Spiral jack is an important lifting equipment commonly used by people when lifting heavy objects. The stability and reliability of the jack are related to the safety and stability of the entire lifting operation. Therefore, the jack production factory uses ductile iron material to build the jack body, which can improve the bearing capacity and corrosion resistance of the jack. If the jack body cracks, the reasons should be found from the following aspects:

1. The main reason is that the welding process is not up to standard, the weld seam is poorly formed, and the subsequent heat treatment process is not implemented as required, resulting in poor strength and toughness of the welding joint. Under the action of external concentrated stress, welding cold cracks are formed and further propagate.

2. During use, the jack is always in a loaded state. When the concentrated stress exceeds the maximum value that the defect area can withstand, the initial crack is generated. Afterwards, the crack extends to both ends under the cyclic action of stress, and the crack will become larger and larger.

The cracking of the ductile iron body of a screw jack often starts from a joint weld, and then the crack extends to both ends of the weld.