1. Problem posing

Pinggang Mine is a large mine with an annual design production capacity of 1 million tons. It is mined in two levels. A set of JK - 2.5/20E single rope tandem hoist winch is equipped between the first and second levels. The model of the hoist wire rope is 6 △ (34) - 28 - 1670 smooth. Due to the lack of understanding of the steel wire rope, a broken rope racing accident occurred shortly after the winch was running; After being used for 10 days, the new steel wire rope with the same model was found to have uniform pitting pits on its surface, which developed rapidly; In addition, similar problems also exist in the management of other winch wire ropes. In view of the above accidents and phenomena, we, together with the mine engineering technicians, carefully analyzed and studied the damage of the wire rope, obtained some regular understanding, and made targeted suggestions, which promoted the safety management of the mine hoisting transportation.

2 Mechanical damage of wire rope

Mechanical damage is one of the main damages of wire rope, including wear, fatigue, trauma, etc.

3 Analysis and protection of mechanical damage

3.1 Wear

According to the wear mechanism, it can also be divided into the following types: the wear caused by the contact between the wire rope and the rope path, bottom plate, rope stopper and other objects during the use process is external wear, the wire rope section will be reduced, the wire on the outer surface will be smoothed, and the breaking load of the wire rope will be reduced. In practice, there are also single cycle wear and full cycle wear. The single cycle wear is worse than the full cycle wear, and uniform wear will be achieved in the full length, That is, all round wear. The surface damage of wire rope caused by vibration and collision is deformation wear, which is a local wear phenomenon. If the steel wire rope on the surface of the drum is impacted by other objects, the steel wire ropes are intertwined, knotted, or bitten, which will cause deformation and wear of the steel wire rope. This deformation and wear will be deformed due to local extrusion, and the cross section of the steel wire rope will extend to both sides at the extrusion point to form wings. Seen from the appearance, the width of the steel wire expands. Although the sectional area of the steel wire rope is not much reduced, the surface material of the steel wire at the local extrusion is hardened, and the wire is easy to break. After a long time, the deformed and protruding parts are often seriously worn, and the outer steel wire is also very easy to break. Moreover, the internal wear factor cannot be ignored: when the wire rope passes through the drum or pulley, all the loads it bears are pressed on one side of the wire, and the radius of curvature of each thin wire cannot be exactly the same. At the same time, due to the bending of the steel wire rope, each thin steel wire inside the steel wire rope will exert force on each other and slip. At this time, the contact stress between strands will increase, causing local indentation between adjacent strands. When repeated cyclic stretching and bending, stress concentration will occur in the deep recesses and they will be broken. How can we reduce all kinds of wear damage? In view of the above analysis, we have taken the following measures:

3.1.1 In order to avoid wear in one week, we regularly replace the winch

Wire rope ends, such as the winch, shall be worn evenly once a quarter.

3.1.2 The inclined shaft towline pulley is replaced by polyurethane towline pulley from cast iron to minimize rigid wear on the wire rope.

3.1.3 Try to avoid the wire rope from winding on the drum and suffering from other impacts.

3.1.4 The structural model of wire rope shall be correctly selected according to the specific working conditions. In order to prevent internal wear, most of the hoisting wire ropes in our mine have been replaced with wire contact wire ropes, and the point contact type has been abandoned. For special places, the contact wire ropes above are being considered.

3.2 Fatigue

The wire rope mainly bears the damage of bending, stretching, twisting, vibration fatigue, and elastic deformation caused by overload. The steel wire rope is repeatedly wound up and down through the pulley or drum, and countless times of bending will easily lead to fatigue of the steel wire, decline in toughness, and finally lead to wire breakage. The fatigue broken wire occurs on the outer steel wire at the side with the most severe bending degree of the strand. In general, the appearance of fatigue broken wire means that the wire rope has been close to the late use. The test shows that the bending fatigue life of wire rope is closely related to D/d ratio (i.e. the ratio of drum diameter D to wire rope diameter d), safety factor and wire rope structure. At the beginning and end of starting and braking, the changing tensile stress and frequent twisting and vibration of wire rope are also the causes of fatigue. Overload: In addition to the static loads such as load and dead weight, the wire rope will also be subject to dynamic loads caused by acceleration and impact. The wire rope will stretch slightly with the increase of load. When the load exceeds the strength limit, the wire rope may break. Even if the overload wire rope does not break, the safety factor will be greatly reduced, greatly shortening the service life.

For the analysis of fatigue, we have taken the following measures:

3.2.1 If conditions permit, increase the diameter of the drum and pulley as much as possible. In the main hoisting inclined roadway, the diameter of the drum cannot be increased, so the diameter of the roller of the rope stopper and the rope tugger is increased; For other occasions, the wire rope diameter and drum diameter shall be selected reasonably.

3.2.2 When arranging pulley layout, reverse bending of wire rope shall be avoided as far as possible. Experience has proved that the damage of reverse bending is about twice as much as that of the same direction bending, especially the main lifting rope of inclined roadway cannot be used for shunting through pulley.

3.2.3 The steel wire rope with good structure shall be selected as far as possible, such as WS, TX and other wires contacting the steel wire rope.

3.3 Trauma

The injury of the wire rope is nothing more than that it jumps out of the baffle plate on the drum in the chute of the pulley and is rolled by the tramcar. As a result, the wire rope is often scrapped due to local rolling damage. Moreover, wire rope kinking is also an important damage factor. Ordinary steel wire ropes have self rotation, especially new steel wire ropes. After being hung, tension is applied without breaking force, which often causes kinks. The direction of the twist is consistent with the rotation direction of the wire rope, which is called positive twist, and vice versa. After the steel wire is twisted and loaded for many times, only part of the rope core is exposed, and generally there is no broken wire. However, the test shows that the strength of steel wire rope will be significantly reduced after kinking damage. The strength of positive kinks is only 50% of the original strength. In severe cases, the strength will be reduced to only 10%~20% of the original. In order to prevent the wire rope from being injured, we suggest the mining party take the following measures:

3.3.1 Strictly enforce the operation procedures, strengthen the post responsibilities of operators, and adhere to the accident investigation system.

3.3.2 Improve the protection capacity of equipment and facilities, such as raising rope guard and setting rope guider.

3.3.3 The newly suspended steel wire rope shall be provided with a rotating device at its free end to achieve the effect of breaking the strength.

3.3.4 Non rotating steel wire rope shall be used for special occasions.

In addition, we have also taken some measures against the chemical corrosion of downhole wire rope to delay the service life of wire rope. Through the exploration and verification of the causes of wire rope damage, simple and feasible countermeasures are taken one by one on this basis, and relevant rules and regulations are formulated and enriched. Effective containment since full implementation

The occurrence of transportation accidents is improved, and the economic benefits are better improved. Taking Pinggang Mine as an example, since the main lifting rope was replaced with galvanized steel wire rope and the above other measures were taken, the service life of each wire rope was more than one year and a half, more than 8 times that before the measures were taken, which greatly improved the safety factor; In terms of economic benefits, it is estimated that over the same period (calculated as one and a half years), 600000 yuan will be saved directly for the mine. If other hoisting wire ropes are included, the amount will be more considerable.