Mold expansion prevention device

The utility model discloses a formwork expansion prevention device, and relates to the technical field of slip form construction. The problems that an existing formwork device does not have the function of reinforcing the bottom of a steel formwork, connecting bolts between an enclosing purlin and the steel formwork are loosened and even disengaged, the formwork expansion phenomenon is caused, and the engineering construction quality is affected are solved. The two annular reinforcing pieces are arranged on the outer side and the inner side of the steel formwork respectively in the circumferential direction, the positions of the two annular reinforcing pieces correspond to each other, the two annular reinforcing pieces are located at the bottom of the steel formwork, and each annular reinforcing piece comprises a plurality of connecting steel bars continuously arranged in the circumferential direction of the steel formwork; the chain blocks are arranged along the outer wall of the steel formwork, each chain b