The mine hoisting system is a crucial link in coal production, serving as a link between the underground and the surface. The malfunction of mine hoisting equipment, especially mine hoists, not only directly affects underground production, but also poses a significant threat to the safety of workers' lives.

1、 Working principle of multi rope friction hoist

According to different working principles, mine hoists can be roughly classified into two categories: single rope winding mine hoists and multi rope friction mine hoists. The single rope winding hoist is suitable for shallow and inclined shafts. In mines with deep burial depth and high lifting intensity, multi rope friction hoists are preferred. The difference between multi rope friction hoist and single rope winding mine hoist lies in the winding and fixing method of the steel wire rope and the main wheel. The steel wire rope of the multi rope friction hoist is set on the drum friction winder insert The two ends of the steel wire rope are suspended at the top of the cage, skip, and balance hammer through the head rope suspension device, and the balance tail rope is suspended at the bottom of the cage, skip, and balance hammer through the tail rope suspension device. When the cage and skip need to run, the motor drives the drum to rotate, and the friction between the steel wire rope and the friction pad drives the steel wire rope to run, ultimately completing the operation of the hoist.

2、 Reliability Analysis of Hydraulic Braking System

The hydraulic system is mainly composed of components such as motor pump device, control valve group, oil tank filter, and accumulator. From the perspective of performance and usage functions of hydraulic systems, their reliability mainly includes the working reliability of hydraulic components, the reliability of various braking conditions, the reliability of electronic control systems, and the reliability of daily maintenance. The reliability of hydraulic components refers to the ability of working components such as oil pumps, solenoid directional valves, relief valves, motors, etc. to reliably operate and complete the functions of the hydraulic system within the specified time. Its reliability is often affected by factors such as whether the oil circuit is unobstructed, whether there are leaks, its own quality, external environment, and maintenance and repair quality. Therefore, fault detection should be carried out on the solenoid valve. Various braking conditions (including working braking) should reflect the hydraulic pressure value of the hydraulic system stably and flexibly according to the position of the driver's operating handle, and generate corresponding braking torque. And safety braking refers to the ability to timely and reliably brake the hoist in case of emergency situations during the lifting process, thereby avoiding the occurrence of malignant accidents such as over rolling, over releasing, pier jar, and rope breakage.

3、 Cause of the accident

1. There is contamination in the hydraulic system and pipelines. The hydraulic station is the core component of the hoist, used to control the operation of the brake. The oil may become contaminated after long-term use, and some particles are inevitably present in the contaminated oil. These particles may cause some hydraulic components to be blocked or stuck, such as the blockage of the overflow valve core. When braking, the system may experience poor oil return, or even inability to return oil, which can cause the brake to brake too slowly or even fail to brake.

2. The residual pressure of the hydraulic station system is too high. The high or low residual pressure of the hydraulic station directly affects the operational performance of the hoist, that is, high residual pressure leads to a rapid increase in working oil pressure during driving, and the corresponding release speed is also fast; Residual pressure is low, resulting in slow oil return speed during braking and corresponding slow closing speed. Especially during emergency braking, if the container travels too long, it can easily lead to safety accidents. Considering that releasing the brake too slowly during normal driving will be inconvenient for elevator operation, there are generally corresponding regulations for the minimum residual voltage. Different types of hydraulic stations have different requirements for residual pressure in the system based on the working pressure level of the system. The reason for excessive residual pressure is usually due to improper adjustment of relevant parameters, such as the TE131 hydraulic station, where the distance between the baffle on the control rod of the electro-hydraulic pressure regulating device and the nozzle is too small or the overflow valve orifice is too large.

3. There is residual air in the brake system pipeline. Every time the system pipeline is opened, external air will enter. Air entering the hydraulic system will form bubbles in the oil, directly causing unstable system pressure. When using a disc brake, the presence of this type of air can easily cause slow braking speed.

4. Insufficient force of brake disc spring.

The disc brake is provided with braking force by a disc spring, and the magnitude of the braking force is achieved by adjusting the preload force of the disc spring. Excessive pre tension can cause excessive braking speed, while insufficient pre tension can lead to insufficient braking force. In addition, disc springs may experience fatigue, damage, and other phenomena after frequent use, such as spring breakage, which can result in a severe decrease in spring force and insufficient braking force. In practice, it is often found that one or several disc springs in the entire set of brakes are damaged, which is difficult to detect without careful inspection and poses a significant safety hazard to the operation of the braking system.

4. The brake shoe clearance is too large, the contact is poor, or the braking force on both sides is uneven.

① The excessive clearance between the brake shoes of the brake system results in a prolonged idle time. When applying safe braking, the hoist requires the braking speed to be as fast as possible while ensuring that there is no excessive impact, in order to ensure timely parking. Therefore, on the premise that other parameters such as braking force meet the requirements, the idle time of the disc brake should be strictly controlled. The size between the brake shoes and the brake disc is the main factor affecting the idle time, so it must be controlled as an important factor The contact area between the brake shoe and the brake disc is insufficient. Newly installed or replaced brake shoes have not been properly run in, resulting in insufficient contact area between the brake shoe and the brake disc, which leads to the braking force not reaching the design value. In addition, due to insufficient contact area, the local contact pressure between the brake shoe and the brake disc is too high, which can easily cause excessive heating and friction damage to the brake shoe or brake disc;

5. Insufficient friction between the friction winder insert and the head rope.

Friction hoist relies on the frictional force generated between the head rope and the friction winder insert groove to transmit power. If there is sliding (sliding rope) between the head rope and the friction winder insert during braking, even if the brake can brake the main shaft device normally, safe braking cannot be achieved. In use, if the wear of each rope groove of the pad is uneven, the diameter of the rope groove will deviate, and the corresponding tension and load-bearing capacity of each rope will be different. The frictional force between each rope and the friction winder insert will also be different, which may cause rope sliding accidents in severe cases. In addition, factors such as aging and weathering of friction winder insert can also cause low friction and result in rope slipping accidents.

4、 Countermeasures

1. Keep the hydraulic system and pipelines clean.

Hydraulic stations should be cleaned and oil changed regularly (once every 6 months and once every 12 months). Regularly clean or replace filters and filter cartridges to keep pipelines and valve cores unobstructed. It is advisable to filter when adding new oil. Each shift manually checks whether the action of each solenoid valve is flexible. If it is found to be stuck or jammed, it should be dealt with immediately.

2. Strictly control the residual pressure of the hydraulic station.

The residual pressure of TE131 and TE161 hydraulic stations should be controlled at 0.3-0.5MPa, and 0.8-1.0MPa for E143 type. For the TE131 hydraulic station, the distance between the baffle on the control rod and the nozzle can be adjusted by the cross spring on the electro-hydraulic pressure regulating device; Change the throttle hole of the overflow valve

Small; Increase the aperture of the fuel injector. For the E143 hydraulic station, adjustments can be made through a proportional relief valve amplifier.

3. When opening and restoring the pipeline system, fully exhaust the air.

After installation, the system should first be filled with oil pressure not exceeding 0.5MPa, and the air in the pipeline should be drained through the exhaust plug. If the brake is found to be releasing slowly, exhaust should be considered first.

4. Check and replace the disc spring in a planned manner, regularly check and adjust the braking force, and ensure that the braking force meets the safety braking requirements (the braking torque shall not be less than 3 times the maximum static torque when lifting or lowering the cargo load)

5. Strictly install, inspect, and adjust the disc brake in accordance with relevant specifications.

Control the brake shoe clearance (standard is 1-2mm) and ensure that the clearance on both sides is equal; Timely replace brake shoes with excessive wear or damage (when the brake shoes are worn to a distance of 2mm from the cylinder lining plate, they must be replaced); The idle time of the disc brake should not exceed 0.3 seconds. Regularly check the contact area between the brake disc and brake shoes, and take timely measures if any abnormalities are found. The specific detection method is: first, clamp the carbon paper between two white sheets of paper, then place it in the gap between the brake shoes, so that the brake shoes stick to the brake. The color of the carbon paper will be printed on the white paper, and this area is the actual contact area. The contact area between the brake shoe and the brake disc should reach more than 60%. If the contact area is insufficient, the method of sticking and grinding the brake shoe can be used on site. It should be noted that during the process of grinding the brake shoe, the operating speed of the drum and the given pressure of the system should be controlled, and the temperature of the brake disc should be constantly monitored to avoid burning or damaging the brake shoe or the brake disc.

6. Choose friction winder insert with better performance.

When the diameter of the pad rope groove exceeds the tolerance, timely turning treatment should be carried out. When selecting friction pads, the friction coefficient, pressure resistance, wear resistance, elasticity, aging resistance, weathering resistance and other properties should be taken into account. If GDM326 high-performance friction winder insert can be considered, its friction coefficient can be greater than 0.3. Multi rope friction hoists are equipped with specialized groove devices, and newly installed and replaced pads must Perform car slot blowing. For the rope groove in use, when the diameter difference of the worn rope groove is greater than 0.8mm, timely turning treatment should be carried out to adjust its diameter to be consistent, so as to ensure that the tension of each rope is equal. If the thickness of the lining is worn to 2/3 or aged and weathered severely, it should be replaced.