In recent years, with the gradual increase of large modern mines, the use of advanced equipment is also increasing. In order to work safely, how to use and maintain correctly is particularly important. Here, the failure forms and causes of friction lining are analyzed, which has certain guiding significance for the use and maintenance of friction lining. There are many kinds of friction lining, among which GDM326 friction lining is widely used as the friction lining of cold rolling mill, multi rope friction hoist and rail car, as well as chairlift, rope liner, wheel liner, barrel liner, winch pad, winch friction lining, winch pad, etc.

2 performance parameters of friction lining

2. 1 friction coefficient

Friction coefficient is the most important parameter of friction lining. Its size determines the lifting capacity and safe and stable operation of the hoist. Different materials, different dual friction pairs, and the media between them are different. The friction coefficient reflected is also different. The friction coefficient on coal mine hoisting is a dual friction pair composed of steel wire rope and liner, which is formed under the condition of grease as the medium. Therefore, the friction coefficient of hoist is determined by the combined action of liner, steel wire rope and grease.

2.2 hardness

The hardness reflects the ability of the material to resist deformation. The hardness of non-metallic materials is much lower than that of steel, but when the steel wire rope is in contact with the liner, the deformation can absorb the kinetic energy generated by the vibration, shaking and torsion of the steel wire rope and reduce the vibration of the equipment. At the same time, the deformation of the friction lining can increase the contact area between the friction lining and the steel wire rope and increase the friction force. Triangular strand and elliptical strand wire rope developed in recent years are designed to increase the contact area between wire rope and liner.

2.3 compressive strength

The working state of the friction lining determines that the friction lining should have a certain compressive strength. The design specification points out that under the normal working state of the hoist, the maximum working pressure borne by the friction lining is below 3Mpa. Considering special circumstances, such as emergency braking, the working pressure borne by the pad increases exponentially.

2.4 aging resistance

Rubber and plastic materials have a fatal weakness, namely aging. Once the material is aged, the mechanical properties will decline sharply. If it is not replaced in time, there will be major hidden dangers of accidents. For example, polyurethane is aged after two years of normal storage. Research and use show that the friction liner made of GDM326 friction lining has almost no change in performance indicators, and has good anti-aging performance, regardless of long-term use or long-term storage.

2.5 environment

The environment, such as temperature, water, snow, ice and dust, has a great influence on the friction coefficient of the liner because it changes the medium state between the liner and the friction pair.

3 failure mode of friction lining

3.1 wear is divided into sliding wear, adhesive wear and non-uniform wear.

(1) Sliding wear

The relative displacement between the wire rope and the friction lining will cause the rough wire rope to pull out the groove on the surface of the friction lining, that is, the friction lining will be subject to sliding wear The longer the relative displacement distance, the more serious the sliding wear The occurrence of sliding wear is closely related to the friction coefficient of the material Under the same conditions, the higher the friction coefficient, the shorter the relative sliding distance and the smaller the sliding wear.

(2) Adhesive wear

During the operation of the hoist, the steel wire rope is in frequent contact with the liner. Under the action of alternating pressure, the surface of the steel wire rope with high strength will adhere to small liner materials, that is, the liner will produce adhesive wear Adhesive wear is related to the intermolecular adhesion of materials If inorganic substances are added to the material, the coherence of the material will be destroyed, the intermolecular adhesion will be reduced, and the adhesive wear will be intensified If the type selection of friction pad material Meet the normal operation of the hoist. Sliding wear and adhesive wear are normal losses

(3) Non uniform wear

Inconsistent wear of rope groove: during the use of gasket, the working state of each rope groove should be the same, and the wear of rope groove should be the same. If the wear of a rope groove is different from that of others, it can be judged that the working condition of a steel wire rope has changed. At this time, the steel wire rope should be adjusted, and the rope groove should also be adjusted. Rope groove grinding deviation: the whole rope groove is elliptical, which is caused by the abnormality of a section of steel wire rope. The abnormality of steel wire rope shall be eliminated, and the rope groove shall be adjusted at the same time.

3.2 pitting and spalling

The equipment operates normally, and the pressure borne by the liner is below 3Mpa, which is far less than the compressive strength of the liner and will not damage the liner There is grease medium between the steel wire rope and the liner, which is mixed with coal ash and other hard points. These hard points will be embedded into the liner under appropriate conditions and form pits on the surface of the liner. The pits will expand under the repeated action of subsequent particles, and then the grease will enter the pits. At this time, the grease in the pits will produce great pressure. When the pressure is greater than the bearing capacity of the material, cracks will occur at the weak part of the material, that is, the edge of the pits. After multiple actions, the crack expands and finally spalls, that is, the pit becomes larger and deeper, and finally becomes one piece. At the same time, the next cycle starts, and the cycle speed is accelerated and the time is shortened. The elasticity and toughness of materials determine the speed of pitting and spalling. For materials with good elasticity, when the particles are pressed in and removed by external force, the pits will recover quickly, that is to say, the pits will form and the particles will act more times; For materials with good toughness, the speed of crack propagation is slow. Therefore, similar materials have high hardness, poor fatigue resistance, poor use effect and great damage to the liner caused by pitting and peeling, which is the main reason for the early failure of the liner. Once it occurs, it will not only accelerate the loss of rope groove material, but also cause a sharp decline in material properties at a certain depth at the bottom of the rope groove. This phenomenon should be avoided as far as possible. In case of occurrence, the excess grease and impurities between the wire rope and the pad surface shall be removed as soon as possible.

3.3 block dropping

friction lining falling usually occurs at the edge of rope groove. There are two main reasons. One is the aging of materials; Another reason is that the material is subjected to large alternating stress. In the first case, because the material properties have changed fundamentally, there is a great danger in the continued use of the gasket, which should be replaced immediately. In the second case, the alternating stress is caused by the mismatch between the rope groove diameter and the wire rope diameter. When the diameter of the steel wire rope is larger than the diameter of the rope groove, when the steel wire rope enters the rope groove, first squeeze the side of the rope groove, especially the sharp corner of the rope groove. The steel wire rope is tightly wrapped. When the steel wire rope leaves the rope groove, the sharp corner is pulled outward, and the extrusion pressure disappears at the same time. After multiple actions, fatigue occurs in the material structure. When the structural force of the structure is less than the external extrusion force, cracks appear and expand at the sharp corners, and then fracture. The diameter of the steel wire rope is equal to the diameter of the rope groove. When the depth of the rope groove is greater than the radius of the steel wire rope, after the steel wire rope enters the rope groove, the liner will deform under the action of pressure, and the distance at the opening should be less than the diameter of the steel wire rope. When the steel wire rope leaves the rope groove, it will have a certain impact on the sharp corner of the rope groove, cyclic action and block falling. If the balance adjustment of the equipment is not good, the wire rope will shake or vibrate when the hoist is running The kinetic energy produced by shaking and vibration Long term action on the gasket will also cause the edge of the weak part of the gasket groove to fall off. However, the block falling in this case changes with the shaking degree of the steel wire rope. The size of the block falling in each groove is different, and the block falling in a circle of rope groove may also occur. Once the pad falls off, first judge what causes it. If all pads fall off evenly, first analyze the material; In case of non-uniform block falling, mechanical reasons shall prevail. The falling block caused by the mechanical action of the steel wire rope usually does not affect the overall quality of the pad and can continue to be used; If it is caused by aging, it must be replaced immediately.