rope of ship unloader and preventive measures
Abstract: The wire rope has been widely used in port machinery, especially in ship unloader machinery, but there are also many safety issues. This article describes the types, failure mechanisms and preventive measures of the main structural deformation (geometric failure) of the steel wire rope. In the process of using the steel wire rope, various deformation factors must be considered comprehensively to prevent the deformation of the steel wire rope in time.
1 Introduction
Since the birth of the steel wire rope, it has been widely used in port machinery, especially in ship unloading machinery, with high strength, wear resistance, impact resistance and other good characteristics. However, due to the harsh working environment of the steel wire rope, it is often subject to corrosion by chemical substances and physical high-strength impact and wear, as well as man-made damage and destruction. As far as ship unloaders are concerned, most of the reasons for scrapping of wire ropes are wire breakage, strand breaking, wear and corrosion. But sometimes the steel wire rope will also have geometric deformation such as loose strands and wire drawing. Although such damage of the steel wire rope is relatively rare, the structural deformation will also bring serious economic losses and hidden safety risks. Therefore, it is necessary to analyze the mechanism of wire rope deformation and summarize the preventive measures.
2 Types of wire rope deformation
2.1 Wavy
The wave shape of the steel wire rope is the longitudinal axis of which appears in a spiral shape. This deformation may not affect the strength of the steel wire rope, but serious deformation will cause the steel wire rope to wear and break.
2.2 Cage distortion
This deformation occurs when the outer steel wire rope is disjointed or longer than the inner steel wire rope. Once this deformation occurs, it is scrapped immediately.
2.3 Strand extrusion
Generally, the appearance of this kind of deformation and cage distortion instruments shows the imbalance of the overall structure of the steel wire rope. Once such deformation occurs, it will be scrapped immediately.
2.4 Wire extrusion
This kind of deformation generally occurs on the side carrying the pulley, which is mainly caused by the sudden increase of the impact load. If the deformation is serious, the wire rope should be scrapped immediately.
2.5 Local kinks of the wire rope
Twisting is caused by the wire rope forming a loop and being pulled closer when it is impossible to rotate around its axis. This deformation will increase the wear and breakage of the wire rope. In severe cases, the wire rope will twist.
2.6 Wire Rope Bending
Most of this situation is caused by humans, especially when the wire rope is worn, the wire rope bends on the ground. Such deformation should be scrapped immediately.
In addition, the deformation of the steel wire rope also includes the deformation of the steel wire rope with a larger diameter, a smaller diameter, flattening, and wire drawing.
3 Stress analysis when the steel wire rope works
The ship unloader is a bridge type crane, and its main operating mechanism is a four-roller mechanism (that is, lifting opening and closing mechanism). The main actions are the opening and closing of the grab and the forward and backward movement of the trolley. The place where the wire rope is wound is the drum, pulley, grab and the connected rope sleeve (such as pear-shaped rope sleeve), as shown in the following figure:
Therefore, according to the use and load of steel wire rope, steel wire rope can be divided into support steel wire rope, traction steel wire rope, open and close steel wire rope and support steel wire rope. The stress of the steel wire rope is relatively complicated, and the specific analysis mainly includes tensile stress, bending stress when the steel wire rope bypasses the pulley, contact stress, squeezing stress, torsion force, friction force and so on. The following figure is a schematic diagram of the wire rope stress of the opening and closing rope winding system of the 800t / h ship unloader of Wuhu Huadian.
4 Analysis of the mechanism of wire rope deformation
Structural deformation occurs mostly in hemp core and fiber core wire rope. The main structural deformations are knotting, twisting of the rope core, loose strands and cage distortion. The following mainly studies the deformation mechanism of these aspects.
Combined with the experience accumulated at the work site of the ship unloader, the analysis of the causes of deformation has the following aspects: [
1. The wire rope itself rotates in the reverse direction. In the case of rotation in the reverse direction (the strands are loosened), the length of the multi-layer strands exceeds the length of the wire rope itself, and the "grown" strands are pushed together by the pulley or drum; On the wire rope twisted and shortened around the direction, the inner strands will also be pushed together under the action of the pulley or the drum, so that knots, loose strands and other deformations will also occur.
2. The twisting of the wire rope around its axis. The twisting around its axis is mainly because when the wire rope enters the pulley or drum at a deflection angle, it first contacts the side edge of the rope groove, and then rolls down and slides to the bottom of the rope groove. The greater the deflection angle, the greater the twisting angle of the wire rope. At the same time, the greater the lifting height of the grab, the greater the degree of twisting. In the multi-rate lifting system, the smaller the gap of the rope, the greater the tendency to twist. During this period, the steel wire rope is most prone to strand extrusion and loose stranding, resulting in a "bird cage" phenomenon.
3. The effect of impact load. Most of the impact load occurs when the grab suddenly rises, suddenly falls, opens the bucket, closes the bucket, and the car suddenly walks and stops. The impact load will not only produce a very large tensile stress on the wire rope, but also increase the degree of twisting of the wire rope itself. The drawing of the tension change of the grab wire rope is as follows, where the upper curve is the closed wire rope tension function curve, and the lower curve is the support wire rope tension function curve. It can be seen from the figure that when the grab is closed and the lifting wire rope is not tensioned in time, the closed wire rope is subjected to the maximum tension:
At this time, the tension on the wire rope is much greater than the tension on the wire rope. The increase in tension will definitely increase the degree of twisting of the wire rope around its axis, which will increase the deformation of the wire rope, such as strand extrusion and loose strands. The probability of occurrence.
4. Unreasonable mechanical structure. The unreasonable mechanical structure will produce great bending stress, contact stress, extrusion stress and frictional force on the wire rope. For example, the choice of the diameter of the drum, if the diameter of the drum is small and the diameter of the wire rope is unchanged, the ratio between the two will decrease, the bending stress on the wire rope will increase, and the fatigue damage of the wire rope will increase, The probability of deformation will increase, and eventually the life of the wire rope will be shortened. In this way, the pulley, drum and wire rope can not meet the working level requirements of the organization. Therefore, a reasonable mechanical structure size must be selected during the mechanical design process.
5. The production of steel wire rope sleeves (such as pear-shaped rope sleeves) is unqualified. Rope sleeves are tools for connecting between steel wire ropes and between steel wire ropes and chains. The quality of the rope sleeves and the degree of fixing of the steel ropes in the rope sleeves will affect the life of the steel wire ropes. The pear-shaped rope sleeve of the ship unloader is complicated to bear. It not only bears the vertical tension of the wire rope, but also withstands the impact force when the wire rope joint enters the pulley or drum, and withstands the lateral force of the self-rotation of the wire rope when it has "air". . If the steel wire rope inside the pear-shaped rope sleeve is not fixed well or the rope sleeve itself has cracks, the steel rope will rotate rapidly or the rope sleeve will break when it enters or exits the pulley. For example, the 800t / h ship unloader of Wuhu Huadian Coal Wharf, the rated lifting weight of the grab is 200KN, when the tension of each steel wire rope reaches 50KN, once the pear-shaped rope sleeve breaks or the internal steel wire rope is loose, the steel wire stress will be released immediately, resulting in huge The impact is very dangerous.
6. An error occurred when wearing the wire rope. When wearing a wire rope on a four-drum, you must pay attention to the wire rope model, specifications, rotation and other elements marked on the drawing. If the rotation of the tooth pattern on the drum is left-handed, then the rotation of the wire rope on the drum must be Right-handed; similarly, if the direction of the tooth pattern of the reel is right-handed, then the direction of rotation of the wire rope on the reel must be left-handed. If there is an error in the rotation direction of the wire rope put on, so that in the subsequent work of the ship unloader, the wire rope will enter the drum along the direction of the tooth pattern of the drum, and the wire rope will rotate around its own axis. The reverse rotation of its own strands will cause deformations such as loose strands and cage distortion.
7. Unreasonable selection of wire rope.
(1) When selecting the wire rope, it must be selected in accordance with the current new wire rope standard. There are problems with the selection criteria for steel wire ropes, which may cause major safety accidents and unnecessary economic losses. For example, in the new standard, the use grades of steel wire ropes are general steel wire ropes and important steel wire ropes, while in the old standards, the use grades of steel wire ropes are divided into No. 1 steel wire ropes and special steel wire ropes; There are only three levels of codenames, which are relatively crude.
When selecting wire rope, the recommended principles are as follows:
1) When lifting a non-guided heavy object once or when lifting a non-guided heavy object multiple times at a larger height, use a non-rotating wire rope.
2). When the guided heavy lifting is performed once or when the guided heavy lifting is performed multiple times at a small height (such as driving), when the left and right rotating steel ropes are used in pairs, ordinary steel ropes can be selected. [
For single-layer winding and non-rotating steel wire rope, the above principles must be strictly followed, otherwise it will cause serious structural deformation of the steel wire rope; for multi-layer steel wire rope winding, the rotation direction of the steel wire rope is determined by the rotation direction of the drum rope groove, one side is the next The first layer lays the foundation, and the friction and pressure between the multiple layers of steel wire ropes around the reel are large, and it is easy to produce disordered ropes. Here, pay attention to the steel wire ropes that are slightly smaller than the rope groove pitch and the diameter of the rope groove.
(2) The performance of the selected wire rope is unreasonable. The contact form of the steel wire rope in the strand is a bit contact type, line contact type and surface contact type. Now point-contact wire ropes are basically not used on ship unloaders, and are replaced by wire-contact wire ropes. At the same time, according to the different properties of the steel wire material and the different core materials, the steel wire rope is divided into soft steel wire rope and hard steel wire rope. Therefore, when selecting the steel wire rope, the steel wire rope must be reasonably selected according to the performance of the ship unloader and the specific parameters of the steel wire rope. If the selected steel wire rope is slightly hard, it will cause the steel wire rope to have poor toughness, and it is easy to produce wear and fatigue deformation; on the contrary, if the steel wire rope is too soft, it will cause the steel wire rope to easily entangle and deform. Now the non-rotating wire rope has been widely used. The mechanism is that the torsional moment of the rope and the strand are opposite and equal in magnitude; the imported non-rotating wire rope is different. The principle is to make the direction of rotation of the rope core opposite to the direction of the rope itself. When the force is applied, the torque generated by the rope core is equal and opposite.
8. The influence of human factors. This is mainly the wire rope damage caused by the unstandard operation of the ship unloader driver. Like the bending caused by the scratch of the wire rope, the wire rope is crushed by a heavy object into a flat shape and so on.
5 Measures to prevent deformation of wire rope
5.1 Reasonable choice of wire rope diameter
There are two ways to select the wire rope diameter:
1) Selection coefficient method
2) Safety factor method
Among them, the material, rotation direction, rope core texture and structure of the wire rope should be selected reasonably. Among them, the wire contact wire rope should be selected, and the wire rope with anti-rotation ability should be selected at the same time.
5.2 The selection of wire rope must be based on the current new standards for wire rope.
5.3 The steel wire rope sleeve (such as a pear-shaped head rope sleeve) must be selected reasonably. When fixing the steel wire rope to the rope sleeve, a formal manufacturer must be selected for processing and strict inspection after production must be done to ensure that the steel wire rope is firmly inside the rope sleeve , Not loose.
5.4 When wearing the reel wire rope, you must work strictly in accordance with the drawings. The wire rope must be seated in the same number. During this period, it must be ensured that the wire rope does not appear artificial or knotted on the ground. After putting on the wire rope, let the single drum wire rope rotate back and forth 2 to 3 times with no load to release the residual torque of the wire rope itself. Do not fix the connection of the two free ends of the wire rope before threading the rope. When the various parts of the wire rope are naturally in place and the kinks of the wire rope are minimum, the two free ends of the wire rope are connected and fixed. At the same time, when installing the wire rope, the left-hand rule and the right-hand rule must also be followed. The wire rope must be wound according to the direction of tight twisting rather than loose twisting, otherwise the wire rope is prone to "twist and loose strands" during use. Seriously affect the life of wire rope.
5.5 The structure of the drum and pulley must be reasonable. Within the scope of the technical requirements, the diameter of the pulley and drum can be slightly increased to reduce the bending stress on the wire rope.
5.6 The ship unloader driver should operate in a standardized and safe manner, and do not operate savagely. Reduce the deformation of the wire rope caused by human factors.
5.7 In order to improve the service life of the steel wire rope, in the steel wire rope winding system, the number of bending of the steel wire rope is reduced as much as possible, especially the number of reverse bending of the steel wire rope. The degree of steel wire fatigue damage caused by the reverse bending is twice that of the positive wire rope. [
5.8 The steel wire rope should be strengthened and maintained. The steel wire rope that needs to be lubricated must be lubricated.
5.9 Regularly inspect the steel wire rope, remove the damage to the steel wire rope in time, and eliminate hidden dangers.
6 Conclusion
The above analyzes the main deformation form and mechanism of the steel wire rope and the preventive measures. It can be seen that there are many reasons for the deformation of the steel wire rope, and the causes are interlaced and complicated. Many deformation problems are likely to occur at the same time. When considering the problem, it is necessary to be comprehensive. If necessary, use a testing instrument to test, specifically analyze the internal mechanism of the steel wire rope problem, and grasp The key to the problem is to take reasonable measures in a timely manner. Once the wire rope is seriously deformed, it should be scrapped and replaced in time.
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