In recent years, with the gradual increase of large-scale modern mines, the use of advanced equipment has also increased. For safe production, how to use and maintain them correctly is particularly important. Here, the analysis of the failure form and cause of the friction pulley lining has certain guiding significance for the use and maintenance of the friction lining.

There are many types of friction linings. Among them, GDM326 friction linings are widely used. They can be used as multi-rope friction linings for cold rolling mills and rail car friction linings, as well as monkey car linings, rope linings, wheel linings, and tube linings. Pads, winch pads, lifter friction pads, winch pads, etc.

2 Performance parameters of friction pads

2.1 Friction coefficient

The coefficient of friction is the most important parameter of the friction pad, and its size determines the lifting capacity of the hoist and the safe and stable operation. Different materials, different dual friction pairs,The dual friction pair is composed of a steel wire rope and a gasket.

It is formed under the condition of the medium. Therefore, the friction coefficient of the hoist is determined by the combined action of the gasket, the steel wire rope and the 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. However, when the steel wire rope is in contact with the gasket, the deformation can absorb the kinetic energy generated by the vibration, jitter and torsion of the wire rope, and reduce the vibration of the equipment. At the same time, the deformation of the liner can increase the contact area between the liner and the wire rope and increase the friction. The triangular strand and the elliptical strand wire rope developed in recent years are designed to increase the contact area between the wire rope and the pad.

2.3 Compressive strength

The working state of the friction pad determines that the pad should have a certain compressive strength. The design specification points out that the maximum working pressure of the pad under the normal working state of the hoist is below 3 MPa, taking into account special circumstances, such as emergency braking , The working pressure of the liner increases exponentially.

2.4 Anti-aging

Rubber and plastic materials have a fatal weakness, that is, aging. Once the material is aging, the mechanical performance will drop sharply. If it is not replaced in time, there will be major accidents. For example, polyurethane aging occurs after two years of normal storage. Research and use show that the performance index of the friction pad made of GDM326 material has hardly changed regardless of long-term use or long-term storage, and its anti-aging performance is good.

2.5 Environment

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

3 Failure modes of friction pads

3.1 Wear

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

(1) Sliding wear

The wire rope and the liner are relatively displaced, and the rough surface of the steel wire rope will pull out traces on the liner surface, that is, the liner will produce 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 mining hoist, the steel wire rope and the liner are in frequent contact. Under the action of alternating pressure, the surface of the high-strength steel wire rope will adhere to the tiny liner material, that is, the liner will produce adhesive wear.

Adhesive wear is related to the bonding force between material molecules. If inorganic substances are added to the material, the continuity of the material will be destroyed, the intermolecular bonding force will be reduced, and adhesive wear will increase. If the selection of the friction liner material satisfies the lifting rotation, sliding wear and adhesive wear are normal losses.

(3) Non-uniform wear

Rope groove wear is inconsistent: During the use of the gasket, the working condition of each rope groove should be the same, and the wear of the rope groove should be the same. If there is a difference between the wear of a certain rope groove and the other, it can be judged that the working condition of a certain wire rope has changed. At this time, the wire rope should be adjusted, and the rope groove should be adjusted at the same time.

Rope groove wear deviation: The entire rope groove is elliptical. The reason is that a certain section of the wire rope is abnormal. The abnormality of the wire rope should be eliminated and the rope groove should be adjusted at the same time.

3.2 Pitting spalling

The equipment operates normally, and the pressure of the liner is below 3 MPa. This pressure value is far less than the compressive strength of the liner and will not cause damage to the liner. There is a grease medium between the wire rope and the liner, and the medium is mixed with other hard points such as coal ash. These hard points will be embedded in the liner under suitable conditions, forming pits on the surface of the liner, and the pits are in the subsequent particles. It will expand under multiple actions, and then the grease will enter the pit. At this time, the grease in the pit will generate a lot of pressure. When the pressure is stronger than the material's bearing capacity, it will be generated at the weak part of the material, that is, the edge of the pit. crack. After multiple actions, the crack expands, and finally peeling occurs, 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 increases and the time is shortened. The elasticity and toughness of the material determine the speed of pitting and spalling. For materials with good elasticity, the pits will recover quickly after the external force is removed. That is to say, when the pits are formed, the particles will act more frequently; with good toughness Material, the speed of crack growth is slow. Therefore, similar materials have high hardness, poor fatigue resistance and poor use effect.

Pitting spalling damages the liner greatly and is the main reason for the early failure of the liner. Once it occurs, it will not only accelerate the loss of the rope groove material, but also cause the material performance at a certain depth at the bottom of the rope groove to drop sharply. This phenomenon should be done as much as possible. Avoid, once it happens, remove excess grease and impurities between the wire rope and the surface of the pad as soon as possible.

3.3 drop block

The liner breakage usually occurs at the edge of the rope groove. There are two main reasons. One reason is the aging of the material; the other reason is that the material is subject to greater alternating stress.

In the first case, since the material properties have undergone fundamental changes, the continued use of the gasket is in great danger and should be replaced immediately.

In the second case, the alternating stress is caused by the mismatch between the diameter of the rope groove and the diameter of the wire rope. When the diameter of the wire rope is greater than the diameter of the rope groove, when the wire rope enters the rope groove, first squeeze the side of the rope groove, especially the sharp corner of the rope groove, and the squeezing force is the largest, and tightly wrap the wire rope, the wire rope leaves the rope groove, the sharp corner At the same time, the squeezing force disappears. After multiple actions, the material structure will be fatigued. When the structural force of the structure is less than the externally applied squeezing force, cracks will occur at the sharp corners and will break after propagation. The diameter of the wire rope is equivalent to the diameter of the rope groove. When the depth of the rope groove is greater than the radius of the rope, after the wire rope enters the rope groove, the liner will deform under the pressure of the liner. The distance between the openings should be less than the diameter of the rope. There will be a certain impact force on the sharp corners of the rope groove, and the cyclic effect will also cause block loss. If the balance of the equipment is not well adjusted, the wire rope will shake or vibrate when the hoist is running. The kinetic energy generated by jitter and vibration, acting on the gasket for a long time, will also cause the weak edges of the gasket groove to fall off. However, the block loss in this case varies with the shaking degree of the wire rope, and the size of the block loss in each groove is different, and it may also be a block in a circle of the rope groove.

Once the lumps of the liner fall off, first determine what caused it. If all the liners fall off evenly, the material should be analyzed first; if non-uniform lumps occur, mechanical reasons should be dominant. The lumps caused by the mechanical action of the steel wire rope usually do not affect the overall quality of the gasket and can be used continuously; if the lumps are caused by aging, they must be replaced immediately.

4 Conclusion

Through the research on friction pads, it has certain guiding significance for the maintenance and use of friction inserts. At the same time, it provides a strong guarantee for the improvement of technical performance and safe operation of large and medium-sized mines.