Parting Line Shutoff Inspection in Plastic Injection Molds
Verifying parting line shutoff lands under true press tonnage with bluing or foil prevents flash and stops premature tool crush.
Steel Shutoff Angle
Meaning
Angular machining faces on telescoping core and cavity inserts create mechanical wedge seals that isolate part features without relying on flat butt contact. Setting an appropriate steel shutoff angle allows vertical mold surfaces to shut off against opposing steel components while minimizing friction and wear during tool opening and closing. Draft angles on these shutoff surfaces facilitate smooth engagement as press clamping tonnage locks the tool halves together.
This angular geometry controls sliding shutoff fit but does not dictate thermal cooling rates within the mold cavity.
Draft Selection
Angle magnitude determines the mechanical clearance created during initial mold opening movement. Specifying a steel shutoff angle of five to seven degrees ensures rapid clearance separation upon mold opening, preventing scuffing and metal pickup between sliding core components. Steeper angles require tighter machining tolerances to achieve complete sealing without flash.
Galling Prevention
Sliding contact under high compressive load risks material transfer between matching tool components. Applying a steel shutoff angle with different hardness values or anti-galling coatings on mating sides prevents steel seizing during continuous operation. Surface treatments like titanium nitride prolong shutoff life on tight-angled slide interfaces.
Thermal Clearance
Differential thermal expansion between core and cavity blocks alters angular shutoff fit at operating temperatures. Calculating steel shutoff angle clearances requires accounting for hot cavity inserts expanding against cooler mold frames. Incorrect thermal clearance causes shutoff binding or flash formation during hot runner operation.