Analysis of safety protection of metallurgical cranes, taking 32 cases of 6 deaths and 6 injuries as a case of steel ladle dumping in a steel plant

Since hoisting machinery can greatly reduce the intensity of manual labor, facilitate the mechanization and automation of the production process, and improve labor productivity, hoisting machinery has become an indispensable mechanical device in modern industry. The lifting machinery has the characteristics of large mechanical load variation, various lifting forms, wide range of activities, and complicated working environment. Under the cooperation of operators, various faults are frequent and extremely harmful.

Metallurgical characteristics crane

(1) Wide application of sensors and control technology

With the continuous updating of computer and sensor technology, metallurgical cranes have also been widely used to improve the operability and automation level of metallurgical cranes.

Programmatic control allows the metallurgical crane to perform specific tasks in a pre-set mode with greater accuracy and timeliness. The remote control of the crane can also be realized by telemetry and remote control technology.

In this way, the crane can be used in harsh environments such as high dust, high pollution and high temperature, which broadens the working range.

(2) Use of safety brakes

Metallurgical cranes have complex lifting objects, including liquid metals, nuclear materials, and large equipment. The safety of personnel and equipment must be ensured during the lifting process. Therefore, a safety brake should be installed in the main lifting mechanism of the metallurgical crane and mechanically controlled by the hydraulic mechanism.

When the metallurgical crane is started, the safety brake first works and the working brake on the high speed shaft starts working again. When the metallurgical crane brakes, the working brake is braked first, and the safety brake is braked according to a preset time delay.

In this way, the safety brake ensures that the object being lifted is still in a safe state when the transmission member in the transmission link is damaged or broken, and does not cause damage to the equipment and the human body.

Metallurgical crane safety case analysis

(1) Accident process

In a production workshop of a special steel limited liability company in a certain year, a ladle containing about 30 tons of molten steel was in the process of lifting. Due to problems in the control system of the metallurgical crane, the ladle suddenly fell and fell over to the workshop, and the molten steel poured in. Indoors, 32 employees who were in the hands of the shifting room were killed on the spot. Six other workers in front of the furnace were injured, and two of them were seriously injured.

(2) Analysis of the cause of the accident

The accident tree analysis of the accident is shown in Figure 1. The design flaws in the electrical control system caused the ladle to run out of control and eventually fall. The brake fails due to the inability of the brake to withstand the impact of the falling of the ladle. The mistakes in the selection of the handover site caused major casualties in the accident. These are the direct causes of the accident.

In addition, the comprehensive failure of metallurgical crane selection, performance of inspection agency duties, electrical design, driver's ability to respond to unexpected situations, equipment maintenance, production organization management, etc. also indirectly led to the occurrence of major casualties. The lessons are profound.

(3) Analysis of electrical control system

The electrical control system of the metallurgical crane is shown in Figure 2. In the control process, the two-phase knife switch 2DK is closed, and the handle of the master controller is placed at the zero position, so that the coil of the zero-position relay LYJ passes through the contact K1 of the master controller and the overcurrent relay contact CLJ. Get power.

When the first gear is raised: the contacts K3, K6, K4, K7 are closed. The contact K3 rise limit switches XS1 and XS2 are connected. The contact K6 energizes the forward-rotating contactor ZC coil, and the motor rotates forward. At this point, the 3 loop is turned The normally closed contact FC acts as an interlock.

The normally closed contact 4JSC in parallel with the ZC interlocking contacts is used to prevent the contactor ZC from energizing when the additional resistance of the rotor is completely removed. When the contact K4 is closed, the 4 circuit is turned on. ZDC brake contactor solenoid coil is energized, the contacts are closed so that the brake magnet electrical connection, the brake Brake.

The contact K7 is closed, the 5 loop is turned on, the contactor 1FJC coil is energized, and the contact is closed to cut off the first resistor in the rotor circuit.

When the gear is lowered: it can be divided into three parts: the preparatory line (1st gear), the brake down (2nd and 3rd gears) and the strong drop (4th, 5th and 6th gears). Also known as "the first three gears", "the last three gears." The direction of rotation of the magnetic field of the first three-speed motor is opposite to the direction of rotation of the motor, and the directions of the latter three gears are the same.

When the first gear is lowered: the contacts K3, K6, K7 and K8 are closed, wherein K3 and K6 turn on the 3 circuit, and the forward contactor ZC is turned on. K7 and K8 turn on the circuit 56, and the coil energizing contacts of the brakes 1FJC and 2FJC are closed, and the two resistors are cut off.

At this time, since the brake electromagnet contactor ZDC does not operate, the brake is still in the braking state, and the motor does not move. This gear is mainly used to reduce the weight of the handle when the handle is pulled from the falling position to the zero position to avoid "snap hook".

Establishment of safety protection system for metallurgical cranes

It can be seen from the above metallurgical crane accident case that the occurrence of the accident is not only caused by one link, but also problems arise from various parts of design to production management.

Therefore, in order to ensure the safe and reliable operation of metallurgical cranes, it is necessary to establish a complete safety protection system from five aspects: equipment operation, regular inspection, precision inspection, defect diagnosis and daily maintenance.

1) During the daily operation of the operator, once a defect is found, it should be reported in time, and the maintenance of the equipment should be done with the cooperation of professional and technical personnel to establish the first line of defense for accident prevention;

2) Conduct regular periodic inspections of key lifting equipment in all aspects of metallurgical production, identify hidden dangers in a timely manner, and organize maintenance work scientifically and reasonably;

3) Precision inspection, analysis and maintenance of metallurgical cranes on the basis of daily and key inspections by precision testing equipment.

With the continuous improvement of people's living standards and safety awareness, the safety of metallurgical cranes has also received much attention. From the current safety production situation, the safety performance of metallurgical cranes has not reached the expected level, resulting in frequent accidents and great harm. This requires improvement in the design, manufacture, installation, operation, maintenance, management and other aspects of the metallurgical crane to achieve the purpose of eliminating the safety hazards of metallurgical cranes.

Glass Holders

Stainless Steel Glass Holders and Brackets are designed to create glass balustrade on staircases.