PURPOSE: To improve work efficiency by placing a metallic elastic body of small specific heat in a tube or hollow part of a hollow plate in the direction of axial line and thereby freezing liquid contained in the hollow part in a short time.

CONSTITUTION: Liquid, such as water, is sealed in a tube 16. Water does not leak since a rubber mat 14 is pressed at the bottom of the tube 16. Specified bending operation is performed after freezing water in the tube 16. In this case, a spring 18 is placed in the tube 16 in the direction of axial line. This means that metal of small specific heat is sealed in place of water corresponding to the volume of the spring 18. Accordingly, water in the tube 16 is frozin in a short time. As elastic deformation of the spring is easy, it gives no impediment to bending work and repeated use is possible.