Basic knowledge questions about wire rope scrapping [Daily question 20090415]

1. The safety level of wire rope use is determined by the following items: Nature and quantity of broken wires ； Broken wire at rope end ； localized collection of broken wires ； Increase rate of broken wires ； Strand breaks ； Reduction in rope diameter includes cases caused by damage to the rope core ； Reduced elasticity ； external wear ； External and internal corrosion ； deformation ； Damage due to heat or arcing ； The rate of increase in permanent elongation. 3. If the entire rope strand breaks, the steel wire rope will also be scrapped. 4. The wear of the steel wire surface of the outer strand of the steel wire rope is caused by its contact and friction with the rope groove of the pulley and drum under the action of pressure. 　Insufficient or incorrect lubrication and the presence of dust and grit during lubrication can increase wear. Wear reduces the cross-sectional area of ​​the wire rope and reduces its strength. When the diameter of the wire rope is reduced by 7% or more relative to the nominal diameter, the wire rope should be scrapped even if no broken wire is found.

Standards for Scraping Steel Wire Ropes When one of the following conditions occurs, the wire rope should be scrapped: (1) When the number of broken wires in a wire rope reaches 10% of the total number of wires in one twist length (5% when the broken wires are concentrated in a certain strand), it should be scrapped. For example, the number of broken wires in the 6×37 type exceeds 22 wires (11 wires in a certain strand). ； (2) The flattened surfaces of the wire ropes are almost connected, the strands are slightly flattened and the wire rope is obviously thinner. ； (3) The entire strand breaks ； (4) When there are deep pits on the surface of the wire rope, serious corrosion and the wire rope is quite loose ； (5) The diameter of the wire rope increases or decreases locally (related to changes in the rope core) ； (6) There is a rope core extruded in the entire length of the wire rope, accompanied by protrusions of the nearby wire rope. ； (7) When the steel wire rope is seriously kinked, bent, brittle, or cracked ； (8) When the wear of the outer wire rope reaches 40% of the single wire diameter ； (9) When the diameter of the wire rope is reduced by 10% relative to the nominal diameter

It depends on the frequency of use. If it is used frequently, it should be replaced every six months to one year. Do not wait until various symptoms appear.

The wire rope scrapping standards are excerpted from "Practical Specifications for Inspection and Scraping of Wire Ropes for Hoisting Machinery" (GB5972-86) 2.5 Scraping Standards 2.5.1 Nature and Number of Broken Wires The overall design of the lifting machinery does not allow the wire rope to have an infinite life. For 6-strand and 8-strand steel wire ropes, wire breakage mainly occurs on the surface. The situation is different for multi-layer wire ropes (typical multi-strand structures). Most of the broken wires in this type of wire rope occur internally, so they are "invisible" breaks. The following table takes these factors into account and therefore, when considered in conjunction with the factors in clauses 2.5.2 to 2.5.11, is applicable to wire ropes of various constructions. 2.5.2 Broken wires at the rope end. When broken wires occur at or near the rope end, even if the number is small, it indicates that the stress in this part is very high. It may be caused by incorrect installation of the rope end, and the cause of the damage should be identified. If the rope length allows, the broken wire should be cut off and reinstalled properly. 2.5.3 Local aggregation of broken wires If the broken wires are close together and form a local aggregation, the wire rope should be scrapped. If such broken wires are gathered in a rope length less than 6d, or 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. 2.5.4 Increase rate of broken wires In some usage situations, fatigue is the main cause of wire rope damage. Broken wires only begin 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 increase rate of broken wires, the increase in broken wires should be carefully inspected and recorded. It was found that this "law" can be used to determine the future scrap date of the wire rope. 2.5.5 Rope strand breakage If the entire rope strand breaks, the wire rope should be scrapped. 2.5.6 Reduction in rope diameter due to damage to the rope core When the fiber core of the steel wire rope is damaged or the steel core (or internal rope strands in a multi-layer structure) breaks, resulting in a significant reduction in rope diameter, the steel wire rope should be scrapped. Minor damage, especially when the stresses in all strands are well balanced, may not be apparent by usual inspection methods. However, this situation will cause the strength of the wire rope to * * reduce. Therefore, if there are any signs of minor internal damage, the inside of the wire rope should be inspected to identify it. Once damage is confirmed, the wire rope should be scrapped. 2.5.7 Reduced elasticity Under certain circumstances (usually related to the working environment), the elasticity of the wire rope will be significantly reduced, and it will be unsafe if it continues to be used. The reduced elasticity of the wire rope is difficult to detect. If the inspector has any doubts, he should seek the advice of a wire rope expert. However, reduced elasticity is usually accompanied by the following phenomena: a. Reduced rope diameter ； b. Wire rope lay length elongation ； c. Due to the mutual compression of each part, there is a lack of space between the steel wires and the rope strands. ； d. Fine brown powder appears in the recesses of the rope strands ； e. Although no broken wire was found, the wire rope was obviously not easy to bend and the diameter decreased much faster than if it were simply caused by wire wear. This situation will cause sudden fracture under the action of dynamic load, so it should be scrapped immediately. 2.5.8 Two situations of wear caused by external and internal wear: a. Internal wear and pitting are caused by the friction between the individual rope strands and the steel wires in the rope, especially when the steel 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 rope groove of the pulley and drum under the action of pressure. This phenomenon is particularly obvious at the contact point between the steel wire rope and the pulley when the hoisting load accelerates and decelerates, and appears as the outer steel wire being ground into a flat shape. Insufficient or incorrect lubrication as well as the presence of dust and sand can increase wear. Wear reduces the cross-sectional area and strength of the wire rope. When the wear of 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 relative 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 likely to occur in marine or industrially polluted atmospheres. It not only reduces the metal area of ​​the wire rope and thus reduces the breaking strength, but also causes surface roughness from which cracks begin to develop and accelerates fatigue. Severe corrosion can also cause a reduction in the elasticity of the wire rope. 2.5.9.1 External Corrosion Corrosion of external steel wires can be observed with the naked eye. When deep pits appear on the surface and the steel wire is quite loose, it should be scrapped. 2.5.9.2 Internal Corrosion Internal corrosion is harder to detect than the external corrosion that often accompanies it. However, the following phenomena can be identified: a. Changes in wire rope diameter. The diameter of the wire rope usually decreases at the bend around the pulley. However, for the steel wire rope in the stationary section, the diameter of the steel wire rope is often increased due to rust accumulation on the outer strands. b. The gap between the outer strands of the steel 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 inspected internally by a competent person. If serious internal corrosion is confirmed, the wire rope should be scrapped immediately. 2.5.10 Deformation: The wire rope loses its normal shape and produces visible deformities, which is called "deformation". This deformed part (or deformed part) may cause changes, which will lead to uneven stress distribution inside the wire rope. The deformation of the wire rope can be distinguished from the appearance and can be mainly divided into the following types:: 2.5.10.1 Wave shape (see picture) The deformation of the wave shape is: The longitudinal axis of the wire rope is in the shape of a spiral. This deformation does not necessarily lead to any loss of strength, but if the deformation is severe, it will cause bounce and irregular transmission. Over time, it will cause wear and tear. When wavy shapes appear, within the range of the wire rope length 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 deformation of the wire rope. 2.5.10.2 Cage Distortion This deformation occurs in wire ropes with a steel core. This deformation occurs when the outer strands become detached or become longer than the inner strands. Wire ropes with cage distortion should be scrapped immediately. 2.5.10.3 Strand extrusion is often accompanied by cage distortion. Extruded strands indicate an unbalanced wire rope. Wire ropes with extruded strands should be scrapped immediately. 2.5.10.4 This kind of deformation of steel wire extrusion is that a part of the steel wire or steel wire bundle arches to form a ring on the side of the steel wire rope carrying the pulley groove. This deformation is often caused by impact loading. If the 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 it may affect a considerable length of wire rope. The increase in rope diameter is usually related to the distortion of the rope core (for example, in special environments, the fiber core expands due to moisture). The inevitable result is that the outer rope strands are unbalanced, resulting in incorrect positioning. Wire ropes with severely enlarged rope diameters should be scrapped. 2.5.10.6 Kink A kink is a deformation caused by a wire rope being stretched in a loop without the possibility of rotating about its axis. The result is uneven lay length, causing extra wear. In severe cases, the wire rope will be twisted, leaving only a very small part of the wire rope's strength. Severely kinked wire ropes should be scrapped immediately. 2.5.10.7 Local reduction in rope diameter. Local reduction in wire rope diameter is often related to the breakage of the rope core. Special care should be taken to check whether there is such deformation at the end of the rope. Wire ropes whose rope diameter is severely reduced locally should be scrapped. 2.5.10.8 Partially flattened The partially flattened wire rope was caused by a mechanical accident. In severe cases, the wire rope should be scrapped. 2.5.10.9 Bending Bending is the angular deformation of the wire rope caused by external influences. Such deformed wire ropes should be scrapped immediately. 2.5.11 Damage caused by heat or arc. When the steel wire rope has undergone special heat and its appearance shows an identifiable color, the steel wire rope should be scrapped. (1) There are two ways to connect steel wire ropes: small connection method and large connection method. The small connection method is within the range of the joint, where the strands of the two ropes are brought together, so the rope ends become thicker and the length of the joint is shorter. The large connection method is to chop the strands of the two rope heads in half, and then plug the two rope heads together. The length of the joint is longer. The thickness of the rope connected by this method remains unchanged, and the position of the joint cannot be seen on the surface. When the steel wire rope is used as a sling, it needs to be manually connected before it can become a sling, commonly known as the small connection method. Wire rope plugging methods can generally be divided into 5 types: That is, one into one plugging method, one into two plugging method, one into three plugging method, one into four and one into five plugging method. The most commonly used is the one-into-three plug-in method, and the one-into-five plug-in method is mostly used for small knots of steel wire ropes. (2) When the steel wire rope is braided and fixed, the braiding length shall not be less than 20 times the diameter of the steel wire rope, and shall not be shorter than 0.3 meters. The braided part should be bundled with fine steel wires. (3) When the steel wire rope is fixed with rope clamps, the number shall not be less than 3, and the distance between the last clamp and the rope end shall not be less than 0.14 meters. The rope clamp splint should be on the side that bears the force. The "U"-shaped bolt must be at the end of the wire rope and must not cross forward or backward. The clamp should be tightened so that the diameter of the two ropes is flattened by about 1/3. After the rope clamp is fixed, the steel wire rope should be tightened again after it is stressed. Rope card matching table: Wire rope diameter mm 10 10~20 21~26 28~36 36~40 Minimum number of rope clamps (pieces) 3 4 5 6 7 Rope clamp spacing mm 80 140 160 220 240 4. Precautions for the use of wire ropes (1) The steel wire rope should be inspected before use. Check scope: Check the degree of wear, corrosion, stretching, bending, deformation, fatigue, broken wires, and exposed rope core of the wire rope to determine its safe lifting capacity (including scrapping). (2) Maintenance precautions: (1) The service life of the wire rope has a great relationship with the method of use. Therefore, it should be used according to regulations. Dragging and throwing are prohibited. Overloading is not allowed during use. The wire rope is not allowed to bend at an acute angle. It is not allowed to change the lifting speed sharply to avoid impact loads. ； (2) If there is rust or dirt on the wire rope, use a wire brush to remove it and apply oil. ； (3) The steel wire rope should be oiled once every 4 months of use. When oiling, it is best to use hot oil (about 50℃) to soak the rope core, and then wipe off the excess grease. ； (4) After the wire rope is coiled, it should be placed in a clean and dry place and must not be stacked to prevent sprains. ； (5) The end of the steel wire rope should be tied tightly with steel wire or welded with an alloy with a low melting point. It can also be tightened with an iron hoop to prevent the rope end from loosening. ； (6) During use, if there are oil droplets squeezed out from the surface of the steel wire rope, it means that the steel wire rope has been subjected to considerable force. At this time, the load should be stopped and inspected, and a new steel wire rope should be replaced if necessary.

According to GB05972-2006 "Specifications for Inspection and Scraping of Steel Wire Ropes for Cranes" 1. The safety of wire rope use is determined by the following items: Nature and quantity of broken wires ； Broken wire at rope end ； localized collection of broken wires ； Increase rate of broken wires ； Strand breaks ； Reduction in rope diameter includes cases caused by damage to the rope core ； Reduced elasticity ； external wear ； External and internal corrosion ； deformation ； Damage due to heat or arc action ； The rate of increase in permanent elongation. 2. The reduction of rope diameter caused by damage to the rope core can be caused by the following reasons:: 1. Internal wear and indentation ； 2. There is internal wear caused by friction between each strand of the wire rope and the steel wire, especially when the wire rope is subjected to bending. ； 3. Damage to fiber rope core ； 4. Fracture of steel wire core ； 5. Breakage of internal strands in a multi-layered strand structure. If these factors cause the actual measured diameter of the wire rope to decrease by 3% (for torsion-resistant wire ropes) or 10% (for other wire ropes) relative to the nominal diameter, the wire rope should be scrapped even if no broken wires are found. 3. If the entire rope strand breaks, the wire rope will also be scrapped. 4. The wear of the steel wire surface of the outer strand of the steel wire rope is caused by its contact and friction with the rope groove of the pulley or drum under the action of pressure. Insufficient or incorrect lubrication and the presence of sand, dust and particles can increase wear. Wear reduces the cross-sectional area of ​​the wire rope and reduces its strength. When the diameter of the wire rope is 7% or more smaller than the nominal diameter, the wire rope should be scrapped even if no broken wire is found.