(1) The braking torque of the brake of the driving device is not enough, and the safety factor is too small;

(2) Single drive and double (multi) drive;

(3) The reliability of the safety device is poor;

(4) Overloading of the hanging cage violates the penalty deduction rules, not according to the product manual;

(5) There is no idler on the back of the meshing position between the driving pinion and the rack, or there is no locking piece on the eccentric shaft of the idler;

(6) No balance weight is set;

(7) Other accidental reasons;

Analysis and comparison of safety devices of drive device 2

2. 1 Brake of cage drive device

A brake is a device that stops a car on the floor. At present, there are roughly two kinds: one is the standard JWZ200 block brake, and its braking torque is 160N? M, a mature product, has a large overall size, the brakes are easy to wear and tear, and improper maintenance is easy to fail. This kind of brake is mostly used in domestic construction elevators produced in the 1980 s, but it is rarely used at present and is gradually eliminated; The other is developed with reference to the ALIMAK prototype imported in the late 1980s. It is a disc friction brake connected with a driving motor. It is a pull-type friction brake connected with a driving motor. This brake is characterized by compact structure, small volume and easy adjustment of the gap between brake pads. At present, this kind of brake is used in domestic construction elevators.

In order to make the hanging cage reliably stop on the rolling layer and ensure that it does not fall, the brake of the braking device must have enough braking torque, and the braking torque of the counterweight-free hanging cage should meet the following requirements:

When the cage rises: m 1 = ((g+q))? R)/i)？ K When the cage goes down: m2 = ((g+q+q 1)? R)/i)？ k

Where: m1-braking torque (n? m)； M2-braking torque (n? m)； Q—— rated load of the hanging cage (kg); Q 1—— Inertia force when cage descends (n); G—— self-weight of hanging cage (kg); I—— transmission ratio of reducer and planar double enveloping torus worm gear reducer, I = 42/3; K- safety factor of braking torque, according to GB/T 10054-96, k>= 1.75; R—— Pitch radius of driving pinion (m).

Under the rated load (without counterweight, the rated load is 1000kg), the hanging cage should be safely and reliably parked at the required position to ensure that the hanging cage does not fall. Through the above formula, the braking torque m is 195N? m .

It can be seen that the braking torque of the above two brakes is small. In order to overcome the small braking torque of the brake and ensure the safe operation of the hanging cage without falling, double drive or counterweight must be adopted.

2.2 Driving devices (single drive and multi-drive)

The number of driving devices depends on the self-weight and rated load of the cage. There were several falling accidents in the early construction of elevator car, so it is considered that single drive is unreliable and only double drive can ensure the safe operation of elevator car. In practice, the safe operation of hanging cages is not determined by the number of driving units.

2.3 Anti-falling safety device

When the driving device of the hanging cage fails and falls, the mechanical device that limits the running speed of the hanging cage and prevents it from falling is called the anti-falling safety device. At present, most construction elevators in China use the second generation product of ALIMAK Company-cone-drum friction anti-fall safety device. Its function process is that when the hanging cage runs at rated speed, the pinion at the shaft end of the anti-falling safety device is in a follow-up state on the rack of the guide rail frame; When the hanging cage runs over speed for some reason, the centrifugal block installed on the gear shaft will be thrown out to mesh with the convex teeth on the inner side of the outer cone under the action of centrifugal force, which will drive the friction cone to rotate and gradually increase the friction resistance moment between the inner cone and the outer cone under the action of the butterfly spring group until the hanging cage stops running. When braking, the sliding stroke of the hanging cage is 0.25- 1.2m, and the braking is stable without obvious impact force, which will prolong the service life of the hanging cage and steel structure.

The anti-falling safety device is characterized by large braking torque, which can reach 3000N? More than m; Compact structure, small volume and safe and reliable use. It is the main supporting product of domestic construction elevator at present.

According to JG5058-95 "Anti-falling Safety Device for Construction Lifts", the anti-falling safety device can only be used within the effective calibration period, and its effective calibration period is two years. The failure of anti-fall safety devices is often caused by not sending them to professional testing units for maintenance and testing in time after exceeding the prescribed time standard. Some vulnerable parts are worn due to long-term use and fatigue, which makes the function of anti-fall safety device invalid.

After years of maintenance, the fall arresters were tested within the recalibration period, and it was found that there was water in the shell of some fall arresters, which made the brake band moldy and deteriorated due to long-term immersion in water. There are oil stains on the surface of the brake band, which greatly reduces the friction coefficient of the brake band and directly affects the braking torque, making it lose its anti-falling function.

2.4 Incorrect operation

Violation of operating procedures, not overloading according to the provisions of the product manual, resulting in a hanging cage falling accident. At present, most construction elevators in China are not equipped with cage overload limit protectors. Papers on the design principle of this center have been reported in magazines, but rarely pass the quality test when it is actually applied to products. In the future, scientific research and design units and factories will jointly tackle key problems, so that cage overload limit protectors can be applied to construction elevators as soon as possible.

2.5 The problem of riding on the wheel at the meshing position between the driving pinion and the rack.

When the driving pinion is engaged with the rack on the guide rail frame, it can be known from the stress situation that apart from the vertical upward or downward force, there are horizontal forces that repel each other, that is, the force that drives the pinion to leave the rack. Generally, there is no proximity device on the drive device produced in the early stage. Due to the rigidity of the transmission plate, the deformation and improper meshing of the gear shaft, the driving pinion is separated from the meshing surface of the rack and the hanging cage falls. 1993, a construction elevator used in Shanghai Baosteel construction site, its cage fell due to going up the ditch, resulting in one death and one injury.

In addition, although some are equipped with supporting wheels, the eccentric shaft of the supporting wheels has no locking piece, and the eccentricity of the shaft automatically moves outward during use, so that the supporting wheels do not play their due role.

2.6 Balance weight problem

The purpose of using counterweight is to balance part or all of the weight of the hanging cage, which can improve the bearing capacity of the hanging cage under the condition that the motor power of the driving device is unchanged, and mainly plays an energy-saving role. However, about 90% of the accidents of elevator car falling in construction occur with or without counterweight, so some people come to the conclusion that counterweight can ensure the safe operation of elevator car. In fact, from the operating principle of rack-and-pinion construction elevator, counterweight can only play an energy-saving role. Judging from the construction procedure descending machines produced at home and abroad, the construction elevators with and without balance weight and without balance heat treatment have more functions.

3 key issues to ensure the safe operation of the construction elevator cage

(1) Ensure the braking quality of the driving device and improve the braking torque. At present, the braking torque of the disc friction brake in use is generally 100N? M or so, the braking torque is small, which needs to be further improved to make the safety factor of braking torque k >；; =2。

(2) At present, most construction elevators adopt conical friction safety devices. From the use situation, the performance is relatively stable, and it is a relatively safe and reliable anti-falling safety device. But the problem is that it must meet the requirements of JG5058-95. When using the anti-fall safety device. The rated load drop test shall be conducted at least once every three months. So as to verify the reliability of the anti-falling safety device. In addition, the anti-fall safety device can only be used during the effective calibration period. After the expiration, it must be sent to a professional testing unit for maintenance and testing in time, and it can be used only after the validity period is re-calibrated. At the same time, maintenance should be strengthened during use, especially to prevent water seepage from the shell and oil stains on the brake band, so as to ensure its working reliability and sufficient braking torque.

(3) Install the overload protection device of the hanging cage to ensure the safe operation of the hanging cage. As mentioned above, at present, there are few overload limiting protection devices used on hanging cages, especially those installed on domestic construction elevators. It is expected to develop a simple, practical, safe and reliable overload limit protector for hanging cages and popularize it.

(4) When the driving pinion is engaged with the rack, a idler must be installed on the back of the rack. So as to ensure that the driving pinion engages with the rack on the right side. At the same time, the eccentric shaft of the idler should be fixed firmly with a lock piece.