Experience and lessons of the hottest tower crane

Experience and lessons of tower crane safety accidents

with the extensive use of tower cranes in the construction industry in recent years, all kinds of tower crane safety accidents have also emerged with the increase of their number. In view of the causes of various accidents, the relevant management departments have also issued a number of management measures to supervise the design, manufacture, installation, use, inspection, maintenance and transformation of cranes, such as production licensing of tower crane manufacturers, qualification management of installation units, acceptance registration before crane installation and use, supervision and random inspection of supervision departments during use, etc, To a certain extent, it reduces the occurrence of safety accidents of tower cranes. However, due to the limited professional and technical level and weak safety awareness of the users of tower cranes in the construction site, there are relatively large security loopholes in the use of tower cranes

such a tower crane safety accident occurred at a construction site. The crane hook was lifting materials when the accident occurred. The hook suddenly slipped when it rose to a height of about 4m. The driver didn't react well. Accidents that cause the hoisted materials and hooks to fall directly to the ground. Relevant departments checked the cause of the accident and found that the weight of the lifted material did not exceed the rated lifting capacity of the crane. The lifting wire rope and its joint are also free from loosening or fracture, so the cause of overload can be preliminarily ruled out. After checking the hoisting mechanism of the accident equipment, it is found that the hoisting mechanism achieves the function of changing the transmission ratio through the engagement of different electromagnetic clutches. The electromagnetic clutch has brush displacement and wear. The under current relay controlling the electromagnetic clutch in the electric control box is short circuited and the adjusting screw is adjusted to the top dead position. Here. We first analyze the control circuit of the electromagnetic clutch of the accident equipment. In the circuit, the current detection coil of the under current relay FS4 is connected in series in the control circuit of the electromagnetic clutch, and the FS4 normally open control contact is connected in series in the circuit controlling the crane brake. During operation, the change-over switch SA controls the engagement of the electromagnetic clutch to transmit different transmission ratios. When the change-over switch SA is turned to gear I or gear II, the intermediate relay KL or K2 is engaged, and the electromagnetic clutch coil Yc1 or YC2 forms a loop with the under current relay current detection coil FS4. The electromagnetic clutch is powered on and engaged, so as to transmit power. When the current passing through FS4 is lower than the set value (that is, the current in the circuit cannot maintain the normal engagement of the electromagnetic clutch), the normally open contact of FS4 in series in the brake circuit is disconnected, and the brake holds. If the normally open contact of the under current relay is short circuited or the set current value is too small, the electromagnetic clutch cannot or cannot completely transmit the power of the motor to the drum, and at this time, the brake will be energized and released, which will cause a hook slipping accident. Referring to the operation manual of this model, it is found that the manual also clearly stipulates that the normally open point of the under current relay cannot be ① The pressure plate (or beam) of the mobile electronic tensile testing machine is adjusted to be normally closed due to the closing delay, otherwise it will cause lifting and sliding hook. Therefore, it can be inferred that the cause of this accident is the displacement and wear of the brush of the electromagnetic clutch, and the under current relay is shorted and the adjusting screw is adjusted to the top dead position. The root cause of the accident was a serious lack of management in the use of equipment. Firstly, the failure of the electromagnetic clutch was not found in time. Secondly, the maintenance personnel adjusted and short circuited the under current relay at will without carefully consulting the instructions, and there was no relevant management personnel to track and check the maintenance, which led to the accident

tower crane, as a special equipment, has undergone a series of strict calculations and tests from design to manufacture. The national supervision and administration department has effectively supervised the production process of the crane. All kinds of mechanisms, safety devices and electrical control systems on the crane have their specific functions and importance, and all comply with the relevant safety technical specifications. According to the regulations on safety supervision of special equipment, the maintenance units of special equipment, including Taizhou enterprises, should have professional technicians and skilled workers suitable for the maintenance of special equipment, as well as necessary testing means, and can engage in corresponding maintenance activities only with the permission of the safety supervision and administration departments of special equipment of provinces, autonomous regions and municipalities directly under the central government. But for general construction enterprises (crane users). Its corresponding professional and technical level is low. Without fully understanding the impact performance degradation caused by the expansion of surface defects and the degradation of fiber matrix interface pointed out by him, arbitrarily adjusting and refitting the safety device and electrical control device on the crane may lead to serious safety accidents. For example, some using units arbitrarily increase the torque limiter and lifting capacity limiter of the crane, and some using cranes assembled from components of different models. From this tower crane safety accident, we can see that there are major problems in the use and management of large lifting machinery by the user unit. The main points are as follows: ① the construction enterprise has not established the corresponding safety management system; ② Failure to implement safety management personnel and systems at corresponding levels: ③ lack of professional and technical level of safety management personnel; ④ The implementation of safety management means requires low displacement accuracy and its implementation. In order to fundamentally solve the problem of safe use of tower cranes in construction sites, construction enterprises must establish a perfect safety management system. I put forward several suggestions on the safety management of lifting machinery on the construction site: ① the user unit should establish the safety technical archives of lifting machinery. Safety technical archives shall include: 1) design documents (including general drawing and electrical and hydraulic schematic diagram), product quality certificate, corresponding manufacturing, installation, transformation, major maintenance supervision and inspection certificate, installation, use and maintenance instructions and other documents of hoisting machinery, as well as installation technical documents and data; 2) Records of regular inspection and self inspection of lifting machinery; 3) Daily use records of lifting machinery; 4) Daily maintenance records of lifting machinery, its safety accessories and safety protection devices; 5) Operation fault and accident records of lifting machinery; 6) Use registration certificate of hoisting machinery. ② The user unit shall establish a safety management system for lifting machinery, allocate safety management personnel with a certain professional and technical level to carry out daily management of the crane, and establish the post responsibilities of personnel at all levels. ③ Crane safety management personnel shall regularly inspect the equipment and make records. Problems found shall be handled in accordance with the corresponding safety technical specifications and technical data. For problems that cannot be handled, the manufacturer or qualified unit shall be consulted. After the problem is solved, the equipment shall be comprehensively inspected and recorded. ④ The user unit shall regularly carry out safety education for operators and regularly collect the use conditions of operators during the use of equipment. ⑤ Operators shall carry out daily maintenance of the equipment, regularly check the safety device of the crane and make records. ⑥ For the maintenance or reconstruction of equipment, the user unit shall employ the manufacturer or a unit with corresponding qualifications to carry out the maintenance or reconstruction, and archive the corresponding data records of the maintenance and reconstruction. It is not allowed to refit or assemble without permission

the experience and lessons of lifting machinery safety accidents tell us that only effective management of all links in the use of equipment can effectively control the dangerous factors in the production process, eliminate the potential safety hazards in the production process, and ensure the smooth progress of normal production activities. Therefore, we should strive to constantly improve our safety production management system and improve our safety production management level