Manufacturing method and apparatus for forming an elongate body having thickness change

A manufacturing method for forming an elongate body having thickness change, comprising the steps of:

• extruding the elongate body of a synthetic resin having a cross-section that forms a gap between a pair of spaced, opposed and separate lips constituting a first portion of the elongate body;
• and
• pressing a portion of said first portion of the elongate body by a press roller at a constant pressure while moving the elongate body in a longitudinal direction within a fixed range, thereby reducing the gap and integrally joining the lips in a predetermined length according to a longitudinal position of the lips so as to define a second portion of the elongate body having a thickness less than said first portion of the elongate body;
• measuring a thickness of the elongate body at predetermined intervals in the longitudinal direction thereof;
• and
• detecting a moving distance of the elongate body between a first measuring position measured in the thickness measuring step and a second measuring position different from the first measuring position,
• said thickness measuring step including the step of determining a longitudinal position of the elongate body on the basis of a thickness of the first measuring position, a thickness of the second measuring position and a difference between the thicknesses of the first measuring position and the second measuring position.