Compass Tip: Two construction elevator accident ThinkingTime：2015-11-11 Click：
Construction hoist is widely used in the construction site of manned lifting equipment, lifts concerning the use of human life and property safety. Elevator accidents often result in serious consequences for personnel Qunsiqunshang must therefore pay close attention.
1 Case mistakenly removed a safety catch
1.1 ACCIDENTS
Construction elevator before the accident belongs to be demolished, intermittent use, install high 109m. A few days before the accident, left the cage downstream anti-dropping system often stop action, maintenance personnel mistakenly thought it was anti-dropping device malfunction problems. Date of the accident, when the cage down to 28 layer anti-dropping action again, three maintenance personnel to carry replaced with anti-dropping device into the cage, after removing the safety catch, cage fall.
Reason 1.2 accidents
1) environmental factors on the brake
Elevator before the accident at Basic deactivated intermittent operation, which is not part of the brake shields installed, wall stone hanging job dust and rain moist air, which environmental conditions of intermittent brake work more dangerous. If the elevator frequent job open because the brake is closed, there is air impact can promptly remove accumulated dust. After the accident, on the two brake inspection found that a station is not closed completely obvious brake disc failure, the impact did not fall from the height of 79m it is reset closed, indicating that the brakes are very serious dust bit card level. In another brake performance test, also found a large number of brake dust adhesion test 5 times the braking torque values were between 75 ~ 160N.m stating that the brake torque rating of only 30 about%.
2) fell to the ground speed of analysis and calculation
Accident antecedents of heavy rope on the sheave Kasheng, the project taking into account the lift has been basically disabled, so the maintenance staff cut heavy rope, placed in the ground to play, so that the cage was left in no counterweight situation. When left cage fall, cage weighs about 2 180kg, no counterweight, a brake has been a complete failure, another brake torque is about 75Nm or less. 1:14 ratio transmission mechanism, the driving gear pitch diameter of 120mm, falling a distance of 79m. If you do not count the resistance and friction, speed hoists landing of 17.5m / s, the cage 26 times normal speed downlink.
3) maintenance personnel to determine the error
The reason in this case from the accident, the cause of frequent anti-dropping action is subject to the environmental impact of a brake failure braking capacity decreased, but staff did not analyze the reasons identified anti-dropping action, mistakenly believe that the presence of anti-dropping device of malfunction in None under heavy circumstances, adventure aerial dismantle anti-dropping device, resulting in a serious accident cage fell to the ground.
2 Case Two anti-dropping device hidden failure
2.1 ACCIDENTS
Heavy lift accident-free for three motor lift, before the accident, the median motor reducer fault, hoists stopped on the 17th floor, when the upper and lower motor brake shields were installed. When the maintenance personnel to install the median motor, hoists suddenly fall in a fall, anti-dropping action, but because of the presence of hidden failures, no effective system to stop the cage, the cage after a brief slowdown, falling to the ground.
Before the accident, the intermediate gear unit failure, maintenance personnel has been installed has been replaced, it is the median motor assembly manual installation. After the accident found that the median motor is not connected to the supply line, and the motor shaft can rotate freely, indicating that the brakes had failed, it did not energize the motor was running. Lower motor brake disc four sliders bent down, brake disc and the fixed body is not closed, the gap reached its upper 5mm, while the lower part is almost no gap, the brake has been completely ineffective. Upper motor braking torque test values minimum 91N.m, was not enough to stop the cage and made several weight maintenance personnel.
Cage in the process of falling, anti-dropping action, but could not stop the cage system, fell to the ground after the cage, micro switch operation; anti-dropping housing severe cracking from three attachment holes. Disintegration anti-dropping device, found brake lining thickness of about 3.0mm, when only half the thickness of the original factory; brake drum braking surface tapered blue phenomenon obviously have a fever; butterfly spring-loaded, a round nut all up, eccentric block mechanism intact; the brake lining surface grinding dust dark mixture layer thickness of about 0.2 ~ 0.3mm, the surface smooth, crisp texture hard, can be easily peeled from the brake pads, which is the brake drum and brake cone The results sheet caused by prolonged grinding.
2.2 Accident Analysis
Before the accident, the host of the motor to be repaired in a few days of downtime is not loaded brake enclosure, due to construction dust more, plus occasional rainy weather, the initial boot will affect braking performance after a long pause, the braking torque Test results about 91N.m. The median of the lift brake malfunction, the entire cage braking capacity decreased, but rarely run as usual cage is full, there are two motor drive system can work to meet the basic requirements for normal operation of the cage, this when the cage operation will not have significant abnormalities. But when the cage occasionally close to the rated load, such as anti-dropping device operating speed of adjustment is negative deviation 1.0m / s in the downlink braking distance is too long will cause the braking action trigger safety catch up slightly tapered drum . This action is in critical operating state, this time did not feel the lift operators have obviously abnormal. But in fact anti-dropping device next line often in quasi-action status, and then because of the anti-dropping several vent holes, when the humidity of the air entering the cone brake drum friction surface high pressure and strong action to lower friction sliding surface caused by high temperature; friction down the dust and moist air to form a low coefficient of friction grinding dust mixture, with a high temperature under constant grinding the mixture hardens, the surface becomes smooth, greatly reducing the Parachute brake performance. At the same time, lift the safety catch often associate the operating state run, will increase the load of the power unit. Theoretically, the three motors on a cage only closely synchronized, but not completely synchronized. Therefore, we should be in the position of the motor speed is greater than the upper and lower motor, resulting in a median motor overload caused recurrent worm gear failure.
Upper and lower motor brake is not installed protective cover, environmental conditions have an impact on the braking force. When the accident, maintenance personnel lifting the motor shaft coupling and reducer high speed shaft coupling to adjust the position when the bit is inserted and the direction of the motor accident rear slide down, just hit the lower position of the brake slider position, slider diameter generally about 12mm, the brake disc opening and closing the sliding guide member, the impact caused by the bending slider, tilt the brake disc, brake failure instantly, but this time the upper braking force of the power unit is insufficient, cage acceleration of falling, reaching defense dropping device at a constant speed operation, due to the anti-dropping device brake pad surface is covered with a mixture of ground to form, the friction coefficient is small, the system can not effectively stop the cage, the cage fell to the ground, also causing safety catch shell cracking.
3 lessons from the accident
The reason these two incidents have a certain commonality and concealment:
1) In the elevator inspection, maintenance work, should be lowered to the ground cage, unable to decline, should use wire rope, chain hoists securely fixed before the job is hoists. In the lift maintenance, while elevating section should remain normal and effective safety catch.
2) anti-dropping action, you must identify the reasons, after the elimination of the fault before resetting put into operation.
3) should pay more attention to environmental impact of meteorological conditions on the performance of the motor brake. Brake shield should be properly and fashion. Disable than three days, or humid environment, under more dust environment, before using the lift every day, should be in the ground station opening and closing the brake several times to disperse dust on the disc brake, maintain normal braking torque inspection shall observe a brake-by opening and closing the case. If necessary, brake performance test.
4) Anti-dropping device should be properly maintained, non-refueling water in the pellet and the brake drum. Annual inspection on time, at least five years should be scrapped. Housing vent should face down, after each round nut action should be reset, hold flag pin position in the normal position. During normal use, the drop test conducted once every three months as required, in order to verify its operation system to stop the situation.
5) Do not use the lift counterweight in no case under counterweight.
