Stretch rod extending device and bottom mold lifting device for stretch blow molding machine

A stretch rod extending device for a stretch blow molding machine, wherein said stretch blow molding machine comprises:

• a blow mold being openable and closable;
• a neck mold holding a preform and closing with said blow mold;
• a core supporting plate holding a blow core member which fits with said neck mold;
• and
• a rod fixing plate holding a stretch rod inserted into said preform through said blow core member;
• wherein said neck mold, said core supporting plate, and said rod fixing plate are movable up and down together or separately, and said rod fixing plate is connected to a stretch rod extending device, and said stretch rod extending device comprises a nut member and a screw shaft which converts the rotation of a electrical servo motor to linear movement, and
• wherein the nut member and the screw shaft comprise a magnetic nut member and a magnetic screw shaft having spiral N magnetic pole and S magnetic pole alternately provided on inner peripheral surface of a cylindrical permanent magnetic member and outer peripheral surface of a permanent magnetic shaft at the same pitch, and said magnetic screw shaft is inserted into a cylindrical plunger having said magnetic nut member equipped inside by keeping required clearance between said magnetic screw shaft and said magnetic nut member so as to match the same magnetic poles.