Causes and preventive measures for common accident

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Causes and preventive measures for common accidents of tower cranes

in recent years, with the continuous development of the construction industry and 2 The industry management of the driving system of the tensile testing machine has been continuously standardized. The group's characteristic material business specializes in producing a wide range of high-performance products. The construction safety situation has gradually improved, but accidents caused by construction machinery still occur from time to time. Therefore, the use and management of large construction machinery has become an important part of the management of construction enterprises. Especially as the main large construction machinery in the construction, the normal use and installation management of the tower crane is very important. Especially the installation and disassembly of tower crane is a dangerous work. The accidents caused by it not only account for a large proportion of the four major injuries in the construction site, but also have great harmfulness, high accident frequency and large economic losses. It is reported that there have been a number of fatal and extraordinarily serious accidents caused by improper use of tower cranes nationwide, which have brought heavy tragedies and losses to the collective interests and the families of the victims. Based on some basic knowledge and years of experience in tower crane work, I will talk about the types and common causes of tower crane accidents from the perspective of safety operation regulations and technology, and put forward relevant safety precautions

I. common accidents during daily use and preventive measures

1 Cause analysis:

① as the spline of the output shaft of the lifting mechanism and the spline of the lifting drum are severely worn beyond the limit, the teeth of the spiral bevel gear pair on the lifting motor shaft and the first stage transmission shaft of the transmission machine are knocked off, causing the lifting mechanism to lose control, causing the lifting object to fall from a high place and injure people during lifting

② for the system controlled by electromagnetic clutch, the electromagnetic clutch is burnt out or the electric brush is too worn to contact and power on, resulting in similar neutral gear during gear shifting, and the hook falls out of control and injures people

③ the main steel wire rope or the auxiliary tools for lifting the hook and sling were not replaced in time after being excessively worn during use, and broke during the lifting of heavy objects, resulting in the sudden weight loss and overturning of the tower crane

④ during the use of the tower body, due to the loosening and falling off of the connecting bolts of the standard section inclined rod, the inclined rod lost its support function, resulting in the destruction of the inclined rod, resulting in the instability of the tower body and overturning

⑤ the lifting torque limiter and weight limiter are tested or inspected within the specified range, resulting in oxidation failure of internal contacts due to long-term rain corrosion, and failure to work when the lifting load is overloaded

2. Preventive measures

① strengthen regular inspection. Method: a group of experienced repairmen and excellent electricians shall first fix the main steel wire rope on the tower with a rope clamp to facilitate the "loosening" of the steel wire rope, and then rotate the roller to judge the gear wear and clearance. If necessary, the reducer can be disassembled for inspection

② remove the electric brush on the electromagnetic clutch after the breaking point, and observe whether the wear is excessive and whether the internal spring has telescopic force. If not, it must be replaced in the center. Use a multimeter to measure whether the clutch coil is within the specified resistance value, and then carefully observe whether the suction plate is burnt out, whether the coil generates a magnetic field during operation, and check whether the snap ring of the valley clamping suction plate is effective. Put into use after it is confirmed to be normal

③ carefully check the steel wire rope, unclipping, hook, sling, etc., strictly implement the wear regulations of the steel wire rope, and immediately replace the rope strand, fiber core damage or steel core fracture, resulting in significant reduction of rope diameter, cage distortion, serious kink and other problems, so as to prevent accidents

④ regularly check the connecting bolts of the standard section with a special wrench and tighten them

⑤ regularly test each limiter, and operate after debugging and confirming sensitivity

II. Common accidents and preventive measures during tower crane disassembly and assembly

1 Common accidents:

① accidents during jacking oil cylinder operation have been described before, and will be repeated here

② when lifting the boom, the lifting point is not accurate, and the selection of lifting rope is wrong, resulting in the instability of the boom, which makes the lifting rope separate from the hook, resulting in falling casualties

③ the steel wire rope was not bound properly, which caused the steel wire rope to hang to the connecting pin of the pull rod during the lowering of the pull rod. Due to the neutral action, the pull rod suddenly fell weightless, resulting in a large swing of the tower crane and a collapse accident

④ when installing the tower cap or balance arm, the crane did not tilt up or down as required, causing the tower top to tilt back, resulting in an accident

⑤ dismantlement: the key points are dismantlement methods, procedures, auxiliary mechanical tools, organization and allocation of labor, environmental status, protection and disassembly, transportation and demobilization of components; The requirements for the preparation of disassembly and installation schemes are consistent and must be specific and clear

⑥ the disassembly and assembly procedure was not strictly followed, especially when the counterweight was disassembled, the jib was disassembled first and then the counterweight, which caused the tower crane center to move backward and overturn

2. Preventive measures and methods:

① before removing the connecting cross pin between the boom root and the tower body transition joint Ф 12.5mm or Ф The 25mm steel wire rope tightens the tower body and the root of the forearm. When the jib is steadily separated from behind the tower, the steel wire body can be removed or the jib can be lowered (the same as the balance arm). The distance L between lifting points shall meet the following requirements: 8m ≤ L ≤ 15mm, and the included angle of steel wire rope is generally not greater than 90. During installation, the lifting point position of the boom and the balance state shall be made and the permanent standard position shall be made (the luffing trolley shall be locked at the root and the position mark shall be made) or the lifting point shall be made in strict accordance with the instructions. Especially in the construction, the boom shall be increased or decreased naturally, which shall be paid more attention

② the steel wire rope is generally used Ф 22.5MM long and 9~11m long are bound in the "Walking Horse" mode, so that when the pull rod is lowered, the steel wire rope can naturally slide down to the specified position along the pull rod connection

③ when installing the tower cap or balance arm, the operation shall be carried out in strict accordance with the requirements of the upward or downward inclination angle specified in the manual

before removing the counterweight and the jib balance arm, the slewing ring must be connected with the standard section with bolts or pin shafts before operation. Do not remove the boom without removing the counterweight. A corresponding counterweight shall be reserved in strict accordance with the requirements of the manual. In addition, it is not allowed to suspend the balance arm overnight during the removal of the boom. Jiuli special materials for nuclear power restart; Small metal

III. common accident prevention measures during foundation and wall attached operation

1 Common problems:

① the ground endurance of the foundation does not meet the requirements of the tower crane, and the blind construction without piling or cast-in-place pile measures leads to the continued appropriate guidance for industrial development. After the installation of the tower crane, the foundation settlement is large, and the verticality inclination exceeds the specification, resulting in accidents

① the accident occurred due to the installation of tower crane due to the shortage of foundation reinforcement, uncompacted concrete pouring and insufficient concrete strength grade before the curing period

③ due to the needs of the engineering structure, the wall attachment distance of the tower crane does not meet the requirements of the factory operation manual, and the attachment rod is too long. There is no special scheme and calculation during the operation, or the attachment rod is made of inferior materials whose quality does not meet the national standards. During welding operation, the weld seam is torn or the rod is broken due to faulty welding, false welding and undercut

2. Preventive measures and methods:

the foundation shall be made in strict accordance with the requirements of the manual, and the ground endurance shall meet the basic requirements

the foundation reinforcement shall be in strict accordance with the requirements of the specification, and shall not be increased or decreased at will. During pouring, the concrete grade shall not be lower than C35. After pouring, water shall be stored for curing, pressure test blocks (two groups of 7D and 28d) shall be made, settlement observation points shall be made, and the whole machine installation shall be carried out after the strength of pressure test concrete reaches more than 95%. After installation, the vertical of the tower crane shall be regularly observed and recorded

the stress on the overlong attached wall shall be checked by the manufacturer's design or the unit's technical engineer and submitted to the superior competent department for approval. It shall be made of qualified raw materials. During the welding process, professional welders with certificates shall be sent for operation, and the welding shall be carried out in strict accordance with the requirements of the wall attachment scheme

in order to prevent major accidents of tower crane, in addition to the above mechanical construction operation requirements, we also make the following suggestions from the perspective of human management through long-term construction time:

1 Organize a professional disassembly and assembly team with high professional quality, strong technical force and rich operation experience to be proficient in the whole process of disassembly and assembly machinery and master the professional technology of this type of work

2. The on-site commander in chief shall have a strong sense of safety, understand the professional technology of electromechanical integration, understand the structural principle, performance and use method of tower crane, be familiar with the disassembly and assembly process, master the hoisting technology, and have certain on-site command, organization ability and emergency response ability to deal with emergencies

3. The professional team must be composed of the person in charge with the title of engineer or above, mechanical and electrical engineers or electromechanical technicians and relevant professionals, equipped with certified mechanical operators, installers, repairmen, electricians and auxiliary workers, and issued with qualification certificates after training by relevant departments. All operators shall work with certificates

4. Strictly implement the scheme approval and safety technical disclosure before tower crane installation and disassembly

5. Relevant departments and on-site safety management personnel shall adhere to the supervision and inspection during the disassembly and assembly of tower crane

in a word, as an important large-scale mechanical equipment on the construction site, the tower crane is the fundamental premise and guarantee for its maximum role and safe operation. All construction units must be people-oriented, develop continuously, strengthen the management of tower crane disassembly and assembly, ensure the implementation of safety production, and resolutely put an end to major and malignant accidents of tower crane. To eliminate all hidden dangers in the process of tower crane disassembly and use, we must solve them from the perspective of safety, effectiveness and reliability, not carelessness, which is the responsibility of the majority of equipment managers and operators

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