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Identification of Major Risk Sources and Prevention Measures for Single-Rope Winding Mine Hoists

2022-07-29

　　1. Major accidents caused by human error, resulting in overwinding and rope breakage leading to runaway vehicles.

　　(1) Incident Case: During an upward transport operation in the original combined main inclined shaft roadway for both machinery and tracks, the mine hoist operator, feeling drowsy and momentarily dozing off, inadvertently pulled the car platform up to the head of the skip hoist. Fortunately, the issue was spotted in time, preventing the situation from escalating into a more serious accident.

　　Preventive measures:

　　① Equipped with 2 mine hoist operators, ensuring they stay alert and avoid drowsiness or dozing off during the night shift.

　　② The mine hoist is equipped with an overwinding protection system. If the operator falls asleep, the overwinding protection immediately activates, bringing the mine hoist to a safe stop.

　　③ Regularly test the overtravel protection system.

　　(2) Accident Case: While lowering the mine hoist to the lower yard, the hoist operator experienced a brief moment of drowsiness or dozing off, causing the steel wire rope on the drum to momentarily jerk, resulting in an over-winding incident.

　　Preventive measures:

　　① The mine hoist is equipped with slack rope protection and is programmed to automatically decelerate as it approaches the lower yard.

　　② Suggestion: Could we install sensor-like devices (such as infrared sensors) beneath the mine hoist drum? These would automatically stop the system as soon as the wire rope starts to slip off the drum, providing dual protection when combined with the slack-rope protection feature.

　　(3) Accident Case: During the downhill operation of the mine hoist, the absence of lighting in the trackway posed a significant safety hazard for transportation tasks. Specifically, because the points were not set to the correct position, there have been incidents where trains mistakenly entered the yard, and in one case, a train became entangled with the car stop barrier.

　　Preventive measures:

　　① Quickly complete the lighting in Track Alley to provide maintenance workers with a safe and efficient working environment. When transporting materials downhill, they can continuously monitor the transport conditions ahead.

　　② The guarding personnel at each yard must constantly monitor the direction of the points and the open/close status of the wheel stops.

　　③ Currently, the interlocking system for the car stop barriers is undergoing debugging. Once fully operational, if the car stop barrier fails to open or close properly during mine hoist operation—even if the control system is equipped with a reaction distance—there remains a risk that, should the accompanying worker and the hoist operator fail to coordinate promptly and stop the train in time, the entire string of cars could become trapped by the barrier. In such a scenario, the overload protection mechanism within the hoist’s control circuit would activate, halting the mine hoist immediately and preventing the steel wire rope from snapping. (In the past, an accident occurred in the old shaft where the steel wire rope got caught on the car stop barrier during support transportation, ultimately leading to a rope break and runaway car.)

　　II. Major accidents caused by electrical and mechanical equipment failures, as well as external factors—such as overwinding, rope breakage, and runaway vehicles. The primary causes of wire rope breakage incidents include: rope slack, vehicle runaway, overwinding, reduced rope strength, and operator error, among others.

　　(1) The main types of rope failures can include: overwinding-related rope breakage, rope breakage caused by shaking, corrosion-induced rope failure, and fatigue-related rope breakage (where the bending of the wire rope at friction or sheave points creates cyclic stress, leading to fatigue and eventual tensile failure). Prolonged, repeated bending significantly reduces the rope's fatigue strength). Additionally, there’s impact and vibration-induced rope breakage—since wire ropes frequently endure various shocks and vibrations during use, the primary causes include:

　　① Impact caused by slack rope.

　　② Impact caused by overwinding.

　　③ Impact and vibration caused by excessive deceleration during emergency stops, which can lead to rope breakage if the impact force exceeds the tensile strength of the wire rope.

　　Accident Prevention: Strengthen the inspection and maintenance of wire ropes, and conduct regular testing of lifting wire ropes. Regularly rotating and cutting off rope ends help redistribute stress, reduce wear and tear, and minimize corrosion points—effectively eliminating potential hazards. This not only extends the lifespan of the wire ropes but also significantly lowers the risk of accidents, enhancing overall reliability.

　　(2) Main causes of hoist overspeed:

　　① The depth indicator has failed—primarily due to mechanical issues such as a broken gear transmission shaft, loose or misaligned transmission gears, snapped pins, and improperly engaged clutches.

　　② The elevator's safety protection device has failed, as have the speed-limiting and overspeed protection systems. Additionally, the elevator's automatic deceleration and warning mechanisms are also malfunctioning.

　　③ The lifting mechanism's braking system has failed—specifically, the hoist's hydraulic brake system is malfunctioning, and the return oil line is blocked, preventing the brake from engaging.

　　Accident Prevention and Control:

　　① Inspect all safety protection devices of the hoist to ensure reliable operation. Utilize advanced electrical control systems and a comprehensive software platform to prevent overwinding and over-lowering accidents caused by equipment malfunctions or programming errors.

　　② Enhance the reliability of the lifting mechanism's braking system and reduce failures in the hoist's hydraulic brake system. Regularly replace the pump station lubricant, and during major overhauls, thoroughly clean the return oil lines of the disc brakes—replacing them if necessary.

　　③ Regularly test all safety protection devices of the mine hoist, conduct thorough inspections, and promptly address any faults that are detected.

　　(3) The main reasons for sports cars:

　　① Insufficient braking power, brake failure, or failure to apply the brakes can lead to runaway car accidents.

　　② Defects in the electronic control system and electrical equipment failures prevented timely brake commands from being issued, resulting in a runaway accident.

　　③ A steel wire rope rupture caused a runaway car accident.

　　④ Improper adjustment of wire rope ends leading to runaway car accidents.

　　⑤ Vehicle runaway caused by inadequate management, maintenance, or operational errors.

　　Accident Prevention and Control:

　　① Choose a safe and reliable hydraulic braking system; all hydraulic lines are made of stainless steel tubing to prevent rusting and subsequent blockages in the oil passages. During maintenance, carefully monitor changes in the hydraulic fluid and promptly remove any impurities from the oil.

　　② Implementing a constant-deceleration hydraulic braking system can effectively prevent runaway accidents caused by wire rope slack or breakage. This is especially critical when lifting large components—since meeting the emergency braking requirements for such heavy loads inherently demands a deceleration rate higher than the natural deceleration of the system, significantly increasing the risk of wire rope slack, breakage, and subsequent runaway incidents. Therefore, it is essential to use a constant-deceleration hydraulic station to ensure the braking system meets safety standards.

　　③ When adjusting the wire rope, the designated parking device must be used according to the prescribed method.

　　④ Steel wire rope adjustment work must involve preparing a construction method, establishing safety measures, obtaining approval, and then presenting these plans to the construction team for discussion and implementation before proceeding with the actual work.

　　III. Other Accident Prevention Measures

　　(1) Prevent motor burnout:

　　① The motor is equipped with temperature protection.

　　② Regularly inspect the motor's insulation performance, and ensure thorough inspection, maintenance, and management.

　　(2) Reverse-Direction Protection: If the mine hoist operates in a direction opposite to the set command, it activates the safety brake.

　　(3) Overspeed Protection: To prevent excessive speed, an overspeed protection system is installed in the mine hoist control circuit. If the hoist’s speed exceeds the preset maximum limit, the hoist will initiate an emergency stop.

　　(4) Speed Limit Protection: A speed limit protection system is installed within the mine hoist control circuit to prevent serious accidents such as overwinding.

　　(5) Deceleration Function Protection: When the mine car reaches the designated deceleration point, it will issue a warning and automatically begin slowing down.

　　(6) Overcurrent and undervoltage protection: When an overcurrent, voltage drop, or undervoltage occurs in the mine hoist's power supply circuit, the overcurrent or undervoltage relay in the control circuit activates, causing the mine hoist to stop immediately.

　　(7) Depth Indicator Failure Protection: When the indicator's transmission system malfunctions, it automatically cuts off power, triggering an emergency stop of the hoist.

　　(8) Brake Gap Protection: To prevent extended brake slack time and reduced braking force during operation, this system automatically alarms or cuts off power when the brake gap exceeds the specified limit.

Common Faults

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Common Faults and Troubleshooting Measures for Mine Hoist Gearboxes

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2022-07-29