What are the precautions for wire rope testing?

Practice has proved that the working conditions of the wire rope have a great impact on its life. Because the wire rope generally moves around a variety of pulleys, and bears a lot of traction and friction between the rope and the rope, it is often bent and deformed during work. It directly affects the service life of the wire rope.

The steel wire rope is subjected to the action of alternating stress during use, coupled with the influence of its own structural characteristics and the physical properties of the steel, the steel wire will undergo elastic elongation and deformation under the action of axial stress. Although the deformation of the wires in the strands can be regarded as synchronous, there is a slight dislocation between the strands. Therefore, the steel wire in the wire rope is actually in the fretting wear environment, and the fretting fatigue can also be regarded as the result of the joint action of fretting wear and fatigue, which is the main reason for the failure of the wire rope.

Fatigue is another main reason for the failure of steel wire ropes. Under the action of high alternating contact stress, fatigue cracks will occur on the friction surface of the steel wire, and the cracks will continue to expand, eventually causing metal particles to fall off the metal surface to form many pitting corrosion, resulting in fatigue Wear until the interconnection causes fatigue fracture of the wire.

In addition, the wear and corrosion of the surface of the steel wire inside the steel wire rope often occur together, and will affect each other, and their alternating action accelerates the wear and aging between the steel wires.

For the common fretting fatigue phenomenon, no expansile microcracks will be generated in the early stage of delamination. With the continuation of the delamination stage, the delaminated material continues to increase and oxidize, and the size of the erosion pit also increases, and the bottom of the erosion pit will gradually become low-lying and uneven and produce large plastic deformation, resulting in large stress concentration. , resulting in the initiation of fatigue cracks at the bottom of the pit.

The structure of the steel wire rope and the complexity of the force during use make the fretting state very complicated. Under the action of bending stress, the surface scratches on the steel wire are very likely to evolve into fatigue micro-cracks and expand along the radial direction of the steel wire, thereby reducing the speed of the steel wire rope. service life.

The existence of friction between the steel wires inside the steel wire rope causes fretting damage on the surface of the steel wire. Under the action of the friction force, the surface of the steel wire gradually undergoes plastic deformation, work hardening, scratches, fretting wear and corrosion, resulting in the failure of the steel wire rope. .

The initiation and expansion of fatigue micro-cracks have a direct causal relationship with the force. When in use, the steel wires in the steel wire rope should simultaneously bear the tensile stress, the contact stress and friction between the steel wires, the torsional stress, the bending stress during elastic deformation around the pulley, and the friction with the pulley, etc.

Stress concentration will promote the initiation and expansion of fatigue micro-cracks, and the increase in bending stress during use will also increase the probability and rate of fatigue micro-cracks expanding radially to the steel wire. Therefore, avoiding stress concentration and reducing bending stress can slow down fatigue fracture and prolong the service time of the wire rope.

Through the split inspection of the failed wire rope and the analysis of the fracture, there are different degrees of wear spots on the surface of the inner wire of the failed wire rope, and the obvious spots are accompanied by cracks. Due to the large number of wear points on the inner layer of the wire rope and the large wear depth, the inner layer often breaks on the inner layer and does not appear immediately on the outer layer. Many failed wire ropes have basically no damage on the outer surface of the surface, but the inner layer is worn and the wire is broken more seriously, so the occurrence is relatively hidden, and it cannot be discovered in time without professional testing.

It should be noted that although the failure analysis of the steel wire rope needs to test the mechanical properties of the steel wire rope, the performance of the rope core and grease, the chemical composition of the split steel wire and the performance of the coating layer, etc., but only passing the test does not necessarily meet the needs of the failure analysis of the steel wire rope. . If necessary and with corresponding conditions, on-site surveys should also be carried out, and necessary inspections, inquiries, data retrieval, measurement, photography, and recording of the following matters should be carried out:

1. The time, place, use environment, failure process and abnormal phenomena before failure, etc. of failure;

2. Characteristic investigation and description of on-site wire rope;

3. Technical documents such as wire rope product quality certificate, acceptance inspection report, installation record;

4. Design specifications or regulations for the use of wire rope products;

5. Records of daily use, inspection, maintenance and upkeep of wire rope;

6. Specifications, models, failure characteristics, etc. of the wire rope;

7. The characteristic parameters and status quo of the reel, roller skating, support roller, connection and other devices in contact with the wire rope.

After understanding the failure analysis of the wire rope, it is possible to better control the state of the wire rope in the process of use, find out the existing problems in time, and ensure the safety of use.