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The hook is an important part of the hoisting machinery. It has complex stress conditions. In addition to bearing the weight of heavy objects, it also has to bear the impact load generated during lifting and braking. The impact load generated during use will inevitably cause cracks in hooks that have been used for a long time. Once the hook cracks during use, it will cause serious personal and equipment injuries. "Safety Regulations for Hoisting Machinery" GB6067-85 and relevant standards and specifications stipulate that cracks are strictly prohibited in hooks. Most enterprises and inspection departments are restricted by many objective factors such as the operating environment. In actual inspections, they generally adopt rough macro inspections. The hooks are not disassembled and they are only observed with the naked eye without taking any measures. Therefore, hidden dangers of missed inspections will inevitably be caused.

First of all, the most commonly used crane hooks in China are forged hooks, especially those below 75t. The commonly used 20# high-quality carbon steel has been forged, stamped and heat treated, and the hook tail is machined and other processes. According to the characteristics and stress conditions of the hook, the hook has three main stress areas A, B, and C (as shown in the figure). These three stress areas are also the areas where the hook is most likely to break. At present, conventional on-site macro inspection methods are adopted, which can only inspect areas A and B, while area C cannot be inspected because it is covered by the hook bearing and beam. Area C is located at the hook neck recess where the cross section suddenly becomes smaller. It is the section where the hook tail bearing part bears the greatest tensile stress and has the weakest strength. Through years of inspection experience and analysis of the causes after accidents, it can be seen that fractures often occur here. Then there are hooks with a long service life and poor use conditions. In the hidden parts, there are often defects such as corrosion damage to the hook tail thread and circumferential wear of the tail shaft due to installation and use. Therefore, the disintegration inspection of the C stress zone is very necessary and must not be ignored.

Secondly, the cracks on the surface of lifting hooks are generally very small, while the surface condition of the hooks in use is generally very poor, the surface is very rough, and there are defects such as scale oil, impurities, burrs, and pits on the main section. For example, the surface of the hook for lifting molten steel has varying degrees of splashes of molten steel, etc. At the job site, due to the limitations of inspection time, conditions, and equipment usage, it is impossible to clean the debris on the surface of the hook. Therefore, it is difficult to find microscopic cracks using macroscopic inspection. If cracks can be found, it means that the cracks are already serious.

The hook is an important part of the hoisting machinery. It has complex stress conditions. In addition to bearing the weight of heavy objects, it also has to bear the impact load generated during lifting and braking. The impact load generated during use will inevitably cause cracks in hooks that have been used for a long time. Once the hook cracks during use, it will cause serious personal and equipment injuries. "Safety Regulations for Hoisting Machinery" GB6067-85 and relevant standards and specifications stipulate that cracks are strictly prohibited in hooks. Most enterprises and inspection departments are restricted by many objective factors such as the operating environment. In actual inspections, they generally adopt rough macro inspections. The hooks are not disassembled and they are only observed with the naked eye without taking any measures. Therefore, hidden dangers of missed inspections will inevitably be caused.

First of all, the most commonly used crane hooks in China are forged hooks, especially those below 75t. The commonly used 20# high-quality carbon steel has been forged, stamped and heat treated, and the hook tail is machined and other processes. According to the characteristics and stress conditions of the hook, the hook has three main stress areas A, B, and C (as shown in the figure). These three stress areas are also the areas where the hook is most likely to break. At present, conventional on-site macro inspection methods are adopted, which can only inspect areas A and B, while area C cannot be inspected because it is covered by the hook bearing and beam. Area C is located at the hook neck recess where the cross section suddenly becomes smaller. It is the section where the hook tail bearing part bears the greatest tensile stress and has the weakest strength. Through years of inspection experience and analysis of the causes after accidents, it can be seen that fractures often occur here. Then there are hooks with a long service life and poor use conditions. In the hidden parts, there are often defects such as corrosion damage to the hook tail thread and circumferential wear of the tail shaft due to installation and use. Therefore, the disintegration inspection of the C stress zone is very necessary and must not be ignored.

Secondly, the cracks on the surface of lifting hooks are generally very small, while the surface condition of the hooks in use is generally very poor, the surface is very rough, and there are defects such as scale oil, impurities, burrs, and pits on the main section. For example, the surface of the hook for lifting molten steel has varying degrees of splashes of molten steel, etc. At the job site, due to the limitations of inspection time, conditions, and equipment usage, it is impossible to clean the debris on the surface of the hook. Therefore, it is difficult to find microscopic cracks using macroscopic inspection. If cracks can be found, it means that the cracks are already serious.