The hook is very important to the safe and reliable work of the crane. To this end, the hook materials and processing have strict requirements. Because the high strength steel is sensitive to cracks and defects, the materials used to make the hook assembly are made of special quality and low quality
Carbon killed steel or low carbon alloy steel, steel grades DG20, DG20Mn steel and DG34CrMo and DG34CrNiMo alloy steel. After the forging and stamping, annealing, and then processed by the mechanical hook group, with high strength, good plasticity and toughness characteristics.
Plate hooks are generally used for large tonnage roast by strong heat. Usually made of A3, 20 or 16Mn steel plates of thickness no less than 20ram, the chip hook can not be broken suddenly, and the reliability is high. The fracture due to the defects is confined to individual steel plates, and the remaining steel plates can support the lifting weight. Only when the individual plates are replaced, the hanger plate can not be broken at the same time, therefore, it has greater safety. But only made into rectangular type hook, so the strength performance can not be fully utilized the hook material.
Because there are many casting material quality defects, such as shrinkage, thermal stress, slag and other defects, easy to crack, is not easy to be found, so the lifting machinery shall not use steel hooks; not by welding hook group, because the pores, slag, incomplete penetration welding, cracks and other defects can not be used; high strength, low impact toughness of steel hook.
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