Common faults and solutions of head sheave wheel of multi rope friction hoist

The floor type multi rope friction hoist is an important transportation equipment in mining. The core component, the head sheave wheel device, supports and guides the hoisting wire rope. Its safety and reliability have a great impact on the safety production of the mine.

The head sheave wheel device is mostly installed on the derrick in the open air and works under low speed and heavy load, frequent starting, repeated reversing, acceleration and deceleration, braking and stopping conditions. The load it bears is very large, especially when starting, accelerating and decelerating, braking and stopping, because of the impact, the load it bears greatly exceeds the maximum static tension of the hoist. The main characteristics of the working condition of the head sheave wheel are large working load, bad service environment and difficult maintenance. With the wide use of the floor type multi rope friction hoist, the head sheave wheel device has also become one of the components with high failure rate of the hoist. Common failure forms include abnormal noise of the head sheave wheel device, shearing of the connecting bolts of bearing pads, serious wear of bearing pads, broken spokes, etc.

1 Structure overview of head sheave wheel

The structure of head sheave wheel device of multi rope friction hoist is shown in Figure 1, which is mainly composed of head sheave wheel shaft, fixed wheel, traveling wheel, bearing bush, bearing seat, main bearing, head sheave wheel liner and clamp. One of the wheels is a fixed wheel, and the others are traveling wheels. The fixed wheel is connected with the head sheave wheel shaft with a flat key; The inner hole of the traveling wheel is equipped with a bearing bush, which is connected with the traveling wheel by bolts. When the linear speed of each wire rope is not the same, each traveling wheel and head sheave wheel shaft can rotate relative to each other to eliminate the additional torque caused by the difference of linear speed of each wheel.

Figure 1 Structure of head sheave wheel device

1. Bearing pedestal 2. Main bearing 3. Flat key 4. Fixed hub 5. Fixed wheel 6. Gasket 7. Runner 8. Traveling hub 9. Bearing bush 10. Clamp 11. head sheave wheel shaft

2 Common fault forms of head sheave wheel device

The head sheave wheel device is subject to large force and poor working environment, so different forms of failures often occur, and it is not convenient for inspection, maintenance or replacement because it is installed on a higher derrick. In case of any problem with the crown wheel device, it may cause production stoppage or safety accident.

Common failure modes of head sheave wheel device are as follows:

(1) The operation noise is high, and the head sheave wheel device makes abnormal noise;

(2) Shearing of bearing bush connecting bolts;

(3) The bearing bush is seriously worn;

(4) The clamp is worn;

(5) Disc weld cracking or disc fracture;

(6) The liner is seriously worn and the rope grooves are of different depths;

(7) The deflection of head sheave wheel is out of tolerance.

Among them, faults (1)~(4) occur relatively frequently, most of which are caused by the lubrication problem of head sheave wheel bearing bush, and each problem is often accompanied; Faults (5) are mostly caused by the environmental problems of the head sheave wheel; Faults (6) and (7) are mostly caused by installation and operation problems of head sheave wheel device.

3. Cause analysis of head sheave wheel failure

3.1 Stress analysis of head sheave wheel bearing bush

Taking the 4-rope head sheave wheel as an example, under ideal conditions, the speed of the four wire ropes is the same and synchronous, and there is no relative rotation between the traveling wheel and the head sheave wheel shaft, but in fact, because of the difference in the tension of each wire rope, the rotation speed of each head sheave wheel body is not completely consistent. The fixed wheel and traveling wheel are designed to adapt to this situation, and a gap of 0.2~0.5 mm is reserved between the wheels, so that the four wheels can achieve different rotation speeds.

When the head sheave wheel device works, the wire rope drives the fixed wheel and the traveling wheel to rotate, and the fixed wheel drives the head sheave wheel shaft to rotate under the action of the flat key. When the rotating speed of the traveling wheel is different from that of the fixed wheel, the bearing bush of the traveling wheel and the head sheave wheel shaft will rotate relatively, and sliding friction will occur between them; At the same time, the connecting bolt between the bearing bush and the traveling hub is subject to the shear force.

The stress of bearing bush is shown in Figure 2. F1 is the friction between the inner hole of the bearing bush and the head sheave wheel wheel shaft, f2 is the friction between the outer end face of the bearing bush and the hub or clamp, and f3 is the friction between the inner end face of the bearing bush flange and the traveling hub due to the bolt engagement. Wherein, f1 is positively related to the positive pressure and friction coefficient of the bearing pad, f2 is positively related to the extrusion force and friction coefficient of the bearing pad end face, and f3 is positively related to the bolt tightening torque. When f1+f2 ＜ f3, the bearing bush is worn and the bolt is not subject to shear force; When f1+f2 ＞ f3, the bearing bush is worn, and the bolt will also be subject to shear force.

Fig. 2 Stress Analysis of Bearing Bush

When the bearing bush is poorly lubricated or the head sheave wheel is subjected to abnormal impact, f1 increases; When there is deviation between the center line of the day wheel device and the center line of the friction wheel, or the traveling wheel moves, or the bearing bush is subjected to axial force, f2 increases, resulting in an increase in the shear force on the connecting bolt. If the head sheave wheel device operates under this condition for a long time, the bearing bush will be seriously worn or the connecting bolt will be sheared, which will cause the head sheave wheel device to produce abnormal noise.

According to experience, when the connecting bolt of bearing bush is sheared, the bearing bush bolts of the traveling wheel adjacent to the fixed wheel and the outermost traveling wheel are seriously damaged. The reason is that the head sheave wheel may be subjected to an axial force caused by some external force, which makes the three traveling wheels deflect along the axis, and the bearing pads extrude and rub against each other. The outermost traveling wheel is subject to a particularly severe extrusion force, which finally increases the friction force on the end face of the bearing pad and the shear force on the connecting bolts of the bearing pad. This external force may be caused by abnormal swing of the lifting container or deviation of the tank channel.

The axial force caused by the wire rope will produce superposition and amplification effect. After the traveling wheel moves to the same side, it will offset the axial clearance of 0.2~0.5 mm of the bearing bush. The force superposition will aggravate the wear and form a vicious circle.

3.2 Impact analysis of environmental factors

The head sheave wheel is divided into fixed wheel (see Figure 3) and movable wheel (see Figure 4). They are generally of cast welded structure, that is, each wheel body is welded by a cast or forged rim, a hub and a spoke composed of channel steel. wheel is subjected to abnormal impact, f1 increases; When there is deviation between the center line of the day wheel device and the center line of the friction wheel, or the traveling wheel moves, or the bearing bush is subjected to axial force, f2 increases, resulting in an increase in the shear force on the connecting bolt. If the head sheave device operates under this condition for a long time, the bearing bush will be seriously worn or the connecting bolt will be sheared, which will cause the crown wheel device to produce abnormal noise.

According to experience, when the connecting bolt of bearing bush is sheared, the bearing bush bolts of the traveling wheel adjacent to the fixed wheel and the outermost traveling wheel are seriously damaged. The reason is that the head sheave wheel may be subjected to an axial force caused by some external force, which makes the three traveling wheels deflect along the axis, and the bearing pads extrude and rub against each other. The outermost traveling wheel is subject to a particularly severe extrusion force, which finally increases the friction force on the end face of the bearing pad and the shear force on the connecting bolts of the bearing pad. This external force may be caused by abnormal swing of the lifting container or deviation of the tank channel.

The axial force caused by the wire rope will produce superposition and amplification effect. After the traveling wheel moves to the same side, it will offset the axial clearance of 0.2~0.5 mm of the bearing bush. The force superposition will aggravate the wear and form a vicious circle.

3.2 Impact analysis of environmental factors

The head sheave wheel is divided into fixed wheel (see Figure 3) and movable wheel (see Figure 4). They are generally of cast welded structure, that is, each wheel body is welded by a cast or forged rim, a hub and a spoke composed of channel steel. wheel is subjected to abnormal impact, f1 increases; When there is deviation between the center line of the day wheel device and the center line of the friction wheel, or the traveling wheel moves, or the bearing bush is subjected to axial force, f2 increases, resulting in an increase in the shear force on the connecting bolt. If the head sheave device operates under this condition for a long time, the bearing bush will be seriously worn or the connecting bolt will be sheared, which will cause the head sheave device to produce abnormal noise.

According to experience, when the connecting bolt of bearing bush is sheared, the bearing bush bolts of the traveling wheel adjacent to the fixed wheel and the outermost traveling wheel are seriously damaged. The reason is that the head sheave may be subjected to an axial force caused by some external force, which makes the three traveling wheels deflect along the axis, and the bearing pads extrude and rub against each other. The outermost traveling wheel is subject to a particularly severe extrusion force, which finally increases the friction force on the end face of the bearing pad and the shear force on the connecting bolts of the bearing pad. This external force may be caused by abnormal swing of the lifting container or deviation of the tank channel.

The axial force caused by the wire rope will produce superposition and amplification effect. After the traveling wheel moves to the same side, it will offset the axial clearance of 0.2~0.5 mm of the bearing bush. The force superposition will aggravate the wear and form a vicious circle.

3.2 Impact analysis of environmental factors

The head sheave wheel is divided into fixed wheel (see Figure 3) and movable wheel (see Figure 4). They are generally of cast welded structure, that is, each wheel body is welded by a cast or forged rim, a hub and a spoke composed of channel steel.

Figure 3 Fixed wheel structure

1. Rim 2. Spoke 3. Fixed hub

Fig. 4 Structure of Runner

1. Rim 2. Spoke 3. Traveling hub

The head sheave wheel spoke is damaged mainly due to the following reasons:

(1) The wheel of head sheave device bears large load, and is affected by alternating stress during operation, which is easy to cause material fatigue;

(2) The head sheave device is located in a harsh environment, often eroded by rain and snow, and prone to corrosion, especially affecting the crown wheel spokes;

(3) The mechanical properties of the head sheave materials will be greatly affected by the natural environment when the head sheave device is in an extremely low or high temperature environment.

The above reasons may lead to abnormal noise of the head sheave, cracking of the spoke weld, or even fracture of the spoke.

3.3 Other influencing factors

3.3.1 Installation problems of head sheave device

Among many requirements for installation of head sheave device, there are two main factors: levelness of head sheave device base, perpendicularity of head sheave shaft centerline and lifting centerline perpendicular to crown wheel shaft. General installation requirements for head sheave device are as follows:

(1) The center line of head sheave device shall coincide with the lifting center line, and the deviation shall not be greater than 1 mm;

(2) The levelness of the head sheave device base shall not exceed 0.05/1000;

(3) The verticality of the head sheave axis line and the lifting center line perpendicular to the head sheave axis in the horizontal plane shall not exceed ± 0.15/1000.

If the above requirements cannot be met due to early installation or derrick deformation, foundation settlement, etc., the stress condition of the head sheave body will be changed, and even axial force will be generated, which will result in eccentric wear of the liner, wheel body, bearing pad, and even the head sheave runout.

3.3.2 Unbalanced tension of wire rope

The diameter deviation of the liner groove, the length deviation of the steel wire rope and the stiffness deviation will make the steel wire rope with larger length subject to smaller tension, and the steel wire rope with smaller length subject to larger tension. In order to balance the force on the wire rope, the rope adjuster is usually used for adjustment. However, the rope adjuster is not used properly, for example, the hydraulic cylinder for rope adjustment leaks liquid, causing no pressure or under pressure in the hydraulic cylinder for rope adjustment, making a wire rope under no force or less force; The elongation of a single wire rope exceeds the adjustment limit of the rope adjusting hydraulic cylinder, which makes a single wire rope free of force or less stressed, and the rope adjuster cannot balance the force on multiple wire ropes; When the lifting center line and the cage path are offset, the cage path will form upward or downward resistance to the cage, so that the force exerted by the cage on the lifting rope is uneven. When the force on each wire rope is uneven, the force on each wheel body is also uneven, causing pad wear, bearing bush wear or abnormal noise of crown wheel.

4 Troubleshooting

For the above influencing factors, the following solutions can be adopted.

4.1 Formulate refueling maintenance system

Formulate and strictly implement the refueling maintenance system to provide good lubrication conditions for the crown wheel device. Grease selection, oil filling maintenance and bearing bush cleaning are recommended according to the following requirements.

(1) Grease selection Bearing bush lubricating grease is generally No. 1-3 extreme pressure lithium base grease. During daily maintenance, users can select the appropriate brand of grease according to different seasons and temperatures.

Lubricant maintenance plan

(3) Bearing bush cleaning method The lubricating grease in the head sheave wheel pipeline and the bearing bush is likely to deteriorate, fail, dry, adhere to the inner wall of the oil pipe and the bearing bush oil groove, or even form a blockage. It must be cleaned regularly to ensure that the oil path is smooth. When cleaning the bearing bush, inject kerosene or other cleaning agents into the oil circuit through the oil injection hole on the rim, and flow out from the oil outlet (which can also be used as the oil injection port) in the middle of the cruise wheel hub. After cleaning, plug it with a screw plug.

4.2 Structure optimization of head sheave device

The failure of the head sheave device is also related to the structure of the head sheave device itself. The adaptability of the head sheave device can be improved by improving and optimizing some structures of the head sheave device.

(1) Increase the specification and strength of bearing bush connecting bolts or increase the number of bolts to improve the overall strength and shear resistance of bearing bush connecting bolts.

(2) The locating key of bearing pad end face (see Fig. 5) is added to improve the shear resistance and reduce the shear force on the bolt.

Fig. 5 Bearing pad locating key

(3) Improve the processing technology and adopt the seamless processing technology (see Figure 6) to improve the processing accuracy and integrity of bearing pads and eliminate the shifting space of bearing pads.

?Fig. 6 Structure of Seamless Bearing Bush

(4) The structure of bearing bush lubricating oil groove shall be improved, and the well shaped crisscross oil groove shall be adopted to increase the effective length and depth of bearing bush oil groove, so as to increase the oil storage and improve the lubrication effect.

4.3 Design of automatic refueling head sheave wheel device

The sheave wheel device is installed on a higher derrick, which is not convenient for manual lubrication, and it is difficult to ensure sufficient refueling frequency on site. At the same time, the sheave wheel wheel device is often lubricated with grease. If the oil is not replenished in time, the lubricating oil will become dry, or even the oil injection hole will be blocked, and finally the bearing bush cannot be lubricated. The sheave wheel wheel device works under the condition of poor lubrication, which will cause serious wear and even burning of the bearing bush. For this reason, an automatic refueling crown wheel device with electric pump is designed, as shown in Figure 7.

Fig. 7 Automatic refueling head sheave wheel device

The automatic refueling head sheave wheel device connects the electric refueling pump with the central hole at one side of the traveling wheel of the crown wheel shaft through the pipeline and the rotary sealing device, and fills the lubricating grease from the axial deep hole of the head sheave wheel shaft and the radial hole at the corresponding position of each traveling wheel to the bearing bush of each traveling wheel. Personnel can control the device in the ground machine room without climbing on the derrick, and can add grease without stopping, so as to achieve the purpose of regular automatic refueling.

4.4 Structural design of rolling bearing type runner

The bearing bush and shaft are of open structure and sliding friction type. Compared with rolling bearings, they feature high oil filling frequency, large maintenance and short service life. Rolling bearings can be used normally for a long time if they are replaced with grease regularly. According to the characteristics of sliding bearing bush and rolling bearing, combined with the actual working conditions of the head sheave device, the structure supported by rolling bearing is adopted on the traveling wheel of the head sheave wheel device, which has significant advantages over the traditional structure supported by bearing bush.

4.5 Installation of head sheave wheel protection facilities

In view of the impact of environmental factors on the material performance of the head sheave wheel spokes, it is suggested that qualified sites can install protective facilities on the head sheave wheel device, such as adding enclosures and rainsheds on the head sheave wheel device derrick installation platform, and even protecting the steel wire rope between the head sheave wheel device and the main shaft device with enclosures (see Figure 8) to optimize the working environment of the head sheave wheel device. This is particularly important for mining equipment in an extremely high/low temperature environment with abundant rain and snow. In southern China, it can reduce the impact of rainwater on the head sheave wheel device; In the northern region, it is conducive to the thermal insulation of the head sheave wheel device, reducing the impact of rain, snow and low temperature environment on the head sheave wheel device.

Figure 8 head sheave wheel with protective facilities on site

4.6 Structural design of spoke head sheave wheel

For mines where it is difficult to increase protection measures due to extremely high mast height or other reasons, spoke plate structure head sheave device can be used, as shown in Figure 9. Unlike the ordinary head sheave body, which adopts channel steel spokes, the rim of the spoke head sheave is connected with the wheel hub by a web plate and a rib plate, and the web plate is welded with the rim and the wheel hub respectively. The force bearing mode of the spoke plate is different from that of the spoke plate, and there will be no fracture.

Fig. 9 Structure of spoke head sheave wheel

4.7 Precautions for use and maintenance

(1) When installing the head sheave device, the user shall install it in strict accordance with the relevant installation specifications and manufacturer's instructions. Pay attention to the lifting method and lifting position during lifting and transportation to ensure that the crown wheel body is not deformed, and use special lifting tools for lifting as much as possible;

(2) In daily use, the oil filling system shall be formulated according to the actual situation, and the bearing bush and oil filling pipeline shall be cleaned regularly to ensure that the oil path is smooth and well lubricated;

(3) Regularly inspect whether the head sheave wheel derrick is deformed and whether the foundation is settled to ensure that the head sheave wheel centerline, levelness and shaft centerline alignment meet the corresponding requirements.

5 Conclusion

The failure of head sheave wheel device is a complex process, which should be comprehensively and systematically analyzed. The author mainly analyzes the abnormal noise of the head sheave wheel, the fracture of the bearing bush bolts and the fracture of the wheel spokes from the aspects of bearing bush lubrication, the environment of the head sheave wheel, installation and use, and puts forward the corresponding solutions.

(1) In terms of bearing bush lubrication, oil filling system can be formulated and strictly implemented, or automatic oil filling type head sheave device or roller bearing type traveling wheel structure head sheave wheel device can be used.

(2) In terms of environmental factors, head sheave wheel protection measures can be added, and spoke plate crown wheel device can also be used.

(2) For the head sheave wheel devices currently in use on site, if the above problems occur, it is recommended that a group of new structure crown wheel devices can be customized as spare parts according to the original installation size when conditions permit, and one group of original head sheave wheel devices can be replaced. After the original head sheave wheel devices are removed, they can be repaired or partially modified. After the repair or partial modification is completed, another group of original head sheave wheel devices can be replaced, and the crown wheel devices can be overhauled without affecting production.