PURPOSE: To fixedly connect a cover to a sole by pressurizing the edge area of a rivet hole with an annular ram, elevating pressurizing force to be not lower than the creep limit of a cover material, permanently deforming the edge area to reduce the load on the ram and then clinching the rivet to deform its free end.

CONSTITUTION: The rivet 4 with a frustoconical leg part 6 is integrally casted on the top surface 2 of the wall of an evaporation chamber, a cover 1 is placed on the surface 2 and the annular ram 7 is moved down on the cover 1 avoiding hitting the rivet 7. The edge area 8 of the rivet hole 5 receives pressurizing force of the ram 7 and moves over the creep limit of the cover material, and the cover 1 flows toward the rivet 4 to surround the axis part of the rivet 4 with the pressurized cover material on every side. After permanently deforming the edge area 8 of the rivet hole 5, the rivet 4 is clinched and its free end 9 is deformed to form a rivet head 10. Thus, the evaporation chamber at the bottom of a steam iron can be closed with the cover 1.