PURPOSE: To obtain continuously a multi-layered pipe having the silencing function effective for radiation sound by maintaining the reduction rate of rolls in a specified range in the stage of forming the double pipe or the multiple-layered pipe provided with an interposing material by electric welding.
CONSTITUTION: An interposing material 6a of glass wool, etc. is inserted into the space part between metallic hoops 1a and 2a for inside and outside pipes to form a three-layered blank material hoop. The hoop is then fed to a forming roll array and is then fed to squeezing rolls 11, by which the hoop is formed to a pipe shape. The electric weld zone 14 thereof is welded by welding devices 9, 10. The reduction rate of a shaping roll array is made ≤1.5% in the stage of shaping the pipe with said array. The composite double steel pipe or the like effective for decreasing radiation sound when used for the exhaust pipe of an automotive engine, etc. is continuously formed with high accuracy by the above-mentioned method.
OOKAKIUCHI AKIHIRO
ENDOU HIROSHI
ZAMA YOSHIMASA
