{"id":1056,"date":"2026-09-14T08:54:02","date_gmt":"2026-09-14T08:54:02","guid":{"rendered":"https:\/\/isbmmolding.com\/?p=1056"},"modified":"2026-09-14T08:54:02","modified_gmt":"2026-09-14T08:54:02","slug":"how-does-a-stretch-rod-work-in-blow-molding","status":"publish","type":"post","link":"https:\/\/isbmmolding.com\/ko\/how-does-a-stretch-rod-work-in-blow-molding\/","title":{"rendered":"How does a stretch rod work in blow molding?"},"content":{"rendered":"

How does a stretch rod work in blow molding?<\/h1>\n
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The stretch rod is the mechanical component that distinguishes injection stretch blow moulding (ISBM) from injection blow moulding (IBM) and extrusion blow moulding (EBM). It is a precision-ground steel rod that descends into the warm preform at the blow station and mechanically extends it axially \u2014 pushing the base downward \u2014 before high-pressure blow air expands it radially. The combination of axial extension by the stretch rod and radial expansion by blow air produces biaxial molecular orientation, which is the physical property responsible for PET bottles\u2019 glass-like clarity, high strength at low wall thickness, and CO\u2082 barrier performance.<\/p>\n

The Stretch Rod\u2019s Role in the ISBM Cycle<\/h2>\n

At the blow station, the preform \u2014 still on its mandrel and at the correct conditioning temperature \u2014 is enclosed within the closed blow mould. The stretch rod enters the preform through its open neck and contacts the preform base dome with a controlled, flat tip. The rod then extends downward at a controlled speed (typically 1\u20132 m\/s), pushing the preform base toward the bottom of the blow mould cavity and elongating the preform body. This is the axial stretch step.<\/p>\n

Simultaneously with or immediately after the stretch rod contact, low-pressure pre-blow air (typically 6\u201310 bar) is introduced through the blow pin to begin inflating the preform radially \u2014 preventing it from folding or collapsing inward as it is extended. The stretch rod continues to travel until the preform base contacts the bottom of the blow mould. High-pressure blow air (25\u201340 bar) is then introduced to complete the radial expansion of the preform body against the mould wall, forming the finished bottle shape. The stretch rod is withdrawn after the bottle is fully blown and the mould continues to cool the bottle before opening.<\/p>\n

\"Stretch<\/p>\n

ISBM blow station \u2014 the stretch rod contacts the preform base and extends axially while pre-blow and blow air expand the preform radially, producing simultaneous biaxial orientation.<\/p>\n

\uc774\ucd95 \ubc30\ud5a5\uc774 \uc911\uc694\ud55c \uc774\uc720<\/h2>\n

The stretch rod\u2019s axial extension and the blow air\u2019s radial expansion together align the PET polymer chains simultaneously in two directions. This biaxial alignment is fundamentally different from the random chain arrangement in unoriented amorphous PET. The oriented chains are much more resistant to deformation and light scattering than randomly arranged chains, producing the following properties in the finished bottle:<\/p>\n