PURPOSE: To expand stepwise heat transfer tubes by means of respective tube expanding balls by forcibly passing a tube expander in which the plural expanding balls having gradually larger outside diameters are arranged into the heat transfer tubes by disposing the ball of the smallest outside diameter at the top.
CONSTITUTION: The outside diameter of a pipe stopping bolt 8 is slightly smaller than the inside diameter of the heat transfer tubes (a) but the outside diameter of the 1st expanding ball 4 is slightly larger than the inside diameter of the heat transfer tubes (a). The outside diameters are set gradually and successively larger with the 2nd expanding ball 5 and the 3rd expanding ball 6. The plural heat transfer tubes (a) are mounted to a holder (d) and mandrels 1 are mounted to a base plate (e) so as to correspond to the respective heat transfer tubes (a) in order to subject the heat transfer tubes (a) to expanding treatment by utilizing such mandrels 1. The base plate (e) is then moved by the effect of an oil pressure or the like to insert and pass the respective mandrels 1 into the heat transfer tubes (a). Then, the tubes are instantaneously expanded from the outside diameter of the expanding ball of the smallest diameter to the expanding ball of the largest diameter by one time of the tube expanding treatment operation, by which the tube expanding rate is greatly enhanced.
KURIHARA YOSHIO
NAKADA YOSHINOBU
