MANUFACTURE OF HOLLOW BODY WITH BUILT-IN RIB

PURPOSE:To manufacture a hollow body, which is rigid to three-dimensional bending, by a method wherein some portions of the side wall of a tubular parison, into which an insert to serve as a vertical rib later has been inserted in advance, are abutted against the insert by advancing ejectors in facing directions from the inner surfaces of the cavities of molding tools in order to form lateral ribs. CONSTITUTION:Firstly, a parison 2 is hangingly extruded from a parison extruder head in between a left and a right molding tools 3 and 4 with ejectors 7 and 8 in retreated state. Secondly, a sheet-shaped synthetic resin insert 2a is inserted in the parison 2. Thirdly, after the molding tools being clamped, the ejectors 7 and 8 are advanced so as to deform some portions of the side wall of the parison 2 inwards in order to abut the tips of the deformed portions against the insert 2a. Fourthly, after the ejectors 7 and 8 are retreated, pressure fluid is blown in the parison 2 in order to form lateral ribs 13 and 14 along the lines of retreat of the ejectors 7 and 8 within a hollow body.